Changes

Designing LID for flood control functions requires integrating large volumes of active storage to temporarily store stormwater while it is released slowly to streams or downstream sewer systems. The mechanisms by which conventional wet ponds provide this temporary storage is shown in the figure below. The permanent pool represents the water quality volume and the ‘active storage’ above the permanent pool provides temporary storage and slow release to reduce peak flows, stream channel erosion control, and flooding.

Designing LID for flood control functions requires integrating large volumes of active storage to temporarily store stormwater while it is released slowly to streams or downstream sewer systems. The mechanisms by which conventional wet ponds provide this temporary storage is shown in the figure below. The permanent pool represents the water quality volume and the ‘active storage’ above the permanent pool provides temporary storage and slow release to reduce peak flows, stream channel erosion control, and flooding.

[[File:Screenshot 2025-09-22 114031.png|500px|thumb|left|Flood and water quality control in stormwater ponds.  Water quality control is provided by the permanent pool, Channel and flood protection are provided by the temporary or active storage above the permanent pool.  Source: (MECP 2003).  Wet ponds do not provide runoff reduction or thermal mitigation benefits.]]

[[File:Screenshot 2025-09-22 114031.png|500px|thumb|center|Flood and water quality control in stormwater ponds.  Water quality control is provided by the permanent pool, Channel and flood protection are provided by the temporary or active storage above the permanent pool.  Source: (MECP 2003).  Wet ponds do not provide runoff reduction or thermal mitigation benefits.]]

The figure below shows how large volume active storage has been integrated into a hybrid stormwater infiltration trench and bioretention facility. The underdrain is close to the bottom of the trench to maximize active storage availability.  Orifices on underdrains help temporarily hold back flows to ensure full utilization of available storage during the 100 year event.  Infiltration of stormwater below the underdrain provides water quality and water balance control. A similar concept can be achieved with stormwater chambers and underground infiltration trenches.   

The figure below shows how large volume active storage has been integrated into a hybrid stormwater infiltration trench and bioretention facility. The underdrain is close to the bottom of the trench to maximize active storage availability.  Orifices on underdrains help temporarily hold back flows to ensure full utilization of available storage during the 100 year event.  Infiltration of stormwater below the underdrain provides water quality and water balance control. A similar concept can be achieved with stormwater chambers and underground infiltration trenches.