Assessing downstream stormwater impacts for urban watershed planning

The urbanization of watersheds has caused debilitating effects to downstream aquatic ecosystems in catchments and streams. The implementation of green infrastructure (GI), such as permeable pavements and bioretention facilities, has been shown to alleviate these effects by both reducing runoff and mitigating pollutants; however, the implements are often not designed with a specific goal of water improvement. This study targets understanding a small, impaired urban watershed, and the benefits green infrastructure may have to provide environmental, social, and economic improvement to the watershed. Portions of Rolla including much of the S&T campus drain into the impaired urban waterbody Frisco Lake, plagued with poor water quality, eutrophication, and a substantial fish kill that took place in 2014. Lake phosphorus (P) concentration serves as a good indicator of freshwater quality due to its pertinence to algal growth. Beginning in the fall of 2014, monitoring methods, involving sampling and laboratory analysis, were used to support the modeling of stormwater runoff flows and P loads at outfalls draining into the contaminated lake. Monitoring results showed TP yields of 17 and 31 kg/ha/yr and mean-annual concentrations of 0.43 and 0.42 mg/L at the stormwater outfalls to the lake and were used in mass balance modeling to determine a required 40% P loading reduction to improve lake quality. Recommendations for upstream stormwater management, including a proposed GI plan were developed. Stormwater improvements were projected and used in a post-GI implemented Frisco Lake mass balance model, resulting in healthy lake P levels. The project methodology and watershed improvement plan are to be utilized by city managers for watershed management planning. --Abstract, page iv