Geo-Spatial HSPF Model Creation: Toward a Digital Watershed

The Sandies and Elm Creeks, located in south central Texas, were placed on the USEPA 303(d) list in 2000 due to depressed dissolved oxygen and elevated bacteria levels. Given the rural, agricultural nature of the watershed, a Total Maximum Daily Load (TMDL) study was initiated to determine the source of the nonpoint source pollution. A model needed to be developed that simulated the agricultural runoff from the watershed. The simulation model, Hydrologic Simulation Program — FORTRAN (HSPF) was chosen. A typical HSPF model was conceived, but during the course of the study circumstances forced the model to develop in an atypical way. The usual source of precipitation forcing data, the National Climatic Data Center (NCDC), lacked point precipitation stations with data during the calibration timeframe; therefore alternate data sources were reviewed and NEXRAD data was chosen as the alternate data source. But, the use of NEXRAD data required that the model be distributed to a greater degree than a classic HSPF model. This type of delineation encouraged the examination of the weaknesses of both HSPF and hydrologic modeling in general.