ARS | Publication request: Variable Source Area Contribution To Stream Flow in Southern Coastal Plain Watersheds

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: June 18, 2007
Publication Date: June 18, 2007
Citation: Feyereisen, G.W., Strickland, T.C., Sheridan, J.M. 2007. Variable Source Area Contribution To Stream Flow in Southern Coastal Plain Watersheds. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE).

Interpretive Summary: Policy-makers rely heavily upon model representations of watershed responses to land use in order to establish targets for water quality criteria. The USDA-NRCS curve number method for estimating the amount of rainfall that runs off into streams is a critical component of many models used by federal research and regulatory agencies to set these water quality criteria. Modeling of the Little River Experimental Watershed (LREW) near Tifton, GA that is based on the NRCS curve number method has shown a tendency to grossly over predict peak flows resulting from late summer or autumnal subtropical storm events and to under predict flows during the wet winter season. The objective of this research is to improve peak flow predictions by developing a simple model to estimate streamflow using measurements of the water storage volume that is available in the riparian (near-stream) areas and in the landscape just upslope from the riparian areas. Measurements of available storage, recorded for a 13-year period on three subwatersheds in the LREW, are used to estimate components of the NRCS curve number equation unique to the LREW. Rainfall and stream flow data records are used to estimate the amount of rainfall required to fill up the available storage before streamflow begins (effective rainfall). The variation in the amount of available storage throughout the year will then be used to estimate the area of the watershed that is contributing streamflow at any given time of the year.

Technical Abstract: Hydrologic modeling of the Little River Experimental Watershed (LREW) based on the NRCS curve number method has shown a tendency to grossly over predict peak flows resulting from late summer or autumnal subtropical storm events. The objective of this research is to improve peak flow predictions by developing a simple model to estimate streamflow using alluvial available storage measurements and variable source area hydrology concepts. Measurements of alluvial available storage, recorded for a 13-year period on three subwatersheds in the LREW, are used to estimate initial abstraction in the NRCS curve number equation. Initial abstraction is subtracted from rainfall resulting in an effective rainfall. Effective rainfall and event stormflow data are used to calculate maximum storage of the system. An estimate of the width of the area surrounding the stream and contributing to flow is made utilizing the volume of flow, contribution of flow from the riparian area, abstraction, and soil properties.