Report to: General Committee Report Date: August 9, 2007

SUBJECT: Storm Water Management System Review and Study in Thornhill

PREPARED BY: Bob Penner, Supervisor, Business Systems Improvement

RECOMMENDATION:

That the staff report entitled “Storm Water Management System Review and Study in Thornhill“, dated September 17, 2007, be received;

AND THAT staff be authorized to prepare and issue an RFP to retain a consultant to complete a storm water management system review and study in the Thornhill area

AND THAT the cost to complete the detailed hydraulic analysis of the storm water system in the Thornhill area will be approximately $500,000 and this will be funded from the Operations Department’s 2006 Capital Budget Rain Storm Damage Account #050-6150-7194-005.

AND THAT this study be used as a template to complete similar studies in other old areas of the Town;

AND THAT staff report back to Council with the proposed recommendations and associated costs from the study when it is complete;

AND THAT Staff be authorized and directed to do all things necessary to give effect to this resolution.

EXECUTIVE SUMMARY:

Not applicable

1. Purpose 2. Background 3. Discussion 4. Financial

5. Others (Environmental, Accessibility, Engage 21st, Affected Units) 6. Attachment(s)

PURPOSE:

The purpose of this report is to obtain Council approval to implement the recommendations of this staff Report so that a detailed study of the storm water system and capacity in the Thornhill area can be completed.

BACKGROUND:

On Friday afternoon, August 19, 2005, the Town of Markham experienced a rainstorm event that dropped more than 120 millimetre (5-inches) rainfall in its three hour duration. This rainfall intensity over a three hour period exceeds a 150 year return period. As a comparison, the minor storm system (sewers) in the Thornhill area was built with a capacity to convey a two-year storm event according to the engineering standards at the time. Thornhill’s major storm system (overland flow routes) does not include provision for the conveyance of flows in excess of the 2-year storm to the adjacent watercourses as is the case for new development areas. The engineering standards prior to the 1980’s did not consider overland flow routes (major systems).

The peak runoff and volume of rainfall during this event completely overwhelmed the storm and sanitary sewer systems in the area. Significant surface flooding occurred in some areas allowing storm water to drain into basements through cracks in the basement walls and through basement windows. This allowed stormwater to drain directly into the sanitary sewer system through the floor drains. Stormwater also possibly entered the sanitary sewer system through roof downspouts and through sanitary manhole lids that are located in areas that are susceptible to surface ponding. In other words, it is possible that most of the basement flooding that occurred in Thornhill on August 19^th was instigated by surface flooding.

Damage from the Storm

Many homes in low lying areas within the catchment areas and in the path of the overland flow route were flooded. River channels were at full capacity or above capacity causing erosion and slope destabilization. A number of culverts were washed out along `with adjacent walkways. There were several road and storm drainage facilities that were also damaged. Staff has estimated the cost for repairs to these public facilities to be over $3 million.

The damage caused to private property from the storm was extensive. Many basements were flooded. Some of the basement floors suffered structural damage. Several properties experienced land erosion. According to the Insurance Bureau of Canada, the expected payout from the approximately 15,000 claims across the Province to help those impacted by the storm will reach $400 million. The Province subsequently denied emergency funding requests from all affected municipalities.

Response to Storm Damage

After the storm ended Operations’ staff responded to emergencies at various locations across the Town, cleared the road and storm system of debris, removed fallen trees, and provided additional residential waste removal of storm damaged materials. Markham Council responded with an immediate initial funding to ensure the clean up and repair work could start without delay. Since the event the Operations Department has been involved with the repair of public infrastructure such as sewers, culverts, roadways, walkways, and watercourse erosion that were damage by the storm. Council has allocated an additional $1.8 million to pay for these repairs.

In addition, approximately 100 kilometres of sanitary sewers has been flushed and cleaned to ensure that maximum capacity of the system is maintained. Approximately 120 kilometres of sanitary sewer and 100 kilometres of storm sewer within Thornhill have also been inspected by Closed Circuit TV camera crews. 

OPTIONS/ DISCUSSION:

Consultant’s Report

The Town retained R. V. Anderson Consulting Engineers to review the Town’s infrastructure and maintenance practices and to assess the reasons for the damages that incurred from the storm. The consultant also undertook a preliminary review of the trunk sewer system in the area. The executive summary and main recommendations of the report are included in Attachment “A”.

