Office of the Auditor General / Bureau du vérificateur général

AUDIT OF THE

WEST END FLOODING EVENT AND THE DEVELOPMENT REVIEW PROCESSES WITHIN THE CARP RIVER WATERSHED

2010

Vérification portant sur l’inondation DU SECTEUR OUEST et sur les processus d’examen des projets d’aménagement dans le bassin hydrographique de la rivière Carp

 

 

Table of Contents

EXECUTIVE SUMMARY.. i

RÉSUMÉ.. xix

1     INTRODUCTION.. 1

2     AUDIT SCOPE.. 4

3     AUDIT OBJECTIVES. 4

4     DETAILED FINDINGS, OBSERVATIONS AND RECOMMENDATIONS. 9

5     CONCLUSION.. 75

6     ACKNOWLEDGEMENT.. 76

Appendix A.. 77

Appendix B.. 89

EXECUTIVE SUMMARY

Introduction

Repeated Carp River watershed flooding in 1996 and 2002 prompted widespread citizen concern, media questions and Council debate concerning the appropriateness of City sub-watershed planning, subdivision development approvals processes and the effectiveness of flood mitigation engineering solutions. The July 24, 2009 flood event has generated a new round of City staff investigations and pending litigation.  Arising from the July 24^th storm event, approximately 1,500 residential west-end flooding incidents have been reported by City staff.

At the September 2^nd, 2009 meeting of Council, Motion 75/9 was tabled and carried:

MOTION NO. 75/9

Moved by Councillor S. Qadri

Seconded by Councillor G. Brooks

WHEREAS on July 24th, 2009 serious flooding occurred in Kanata and Stittsville and resulted in over 800 residences being damaged by water and sewage;

AND WHEREAS previous flooding has also occurred in other area of Ottawa, including Orléans in 2006;

AND WHEREAS the City of Ottawa has previously spent over $7 million in remedial measures to prevent further flooding in the Glen Cairn area and these measures failed;

AND WHEREAS the Glen Cairn community is partially built in an environmentally sensitive area, flood plain of the Carp River and as other city development continues to occur in environmentally sensitive/risky areas;

AND WHEREAS in 2007 the Office of the Auditor General completed an Audit of Carp River Watershed Study and Related Projects, which included an in-camera report on the Glen Cairn Channelization;

THEREFORE BE IT RESOLVED that the Auditor General be requested to consider modifying his 2010 Audit Plan to include an Audit of the City of Ottawa's Development Review Process, both currently and for the developments that drain into the Carp River, in relation to approval of water, wastewater and stormwater servicing, and an Audit of the City of Ottawa's ongoing operations and maintenance practices in relation to protecting the water environment.

AND THEREFORE BE IT RESOLVED that, further, this audit include a review of the remedial measures regarding Glen Cairn, both already undertaken and planned for the future, and that prior to tabling his report with Council he review his findings with the City Clerk and Solicitor for advice on which findings can be delivered in open session and those which should be delivered in camera.

CARRIED

Audit Objectives and Scope

Audit Objective #1 - Establish and document the City’s development approvals historic timelines in the Carp River watershed.

Audit Objective #2 - Create a Carp River watershed development approvals age-identified flooding map/profile.

Audit Objective #3 - Evidence based selection of subdivision development approval sample files for comprehensive due diligence process review.

Audit Objective #4 - Evidence based execution of subdivision development approval sample files for comprehensive due diligence process review.

Audit Objective #5 - Review City policy formulation and implementation processes for Home Rules model.

Audit Objective #6 - Review proactive actions by City to convince/compel Carp River watershed development applicants to voluntary compliance with enhanced post-2004 standards.

Audit Objective #7 - Examine and evaluate the processes and methodologies used for the operation and maintenance of sanitary and storm drainage systems.

Audit Objective #8 - Determine if the Operation and Maintenance processes and methodologies meet the City’s, Province’s and Industry standards, and are consistent with relevant policies, procedures, legislation, and regulations.

Audit Objective #9 - Examine and evaluate the planning and design of the existing and proposed Glen Cairn flood remedial measures.

Audit Objective #10 - Determine if the Glen Cairn flood remedial measures are consistent with relevant policies, procedures, legislation, and regulations.

Audit Objective #11 - Determine if the Glen Cairn flood remedial measures addressed all the potential issues known at the time that they were planned and implemented.

Audit Objective #12 - Determine whether the planned work to remedy flooding in Glen Cairn addresses the potential issues known now.

Audit Objective #13 - Evaluate the value for dollar of the Glen Cairn flood remedial measures.

Audit Scope

The audit has been designed and executed using a two-track approach that moves from a broad “due diligence” review of City development application process execution, to a more specific and detailed review of stormwater and servicing engineering design solutions and operations/maintenance practices.

Consistent with Council motion 75/9, the first track of the audit, addressing development applications and approvals process execution review focussed on residential development files for lands and properties located within the Carp River watershed – communities such as Glen Cairn, Stittsville, and Kanata West. 

The audit’s second track addressed the “due diligence” exercised by the City pertaining to engineering solutions put in place to manage and mitigate a potential flood event (i.e., sewer servicing and stormwater management).

Summary of Key Findings

1.        The new City of Ottawa was formed on January 1, 2001, with the amalgamation of the Regional Municipality of Ottawa-Carleton (RMOC) and the local municipalities of Cumberland, Gloucester, Goulbourn, Kanata, Nepean, Osgoode, Ottawa, Rideau, Rockcliffe Park, Vanier, and West Carleton.  In the discussion that follows, four periods are noted, namely, Approvals Prior to 1995, the period from 1995 to 2000 is labelled Recent Pre-amalgamation Approvals; the period from January 1, 2001 to 2004, is labelled Home Rules; and, the period after the current Ottawa Sewer Design Guidelines came into force in November 2004 is labelled Harmonized Engineering Standards or Post-amalgamation City-wide Design Standards.

 

Approvals Prior to 1995	Recent	Post-Amalgamation Home Rules	Post-Amalgamation City-wide Design Standards
(1960-1994)	(1995-2000)	(2001-2004	(2004-current)
975 flooded homes	34 flooded homes	144 flooded homes	11 homes
84% of Total	3% of Total	12% of Total	1% of Total

Table 1 – Approval Periods

It should be noted that the 11 homes that were flooded in subdivisions approved using the Post-amalgamation City-wide Design Standards are located in a subdivision that was under construction, and therefore did not have all the required stormwater management devices installed at the time of the storm.

2.        The radar derived 24 hour average rainfall map prepared by the City after the July 24, 2009 rainstorm (see Figure 1) is not completely instructive in understanding the storm event’s propensity to cause flooding. At various times in various Carp River watershed locations, the storm event reached 100 year levels of precipitation intensity for a 24 hour period.  However, it appears that peak precipitation intensity from the July 24th storm event (i.e., represented by the dark purple rainfall areas) did not directly impact the residential development areas that experienced flooding.  The purple precipitation areas, which have 24-hour cumulative rainfalls exceeding the 100 year return period precipitation, were in fact centred over undeveloped parcels of land and non-residential developments without basements.  Therefore, some uncertainty exists whether this acknowledged 100 year storm event was in fact a 100 year potential flooding event – when viewed from a residential development location perspective.  It is critical to gauge the extent of flooding, and engineering solution performance, against an accurate measure of storm event intensity.  It is our understanding that the City’s Phase 3 investigation is addressing this issue.

Examination of the radar rainfall data provided by the City for 1-hour and 3-hour accumulation indicates that the rainfall intensities reached the 50 year level for 1-hour duration in the Fringewood Subdivision and Old Stittsville areas, and 5 year return period intensities everywhere else.  The 3-hour rainfall accumulations were less than the 2 year return period rainfall intensities.

After reviewing available precipitation intensity data across a number of timeframes, the July 24, 2009 storm event that occurred over west-end residential development does not appear to have been a 100 year flood event.  Subsequent residential flooding clusters cannot be solely, or even primarily, attributed to a storm event that failed to exceed City stormwater engineering design capacity.   It should be noted that the City’s investigations are addressing this finding in the Phase 3 study.

Figure 1 – Rain Event July 24, 2009

3.        Data overlay mapping prepared for this audit documents the fact that residential subdivision developments approved under the City’s current Post-amalgamation City-wide Design Standards did not experience flooding during the July 24^th, 2009 storm event.  The flood resistance correlation with Kanata and Goulbourn pre-amalgamation and City Home Rules design standards is less clear, since similar sub–division developments facing similar precipitation intensity levels demonstrated vastly different flood resistance outcomes.  While the presence or absence of inlet control devices[1] or backwater prevention valves[2] seems to be a critical flood resistance factor, there also appear to be other potential causation factors beyond approval era of origin.  This aspect is discussed further in subsequent points of this Executive Summary and in the report.

4.        The following conclusions can be made as a result of the observations from the “due diligence” process execution audit of the files:

·    The development review process and risk management linkages were maintained by staff for all the audited subdivisions where there was no flooding;

·    The development review process and risk management linkages were maintained by staff for all the audited subdivisions where there was flooding;

·    When the development review processes are compared between the subdivisions that flooded versus those that did not, staff managed risk appropriately in the process since we found no substantive anomalies;

·    In the case of the Fringewood and the Westwood Phase 2 subdivisions, staff demonstrated an ability to adaptively manage risk, by requiring these subdivisions to comply with the Upper Poole Creek Subwatershed Study which had come into effect while the subdivisions were still being processed; and,

·    We did not carry out a detailed review of the engineering studies. 

5.        In the case of the Westwood Subdivision, Phase 1 – approved before amalgamation – had inlet control devices specified and the houses were required to have their foundation levels above the 100 year hydraulic grade line, similar to the current engineering requirements.  However, Phase 2 – approved during the Home Rules period – was not designed to the same standards as Phase 1.  In this case, the Home Rules were applied during review of Phase 2 of the subdivision and resulted in a lower flood protection for the newer phase of the subdivision than was provided for in the phase approved before amalgamation.

Figure 2 documents the selected files.

Figure 2: Audit Files Compared to the July 24, 2009 Rain Event

6.        The transition period between the Stittsville Master Drainage Plan (1994) and the Upper Poole Creek Subwatershed Study (2000) provides an opportunity to examine the potential for adaptive management across multi-year development review process timeframes.  Adaptive management requires the City to amend its processes and review criteria across a changing regulatory landscape for any given application.

From 1994, the Stittsville Master Drainage Plan addressed the stormwater management design requirements for the village of Stittsville since no previous subwatershed study was in effect.  In 2000, the Upper Poole Creek Subwatershed Study was approved, and effectively superseded the Stittsville Master Drainage Plan where the two overlapped.  If there was a culture of adaptive management present, then any subdivisions being originally considered under the Stittsville Master Plan should have been made subject to the Upper Poole Creek Subwatershed Study before final approval.  The Westwood Phase 2 Subdivision and the Fringewood Subdivision both had the potential to demonstrate adaptive management since both developments were applied for while the Stittsville Master Drainage Plan was in effect with the Upper Poole Creek Subwatershed Study coming into effect while the developments were being processed.  In both cases, the development agreements required the subdivision’s stormwater management system to conform to the Upper Poole Creek Subwatershed Plan, which demonstrates that staff acted with diligence in attempting to manage risk during the development review process by ensuring a linkage to the new subwatershed study.

As noted in item 5, the engineering design review component of the planning and development review did not demonstrate the same level of adaptive management.  This is problematic given that both Goulbourn and Kanata had similar stormwater management design criteria, based on the Urban Drainage Design Guidelines (1987) and that inlet control devices were used in some subdivisions in both municipalities.  We note that the design standards did not require the use of the inlet control devices, but they were applied by some pre-amalgamation municipalities in certain new developments.

7.        Although the focus of the audit is on the development review process of the City of Ottawa and former municipalities, the Mississippi Valley Conservation Authority and Rideau Valley Conservation Authority are important agencies in the subdivision approval process.  The role that the Conservation Authority takes is a role that has been devolved from the Province of Ontario and all subdivision applications must be circulated to the appropriate Conservation Authority for review and comment.

If the Conservation Authority had identified a stormwater management issue with a subdivision during the development review process but the municipality went ahead with approval of the subdivision, there would be concern about the viability of the subdivision’s stormwater management system.  However, through a review of all the correspondence in the audit files, we observed no discord between either the Mississippi Valley Conservation Authority or Rideau Valley Conservation Authority and the local municipality.  There appears to have been solidarity among the Conservation Authorities and municipality when an issue arose.  In one situation, the concerns shared by the Conservation Authority and municipality regarding stormwater management and the depth of basements ultimately resulted in the developer revising the proposed development to housing units without basements.

8.        Following amalgamation in January 1, 2001, the Home Rules design standards used by the City varied significantly across the amalgamated local municipalities.  For instance, in Gloucester, City staff report that the requirement for installed inlet control devices was considered “standard operating procedure” and became a requirement in practice although not written in the design standards.  However, in Kanata and Goulbourn Township, inlet control devices to protect basements were not required by their design standards, and were not part of the “standard operating procedure”. 

While City staff were working between 2001 and 2004 on new City-wide stormwater and servicing design standards, it is not clear why the design practices were not amended to mirror those in place in Gloucester, where inlet control devices were generally used (although not a requirement of the Gloucester standards, staff informed us that it was standard practice to require them).  This is more so, given that inlet control devices and other stormwater management requirements had already been implemented pre-amalgamation in some developments in both Goulbourn Township and the City of Kanata.

9.        In our opinion, draft plan conditions can be amended if necessary and this is specifically permitted by the Planning Act.  A subdivision agreement includes the draft plan conditions as a schedule, which allows the ability to ensure that engineering drawings and standards are updated.  Therefore, for practical purposes, it is our opinion that the City can modify the requirements of the subdivision agreement up to the point where it gives final approval of the works as constructed. As further discussed below, management does not agree with our opinion.

Our Office obtained a legal opinion, from an outside firm, indicating that the existing conditions of subdivision agreements are broadly defined such that “the City can modify the requirements of a subdivision agreement up to the point where it gives final approval of the works as constructed”. The legal opinion indicates that this is possible because the subdivision agreement conditions stipulate that everything must be done “to the satisfaction of” an identifiable individual representing the City. Clearly the individual should not be satisfied unless the current standards are met.

City staff provided a confidential legal opinion in which they were not able to fully endorse the external opinion. The City should on a go-forward basis, ensure the wording in the subdivision agreement clearly indicates that where engineering design standards have changed, since the time of registration of the subdivision agreement, that the developer shall be responsible at its expense, to update its design and construction to meet the current engineering standards, to the satisfaction of the City.

10.    Stormwater management to account for the minor and major drainage systems, including measures to prevent surcharging of foundation drains and prevention of downstream flooding have been used in Ontario since circa 1976.   As in any field of engineering, the scope and approaches to stormwater management have changed since then and continue to change.  Nevertheless, the main objective of managing urban runoff to prevent flooding by overland runoff and basement flooding is a constant.

11.    Provision of detention storage of large rainfall events to prevent downstream flooding as a result of development dates to the same time.  In this respect, the current standards reflect the methodology used for stormwater management in Ontario since circa 1976.  City staff have informed us that these standards were not applied in the City (including the former municipalities) until the 1980s.  The review of the files indicate that, with the exception of the use of inlet control devices, the standards used since pre-amalgamation provided for the minor and major systems, detention storage, and for protection of basements up to and including the 100 year storm level.

12.    Engineering Reviews of the Subdivision Engineering Drawings carried out by Planning and Growth Management (PGM) met the required standards.  However, as noted in item 5, the application of the Home Rules standards for Goulbourn in Phase 2 of the Westwood subdivision actually applied a lower standard of protection than was used in Phase 1, approved prior to amalgamation.

13.    Since amalgamation, construction reviews are carried out by the City to oversee that construction of municipal services is completed in accordance with the approved engineering drawings.  The developer’s engineer is responsible to provide full-time site inspection.  With the exception of watermain installation, the City staff provides oversight to confirm general compliance.  For watermain installations, the City provides full-time site inspection.

14.    The City does not have a procedure in place to capture the as-built elevation of the basement slabs and foundation elevations in the field.  This is an exception to a process that comprises reviews and checks of the engineering drawings, the stormwater management report and drainage design, field review of road and lot grades, field review of sanitary and storm sewer systems, and inspection of watermain construction.  Although the City inspectors do a qualitative review of conformance of the lot grades and house general elevations in relation to the design elevations, the City does not have any field documentation to confirm that the houses were actually placed at or above the elevation required by the stormwater management design.

15.    Responsibility for checking that house foundations are constructed at the grades required by the engineering drawings now falls under PGM’s inspectors since 2009.   Since 2001 basement elevations have been captured through the approval of lot grading plans and as part of the As-Built certification by the developer’s engineer of record; however, there is no formal method to confirm that the footings and the basements have been constructed in accordance with the engineering drawings.

16.    The City’s Operation and Maintenance procedures for sanitary and storm sewer systems are carried out according to a schedule that meets industry accepted practices.  The Operation and Maintenance procedures are not condensed in an Operations and Maintenance Manual.

17.    The information regarding the sanitary and storm system existing assets and their maintenance reside currently in the Infrastructure Management System (ITX) database.  Because ITX does not have GIS capabilities, the Asset Management group manages a GIS database, which it shares with Wastewater and Drainage.  The Integrated Infrastructure Management System (IIMS) project, which has been underway since 2007, is intended to replace these systems.

18.    The Glen Cairn flood remedial measures completed after the 2002 flood event examined an appropriate range of alternative remedial measures for control of flooding from the Carp River, including improvements to the southwest quadrant of the Glamorgan area to reduce flooding from overland runoff originating in the subdivision (i.e., not in the river).  The City narrowed the scope of the remedial measures to focus on the river channel and culvert improvements.

19.    The Glen Cairn flood remedial measures recommended solution, as implemented, provided an effective solution to the flood risk from the Carp River.  However, known problems with overland storm runoff and the storm sewer systems in the Glamorgan Drive, Uxbridge Crescent, Dundegan Drive area were not resolved.

20.    Remedial measures recommended by a consultant to reduce the risk of flooding from overland runoff in the Glamorgan Drive, Uxbridge Crescent, Dundegan Drive area were postponed by the City for further investigation, as part of a Needs Study, but were later discarded without further investigation because they appeared not feasible.  We confirmed that these recommended remedial measures would not have been feasible under the constraints existing at the time.

21.    The City realized that further studies were required to determine the necessary improvements to the Glamorgan Drive, Uxbridge Crescent, Dundegan Drive area, but postponed the studies.

22.    The City subsequently made improvements to the sanitary sewer to reduce potential inflow from stormwater ponded on top of sanitary manholes, and to improve the hydraulic conditions of the sewers in the area.   In the course of designing these improvements, the City realized that there were segments of the sanitary sewer that might be undersized, and decided to include any further analysis with a Needs Study for storm and sanitary sewers in the area. 

23.    During the preparation of the Terry Fox Drive Master Drainage Study, the consultant found that the storage in the Glen Cairn pond was less than the storage volumes in the 1978 pond design drawings, which were less than those reported in the 1978 design report.  This information was conveyed to the City, and the consultant offered to undertake further analyses.  However, the City informed the consultant that the analysis of the detention pond would be carried out after completion of the Carp River Watershed/Subwatershed Study.  Although there were communications, including meetings, between City departments in this regard, the Carp River study did not address the Glen Cairn Pond.

24.    None of the reports completed to date have addressed the issue of the effect of the Glen Cairn pond on the hydraulic performance of the storm and sanitary sewers in the Glamorgan area.  It is recognized that the storm sewers were designed based on the design standards that were valid at the time, namely a 2 or 5 year design storm.  However, examination of the area shows that when the water level in the pond reaches the 100 year water level determined in the 2003 Performance Review report and the Terry Fox Drive Extension stormwater management report (95.5 m), storm water will surcharge the Glamorgan area storm sewer system by more than 1 metre.  This is a serious impact on the performance of these sewers.  We understand that the current study being done as Phase 3 is addressing this issue.

25.    Information in reports prepared for the design of the Glen Cairn pond in 1978 indicates that the design high water level in the pond, under the 100 year flood, is 94.72 m.  This is consistent with the grades and storm sewer inverts in the Glamorgan subdivision and Castlefrank Road area, as it would not result in backwater into the sewers and the road drainage would be able to flow into the pond. 

26.    The currently accepted 100 year water level (determined by the Mississippi River Conservation Authority) is substantially higher than the corresponding value used in the design of the pond in 1978.  However, no adjustment has been made to address the effects of this higher water level and storage requirements, in particular with respect to surcharging of the sewers discharging into the pond. 

27.    Review of the Terms of Reference for the West End Flooding Investigation – Phase 3, currently in progress, indicates that the issues noted above have been identified as matters to be addressed in the Phase 3 investigation.

28.    It is our opinion that some clarification may be required regarding information that was provided to Council during the September 2, 2009 meeting and in the Phases 1 and 2 Report, particularly pertaining to design criteria and stormwater management practices:

·    Management indicated that the “communities affected by basement flooding were built to former standards that do not include engineered provisions to deal with large, infrequent rainstorm events”.   Based on our findings, this assertion applies to a large percentage of the homes affected, although a number of the affected homes were built since the 1980s, when the Urban Drainage Design Guidelines (1987) were published and generally in place.  The dual drainage concept using minor and major systems has been used in some parts of the City since at least 1989.

·    Management indicated that the dual drainage principle is a relatively new policy.  As discussed in this audit report, the minor and major system dual drainage system philosophy of the current City sewer design standards is not new, and has been used in North America since at least 1976, formalized by APWA in 1981, and in Ontario, including some  Ottawa municipalities, since at least 1987.

·    Management indicated that inlet control devices were not a requirement prior to the current City guidelines being issued.  Although factually correct, it should be noted that inlet control devices were used in some parts of the City since before amalgamation. In some Home Rules they were practices, albeit unwritten, operating procedure.

·    Management indicated that the 2003 Glen Cairn investigation made suggestions for solving the overland runoff problems in the Castlefrank Road and Glamorgan Drive area.  We found that the 2003 Glen Cairn investigation confirmed that flooding by storm overland runoff in this area would remain a concern after the Carp River improvements; the investigation made recommendations for improvements to the area of Castlefrank Road and Glamorgan Drive.

·    Management indicated that one of the areas flooded was designed based on the 5 year storm.  We found that in many of the areas flooded the sewers were designed to convey the 5 year storm but also were designed so that the basements would be located at least 0.3 m higher than the 100 year hydraulic grade line in the sewer.

·    Management indicated that the Westwood subdivision was designed using practices in use before the current City standards.  We found that the Westwood subdivision Phase 1, which had not flooded on July 24th, was designed using similar standards to those in effect at present, including inlet control devices, but Phase 2, which had flooded dwellings, was designed based on the local municipality design standard, providing a lower level of flood protection.

·    Management indicated that the Westwood subdivision design could not be changed since the subdivision agreement had been registered. As we discussed in point 9 above, it is our opinion that management could have required changes to the design standards.

Recommendations and Management Responses

Recommendation 1

That the City ensure that the work plan of the investigation of the July 24^th flood includes an in-depth analysis of the storm’s mapped precipitation intensity colour coded “contours” on an hourly basis.  Such an analysis may explain why the mapped 24 hour average precipitation intensity colour coded contours seem relatively benign over top of development that experienced intense basement flood clusters.

Management Response

Management agrees with this recommendation. The analysis of the contours was included as part of management’s investigation of the flooding events of July 24^th, 2009.

Recommendation 2

That the City require staff to document and report on the number and location of residential dwelling units approved after the 2002 flood event under Kanata and Goulbourn Home Rules.  City staff should also report on any projected future Carp watershed residential dwelling units to be approved in subsequent phases of development applications originally approved under these Home Rules.

