SWMM - LID Controls - Bio-Retention Cell

Filtration catchments - or bio-retention cells are depressions that contain vegetation grown in an engineered soil mix placed above a gravel drainage bed. They provide storage, infiltration and evaporation of both direct rainfall and runoff captured from surrounding areas.

Schematically:

• SWMM
  • Storage
    • Storage Height - Gravel layer thickness or Rain Barrel height
    • Clogging Factor - Total volume of treated runoff required to completely clog the bottom of the layer divided by the void volume of the layer
    • Voice Index - The volume of void space in relation to the volume of solids in the layer
    • Infiltration rate - The rate at which water penetrates the native soil below the layer
  • Deep Drain
    • drainage Coefficient - The drainage coefficient (C) and exponent (n) determine the rate of flow through a drain as a function of the height of stored water above the drain displacement q = C * h ^ n
    • Control Curve - The name of an optional control curve that adjusts the calculated drain flow as a function of the head of water above the drain
    • Exponent - The drainage coefficient (C) and exponent (n) determine the rate of flow through a drain as a function of the height of stored water above the drain displacement
    • Opening Level - The height in the drain's Storage Tier that causes the drain to automatically open when the water level rises above it
    • Closing Level - The height in the Drain Storage Tier that causes the drain to automatically close when the water level drops below it
    • Offset - This is the height of the drain line above the bottom of a storage layer or rain barrel
    • Wait Time - The number of hours of dry weather that must elapse before the drain line on a rain barrel opens
  • Pollutant Removal - Specifies the removal rates for each pollutant
    Note: Do not repeat the pollutant and do not leave the value at zero
  • Soil
    • Field Capacity - Volume of pore water in relation to total volume after soil drains completely
    • Hydraulic Conductivity - Hydraulic Conductivity for fully saturated soil
    • Conductivity Slope - Slope of the curve of log (Conductivity) versus soil moisture content (dimensionless)
    • Thickness - Thickness of the soil layer
    • Wilting Point - Volume of pore water in relation to total volume for a very dry soil, where only bound water remains
    • Porosity - The volume of pore space in relation to the total soil volume
    • Suction Potential - The average value of soil capillary suction along the wetting front
  • Surface
    • Vegetable Coverage - Vegetal Coverage
    • Slope - Surface slope
    • Side Slope - Slope of the side walls of a cross section of a ditch
    • Storage Depth - Storage Depth
    • Surface Roughness - Roughness