Increasing HSPF model performance by improving FTABLEs: case studies on the Illinois River basin

Using the U.S. Environmental Protection Agency (USEPA) Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) system, a Hydrologic Simulation Program - Fortran (HSPF) model for the Illinois River basin was developed. Values of the HSPF model parameters were based on calibrations for three representative watersheds within the basin. Over the 1985-1995 simulation period, monthly and annual mass balances correlated well with observed discharges at three gaging stations along the Illinois River. However, the correlation for daily flows was poor due largely to the inability of the HSPF model to route dynamic flows through the complicated Illinois River system. In particular, the HSPF model uses the depth, area, volume, outflow relationship (FTABLE) for channel flow routing. River reach data used in the BASINS 3.0 system for developing the FTABLE contains only rudimentary channel characteristics and does not adequately describe the hydraulic behavior of channels and reservoirs. The goal of this study was to examine effects of FTABLE improvements on HSPF modeling accuracy for the Illinois River basin. Three sets of FTABLEs were developed. The first set created by the BASINS modeling system uses the rudimentary reach file (RF1); the other two sets were based on the natural channel geometry data. The second set FTABLEs used the Manning's equation to compute flow, volume, and water depth relations. The third set of FTABLEs used flows and stages simulated from the one-dimensional unsteady state flow model UNET for computations. The HSPF simulations using these three sets of FTABLEs were performed from 1985 to 1995. This study suggests that FTABLE modifications can increase HSPF modeling accuracy. The FTABLEs can be improved with minimal additional data on the channel geometry and stage-flow relation. Copyright ASCE 2005.