Management Response

Management agrees with this recommendation. The number and location of residential dwelling units draft approved after the 2002 flood event in Stittsville under Kanata and Goulbourn Home Rules will be the subject of an information report to Planning and Environment Committee by the Planning and Growth Management department in Q1 2011.  Management will also confirm in this same report, that there are no further future phases of development originally approved under Home Rules that will be developed under Home Rules.

Recommendation 3

That the City seek legal advice concerning the potential liability associated with the City using design practices that were lower than the practices of some pre-amalgamated municipalities regarding inlet control devices (ICD).

Management Response

Management agrees with this recommendation.  Legal Services has confirmed that in the event that legal claims are filed with the City, this would be a standard step followed in all litigation in assessing the City’s response to such claims.

Recommendation 4

That the City should on a go forward basis, ensure the wording in the subdivision agreement clearly indicate that where engineering design standards have changed, since the time of registration of the subdivision agreement, that the developer shall be responsible at their expense, to update their design and construction to meet the current engineering standards, to the satisfaction of the City.

Management Response

Management agrees with this recommendation. Standard subdivision agreement wording will be revised by Planning and Growth Management under delegated authority in Q1 2011.

Recommendation 5

That the City document the operation and maintenance requirements for sewers in an Operations and Maintenance Manual.

Management Response

Management agrees with this recommendation. Operation and maintenance requirements are defined and documented, but in a number of files, formats and locations.  Staff are currently working to develop a system-wide comprehensive operations manual.  This will be complete in Q4 2011 as a part of the ongoing development of the environmental management system (EQMS – ISO 14001).

Recommendation 6

That the City ensure that the proposed Asset Management System, currently in the procurement stage, enables the City to combine the information currently available in two separate management systems.

Management Response

Management agrees with this recommendation.  The City currently uses two separate stand-alone information management systems.  Information is duplicated into a tabular information system (ITX) and a mapping system (GIS), with staff able to access both systems, depending on the information required.

A Request for Proposal is currently on the market to select a leading edge information and work management system that will combine the two ways to access the available information.   Until such time as a review of the submitted proposals has been completed, management is not in a position to state whether or not this single data source has been achieved, but it is certainly the intent of staff to meet this objective. The tendering process will be complete by Q1 2011 and the successful proponent should be selected by management in Q2 2011. 

It should be noted that the availability of information, currently available in two different systems, had absolutely no role to play in the flooding events of July 24^th, 2009 or the application review system.

Recommendation 7

That the City consider during the investigation of flood remedial measures, currently underway, options to increase the storage and reduce the water levels in the Glen Cairn stormwater management pond.

Management Response

Management agrees with this recommendation.  This is being considered as part of a variety of options under consideration as part of management’s investigation.  The ultimate recommended solutions will be the subject of a report to Council by Infrastructure Services Department in Q2 2011.

Recommendation 8

That the City consider in the investigation of flood remedial measures, currently underway, all issues that have been raised in this report, including:

a)      Checking of the basement elevations vs. those required by the engineering drawings;

b)     Glen Cairn stormwater management pond capacity and water levels;

c)      Effect of the Glen Cairn pond on surcharging of the Glen Cairn sewers;

d)     Calculation of the 100-year hydraulic grade line and verification of the design values; and,

e)      Remedial measures to prevent basement flooding in the Glamorgan Drive, Uxbridge Crescent and Dundegan Drive areas specifically and Glen Cairn vicinity generally.

Management Response

Management agrees with this recommendation. The issues raised in this report, including the list above, have been included in management’s investigation undertaken throughout 2010.  With respect to the first statement, management have undertaken a targeted sampling of basement elevations at critical locations through fieldwork to understand their elevation compared to projected hydraulic grade lines.  A field review of approximately 1,000 homes would be exhaustive from a resource perspective.

Infrastructure Services will bring forward a report on the recommended solutions to Planning and Environment Committee in Q1 2011.

Conclusion

Stormwater management and sewer design standards in the City have been similar since circa 1989, except for the consistent application of inlet control devices and backflow prevention valves.

This audit found that residential subdivision developments approved under the City’s current harmonized engineering design standard proved flood-resistant during the July 24, 2009 event. 

Although the rainfall event had areas where the 24-hour rainfall equalled or exceeded the 100 year storm intensities for that period, these did not occur over residential areas.  Furthermore, the rainfall intensities over areas that suffered flooding were equivalent to the 2 to 5 year period rainfall for durations of 1 hour and 3 hours.  It should be noted that sewers can surcharge as a result of the cumulative effect of the rainfall pattern, downstream effects, and other causes; these are being investigated in the Phase 3 report.

In addition, similar subdivision developments approved during the 2001-2004 period when Home Rules design practices were applied and subjected to similar precipitation intensity levels, demonstrated vastly different flood resistance.  Inlet control devices and backwater prevention valves appear to have a critical impact on flood resistance, but there appear to be other potential causes of flooding.  These other causes of flooding are outlined in the Phases 1 and 2 Report by the City.

This audit found no substantive development approvals process anomalies or deficiencies in the review of the sample developments that were investigated in detail.  However, the failure to require inlet control devices was problematic.  In the Westwood subdivision, the application of the Home Rules standards resulted in a lower level of protection to the second phase of the development than was required in Phase 1, which was approved prior to amalgamation.

The City provides reviews during construction and requires certifications of the construction of the sewers and lot grades, but it does not have in place a method to obtain confirmation that the constructed house footings and lowest living space floor elevations meet the requirements of the engineering design.

The Glen Cairn flood remedial works constructed after the 2002 flood provided an effective solution to flood risk from the Carp River.  However, changes to the drainage area, developed area, and volume of runoff tributary to the Glen Cairn stormwater detention pond, and the resulting higher water level in the pond appear to have had a serious adverse effect on the Glamorgan area sewers, and must be investigated in detail. Management has indicated this will be investigated in their Phase III report.

Acknowledgement

We wish to express our appreciation for the cooperation and assistance afforded the audit team by management.

RÉSUMÉ

Introduction

Les inondations répétées dans le bassin hydrographique de la rivière Carp en 1996 et en 2002 ont suscité une inquiétude généralisée chez les citoyens et de nombreuses questions des médias, et elles ont provoqué des débats au Conseil quant à la pertinence de la planification des sous‑bassins hydrographiques de la ville, des processus d’approbation des plans de lotissement et de l’efficacité des mesures de prévention des inondations. L’inondation du 24 juillet 2009 a déclenché une nouvelle ronde d’enquêtes par le personnel municipal et de litiges encore en instance. De plus, à la suite de l’orage du 24 juillet, le personnel de la Ville a recensé environ 1 500 inondations de domiciles dans la partie ouest de la ville.

Lors de la réunion du Conseil du 2 septembre 2009, la motion 75/9 a été présentée et adoptée :

 MOTION N^O 75/9

Motion du conseiller S. Qadri

Appuyée par le conseiller G. Brooks

ATTENDU QUE le 24 juillet 2009, les secteurs de Kanata et de Stittsville ont connu des inondations majeures, à la suite desquelles plus de 800 résidences ont subi des dommages causés par l’eau et le refoulement des égouts;

ATTENDU QUE d’autres secteurs d’Ottawa ont également connu des inondations auparavant, notamment Orléans, en 2006;

ATTENDU QUE la Ville d’Ottawa a déjà dépensé plus de 7 millions de dollars pour mettre en place des mesures correctives afin d’éviter les inondations dans le secteur Glen Cairn et que ces mesures se sont avérées vaines;

ATTENDU QUE la communauté de Glen Cairn est en partie construite dans une zone fragile sur le plan environnemental, la plaine inondable de la rivière Carp, et que d’autres aménagements urbains sont en cours dans des secteurs considérés comme fragiles ou à risque sur le plan environnemental;

ATTENDU QU’en 2007, le Bureau du vérificateur général a effectué une vérification intitulée Vérification de l’étude sur le bassin hydrographique de la rivière Carp et des projets connexes, qui comportait un rapport présenté à huis clos concernant la canalisation de Glen Cairn;

PAR CONSÉQUENT IL EST RÉSOLU QUE le vérificateur général sera prié de modifier son plan de vérification de 2010 pour y inclure une vérification du processus d’examen des demandes d’aménagement, tant pour les lotissements actuels que pour ceux dont les eaux s’écoulent dans la rivière Carp, en ce qui concerne l’approbation du raccordement aux réseaux d’aqueduc, d’égouts séparatifs et d’égouts pluviaux, de même qu’une vérification de l’incidence, sur la protection du milieu aquatique, des pratiques courantes de la Ville en matière d’exploitation et d’entretien de ces réseaux;

IL EST EN OUTRE RÉSOLU QUE, de plus, cette vérification comprendra un examen des mesures correctives applicables au secteur Glen Cairn, tant celles qui ont déjà été prises que celles qui sont envisagées, et qu’avant de déposer son rapport, le vérificateur consultera le greffier municipal et chef du contentieux afin de déterminer lesquelles de ses constatations peuvent être dévoilées dans une séance publique et lesquelles doivent être présentées à huis clos.

ADOPTÉE

Objectifs et portée de la vérification

Objectif n^o 1 : Établir et étayer la chronologie des aménagements approuvés dans le bassin hydrologique de la rivière Carp.

Objectif n^o 2 : Créer une carte ou un profil des aménagements du bassin hydrographique de la rivière Carp et des inondations qui y sont survenues, avec les dates auxquelles elles se sont produites.  

Objectif n^o 3 : À partir des données disponibles, sélectionner un échantillon de dossiers d’approbation de plans de lotissement aux fins d’un examen complet du processus de vérification préalable.

Objectif n^o 4 : À partir des données disponibles, réaliser un échantillon de dossiers d’approbation de plans de lotissement aux fins d’un examen complet du processus de vérification préalable.

Objectif n^o 5 : Examiner les processus de formulation et de mise en œuvre des politiques de la Ville en ce qui a trait au modèle de l’application des règlements des anciennes municipalités (« Home Rules »).

Objectif n^o 6 : Examiner les mesures proactives prises par la Ville pour convaincre les demandeurs d’aménagement dans le bassin hydrographique de la rivière Carp de se plier volontairement aux normes améliorées postérieures à 2004 ou les y contraindre.

Objectif n^o 7 : Examiner et évaluer les méthodes et les processus utilisés pour l’exploitation et l’entretien des réseaux d’égouts séparatifs et pluviaux.

Objectif n^o 8 : Déterminer si les processus et les méthodes d’exploitation et d’entretien répondent aux normes de la Ville, de la province et de l’industrie et sont conformes aux politiques, procédures, lois et règlements pertinents.

Objectif n^o 9 : Examiner et évaluer la planification et la conception des mesures correctives proposées et existantes pour la prévention des inondations à Glen Cairn.

Objectif n^o 10 : Déterminer si les mesures correctives pour la prévention des inondations à Glen Cairn sont conformes aux politiques, procédures, lois et règlements pertinents.

Objectif n^o 11 : Déterminer si les mesures correctives pour la prévention des inondations à Glen Cairn ont tenu compte de tous les problèmes potentiels connus à l’époque où elles ont été planifiées et mises en œuvre.

Objectif n^o 12 : Déterminer si les travaux envisagés pour prévenir les inondations à Glen Cairn tiennent compte des problèmes potentiels connus aujourd’hui.

Objectif n^o 13 : Évaluer le rapport rendement-coût des mesures correctives pour la prévention des inondations à Glen Cairn.

Portée de la vérification

La vérification a été conçue et réalisée selon une approche en deux volets, qui consiste d’abord à procéder à une vérification préalable de l’exécution du processus d’examen des demandes d’aménagement de la Ville dans une plus large mesure, et ensuite à un examen plus circonscrit et plus approfondi des pratiques d’exploitation et d’entretien et des solutions techniques précises aux problèmes d’eau pluviale et d’entretien.

Conformément à la motion du Conseil 75/9, le premier volet de la vérification, qui touche l’exécution du processus d’approbation et de demande d’aménagement, a porté sur les dossiers d’aménagement résidentiel des terrains et des propriétés qui font partie du bassin hydrographique de la rivière Carp, dans des collectivités telles que Glen Cairn, Stittsville et Kanata-Ouest. 

Le deuxième volet de la vérification concernait la diligence raisonnable exercée par la Ville en ce qui a trait aux solutions techniques mises en place pour la gestion et l’atténuation d’éventuelles inondations (c.-à-d. l’entretien des égouts et la gestion des eaux pluviales).

Sommaire des principales constatations

1.      La nouvelle Ville d’Ottawa a été formée le 1^er janvier 2001 à la suite de la fusion de la Municipalité régionale d’Ottawa‑Carleton (MROC) et des municipalités de Cumberland, Gloucester, Goulbourn, Kanata, Nepean, Osgoode, Ottawa, Rideau, Rockcliffe Park, Vanier et West Carleton. Dans l’analyse qui suit, quatre périodes sont définies, soit celle des aménagements approuvés avant 1995, celle des aménagements récents approuvés avant la fusion (de 1995 à 2000), la période des règlements des anciennes municipalités (« Home Rules », de 2001 à 2004) et celle des normes de conception technique harmonisées, ou normes uniformes de conception de la Ville après la fusion (après l’entrée en vigueur, en novembre 2004, des lignes directrices actuelles de la Ville d’Ottawa pour la conception des égouts).

Tableau 1 – périodes d’approbation

Il est à noter que les 11 maisons qui ont été inondées dans des lotissements approuvés en fonction des nouvelles normes de conception qui ont suivi la fusion se trouvent dans un lotissement qui était en construction à l’époque et, par le fait même, n’était pas doté de tous les dispositifs de gestion des eaux pluviales nécessaires lorsque l’orage est survenu.   

2.        La carte radar des précipitations moyennes sur 24 heures préparée par la Ville à la suite de l’orage du 24 juillet 2009 (figure 1) ne permet pas de comprendre exactement pourquoi l’orage du 24 juillet a provoqué autant de cas d’inondations. À divers moments, dans divers endroits du bassin hydrographique de la rivière Carp, l’intensité des précipitations a atteint des niveaux centennaux pour une période de 24 heures. Toutefois, il semble que les précipitations les plus fortes de l’orage du 24 juillet (représentées en violet sur la carte) n’aient pas touché directement les zones résidentielles qui ont été inondées. Les zones violettes, dont les précipitations cumulées dépassent la période de récurrence de 100 ans, étaient en fait concentrées sur des parcelles de terrain non aménagées et sur des aménagements non résidentiels sans sous‑sol. En conséquence, certaines incertitudes persistent quant à savoir si cette averse centennale était bel et bien une inondation centennale potentielle, du point de vue de l’emplacement des aménagements résidentiels. Il est essentiel de mesurer l’étendue des inondations et l’efficacité des solutions techniques en fonction de mesures précises de l’intensité des précipitations. Nous croyons comprendre que la phase 3 de l’enquête de la Ville se penche sur cet aspect de la question.

L’examen des données radar de précipitations de la Ville relatives aux accumulations en une heure et en trois heures révèle que l’intensité des précipitations a atteint une période de retour de 50 ans pour une durée d’une heure dans les secteurs de Fringewood et du vieux Stittsville, et de cinq ans partout ailleurs. En tout, les accumulations de précipitations sur trois heures étaient moindres que celles d’une période de retour de moins de deux ans.

Au terme de l’examen des données d’intensité des précipitations disponibles sur une longue période, l’orage qui s’est abattu le 24 juillet 2009 sur les aménagements résidentiels de l’ouest de la ville ne semble pas avoir été une inondation centennale. Les inondations combinées dans les zones résidentielles subséquentes ne peuvent pas être uniquement, ni même principalement, attribuées à cet orage, qui n’a pas dépassé la capacité des dispositifs de gestion des eaux pluviales de la Ville. On doit noter que les enquêtes de la Ville se penchent sur ces conclusions dans l’étude de phase 3.

Figure 1 – Précipitations du 24 juillet 2009

3.        Les cartes de superposition des données préparées aux fins de la présente vérification montrent qu’aucun des aménagements résidentiels approuvés en vertu des normes de conception technique actuelles de la Ville n’a subi d’inondation lors de l’orage du 24 juillet 2009. La corrélation relative à la résistance à l’inondation est toutefois plus difficile à établir dans le cas des normes de conception précédant la fusion de Kanata et Goulbourn et de celles des règlements des anciennes municipalités. En effet, des lotissements semblables sujets à des précipitations d’intensité similaire ont résisté de façon bien différente aux inondations. Même si la présence ou l’absence de dispositifs de contrôle du débit[3] ou de clapets anti‑retour[4] semble être un facteur essentiel dans la résistance aux inondations, il semble que d’autres facteurs que le moment de l’approbation d’origine aient joué un rôle dans ce contexte. Cet aspect est analysé plus en profondeur plus loin dans ce résumé et dans le rapport.

4.        La vérification préalable de l’exécution du processus de diligence requise permet de tirer les conclusions suivantes :

·    Pour tous les lotissements vérifiés qui n’ont pas été inondés, le personnel a maintenu le lien entre le processus d’examen du projet d’aménagement et la gestion des risques;

·    Pour tous les lotissements vérifiés qui ont été inondés, le personnel a maintenu le lien entre le processus d’examen du projet d’aménagement et la gestion des risques;

·    En comparant les processus d’examen des projets d’aménagement des lotissements inondés et non inondés, on peut conclure que le personnel a bien géré les risques dans le cadre du processus, puisque nous n’avons constaté aucune anomalie importante; 

·    Dans le cas des lotissements de Fringewood et de la phase 2 de Westwood, le personnel a démontré ses compétences en gestion des risques adaptative en exigeant que ces lotissements se conforment aux recommandations de l’Étude du sous‑bassin hydrographique du tronçon supérieur du ruisseau Poole, entrées en vigueur lorsque les demandes d’aménagement de ces lotissements étaient en cours de traitement;

·    Nous n’avons pas procédé à un examen détaillé des études techniques. 

5.        Pour ce qui est du lotissement de Westwood, approuvé avant la fusion, la phase 1 du projet était dotée de dispositifs de contrôle du débit et les fondations de ses bâtiments devaient se situer au‑dessus de la ligne piézométrique de 100 ans, ce qui est le cas également pour les exigences actuelles. Toutefois, le lotissement de la phase 2, approuvé pendant la période où prévalaient les règlements des anciennes municipalités, n’a pas été conçu selon les mêmes normes que la phase 1. Dans ce cas, les règlements des anciennes municipalités ont été appliqués au cours de l’examen de la phase 2, ce qui a fait en sorte que la phase la plus récente du projet bénéficiait d’une protection moindre que la portion du projet approuvée avant la fusion.

La figure 2  précise quels dossiers ont été sélectionnés.

Figure 2: Audit Files Compared to the July 24, 2009 Rain Event

6.        La période de transition qui se situe entre le Stittsville Master Drainage Plan (Plan directeur de drainage de Stittsville) (1994) et l’Étude du sous-bassin hydrographique du tronçon supérieur du ruisseau Poole (2000) donne une occasion d’examiner les possibilités d’une gestion adaptative dans le cadre du processus pluriannuel d’examen des aménagements. Selon le principe de la gestion adaptative, la Ville doit modifier ses processus et réviser ses critères en tenant compte de la réglementation changeante, et ce, pour toutes les demandes. 

À partir de 1994, le Plan directeur de drainage de Stittsville a regroupé les exigences de conception pour la gestion des eaux pluviales du village de Stittsville, puisqu’aucune étude du sous‑bassin hydrographique n’était en vigueur. En 2000, l’Étude du sous-bassin hydrographique du tronçon supérieur du ruisseau Poole a été approuvée, et dès lors, on a convenu que celle-ci aurait préséance sur le Plan directeur de drainage de Stittsville en cas de recoupement. Si une culture de la gestion adaptative avait été en place, tous les lotissements examinés à la lumière du Plan directeur de drainage de Stittsville l’auraient également été à la lumière de l’Étude du sous-bassin hydrographique du tronçon supérieur du ruisseau Poole avant de recevoir leur approbation finale. Les lotissements de Fringewood et de la phase 2 de Westwood représentaient tous deux des occasions de faire preuve de gestion adaptative, car leur demande d’examen a été faite alors que le Plan directeur de drainage de Stittsville était en vigueur et leurs dossiers ont été traités pendant que l’Étude du sous-bassin hydrographique du tronçon supérieur du ruisseau Poole est entrée en vigueur. Dans les deux cas, en vertu des ententes d’aménagement, les réseaux de gestion des eaux pluviales devaient se conformer au plan du sous-bassin hydrographique du tronçon supérieur du ruisseau Poole, ce qui démontre que le personnel a agi avec diligence dans sa gestion des risques pendant le processus d’examen des projets d’aménagement en s’assurant que ceux-ci sont tenus de respecter les normes établies par la nouvelle étude.

Comme on l’a fait remarquer au point 5, le volet relatif à l’examen de la conception technique du processus de planification et d’examen des projets d’aménagement n’a pas fait l’objet de la même gestion adaptative. Cette situation est problématique, car Goulbourn et Kanata avaient adopté des critères de conception d’installations de gestion des eaux pluviales similaires, basés sur les Urban Drainage Design Guidelines (Lignes directrices de conception des réseaux de drainage en milieu urbain) de 1987 et que des dispositifs de contrôle du débit étaient utilisés dans certains lotissements des deux municipalités.  Nous remarquons que les normes de conception n’exigeaient pas la mise en place de dispositifs de contrôle de débit, mais qu’elles étaient appliquées par certaines municipalités avant la fusion, pour certains nouveaux projets d’aménagement.

7.        Bien que l’objet de la vérification porte sur le processus d’examen des projets d’aménagement de la Ville d’Ottawa et des anciennes municipalités, l’Office de protection de la nature de la vallée de la rivière Mississippi et l’Office de protection de la nature de la vallée Rideau sont des organismes qui jouent un rôle important dans le processus d’approbation des lotissements. Le rôle de ces organismes de protection de la nature leur a été délégué par le gouvernement de l’Ontario et toutes les demandes de lotissement doivent être transmises à l’Office de protection de la nature approprié pour examen et commentaires.

Si l’Office de protection de la nature avait constaté un problème dans la gestion des eaux pluviales d’un lotissement au cours du processus d’examen du projet d’aménagement, mais que la municipalité avait quand même décidé d’aller de l’avant et d’approuver la demande, la viabilité du réseau de gestion des eaux pluviales de ce lotissement pourrait être mise en doute. Toutefois, l’examen de toute la correspondance dans les dossiers vérifiés n’a permis de mettre à jour aucun désaccord entre l’Office de protection de la nature de la vallée de la rivière Mississippi ou l’Office de protection de la nature de la vallée Rideau et la municipalité concernée. En cas de problème, il semble y avoir solidarité entre les offices de protection de la nature et la municipalité. À une occasion, les préoccupations partagées par l’office de protection de la nature et la municipalité au sujet de la gestion des eaux pluviales et de la profondeur des sous‑sols ont amené le promoteur à revoir son projet et à construire plutôt des unités d’habitation sans sous‑sol.

8.        À la suite de la fusion, le 1^er janvier 2001, les normes de conception des règlements des anciennes municipalités utilisées par la Ville variaient considérablement entre les anciennes municipalités désormais regroupées. Le personnel de la Ville rapporte par exemple que dans les règlements de l’ancienne municipalité de Gloucester, l’installation de dispositifs de contrôle du débit était considérée comme une procédure opérationnelle qui allait de soi, au point de devenir une exigence incontournable, même sans être consignée par écrit dans les normes de conception. Toutefois, à Kanata et dans le Canton de Goulbourn, les dispositifs de contrôle du débit pour protéger les sous-sols n’étaient pas obligatoires et leur installation ne faisait pas partie des procédures opérationnelles normales. 

