To help track progress toward total maximum daily load (TMDL) implementation for water quality impairments and to assess the design of capital improvement plan projects, the Bassett Creek Watershed Management Commission hired Barr for a watershed-wide update of its water quality model. We used the commission’s existing water-quality models, current topographic data, storm sewer data, and pond and wetland storage data to provide total phosphorus (TP) and total suspended solids (TSS) loading estimates for approximately 600 ponds and wetlands. The updated model was tested for calibration against the Metropolitan Council’s watershed outlet monitoring program (WOMP) data using estimates of watershed precipitation, water-quality and flow monitoring, and TP and TSS loading.
Because the watershed model is consistent with the model used for approved TMDLs, it has been used to evaluate the effect of proposed projects. The model output was used to demonstrate how cities in the watershed can use the model to target and evaluate individual best management practices (BMPs), determine treatment effectiveness for permit requirements, and prioritize BMP maintenance in their jurisdictions.
Barr documented the model update results and calibration process in a technical report. For all modeled watersheds, we described the methodology, developed stormwater hotspot mapping to target the highest pollutant-loading subwatersheds for future BMP implementation, and created prioritized lists and mapping to help cities target basins that combine effective pollutant removal with high sedimentation-filling rates. Barr continues to maintain and update the revised model, which is available for the commission‘s communities to use.