Sameer Dhalla Overview of the Stormwater Management Criteria Document and the move toward a water balance approach

1. Stormwater Management
Green Building Festival
October 11 2012
Sameer Dhalla, P.Eng.
Toronto and Region Conservation Authority

2. TRCA Jurisdiction
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:
• Etobicoke Creek • Rouge River
• Mimico Creek • Petticoat Creek
• Humber River • Duffins Creek
• Don River • Carruthers Creek
• Highland Creek
The TRCA’s jurisdiction also
extends into Lake Ontario to a
point defined by the Territorial
Divisions Act, R.S.O. 1980
The population in 2004 within TRCA’s jurisdiction is approximately 4,300,000
(37% of Ontario’s population).

3. Impacts of Urbanization on Hydrologic Cycle
Up to 500% more runoff

4. Consequences of Poor
Stormwater Management
 Stream bank 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

5. Evolution of Stormwater Management

6. Stormwater Management Practices
Impacts are mitigated through the implementation of
Stormwater Management Practices consisting of:
Source Controls
Conveyance Controls
End-of-Pipe Controls
Porous Pavers
CWC / Infiltration
Systems
Wet
Pond
Treatment Train Approach

7. TRCA Stormwater Management
WHERE WE ARE TODAY
 77% of urban areas do
not have adequate
stormwater controls (mostly
older areas that were
developed prior to the
required implementation of
stormwater management
controls)
 Over 800 SWM Ponds
have been constructed
 Very few Source and
Conveyance Controls (LID
sites)

8. The Solution to Stormwater Pollution
1. Implement Municipal Stormwater
Retrofit Projects (e.g. Toronto Wet Weather
Flow Management Plan and Municipal SWM
Pond Retrofits such as Pioneer Park and Earl
Bales Park)
2. Maintain existing stormwater
management infrastructure (e.g. pond
clean-outs)
3. Encourage existing communities to
implement lot level controls on private
property (e.g. rain gardens/barrels, SNAP,
PPG)
4. Ensure that all new developments
(including redevelopments) are
designed to comply with the
updated Stormwater Management
Criteria

9. New Development

10. End of Pipe Controls (SWM Ponds)
 Mitigates increased peak flows from urban areas (no volume control)
 Reduces pollutant loadings (does not provide thermal benefits)
 Currently the standard practice for stormwater treatment (usually the
only practice employed in the “treatment train”)
Post (no
SWM)
Discharge
Post (w/
Detention)
Pre-
Development
Time

11. WHY DO WE NEED TO IMPROVE CURRENT PRACTICES?
Conventional strategies don’t address all impacts
Changes to water balance (increased runoff
volume & decreased recharge & ET)
• Accelerated stream channel erosion and/or
sedimentation;
• Risk of damage to infrastructure &
property;
• Degraded aquatic and terrestrial habitats;
• Degraded water quality (increased
temperature and pollutant loads);
• Less diverse aquatic and terrestrial
communities.

12. Stormwater Management Criteria Document
Goal: That stormwater management effectively mitigate the impacts of
urbanization on the natural water cycle (Water Balance Approach)
Objectives:
 To prevent increases in flood risk;
 To prevent undesirable
geomorphic changes in
watercourses;
 To protect water quality;
 To preserve groundwater and
baseflow characteristics;
 To maintain an appropriate
diversity of terrestrial and aquatic
life and opportunities for human
use.

13. Stormwater Management Criteria Overview
SWM Objective SWM Criteria What’s New
1. Flood Protection Control Peak Flows to Pre- Need to assess impacts to Regulatory
Development Levels Storm as well as the 2-100 year design
storms
2. Erosion Protection Mitigate increases in flow rates Need for volume control (site retention
and volumes to protect of stormwater through infiltration,
watercourses from stream bank evapo-transpiration and/or reuse -
erosion LID). Minimum 5mm for small sites
that do not require a detailed analysis
3. Water Quality Enhanced level of protection Need for thermal protection for
Control (80% TSS Removal MOE, 2003) coldwater species and the need for
clean water (eg. Roof drainage) to
wetlands. Credit for LID
4. Water Balance Maintain Water Balance for This is a new criteria, need for LID in
Significant Recharge Areas and environmentally sensitive areas
Ecologically Significant Areas
(sensitive wetlands and
woodlots)

14. Need to Move Towards a Water Balance Approach
(Low Impact Development)
• Mitigates impacts to hydrologic cycle
• Reduces generation of excess runoff
volume
• Restores natural flow pathways and
patterns
• Reduces temperature impacts
Conventional “end-of-pipe” strategy Low Impact Development strategy

15. SWM and LID PRACTICES and DESIGN PRINCIPLES
1. Integrate Stormwater into Planning
(Multi Disciplinary Approach)
2. Focus on runoff prevention
(innovative planning, LID practices)
3. Treat stormwater close to the source
(respect natural flow paths,
stormwater is a resource)
4. Create multifunctional landscapes
(site aesthetics, energy, conserve
potable water, wildlife, parks)
5. Educate and maintain (maintenance
plans)

16. Stormwater Management – Water Balance Approach

17. “Integrated design teams and the treatment train approach are essential ingredients
for the implementation of successful stormwater management strategies, where the
environment and our communities are soundly protected by infrastructure that is
integrated within the urban fabric.” (TRCA SWM Criteria Document, 2012)

18. Contact Information
TRCA website:
Sameer Dhalla, P.Eng.
www.trca.on.ca
Phone: 416 661 6600 x 5350
Email: sdhalla@trca.on.ca
STEP website:
www.sustainabletechnologies.ca

19. Key Recommendations –
Resolution 4 – 2012M
 WHEREAS, stormwater has been recognized by the International Joint
Commission (IJC) and Canadian and US regulatory authorities as the
leading non-point sources of pollutants to nearshore water quality in
the Great Lakes and St. Lawrence; and
 WHEREAS, the volume and frequency of untreated stormwater
discharged to the nearshore can only be expected to increase in the
foreseeable future – due to more severe and numerous weather events and
climate change, compounded in urban areas by planned growth and
intensification – unless more proactive stormwater planning and
management is applied and implemented in urban and rural areas; and
 WHEREAS, support for naturalized infrastructure in the management of rural
stormwater run-off also helps landowners and municipalities adapt to the
impacts of climate change in ways that help to mitigate climate change
because natural infrastructure takes carbon out of the atmosphere and
locks it up in plant material.

20. LOW IMPACT DEVELOPMENT BENEFITS
Lower Construction Costs
Higher Lot Yield
Project Conventional Low Impact Difference
2nd Avenue SEA $868,803 $651,548 25%
Street (Wash.)
Auburn Hills $2,360,385 $1,598,989 32%
(Wisconsin)
Gap Creek $4,620,600 $3,942,100 15%
(Arkansas)
Somerset $2,456,843 $1,671,461 32%
(Maryland)
Tellabs Campus $3,162,160 $2,700,650 15%
(Illinois)
Source: US EPA, 2007, Reducing Stormwater Costs Through Low Impact Development Strategies and Practices
(in US dollars)