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[[File:Geothermal cooling exchange system.PNG|thumb|700px|A simplified 3D cross section of a geothermal cooling system used in a SWM pond in Brampton, Ontario. The system contains a closed hydronic circuit where piping connected a surface water heat exchanger (SHX) to a ground heat exchanger (GHX). A pump continuously circulates a cool hydronic fluid around the circuit. The SHX (placed in the path of the pond outflow) has the water pass through it. The hydronic fluid circulating through the SHX is cooler than warm stormwater outflows. This temperature difference forces heat energy from the stormwater into the hydronic fluid, thus cooling the stormwater leaving the pond. Read more about the system [https://www.chijournal.org/C483 Here]. Photo Source: (Janssen and Van Seters,2022.)<ref>Janssen, E. and Van Seters, T. 2022. Thermal Mitigation of Stormwater Management Pond Outflows Using Geothermal Cooling. Journal of Water Management Modeling. https://www.chijournal.org/Content/Files/C483.pdf</ref>]]

[[File:Geothermal cooling exchange system.PNG|thumb|700px|A simplified 3D cross section of a geothermal cooling system used in a SWM pond in Brampton, Ontario. The system contains a closed hydronic circuit where piping connected a surface water heat exchanger (SHX) to a ground heat exchanger (GHX). A pump continuously circulates a cool hydronic fluid around the circuit. The SHX (placed in the path of the pond outflow) has the water pass through it. The hydronic fluid circulating through the SHX is cooler than warm stormwater outflows. This temperature difference forces heat energy from the stormwater into the hydronic fluid, thus cooling the stormwater leaving the pond. Read more about the system [https://www.chijournal.org/C483 Here]. Photo Source: (Janssen and Van Seters,2022.)<ref>Janssen, E. and Van Seters, T. 2022. Thermal Mitigation of Stormwater Management Pond Outflows Using Geothermal Cooling. Journal of Water Management Modeling. https://www.chijournal.org/Content/Files/C483.pdf</ref>]]

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==Overview==

==Overview==

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===Cooling Trenches===

===='''Cooling Trenches'''====

Cooling trenches typically consist of one or more geotextile wrapped perforated pipes embedded in a clear stone filled trench that is buried underground.  Water temperatures are reduced through heat transfer from the water passing through the trench to the stone and surrounding soils.  Cooling trenches may be installed downstream of the primary pond outlet or draw from a secondary orifice controlled outlet draining water from the pond at or below the permanent pool water level (e.g Van Seters and Graham, 2013<ref> Van Seters, T., Graham, C. 2013. Evaluation of an Innovative Technique for Augmenting Stream Baseflows and Mitigating the Thermal Impacts of Stormwater Ponds. Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority, Toronto, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/08/Cooling-trench-final-2013a.pdf</ref>.; TRCA, 2020<ref>Toronto and Region Conservation Authority (TRCA) 2020. Evaluation of a Thermal Mitigation System on the Heritage at Victoria Square Pond in Markham. Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2021/01/TM-Heritage-report-2021R.pdf</ref>). Further information about these innovative cooling trench features installed as part of the stormwater pond

Cooling trenches typically consist of one or more geotextile wrapped perforated pipes embedded in a clear stone filled trench that is buried underground.  Water temperatures are reduced through heat transfer from the water passing through the trench to the stone and surrounding soils.  Cooling trenches may be installed downstream of the primary pond outlet or draw from a secondary orifice controlled outlet draining water from the pond at or below the permanent pool water level (e.g Van Seters and Graham, 2013<ref> Van Seters, T., Graham, C. 2013. Evaluation of an Innovative Technique for Augmenting Stream Baseflows and Mitigating the Thermal Impacts of Stormwater Ponds. Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority, Toronto, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/08/Cooling-trench-final-2013a.pdf</ref>.; TRCA, 2020<ref>Toronto and Region Conservation Authority (TRCA) 2020. Evaluation of a Thermal Mitigation System on the Heritage at Victoria Square Pond in Markham. Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2021/01/TM-Heritage-report-2021R.pdf</ref>). Further information about these innovative cooling trench features installed as part of the stormwater pond

operation design in two sites located in Markham, ON. visit the [https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/thermal-mitigation/thermal-mitigation-system-evaluation/ STEP project page]. The permanent pool of stormwater management ponds acts as a heat sink during the summer, resulting in warmer summer discharges during both storm and baseflow conditions.  

operation design in two sites located in Markham, ON. visit the [https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/thermal-mitigation/thermal-mitigation-system-evaluation/ STEP project page]. The permanent pool of stormwater management ponds acts as a heat sink during the summer, resulting in warmer summer discharges during both storm and baseflow conditions.  

