Application of the SUSTAIN model to a watershed-scale case for water quality management

Low impact development (LID) has been widely accepted at lot-scale design but less so for watershed-scale cases because of the absence of appropriate assessment tools. The USEPA developed the System for Urban Stormwater Treatment and Analysis Integration Model (SUSTAIN) to evaluate the performance of LID practices at different spatial scales; however, the application of this model has been limited relative to the large number of LID cases. In this study, the SUSTAIN model was applied to a Taiwanese watershed to determine the feasibility of applying the model to international cases. Model calibration and verification were performed, and different types of LID facilities were evaluated. The results showed that infiltration was the dominant contribution to LID performance and that the plant intercept had a minor effect on the treatment. The number of units also influenced the overall performance. Increasing the number of LID units further decreased the pollution. The results of a watershed-scale simulation were used to rank the primary areas for nonpoint source pollution and to identify effective LID practices.