Thermal Impacts of Urban Development and Design Considerations - - PowerPoint PPT Presentation

December 4, 2009

Thermal Impacts of Urban Development and Design Considerations

Background and Objectives Sources of Thermal Impacts

Deborah Sinclair, M.A.Sc.

December 4, 2009

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Background

• The CVC has prepared a series of documents to understand and

implement sustainable stormwater planning and practices in the Credit River watershed

– CVC Water Management Guidelines (CVC 1996) – CVC Stormwater Management Criteria Document – CVC/TRCA Low Impact Development Stormwater Manual (Draft, 2008) – Stormwater Management Planning and Design Manual (MOE 2003)

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Background

• SWM ponds have been designed to mitigate effects of surface runoff

associated with storm events

• Studies have shown that stormwater ponds can increase the

temperature of water discharging to a receiving waterbody

• Galli (1990) found that there is an increase in water temperature with

all types of urban development SWMPs.

SWMP Type Temperature Increase (° C) Infiltration Basin 1.4 Wetland (extended detention) 3.4 Dry Pond (extended detention) 2.9 Wet Pond (extended detention) 5.1

(MOE 2003)

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Temperature Influences on Aquatic Life

• One of the most important factors influencing the distribution of aquatic
• rganisms.
• The Credit River Fisheries Management Plan classifies fish

communities into three categories of temperature

Classification Temperature Range (° C) Representative Species Coldwater Fish species intolerant of water temperatures exceeding 22° C

• Brook Trout
• Sculpins

Mixed Water Fish species intolerant of water temperatures exceeding 24° C

• American Brook Lamprey
• Redside Dace (threatened species)

Warmwater Fish species can tolerate temperatures exceeding 26° C

• Creek Chub
• Blacknose Dace
• Brook Stickelback

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Temperature Influences on Aquatic Life

• Increase as well as the rate of change in temperature in receiving

watercourses may pose an ecological stress to fish and aquatic biota

– Acute mortality at upper tolerable temperatures – Altered food requirements, digestion rate – Change in growth rates

• Aquatic biota that slowly acclimate to elevated water temperatures can

tolerate a higher maximum temperature up to a point

– Rainfall events can cause sudden increases in the temperature of water

• Other parameters affected by temperature:

– Dissolved oxygen – Thermal gradient – Macrophyte and algal decomposition

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Temperature Influences on Aquatic Life

• The effects may be particularly severe during summer low flow

periods.

• The use and construction of SWMPs is increasing in the rapidly

developing areas of Southwestern Ontario

– Several municipalities have hundreds of SWMPs within a single watershed – The potential for individual, combined and cumulative impacts within a watershed is significant

• Succession from a cold-water to a warm-water fishery

– Native brook trout displaced by brown trout in Southern Ontario

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Objectives of Study

• The intent of the report is to enhance the MOE’s 2003 Design Manual

and provide further information on design considerations to mitigate increases in water temperature from inlet-to-outlet-to-receiving streams.

• The report will become an appendix to the CVC Water Management

Guidelines

– Intended to provide guidance with respect to optimizing new and/or existing stormwater management ponds for water quality and specifically to minimize increases in water temperature from the outlet of stormwater ponds

• Low Impact Development (LID)

– Documented in the CVC/TRCA Low Impact Development Stormwater Manual (Draft, 2008)

Sources of Thermal Impact

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Where can temperature increases occur?

Conceptual schematic of stormwater zones

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Where can temperature increases occur?

ZONE 1 ZONE 2 ZONE 3 ZONE 4 ZONE 5

Conceptual cross-section of stormwater zones

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Zone 1. Upgradient

• Surface runoff up-gradient of the stormwater

pond and extends to the inlet structure

– Rooftops – Roadways – Overland flow

• Impervious surfaces such as asphalt and concrete absorb solar

radiation resulting in an increase in their temperature, and at the same time reducing infiltration of stormwater runoff

• During a storm event the heat from the pavement can be transferred to

runoff water which in turn increases the temperature of that water

ZONE 1 ZONE 1

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Zone 1. Upgradient

• Van Buren et al., (2000)

developed a heat transfer model

• Asphalt surface temperatures can

exceed 45° C

• During the initial stages of the

storm event, runoff temperatures exceeded 24° C

• Runoff temperatures on grassy

channels kept temperatures relatively stable

(Van Buren et al., 2000)

