Changes

===Active storage volume===

===Active storage volume===

LID practices are typically designed to manage more frequent and lower magnitude rainfall events. They work by detaining runoff and releasing it slowly over time. However, larger events can overwhelm the capacity of LID practices.  Once their storage capacity is full, the [[overflow]] rapidly discharges excess water into storm sewers, thus limiting their ability to mitigate large flood events. LID designed for flood control should integrate large active storage volumes to temporarily store stormwater and slowly release it to streams or downstream sewer systems. The mechanisms by which conventional wet ponds and hybrid stormwater infiltration trench/bioretention facility provide this temporary storage are shown in the figures on the right.

LID practices are typically designed to manage more frequent and lower magnitude rainfall events. They work by detaining runoff and releasing it slowly over time. However, larger events can overwhelm the capacity of LID practices.  Once their storage capacity is full, the [[overflow]] rapidly discharges excess water into storm sewers, thus limiting their ability to mitigate large flood events. LID designed for flood control should integrate large active storage volumes to temporarily store stormwater and slowly release it to streams or downstream sewer systems. The mechanisms by which conventional wet ponds and hybrid stormwater infiltration trench/bioretention facility provide this temporary storage are shown in the figures on the right.

[[File:Screenshot 2025-09-22 161822.png|600px|thumb|center|Hybrid trench and bioretention system: Combines flood protection with water quality and water balance benefits. Active storage above the underdrain provides channel and flood control, while infiltration below the underdrain improves water quality and maintains water balance. The underdrain is positioned close to the trench bottom to maximize storage capacity and may be fitted with an orifice to regulate release rates, ensuring full use of storage even during the 100-year event. Because infiltration rates increase with hydraulic head, this design can achieve higher volume reduction than conventional LID practices not intended for flood control. Inlets consist of a distributed network of curb cuts connected to high-flow cobble/gravel columns (about 1 × 2 m). A similar concept can also be applied using stormwater chambers or underground infiltration trenches. Base Image: Schollen and Co<ref>https://www.toronto.ca/ext/digital_comm/pdfs/transportation-services/green-streets-technical-guidelines-document-v2-17-11-08.pdf</ref>.)]]

[[File:Screenshot 2025-09-22 114031.png|600px|thumb|left|Wet pond: The permanent pool provides water quality control, while the ‘active storage’ above the permanent pool provides temporary storage and slow release to reduce peak flows, stream channel erosion control, and flooding. Wet ponds do not provide runoff reduction or thermal mitigation benefits (MOE, 2003)<ref>Ontario Ministry of Environment. 2003. Stormwater Management Planning and Design Manual. https://www.ontario.ca/document/stormwater-management-planning-and-design-manual/stormwater-management-plan-and-swmp-design</ref>.]][[File:Screenshot 2025-09-22 161822.png|600px|thumb|right|Hybrid trench and bioretention system: Combines flood protection with water quality and water balance benefits. Active storage above the underdrain provides channel and flood control, while infiltration below the underdrain improves water quality and maintains water balance. The underdrain is positioned close to the trench bottom to maximize storage capacity and may be fitted with an orifice to regulate release rates, ensuring full use of storage even during the 100-year event. Because infiltration rates increase with hydraulic head, this design can achieve higher volume reduction than conventional LID practices not intended for flood control. Inlets consist of a distributed network of curb cuts connected to high-flow cobble/gravel columns (about 1 × 2 m). A similar concept can also be applied using stormwater chambers or underground infiltration trenches. Base Image: Schollen and Co<ref>https://www.toronto.ca/ext/digital_comm/pdfs/transportation-services/green-streets-technical-guidelines-document-v2-17-11-08.pdf</ref>.)]]<br clear="all" />

Kim & Han (2008)<ref>Kim, Y., & Han, M. (2008). Rainwater storage tank as a remedy for a local urban flood control. Water Science and Technology: Water Supply, 8(1), 31-36.</ref> and Han & Mun (2011)<ref>Han, M. Y., & Mun, J. S. (2011). Operational data of the Star City rainwater harvesting system and its role as a climate change adaptation and a social influence. Water Science and Technology, 63(12), 2796-2801.</ref> conducted studies in Seoul, South Korea, to assess the extent to which the installation of rainwater harvesting cisterns could help mitigate existing urban flooding problems without expanding the capacity of the existing urban drainage system. System operational data showed that 29 mm of rainwater storage per square meter of impervious area (3000 m3 cistern in this instance) provided sufficient storage for a one in 50 year period storm without the need to upgrade downstream sewers designed to 10 year storm capacity. Stormwater chambers, [[infiltration chambers]], [[bioretention]] and other LID systems designed with large volumes of temporary storage could have similar benefits, while also reducing runoff volumes and providing other co-benefits.

Kim & Han (2008)<ref>Kim, Y., & Han, M. (2008). Rainwater storage tank as a remedy for a local urban flood control. Water Science and Technology: Water Supply, 8(1), 31-36.</ref> and Han & Mun (2011)<ref>Han, M. Y., & Mun, J. S. (2011). Operational data of the Star City rainwater harvesting system and its role as a climate change adaptation and a social influence. Water Science and Technology, 63(12), 2796-2801.</ref> conducted studies in Seoul, South Korea, to assess the extent to which the installation of rainwater harvesting cisterns could help mitigate existing urban flooding problems without expanding the capacity of the existing urban drainage system. System operational data showed that 29 mm of rainwater storage per square meter of impervious area (3000 m3 cistern in this instance) provided sufficient storage for a one in 50 year period storm without the need to upgrade downstream sewers designed to 10 year storm capacity. Stormwater chambers, [[infiltration chambers]], [[bioretention]] and other LID systems designed with large volumes of temporary storage could have similar benefits, while also reducing runoff volumes and providing other co-benefits.