HYDROLOGIC MODEL APPLICATION OF THE LOWER CHEYENNE RIVER WATERSHED USING HSPF

The Cheyenne River in western South Dakota is currently listed as impaired for total suspended solids (TSS) and fecal coliform bacteria. A Total Maximum Daily Load (TMDL) assessment project for the Cheyenne River Watershed in western South Dakota was initiated in the spring of 2007. A watershed model application of the Lower Cheyenne River Watershed was developed using Hydrologic Simulation Program Fortran (HSPF) to help satisfy objectives and concerns of the project.

HSPF is widely considered a state-of-the-art comprehensive hydrology and water-quality modeling system. Land surface and subsurface hydrology is integrated with stream and reservoir processes with the capability of including a wide range of water-quality constituents. The Lower Cheyenne River Watershed Model application simulates hydrology as well as fecal coliform bacteria and sediment. Results were used to aid in TMDL development and also to substantiate congruent research for the Lower Cheyenne River Watershed Assessment Project.

This portion of the project focuses on the development and calibration of the model application for hydrology and sediment. The model application was developed using spatial datasets representing watershed characteristics, meteorological and stream monitoring data, and general research characterizing the watershed. The simulation of sediment in the model application was developed using information obtained from sediment source tracking, physical habitat assessments, the Revised Universal Soil Loss Equation (RUSLE), and water-quality monitoring. In turn, the model was used to confirm the validity and congruency of the research performed on the Lower Cheyenne River Watershed. Best management practices (BMP) were represented within the model application to assess the potential of reducing pollutant loads in the watershed. The model results were ultimately used to measure the impact of the BMPs and their ability to attain the TMDL standard.