Requirements, recommendations and information for using stormwater disconnection (impervious disconnection) BMPs in the MIDS calculator
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This page is in development and will contain guidance on using stormwater disconnection of impervious surfaces as a BMP in the MIDS calculator
This page is in development and will contain guidance on using stormwater disconnection of impervious surfaces as a BMP in the MIDS calculator
Stormwater disconnection (Impervious Disconnection)
Stormwater disconnection/Impervious surface disconnection spreads runoff generated from parking lots, driveways, rooftops, sidewalks and other impervious surfaces onto adjacent pervious areas where it can be infiltrated. All pollutants in the infiltrated water are credited as being reduced. Pollutants in the stormwater that bypasses the BMP receive 68% removal for TSS and 0% reduction for both dissolved and particulate phosphorus.
MIDS calculator user inputs for underground infiltration
For stormwater disconnection systems, the user must input the following parameters to calculate the volume and pollutant load reductions associated with the BMP.
- Watershed tab
- BMP Name: this cell is auto-filled but can be changed by the user.
- Routing/downstream BMP: if this BMP is part of a treatment train and water is being routed from this BMP to another BMP, the user selects the name of the BMP from the dropdown box to which water is being routed. All water must be routed to a single downstream BMP. The User must include the BMP receiving the routed water in the Schematic or the BMP will not appear in the dropdown box.
- BMP Watershed Area: BMP watershed areas are the areas draining directly to the BMP. Values can be added for four soil types (Hydrologic Soil Groups (HSG) A, B, C, D) and for three Land Cover types (Forest/Open Space, Managed Turf and impervious). The surface area of the BMP should be included as a managed turf land cover under the hydrologic soils group of the native soils located under the BMP. Units are in acres
- BMP Parameters tab
- Redirected impervious area routed to pervious area (Ai indirect): The area of impervious area redirected to pervious area. The user enters the value in square ft.
- “Effective pervious area receiving redirected impervious runoff (AP eff): The effective pervious area receiving the runoff from the redirected impervious areas. The flow length must be less than 100 ft. After 100 ft flows have a tendency to channelize reducing the effectiveness of infiltration. The user enters the value in square ft.
- Average soil type of effective pervious area – Hydrologic soil group: the hydrologic soil group (HSG) associated with the effective pervious area. The user selects the average HSG value for the effective pervious area. HSG values of A, B, C, and D can be selected.
- BMP Summary Tab: The BMP Summary tab summarizes the volume and pollutant reductions provided by the specific BMP. It details the performance goal volume reductions and annual