Implementation of R.V. Anderson Report’s Recommendations

The purpose of this report is to obtain Council approval to solicit a consultant to complete a study which will provide a detailed hydraulic analysis of the storm water system in the Thornhill area. This will address one of the main recommendations in R. V. Anderson’s report which suggested that:

the Town conduct a storm drainage study that addresses both the major storm system (overland flow) and the minor storm system (catchbasins and underground pipes) in order to identify existing bottlenecks and the improvements required to handle peak flows (e.g. larger sewers, in-line or off-line storage, inlet controls).

The focus of the study will be to complete a more detailed analysis to identify the causes of local flooding. The study will provide recommendations and associated costs to improve the conveyance capacity of the minor system (2 year storm) and the major system (overland flows) by identifying problem areas and bottle necks to be eliminated.

The study will be data intensive and will require a significant effort in order to compile, survey and retrieve the necessary data so that the model will be able to accurately simulate the existing situation.

It is recommended that the major and minor storm systems in the older part of the Town of Markham, which are below current standards, be studied in a similar fashion. The study being asked for in this report will form the basis and will provide a template for future studies to cover the rest of the Town.

R. V. Anderson’s recommendations dealing with the sanitary sewer system are currently being addressed by the Waterworks Department. A report to Council from the Waterworks Department dealing with the award of a contract to complete a Inflow / Infiltration study in the Thornhill area is currently being prepared. Waterworks staff are undertaking the modelling of the sanitary system in house.

Management recommendations will be covered as part of an overall strategy of storm and sanitary sewer management carried out by the Waterworks, Asset Management, Operations and Engineering Departments.

There will be a significant staff resource requirement to manage this project and to oversee the consultant team who will be conducting the study. Currently, Asset Management does not have staff resources to handle this additional work-load and has submitted a request for the 2008 budget requesting a new staff position to manage storm water related projects including the Thornhill one.

FINANCIAL CONSIDERATIONS AND TEMPLATE: (external link):

Account 050-6150-7194-005 is the Rain Storm Damage account. The Asset Management Department is requesting authority from Council to prepare and advertise a RFP to retain a consultant to complete the storm water system assessment for the Thornhill area. It is requested that funding for this project be supplied from the Operations Department’s 2006 Capital Budget Rain Storm Damage Account #050-6150-7194-005.

The budget for this account originally included $860,000 for Riverbank Stabilization. Some of this work will be completed by the Town-wide Erosion Implementation project currently being managed by the Engineering Department leaving funds available for the storm water analysis study discussed in this report.

The following table is a summary of the financial considerations for this report:
Original Budget and Account #	$1,783,500	050-6150-7194-005 Rain Storm Damage
Current Budget Available (unspent)	$507,297
Less Cost	($500,000)	Awarded to
Less Contingency
Budget Remaining	$7,297
Funding for Shortfall
Total
Close upon final payment:	NO
Future Financial Impact:	YES
Finance Department Comments:	YES

ENVIRONMENTAL CONSIDERATIONS:

Improvements and the elimination of bottle necks in the storm systems will improve the environment in the affected areas by reducing damage and flooding caused by severe rainfall events.

ACCESSIBILITY CONSIDERATIONS:

Not applicable

ENGAGE 21^ST CONSIDERATIONS:

Not applicable

BUSINESS UNITS CONSULTED AND AFFECTED:

The Finance and Operations Departments have reviewed this report and their comments have been incorporated in this report.

The Engineering Department may wish, at various stages of the project to request for additional sewer modellling / analysis for:

• Intensification along Yonge St. and Steeles Ave.
• Development of the Langstaff Site
• Hy & Zels Development

Engineering has included in their 2008 budget sufficient funds to cover the required analysis/ modeling for the above mentioned projects or share the cost of the work. The additional modeling / analysis will include assessment of the impact of the projects mentioned above on the upstream lands and also assessment of sewer capacity downstream of the projects.

Engineering will participate in this project and provide information from the following projects:

• Flood emergency response plan
• Pomona Mills creek rehabilitation study
• Town-wide storm water management strategy
• Don Mills channel capacity study
• Town-wide erosion implementation study
• New town storm water management guideline (to be completed in early 2008)

The Legal Department has reviewed and approved this report.

RECOMMENDED BY:

________________________ ________________________

Steve Andrews, P. Eng. Peter Loukes, P. Eng.

Director of Asset Management Commission Lead, Operations and Asset Management

ATTACHMENTS:

Attachment “A” - Executive Summary and recommendations of R.V. Anderson’s report

Attachment “B” - Financial Template

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