Changes

*''C'' = heat capacity of water (4187J/kg°C)}}  

*''C'' = heat capacity of water (4187J/kg°C)}}  

Since urban runoff volumes often increase by 2 to 5 times after development, and stormwater pond effluent temperatures are between 4 and 11°C warmer than pond influent temperatures in the summer, the overall thermal load increases to streams can be very significant ([https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf Van Seters ''et al''. 2019]).<ref>Van Seters, T., Graham, C., Dougherty, J., Jacob-Okor, C., and David, Y. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>

Since urban runoff volumes often increase by 2 to 5 times after development, and stormwater pond effluent temperatures are between 4 and 11°C warmer than pond influent temperatures in the summer, the overall thermal load increases to streams can be very significant ([https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf Van Seters and Dougherty, 2019]).<ref>Van Seters, T., and Dougherty, J. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>

==Temperature Target Selection==

==Temperature Target Selection==

Any measure that decreases runoff volumes or temperatures or both can help mitigate thermal loads to streams or downstream treatment facilities.  Examples include [[bioretention]], [[infiltration trenches]] or [[infiltration chambers|chambers]], [[enhanced swales]], [[permeable pavements]], [[rain gardens|absorbent landscaping]] and increased canopy cover.  The temperature (event mean temperature) and thermal load benefits of the practices are shown in figures 1 to 3 below.  The most effective practices were deeper systems such as trenches, some deep bioretention facilities, and practices that promote significant runoff volume reductions. Beyond reducing temperatures and runoff volumes, enhancing [[infiltration]] also helps re-establish the natural baseflow regime that existed prior to development.<br>

Any measure that decreases runoff volumes or temperatures or both can help mitigate thermal loads to streams or downstream treatment facilities.  Examples include [[bioretention]], [[infiltration trenches]] or [[infiltration chambers|chambers]], [[enhanced swales]], [[permeable pavements]], [[rain gardens|absorbent landscaping]] and increased canopy cover.  The temperature (event mean temperature) and thermal load benefits of the practices are shown in figures 1 to 3 below.  The most effective practices were deeper systems such as trenches, some deep bioretention facilities, and practices that promote significant runoff volume reductions. Beyond reducing temperatures and runoff volumes, enhancing [[infiltration]] also helps re-establish the natural baseflow regime that existed prior to development.<br>

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[[File:Influent Effluent EMT.PNG|500px|thumb|right|Influent and effluent event mean temperatures (EMT) for common LID practices. Source: (Van Seters, ''et al.'' 2019).<ref>Van Seters, T., Graham, C., Dougherty, J., Jacob-Okor, C., and David, Y. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]]

[[File:Influent Effluent EMT.PNG|500px|thumb|right|Influent and effluent event mean temperatures (EMT) for common LID practices. Source:  

[[File:1EMT reduction LID.PNG|500px|thumb|left|Event mean temperature (EMT) reduction for common LID practices. Source: (Van Seters, ''et al.'' 2019).<ref>Van Seters, T., Graham, C., Dougherty, J., Jacob-Okor, C., and David, Y. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]]

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[[File:Thermal load reduction LID.PNG|500px|thumb|center|Thermal load reductions for common LID practices. Source: (Van Seters, ''et al.'' 2019).<ref>Van Seters, T., Graham, C., Dougherty, J., Jacob-Okor, C., and David, Y. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]]<br>

[[File:1EMT reduction LID.PNG|500px|thumb|left|Event mean temperature (EMT) reduction for common LID practices. Source: (Van Seters and Dougherty, 2019).<ref>Van Seters, T., and Dougherty, J. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]]

[[File:Thermal load reduction LID.PNG|500px|thumb|center|Thermal load reductions for common LID practices. Source: (Van Seters and Dougherty, 2019).<ref>Van Seters, T., and Dougherty, J. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]]<br>

