Slide 96 of 119
Notes:
Dry swales are similar in design to bioretention areas (See Bioretention). These designs incorporate a fabricated soil bed into their design. That is, the existing soil is replaced with a sand/soil mix that meets minimum permeability requirements. An underdrain system is used under the soil bed. This system is a gravel layer which encases a perforated pipe. Stormwater treated in the soil bed flows through the bottom into the underdrain, which conveys this treated stormwater to the storm drain system. Dry swales are a relatively new design, but studies of swales with a native soil similar to the made soil bed of dry swales suggest high pollutant removal. In a dry swale the entire water quality volume is temporarily retained by checkdams during each storm. The swale is designed to rapidly dewater which makes this practice a good choice for low density residential projects or for very small impervious areas.