De 2001 à 2004, alors que le personnel de la Ville travaillait à élaborer de nouvelles normes de conception pour les égouts et la gestion des eaux pluviales, les raisons pour lesquelles les pratiques en matière de conception n’ont pas été modifiées pour s’harmoniser à celles en vigueur à Gloucester, où des dispositifs de contrôle du débit étaient généralement utilisés (même si cela ne faisait pas partie des exigences en vertu des normes de Gloucester, le personnel nous a informés que le fait d’exiger de tels dispositifs constituait une pratique usuelle) ne sont pas claires, d’autant plus que les dispositifs de contrôle du débit et les autres exigences touchant les eaux pluviales avaient déjà été mises en place avant la fusion dans certains projets d’aménagement tant dans le Canton de Goulbourn que dans la ville de Kanata.  

9.        À notre avis, il est possible, au besoin, d’apporter des modifications aux conditions d’un plan provisoire et cela est bel et bien permis en vertu de la Loi sur l’aménagement du territoire. L’accord de lotissement comprend un calendrier des conditions du plan provisoire, qui permet de s’assurer que les normes et les dessins conceptuels sont mis à jour. En conséquence, pour des raisons pratiques, nous sommes d’avis que la Ville peut modifier les exigences d’un accord de lotissement jusqu’au moment où elle donne son approbation finale aux travaux tels que construits. Comme nous le mentionnons plus loin, la direction est en désaccord avec notre opinion. 

Notre bureau a obtenu un avis juridique d’un cabinet externe, lequel a indiqué que les conditions existantes d’un accord de lotissement sont définies au sens large de façon que « la Ville puisse modifier les exigences d’un accord de lotissement jusqu’à ce qu’elle accorde son approbation finale aux travaux tels que construits ». Cet avis juridique précise que c’est possible parce qu’il est stipulé dans les conditions d’un accord de lotissement que tout doit être fait « à la satisfaction » d’un particulier identifiable représentant la Ville. Il apparaît donc clair que cette personne ne peut pas être satisfaite tant que les normes actuelles en vigueur ne le sont pas elles aussi.

Le personnel municipal a fourni une opinion juridique confidentielle selon laquelle il n’était pas en mesure d’appuyer entièrement l’opinion externe.  La Ville doit aller de l’avant et s’assurer que le libellé de l’accord de lotissement indiquera que lorsque les normes de conception technique auront changé depuis la date d’enregistrement de l’accord de lotissement, le promoteur sera responsable, à ses frais, des modifications qu’il devra apporter à la conception et à la construction de son projet afin de satisfaire aux normes techniques en vigueur, à la satisfaction de la Ville.

10.    En Ontario, on a commencé à utiliser, vers 1976, des méthodes de gestion des eaux pluviales qui tiennent compte des réseaux majeurs et mineurs de drainage, ce qui comprend des mesures visant à éviter la surcharge des drains de fondation et à prévenir les inondations en aval. Comme dans tous les secteurs du génie, la portée et les approches utilisées pour la gestion des eaux pluviales ont changé et continueront d’évoluer. Néanmoins, le principal objectif qui consiste à assurer la gestion des eaux de ruissellement en milieu urbain en vue de prévenir les inondations causées par l’écoulement de surface et l’inondation des sous-sols demeure toujours le même.

11.    Les clauses prévoyant la rétention temporaire des eaux de grandes pluies afin d’éviter les inondations en aval à la suite d’un aménagement datent de la même époque. À cet égard, les normes actuelles reflètent la méthodologie employée dans la gestion des eaux pluviales en Ontario depuis 1976 environ. Le personnel de la Ville nous a informé que ces normes n’avaient pas été appliquées par la Ville (ni par les anciennes municipalités) jusque dans les années 1980. L’examen des dossiers révèle qu’à l’exception de l’utilisation de dispositifs de contrôle du débit, les normes qui ont cours depuis la période précédant la fusion prévoyaient des réseaux majeurs et mineurs, la rétention temporaire et la protection des sous‑sols contre des précipitations centennales.

12.    Les examens des dessins techniques des lotissements effectués par le Service de l’urbanisme et de la gestion de la croissance étaient conformes aux normes. Toutefois, comme nous l’avons indiqué au point 5, l’application des normes de la réglementation des anciennes municipalités pour Goulbourn à la phase 2 du lotissement de Westwood a, dans les faits, assuré une protection inférieure à celle fournie par les normes employées pour la phase 1, qui avaient été approuvées avant la fusion.

13.    Depuis la fusion, la Ville effectue l’examen des constructions afin de s’assurer que les services municipaux sont construits conformément aux dessins techniques approuvés. L’ingénieur du promoteur est responsable de l’inspection à temps plein du chantier. Le personnel de la Ville surveille le chantier, à l’exception des conduites d’eau principales, pour assurer sa conformité générale. Dans le cas des conduites d’eau principales, la Ville assure une inspection à temps plein du chantier.

14.    La Ville n’a pas établi de procédure pour effectuer sur le terrain le relevé de la hauteur définitive des dalles de sous‑sol et des fondations. Il s’agit d’une exception dans un processus qui comprend des examens et des vérifications des dessins techniques, un rapport sur la gestion des eaux pluviales et la conception du drainage, un examen sur le terrain du niveau des routes et des terrains, un examen sur le terrain des réseaux d’égouts séparatifs et pluviaux et l’inspection de la construction des conduites d’eau principales. Bien que les inspecteurs de la Ville effectuent un examen qualitatif pour vérifier la conformité du niveau des terrains et de la hauteur générale des maisons par rapport aux dessins techniques, la Ville ne dispose d’aucun document permettant de confirmer que les maisons ont été construites à la hauteur requise ou à une hauteur supérieure à celle requise par la conception des mécanismes de gestion des eaux pluviales.

15.    Depuis 2009, la responsabilité de vérifier que les fondations des maisons sont construites aux niveaux exigés par les dessins techniques incombe aux inspecteurs du Service de l’urbanisme et de la gestion de la croissance. Depuis 2001, la hauteur des sous‑sols est établie au moment de l’approbation des plans de niveau du terrain et dans le cadre de la certification de conformité à l’exécution fournie par l’ingénieur du promoteur; cependant, il n’existe pas de méthode systématique permettant de confirmer que la construction des semelles et des sous‑sols respecte bien les dessins techniques.

16.    Les procédures d’exploitation et d’entretien des égouts séparatifs et pluviaux de la Ville sont effectuées selon un calendrier qui répond aux normes généralement acceptées dans l’industrie. Ces procédures n’ont pas fait l’objet d’un manuel de l’exploitation et de l’entretien.

17.    L’information relative aux réseaux d’égouts séparatifs et pluviaux existants et à leur entretien est conservée dans la base de données du Système de gestion de l’information, soit ITX. Et comme l’ITX ne possède pas de capacité d’information géographique (SIG), le Service de gestion des biens administre une base de données à SIG, qu’il partage avec la Direction des eaux usées et du drainage. Le projet de système de gestion intégré de l’infrastructure, en cours depuis 2007, vise le remplacement de ces systèmes.

18.    Les mesures correctives proposées à la suite des inondations de Glen Cairn en 2002 comprenaient une gamme appropriée d’autres mesures correctives permettant de contrôler les débordements de la rivière Carp. Ces mesures comprenaient entre autres des améliorations au quadrant sud‑ouest du secteur Glamorgan visant à réduire les inondations causées par le ruissellement en surface provenant du lotissement (et non de la rivière). La Ville a finalement limité la portée des mesures correctives afin de concentrer ses efforts sur les mesures correctives ciblant le lit de la rivière et les ponceaux.

19.    Les mesures correctives recommandées après les inondations de Glen Cairn, telles que mises en œuvre, constituaient une solution efficace au risque d’inondation par la rivière Carp. Toutefois, certains problèmes connus liés au ruissellement en surface des eaux pluviales et au réseau d’égouts pluviaux du secteur de la promenade Glamorgan, du croissant Uxbridge et de la promenade Dundegan n’ont pas été résolus.

20.    Les mesures correctives recommandées par un consultant pour réduire le risque d’inondation causé par le ruissellement en surface dans le secteur de la promenade Glamorgan, du croissant Uxbridge et de la promenade Dundegan ont été retardées par la Ville pour permettre une investigation plus poussée dans le cadre d’une étude des besoins, mais ont été écartées par la suite, sans que d’autres études aient été réalisées, parce qu’elles ne semblaient pas réalisables. Nous avons confirmé que ces mesures correctives recommandées n’auraient pas été réalisables compte tenu des contraintes qui existaient à l’époque.

21.    La Ville s’est rendu compte que de nouvelles études s’imposaient pour déterminer les améliorations nécessaires au secteur de la promenade Glamorgan, du croissant Uxbridge et de la promenade Dundegan, mais elle a reporté ces études.

22.    Par la suite, la Ville a apporté des améliorations aux égouts séparatifs afin de réduire l’afflux potentiel d’eau pluviale retenue au‑dessus des regards d’égout et d’améliorer l’état hydraulique des égouts du secteur. Au cours de la conception de ces améliorations, la Ville a constaté que certains segments des égouts séparatifs étaient possiblement trop petits et elle a donc décidé de jumeler les nouvelles analyses des égouts pluviaux et séparatifs du secteur avec une étude des besoins.

23.    Au cours de la préparation du Terry Fox Drive Master Drainage Study (Étude directrice du drainage de la promenade Terry Fox), le consultant a découvert que la capacité du bassin de rétention des eaux pluviales de Glen Cairn était moins importante que la capacité prévue selon les dessins techniques du bassin de 1978, qui était elle‑même moins élevée que celle indiquée dans le rapport de conception de 1978. Le consultant a relayé cette information à la Ville et a offert d’effectuer de nouvelles analyses. Cependant, la Ville a informé le consultant que l’analyse du bassin de rétention des eaux pluviales serait effectuée après la fin de l’Étude sur le bassin/sous-bassin hydrographique de la rivière Carp. Même s’il y a eu des communications, y compris des réunions entre les services de la Ville à ce sujet, l’étude de la rivière Carp n’a pas abordé la question du bassin de rétention de Glen Cairn.

24.    Aucun des rapports déposés à ce jour n’a abordé la question de l’effet de l’étang de retenue des eaux pluviales de Glen Cairn sur le rendement hydraulique des égouts pluviaux et séparatifs du secteur Glamorgan. Il est reconnu que les égouts pluviaux ont été conçus selon les normes de conception qui étaient en vigueur à l’époque, qui permettaient de résister à une tempête de deux à cinq ans. Toutefois, un examen du secteur a démontré que si l’eau de l’étang atteint le niveau centennal établi dans le rapport de rendement de 2003 et dans le Terry Fox Drive Extension stormwater management report (Rapport sur la gestion des eaux pluviales du prolongement de la promenade Terry-Fox), soit 95,5 mètres, les eaux pluviales vont surcharger le système d’égouts pluviaux du secteur Glamorgan de plus de un mètre. Cette situation a des répercussions graves sur le rendement de ces égouts. Nous comprenons que l’étude actuelle en cours de réalisation dans le cadre de la phase 3 traite de ce problème.

25.    Selon les rapports préparés en vue de la conception du bassin de Glen Cairn en 1978, le niveau des hautes eaux du bassin, en fonction d’une inondation centennale, est de 94,72 mètres. Ce calcul est conforme aux niveaux et aux radiers des égouts pluviaux du lotissement Glamorgan et du secteur du chemin Castlefrank, car il ne causerait pas de retenue dans les égouts et l’eau de la route pourrait donc s’écouler dans le bassin. 

26.    Le niveau d’eau centennal actuellement accepté (calculé par l’Office de protection de la nature de la vallée de la rivière Mississippi) est bien plus élevé que les valeurs correspondantes utilisées dans la conception du bassin en 1978. Toutefois, aucun ajustement n’a été effectué pour atténuer les effets de ce niveau d’eau supérieur et des exigences accrues en termes de capacité, en particulier en ce qui a trait à la surcharge des égouts qui se déversent dans le bassin.

27.    L’examen du cadre de référence de la phase 3 de l’enquête sur les inondations du secteur Ouest, actuellement en cours, permet de constater que les questions soulevées ci‑dessus ont été retenues afin d’être abordées dans le cadre de la phase 3 de l’enquête.

28.    Nous sommes d’avis que certains éclaircissements pourraient être nécessaires concernant les renseignements fournis au Conseil dans le cadre de la réunion du 2 septembre 2009 et dans le rapport sur les phases 1 et 2, particulièrement en ce qui concerne les critères de conception et les pratiques de gestion des eaux pluviales :

·    La direction a indiqué que les « secteurs où les inondations de sous‑sols se sont produites ont été bâtis selon les anciennes normes, qui ne prévoyaient pas de dispositions techniques permettant de gérer d’importantes averses occasionnelles ». Selon nos constatations, s’il est vrai que cette assertion s’applique à un pourcentage important des maisons touchées, il n’en demeure pas moins qu’un grand nombre des maisons touchées ont été construites dans les années 1980, après la publication et l’usage généralisé des Urban Drainage Design Guidelines (Lignes directrices sur la conception des réseaux de drainage urbain) (1987). De plus, le concept du réseau de drainage double divisé en réseaux mineur et majeur est en usage à la Ville depuis 1989, sinon plus tôt.

·    La direction a indiqué que le principe de réseau de drainage double constitue une politique relativement nouvelle. Comme le montre le présent rapport de vérification, le principe de réseau de drainage double divisé en réseaux mineur et majeur intégrés aux normes actuelles de conception des égouts de la Ville n’est pas nouveau; il est en usage en Amérique du Nord depuis 1976, sinon plus tôt, et a été formalisé par l’APWA en 1981 et par l’Ontario, y compris certaines municipalités de la région d’Ottawa, depuis 1987, sinon plus tôt.

·    La direction a indiqué que les dispositifs de contrôle du débit n’étaient pas requis avant l’adoption des lignes directrices actuelles de la Ville. Même si cette affirmation est exacte dans les faits, il est important de souligner que les dispositifs de contrôle du débit étaient utilisés dans certains secteurs de la ville depuis avant la fusion. Dans certains règlements des anciennes villes, l’utilisation de ces dispositifs faisait partir des pratiques usuelles, même s’il ne s’agissait pas d’une procédure écrite. 

·    La direction a indiqué que le rapport de l’enquête de 2003 à Glen Cairn comportait des suggestions pour résoudre les problèmes de ruissellement en surface dans le secteur du chemin Castlefrank et de la promenade Glamorgan. Nous avons constaté que l’enquête de 2003 à Glen Cairn a confirmé que l’inondation par ruissellement en surface dans ce secteur demeurerait un problème préoccupant, même après les améliorations apportées à la rivière Carp; l’enquête comportait des recommandations pour des améliorations dans le secteur du chemin Castlefrank et de la promenade Glamorgan.

·    La direction a indiqué que l’un des secteurs inondés avait été aménagé de façon à résister à une tempête de cinq ans. Nous avons constaté que dans de nombreux secteurs inondés, les égouts étaient conçus pour résister à une tempête de cinq ans, mais étaient aussi aménagés de façon que leurs sous‑sols soient situés au moins 0,3 mètre plus haut que la ligne piézométrique centennale de l’égout.

·    La direction a indiqué que le lotissement de Westwood a été aménagé selon des normes précédant les normes actuelles de la Ville. Nous avons constaté que le lotissement de la phase 1 de Westwood, qui n’a pas subi d’inondations le 24 juillet, avait été conçu selon des normes semblables à celles actuellement en vigueur, ce qui comprend l’installation de dispositifs de contrôle de débit, alors que le lotissement de la phase 2, où certaines unités d’habitation ont été inondées, avait été aménagé selon les normes de la municipalité d’alors, offrant par le fait même une moins bonne protection contre les inondations.

·    La direction a indiqué que la conception du lotissement de Westwood ne pouvait être changée, étant donné que l’accord de lotissement avait été enregistré. Comme nous le mentionnons au point 9, nous sommes d’avis que la direction aurait pu demander des changements aux normes de conception.

Recommandations et réponses de la direction

Recommandation 1

Que la Ville s’assure que le plan de travail de l’enquête sur les inondations du 24 juillet comprend une analyse approfondie heure-par-heure des « contours » de couleur sur la carte de l’intensité des précipitations. Cette analyse pourrait permettre d’expliquer pourquoi les contours de couleur sur la carte de l’intensité des précipitations indiquent une intensité relativement faible au‑dessus des secteurs aménagés qui ont subi des inondations de sous-sol fortes.

Réponse de la direction

La direction est d’accord avec cette recommandation. L’analyse des contours a été intégrée à l’enquête de la direction sur les inondations survenues le 24 juillet 2009.

Recommandation 2

Que la Ville demande à son personnel de produire un rapport sur le nombre et l’emplacement des unités résidentielles approuvés après les inondations de 2002 en vertu de l’ancienne réglementation de Kanata et de Goulbourn. Le personnel devrait également faire rapport sur tout projet d’unité résidentielle futur dans le bassin hydrographique de la rivière Carp dont la demande d’aménagement en est aux dernières phases d’approbation et dont cette même demande a initialement été approuvée en vertu de l’ancienne réglementation susmentionnée.

Réponse de la direction

La direction est d’accord avec cette recommandation. Le nombre et l’emplacement des projets d’unités résidentielles approuvés après les inondations de 2002 à Stittsville, en vertu des anciens règlements municipaux de Kanata et de Goulbourn, feront l’objet d’un rapport d’information à l’intention du Comité de l’urbanisme et de l’environnement préparé par le Service d’urbanisme et de gestion de la croissance au court du premier trimestre de 2011. La direction confirmera également, dans ce rapport, qu’aucune autre phase de quelque projet que ce soit déjà approuvé en vertu des anciens règlements ne sera mise en œuvre en fonction de ces règlements.

Recommandation 3

Que la Ville obtienne un avis juridique concernant sa responsabilité potentielle liée à son utilisation de pratiques de conception relatives aux dispositifs de contrôle du débit dont les normes étaient inférieures aux pratiques qui étaient en vigueur dans certaines municipalités avant la fusion.

Réponse de la direction

La direction est d’accord avec cette recommandation. Les Services juridiques ont confirmé qu’advenant une réclamation fondée en droit auprès de la Ville, il s’agirait, dans tous les cas de litige, d’une étape normale en vue de la préparation de la réponse de la Ville à une telle réclamation.

Recommandation 4

Que la Ville s’assure désormais que le libellé de chaque accord de lotissement indique clairement que lorsque les normes de conception ont changé depuis l’enregistrement de l’accord de lotissement, le promoteur sera responsable, à ses propres frais, de modifier son projet et la construction qui s’y rattache afin de satisfaire aux normes de conception en vigueur, à la satisfaction de la Ville. 

Réponse de la direction

La direction est d’accord avec cette recommandation. Le libellé habituel des accords de lotissement sera révisé par le Service d’urbanisme et de gestion de la croissance, sous un pouvoir délégué, au cours du premier trimestre de 2011.

Recommandation 5

Que la Ville rassemble les exigences en matière d’exploitation et d’entretien des égouts dans un manuel de l’exploitation et de l’entretien.

Réponse de la direction

La direction est d’accord avec cette recommandation. Les exigences en matière d’exploitation et d’entretien des égouts sont bien définies et rassemblées, mais le sont toutefois dans un certain nombre de dossiers, sous diverses formes et dans des lieux divers. Le personnel de la Ville travaille présentement à la préparation d’un manuel d’exploitation et d’entretien à l’échelle de toute l’administration. Ce manuel sera terminé au cours du quatrième trimestre de 2011 dans le cadre du processus de développement continu du système de gestion environnementale (EQMS – ISO 14001).

Recommandation 6

Que la Ville s’assure que le projet de système de gestion des biens, actuellement à l’étape de l’achat, lui permet de combiner les renseignements qui sont en ce moment disponibles dans deux systèmes de gestion différents.

Réponse de la direction

La direction est d’accord avec cette recommandation. La Ville utilise présentement deux systèmes indépendants de gestion de l’information. L’information est dédoublée dans un système d’information tabulaire (ITX) et dans un système de cartographie (SIG) et un personnel a accès aux deux systèmes, selon l’information requise. 

Un appel de propositions est en cours pour la sélection d’un système de gestion de l’information et du travail d’avant-garde qui combinera les deux méthodes d’accès à l’information disponible. Tant et aussi longtemps que l’examen des propositions soumises n’aura pas été réalisé, la direction ne sera pas en position de confirmer si on est parvenu à n’utiliser qu’une seule source de données. Or, il est clair que le personnel a bien l’intention d’y parvenir. Le processus d’appel d’offres sera complété au cours du premier trimestre de 2011 et le soumissionnaire qui l’emportera sera choisi par la direction au cours du deuxième trimestre de 2011. 

On doit souligner que la disponibilité de l’information dans deux systèmes n’a joué aucun rôle dans les inondations du 24 juillet 2009, ni dans l’application du système d’examen.  

Recommandation 7

Que la Ville s’assure que l’étude sur les mesures correctives visant à prévenir les inondations, en cours actuellement, intègre des mesures pour augmenter la capacité et réduire le niveau d’eau du bassin de rétention des eaux pluviales de Glen Cairn.

Réponse de la direction

La direction est d’accord avec cette recommandation. L’intégration de ces mesures est présentement considérée comme une possibilité parmi plusieurs autres dans le cadre de l’analyse que réalise la direction. Les solutions définitives recommandées feront l’objet d’un rapport préparé par les Services d’infrastructure pour le Conseil et qui sera déposé au cours du deuxième trimestre de 2011.

Recommandation 8

Que la Ville intègre à l’étude sur les mesures correctives visant à prévenir les inondations, en cours actuellement, toutes les questions soulevées dans le présent rapport, notamment :  

a)      la vérification de la hauteur des sous‑sols, qui doit correspondre à celle qui est prévue selon les dessins techniques;  

b)     la capacité du bassin de rétention des eaux pluviales de Glen Cairn et les niveaux d’eau;

c)      l’effet du bassin de Glen Cairn sur la surcharge des égouts de Glen Cairn;

d)     le calcul de la ligne piézométrique de 100 ans et la vérification des valeurs de conception;

e)      les mesures d’atténuation visant à prévenir l’inondation des sous-sols dans le secteur de Glen Cairn, et plus précisément dans celui de la promenade Glamorgan, du croissant Uxbridge et de la promenade Dundegan.

Réponse de la direction

La direction est d’accord avec cette recommandation. Les questions soulevées dans ce rapport, y compris celles de la liste ci-dessus, ont été incluses dans l’enquête réalisée par la direction au cours de 2010. En ce qui concerne le premier point, la direction a entrepris un échantillonnage ciblé des hauteurs de sous-sols à des endroits plus à risques dans le cadre de travail sur le terrain afin de comprendre leur élévation comparativement aux lignes piézométriques projetées. Sur le plan des ressources, un échantillonnage d’environ 1 000 maisons serait suffisamment complet.

Les Services d’infrastructure présenteront un rapport au Comité de l’urbanisme et de l’environnement au cours du premier trimestre de 2011. 

Conclusion

Hormis l’installation de dispositifs de contrôle du débit et de clapets anti‑retour, la gestion des eaux pluviales et les normes de conception des égouts n’ont pas changé depuis 1989.

La présente vérification a permis de constater que les aménagements de lotissements approuvés en vertu des normes harmonisées de conception technique actuelles de la Ville ont su résister aux inondations dues à l’averse du 24 juillet 2009.

Même si les précipitations sur 24 heures correspondaient en certains secteurs à une intensité centennale ou plus, cela n’a pas été le cas dans les zones résidentielles. De plus, l’intensité des précipitations dans les secteurs inondés équivalait à une période de récurrence de deux à cinq ans pour des durées d’une heure et de trois heures. Il est important de noter que les égouts peuvent être surchargés en raison de l’effet cumulatif des modèles d’averse, des effets en aval et d’autres causes; celles-ci font l’objet d’une enquête dans le rapport sur la phase 3.

