Conversion of a Drainage Ditch to Constructed Wetlands to Treat Stormwater Runoff

A drainage ditch near Laney High School in Wilmington, N.C., designed to collect runoff from athletic fields and parking lots and deliver it to Smith Creek, was converted to a constructed wetland in August 2005: The approximately 0.1 ha wetland collects and treats drainage water from a 12 ha watershed, 2.4 ha of which is impervious surface. The wetland was designed with a variety of elevation features and planted with over 15 species of wetland plants, to encourage sedimentation, biogeochemical transformations of nutrients associated with runoff, and ecological diversity. Retention times are estimated to be 3–4 days. As of summer 2006, the wetland was vegetated and on-line. Preliminary nutrient data indicate a 50% reduction in TN and TP concentrations, and a 40% reduction in TSS.