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Stormwater ponds and constructed wetlands are designed to meet water quality targets based on drainage area imperviousness. Pollutant removal occurs mainly in the permanent pool, with effectiveness depending on hydraulic residence time—longer times improve sedimentation and biological uptake. In Ontario, most facilities must achieve 80% TSS removal, with storage requirements based on a 24-hour drawdown time (MOE, 2003).
Stormwater ponds and constructed wetlands are designed to meet water quality targets based on drainage area imperviousness. Pollutant removal occurs mainly in the permanent pool, with effectiveness depending on hydraulic residence time—longer times improve sedimentation and biological uptake. In Ontario, most facilities must achieve 80% TSS removal, with storage requirements based on a 24-hour drawdown time (MOE, 2003)<ref name="MOE"></ref>.
Dry ponds may include a deep pool in the sediment forebay to minimize scour and sediment resuspension, but the main basin does not retain a permanent pool of water. As a result, contaminants cannot settle between storm events, nor is there dilution of pollutants during storms. Consequently, while dry ponds are effective for [[Erosion|erosion]] and flood control, they may need to be paired with other LID features in a [[Treatment train|treatment train]] to improve water quality beyond the basic treatment level of 60% long-term TSS removal.
Dry ponds may include a deep pool in the sediment forebay to minimize scour and sediment resuspension, but the main basin does not retain a permanent pool of water. As a result, contaminants cannot settle between storm events, nor is there dilution of pollutants during storms. Consequently, while dry ponds are effective for [[Erosion|erosion]] and flood control, they may need to be paired with other LID features in a [[Treatment train|treatment train]] to improve water quality beyond the basic treatment level of 60% long-term TSS removal (MOE, 2003)<ref name="MOE"></ref>.
To assess whether a SWMF needs sediment removal, three factors are required:
*Current storage capacity (from sediment depth measurements or TSS load modelling).
*Minimum efficiency allowed (5% reduction, per MOE 2003).
*The facility’s efficiency–storage relationship, to compare storage loss with the 5% efficiency threshold.
==Modeling==
==Modeling==