Application of the Distributed Hydrological Model, TOPNET, to the Big Darby Creek Watershed, Ohio, USA

Evaluation of the applicability and utility of watershed hydrologic models in different hydro-geologic and soil conditions is necessary for a range of spatial scales and to assess the utility of these models as watershed water resources management tools. This study presents the application of the hydrological model TOPNET to the Big Darby Creek watershed, Ohio, United States. It focuses on the simulation modeling of stream flow in the watershed based on meteorological data for the eight year period of 1992-1999. Visual comparison of time series plots and statistical measures namely, Nash-Sutcliffe efficiency (NS), coefficient of correlation (R-2), and the percent bias (PBIAS) were used to assess the model performance. The statistical model evaluation results indicated that the model has a relatively high confidence and can give a good representation of the flow hydrographs for the watershed. For the calibration period simulations of annual stream flow were accurate with a mean R-2 and NS of 86% and 85% for the Big Darby at Darbyville gaging station. For the little Darby at West Jefferson gaging station a mean R-2 of 81% was obtained while the NS averaged 78%. Further analysis based on the aggregation of the water years into wet seasons and dry seasons, the model was also able to adequately simulate stream flow for both gaging stations and for both low flow periods and high flow periods. Statistical analysis for the validation period also yielded high R-2 values of 88% and 83% for the Darby at Big Darby at Darbyville gaging station and Little Darby at West Jefferson gaging station respectively. The worst PBIAS obtained for both calibration and validation period was 18% and this is better than recommended values for satisfactory daily simulations of +/- 25% for PBIAS. The encouraging simulation results obtained in this study shows the utility and usefulness of the TOPNET model in hydrological modeling and ultimately as a water resources management tool.