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===Infiltration Systems===

===='''Infiltration Systems'''====

Infiltration systems may be used as an alternative to cooling trenches for mitigating the thermal effects of pond outflows in areas not constrained by water tables and space.  As with cooling trenches, these may be installed on the main pond outlet or a secondary outlet.  Since water tables at the pond outlet are often high, large void chambers may be more suitable than trenches as they provide greater storage per unit depth.   

Infiltration systems may be used as an alternative to cooling trenches for mitigating the thermal effects of pond outflows in areas not constrained by water tables and space.  As with cooling trenches, these may be installed on the main pond outlet or a secondary outlet.  Since water tables at the pond outlet are often high, large void chambers may be more suitable than trenches as they provide greater storage per unit depth.   

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===Geothermal Cooling===

===='''Geothermal Cooling'''====

This innovative approach uses one or more deep (180 m) geothermal boreholes connected in a closed loop with a pond heat exchanger to cool outflows from stormwater ponds.  A metal or polyethylene heat exchanger is installed in an enclosure at the outlet of the pond.  A heat transfer fluid is pumped through the closed loop to maximize transfer of heat energy from the warm water to the much colder ground.  Warm outflows from the pond enter the enclosure and pass over the pond heat exchanger, which transfers energy from the water to the closed loop and into the ground. The approach was piloted by TRCA/STEP, in partnership with the City of Brampton, on a small pond in Brampton (Janssen and Van Seters, 2021<ref>Erik Janssen and Tim Van Seters. 2021. Geothermal-based Thermal Mitigation of Stormwater Retention Pond Outflows: Report Addendum. Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2022/03/Geo_Cooling_Report_2021.pdf</ref> and 2022<ref>Janssen, E. and Van Seters, T., 2022. Thermal Mitigation of Stormwater Management Pond Outflows Using Geothermal Cooling. Journal of Water Management Modeling.https://www.chijournal.org/C483</ref>)  

This innovative approach uses one or more deep (180 m) geothermal boreholes connected in a closed loop with a pond heat exchanger to cool outflows from stormwater ponds.  A metal or polyethylene heat exchanger is installed in an enclosure at the outlet of the pond.  A heat transfer fluid is pumped through the closed loop to maximize transfer of heat energy from the warm water to the much colder ground.  Warm outflows from the pond enter the enclosure and pass over the pond heat exchanger, which transfers energy from the water to the closed loop and into the ground. The approach was piloted by TRCA/STEP, in partnership with the City of Brampton, on a small pond in Brampton (Janssen and Van Seters, 2021<ref>Erik Janssen and Tim Van Seters. 2021. Geothermal-based Thermal Mitigation of Stormwater Retention Pond Outflows: Report Addendum. Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2022/03/Geo_Cooling_Report_2021.pdf</ref> and 2022<ref>Janssen, E. and Van Seters, T., 2022. Thermal Mitigation of Stormwater Management Pond Outflows Using Geothermal Cooling. Journal of Water Management Modeling.https://www.chijournal.org/C483</ref>)  

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===Other Options===

===='''Other Options'''====

Vegetated channels installed downstream of pond outlets can help to reduce temperatures through shading, although typically a long channel is needed to have an appreciable benefit on temperatures.   

Vegetated channels installed downstream of pond outlets can help to reduce temperatures through shading, although typically a long channel is needed to have an appreciable benefit on temperatures.   

Ponds with large length to width ratios, oriented east-west with shading on the south side can also provide shading, although it will take several years for the shade to become established.<br>

Ponds with large length to width ratios, oriented east-west with shading on the south side can also provide shading, although it will take several years for the shade to become established.<br>

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====Shade balls====

===='''Shade balls'''====

[[File:Shade balls brampton.jpg|thumb|500px|White shade balls were used to cover this pond as part of a thermal mitigation pilot project in the City of Brampton. Photo Source: TRCA, 2020<ref>Rocha, L., and VanSeters, T.2020. Evaluation of shade balls for mitigating summer heating of stormwater management ponds. Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/thermal-mitigation/evaluation-shade-balls-mitigating-summer-heating-stormwater-management-ponds/</ref>]]

[[File:Shade balls brampton.jpg|thumb|500px|White shade balls were used to cover this pond as part of a thermal mitigation pilot project in the City of Brampton. Photo Source: TRCA, 2020<ref>Rocha, L., and VanSeters, T.2020. Evaluation of shade balls for mitigating summer heating of stormwater management ponds. Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/thermal-mitigation/evaluation-shade-balls-mitigating-summer-heating-stormwater-management-ponds/</ref>]]