BMPs with an underdrain |
BMPs having an underdrain are designed to filter water prior to being discharged to the underdrain. These BMPs include bioretention, permeable pavement, sand filters, and tree trenches/boxes. Most of the water entering these BMPs is passed to the underdrain. In a harvest and use system, water passing through the underdrain must be discharged back to the harvest and use system. As water passes through the filter media, particulates are trapped and nutrients are removed via plant uptake. Note that media mixes with high organic matter may contribute nutrients and impart a dark color to the discharge water. Information on design, construction, maintenance, and performance assessment can be found in the appropriate section of this manual. |