Requirements, recommendations and information for using bioretention BMPs in the MIDS calculator
Below is a summary of requirements, recommendations and other information for using the Minimal Impacts Design Standards (MIDS) calculator for bioretention BMPs. Links to MIDS pages and the MIDS calculator are included at the bottom of this page.
Requirements
Warning: The following are requirements of the Minnesota Construction Stormwater General Permit
- 3 foot separation from the bottom of the bioretention system to seasonal high water table
- Use most restrictive infiltration rate within 3 feet of the bottom of the BMP
- Drawdown time of 24 hours for trout streams
- For measured infiltration rates, apply a safety factor of 2
- Pretreatment
Recommendations
Caution: The following are recommendations for inputs into the MIDS calculator
- 5 acres or less for contributing area
- Maximum ponding depth of 18 inches, reduced to 6 inches if there is no site information
- Field tested infiltration rates rather than table values
Information
Information: The following information may be useful in determining inputs for the MIDS calculator
- Guidance on determining infiltration rates
- Information on site constraints (shallow soil, karst, etc.)
- Information on assessing BMPs
- Information on design metrics (high flow bypass, ponding depths, drawn down)
- Guidance on pretreatment
- Information on soil mixes
- Plant information, including species list that show water tolerance, potential effects of different species on infiltration rates, planting guidance
- Construction specifications
- Information on operation and maintenance of bioretention BMPs.