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Examining alternative ways to estimate stream cross-section inputs for HSPF

The Hydrological Simulation Program - FORTRAN (HSPF) is frequently used to develop TMDLs. HSPF is a continuous watershed simulation model designed to simulate water quantity and quality processes occurring in a watershed. These processes include sediment transport and the movement of contaminants. HSPF is a lumped parameter model, which allows the program to represent spatial variability by dividing the watershed into hydrologically homogenous land segments. Runoff and pollutant losses are simulated independently for each land segment. Simulation with HSPF requires the further delineation of watersheds into subwatersheds and reaches (stream segments). Each of these reaches requires the input of a function table (FTABLE); in HSPF, the total volume of water in the reach is used to compute discharge, stage, and surface area by linear interpolation between volumes provided in the FTABLE.

When developing FTABLES for use in HSPF, the modeler is presented with two basic options: use some manner of field data (e.g., cross-sectional profile surveys) or digital data (e.g., digital elevation models (DEMs)).  The objective of this project was to determine if the method used to develop FTABLES affected average daily discharge rates simulated by HSPF. Analysis compared simulated discharge rates using ‘field-based’ FTABLES (those generated using detailed cross-sectional surveys) and ‘digital-based’ FTABLES (those generated using DEMs and Natural Resource Conservation Service (NRCS) Regional Hydraulic Geometry Curves). This study tested the null hypothesis that flow rates simulated by HSPF using FTABLES from five scenarios (four field-based and one digital-based) are not significantly different.

This projects was completed by NSF Undergraduate Research Fellows Nathan Staley and Tiffany Bright worked with Center staff in the summer of 2005 on a project that was presented at the 2005 American Society of Agricultural Engineers Annual International Meeting in Tampa, Florida (July 17-20, 2005).  A full report on the project has been submitted to the Journal of the American Water Resources Association, and is approved.

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