De plus, des aménagements de lotissements similaires approuvés entre 2001 et 2004, au cours de la période des règlements des anciennes municipalités, et qui ont subi des précipitations d’une intensité comparable, ont montré une résistance aux inondations très différente. Si les dispositifs de contrôle du débit et les clapets anti‑retour semblent avoir un effet considérable sur la résistance aux inondations, il semble néanmoins qu’il puisse exister d’autres causes possibles à ces inondations. Ces autres causes sont mentionnées dans le rapport sur les phases 1 et 2 préparé par la Ville.

La vérification n’a permis de constater aucune anomalie importante dans le processus d’approbation des projets d’aménagement ni aucune déficience dans l’examen de l’échantillon de dossiers d’aménagement que nous avons analysés en détail. Toutefois, le fait de ne pas avoir exigé d’installation de dispositifs de contrôle du débit est jugé problématique. Dans le lotissement de Westwood, l’application des normes des anciennes municipalités a donné lieu à une protection inférieure dans la seconde phase de l’aménagement par rapport à la première, approuvée avant la fusion.

La Ville procède à des inspections pendant la construction et exige la certification de la construction des égouts et des niveaux des terrains, mais elle ne dispose d’aucun moyen pour confirmer que les semelles et la hauteur de l’étage d’habitation le plus bas sont conformes à la conception technique.

Les travaux correctifs effectués à la suite des inondations de 2002 à Glen Cairn représentaient une solution efficace au risque d’inondation par la rivière Carp. Cependant, des changements dans la zone de drainage, la zone aménagée et le volume du ruissellement tributaire du bassin de rétention des eaux pluviales de Glen Cairn, de même que l’augmentation du niveau d’eau du bassin résultant de ces changements semblent avoir eu un important effet négatif sur les égouts du secteur Glamorgan et doivent donc faire l’objet d’une enquête approfondie. La direction a fait savoir qu’elle procéderait à une telle enquête dans le rapport sur la phase 3.

Remerciements

Nous tenons à remercier la direction pour la coopération et l'assistance accordées à l’équipe de vérification.

1      INTRODUCTION

Repeated Carp River watershed flooding in 1996 and 2002 prompted widespread citizen concern, media questions and Council debate concerning the appropriateness of City sub-watershed planning, subdivision development approvals processes and the effectiveness of flood mitigation engineering solutions. The July 24, 2009 flood event has generated a new round of City staff investigations and pending litigation.  Arising from the July 24^th storm event, approximately 1,500 residential west-end flooding incidents have been reported by City staff.

At the September 2^nd 2009 meeting of Council, Motion 75/9 was tabled and carried:

MOTION NO. 75/9

Moved by Councillor S. Qadri

Seconded by Councillor G. Brooks

WHEREAS on July 24th, 2009 serious flooding occurred in Kanata and Stittsville and resulted in over 800 residences being damaged by water and sewage;

AND WHEREAS previous flooding has also occurred in other area of Ottawa, including Orléans in 2006;

AND WHEREAS the City of Ottawa has previously spent over $7 million in remedial measures to prevent further flooding in the Glen Cairn area and these measures failed;

AND WHEREAS the Glen Cairn community is partially built in an environmentally sensitive area, flood plain of the Carp River and as other city development continues to occur in environmentally sensitive/risky areas;

AND WHEREAS in 2007 the Office of the Auditor General completed an Audit of Carp River Watershed Study and Related Projects, which included an in-camera report on the Glen Cairn Channelization;

THEREFORE BE IT RESOLVED that the Auditor General be requested to consider modifying his 2010 Audit Plan to include an Audit of the City of Ottawa's Development Review Process, both currently and for the developments that drain into the Carp River, in relation to approval of water, wastewater and stormwater servicing, and an Audit of the City of Ottawa's ongoing operations and maintenance practices in relation to protecting the water environment.

AND THEREFORE BE IT RESOLVED that, further, this audit include a review of the remedial measures regarding Glen Cairn, both already undertaken and planned for the future, and that prior to tabling his report with Council he review his findings with the City Clerk and Solicitor for advice on which findings can be delivered in open session and those which should be delivered in camera.

CARRIED

A City staff investigation of the July 2009 flooding event has been proceeding in parallel to this audit.  This City staff investigation, led by Infrastructure Services, has documented the storm profile in terms of precipitation intensity.  The storm profile was created using a combination of rain gauges and Environment Canada weather radar data.  Figure 1 displays the relative 24-hour rainfall accumulation according to colour coded contours.

At various times in various Carp River watershed locations, the storm event reached 100 year levels of precipitation intensity.  However, it appears that peak precipitation intensity from the July 24^th storm event (i.e., represented by the dark purple rainfall areas) did not directly impact the residential development areas that experienced flooding.  The purple 100 year intensity precipitation areas were in fact centred over undeveloped parcels of land and non-residential developments without basements.  Therefore, some uncertainty exists whether this acknowledged 100 year storm event was in fact a 100 year potential flooding event – when viewed from a residential development location perspective. The City investigation is addressing the issue of the storm intensity that actually impacted residential developed areas.  It is critical to gauge the extent of flooding, and engineering solution performance, against an accurate measure of storm event intensity.

Figure 1 – Rain Event July 24, 2009

2      AUDIT SCOPE

The audit has been designed and executed using a two-track approach that moves from a broad “due diligence” review of City development application process execution, to a more specific and detailed review of specific stormwater and servicing engineering design solutions and operations/maintenance practices.

Consistent with Council Motion 75/9, the first track of the audit, addressing development applications and approvals process execution review focussed on residential development files for lands and properties located within the Carp River watershed – communities such as Glen Cairn, Stittsville, and Kanata West. 

The primary focus of the due diligence development applications review was on residential subdivision development files approved since amalgamation under Home Rules, or the harmonized post-2004 City-wide engineering design standard. 

A secondary focus was on appropriate selected residential subdivision development files originally approved by the two-tier regional government system prior to amalgamation in 2000.  All selected development approval files for review pertained to lands and properties materially impacted by the July 24^th, 2009 precipitation event.

The audit’s second track addressed the “due diligence” exercised by the City pertaining to engineering solutions put in place to manage and mitigate a potential flood event (i.e., sewer servicing and stormwater management). 

Consistent with Council Motion 75/9, the second track engineering solutions review also focussed on i) the review of ongoing operations and maintenance practices in relation to protecting the water environment and ii) the review of the remedial measures regarding Glen Cairn, both already undertaken and planned for the future.

3      AUDIT OBJECTIVES

3.1       Audit Objective #1 - Establish and document the City’s development approvals historic timelines in the Carp River watershed

Criteria:

·         To what extent was Carp River watershed residential development approved/registered prior to the creation of the amalgamated City of Ottawa?

·         To what extent was Carp River watershed residential development approved/registered after the creation of the amalgamated City of Ottawa – but using the fragmented Home Rules model for design standards?

·         To what extent was Carp River watershed residential development approved/registered after the adoption of 2004 harmonized design standards?

·         To what extent was post-2004 Carp River watershed residential new phased development (with original approvals dating from periods prior to 2004) subject to grandfathered Home Rules standards?

3.2       Audit Objective #2 - Create a Carp River watershed development approvals age-identified flooding map/profile

Criteria:

·         What is the development approvals/registration “timeline” profile for the flooded residential property clusters arising from the July 24, 2009 flood event?

·         To what extent were the flood-impacted residential developments approved prior to the creation of the amalgamated City?

·         To what extent were the flood-impacted residential developments approved by the City after amalgamation using Home Rules design standards of its choice?

·         To what extent were the flood-impacted residential developments approved by the City using 2004 harmonized design standards?

·         Is there a correlation between the development approvals/registration time period (i.e., associated design standards) and the existence/location of flood event clusters?  More precisely, did development approved after 2004 using the City’s harmonized design standards experience intense precipitation (i.e., 100 year precipitation event) with fewer reported flood events and clusters?

3.3       Audit Objective #3 - Evidence based selection of subdivision development approval sample files for comprehensive due diligence process review

Criteria:

·         Will comprehensive review of sample files demonstrate overall process execution due diligence - conformity and compliance with City policies and process guidelines in place at the time of each subdivision registration?

·         Will comprehensive audit review of sample files demonstrate a significant gap between the Home Rules design standards (i.e., servicing and stormwater) approved/applied to Carp River development applications versus the home rules standards applied in other pre-amalgamation area-municipalities at the same time?

·         Is there any evidence that City staff considered the repeated application of “generic” Home Rules engineering standards insufficient - given the high risk profile associated with Carp River watershed flood plain residential development after the 1996 and 2002 flood events?

·         Will comprehensive review of sample files demonstrate evidence of pro-active City attempts/tactics to work with applicants to strengthen “typical” design standards in subdivision development agreements (i.e., beyond potentially weak home rules)?

3.4       Audit Objective #4 - Evidence based execution of subdivision development approval sample files for comprehensive due diligence process review

Criteria:

·         Did the City execute development review/approvals process for Carp watershed files according to the due diligence process standards in place at the time?

·         Were servicing and storm water requirements consistent with “best practice” standards of area municipalities at the time?  If not, were City officials transparent in noting that flood plain development was being approved according to outdated or deficient standards?

·         Was the City rigorous in considering/refining technical comments from the Conservation Authority on Carp River development files, given the higher risk profile associated with previous flooding incidents?

·         Is there evidence of heightened rigor in addressing servicing and storm water risk for residential development projects following the 2002 flooding?

3.5       Audit Objective #5 - Review City policy formulation and implementation processes for Home Rules model

Criteria:

·         Was the development risk profile for the Carp River watershed (i.e., repeated flooding events) raised as a specific concern by City staff when designing and implementing the Home Rules model?

·         Did the decision-making process resulting in the adoption of Home Rules ever consider elevating the standards for Carp River development files to the “best available” storm water and flood protection standard in place at the time within the City - as opposed to a demonstrably lower standard in the specific area in question?

·         Are there precedents in other parts of the City where generic Home Rules practices were modified to address unique issues, risks or characteristics of development deemed critical to the public interest or public safety?

3.6       Audit Objective #6 - Review proactive actions by City to convince/compel Carp River watershed development applicants to voluntary compliance with enhanced post-2004 standards

Criteria:

·         Were City development approvals typically “mechanical” or rigid in the sense that staff applied the same flood control/storm water processes and criteria (appropriate for the majority of low risk files across the City) to the demonstrably higher risk Carp River watershed files?

·         Did the City voluntarily agree to grandfather post-2004 Carp watershed development file phases to original pre-amalgamation or post-amalgamation Home Rules?  If so, was there any consideration of exempting the post-2004 phases of Carp River development files from the original storm water/flood control standards and requiring 2004 City-wide standards be applied?

·         Did the City ever consider the use of de-registration or other tools to compel compliance with higher recent engineered flood protection standards?

·         Is there documentation/evidence of City staff attempting to secure applicant voluntary compliance with higher stormwater/flood control measures beyond strictly legal (i.e., older/dated development agreements) or policy driven minimum requirements?

3.7       Audit Objective #7 - Examine and evaluate the processes and methodologies used for the Operation and Maintenance of sanitary and storm drainage systems

Criteria:

·         Asset management database information available for sanitary and storm systems

·         Operation manuals

·         Inspection and Maintenance manuals

·         Inspection and Maintenance procedures, recording, follow-up

·         Maintenance

3.8       Audit Objective #8 - Determine if the Operation and Maintenance processes and methodologies meet the City’s, Province’s and Industry standards, and are consistent with relevant policies, procedures, legislation, and regulations

Criteria:

·         Ministry of the Environment regulations, standards, manuals

·         City’s Operation and Maintenance Policies and Procedures

·         Industry standards

·         Environmental Protection Act

·         Ontario Water Resources Act

·         Planning Act

3.9       Audit Objective #9 - Examine and evaluate the planning and design of the existing and proposed Glen Cairn flood remedial measures

Criteria:

·         Examination of flooding history

·         Definition of scope of investigations

·         Range and quality of alternatives examined

·         Evaluation methodology and criteria

·         Implementation methods

3.10   Audit Objective #10 - Determine if the Glen Cairn flood remedial measures are consistent with relevant policies, procedures, legislation, and regulations

Criteria:

·         Ministry of the Environment and of Natural Resources regulations, standards, manuals

·         City’s Operation and Maintenance Policies and Procedures

·         Environmental Protection Act

·         Conservation Authorities Act and Regulations

·         Ontario Water Resources Act

·         Planning Act

3.11   Audit Objective #11 - Determine if the Glen Cairn flood remedial measures addressed all the potential issues known at the time that they were planned and implemented

Criteria:

·         Review of past flooding events

·         Known flooding problems

·         Drainage constraints

·         City’s design standards

3.12   Audit Objective #12 - Determine whether the planned work to remedy flooding in Glen Cairn addresses the potential issues known now

Criteria:

·         Review of past flooding events

·         Known flooding problems

·         Drainage constraints

·         City’s design standards

3.13   Audit Objective #13 - Evaluate the value for dollar of the Glen Cairn flood remedial measures

Criteria:

·         Examine potential flood damages eliminated by works

·         Determine if more could have been done

4      DETAILED FINDINGS, OBSERVATIONS AND RECOMMENDATIONS

The results of the audit analysis and associated findings are presented in this section following the Audit Objectives. For ease of reference, the Audit Objectives and the Criteria used are repeated here and the findings are discussed in relation to the criteria.

4.1       Audit Objective #1 - Establish and document the City’s development approvals historic timelines in the Carp River watershed

Criteria:

·         To what extent was Carp River watershed residential development approved/registered prior to the creation of the amalgamated City of Ottawa?

·         To what extent was Carp River watershed residential development approved/registered after the creation of the amalgamated City of Ottawa – but using the fragmented Home Rules model for design standards?

·         To what extent was Carp River watershed residential development approved/registered after the adoption of 2004 harmonized design standards?

·         To what extent was post-2004 Carp River watershed residential new phased development (with original approvals dating from periods prior to 2004) subject to grandfathered Home Rules standards?

4.1.1    Findings

We assembled a development approvals process timeline that creates historic “eras” of residential development approvals.  The timeline eras set out in Figure 3 below are as follows:

29.    Approvals Prior to 1995 Era encompasses all pre-1995 approvals.  This era is typically characterized by the two-tier RMOC development approvals process and extends backwards into the 1980s, 1970s and even into the late 1960s.  For audit purposes, development approval files may or may not exist, may or may not be available, and are typically incomplete.  If files are available, their practical value is extremely limited and the engineering standards of the day are no longer relevant.

30.    The Recent Pre-amalgamation Approvals Era encompasses files reviewed and registered between 1995 and amalgamation in 2001. These more recent files are characterized by the two-tier (RMOC and local municipality) development approvals process and current stormwater and serving design standards – including inlet control devices to limit sewer surcharge impacts and prevent basement flooding.  For audit purposes, development approval files are available and typically complete.

31.    The Home Rules Era encompasses files reviewed and registered by the post-amalgamation City of Ottawa until late 2004.  As a transition strategy during the complex implementation period of amalgamation, the new City opted to use the various stormwater and sewer servicing standards of the application’s previous area-municipality.  Homes Rules across the diverse RMOC area-municipalities varied in a number of important aspects – most significantly the inclusion or exclusion of inlet control devices as a mandatory flood mitigation line of defense.  (We have included an explanation of inlet control devices, design storms, and hydraulic grade lines in Appendix B).  Although not specifically included in the design standards, such devices were considered “standard operating procedures” in some area-municipalities, while others did not consistently require them.  Home Rules approvals during 2001-2004 often applied to multiple phases of a subdivision application beyond 2004 – depending on the specifics of the subdivision development agreement that served as a contract for guaranteed levels of flood protection associated with stormwater and sewer design standards. 

32.    The City-wide Design Standards Era encompasses files reviewed and registered by the post-amalgamation City of Ottawa after 2004 following passage of the City of Ottawa Sewer Design Guidelines in November 2004.  The City-wide stormwater and engineering design standards features the installation of inlet control devices and backflow prevention valves as standard operating procedure City-wide, including the Carp River watershed residential development parcels. It is noted that backwater prevention valves were required in some local municipality design standards.

 

Figure 3 – DRP Approval Eras and Flooding Timeline 1

Using the four era timeline, it becomes possible to plot residential flood incidents (i.e., clusters) from the July 24^th storm event across the eras of original subdivision approvals.  The flood incidents are organized in a fashion consistent with City staff’s flood investigation reporting for ease of cross-referencing.

The following four paneled figures will be referred to in the timeline analysis that follows.

Figure 4 – DRP Approval Eras and Flooding Timeline 2

The above panel (Figure 4) reveals that a large portion of the total July 24^th, 2009 flood incidents were originally approved prior to the creation of the amalgamated City during the Approval Prior to 1995 era.  Glen Cairn development occurred primarily in the 1970s and 1980s.  The same can be said of the Katimavik flood cluster.  From a development applications file audit perspective, this era of development is not suitable for detailed process review.

 

Figure 5 – DRP Approval Eras and Flooding Timeline 3

The above panel (Figure 5) demonstrates that 65 Ward 4 flood events were also approved in the Approval Prior to 1995 era.  They are not suitable for development applications process execution audit review.

 

Figure 6 – DRP Approval Eras and Flooding Timeline 4

The above panel (Figure 6) demonstrates that about half of the Ward 6 flood clusters in Kanata West and Stittsville were approved just before amalgamation and onwards - during the Recent Pre-amalgamation, Homes Rules, and Harmonized City Standards eras.  The development approval files associated with these flooding clusters are appropriate for file audit purposes to determine the due diligence of staff during process execution.

Figure 7 – DRP Approval Eras and Flooding Timeline 5

The above panel (Figure 7) demonstrates that 34 Ward 5 flood events were approved in the Recent Pre-amalgamation era.  They are suitable for development applications process execution audit review.

The summary table (1) below is helpful in terms of summarizing the insights of the assembled timeline of flood incidents and original Carp River watershed subdivision development approvals.  Over 80% of the clustered flood incidents correlate with residential development approvals (and associated engineering design standards) from those that pre-date the RMOC (distant) era.  The remaining 16% of clustered flood incidents fall into the development approval eras suitable for a file audit of “due diligence” in executing development approvals under current engineering design standards.

33.    Table 1 - Approval Periods

Approvals Prior to 1995	Recent	Post-Amalgamation Home Rules	Post-Amalgamation City-wide Design Standards
(1960-1994)	(1995-2000)	(2001-2004	(2004-current)
975 flooded homes	34 flooded homes	144 flooded homes	11 homes
84% of Total	3% of Total	12% of Total	1% of Total

4.2       Audit Objective #2 - Create a Carp River watershed development approvals age-identified flooding map/profile

Criteria:

·         What is the development approvals/registration “timeline” profile for the flooded residential property clusters arising from the July 24, 2009 flood event?

·         To what extent were the flood-impacted residential developments approved prior to the creation of the amalgamated City?

·         To what extent were the flood-impacted residential developments approved by the City after amalgamation using Home Rules design standards of its choice?

·         To what extent were the flood-impacted residential developments approved by the City using 2004 harmonized design standards?

·         Is there a correlation between the development approvals/registration time period (i.e., associated design standards) and the existence/location of flood event clusters?  More precisely, did development approved after 2004 using the City’s harmonized design standards experience intense precipitation (i.e., 100 year precipitation event) with fewer reported flood events and clusters?

4.2.1  Findings

34.    Having already established the timeline of flood events and associated Carp River watershed development approval eras, it is useful to understand the actual approval era of flooded versus flood resistant subdivision development parcels.  Is there a correlation between a given approval era and propensity to flood or no flood for development parcels facing similar precipitation intensity during the storm event? 

35.    Working in cooperation with City professional and technical staff from Planning and Growth Management department, we produced the map in Figure 8, which shows the development approvals parcels impacted by the July 24^th, 2009 storm event (according to 24-hour rainfall contours).

36.    The data overlays are as follows:

·    24 hour average precipitation profile of the July 2009 storm event.  The colour coded contours represent the different rainfall experienced in various geographic locations;

·    Reported residential flooding event clusters;

·    Red bordered Carp watershed development ‘parcels” that have been approved and constructed under RMOC and amalgamated City review processes;

·    The mapping is supported by an “age of approvals” log extracted from the City’s MAP application.  The log contains the approval date/era for each red bordered parcel on the map.

Figure 6: Development Approvals Files Compared to the July 24, 2009 Rain Event

The mapping data overlays demonstrate a number of noteworthy observations:

37.    No residential flooding occurred within the 24 hour average precipitation “peaks” represented by the darkest purple contours.  The 24 hour storm peaks were located above undeveloped land or non-residential parcels without basements.

38.    Relatively little subdivision flooding occurred in the secondary peak areas of heavy precipitation represented by dark brown contours (93 mm in 24 hours).  The City’s Sewer Design Guidelines (SDG) indicates that the 50 year return period 24-hour rainfall is 93.6 mm.

39.    Most subdivision flooding occurred in mid-level green (62 mm or less) and light brown (84 mm or less) precipitation contours.  The SDG indicate that the 5 year return period 24-hour rainfall is 62.4 mm, and the 25 year 24-hour rainfall is 84 mm.  Although designed to ensure that basement floor elevations were above the 100-year hydraulic grade line, it is a fact that subdivisions without inlet control devices could be more prone to flooding due to the sewer surcharges for storms less frequent than the 5-year return period.

40.    No subdivisions approved under the City’s post-2004 harmonized engineering standards experienced material levels of flooding – regardless of precipitation intensity.  These subdivisions all featured inlet control devices and backwater prevention valves to protect basements from sewer surcharge back-ups. The post-2004 approved Jackson Trail subdivision, which was under construction in July 2009, experienced flooding in 11 homes - caused by open drains on five excavated construction sites.  Construction process deficiencies on the site rather than approved design shortcomings were the culprit.

41.    Approved subdivisions featuring Kanata and Goulbourn pre-amalgamation design standards experienced substantial flooding – even at moderate levels of 24 hour average precipitation intensity.  Inlet control devices and backwater prevention valves were not uniformly applied under these Home Rules design standards, but the sewers were required to be designed to convey the 100 year return period storm without flooding of basements.

42.    Subdivisions approved based on Pre-amalgamation and Home Rules featuring Kanata and Goulbourn design standards also proved to be flood resistant at the same/greater precipitation intensity levels associated with adjacent flooded parcels. Inlet control devices and backwater prevention valves were not required under these standards.

43.    The data overlay mapping profile documents the fact that residential subdivision developments approved under the City’s current harmonized engineering design standard were not affected by basement flooding during the July 24^th, 2009 storm event.  The correlation of basement flooding with Kanata and Goulbourn pre-amalgamation and City Home Rules design standards is less clear – similar subdivision developments facing similar precipitation intensity levels demonstrated vastly different flooding outcomes.  While the presence or absence of inlet control devices and backwater prevention valves seems to be a critical factor in preventing basement flooding, there also appear to be other potential causation factors beyond approval era of origin.  These are under investigation in the Phase 3 study.

44.    The City provided the graphical contours for the critical 1 hour rainfall and the 3 hour accumulation, as shown on Figures 9 and 10.  Examination of the data indicates that the critical 1-hour intensities exceeded the intensity corresponding to the 50 year rainfall intensity in the Fringewood Subdivision and Old Stittsville areas, and 5 year intensities everywhere else.  The 3-hour rainfall accumulations translate into hourly intensities that correspond to the 2 year return period intensities for the entire area.

 

Figure 9 – 1-hour Rainfall

Figure 10 – 3-hour Rainfall

The City also provided rainfall data at 5 minute intervals, as recorded by the City for the March and Carp Pumping Stations, and Maple, Monahan, and Kinburn facilities.  Based on an analysis of these data, it was found that the 2-hour and 12-hour rainfall volumes at the Carp and March Pumping Stations exceeded the 100 year hourly intensities.  However, examination of the graphical distribution of rainfall for 3-hour accumulation indicates that the hourly intensities for this period reached less than the 2 year return period.

On the basis of this analysis, we conclude that the rain storm itself may have had intensities that exceeded the 100 year return period in some areas, but that the most severe rainfall may not have occurred directly over areas of the City that suffered flooding.

