Urban storm water management practices: Retrofitting storm water improvements

Storm water quality improvements, or practices, have been successfully used in areas with sufficient space for detention and retention basins. The improvements have been primarily set in suburban or developing areas where there's no impact on residents, land is reasonably priced, and development often pays for their installation. The challenge for engineers has been to design effective storm water quality practices for developed areas that lack the large, open spaces needed to install conventional practices. This paper presents two storm water quality projects that met that challenge. We designed, constructed, and monitored storm water quality practices for two city of Monona, Wisconsin, projects-Interlake Outfall and Lottes Park-which we chose based on their feasibility study results, developed areas, limited areas for treatment, small drainage areas, and opportunity to monitor outcomes: Interlake Outfall. At this site, we designed a staged treatment system in an existing discharge area. Treatment practices included a porous pavement detention area that allows infiltration and cleaning of the basin bottom with vehicles. We used gabions as an outlet weir structure, which provides for the placement and removal of fiber filter pillows to trap heavy metals and petroleum products. Lottes Park. A four-stage storm treatment system in an existing lagoon is being used at this site to improve water quality: (1) a three-chambered oil/grit separator for primary treatment of debris and large particles; (2) a wet detention area to provide for particle settlement; (3) a planted wetland to provide for phosphorus and nitrogen uptake; and (4) a gabion outlet weir wrapped with fabric to provide further detention treatment. Another advantage to the designs is that we used common construction materials and processes, along with multiple practices, to work within site limitations. The Interlake Outfall and Lottes Park projects show that it's possible to develop cost-effective solutions using relatively basic engineering methods.