Regional Watershed Spreadsheet Model (RWSM) Year 5 Progress Report

The Regional Watershed Spreadsheet Model (RWSM) is a regional-scale planning tool developed primarily to estimate long-term average annual loads from the small tributaries surrounding San Francisco Bay, and secondarily to provide supporting information for prioritizing watersheds or areas within watersheds for management actions. The RWSM has been in development since 2010. In previous years, obstacles to calibrating the PCB and Hg models included issues associated with GIS data underlying the Model, a simplistic model structure and parameterization, lack of available empirical data for calibrating concentrations associated with specific land uses and source areas, and the high uncertainty with the empirical calibration dataset. The modeling effort in Years 2014 and 2015 (Year 4 and 5 of the model development) focused on improving the model calibration to attempt to resolve these issues.

The major changes included switching from a sediment-based model to a water-based model, elimination of double counting of source areas on top of general land uses, changes in the model calibration approach, and changes to the land use grouping.