Simulation and design optimization of rain gardens via DRAINMOD and response surface methodology

Abstract

Many studies have been conducted on the regulation effects of rain gardens on rainfall runoff. However, the parameters of rain gardens have been rarely simulated and optimized. In this study, the design parameters of rain gardens were optimized through combining the DRAINMOD model and the response surface methodology. On the basis of the monitoring data of a rain garden in the Xi’an University of Technology campus in China from 2016 to 2017, the parameter sensitivities in the DRAINMOD-H and DRAINMOD-N modules were analyzed, and the DRAINMOD model was calibrated and validated. The determination and Nash efficiency coefficients were approximately 0.8 and above 0.6, respectively, confirming that the water volume and nitrogen regulation effects of rain gardens can be simulated with DRAINMOD. Different scenarios were set up to simulate and analyze the reduction effects of rain gardens on water volume and nitrogen load. The influences of various factors, including the influent nitrogen concentration, the confluence ratio, the thickness of the filler layer, and the depth of submerged zone on the regulation effects of rain gardens were discussed. According to simulation results, these factors were optimized by using the response surface methodology to obtain the design values under different targets. The optimized minimum thickness of the filler layer is 37 cm and the maximum is 80 cm. The optimized depth of the submerged zone is at least 22 cm and the maximum is 45 cm. The treatment effects of the rain gardens are better after parameter optimization. Results can provide a scientific basis for the construction of rain garden facilities.