Simulation of Baseflow and Low Streamflow Statistics Using the SAC-SMA Model and a SAC-SMA/Hillslope-Storage Boussinesq Model

Low flow statistics are needed in water supply planning, and for the determination of minimum downstream release requirements from hydropower, irrigation, water supply, cooling plants and other facilities. In addition, allowable surface water discharge quantities and concentrations are based on critical low flow conditions specified by low flow statistics. When historic streamflow measurements are available, low streamflow statistics can be calculated using a frequency analysis. For locations with little or no historical streamflow data regional regression and baseflow correlation represent the most commonly used methods to estimate low flow statistics. In this study a physics-based approach is applied to estimate low flow statistics at ungauged river sites. A physics-based model is more flexible to handle changes in climate and land use that may occur over time. Output from the SAC-SMA model will be compared with simulations resulting from combining recharge outputs from SAC-SMA with a dynamic solution of the Hillslope-Storage Boussinesq model (HSB) to estimate baseflow and low flow statistics at a watershed scale. The partitioning of a watershed in hillslopes accounts for changes in topographic factors across the watershed, which impact flow processes. A case study within the Conodoguinet Creek and Yellow Breeches Creek watersheds in Pennsylvania is presented. The effectiveness of using the dynamic solution of the HSB model to simulate groundwater discharge under low flow conditions is further evaluated by simulating baseflow in watersheds representing different hydrogeologic characteristics.