Towards the cost-effective design of stormwater infiltration trenches: a hybrid model integrating cost–benefit analysis and an analytical stochastic approach†

Infiltration-based low-impact development practices are effective in sustainable urban stormwater management. The current design criteria (or design rainfall depth) for infiltration trenches in China rely on the requirements of the total annual runoff control rate. However, without considering the cost benefits, such a design criterion may overestimate the facility size and not be cost-effective. By integrating an analytical stochastic model for quantifying the runoff capture efficiency of infiltration trenches with two types of life-cycle cost approaches, this study proposed an analytical tool to determine more appropriate design criteria. An example case study of infiltration trenches implemented in Beijing, China, was performed to evaluate stormwater control performance and costs. The results indicate that the current design rainfall depth at the 75th to 85th percentiles obtained using rainfall event data following the method recommended by the design guideline may be overestimated and not cost-effective. The more economically effective design standard is recommended to range between 26.2 and 40 mm under different design conditions at the 75th to 85th percentiles, with a contributing catchment area of less than 4500 m² and soil infiltration rate between 5 and 25 mm h⁻¹. Substantial economic savings can be achieved with lower but proper design criteria, and the proposed analytical approach is thus recommended for policy makers for the cost-effective design of infiltration trenches.