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Minnesota Stormwater Manual

Structural BMP use in karst settings
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Stormwater BMP selection in karst settings. Sources Karst Working Group, 2009; Minnesota Stormwater Wiki; Tennessee Permanent Stormwater Management and Design Guidance.
Link to this table

BMP Suitability in karst regions Karst considerations
Impervious area disconnect Preferred *Strongly recommended for most residential lots less than 6,000 square feet.
  • Discharge point from the disconnect should extend at least 15 feet from any building foundation.
Bioretention with underdrain (biofiltration) Preferred *Requires 3 foot minimum separation distance between practice bottom and bedrock. If this is not possible, an underdrain should be used to convey the water away.
  • It’s recommended that the drainage area to an individual bioretention BMP be kept less than 20,000 square feet.
  • Larger designs that rely on exfiltration of treated runoff into the soils below are not recommended.
Rain tank/cistern Preferred *Above ground tanks are preferred to below ground.
  • Overflow of tank should extend at least 15 feet from building foundation.
Rooftop disconnect Preferred *15 feet foundation set back.
  • Runoff should be spread diffusely across landscape.
Green roofs Preferred *Runoff should be spread diffusely across landscape.
Dry swale or grassed channel Preferred *Line with underdrains.
  • Incorporate compost amendments into the bottom of the channel to improve runoff reduction for vegetative uptake, and transpiration.
  • Do not incorporate check dams unless the swale or channel incorporates an underdrain. Otherwise small areas of infiltration would develop in the zones upgradient of the check dam where the water is captured without adequate outlet.
Media filter Preferred *Recommended practice in areas of shallow bedrock and soil.
Vegetative filter Preferred *Recommended practice in areas of shallow bedrock and soil.
Soil compost amendment Adequate
Small scale infiltration/micro-bioinfiltration Adequate *Create multiple small sized infiltration BMPs to infiltrate impervious areas of 250 to 2,500 square feet.
  • Not recommended for sites identified as a stormwater hotspot.
Permeable pavement Adequate
Infiltration trench or basin Adequate *Surface area to depth ratios of practices may need to be larger than typical basin designs to minimize depth of the BMP.
  • Confirm suitability with supporting geotechnical investigations and calculations.
  • Not recommended for sites identified as a stormwater hotspot.
  • Incorporate pre-treatment to limit risk of groundwater contamination in the event of future failure of the BMP associated with development of a karst feature. Local review authority should be consulted for approval.
Constructed wetlands Adequate *Requires larger surface area to drainage area ratios to limit the depth of the wetland.
  • Bedrock should act like a liner and help to maintain a permanent pool, unless fracture zone is present.
  • Use liner and liner cells.
Dry extended detention (ED) ponds and wet ponds Adequate *Requires larger surface area to drainage area ratios to limit the depth of the basin or pond. If analysis shows that the soils can support the weight of a pond then a liner should be used.to prevent infiltration
Wet swale Discouraged Not feasible
Large scale infiltration Discouraged *Use small scale infiltration practices instead.
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