Recommendation 1

That the City ensure that the work plan of the investigation of the July 24^th flood includes an in-depth analysis of the storm’s mapped precipitation intensity colour coded “contours” on an hourly basis.  Such an analysis may explain why the mapped 24 hour average precipitation intensity colour coded contours seem relatively benign over top of development that experienced intense basement flood clusters.

Management Response

Management agrees with this recommendation. The analysis of the contours was included as part of management’s investigation of the flooding events of July 24^th, 2009.

4.3       Audit Objective #3 - Evidence based selection of subdivision development approval sample files for comprehensive due diligence process review

Criteria:

·         Will comprehensive review of sample files demonstrate overall process execution due diligence - conformity and compliance with City policies and process guidelines in place at the time of each subdivision registration?

·         Will comprehensive audit review of sample files demonstrate a significant gap between the Home Rules design standards (i.e., servicing and stormwater) approved/applied to Carp River development applications versus the Home Rules standards applied in other pre-amalgamation area-municipalities at the same time?

·         Is there any evidence that City staff considered the repeated application of “generic” Home Rules engineering standards insufficient - given the high risk profile associated with Carp River watershed flood plain residential development after the 1996 and 2002 flood events?

·         Will comprehensive review of sample files demonstrate evidence of pro-active City attempts/tactics to work with applicants to strengthen “typical” design standards in subdivision development agreements (i.e., beyond potentially weak home rules)?

4.3.1  Findings

1.      In order to deliver an evidence based assessment of municipal “due diligence” in processing Carp watershed residential development applications, an appropriate sample of files must first be selected. Then the various audit criteria for Audit Objectives 3 and 4 can be addressed according to the resulting analysis of file sample process performance evidence.  A sample of 10-12 residential files (with an associated portfolio of studies) was deemed appropriate in the approved audit work plan.

2.        File selection for the sample needs to balance the following considerations and criteria:

·         Diverse sample file distribution across eras - from Recent Pre-amalgamation era versus City Home Rules versus City Harmonized development eras.

·         Both Kanata and Goulbourn engineering design standards must be addressed in the sample.

·         A flood-resistant control group of subdivision files must be selected to compare potential differences in process execution versus subdivision flood files. Precipitation intensity must be balanced.

·         Distribution of the sample across flood impacted Council Wards is desirable.

The following Table (2) documents the sample files selected for the audit’s due diligence of development application processing. Sample files are also displayed on the accompanying map on Figure 11 to demonstrate successful balancing of the above noted criteria.

 

Table 2:  Sample Files of Development Application Processing

 

4.4       Audit Objective #4 - Evidence based execution of subdivision development approval sample files for comprehensive due diligence process review

Criteria:

·         Did the City execute development review/approvals process for Carp watershed files according to the due diligence process standards in place at the time?

·         Were servicing and storm water requirements consistent with “best practice” standards of area municipalities at the time?  If not, were City officials transparent in noting that flood plain development was being approved according to outdated or deficient standards?

·         Was the City rigorous in considering/refining technical comments from the Conservation Authority on Carp River development files, given the higher risk profile associated with previous flooding incidents?

·         Is there evidence of heightened rigor in addressing servicing and storm water risk for residential development projects following the 2002 flooding?

4.4.1  Findings

The Subdivision Process and Linkages to Stormwater Management

Linkages between regional studies and area-specific development to manage risk are inherent in the land use planning and stormwater management framework in Ontario.  These linkages are described in detail below and illustrated in Figure 12.

 

 

Figure 12  Plan of Subdivision Process Chart Highlighting Linkages to Stormwater Management Planning

An Overview of the Current Subdivision / Stormwater Management Linkages

Subwatershed Study and Secondary Plan

As areas of the City are identified for growth, the environmental characteristics of these areas are evaluated by a Subwatershed Study and the future mix of land uses is evaluated through a Secondary Plan.  The Subwatershed Study and Secondary Plan have a relationship since the stormwater management requirements determined by the Subwatershed Study are based on the development concept in the Secondary Plan.  It is intended that development will build-out in accordance with the Secondary Plan, so that the stormwater facilities required by the Subwatershed Study are able to manage the stormwater quantity and quality in the area.

It should be noted that co-ordinated subwatershed studies and secondary plans were not common in all Ontario municipalities 20 years ago; however, it is expected that this linkage exists in all modern plans of subdivisions in a greenfield growth area of Ottawa.

First Subdivision and Stormwater Study

During development review, the first plan of subdivision in the area must be accompanied by a Stormwater Study (Figure 7, Linkage A) that demonstrates how the development meets the requirements of the Subwatershed Study (Figure 7, Linkage B).  In the cases of very large development by a single developer that is phased in by numerous subdivision applications, it is common that a Conceptual Stormwater Management Study is undertaken which addresses all phases of development.  A Conceptual Stormwater Management Study must also demonstrate how the development meets the requirements of the Subwatershed Study.

Stormwater Study and Stormwater Guidelines

Regardless of whether a subdivision application includes a Conceptual Stormwater Study, either study is expected to be generally undertaken in accordance with the Provincial and municipal stormwater guidelines in effect at the time (Figure 7, Linkage C).  With respect to the Province, there are four generations of stormwater guidelines:

·         Urban Drainage Design Guidelines, 1987

·         Stormwater Quality Best Management Practices, 1991

·         Stormwater Management Practices Planning and Design Manual, 1994

·         Stormwater Planning and Design Manual, 2003

With respect to the post-amalgamation City of Ottawa, the Sewer Design Guidelines (November 2004) also establish requirements for stormwater management facilities.

The Urban Drainage Design Guidelines were published by the ministries of the Environment, Natural Resources, Transportation, and Municipal Affairs, in collaboration with the Association of Conservation Authorities of Ontario, the Municipal Engineers Association, and the Urban Development Institute.

First Subdivision’s Development Agreement

Generally, the approval of a subdivision results in the execution of a development agreement.  To complete the circle of risk management which began with the Subwatershed Study, the development agreement is expected to reference the overall Subwatershed Study and the subdivision’s Conceptual Stormwater Study (Figure 7, Linkage D); this commits the developer to provide stormwater facilities in accordance with the prevailing stormwater management framework.

Subsequent Subdivision and Stormwater Study

When a subsequent subdivision is proposed for development, it must be accompanied by a Stormwater Site Management Study (Figure 7, Linkage E) that demonstrates how the development meets the requirements of the Subwatershed Study.  However, if a prior development proposed a change of land use from the Secondary Plan’s development concept that would materially affect stormwater management in the area, it is important that the Stormwater Site Management Study for the new subdivision have regard for the earlier subdivision’s Stormwater Study (Figure 7, Linkage F).  In doing so, stormwater management for a specific development continues to be analyzed, evaluated and implemented as part of a system.  In situations where this occurs, it is expected that the Stormwater Study of the proposed subdivision should reference any previous relevant stormwater studies and continue to reference the Subwatershed Plan (Figure 7, Linkage G).

Subsequent Stormwater Studies and Stormwater Guidelines

All stormwater studies are expected to be undertaken with the Provincial and municipal guidelines in effect at the time, as described above (Figure 7, Linkage H)

Subsequent Subdivision’s Development Agreement

In the case where a new subdivision had to have regard for a previous subdivision’s stormwater management study, the development agreement is expected to reference the overall Subwatershed Study, the previous subdivision’s stormwater study, and the current subdivision’s stormwater study (Figure 7, Linkage I).

The Subdivision Process as an Evaluation Tool for the Audit

The relationship between plans of subdivisions, stormwater studies and stormwater guidelines – and the management of risk that was intended through these linkages – has been in place for two decades in Ontario.

 

The subdivision files that were audited have been compared to the model subdivision process to determine whether variation from the process may have contributed to a disconnect in the risk management linkages.

The comparison against the model subdivision process also allows for insight to be gained by comparing the development review process of subdivisions which experienced flooding versus those that did not.

Findings from the Audit Files

The summary of audit files below is organized into two groups.  Group ‘A’ are the subdivisions which experienced flooding in July 2009 and Group ‘B’ are those that did not.  The details of the audit observations are illustrated in Appendix A, Figures A1 to A11 using the subdivision process chart.

Audit File #A1 – Jackson Trails Phase 2 Subdivision

Portions of the Jackson Trails Phase 2 Subdivision experienced flooding in July 2009; however, it is important to recognize that the subdivision was still under construction at the time.

The subdivision was processed during the period when harmonized City standards were in place.

In effect at the time were the Carp River Watershed/Subwatershed Report Card[5], the City of Ottawa Sewer Design Guidelines, and the MOE Guidelines.

 

Process Linkages – Jackson Trails Phase 2 Subdivision	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing previous stormwater studies	Yes
Stormwater Study referencing Subwatershed Study	Yes
Stormwater Study referencing guidelines in effect at the time	Yes
Development Agreement referencing Subwatershed Study	Not applicable
Development Agreement referencing Stormwater Study	Yes

 

The audit confirms that the subdivision application was accompanied by various stormwater studies, the last in the series being the “Tamarack Lands Stormwater Management Design Brief.”  The reports made appropriate references to the Carp River Subwatershed Study, and referenced the MOE Guidelines and City of Ottawa Sewer Design Guidelines.

The stormwater studies submitted for the subdivision also referenced and had regard for previous subdivisions and their stormwater studies, including the EcoWood subdivision from 2001 and the Timbermere study from 1999.

The development agreement referenced the stormwater management studies that had been reviewed with the subdivision application.

The development agreement was not expected to reference the Carp River Watershed/Subwatershed Report Card, since this was only the first phase of the watershed/subwatershed study.  Had the subwatershed study been complete, it would have then been appropriate for the development agreement to refer to it.

Audit File #A2 – Westwood Phase 2 Subdivision

The Westwood Phase 2 Subdivision experienced flooding in July 2009.

The subdivision is located in the former Township of Goulbourn and was processed during the Home Rules period.

In effect at the outset of the development approval process were the Stittsville Master Drainage Plan and MOE Guidelines.  While the development was still being reviewed, the Upper Poole Creek Subwatershed Study came into effect.

Process Linkages – Westwood Phase 2 Subdivision	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing Subwatershed Study	Not applicable
Stormwater Study referencing Master Drainage Plan	No (see discussion)
Stormwater Study referencing previous stormwater studies	Yes
Stormwater Study referencing guidelines in effect at the time	Yes
Development Agreement referencing Subwatershed Plan	Yes (see discussion)
Development Agreement referencing Stormwater Study	Yes

 

The audit confirms that the subdivision application was accompanied by a stormwater study, the “Westwood Subdivision, Stittsville, Ontario – Site Servicing Report.”  The report indicated that the design for Phase 2 of the subdivision had been incorporated in the design for Phase 1 of the subdivision.  Further research into the Phase 1 files for Westwood confirmed that a stormwater study had been completed, the “Westwood Stormwater Management Report,” and that this report did make appropriate reference to the Stittsville Master Drainage Plan and the MOE Guidelines.

 

In the development agreement, the subdivision’s stormwater management system was required to meet the stormwater study.

It is also important to recognize that the Upper Poole Creek Subwatershed Plan came into effect while the Westwood Phase 2 Subdivision was in process and how this was handled.  We note that the development agreement required the subdivision’s stormwater management system to conform to the Upper Poole Creek Subwatershed Plan, which demonstrates that staff acted with diligence in attempting to manage risk during the development review process by ensuring a linkage to the subwatershed study.

We recognize that the stormwater study for Westwood Phase 2 did not specifically reference the Stittsville Master Drainage Plan.  However, we do not believe that this element of the process is significant, since stormwater for the entire development had been assessed and approved by the agencies during Phase 1 and since the development agreement included reference to the recently completed Upper Poole Creek Subwatershed Plan.

Review of Westwood Phase 1 stormwater management report and engineering drawings revealed that the design included provision for inlet control devices and calculation of the 100 year hydraulic grade line in the storm sewer.  The foundation elevations were required to be placed a minimum of 0.3 m above the 100 year hydraulic grade line.  However, the design of the Westwood Phase 2 did not include inlet control devices.

The reason for the difference in protection criteria is the application of the home rules, although the more stringent requirements could have been applied to the Phase 2 development, even if formal drainage policies were not in place.

Audit File #A3 – Fernbank (Maguire) Subdivision

The southeast portion of the Fernbank (Maguire) subdivision experienced flooding in July 2009.

The subdivision is located in the former Township of Goulbourn and was processed during the pre-amalgamation period.

In effect at the time were the Stittsville Master Drainage Plan, the Richmond Master Drainage Plan, and MOE Guidelines.

Process Linkages – Fernbank (Maguire) Subdivision	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing Master Drainage Plan	Yes
Stormwater Study referencing Subwatershed Study	Not applicable
Stormwater Study referencing guidelines in effect at the time	Yes
Development Agreement referencing Master Drainage Plan	Yes
Development Agreement referencing Stormwater Study	No (see discussion)

 

The audit confirms that the subdivision application was accompanied by a stormwater study, the “Fernbank Subdivision Stormwater Management Concept Report.”  The report made appropriate reference to the Stittsville Master Drainage Plan and indicated that it had been prepared with respect to the guidelines of the Ministry of Environment and Energy, Ministry of Natural Resources, and Rideau Valley Conservation Authority.

Since there was no subwatershed study in place at the time, then no linkage is applicable to a subwatershed study for the Fernbank (Maguire) Subdivision.

In the development agreement, the subdivision’s stormwater management system was required to meet the Stittsville Master Drainage Plan and Richmond Master Drainage Plan.

The development agreement did not reference the stormwater study that was reviewed with the subdivision application.  However, we do not believe that this element of the process is significant, since reference to the master drainage plans existed in the development agreement which is considered the minimum necessary for managing risk.

Audit File #A4 – Westcreek Meadows Phase 1 Subdivision

The Westcreek Meadows Phase 1 subdivision experienced flooding in July 2009.

The subdivision is located in the former City of Kanata and was processed during the pre-amalgamation period.

The MOE Guidelines were in effect at the time.

Process Linkages – Westcreek Meadows Phase 1 Subdivision	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing Subwatershed Study	Not applicable
Stormwater Study referencing guidelines in effect at the time	Cannot confirm
Development Agreement referencing Subwatershed Study	Not applicable
Development Agreement referencing Stormwater Study	Yes

 

The audit confirms that the subdivision application was accompanied by a stormwater study, the “Preliminary Stormwater Management Report for Wedgewood Terry Fox Subdivision.”  A copy of the report did not exist in the City’s files, but one was provided to us upon request.  Based on the information contained in the report, we conclude that it addressed the effects of the development on water levels in the Carp River and the requirements for stormwater quality control.  However, it did not contain any information on the design of the major and minor system.  Based on this, we determined that the report was completed in accordance with the MOE Guidelines.

In the development agreement, the subdivision’s stormwater management system was required to meet the stormwater study.

The City and MVC required in the Draft Plan Approval document that the finished elevation of the underside of the floor slabs of all residential spaces be a minimum of 300 mm above the MVC’s established 100 year flood plain elevation of 95.2 m.

Audit File #A5 – Fringewood Subdivision

The Fringewood[6] Subdivision experienced flooding in July 2009.

The subdivision is located in the former Township of Goulbourn and was processed during the pre-amalgamation period.

In effect at the outset of the development approval process were the Stittsville Master Drainage Plan and the MOE Guidelines.  While the development was still being reviewed, the Upper Poole Creek Subwatershed Study came into effect.

Process Linkages – Fringewood Subdivision	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing Subwatershed Study	Not applicable
Stormwater Study referencing Master Drainage Plan	Yes
Stormwater Study referencing guidelines in effect at the time	Yes
Development Agreement referencing Subwatershed Plan	Yes (see discussion)
Development Agreement referencing Stormwater Study	Yes

 

The audit confirms that the subdivision application was accompanied by a stormwater study, the “Fringewood Subdivision – Site Servicing Report.”  The report indicates that the stormwater study was undertaken so that the “final outflow will meet Ministry of Environment, Ministry of Natural Resources and Mississippi Valley Conservation requirements.”  The report also indicated that it was prepared in conformity to the Stittsville Master Drainage Plan.

In the development agreement, the subdivision’s stormwater management system was required to meet the stormwater study.

It is also important to recognize that the Upper Poole Creek Subwatershed Plan came into effect while the Fringewood Subdivision was in process and how this was handled.  We note that the development agreement required the subdivision’s stormwater management system to conform to the Upper Poole Creek Subwatershed Plan, which demonstrates that staff acted with diligence in attempting to manage risk during the development review process by ensuring a linkage to the new subwatershed study.

The Township of Goulbourn prepared an Urban Drainage Policy in 1989 which required that basements be protected from flooding up to and including the 100 year event.  The document indicates that the stormwater management plans will be in accordance with the Urban Drainage Policy, the Townships of Goulbourn Engineering Standards, and the Provincial Urban Drainage Design Guidelines, 1987.

The Draft plan approval required that the footings be located not lower than 100 year water level determined in the Stormwater Site Management Plan.

Audit File #A6 – Castlefrank Townhouses

The Castlefrank Townhouses experienced flooding in July 2009.

The development is located in the former City of Kanata and was processed during the pre-amalgamation period.

The MOE Guidelines were not established when the Castlefrank Townhouse development was processed.

Process Linkages – Fringewood Subdivision	Complied
Stormwater Study submitted for development review	Not applicable for Plan of Condo; cannot confirm for Site Plan (see discussion)
Stormwater Study referencing Subwatershed Study	Not applicable
Stormwater Study referencing guidelines in effect at the time	Not applicable
Development Agreement referencing Subwatershed Plan	Not applicable
Development Agreement referencing Stormwater Study	Not applicable

 

The documentation audit included the Plan of Condominium application and Site Plan Agreement files, rather than a Plan of Subdivision application, and therefore the stormwater linkages do not apply in the same way.

A stormwater study is not typically required for a Plan of Condominium.  The age of the development also pre-dates the Province’s Urban Drainage Design Guidelines (1987) and the Stormwater Quality Best Management Practices (1991) guideline.

In the Plan of Condo development agreement, the developer was required to provide a grade and drainage plan.

A townhouse development would have been subject to a Site Plan approval, during which it is anticipated that a stormwater study would have been required.  However, due to the age of the development Site Plan approval records were not available for review and only the Site Plan agreement was available for review.  We are therefore not able to confirm if a stormwater study was prepared for the development.

In the Site Plan agreement, the developer was required to provide a grade and drainage plan.

Audit File #B1 – Fairwinds South

The Fairwinds South subdivision did not experience flooding in July 2009.

The subdivision was processed during the period when harmonized City standards were in place.

In effect at the outset of the development were the Carp River Restoration Class EA, the Carp River Watershed/Subwatershed Study, the MOE Guidelines, and the City of Ottawa Sewer Design Guidelines.

Process Linkages – Fairwinds South	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing Subwatershed Study	Yes
Stormwater Study referencing guidelines in effect at the time	Yes
Development Agreement referencing Subwatershed Plan	Yes
Development Agreement referencing Stormwater Study	Yes

 

The audit confirms that the subdivision application included a stormwater study, the “Fairwinds South – Stormwater Management Design Brief.”  The report indicates that it was prepared in accordance with the Class Environmental Assessment for the Restoration of the Carp River and the Carp River Watershed/Subwatershed Study.  The report also indicated that it was prepared in accordance with the guidelines of the Ministry of Environment and the City of Ottawa.

In the development agreement, the subdivision’s stormwater management system was required to meet the stormwater study and the subwatershed study.

Audit File #B2 – Fairwinds North Phase 1 Subdivision

The Fairwinds North Phase 1 Subdivision did not experience flooding in July 2009.

The subdivision was processed during the period when harmonized City standards were in place.

In effect at the outset of the development approval process were the Carp River Restoration Class EA, the Carp River Watershed/Subwatershed Study, the MOE Guidelines, and the City of Ottawa Sewer Design Guidelines.

Process Linkages – Fairwinds North	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing Subwatershed Study	Yes
Stormwater Study referencing guidelines in effect at the time	Yes
Development Agreement referencing Subwatershed Plan	Yes
Development Agreement referencing Stormwater Study	Yes

 

The audit confirms that the subdivision application included a stormwater study, the “Servicing Brief for Fairwinds North, Phase 1.”  The report indicates that it was prepared in accordance with the Class Environmental Assessment for the Restoration of the Carp River and the Carp River Watershed/Subwatershed Study.  The report also indicated that it was prepared in accordance with the guidelines of the Ministry of Environment and the City of Ottawa.

In the development agreement, the subdivision’s stormwater management system was required to meet the stormwater study and the subwatershed study.

The audit was able to further confirm that the stormwater management considerations for Fairwinds Phase 2 were being addressed through the anticipated process.

Audit File #B3 – Westridge Estates Phase 3B

The Westridge Estates Phase 3B Subdivision did not experience flooding in July 2009.

The subdivision is located in the former Township of Goulbourn and was initially processed during the pre-amalgamation period and completed during the home rules period.

In effect at the outset of the development approval process were the Upper Poole Creek Subwatershed Study and the MOE Guidelines.

Process Linkages – Westridge Estates Phase 3B Subdivision	Complied
Stormwater Study submitted for development review	References past study
Stormwater Study referencing Subwatershed Study	Cannot confirm
Stormwater Study referencing Master Drainage Plan	Cannot confirm
Stormwater Study referencing previous stormwater studies	Yes (see discussion)
Stormwater Study referencing guidelines in effect at the time	Cannot confirm
Development Agreement referencing Subwatershed Plan	Yes
Development Agreement referencing Stormwater Study	Yes

 

The audit confirms that the subdivision application did not include its own standalone stormwater study but based on correspondence in the file, we understand that the stormwater design for Phase 3A also took into account the development for Phase 3B.  This study was the “Westcreek Conceptual Stormwater Site Management Plan, West Ridge Estates,” which correspondence indicates had been previously approved.  A copy of this report does not exist in the City’s files so we are unable to determine whether the report was completed in accordance with the Upper Poole Creek Subwatershed Study or the MOE Guidelines.

In the development agreement, the subdivision’s stormwater management system was required to meet the previously approved stormwater study and was also required to meet the Upper Poole Creek Subwatershed Study.

Audit File #B4 – Fernbank (Ray Bell) Subdivision

The Fernbank (Ray Bell) Subdivision did not experience flooding in July 2009.

The subdivision is located in the former Township of Goulbourn and was processed during the pre-amalgamation period.

The MOE Guidelines were in effect at the outset of the development approval process and the Stittsville Master Drainage Plan was pending approval by the authorities.

 

Process Linkages – Fernbank (Ray Bell) Subdivision	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing Master Drainage Plan	Yes
Stormwater Study referencing guidelines in effect at the time	Yes
Development Agreement referencing Subwatershed Plan	Cannot confirm
Development Agreement referencing Stormwater Study	Cannot confirm

 

The audit confirms that the subdivision application was accompanied by a stormwater study, the “Fernbank Subdivision SWM Concept Report.”  The report indicates that although the Stittsville Master Drainage Plan was pending approval, the “conclusions and recommendations which directly affect the Fernbank subdivision serve as a guideline” for the subdivision’s stormwater management system.  The report also indicated that it was prepared in accordance with the guidelines of the Ministry of Environment, Ministry of Natural Resources, and Rideau Valley Conservation Authority.

A copy of the development agreement could not be located in the file so we were not able to confirm if the developer was obligated to implement the subdivision’s stormwater system in accordance with the Stittsville Master Drainage Plan or stormwater study.

Audit File #B5 – Westcreek Meadows Phase 2 Subdivision

The Westcreek Meadows Phase 2 Subdivision did not experience flooding in July 2009.

The subdivision is located in the former City of Kanata and was processed during the pre-amalgamation period.

The MOE Guidelines were in effect at the outset of the development approval process.

