Thermal Impacts of Urban Development and Design Considerations December 4, 2009
Background and Objectives Sources of Thermal Impacts Deborah Sinclair, M.A.Sc. December 4, 2009
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) Client logo
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) Client logo
Temperature Influences on Aquatic Life • One of the most important factors influencing the distribution of aquatic organisms. • The Credit River Fisheries Management Plan classifies fish communities into three categories of temperature Classification Temperature Range (° C) Representative Species •Brook Trout Coldwater Fish species intolerant of •Sculpins water temperatures exceeding 22° C •American Brook Lamprey Mixed Water Fish species intolerant of •Redside Dace (threatened species) water temperatures exceeding 24° C Warmwater Fish species can tolerate •Creek Chub •Blacknose Dace temperatures exceeding •Brook Stickelback 26° C Client logo
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 Client logo
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 Client logo
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) Client logo
Sources of Thermal Impact
Where can temperature increases occur? Conceptual schematic of stormwater zones Client logo
Where can temperature increases occur? Conceptual cross-section of stormwater zones ZONE 1 ZONE 2 ZONE 3 ZONE 4 ZONE 5 Client logo
Zone 1. Upgradient ZONE 1 ZONE 1 • 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 Client logo
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) Client logo
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 Client logo
Wet Pond Design - Lenoir, North Carolina Lenoir Wet Pond : Inlet temperature measurements 2006 Temperature ( ° C) 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 ( Adapted from Jones, 2008) Runoff from 56 500 m 2 rooftop and asphalt parking lot
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 Client logo
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 Client logo
CVC Effectiveness Monitoring Program, 2006 Homestead Pond (EM2) • Extended detention wetland • Drainage area: 127 ha, highly urbanized Client logo
CVC Effectiveness Monitoring Program, 2006 Homestead Pond average daily maximum temperatures (° C) (June to September 2004-2006) Average Daily Maximum Temperature 2004 2005 2006 Inlet 16.6 16.8 16.9 Outlet 22.0 22.9 21.9 (CVC, 2006) Homestead Pond maximum temperatures (° C) (June to September 2004-2006) Maximum Temperature 2004 2005 2006 23.4 26.0 25.8 Inlet 26.3 28.4 29.2 Outlet (CVC, 2006) Client logo
CVC Effectiveness Monitoring Program, 2006 Homestead Pond inlet and outlet water temperatures (June to October 2008) Inlet Outlet Precipitation Client logo
Summary SWAMP Monitoring Results Maximum temperatures and temperature increases from the inlet to outlet in July and August Facility Drainage Basin Outlet Max Increase Characteristics Outlet (° C) (° C) Heritage Estates Pond 52 ha Top draw 31 6 to 11 90-100% residential Harding Park, Richmond 16.8 ha Top draw 31 6 to 9 Hill 90-100% residential Dunkers FBS, Toronto 174 ha Top draw 29 5 to 11 100% developed Rouge River Pond 129 ha Bottom 27 5 to 7 draw 25% residential 75% transport Pond-Wetland, 600 ha Bottom 24 4 to 10 Markham draw 70% developed Aurora wetland 82 ha, Top and 24 n/a Bottom 70% residential draw (TRCA, 2005) Client logo
Temperature Gradients – SWAMP Monitoring Results Temperature readings at the Harding Park Stormwater Pond Outlet (1997) Sampling Date Depth 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 (TRCA, 2003) Client logo
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 Client logo
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 Client logo
Thank You Deborah.Sinclair@aecom.com
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