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Line 142: − [[File:Screenshot 2025-09-22 113355.png|600px|thumb|right|Peak flow reductions of different LID types during frequent rain events. Top left: Grey and green roof at York University; bottom left: permeable pavement, bioretention and asphalt at Seneca College; right: Kortright permeable pavement and asphalt.]] − Line 271:
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→Case Studies
Flood mitigation strategies that incorporate Low Impact Development (LID), traditional stormwater management, and hybrid infrastructure can manage stormwater effectively and reduce flood impacts.
Flood mitigation strategies that incorporate Low Impact Development (LID), traditional stormwater management, and hybrid infrastructure can manage stormwater effectively and reduce flood impacts.
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==Types of flooding==
==Types of flooding==
! Pluvial (surface) flooding
! Pluvial (surface) flooding
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[[File:Reflecting-on-the-devastating-2013-storm-mississauga-takes-lead-in-municipal-flood-resilience-the-pointer-be39ea9b.jpg|300px|thumb|right|Street flooding in Mississauga (The Pointer, 2023)<ref>The Pointer. 2013. Reflecting on the devastating 2013 storm, Mississauga takes lead in municipal flood resilience. https://thepointer.com/article/2023-07-30/reflecting-on-the-devastating-2013-storm-mississauga-takes-lead-in-municipal-flood-resilience</ref>.]]
[[File:Reflecting-on-the-devastating-2013-storm-mississauga-takes-lead-in-municipal-flood-resilience-the-pointer-be39ea9b.jpg|400px|frameless|center]] Street flooding in Mississauga (The Pointer, 2023)<ref>The Pointer. 2013. Reflecting on the devastating 2013 storm, Mississauga takes lead in municipal flood resilience. https://thepointer.com/article/2023-07-30/reflecting-on-the-devastating-2013-storm-mississauga-takes-lead-in-municipal-flood-resilience</ref>.
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* Caused by intense rainfall that exceeds soil infiltration and storm sewer capacity, especially in urban areas with impervious surfaces.
* Caused by intense rainfall that exceeds soil infiltration and storm sewer capacity, especially in urban areas with impervious surfaces.
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! Fluvial (riverine) flooding
! Fluvial (riverine) flooding
| [[File:Screenshot 2025-09-22 100405.png|300px|thumb|right|Don River floods DVP (City News, 2024)<ref>City News. 2024. From the scene: Don Valley River floods section of DVP, stranding drivers. https://www.youtube.com/watch?v=fbyaYZy0d0A&t=68s</ref>]]
| [[File:Screenshot 2025-09-22 100405.png|400px|frameless|center]]Don River floods DVP (City News, 2024)<ref>City News. 2024. From the scene: Don Valley River floods section of DVP, stranding drivers. https://www.youtube.com/watch?v=fbyaYZy0d0A&t=68s</ref>.
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* Occurs when rivers exceed their capacity due to heavy rain or snowmelt, resulting in water overtopping the banks and flowing into adjacent areas.
* Occurs when rivers exceed their capacity due to heavy rain or snowmelt, resulting in water overtopping the banks and flowing into adjacent areas.
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! Coastal (shoreline) flooding
! Coastal (shoreline) flooding
|[[File:Screenshot 2025-09-19 115121.png|300px|thumb|right|Lake Ontario floods Toronto Island (Toronto Life, 2017)<ref>Toronto Life. 2017. Flooding on the Toronto Islands is terrible—but also weirdly beautiful. https://torontolife.com/life/flooding-toronto-islands-terrible-also-weirdly-beautiful/</ref>]]
|[[File:Screenshot 2025-09-19 115121.png|400px|frameless|center]]Lake Ontario floods Toronto Island (Toronto Life, 2017)<ref>Toronto Life. 2017. Flooding on the Toronto Islands is terrible—but also weirdly beautiful. https://torontolife.com/life/flooding-toronto-islands-terrible-also-weirdly-beautiful/</ref>.
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* Driven by storm surges and lake-level rise due to storm surges or seiches.
