Enhanced HSPF Model Structure for Chesapeake Bay Watershed Simulation

Abstract

For more than two decades, an HSPF-based watershed model has been used to simulate nutrient and sediment load delivery to the Chesapeake Bay. Over time, the watershed model has increased in complexity commensurate with the management challenges in Chesapeake Bay restoration. The increased complexity poses challenges to the standard application of HSPF for efficient operation of the model in a large-scale watershed, as well as difficulties in incorporating changes in best management practices (BMPs) and land uses over time. In response, the U.S. Environmental Protection Agency’s Chesapeake Bay Program Office developed a software solution that enhances the existing HSPF model structure. The software system, consisting of preprocessors, an external transfer module, and postprocessors, was devised to conveniently generate and update parameter files essential to operations of a large and complex watershed-modeling system and to implement land-use and non-point-source-pollution management changes on any timescale greater than or equal to daily. The developed model system is demonstrated through comparison of the hydrologic calibrations of the current Phase 5 model and the previous Phase 4.3 model at 14 stations, as well as by several key scenario runs. The results show that the combined upgrades in segmentation, input data, and functionality improved model calibration; however, simply incorporating changes in land use did not significantly improve model calibration. The developed software provides a means to represent the key forcing functions in more detail and to address issues of flexibility that are difficult to manage in traditional HSPF applications.