 

Process Linkages – Westcreek Meadows Phase 2 Subdivision	Complied
Stormwater Study submitted for development review	Yes
Stormwater Study referencing previous study	Cannot confirm
Stormwater Study referencing guidelines in effect at the time	Cannot confirm
Stormwater Study referencing Subwatershed Study	Not applicable
Development Agreement referencing Subwatershed Plan	Not applicable
Development Agreement referencing Stormwater Study	Yes

 

The audit confirms that the subdivision application was accompanied by a stormwater study, the “Westcreek Meadows Claridge Homes (Kanata) Stormwater Management Plan.”  Correspondence in the file indicates that the stormwater management approach was developed in accordance with the requirements of the City of Kanata, Mississippi Valley Conservation Authority, Regional Municipality of Ottawa-Carleton, and Ministry of Environment.

A copy of the report did not exist in the City’s files, but one was provided to us upon request.  Based on the information contained in the report, we conclude that it addressed the effects of the development on water levels in the Carp River and the requirements for stormwater quality control.  However, it did not contain any information on the design of the major and minor system.  Based on this, we determined that the report was completed in accordance with the MOE Storm Water Quality Guidelines, but not the Urban Drainage Design Guidelines.

In the development agreement, the subdivision’s stormwater management system was required to meet the stormwater study.

The City and MVC required in the Draft Plan Approval document that the finished elevation of the underside of the floor slabs of all residential spaces be a minimum of 300 mm above the MVC’s established 100 year flood plain elevation of 95.2 m.

Conservation Authority and Municipal Relationships

Although the focus of the audit is on the development review process of the City of Ottawa and former municipalities, the Mississippi Valley Conservation Authority and Rideau Valley Conservation Authority are important agencies in the subdivision approval process.  The role that the Conservation Authority takes is a role that has been devolved from the Province of Ontario and all subdivision applications must be circulated to the appropriate Conservation Authority for review and comment.

If the Conservation Authority had identified a stormwater management issue with a subdivision during the development review process but the municipality went ahead with approval of the subdivision, there would be concern about the viability of the subdivision’s stormwater management system.  However, through a review all the correspondence in the audit files, we observed no discord between either the Mississippi Valley Conservation Authority or Rideau Valley Conservation Authority and the local municipality.  There appears to have been solidarity among the Conservation Authorities and municipality when an issue arose.  In one situation, the concerns shared by the Conservation Authority and municipality regarding stormwater management and the depth of basements ultimately resulted in the developer revising the proposed development to housing units without basements.

Stormwater Management Design Criteria

In the presentation to Council on September 2, 2009 and the Phases 1 and 2 Report, City staff have indicated that subdivisions constructed in the 1960s to 1990s were designed based on capturing frequent rainfall events with little or no provision for large events.  The statements also indicate that only in the mid 1980s and 90s overland drainage was taken into consideration in the drainage design.  As well, the statements indicate that new developments started to provide detention for large rainfall events in the 1990s.  City staff has indicated that their intent was to highlight that across the various municipalities the approaches varied and took many forms which ranged from a low standard to a higher standard as time progressed.

The dual drainage system concept, incorporating the design of the minor system for conveyance of frequent rainfall events and the major system for conveyance of large events, has been applied in Ontario since the mid-1970s.  Provision of detention storage of large rainfall events to prevent downstream flooding as a result of development dates to the same time.  In the affected area, the Glen Cairn pond, discussed in detail under Audit Objectives No. 11 and 12, was conceived in 1975 and designed in 1978.

The Urban Drainage Design Guidelines (UDDG) presented the concept of the Major and Minor Drainage Systems in Ontario Guidelines for the first time.  However, it is notable that the concept had been applied in several major municipalities in Ontario since the mid 1970s, and the advantages of stormwater management in terms of cost savings is presented in the Guidelines.  Because these were Guidelines, municipal Councils varied in the level of service they provided; however, it is fair to say that the Guidelines were the desirable level of service.

The UDDG document also discusses potential measures for protecting foundation drains from the potential effects of storm sewer surcharging.  Although inlet control devices were not discussed in the UDDG document, the concept of preventing surcharged storm sewers from backing up into foundation drains has been used in Ontario since the late 1970s.

Correspondence between a City project manager who was employed by the City of Kanata prior to amalgamation and the project manager for the Carp River flood improvements, dated July 2002, following the June 2002 flood, indicates that the City of Kanata applied the minor and major system concept, required provision of overland flow routes for the 100 year storm flow, required storage to restrict post-development increases in flow, and used inlet control devices in some subdivisions.

The same correspondence indicates that,

“In the early 1980's, SWM modelling was undertaken in the first three phases of Glen Cairn and in the Beaverbrook Community. Areas of pipe surcharge and roadway flooding were determined since these subdivisions were not designed using the dual drainage system. Subsequent developments have been subject to Storm Water Management Plans, Storm Water Design Plans, Master Drainage Plans, Environmental Management Plans and Subwatershed Plans. In the Bridlewood Community for an example, the initial phases were not required to consider water quantity and only was required to consider the 5 year pipe flow for quality resulting in the Bridlewood Quality Pond. However, in doing the total community design, the consultant did consider quantity and developed the subdivisions following the dual drainage principles. Once again, more recent phase had the requirements for Storm Water Design Reports that were in accordance with the Master Drainage Plan.”

 

It can be said that in general terms, the current standards reflect the practice of stormwater management used since 1980.  The review of the files indicate that with the exception of the consistent and uniform use of inlet control devices, the standards used since pre-amalgamation provided for the minor and major systems, and for protection of basements up to and including the 100 year storm level.  It is accepted that the inlet control devices constitute a significant improvement to the standards, in that they provide protection against surcharging of the storm sewer system.

Engineering Review and Approvals

Although the focus of the audit is on the development review process of the City of Ottawa and former municipalities, the audit examined the controls that the City had in place during the period from 2001 to 2004, and post-2004 period.  We did not carry a detailed review of the engineering studies. 

Based on the review of the files examined and discussions with City staff responsible for the engineering review of the developments, we found as follows:

3.        The engineering drawings for the subdivisions are reviewed and approved by engineering staff in Planning and Growth Management (PGM).

4.        The stormwater management report and the sewer design calculations are also reviewed by PGM.

5.        Staff in PGM are responsible to review the hydraulic grade line information on the Plan & Profile drawings which is usually based upon modeling completed by the developer’s engineer.  This applies for 2001-2004 and after 2004.  Infrastructure Services Department (ISD) provides support to PGM in reviewing modeling completed to determine the hydraulic grade line information.

6.        PGM Development Review does not have any qualified modelers on staff, nor do they have the software to analyse models. That expertise and software resides with Infrastructure Services.  There is an internal letter of understanding about each department’s responsibilities.  ISB does modeling. Because of this, all modeling is sent to ISB for professional review, analysis and opinion. Upon acceptance of the modeling reports, PGM can then check the hydraulic grade line on the drawings with confidence.

Construction Reviews

Until 2009, construction reviews of subdivisions were done by Infrastructure Services.  Now this responsibility rests with PGM.  The City has advised that the responsibilities of the construction inspection was to oversee that construction of municipal services was being completed in accordance with the approved construction drawings.  The developer’s engineer was responsible to provide full-time site inspection.  With the exception of watermain installation, Infrastructure Services staff provided oversight to confirm general compliance.  For watermain installations, Infrastructure Services provided full-time site inspection.  Infrastructure Services was not involved in inspections related to works taking place outside the municipal road allowance or registered drainage easements.  The developer's consultants are required to produce certified As-Built record drawings.

Responsibility for checking that house foundations are constructed at the grades required by the engineering drawings now falls under PGM’s inspectors since 2009 and to a lesser degree Building Code Services.   Since 2001 basement elevations have been captured through the approval of lot grading plans and as part of the As-built certification by the developer’s engineer of record; however, there is no formal method to confirm that the footings and the basements have been constructed in accordance with the engineering drawings.

The City does not have a procedure in place to capture the as-built elevation of the basement slabs and foundation elevations in the field.  This is an exception to a process that comprises reviews and checks of the engineering drawings, the stormwater management report and drainage design, field review of road and lot grades, field review of sanitary and storm sewer systems, and inspection of watermain construction.  Although the City inspectors do a qualitative review of conformance of the lot grades and house general elevations in relation to the design elevations, the City does not have any field documentation to confirm that the houses were actually placed at or above the elevation required by the stormwater management design.

Summary of Findings from the File Audit

The following conclusions can be made as a result of the observations from the audit of the files:

·         The development review process and risk management linkages were maintained by staff for all the audited subdivisions where there was no flooding;

·         The development review process and risk management linkages were maintained by staff for all the audited subdivision were there was flooding;

·         When the development review processes are compared between the subdivisions that flooded versus those that did not, staff managed risk appropriately in the process since we found no substantive anomalies;

·         In the case of the Fringewood and the Westwood Phase 2 subdivisions, staff demonstrated an ability to adaptively manage risk, by requiring these subdivisions to comply with the Upper Poole Creek Subwatershed Study which had come into effect while the subdivisions were still being processed; and,

·         In the case of the Westwood Subdivision, Phase 1 – approved before amalgamation – had inlet control devices specified and the houses were required to have their foundation levels above the 100 year hydraulic grade line, similar to the current engineering requirements in the City’s Sewer Design Guidelines.  However, Phase 2 – approved during the Home Rules period – was not designed to the same standards.  In this case, the Home Rules were applied, but resulted in a lower level of flood protection for the newer subdivision.

4.5       Audit Objective #5 - Review City policy formulation and implementation processes for Home Rules model

Criteria:

·         Was the development risk profile for the Carp River watershed (i.e., repeated flooding events) raised as a specific concern by City staff when designing and implementing the Home Rules model?

·         Did the decision-making process resulting in the adoption of Home Rules ever consider elevating the standards for Carp River development files to the “best available” storm water and flood protection standard in place at the time within the City - as opposed to a demonstrably lower standard in the specific area in question?

·         Are there precedents in other parts of the City where generic Home Rules practices were modified to address unique issues, risks or characteristics of development deemed critical to the public interest or public safety?

4.5.1  Findings

Following amalgamation in 2001, the Home Rules design practices used by the City varied significantly across the previous RMOC area municipalities.  For instance in Gloucester Home Rules model, City staff report that the requirement for installed inlet control devices was considered “standard operating procedure” and became a de-facto mandatory practice, although not written in the design standards.  However in Kanata and Goulbourn Township, inlet control devices to protect basements were not required, and were not part of the “standard operating procedure”.  To the extent that inlet control devices were included in a given development engineering solution; the decision was isolated and discretionary on the part of City engineering staff involved with the file.  The contrast between the Gloucester and Kanata and Goulbourn is significant from a flood mitigation and risk management perspective.  As already noted, no flooding occurred in the post-2004 Carp River watershed subdivision developments equipped with inlet control devices, so there is a strong linkage with flood protection.

While City staff were working between 2001 and 2004 on new City-wide stormwater and servicing design standards, it is not clear why the design standards and practices were not amended to mirror those simultaneously in place in Gloucester area where inlet control devices generally used (although not a requirement of the Gloucester standards, staff informed us that it was standard practice to require them).  This is more so, given that inlet control devices and other stormwater management requirements had already been implemented in some developments in both Goulbourn Township and the City of Kanata.

Furthermore, situations such as that observed in the Westwood Phase 1 and Phase 2, where Phase 1, approved prior to amalgamation was required to have inlet control devices and Phase 2, designed and approved during the Home Rules period between 2001 and 2004, was not, indicate that the application of the more stringent requirements may not have been considered even at the individual subdivision level.

Recommendation 2

That the City require staff to document and report on the number and location of residential dwelling units approved after the 2002 flood event under Kanata and Goulbourn Home Rules.  City staff should also report on any projected future Carp watershed residential dwelling units to be approved in subsequent phases of development applications originally approved under these Home Rules.

Management Response

Management agrees with this recommendation. The number and location of residential dwelling units draft approved after the 2002 flood event in Stittsville under Kanata and Goulbourn Home Rules will be the subject of an information report to Planning and Environment Committee by the Planning and Growth Management department in Q1 2011.  Management will also confirm in this same report, that there are no further future phases of development originally approved under Home Rules that will be developed under Home Rules.

Recommendation 3

That the City seeks legal advice concerning the potential liability associated with the City using design practices that were lower than the practices of some pre-amalgamated municipalities regarding inlet control devices (ICD).

Management Response

Management agrees with this recommendation.  Legal Services has confirmed that in the event that legal claims are filed with the City, this would be a standard step followed in all litigation in assessing the City’s response to such claims.

4.6       Audit Objective #6 - Review proactive actions by City to convince/compel Carp River watershed development applicants to voluntary compliance with enhanced post-2004 standards

Criteria:

·         Were City development approvals typically “mechanical” or rigid in the sense that staff applied the same flood control/storm water processes and criteria (appropriate for the majority of low risk files across the City) to the demonstrably higher risk Carp River watershed files?

·         Did the City voluntarily agree to grandfather post-2004 Carp watershed development file phases to original pre-amalgamation or post-amalgamation Home Rules?  If so, was there any consideration of exempting the post-2004 phases of Carp River development files from the original storm water/flood control standards and requiring 2004 City-wide standards be applied?

·         Did the City ever consider the use of de-registration or other tools to compel compliance with higher recent engineered flood protection standards?

·         Is there documentation/evidence of City staff attempting to secure applicant voluntary compliance with higher stormwater/flood control measures beyond strictly legal (i.e., older/dated development agreements) or policy driven minimum requirements?

4.6.1  Findings

The transition period between the Stittsville Master Drainage Plan (1994) and the Upper Poole Creek Subwatershed Study (2000) provides an opportunity to examine due diligence in the development review process.  From 1994, the Stittsville Master Drainage Plan addressed the stormwater management design requirements for the village of Stittsville since no previous subwatershed study was in effect.  In 2000, the Upper Poole Creek Subwatershed Study was approved, and effectively superseded the Stittsville Master Drainage Plan where the two overlapped.  If there was a culture of adaptive management present, then any subdivisions being originally considered under the Stittsville Master Plan should have been made subject to the Upper Poole Creek Subwatershed Study before final approval.  The Westwood Phase 2 Subdivision and the Fringewood Subdivision both had the potential to demonstrate adaptive management since both developments were applied for while the Stittsville Master Drainage Plan was in effect with the Upper Poole Creek Subwatershed Study coming into effect while the developments were being processed.  In both cases, the development agreements required the subdivision’s stormwater management system to conform to the Upper Poole Creek Subwatershed Plan, which demonstrates that staff acted with diligence in attempting to manage risk during the development review process by ensuring a linkage to the new subwatershed study.

On the other hand, the difference in requirements applied to the Westwood subdivision Phases 1 and 2, would indicate that in some cases the Home Rules were applied without regard to previous experience.

Management has indicated that the Westwood subdivision “was approved before the new standards [2004 Sewer Design Guidelines], and because they had a registered agreement they were permitted to proceed”.  We noted two issues in this respect:

a)      As noted, Phase 1 was approved before amalgamation and included higher standards than Phase 2.

b)     The subdivision agreements for Phase 2 were registered after amalgamation and easily could have included the same standards as Phase I.

In our opinion draft Plan Conditions can be amended if necessary and this is specifically permitted by the Planning Act.  A subdivision agreement includes the draft plan conditions as a schedule, which allows the ability to ensure that engineering drawings and standards are updated.  Therefore, for practical purposes it is our opinion that the City could modify the requirements of the subdivision agreement up to the point when it gives final approval of the works as constructed. As further discussed below management does not agree with our opinion.

Our Office obtained a legal opinion, from an outside firm, that indicated that the existing conditions of subdivision agreements are broadly defined such that “the City can modify the requirements of a subdivision agreement up to the point where it gives final approval of the works as constructed”. The legal opinion indicates that this is possible because the subdivision agreement conditions stipulate that everything must be done “to the satisfaction of” an identifiable individual representing the City. Clearly the individual should not be satisfied unless the current standards are met.

City Legal staff provided a confidential legal opinion in which they were not able to fully endorse the external opinion.  The City should on a go-forward basis, ensure the wording in the subdivision agreement clearly indicate that where engineering design standards have changed, since the time of registration of the subdivision agreement, that the developer shall be responsible at their expense, to update their design and construction to meet the current engineering standards, to the satisfaction of the City.

Recommendation 4

That the City should on a go forward basis, ensure the wording in the subdivision agreement clearly indicate that where engineering design standards have changed, since the time of registration of the subdivision agreement, that the developer shall be responsible at their expense, to update their design and construction to meet the current engineering standards, to the satisfaction of the City.

Management Response

Management agrees with this recommendation. Standard subdivision agreement wording will be revised by Planning and Growth Management under delegated authority in Q1 2011.

4.7       Audit Objective #7 - Examine and evaluate the processes and methodologies used for the Operation and Maintenance of sanitary and storm drainage systems

Criteria:

·         Asset management database information available for sanitary and storm systems

·         Operation manuals

·         Inspection and Maintenance manuals

·         Inspection and Maintenance procedures, recording, follow-up

·         Maintenance

 

4.7.1  Findings

The Asset Management Branch maintains a database of the sanitary and storm sewer systems within the City, and was able to provide the data for our review and use in Geographical Information System (GIS) format.  Review of this data for the areas affected by flooding revealed that it contains the information that would be expected from a GIS database.  It should be noted that we did not do any checks of the data within the database, but simply confirmed that the data is available in a readily useable format.

Discussion with senior staff in Asset Management (AM) disclosed that the Infrastructure Asset Management database system that will comprise the complete scope of the Asset Management responsibilities is currently in the procurement stage.  Given that WDO and AM have separate databases of City infrastructure assets, it would appear logical to ensure that the proposed asset management system includes in a single location the information now available in the two separate database systems.

The Wastewater and Drainage Operations Branch (WDO) is in charge of the operation and maintenance of the sanitary and storm sewers in the City.  The WDO currently uses the database of the City’s sanitary and storm sewers in the City’s Maintenance Management System (MMS).  For some activities, such as closed circuit television (CCTV) inspections, the information is taken directly from the Asset Management database. 

Information provided by WDO with respect to General Inspection and Cleaning is that frequency of inspection and cleaning varies depending on the history, size and location of the structure. General information regarding the City’s regular maintenance program was provided by WDO, as summarized in Table 3.

Information provided by the Manager, WDO is that the City does not have an Operation and Maintenance Manual for the sanitary and storm sewer systems.  However, the operation and maintenance is performed as follows:

a)      For sanitary sewers, inspections using CCTV are done every 5 to 18 years, based on need and schedule set by the Infrastructure Services Department, Asset Management.

b)     Cleaning of sanitary sewers is done every 5 years, based on the rotation of five  City zones.

c)      For storm sewers, CCTV and other inspections are done every 18 to 20 years, based on need and the Asset Management schedule.

d)     Cleaning of storm sewers is done as required, unless there is a history of sedimentation problems.

If repairs to the sewers are required urgently, WDO issues a work order for repairs to be done by City workers or contractors, depending on the type and magnitude of the required repairs. 

Where the repairs are of a routine non-urgent nature, they are recorded by Asset Management in the City’s asset database.  The database information is then used by Asset Management to determine renewal needs.

The following table summarizes the inspection and cleaning frequency for the sanitary and storm sewer systems.

Table 3 - Sanitary and Storm Sewer Inspection and Cleaning Frequency
SANITARY SEWERS
Structure	(CCTV /Other) Inspection	Cleaning Activity
Sanitary Sewers	·         Every 5 – 18 years ·         More often as required	·         Every 5 years ·         More often as required ·         Every 3 months or more often if defects are identified and special cleaning is required
Large Trunk Sewers	·         Every 5 – 18 years ·         More often as required	·         Self cleaning ·         Scheduled more frequently in locations prone to accumulation of solids and debris
STORM SEWERS
Structure	(CCTV /Other) Inspection	Cleaning Activity
Storm Sewers	·         Every 18 to 20 years	·         As required based on location and history of sedimentation
Inlet Control Devices	·         Various §  monthly §  post rain event §  yearly	·         Varies with history §  monthly §  post rain event §  yearly
Outfall Grates	·         Various (as above)	·         Varies with history (as above)
Catch Basins	·         Every 2 years, or ·         In response to complaints	·         Every 2 years, or ·         As required, following inspection

 

Information relating to the inspection and cleaning of sanitary and storm sewer structures in the affected areas, prior to the July 24, 2009 floods, is summarized as follows:

Table 4 - Sanitary and Storm Sewer Tasks in Kanata and Stittsville since 2003
Structure	Area	Date	Activity
Sanitary & Storm Sewers	·         Kanata §  Glen Cairn §  Beaverbrook §  Bridlewood §  Katimavik	·         2003	·         CCTV storm and sanitary sewers following flooding in 2002
	§  Beaverbrook	·         2005	·         CCTV and cleaned storm & sanitary sewers
	§  Dundegan	·         Sept 2004 ·         2006 ·         Every 5 years	·         Cleaned by City of Kanata ·         Sanitary sewer cleaned ·         schedule of cleaning Regular
	·         Kanata	·         2007 ·         quarterly*	·         Sanitary sewer cleaning ·         Special cleaning
	·         Stittsville	·         2006 ·         quarterly*	·         Sanitary sewer cleaning ·         Special cleaning
*  Note: Sanitary sewers on several streets in Kanata and Stittsville are on the special cleaning list and can be cleaned as often as every 3 months if there are known problems such as sags or grease accumulation.

Recommendation 5

That the City documents the operation and maintenance requirements for sewers in an Operations and Maintenance Manual.

Management Response

Management agrees with this recommendation. Operation and maintenance requirements are defined and documented, but in a number of files, formats and locations.  Staff are currently working to develop a system-wide comprehensive operations manual.  This will be complete in Q4 2011 as a part of the ongoing development of the environmental management system (EQMS – ISO 14001).

Recommendation 6

That the City ensures that the proposed Asset Management System, currently in the procurement stage, enables the City to combine the information currently available in two separate management systems.

Management Response

Management agrees with this recommendation.  The City currently uses two separate stand-alone information management systems.  Information is duplicated into a tabular information system (ITX) and a mapping system (GIS), with staff able to access both systems, depending on the information required.

A Request for Proposal is currently on the market to select a leading edge information and work management system that will combine the two ways to access the available information.   Until such time as a review of the submitted proposals has been completed, management is not in a position to state whether or not this single data source has been achieved, but it is certainly the intent of staff to meet this objective. The tendering process will be complete by Q1 2011 and the successful proponent should be selected by management in Q2 2011. 

It should be noted that the availability of information, currently available in two different systems, had absolutely no role to play in the flooding events of July 24^th, 2009 or the application review system.

4.8       Audit Objective #8 - Determine if the Operation and Maintenance processes and methodologies meet the City’s, Province’s and Industry standards, and are consistent with relevant policies, procedures, legislation, and regulations

Criteria

·         Ministry of the Environment regulations, standards, manuals

·         City’s Operation and Maintenance Policies and Procedures

·         Industry standards

·         Environmental Protection Act

·         Ontario Water Resources Act

·         Planning Act

4.8.1  Findings

The Ministry of the Environment does not currently have specific guidelines or regulations for the inspection, cleaning, and maintenance of sanitary or storm sewers.  The MOE published in 2008 the “Design Guidelines for Sewage Works”, which make mention of operation and maintenance, but do not give specific requirements.

Review of the maintenance programs of two other municipalities in North America (Toronto, Columbus, OH) reveals that they all have similar schedules for cleaning of sewers (5 year intervals).  Inspection intervals are based on the sewer inventory and historical information, which is used to rank the sewer lines for inspection.

In addition, a literature review indicates that the inspection and cleaning intervals used by the City conform to accepted industry practices and standards.

The Ontario Environmental Protection Act and regulations do not contain specific requirements for sewer inspection and maintenance; however, the Act and regulations govern potential environmental effects due to discharges to the environment.

