Optimizing the LID Facility Layout Considering the Impacts of the Terrain Slope and Rainfall Frequency on the Implementation Cost

Studies have focused on evaluating and optimizing sponge city (SPC) performance, yet few have examined the cost efficiency of low-impact development (LID) layouts within SPCs at the project scale while considering varying storm frequencies and terrain slopes. This study investigated the hydrological response to storm events on a university campus in Wuhan, China. Using the Storm Water Management Model (SWMM) 5.2, two distinct design variants were simulated: Variant A treats the study area as a single entity, whereas Variant B considers 20 subcatchments. Each variant was further subdivided into scenarios featuring 30%, 50%, and 70% LID coverage. Runoff simulations were conducted under various storm conditions to assess the hydrological performance of LID facilities. The results demonstrate that the latter consistently outperforms the primer in both peak runoff reduction and total runoff volume, particularly during extreme storm events, aligning LID features with natural topographical gradients in subcatchments. A cost analysis reveals that while higher LID coverage increases implementation costs, the suggested design offers a more cost-effective approach, achieving superior performance with an optimized LID layout. In particular, aligning LID features with natural topographical gradients in subcatchments leads to more efficient water retention and infiltration, optimizing both performance and cost efficiency. This highlights the importance of strategically positioning LID facilities based on terrain slopes to enhance hydrological outcomes while minimizing financial burdens. Moreover, this study provides practical guidelines for urban planners and policy-makers seeking cost-effective flood mitigation solutions, emphasizing the broader applicability of this method to other urban areas with complex topographies. Graphical Abstract