* Driven by storm surges and lake-level rise due to storm surges or seiches.
===Hybrid approaches===
===Hybrid approaches===
[[File:Corktown3-2048x-q60.jpg|450px|thumb|right|Corktown Common in Toronto is a levee designed with sustainable stormwater management, recreation, and biodiversity in mind. The previous brownfield site was a gateway for Don River floodwaters that put 500 acres of the city at risk. A series of trails lined with native vegetative, playground, and splash pad and were built on top of the 13 foot clay levee. A marsh was constructed on the west side of the levee which collects rainwater for park irrigation, conserving up to 145,000 gallons per day (Michael Van Valkenburgh Associates Inc, ND)<ref>Michael Van Valkenburgh Associates Inc. ND. Corktown Common. https://www.mvvainc.com/projects/corktown-common </ref>.]]
[[File:Corktown3-2048x-q60.jpg|400px|thumb|right|Corktown Common in Toronto is a levee designed with sustainable stormwater management, recreation, and biodiversity in mind. The previous brownfield site was a gateway for Don River floodwaters that put 500 acres of the city at risk. A series of trails lined with native vegetative, playground, and splash pad and were built on top of the 13 foot clay levee. A marsh was constructed on the west side of the levee which collects rainwater for park irrigation, conserving up to 145,000 gallons per day (Michael Van Valkenburgh Associates Inc, ND)<ref>Michael Van Valkenburgh Associates Inc. ND. Corktown Common. https://www.mvvainc.com/projects/corktown-common </ref>.]]
Combining green and grey infrastructure enhances flood resilience. Examples include:
Combining green and grey infrastructure enhances flood resilience. Examples include:
==Modelling Flood Mitigation Potential of Conventional LIDs==
==Modelling Flood Mitigation Potential of Conventional LIDs==
[[File:Screenshot 2025-09-22 113355.png|700px|thumb|right|Peak flow reductions of different LID types during frequent rain events. Top left: Grey and green roof at York University; bottom left: permeable pavement, bioretention and asphalt at Seneca College; right: Kortright permeable pavement and asphalt.]]
TRCA conducted [[modeling]] to evaluate the capacity of different stormwater management measures (LID and Ponds) to mitigate impacts of development on the peak flow and runoff volume. A sub-catchment in Humber River was selected that has an area of 35.7 ha. The existing land use in the sub-catchment is agriculture and the proposed future land use is employment land with 91% total imperviousness.
TRCA conducted [[modeling]] to evaluate the capacity of different stormwater management measures (LID and Ponds) to mitigate impacts of development on the peak flow and runoff volume. A sub-catchment in Humber River was selected that has an area of 35.7 ha. The existing land use in the sub-catchment is agriculture and the proposed future land use is employment land with 91% total imperviousness.
===Peak Flow===
===Peak Flow===
*The 25 mm on-site retention using LID measures reduced post-development peak flows generated from 2 to 5 year design storms by over 26%,
*The 25 mm on-site retention using LID measures reduced post-development peak flows generated from 2 to 5 year design storms by over 26%,
*For 50 and 100 year design storms it reduces only 4% and 1% respectively.
*For 50 and 100 year design storms it reduces only 4% and 1% respectively.
# Smart blue roof systems can regulate rooftop runoff by storing and controlling the release of rainwater
# Smart blue roof systems can regulate rooftop runoff by storing and controlling the release of rainwater
# In addition to peak flow control, blue roof systems can facilitate runoff reduction through rainwater reuse and evaporative rooftop cooling
# In addition to peak flow control, blue roof systems can facilitate runoff reduction through rainwater reuse and evaporative rooftop cooling
===Example 5: [https://sustainabletechnologies.ca/app/uploads/2020/09/CVC-Glendale-Rain-Garden-Case-Study.pdf Glendale Public School Rain Garden]===
===Example 5: [https://sustainabletechnologies.ca/app/uploads/2020/09/CVC-Glendale-Rain-Garden-Case-Study.pdf Glendale Public School Rain Garden]===