The Ontario Water Resources Act and regulations govern the design and operation of sewage works, which include sanitary and storm sewers.  Clause 61 of the Act

Sewage works to be kept in repair
61.  Sewage works shall at all times be maintained, kept in repair and operated in such manner and with such facilities as may be directed from time to time by a Director. R.S.O. 1990, c. O.40, s. 61.

The City’s operation and maintenance procedures are in accordance with industry standards and meet legislative requirements.

 

4.9       Audit Objective #9 - Examine and evaluate the planning and design of the existing and proposed Glen Cairn flood remedial measures

Criteria

·         Examination of flooding history

·         Definition of scope of investigations

·         Range and quality of alternatives examined

·         Evaluation methodology and criteria

·         Implementation methods

4.9.1  Findings

At the outset of this audit it was the intention to review both the existing and proposed Glen Cairn flood remedial measures.  However, the timing of the City’s investigation does not allow the review of the proposed measures.  Therefore, the majority of the discussion herein will address the existing flood remedial measures.  Based on this assessment, we have determined issues that must be addressed by the Glen Cairn Flooding Investigation – Phase 3.

The Glen Cairn area has suffered flooding on two occasions in addition to the event of July 24, 2009.  Documented flooding in the Glen Cairn area occurred in July 30-31, 1996 and on June 27, 2002. During the September 9, 2004 storm associated with the remnants of Hurricane Frances there was no documented flooding in this area of the City.

June 1996 Flood

In June 1996, flow in the Carp River overtopped the river banks, and caused flooding in the Glamorgan area.  An evaluation of the flooding event by a consultant retained by the City of Kanata concluded that the flood event exceeded the design criteria used by the City of Kanata for the design of the Castlefrank Road culvert.

According to the Expert Witness Report on July 31, 1996 Flooding prepared by a consultant for  the former City of Kanata, significant surface flows were observed on Castlefrank Road and Old Colony Road due to spills from  the Upper Carp River bank upstream of the culverts under Castlefrank Road and Old Colony Road. Around the  culverts under Castlefrank Road, the  spill occurred over  the lowest bank elevation within the park, south of the river channel.

The scope of the 1996 flood investigations was defined as follows:

a)      To investigate the July 31, 1996 storm with the objective of estimating the return period of the storm within the affected area.

b)     To investigate the causes of flooding

c)      To review and comment on the criteria and standards used in the design of the Glen Cairn drainage system, and the extent of upgrading and maintenance done by the City of Kanata.

It is noted that the report was commissioned by the City of Kanata as part of the defense against lawsuits that were commenced as a result of the 1996 flooding .

Rainfall analysis carried out by the 1996 consultant concluded that the maximum rainfall intensities in the Carp River watershed had return periods between 2 and 25 years, depending on the location in the watershed; this is due to the areal variation in the rain storm.  The total rainfall amounts ranged from 40 mm to 70 mm, depending on the location in the Upper Carp River watershed.

According to the 1996 Consultant Report, the water levels in the Carp River rose rapidly during the storm, and the river overtopped its banks.  At Castlefrank Road the flood waters spilled to Pump House Park, where the flood depths appear to have reached 1 m.  The flood waters flowed out of the park into Castlefrank Road, and continued along the road.  The report indicates that significant quantities of water were observed ponded or flowing on Glamorgan Drive, Dundegan Drive, Rothesay Drive, Uxbridge Crescent, Old Colony Road, and Country Lane West.  The water ponded to a depth of 1 m or more at the intersection of Glamorgan Drive and Uxbridge Crescent, and then spilled between the properties on the south side of Glamorgan Drive to the low lying area behind the properties.  Presently, the low lying area is occupied by the Castle Glen subdivision.

The 1996 Consultant Report indicates that flooding of basements was reported mostly along the streets listed above.  Because the ponded water depths were not sufficient to flood the houses directly, the report author concluded that basement flooding was likely due to sewer back-ups into the basements, or direct local inflow. 

The 1996 Consultant Report indicated that the extra inflow caused by water flowing down the streets exceeded the inflow allowance used in the design of the sanitary sewer system, resulting in surcharging of the sewer pipes and eventual backup into basements.  The report concludes that basement flooding was not the result of sewer hydraulic inadequacy, but of the large volume of water that entered the system under the circumstances, caused by a flood having – in that author’s opinion – a return period of more than 100 years.

Similarly, the 1996 report concludes that the storm sewer was filled to capacity and surcharged to street level.  Furthermore, the outlets of the storm sewer system to the Carp River and the Glen Cairn stormwater management pond were submerged, further reducing the flow conveyance capacity of the storm sewers.

The 1996 report did not include any assessment of potential improvements, and made no recommendations for improvements to the Carp River, the sanitary sewer system, or the storm sewer system.

June 2002 Flood

On June 27, 2002, another flood took place that again overtopped the river’s banks and resulted in widespread flooding in the same area that had been affected in 1996.  The City of Ottawa retained another consulting firm to investigate the watercourse.  The overall objective of that study  was to review and evaluate the performance of the Glen Cairn drainage system,  identify  the cause of  flooding and drainage-related problems, determine adequate mitigation measures for flood control, and make recommendations to minimize flooding  risk within the Glen Cairn Community in accordance with current design practices.

The 2003 Performance Evaluation study was initiated by the City of Ottawa in response to the flooding that occurred in June 2002.  The consultant commenced work in August 2002 and presented a Performance Evaluation report in March 2003.  The scope of the investigation was defined as follows:

·         Review of background information and reports

·         Review of 2002 flooding complaints and rainfall data

·         Existing physical components of the channel and culverts

·         Tributary drainage system (minor and major)

·         Hydrologic analysis

·         Capacity analysis of the existing channel and culverts

·         Development of alternative remedial measures

·         Analysis of Castlefrank Road overland flow route

·         Minor system surcharge analysis

·         Evaluation of alternative remedial measures

·         Pre-design of the selected alternative

·         Report

The flood event in June 2002 was very similar to the 1996 event.  The 2003 Performance Evaluation Report indicates that the culverts had vertical grates designed  to prevent entry of debris into the culvert. The trapped debris restricted the flow capacity of the Castlefrank Road culverts.  Once flow spilled from the south bank upstream of Castlefrank Road,  the roadway and adjacent open space area became  inundated.  Most of  the spill went on  to Castlefrank  Road, however,  flows continued through rear yard areas to  adjacent  streets with  very flat  grades.  The combination of high  flow along Castlefrank Road and ponding along other streets and within the park resulted in high inflow rates to both storm and sanitary sewers.  These sewers were not designed to convey such large inflows.  The resulting surcharged  conditions  caused water  to  back  up above basement levels.  In addition, surface flow not captured by the sewers  continued to low  points  on Glamorgan  Drive, where  it flowed across private property to the ditch along the Trans Canada Trail or former railway. Damage to private property occurred as a result of  the  flooding of basements and erosion created by the high rate of surface flow.  About 113 residential properties were impacted by the flooding in this area.

The March 2003 Performance Evaluation report examined three alternatives for reducing flood levels in the Carp River:

Option 1: 

Construct a stormwater detention pond within the open space located immediately downstream of Old Colony Road on the north side of the Carp River to attenuate major flows  from the local drainage area tributary to the road crossing and release water  from this pond into the Carp River at a controlled rate in order to reduce peak flows downstream of Old Colony Road.

Option 2: 

Increase the flow conveyance capacity at Castlefrank Road by adding one additional 1,350 mm diameter CSP culvert and reduce downstream peak flows by using Castlefrank Road as a major flood water conveyance channel to split major flows  at Culvert #3 as much as possible (with a maximum road surface ponding depth below of 0.3 m).  This flow would drain on the road surface to the Glen Cairn stormwater management pond, west of Terry Fox Drive.

Option 3: 

Improve the overall flood conveyance capacity of the Carp River within the Glen Cairn Community by enlarging culverts and reshaping  the river channel,  if necessary to minimize flooding risk.  Ten scenarios were studied as variations to this Option.

These three options were compared and assessed using the following evaluation criteria:

·         Effectiveness on peak flow reduction

·         Water level reduction

·         Structure requirements

·         Cost

·         Land acquisition requirements

·         Impacts on individuals or institutions

·         Environmental impacts

·         Feasibility

Based on their evaluation, the 2003 consultants concluded that Options 1 and 2 would produce relatively little improvements when compared to the costs of implementation.  The Performance Evaluation Report concluded that the only effective and feasible solution is Option 3.

Option 3 was examined by the consultant in more detail, including variations in the number and size of culverts, the extent and configuration of channel improvements, including examination of the effects on water levels of complete culvert removals.  In our opinion, the range of alternatives examined for Option 3 was comprehensive.

We examined other alternatives that could have been considered, but concluded that they have little possibility of success, as discussed below.

Other Alternatives	Feasibility or benefit
Reduction of the flow generated by the drainage catchment located east of Eagleson Road (Bridlewood Community) by enlarging the storage available in the exiting detention pond located north of the Trans Canada Trail.	Examination of this option as part of this Audit disclosed that the flood reduction that could be achieved by reducing the 100 year flood to the 5 year flood peak flow would be marginal.
Construction of a flood storage area upstream of Castlefrank Road, similar to the existing Glen Cairn stormwater management pond, would reduce peak flows by a factor of 4.	Although possibly feasible, it could be expected that this solution would encounter significant resistance from the adjacent property owners.
Property acquisition of vulnerable properties.  The 2003 report indicates that about 113 residential properties were affected.	Assuming that the average value of a house in the Glen Cairn community in January 2003 was $240,000, the cost of purchasing 12 houses would exceed the estimated cost of the recommended solution.  Evidently, this is not a reasonable solution.
Flood proofing of vulnerable properties, by providing sealed basement windows, backflow valves where not in place, inlet control devices, and lot grading modifications where required.	Assuming an average cost per house of $15,000, the cost of this option for the 113 houses affected would amount to $2.0 Million. Without examination of the feasibility of this alternative on a house-by-house basis, it is difficult to determine whether it would be effective.

Based on the comments in the above table, we have concluded that the range of options examined was reasonable, and consider that the recommended solution, as implemented, provided an effective solution to the flood risk from the Carp River.

The terms of reference prepared by the City and the proposal by the 2003 consultant included the analysis of the overland flow problem in the Glamorgan Drive, Uxbridge Crescent, Dundegan Drive area.  The 2003 consultant found that the recommended improvements to the Carp River channel and culverts would not completely eliminate the risk of flooding during a rare storm event.  The Performance Review report noted that the surface runoff generated west of the Carp River could accumulate at three major low spots (LP for Low Point) within the southwest area of the community, namely at the southwest end of Glamorgan Drive near Castlefrank Road (LP1), along the middle portion of Dundegan Drive (LP2), and at the intersection of Uxbridge Crescent and Glamorgan Drive (LP3).

The 2003 consultant examined alternative remedial measures for the three low spots, and recommended that the City further examined the following potential remedial measures:

Low Point Label	Description	Recommended Remedial Measure
LP1	Southwest end of Glamorgan Drive near Castlefrank Road	Lower Castlefrank Road at Glamorgan Drive and construct a drainage channel on the north side of Castlefrank Road to carry surface runoff to the Glen Cairn stormwater management pond via a culvert under Terry Fox Drive.
LP2	Middle portion of Dundegan Drive	Raise the road surface level at the northwest entrance to Dundegan Drive to prevent major system flow along Castlefrank Road from entering Dundegan Drive.
LP3	Intersection of Uxbridge Crescent and Glamorgan Drive	Provide an overflow channel or culvert to drain the low point to the Monahan Drain.

The City realized that further studies were required to determine the necessary improvements to the Glamorgan Drive, Uxbridge Crescent, Dundegan Drive area, but postponed the studies.

A memorandum dated April 11, 2003 indicates that the Report Terms of reference specified a solution for dealing with the performance of the channel for a 100 year flood, as well as formulating a solution for the local major overland flow in the Glamorgan area to the south.   The modifications to the local major overland flow on Glamorgan will require additional analysis, as the recommended approach in this report will not be possible, due to constraints on the Monahan Drain.  It recommended that this analysis be done in conjunction with a complete Needs Study of the area, and indicated that the final solution for this overland flow may be to do nothing at all.  Limitations on funds require that the Glamorgan work be postponed to 2004, to be done in conjunction with the sanitary sewer modifications planned for Glamorgan by the Needs & Programming Group.

The full text of the memorandum follows:

·         The reports’ Terms of Reference specified a solution for dealing with the performance of the channel under a 1 in 100 year storm return period, as well as formulating a solution for the local major overland flow in the Glamorgan area to the south.

·         As mentioned, the channel modifications will commence this September, with a new culvert constructed at Castlefrank.  The available budget for 2003 will most likely only allow the construction of this culvert and the channel modifications between Castlefrank Rd. and Rickey Place.  All other work on the channel and related culverts will occur in subsequent years.

·         The modifications to the local major overland flow on Glamorgan will require additional analysis, as the recommended approach in this report will not be possible, due to constraints on the Monahan Drain.  We are recommending that this analysis be done in conjunction with a complete need’s study of the area.  The final solution for this overland flow may be to do nothing at all.

·         Since funds are limited for 2003, and additional analysis is required on Glamorgan, this phase will be deferred to 2004.

·         The sanitary sewer modifications planned for Glamorgan by your group should be implemented at the same time as the overland flow solution for that street.  These modifications should therefore be planned for the 2004 construction season as well.

The City subsequently made improvements to the sanitary sewer to reduce potential inflow from stormwater ponded on top of sanitary manholes, and to improve the hydraulic conditions of the sewers in the area.   In the course of designing these improvements, the City realized that there were segments of the sanitary sewer that might be undersized, and decided to include any further analysis with a Needs Study for storm and sanitary sewers in the area. 

The evaluation of alternatives was carried out using standard planning methods.  The City proceeded with the Class Environmental Assessment in accordance with the Municipal Class Environmental Assessment.

The project was implemented over 4 years, beginning with replacement of the Castlefrank Road culvert and localized channel improvements in the fall and winter of 2003.

The remedial measures to reduce the risk of flooding by overland flow in the Glamorgan Drive area were not pursued, although it was clear that there is a problem in the area.  Following transmittal of the Performance Review report to the Design and Construction section, correspondence shows that the Carp River channel and culvert improvements were phase one of a two-phase project that includes the major overland flow and sanitary sewer improvements.

4.10   Audit Objective #10 - Determine if the Glen Cairn flood remedial measures are consistent with relevant policies, procedures, legislation, and regulations

Criteria:

·         Ministry of the Environment and of Natural Resources regulations, standards, manuals

·         City’s Operation and Maintenance Policies and Procedures

·         Environmental Protection Act

·         Conservation Authorities Act and Regulations

·         Ontario Water Resources Act

·         Planning Act

4.10.1 Findings

The Ministry of the Environment does not have specific regulations for the design and construction of flood remedial measures, resulting from watercourse flooding or basement flooding from sewer surcharge.  The jurisdiction of the MOE is related to the application of the Environmental Assessment Act to the planning and design of remedial measures.  In the case of the Glen Cairn flood control project, the City proceeded with implementation of Option 3 as described under Audit Objective No. 9 and elected to postpone the study of potential improvements for the major system flow, as discussed above.

In our opinion, this decision did not affect the subsequent studies conducted to satisfy the requirements of the EA Act.  The major system improvements would have been subject to a separate environmental assessment study.

The Ministry of Natural Resources and the Conservation Authority would have had jurisdiction in the approval of the flood remedial measures, consisting of the channelization and culvert replacements.  As far as we could determine the City obtained all the required permits for the implementation of the project.

The planning and design of the project followed the policies and procedures in effect at the time of the project.  The selection of the consultant was made based on the standard consultant engagement procedures and had the required management approval.  The consultant was selected based on their ability to complete the study within the schedule requirements as set by the City.  In turn, the schedule was driven by the need to implement solutions as soon as possible.

Detailed design of the project was done by the same firm that completed the Class Environmental study for the project.  We consider that this is not an issue.  Construction supervision and contract administration was done by the City with its own staff.

The Environmental Protection Act, the Ontario Water Resources Act, and the Planning Act did not apply to the project.

 

4.11   Audit Objective #11 - Determine if the Glen Cairn flood remedial measures addressed all the potential issues known at the time that they were planned and implemented

Criteria:

·         Review of past flooding events

·         Known flooding problems

·         Drainage constraints

·         City’s design standards

4.11.1    Findings

Past flooding events in the Glen Cairn area are documented in the 1996 Expert Witness report and the 2003 Performance Review report.

As discussed under Audit Objective No. 9, the City was aware and the 2003 consultant confirmed and brought to the attention of the City that in addition to the recommended improvements to the Carp River channel and culverts, it would be necessary to address the potential for flooding due to the accumulation of surface runoff in road sags in the southwest corner of the study area.  The consultant examined possible remedial measures, and made recommendations for improvements.

The City carried out an assessment of the recommendations for the road sag flooding, and decided to address them separately from the proposed improvements to the Carp River channel and the road culverts. 

The original proposal by the 2003 consultant included the major overland flow analysis and a provisional item for analysis of the minor system.  Given that the purpose of the project was to reduce flooding risk in the area, and that it was known that overland flow was a problem due to culvert restrictions.

The City realized that further studies were required to determine the necessary improvements to the Glamorgan Drive, Uxbridge Crescent, Dundegan Drive area, but postponed the studies.  The decision to put “on hold” any solution to this problem was done in May 2003.

In early 2003 the City initiated the Jock River Reach 2 Subwatershed Study, which encompassed the Monahan Drain catchment.  However, the subwatershed study did not include an examination of the possibility of receiving the Glamorgan Drive overflow.

We found no information regarding any further investigations of the three recommendations.  However, we undertook a cursory examination of their feasibility, using only the available information contained in study reports, design drawings, and topographic data provided by the City.  On the basis of that evaluation, we have concluded as follows:

Low Point Label	Description	Recommended Remedial Measure	Audit Comments
LP1	Southwest end of Glamorgan Drive near Castlefrank Road	Lower Castlefrank Road at Glamorgan Drive and construct a drainage channel on the north side of Castlefrank Road to carry surface runoff to the Glen Cairn stormwater management pond via a culvert under Terry Fox Drive.	This solution is not feasible by itself, as the 100 year water level in the Glen Cairn pond is 95.5 m, the same level as the intersection of Glamorgan Drive and Castlefrank Road.  Without a lowering of the water levels in the pond, it is not possible to drain the intersection during flood events.
LP2	Middle portion of Dundegan Drive	Raise the road surface level at the northwest entrance to Dundegan Drive to prevent major system flow along Castlefrank Road from entering Dundegan Drive.	This recommendation may have been effective, in combination with inlet control devices to control ponding on Dundegan Drive.
LP3	Intersection of Uxbridge Crescent and Glamorgan Drive	Provide an overflow channel or culvert to drain the low point to the Monahan Drain.	The approximate grade of the ditch at the back of the houses backing to the Trans Canada Trail is 94.5 m± at the location corresponding to the projection of Didsbury Road.  The Monahan Drain along the same road is higher or at the same elevation for over 300 m.

 

On the basis of the above, and if the Glen Cairn pond water level under 100 year flow conditions is 95.5 m, the recommended improvements are not feasible without removing existing drainage constraints, in particular the storage volumes and 100 year water levels in the Glen Cairn pond.  

The remedial measures to reduce the risk of flooding by overland flow in the Glamorgan Drive area were not pursued, although it was clear that there is a problem in the area. Correspondence indicates that the City considered the Carp River channel and culvert improvements as Phase 1 of a two-phase project that includes the major overland flow and sanitary sewer improvements.

The City has indicated in the 2010 Phase 1 and 2 Report on the Investigation of the July 24, 2009 West End Flooding that the City carried out additional analysis to rectify local problems; these are discussed in the Phases 1 and 2 Report, and can be summarized as follows:

a)      Improve the sanitary sewer hydraulics at the intersection of Glamorgan Drive and Castlefrank Road by shortening the sewer.

b)     Similar improvements were made at the intersection of Uxbridge Crescent and Glamorgan Drive.

c)      High-density Polyethylene bowls were placed under the sanitary manhole covers in the Glamorgan Drive and Uxbridge Crescent area.

Inlet control devices in this area may have helped in reducing inflow from ponded water on the streets, but we found no evidence that they were considered by the City.  The consultant for the Terry Fox Drive Extension recommended use of the inlet control devices for the houses backing to the Trans Canada Trail in 2003.  We found no record of any action by the City in this regard.

There is no discussion in the 2010 Phases 1 and 2 Report regarding the recommendations by the 2003 consultant or of any follow-up work in this regard. 

During the preparation of the Terry Fox Drive Master Drainage Study, the consultant found that the storage in the Glen Cairn pond was less than the storage volumes in the 1978 pond design drawings, which were less than those reported in the 1978 design report.  This information was conveyed to the City at the time, and the consultant offered to undertake further analyses.  However, the City informed the consultant that the analysis of the detention pond would be carried out after completion of the Carp River Watershed/Subwatershed Study.  Although there were communications, including meetings, between City departments in this regard, the Carp River study did not address the Glen Cairn Pond.

 

None of the reports have addressed the issue of the effect of the Glen Cairn stormwater management pond on the hydraulic performance of the storm and sanitary sewers in the Glamorgan area.  As we noted previously, the 2003 Performance Review and the Terry Fox Drive Major System reports indicate that the 100 year storm water level in the detention pond is 95.5 m±.  The reports do not identify this, but this is a problem, because when the pond is at that water level, the backwater created by the pond will surcharge the storm sewers along Castlefrank Road as far as the intersection of the north leg of Glamorgan Drive and Heathcliffe Court.  The depth of surcharging, with no flow in the sewer, at the intersection of Glamorgan Drive and Castlefrank Road is about 1 m± above the top of the 1050 mm diameter sewer.  Calculations of sewer flow based on the maximum water level recorded for the Glen Cairn pond by the MVCA for the July 24, 2009 flood (95.0 m), indicate that the 5 year flow could potentially result in the hydraulic grade line in the sewer being about 1.0 m above the road elevation at the southerly intersection of Castlefrank Road and Glamorgan Drive.  This is consistent with the observations in 2002 and 2009.

Information in reports prepared for the design of the Glen Cairn pond in 1975 and 1978 indicates that the design high water level in the pond, under the 100 year flood, is 94.72 m.  This is consistent with the grades and storm sewer inverts in the Glamorgan subdivision and Castlefrank Road area, as it would not result in backwater into the sewers and the road drainage would be able to flow into the pond.  However, with several studies the flood level has been increased, without regard to the effect of the increase on the storm and sanitary sewer systems in the Glamorgan area.

The MVCA has indicated that the 100-year flood level in the Glen Cairn pond is 95.5 m, but has not explained the reason for the difference with the 1978 design report.

Information provided by the Mississippi Valley Conservation Authority to the City regarding high water marks measured after the July 24, 2009, indicates that the high water elevation in the Glen Cairn Pond was 95.0 m±.  This water level is about 0.3 m± higher than the original design water level.

The Performance Review proceeded concurrently with the design of the Terry Fox Drive Extension (TFDE) between Hazeldean Road and Fernbank Road.  As part of the planning of the roadway, the TFDE consultant completed an examination of methods for the management of the major system runoff in the TFDE.  This work was coordinated with the Performance Review study.  The TFDE Major System report recommended construction of an additional 3000 mm diameter CSP culvert to convey the Carp River flow under Terry Fox Drive.  The TFDE studies also examined the methods available to convey the major system flows to the Glen Cairn stormwater management pond.

