Summary

The goal of this study was to develop an HEC-HMS model of the Kaskaskia basin and create forecast alternatives to view and analyze the results of two precipitation forecasts. Model development included developing a basin model of the Kaskaskia River watershed. Multiple parameter sets were developed to represent both a wet/typical and a dry condition. Both watershed conditions were calibrated to historic events to develop final parameters.

Forecast alternatives allowed the forecaster to analyze two precipitation forecasts and quickly and easily compare the results. The forecaster developed two zone configurations; the gage configuration was assigned to transform and baseflow parameters, and the soils configuration was assigned to loss parameters. The forecaster initialized baseflow and reservoir elevations using observed stream gage and stage gage data. Loss and transform parameters were efficiently calibrated using the Forecast Parameter Adjustment editor and the Slider Bar editor. Computed flows were compared to observed flows by systematically calibrating the model from upstream to downstream utilizing the compute to point compute option. The built-in model computational efficiency measures in HEC-HMS limited the simulation run time by only computing results for those elements that required results to be updated. Forecast blending was used to replace computed flows in the look back period with observed flows. The results of each forecast alternative were quickly compared and were ready for use as inflows for reservoir operations and inundation mapping.