StormwaterManagement Criteria for Watershed Protection

November 17 2010

Sameer Dhalla, P.Eng. Toronto and Region Conservation Authority2010 A.D. Latornell Conservation Symposium

TRCA Jurisdiction

•Rouge River•Petticoat Creek•Duffins Creek•Carruthers Creek

The TRCA's area of jurisdiction includes:•3,467 sq. km: 2,506 on land and 961 water-based.

This area is comprised of nine watersheds including:

The TRCA’s jurisdiction also extends into Lake Ontario to a point defined by the Territorial Divisions Act, R.S.O. 1980

•Etobicoke Creek•Mimico Creek•Humber River•Don River•Highland Creek

The population in 2004 within TRCA’s jurisdiction is approximately 4,300,000(37% of Ontario’s population).

Impacts of Urbanization on Hydrologic Cycle(Hydromodification)

• Streambank erosion and bed degradation

• Increased peak flows - flooding

• Increase pollutant loading (including thermal impacts)

• Reduction of groundwater and baseflow

• Loss of aquatic habitat and natural features

• Risk to Infrastructure

Consequences of Hydromodification

Water Quality

Water Quality

2003-2007 RWQMN Median Values for Don River Stations

Parameter PWQO Guideline West Don East Don German Mills * Taylor Massey Lower Don

E. coli (counts / 100 mL) 100 590 2150 940 2400 690

Chloride (mg/L) 150 332 172 204 401 207

Phosphorus (mg/L) 0.03 0.06 0.06 0.04 0.06 0.156

Total Suspended Solids (mg/L) 30 10 6 9 6 11

* Stations with less than 30 samples

Percent of Samples Exceeding PWQO Guidelines 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

West Don East Don German Mills Taylor Massey Lower Don 

Total Suspended Solids Chloride Phosphorus E. coli

FloodingLocation: Highland Creek at Ellesmere and Birkdale Road

Streambank Erosion

Risk to Infrastructure

Location: Black Creek at Finch Avenue –Note Complete Failure of Embankment and Roadway

(Aug. 19/05)

Manage Stormwater to protect and improve watershed health, promote a more resilient stromwater system and adapt to the effects of a changing climate

Manage Stormwater to protect and improve watershed health, promote a more resilient stromwater system and adapt to the effects of a changing climate

Objective

Ensure stormwater volumes and rates are effectively managed to:

• Protect water quality

• Prevent increases in flood risk

• Preserve groundwater and baseflow

• Prevent undesirable erosion

• Maintain hydrological and ecological functions; and

• Protect aquatic and terrestrial habitat

Objectives of Stormwater Management Criteria:

Stormwater Management PracticesCriteria to be addressed through the implementation of a Stormwater Management Practices consisting of:

Source Controls

Porous Pavers

CWC / Infiltration Systems

Conveyance Controls

Wet Pond

End-of-Pipe Controls

• The SWM Criteria Document will provide sizing criteria (i.e determining storage volumes) How Much

• The LID Guide and MOE Manual provide design guidance How To

• Enhanced Level of Protection is required as per 2003 MOE Stormwater Management Planning and Design Manual

• Additional water quality control may be required as per Municipal criteria (i.e City of Toronto along the waterfront where enhanced removal of bacteria is required)

Water Quality Criteria

•MOE Table 2.3 to be used for determining Water Quality Volume •For LID Infiltration Practices, Infiltration row to be used•For Green Roofs and Rainwater Harvesting (Dual Use), it is proposed that the roof area can be subtracted from total impervious area•For LID practices on private property mechanisms must be in place to ensure long term maintenance and operations (i.e. legal agreements, bylaws etc.)

Water Quality Criteria

• Criteria throughout TRCA jurisdiction has been established through detailed hydrology studies for each watershed

• Flow criteria map illustrating the types of control required, unit flow rates and flow targets at key locations will be provided

• Additional water quantity control may be required as per Municipal criteria (i.e urban flooding - minor / major system capacity)

Flood Flow Criteria

• Overview as to the type of approaches required to develop erosion control criteria

• Simplified vs. Detailed Approach

• Need to manage volume and rate

• Credit for LID practices

Erosion Control

Groundwater Recharge• Infiltration targets on a watershed

basis to be provided as framework for target setting (i.e maintain pre development recharge in all significant groundwater recharge areas)

Feature Based Guidelines• For significant ecological features

(wetlands and woodlots), maintain flow regime to features

Water Balance

** Minimum criteria – 5 mm of runoff should be retained on site to mitigate impacts (Consistent with City of Toronto WWF Management Guidelines)

TRCA Stormwater ManagementWHERE WE ARE TODAY

•Approx. 70% of the Developed / Urban Area does not have any stormwater controls in place

•Over 800 Stormwater Management Ponds have been constructed

•Very few LID sites (see iswm.ca)

End of Pipe Controls (SWM Ponds)• Mitigates increased peak

flows from urban areas (flood and erosion protection)

• Reduces pollutant loadings (water quality control)

• Currently the standard practice for stormwater treatment for areas greater than 5ha.

• Usually the only practice employed in the “treatment train”

Need for Volume Control

• There may not be a “safe” way to discharge 500% more runoff

• Cumulative effects of watershed development are not managed

• Design assumptions are unrealistic

• Still causes a profound alteration to streamflow regimes

• Does not mitigate loss of natural flow pathways or temperature impacts

Post (no SWM)

Pre-Development

Post (w/ Detention)

Time

Dis

char

ge

Flaws in the Extended Detention Approach

Criteria to Encourage an Integrated Strategy for Stormwater Management

Need More Source and Conveyance Controls(Low Impact Development)

• Mitigates impacts to hydrologic cycle and restores natural flow pathways and patterns (protection of aquatic and terrestrial habitat)

• Reduces generation of excess runoff volume (mitigates erosion and water quality impacts, including temperature)

• Addresses climate change (more resilient stormwater system)

• Opportunity to incorporate into new development and re-development

Contact Information

Sameer Dhalla, P.Eng.Phone: 416 661 6600 x 5350Email: sdhalla@trca.on.ca

TRCA website:www.trca.on.ca

STEP website:www.sustainabletechnologies.ca