Estimation of annual baseflow at ungauged sites in Indiana USA

This study developed regression models for predicting baseflow and baseflow index (BFI) (baseflow/total streamflow) at ungauged sites by using long-term baseflow data, land use, and watershed physiographic characteristics. Baseflow data were derived from daily streamflow records with a recursive digital filter method for baseflow separation for 22 watersheds in Indiana. Filtered average annual baseflow varies between 150 and 320 mm for the study watersheds. BFI varies between 0.40 to 0.88 with an average of 0.60, suggesting that 60% of long-term streamflow in Indiana is likely supported by ground water discharge and shallow subsurface flow. Three regression equations (one for baseflow and one for BFI) were developed and evaluated in the study watersheds. Results showed that the models reasonably estimate baseflow with relative errors (RE) ranging from 0% to 30%, except in one watershed where the RE was 50% during the validation period. These equations can be used to estimate baseflow and BFI at ungauged sites in Indiana. The present work would have implications for improving the capabilities of simple hydrologic/water quality models, and support planning and management of water resources. The methodology used in this study can be applied in other locations and regions.