As part of the investigations carried out for the TFDE drainage design, the TFDE consultant identified that the Glen Cairn stormwater management pond would cause a backup into the area east of Terry Fox Drive and north of the Trans Canada Trail.  The consultant noted that the 100 year water level in the Glen Cairn stormwater management pond is 95.5 m, and that the drainage system from the Castle Glen Subdivision had been designed based on a 100 year water level of 94.72 m, which is 0.78 m lower.  The 94.72 m high water level corresponds to the 100 year flood water level used for the design of the pond in 1978.  Based on their investigations, the TFDE consultant recommended using a flap gate to prevent backflow from the pond to the storm drainage system in the Castle Glen subdivision.  Use of a flap gate under this condition is unusual, and may not provide a solution since the flow in the storm sewer system will not be able to outlet in some cases.  The City has indicated that the use of the flap gate is predicated on the basis that the flap gate will open when the water level on the upstream side of the flap gate is higher than the downstream side, allowing flow through; the surface flooding impacts would be proportional to the local drainage area.   However, we consider that the problem is the constraint posed by the water levels in the Glen Cairn pond.

As part of their investigations, the TFDE consultant found that the Castle Glen development had not properly constructed a drainage channel along the Trans Canada Trail.  At a meeting in May 2003, the City undertook to provide a written recommendation to Development Approvals that the major storm ditch on the south side of Castle Glen should be regraded to its design configuration and the culverts installed should be removed; and to advise them that inlet restrictors should be installed in the backyard basins adjacent to the TCT ditch.  Based on contour information provided by the City it can be concluded that the subject ditch was regraded after 2003 to provide a larger section than was found by the TFDE consultant, but only to 4.5 m± bottom width, about 2/3 as wide as the subdivision design drawings required (6.65 m width).

The most significant issue we have found in this regard is that the 100 year water level in the Glen Cairn pond increased over 25 years and no attempt was made to determine the reason for the increase.  However, the reports discuss at length the fact that the calculated peak flows in the river are higher than those computed by the predecessor consultant. The following table illustrates this.

Table 5 - Changes in Watershed Tributary to Glen Cairn SWM Pond Since Original Design

 

The following table summarizes the changes to the pond storages since it was designed in 1978:

Table 6 - Changes in Storage in Glen Cairn SWM Pond Since Original Design

 

The following table shows the changes in peak inflow to the pond:

Table 7 - Changes in Peak Flows into Glen Cairn SWM Pond Since Original Design

 

No investigation of the effect of these changes on the sewer systems has been carried out, until now.  The City has advised that this issue is being addressed in the Glen Cairn Flooding Investigation – Phase 3  Study currently under way.

Recommendation 7

That the City consider during the investigation of flood remedial measures, currently underway, options to increase the storage and reduce the water levels in the Glen Cairn stormwater management pond.

Management Response

Management agrees with this recommendation.  This is being considered as part of a variety of options under consideration as part of management’s investigation.  The ultimate recommended solutions will be the subject of a report to Council by Infrastructure Services Department in Q2 2011.

 

4.12   Audit Objective #12 - Determine whether the planned work to remedy flooding in Glen Cairn addresses the potential issues known now

Criteria:

·         Review of past flooding events

·         Known flooding problems

·         Drainage constraints

·         City’s design standards

4.12.1  Findings

Background data provided for this Audit indicates that the Glamorgan Area was constructed based on a 100 year flood plain elevation of approximately 94.5 m±.  The 1978 Report for the Glen Cairn pond indicates that the 100 year flood level in the pond will reach a high water level of 310.75 ft (94.72 m).  This elevation is almost 0.8 m lower than the 100 year flood level in the Glen Cairn pond given in the 2003 Performance Review report.

Although the Glen Cairn Flooding Investigation – Phase 3 is currently under way by a consultant retained by the City in early 2010, and consequently it is not possible in this report to comment on whether the planned remedial measures address the potential issues that are known now, it is possible to provide some preliminary comments on the matters that should be addressed by the report.

·    Glen Cairn stormwater management pond capacity and water levels.

·    Effect of the Glen Cairn pond on surcharging of the Glen Cairn sewers.

Recommendation 8

That the City consider in the investigation of flood remedial measures, currently underway, all issues that have been raised in this report, including:

a)      Checking of the basement elevations vs. those required by the engineering drawings;

b)     Glen Cairn stormwater management pond capacity and water levels;

c)      Effect of the Glen Cairn pond on surcharging of the Glen Cairn sewers;

d)     Calculation of the 100-year hydraulic grade line and verification of the design values; and,

e)      Remedial measures to prevent basement flooding in the Glamorgan Drive, Uxbridge Crescent and Dundegan Drive areas specifically and Glen Cairn vicinity generally.

Management Response

Management agrees with this recommendation. The issues raised in this report, including the list above, have been included in management’s investigation undertaken throughout 2010.  With respect to the first statement, management have undertaken a targeted sampling of basement elevations at critical locations through fieldwork to understand their elevation compared to projected hydraulic grade lines.  A field review of approximately 1,000 homes would be exhaustive from a resource perspective.

Infrastructure Services will bring forward a report on the recommended solutions to Planning and Environment Committee in Q1 2011.

4.13   Audit Objective #13- Evaluate the value for dollar of the Glen Cairn flood remedial measures

Criteria:

·         Examine potential flood damages eliminated by works

·         Determine if more could have been done

4.13.1  Findings

Examination of the high water data provided by the City in Appendix 2 of the Phases 1 and 2 report issued in January 2010 indicates that the highest water levels in the Carp River at Castlefrank Road represented a flow depth of approximately 1.3 m.  By reference to the hydraulic performance data for the culvert at Castlefrank Road, it can be concluded that the peak flow in the river was about 18 m³/s, which corresponds to a 5 year storm flow.

Based on the data available for the conditions that existed in 2002, it is possible to determine that the same flow would have overtopped the previously existing culvert.  The conditions would have been similar to those that existed during the 1996 flood event.  On this basis, it can be concluded that the culvert and channel improvements did help in reducing the extent of flooding that would otherwise have occurred.

It is becoming clear that the inflow, storage, and high water levels in the pond do not correspond to the design conditions, and that no investigation has been undertaken to address this.  It is expected, based on the Terms of Reference, that the Glen Cairn Flooding Investigation – Phase 3 will address this question.

Stormwater Management Criteria

In our opinion there have been several statements made in Management presentations to City Council and other forums regarding the stormwater management criteria used for the design of developments affected by flooding in July 2009 that may require additional clarification.  Although they have been discussed in the findings in the appropriate sections, we believe it is prudent to discuss them specifically and separately in this and the following sections of this audit report. 

The concept of dual drainage systems, using the minor and major systems, and the philosophy of designing for the 100-year storm level dates back to at least 1976, if not earlier.  The City indicates that the concept was not widely used by Ottawa former municipalities until the late 1980s to early 1990s, and that its application has evolved over time, with greater focus on preventing basement backup, including measures to protect the minor system from surcharging.  Each municipality can adopt the standards that it wishes to endorse.

Until about the middle of the 1970s, storm drainage in urban areas was designed with the objective of removing storm runoff from the urban area to an outlet as quickly and efficiently as possible.  In general, storm sewers were designed to convey the runoff generated by a design rainfall with a return period[7] of 2 or 5 years.  Generally speaking, the basic philosophy was removing the runoff as quickly as possible.  However, the resulting increased occurrence of flooding and erosion in downstream reaches resulted in concerns that changed the philosophy of stormwater management.

Starting in the second part of the 1970s, the Ministry of the Environment, the U.S. EPA and Environment Canada carried out several studies and reports on the impacts of storm runoff, stormwater management methods, and urban drainage modelling.  Concurrently, stormwater management started to identify the need to provide means of conveying the runoff from frequent storms (the minor drainage system) and from infrequent storms (the major drainage systems), and to control the outflow from new developments to minimize potential effects of development on downstream reaches and on receiving lands and watercourses.

An early example of this understanding in Ontario is the Storm Drainage Manual for the City of Burlington, which was prepared in 1977.  Some municipalities in Ontario soon followed in implementing drainage policies that required design of storm sewers and drainage systems using the minor and major system concept (dual drainage concept) to prevent flooding of urban development.

The American Public Works Association published Special Report No. 49, entitled “Urban Stormwater Management” (APWA SP 49) which discussed in detail the concepts of the dual drainage systems, including methods for calculating the volume of runoff that would enter the storm sewer systems via inlets and methods for calculating the hydraulic grade line in the storm sewer system.  In particular, the APWA SP 49 recommends that “the 100-year post-development frequency event should be routed and checked for damage potential to real property and assessment of hazard potential to human life.”

The Township of Goulbourn had in place a Drainage Policy Document, prepared in 1989, which incorporated the dual drainage concept.  Storm sewers were designed to convey the runoff produced by the 5-year return period rainfall, and the major system was required to convey the 100-year rainfall without flooding.  As part of their development requirements, Goulbourn’s practices required that the 100 year hydraulic grade line be computed and that the bottom of the basement slabs be placed at least 0.3 m above the 100 year hydraulic grade line.

We could not find a similar drainage policy for the City of Kanata.  However, we found correspondence that indicates that the City of Kanata’s practices applied the minor and major system concept, required provision of overland flow routes for the 100 year storm flow, required storage to restrict post-development increases in flow, and used inlet control devices in some subdivisions.  We noted that storm sewers also were designed to convey the 5-year storm runoff, and that as part of their development approval requirements in the files examined (in draft plan approval and subdivision agreements), Kanata required calculation of the 100 year hydraulic grade line and that the bottom of footings be placed above the 100 year hydraulic grade line.

Discussion with City staff familiar with other former municipalities that now form part of the City of Ottawa revealed that the requirements in Nepean, Gloucester and Cumberland were similar to those in Goulbourn.

On this basis, it can be concluded that since at least 1989 the design level for urban developments in the City of Ottawa has been the 5 year storm for storm sewers and the 100 year storm for the major system, including protection of basement flooding.  However, inlet control devices were not a requirement until 2004, although they were used in practice by several of the former municipalities.  Examination of the flooding patterns would indicate that these devices are very important in preventing surcharging of the storm sewers.  Although City staff assures us that backflow prevention valves were required in the storm sewer systems of former Ottawa municipalities, we did not find any documentation indicating that backwater valves were required.

The current Sewer Design Guidelines (SDG) were issued by the City of Ottawa in November 2004.  Review of the City’s Guidelines reveals that the City requires that storm sewers in new developments be designed to convey the 5 year storm runoff and that the major system provides protection against flooding for at least the 100 year storm level.  In addition, the current Guidelines require that storm sewer systems be provided with inlet control devices and that foundation drains connect to storm sewers be fitted with backwater prevention valves.

Design Storm

The City’s Sewer Design Guidelines (SDG) specify level of service and return period requirements for design of the drainage system, including the minor and major systems.  The design flows are calculated using Intensity-Duration-Frequency (IDF) curves that relate the rainfall intensity for a given rainfall duration and return period (hence their title).  The SDG states that the IDF curves in the guidelines are derived from rainfall data recorded by the Meteorological Services of Canada (MSC), part of Environment Canada, at the Macdonald-Cartier airport meteorological station from 1967 to 1997.  The analysis was done by MSC.

The SDG specifies that the design of  new drainage systems must be checked using the rainfall data recorded for the storms of July 1, 1979, August 4, 1988, and August 8, 1996, three severe historical storms recorded in the City.

Inlet Control Devices

In cases where a storm sewer inlet, such as a road or yard catchbasin or a ditch inlet are submerged, as is the case when the roadway is inundated as a result of a large storm, storm runoff can enter the sewer as quickly as the pipe that connects the catchbasin to the storm sewer can carry it.  In those circumstances, the storm sewer will receive substantially more flow than its free flow hydraulic capacity.  An inlet control device (ICD) is an orifice that permits a pre-determined flow rate into the storm sewer system, the minor system.  Even with ponding on the street, the storm sewer flow does not grossly exceed the capacity of the sewer pipes.  We provide more information on the ICD in Appendix B.

Backflow Prevention Valves

The City Sewer Design Guidelines state in Clause 5.7.5 that foundation drains should not surcharge.  In the design of new storm sewer systems the underside of footing elevation must be a minimum of 0.3 m above the 100-year hydraulic grade line.  Both the top of footing and the hydraulic grade line elevation must be shown on the storm sewer profile drawings.

In Clause 5.7.7, the Guidelines state that storm backwater valves, or backflow prevention devices, are required on all foundation drain systems connecting to storm or combined sewer systems to minimize backup of stormwater.  The Standard lists the approved valves.

We note that if the sewer is designed to not surcharge, then backflow prevention valves should not be needed.  However, although these two requirements are not consistent, we agree that the backflow prevention valves provide additional flood protection.

City of Ottawa Standard Drawing S-14 shows the standard arrangement for foundations drain backflow prevention valves.  Standard Drawing S-16 makes reference to City Standard Specification MS22.15.  Upon review of the standard (MS22.15), it is noted that it specifies that the backwater valve for foundation drains is for use in exterior retrofit applications only.  This is not consistent with the Guidelines or the Standard Specification.

It is fair to comment that most municipalities install backflow prevention valves in the sanitary sewer system and not the storm sewer system.  Based on a brief survey of other municipalities, Ottawa appears to be the only municipality in Ontario that has a standard BWV for the foundation drains.  All other municipalities we found require use of a sump pump if there is concern with respect to surcharging of storm sewers and backflow from them into basements; and specify backwater valves to prevent sanitary sewer backup. Management indicated that Toronto also has a requirement for backwater valves for gravity connections to storm sewers.

Backflow prevention valves in sanitary sewers are very useful in preventing basement flooding by sanitary sewer surcharge.  The City does not specify backflow prevention valves for the sanitary services in the Guidelines or in the Standard Specifications.

The City has the Residential Protective Plumbing Grant Assistance Program for assistance to residents in installing backflow prevention valves in the sanitary sewer system.  From the information that we received, this program is to a large degree a reactive, rather than proactive, program.  We say this because the program is geared to help mostly homeowners who have already suffered basement flooding, and until recently it appears to not have widespread communication to residents; aside from the information in the City’s website, the program was not promoted actively.  Information provided by City staff indicates that it was promoted more in the past.  Following the July 24th flooding, the City has publicized the program in the City’s website and communicated directly with people affected by delivery of pamphlets and presentations at public meetings.

Information Provided to Council

September 2, 2009 Presentation to Council

We have reviewed the September 2, 2009 Presentation to Council and provide the following comments with respect to the information presented:

·         Management indicated that the “communities affected by basement flooding were built to former standards that do not include engineered provisions to deal with large, infrequent rainstorm events”.   Based on our findings, this assertion applies to a large percentage of the homes affected, although a number of the affected homes were built since the 1980s, when the Urban Drainage Design Guidelines (1987) were published and generally in place.  The dual drainage concept using minor and major systems has been used in some parts of the city since at least 1989.

·         Management indicated that the dual drainage principle is a relatively new policy.  As discussed in this audit report, the minor and major system dual drainage system philosophy of the current City sewer design standards is not new, and has been used in North America since at least 1976, formalized by APWA in 1981, and in Ontario, including some  Ottawa municipalities, since at least 1987.

·         Management indicated that inlet control devices were not a requirement prior to the current City guidelines being issued.  Although factually correct, it should be noted that inlet control devices were used in some parts of the City since before amalgamation. In some Home Rules they were practices, albeit unwritten, operating procedure.

·         Management indicated that the 2003 Glen Cairn investigation made suggestions for solving the overland runoff problems in the Castlefrank Road and Glamorgan Drive area.  We found that the 2003 Glen Cairn investigation confirmed that flooding by storm overland runoff in this area would remain a concern after the Carp River improvements; the investigation made recommendations for improvements to the area of Castlefrank Road and Glamorgan Drive.

·         Management indicated that one of the areas flooded were designed based on the 5 year storm.  We found that in many of the areas flooded the sewers were designed to convey the 5 year storm but also were designed so that the basements would be located at least 0.3 m higher than the 100 year hydraulic grade line in the sewer.

·         Management indicated that the Westwood subdivision was designed using practices in use before the current City standards.  We found that the Westwood subdivision Phase 1, which had not flooded on July 24th, was designed using similar standards to those in effect at present, including inlet control devices, but Phase 2, which had flooded dwellings, was designed based on the local municipality design standard, providing a lower level of flood protection.

·         Management indicated that the Westwood subdivision design could not be changed since the subdivision agreement had been registered. As we discussed under Audit Objective 6, it is our opinion that management could have required changes to the design standards.

Phases 1 and 2 Report

In the discussion regarding Design Standards, the Report indicates that only in the mid 1980s and 90s that consideration started to be given to the larger, infrequent rainfall events.  As has been discussed in the previous section, these considerations date back to the late 1970s and was formalized in North America in 1981 and in Ontario in 1987.  Storage of runoff in ponds has been used since at least 1976.

Current urban drainage standards are in fact similar to those used since 1977 (see Burlington Drainage Policy document).  The main idea is that the concept is not new.

We agree that the recommendation to install sump pumps in the Glen Cairn area tributary to the Glen Cairn pond does not address the source of the problem and that it should be considered a stop-gap solution.  In our opinion, as has already been stated in this report, the higher-than-designed storage volumes and water levels in the Glen Cairn pond must be addressed.

5      CONCLUSION

Stormwater management and sewer design standards in the City have been similar since circa 1989, except for the consistent application of inlet control devices and backflow prevention valves.

The audit found that residential subdivision developments approved under the City’s current harmonized engineering design standard proved flood-resistant during the July 24, 2009 event. 

Although the rainfall event had areas where the 24-hour rainfall equalled or exceeded the 100 year storm intensities for that period, these did not occur over residential areas.  Furthermore, the rainfall intensities over areas that suffered flooding were equivalent to the 2 to 5 year period rainfall for durations of 1 hour and 3 hours. It should be noted that sewers can surcharge as a result of the cumulative effect of the rainfall pattern, downstream effects, and other causes; these are being investigated in the Phase 3 report.

In addition, similar subdivision developments approved during the 2001-2004 period when Home Rules design practices were applied and subjected to similar precipitation intensity levels, demonstrated vastly different flood resistance.  Inlet control devices and backwater prevention valves appear to have a critical impact on flood resistance, but there appear to be other potential causes of flooding.  These other causes of flooding are outlined in the Phases 1 and 2 Report by the City.

This audit found no substantive development approvals process anomalies or deficiencies in the review of the sample developments that were investigated in detail.  However, the failure to require inlet control devices was problematic. In the Westwood subdivision, the application of the Home Rules standards resulted in a lower level of protection to the second phase of the development than was required in Phase 1, which was approved prior to amalgamation.

The City provides reviews during construction and requires certifications of the construction of the sewers and lot grades, but it does not have in place a method to obtain confirmation that the constructed house footings and lowest living space floor elevations meet the requirements of the engineering design.

The Glen Cairn flood remedial works constructed after the 2002 flood provided an effective solution to flood risk from the Carp River.  However, changes to the drainage area, developed area, and volume of runoff tributary to the Glen Cairn stormwater detention pond, and the resulting higher water level in the pond appear to have had a serious adverse effect on the Glamorgan area sewers, and must be investigated in detail.  Management has indicated this will be investigated in their Phase III report.

6      ACKNOWLEDGEMENT

We wish to express our appreciation for the cooperation and assistance afforded by management and staff.

 

Appendix A

 

 

 

 

 

 

 

 

Appendix B

 

The information provided in this Appendix illustrates schematically some of the engineering terminology.

 

Minor System Design Storm

 

The minor system design storm results in the peak flows in the storm sewer system flowing without exceeding the pipe capacity.

 

Major System Design Storm

 

The major system design storm is the storm that is used to design the overland flow system, consisting of roads, swales and channels.  The idea is that when a large storm occurs that results in flows greater than the minor system capacity, the major system will convey the flow safely to the system outlet.  Generally, when the major system is operational, there is significant flow on the streets, and ponding at some locations.

 

 

Inlet Control Devices

In cases where a storm sewer inlet, such as a road or yard catchbasin or a ditch inlet are submerged, as is the case when the roadway is inundated as a result of a large storm, storm runoff can enter the sewer as quickly as the pipe that connects the catchbasin to the storm sewer can carry it.  In those circumstances, the storm sewer will receive substantially more flow than its free flow hydraulic capacity.  An inlet control device is an orifice that permits a pre-determined flow rate into the storm sewer system, the minor system.  Even with ponding on the street, the storm sewer flow does not grossly exceed the capacity of the sewer pipes.

 

The following figures, extracted from the IPEX website, illustrate the concept.

 

 

Inlet Control Device Concept

Inlet Control Device example

 

Hydraulic Grade Line

 

The hydraulic grade line in an open channel, such as a ditch or river, is the water surface.  A sewer pipe carrying a flowrate equal or less than the pipe hydraulic capacity is also an open channel, and the hydraulic grade line corresponds to the water surface in the pipe.

 

Once the pipe is overloaded, for example in the case of a pipe that receives more flow than its hydraulic capacity, the pipe carries the flow under pressure.  In that case, the hydraulic grade line is above the top of the pipe; it can be determined by the level to which the water rises in an open vertical tube attached to the pipe.  As a result, in case of a surcharged sewer, the hydraulic grade line will rise in manholes above the top of the pipe.  Since house connections are attached to the pipe, a surcharged sewer will force flow into the house basements, to the level of the hydraulic grade line. 

 

The following figure shows the a profile view of a sewer, the manhole chimneys, and the hydraulic grade line for surcharged conditions.

 

The above profile corresponds to the following plan of a typical street.

 

 

Grading Plan

 

The City requires that a Grading Plan be prepared as part of the Subdivision Engineering Drawings.  The following figure shows a typical (part) grading plan, showing the elevations of the lots, the lot grading, and the footing and finished floor elevations.

 

 

The legend is shown below:

 

Backflow Prevention Valves

 

The City Sewer Design Guidelines state in Clause 5.7.5 that foundation drains should not surcharge.  In the design of new storm sewer systems the underside of footing elevation must be a minimum of 0.3 m above the 100-year hydraulic grade line.  Both the top of footing and the hydraulic grade line elevation must be shown on the storm sewer profile drawings.

In Clause 5.7.7, the Guidelines state that storm backwater valves, or backflow prevention devices, are required on all foundation drain systems connecting to storm or combined sewer systems to minimize backup of stormwater.  The Standard lists the approved valves.

We note that if the sewer is designed to not surcharge, then backflow prevention valves are not needed.  These two requirements are not consistent.  Nevertheless, the backflow prevention valve provides additional protection, provided that they are installed correctly and are maintained properly.

Standard Drawing S-16 shows the arrangement for foundations drain backflow prevention valves.  Standard Drawing S-16 makes reference to Standard Specification MS22.15.  Upon review of the Standard (MS22.15), it is noted that it specifies that the backwater valve for foundation drains is for use in exterior retrofit applications only.  This is not consistent with the Guidelines or the Standard Specification.

The valves specified in MS22.15 are certified by CSA.  The certification by CSA requires that the valve be able to withstand a pressure of 10 kPa.

It is fair to comment that most municipalities install backflow prevention valves in the sanitary sewer system and not the storm sewer system.  Based on a brief survey of other municipalities, it appears that Ottawa may be the only municipality in Ontario who has a standard BWV for the foundation drains.  Most other municipalities would require use of a sump pump if there is concern with respect to surcharging of storm sewers and backflow from them into basements.

Backflow prevention valves in sanitary sewers are very useful in preventing basement flooding by sanitary sewer surcharge.  The City does not specify backflow prevention valves for the sanitary services in the Guidelines or in the Standard Specifications.

The City has the Residential Protective Plumbing Grant Assistance Program for assistance to residents in installing backflow prevention valves in the sanitary sewer system.  From the information that we received, this program was to a large degree a reactive, rather than proactive, program.  We say this because the program is geared to help homeowners who have already suffered basement flooding, and it appears to not have had widespread communication to residents; aside from the information in the City’s website, the program was not promoted actively.

Following the July 24^th flooding, the City has publicized the program in the City’s website and communicated directly with people affected by delivery of pamphlets and presentations at public meetings.

The following is a schematic view of a backwater prevention valve, taken from Appendix 13 of the Phases 1 and 2 Report.