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Zone 2. Inlet Structure

• Open ditches or channels

– Conventional type – Exposed to solar radiation and potentially warm air temperatures; exacerbating temperature issues

• Buried pipes

– Materials: concrete, steel or plastic – Shielded from solar radiation and warmer air temperatures – Surrounded by the cooling influence of the ground

Wet Pond Design - Lenoir, North Carolina

(Adapted from Jones, 2008)

Temperature (°C) 2006 May June July Aug Sept Oct Median Runoff 18.08 24.70 26.55 25.72 22.61 19.94 Median Metal Inlet 15.23 18.66 18.76 21.71 18.28 15.90 Median Concrete Inlet 16.38 22.19 23.05 24.61 21.52 17.43

Lenoir Wet Pond : Inlet temperature measurements Runoff from 56 500 m2 rooftop and asphalt parking lot

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Zone 3. Stormwater Pond

• Four factors that contribute to heating of a stormwater pond:

– Solar radiation – Surface area – Ambient air temperature

• The degree to which ponds warm water are affected by:

– Pond shape – Pond orientation – Shading

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Zone 3. Stormwater Pond

• Thermal impacts are most severe when rainfall events are short and

preceded by full or partial sun.

– Most temperature impacts occur late afternoon with low total rainfall amounts (<10mm), and warm pavement runoff from is a significant fraction (Jones et al., 2000) – Heated pond water is displaced by the incoming surface runoff

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CVC Effectiveness Monitoring Program, 2006

Homestead Pond (EM2)

• Extended detention wetland
• Drainage area: 127 ha, highly

urbanized

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CVC Effectiveness Monitoring Program, 2006

Average Daily Maximum Temperature 2004 2005 2006 Inlet 16.6 16.8 16.9 Outlet 22.0 22.9 21.9 Maximum Temperature 2004 2005 2006 Inlet 23.4 26.0 25.8 Outlet 26.3 28.4 29.2

Homestead Pond average daily maximum temperatures (° C) (June to September 2004-2006) Homestead Pond maximum temperatures (° C) (June to September 2004-2006)

(CVC, 2006) (CVC, 2006)

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CVC Effectiveness Monitoring Program, 2006

Precipitation Inlet Outlet

Homestead Pond inlet and outlet water temperatures (June to October 2008)

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Summary SWAMP Monitoring Results

Facility Drainage Basin Characteristics Outlet Max Outlet (° C) Increase (° C) Heritage Estates Pond 52 ha 90-100% residential Top draw 31 6 to 11 Harding Park, Richmond Hill 16.8 ha 90-100% residential Top draw 31 6 to 9 Dunkers FBS, Toronto 174 ha 100% developed Top draw 29 5 to 11 Rouge River Pond 129 ha 25% residential 75% transport Bottom draw 27 5 to 7 Pond-Wetland, Markham 600 ha 70% developed Bottom draw 24 4 to 10 Aurora wetland 82 ha, 70% residential Top and Bottom draw 24 n/a

Maximum temperatures and temperature increases from the inlet to outlet in July and August

(TRCA, 2005)

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Temperature Gradients – SWAMP Monitoring Results

Depth Sampling Date June 27 July 16 Aug 1 Aug 20 Sept 5 0 m 29 28.5 23 20 21 1 m 22.5 24 23 19 18 2 m 15 16 18 17.5 17 T 0-2 m 14 12.5 5 2.5 4

Temperature readings at the Harding Park Stormwater Pond Outlet (1997)

(TRCA, 2003)

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Zone 4. Outlet Structures

• Open ditches or channels

– Conventional type – Exposed to solar radiation and potentially warm air temperatures; exacerbating temperature issues

• Buried pipe

– Materials: concrete, steel or plastic – Shielded from solar radiation and warmer air temperatures – Surrounded by the cooling influence of the ground

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Summary

• There are four distinct zones where temperature can be

elevated:

– Upgradient of the pond – Pond inlet structure – Pond – Pond outlet structure

• Factors in each zone determine how much heat is

transferred

• Combination of these factors will determine the differential

between the receiving watercourse and the outlet water temperature

Thank You

Deborah.Sinclair@aecom.com