Hydrological impacts of urban imperviousness in white rock creek watershed
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Urban development within a watershed area can significantly impact the natural flow in a stream network, mainly due to increase in surface runoff and alteration of spatial flow patterns. The objective of this study is to assess the impacts of urbanization on the hydrological behavior of the White Rock Creek watershed in Collin and Dallas counties, Texas, using a comprehensive integrated hydrologic model, SWAT-SWMM. The model has been developed to better reproduce runoff characteristics of both urban and natural areas, and to consider complex channel/pipe drainage systems in urban areas. The SWAT-SWMM model was calibrated and validated for a period from 2004 to 2007 at the White Rock Creek gauging station at Dallas, Texas. The predicted daily streamflow matched the observed values with a coefficient of determination (R2) of 0.73 and Nash-Sutcliffe efficiency of 0.70 during calibration, and 0.80 and 0.78, respectively, during validation. The calibrated model was then run for the same period to simulate the main components of the hydrological cycle and to predict the hydrological impacts of imperviousness changes in the urban area. It was predicted that doubling the imperviousness would lead to increases of 26% in surface flow and 12% in total runoff and reductions of 35% in groundwater discharge and 16% in actual evapotranspiration on an annual basis for the subwatershed governed by the SWMM model. It was also revealed that the changes in annual total runoff simulated by SWAT-SWMM with an increasing impervious area were less than the results simulated by SWAT alone. The potential changes in daily runoff were also examined considering the magnitudes of rainfall amount and imperviousness. The results revealed that runoff increases approximately linearly as the impervious area increases, showing that small peaks are more sensitive to an increase of imperviousness than large peaks. The study successfully demonstrates that SWAT-SWMM can be useful in understanding the impact of urbanization on the hydrological process of a watershed. 2011 American Society of Agricultural and Biological Engineers ISSN 2151-0032.
