For practices without an underdrain, the active water storage components include the surface ponding, mulch and filter media depths (i.e. total depth of the practice). The active water storage depth of the practice can be calculated as: | For practices without an underdrain, the active water storage components include the surface ponding, mulch and filter media depths (i.e. total depth of the practice). The active water storage depth of the practice can be calculated as: |