Detention pond design and land use planning for watershed management

Nonpoint source management using wet detention ponds to reduce pollutant loading into receiving water bodies is a common practice. Design of these ponds is typically carried out individually to meet a target total suspended solids (TSS) removal level. An improvement to this approach is to generate cost-effective pond configurations that meet system-wide targets for removal of pollutant loadings, including TSS, total nitrogen, and total phosphorus, corresponding to a specific build-out land use plan. The amount of pollutant loading can be managed better through appropriate land use allocation planning conducted simultaneously with the design of detention pond configurations. This paper presents a modeling approach to address this problem and its solution via a genetic algorithm-based search procedure. Application of this approach is demonstrated using an illustrative case study involving the City Lake watershed in North Carolina. The results show cost improvements when considering land management simultaneously with the decisions for pond locations and sizes. Through iterative application of this method, the tradeoff between cost and removal level of each pollutant is also generated.