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ENHANCING HSPF MODEL CHANNEL HYDRAULIC REPRESENTATION
Citation:
MOHAMOUD, Y. M. ENHANCING HSPF MODEL CHANNEL HYDRAULIC REPRESENTATION . Presented at American Water Resources Association Annual Water Resources Conference, Baltimore, MD, November 06 - 09, 2006.
Impact/Purpose:
The main objective of this research is to identify deficiencies in the current watershed modeling approaches and conduct research that makes the Hydrologic Simulation Program-Fortran (HSPF) more accurate, more efficient, and more applicable to the needs of the resource managers and decision makers. The ultimate goal is to have watershed models that can simulate the cumulative impacts of alternative development scenarios and present the risks associated with different scenarios under an adaptive management framework where scenarios impacts are tested, model results analyzed, lessons learned, and management decisions made through an iterative process.
Description:
The Hydrological Simulation Program - FORTRAN (HSPF) is a comprehensive watershed model, which employs depth-area-volume-flow relationships known as hydraulic function table (FTABLE) to represent stream channel cross-sections and reservoirs. An accurate FTABLE determination for a stream cross-section site requires an accurate determination of mean flow depth, mean flow width, roughness coefficient, longitudinal bed slope, and length of the stream reach. A method that uses regional regression equations to estimate mean flow depth, mean flow width, and roughness coefficient is presented. Comparisons of FTABLES generated by the proposed method (alternative method) and FTABLES generated by the BASINS method were made. The alternative method is considered as an enhancement over the BASINS method. First, the alternative method employs a spatially variable roughness coefficient whereas the BASINS method employs an arbitrarily selected spatially uniform roughness coefficient. Second, the alternative method uses mean flow width and mean flow depth estimated from regional regression equations whereas the BASINS method uses mean flow width and depth extracted from the National Hydrography Dataset (NHD). Third, the alternative method offers users the option to use separate roughness coefficients for the in-channel and the floodplain sections of compound channels. Fourth, the alternative method has higher resolution in the sense that area, volume, and flow data are calculated at smaller depth intervals than the BASINS method. To test whether the alternative method enhances channel hydraulic representation over the BASINS method, comparisons of observed and simulated streamflow, flow velocity, and suspended sediment were made for four test watersheds. The results of the comparisons show that the method used to estimate the FTABLE has little influence on hydrologic calibration whereas it has great influence on hydraulic and sediment calibration. The hydrologic calibration results show that observed and simulated daily streamflow comparisons had Nash-Sutcliffe efficiencies that ranged from 0.50 to 0.61 and monthly comparisons had efficiencies that ranged from 0.61 to 0.84. Comparisons of observed and simulated suspended sediments had model efficiencies that ranged from -0.13 to 0.56 for the daily and 0.26 and 0.70 for the monthly comparisons. The overall results of the hydrological, hydraulic, and sediment comparisons show that the alternative method determines a relatively more accurate FTABLE than the BASINS method. We conclude that hydraulic calibration enhances sediment simulation performance, but further improvement in sediment calibration can only be achieved only when hydrological simulation performance is improved with the use of representative precipitation data that has the correct temporal and spatial distribution over the watershed.