Assessment of Water Quality at Moore's Mill Creek Watershed using PCSWMM

Besides the typical applications for the management of urban stormwater systems, EPA SWMM 5 can also be a helpful tool for watershed management planning. SWMM can provide hydrological and water quality predictions that can be used in the development of best management practices (BMPs) to prevent issues such as flooding or pollution. Such features are important for Moores Mill Creek (MMC) watershed in Lee County, Alabama, which is experiencing high levels of siltation. This is likely linked to rapid urban development of the Auburn-Opelika metropolitan area in recent years that produces construction runoff. As a new watershed management plan is being developed to propose a remediation approach for siltation, SWMM models are being developed as a part of an ongoing project to provide guidance as to what sub-watersheds would benefit most from BMP implementation. The overall objective is to create a SWMM model of the entire MMC watershed that accurately represents flow, depth, and water quality in terms of total suspended solids (TSS). A model of the upper reaches of MMC in the Opelika, AL area was previously calibrated to account for groundwater-surface water interactions assuming a uniform aquifer object and interflow parameters. It was found that these inclusions improved the model predictions of stream depth compared to measured depths, and the single aquifer approach was valid for this model. Recently, data has been collected for turbidity and TSS concentration at one MMC location over multiple rain events. The resulting turbidity curve allows for the calibration of pollutant buildup and washoff factors for this station. The calibrated model will offer critical insights for implementing different BMPs to restore water quality in the MMC watershed.