Evaluating the SWMM LID Editor rain barrel option for the estimation of retention potential of rainwater harvesting systems

The low-impact development (LID) Editor rain barrel option of release 5.5 of the EPA storm water management model (SWMM) software does not allow the consideration of demand-driven behaviour of domestic rain water harvesting (RWH) systems to evaluate their runoff retention potential. This paper compares the results of the LID Editor with those obtained by a detailed demand-driven tank model scheme – used as a benchmark – and developed using basic functions of SWMM. The comparison showed the LID Editor-based model to generally overestimate the benchmark model in the evaluation of both volumetric and peak retention efficiency. The high variability of the results of the comparison suggests the use of the LID Editor rain barrel option for long-term simulation but not for single event analysis. A sensitivity analysis revealed that the overestimation provided by the rain barrel option is significant for tanks smaller than 2 m3, tank sizes of major diffusion for domestic RWH.