Stormwater Management Green Building Festival

October 11 2012

Sameer Dhalla, P.Eng.

Toronto and Region Conservation Authority

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

Up to 500% more runoff

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

Consequences of Poor

Stormwater Management

Evolution of Stormwater Management

Stormwater Management Practices

Impacts are mitigated through the implementation of

Stormwater Management Practices consisting of:

Source Controls

Porous Pavers

CWC / Infiltration Systems

Conveyance Controls

Wet Pond

End-of-Pipe Controls

Treatment Train Approach

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)

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

New Development

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)

Pre-

Development

Post (w/

Detention)

Time

Dis

ch

arg

e

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.

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.

Stormwater Management Criteria Document

Stormwater Management Criteria Overview

SWM Objective SWM Criteria What’s New

1. Flood Protection Control Peak Flows to Pre-

Development Levels

Need to assess impacts to Regulatory

Storm as well as the 2-100 year design

storms

2. Erosion Protection Mitigate increases in flow rates

and volumes to protect

watercourses from stream bank

erosion

Need for volume control (site retention

of stormwater through infiltration,

evapo-transpiration and/or reuse -

LID). Minimum 5mm for small sites

that do not require a detailed analysis

3. Water Quality

Control

Enhanced level of protection

(80% TSS Removal MOE, 2003)

Need for thermal protection for

coldwater species and the need for

clean water (eg. Roof drainage) to

wetlands. Credit for LID

4. Water Balance Maintain Water Balance for

Significant Recharge Areas and

Ecologically Significant Areas

(sensitive wetlands and

woodlots)

This is a new criteria, need for LID in

environmentally sensitive areas

Conventional “end-of-pipe” strategy Low Impact Development strategy

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

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)

SWM and LID PRACTICES and DESIGN PRINCIPLES

Stormwater Management – Water Balance Approach

“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)

Contact Information

Sameer Dhalla, P.Eng.

Phone: 416 661 6600 x 5350

Email: sdhalla@trca.on.ca

TRCA website:

www.trca.on.ca

STEP website:

www.sustainabletechnologies.ca

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.

LOW IMPACT DEVELOPMENT BENEFITS

Lower Construction Costs

Higher Lot Yield Project Conventional Low Impact Difference

2nd Avenue SEA

Street (Wash.)

$868,803 $651,548 25%

Auburn Hills

(Wisconsin)

$2,360,385 $1,598,989 32%

Gap Creek

(Arkansas)

$4,620,600 $3,942,100 15%

Somerset

(Maryland)

$2,456,843 $1,671,461 32%

Tellabs Campus

(Illinois)

$3,162,160 $2,700,650 15%

Source: US EPA, 2007, Reducing Stormwater Costs Through Low Impact Development Strategies and Practices

(in US dollars)