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[[File:Subsurface draw outlet.PNG|500px|thumb|Schematic of a reverse sloped subsurface draw outlet to help ensure cooler outflows occur from stormwater ponds (MOE, 2003).<ref>Ministry of the Environment. 2003. Stormwater Management Planning and Design Manual. March, 2003. ISBN 0-7794-2969-9. PIBS 4329e. https://dr6j45jk9xcmk.cloudfront.net/documents/1757/195-stormwater-planning-and-design-en.pdf</ref>]]

[[File:Subsurface draw outlet.PNG|500px|thumb|Schematic of a reverse sloped subsurface draw outlet to help ensure cooler outflows occur from stormwater ponds (MOE, 2003).<ref>Ministry of the Environment. 2003. Stormwater Management Planning and Design Manual. March, 2003. ISBN 0-7794-2969-9. PIBS 4329e. https://dr6j45jk9xcmk.cloudfront.net/documents/1757/195-stormwater-planning-and-design-en.pdf</ref>]]

There are several opportunities to mitigate thermal impacts both within the pond itself and/or implemented within the upstream drainage area (and the lands surrounding) of the pond.  Options shown in past studies to provide appreciable thermal mitigation benefits include (Van Seters and Dougherty, 2019)<ref>Van Seters, T., Graham, C., Dougherty, J., Jacob-Okor, C., and David, Y. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>

There are several opportunities to mitigate thermal impacts both within the pond itself and/or implemented within the upstream drainage area (and the lands surrounding) of the pond.  Options shown in past studies to provide appreciable thermal mitigation benefits include (Van Seters and Dougherty, 2019).<ref>Van Seters, T., and Dougherty, J. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref></ref>

===Subsurface Draw Outlets===

===Subsurface Draw Outlets===

====Design Considerations====

====Design Considerations====

*Optimal 8 hour duration for night time release outlets was found to be between 3 AM and 10 AM inclusive based on data from 4 ponds  

*Optimal 8 hour duration for night time release outlets was found to be between 3 AM and 10 AM inclusive based on data from 4 ponds  

*Optimal 4 hour duration release times were found to be between 6 and 9 AM inclusive (Van Seters and Dougherty, 2019)<ref>Van Seters, T., Graham, C., Dougherty, J., Jacob-Okor, C., and David, Y. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]].

*Optimal 4 hour duration release times were found to be between 6 and 9 AM inclusive (Van Seters and Dougherty, 2019).<ref>Van Seters, T., and Dougherty, J. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]].

*Robust automation technology is critical to avoid excessive repairs and down time.  

*Robust automation technology is critical to avoid excessive repairs and down time.  

*Electrical supply and back-up power are typically needed at the outlet to reduce operation and maintenance requirements

*Electrical supply and back-up power are typically needed at the outlet to reduce operation and maintenance requirements

The volumes infiltrated may also be used to meet site water balance requirements.  Proponents will need to consult with local approval agencies to determine whether the typical 1 meter separation depth to groundwater may be waived given that the infiltrated water has been treated through the pond.   

The volumes infiltrated may also be used to meet site water balance requirements.  Proponents will need to consult with local approval agencies to determine whether the typical 1 meter separation depth to groundwater may be waived given that the infiltrated water has been treated through the pond.   

Analysis of temperature and thermal load data from three monitored ponds showed that the bottom area of the infiltration area would need to be up to 7% that of the pond area depending on the infiltration capacity of the native soils.  These areas could be reduced by 40% if the outlet draws water from 0.25 m below the surface, and further reduced for deeper outlets (Van Seters and Dougherty, 2019).<ref>Van Seters, T., Graham, C., Dougherty, J., Jacob-Okor, C., and David, Y. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]].  

Analysis of temperature and thermal load data from three monitored ponds showed that the bottom area of the infiltration area would need to be up to 7% that of the pond area depending on the infiltration capacity of the native soils.  These areas could be reduced by 40% if the outlet draws water from 0.25 m below the surface, and further reduced for deeper outlets (Van Seters and Dougherty, 2019).<ref>Van Seters, T., and Dougherty, J. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]].  

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