Baseflow Analysis of the Upper Vermillion River, Dakota County, Minnesota

Estimates of groundwater recharge are important for water resources planning and management, e.g. to determine the sustainability of groundwater resources. Estimates of groundwater recharge can be obtained by streamflow, especially baseflow, analysis. The Vermillion River, located at the southern fringe of the Minneapolis-St. Paul Metropolitan Area, is a DNR-designated groundwater-fed trout stream. How the stream flow in the Vermillion River and its tributaries is affected by urban development encroaching into the watershed is a pressing question. The baseflow in the Upper Vermillion River was therefore analyzed to determine the river’s groundwater recharge and minimum flow potential. The study site watershed includes approximately 129 square miles of the 338 square miles of drainage area within Dakota and Scott Counties. Two methods, the baseflow-separation method and the recession-curve-displacement method, were applied to the streamflow data from the USGS stream gauging site #05435000 near Empire, MN, to estimate baseflow and groundwater recharge in the Upper Vermillion River. The USGS computer programs PART and RORA were used to perform the baseflow analysis. The results of the analysis were used in conjunction with a water budget to estimate other hydrologic variables in the Upper Vermillion River basin at the annual timescale. It was determined that about 24% of the average annual precipitation reaches the stream as either baseflow or direct runoff. About 20% of the annual precipitation or approximately 80% of the annual streamflow in the Upper Vermillion River is baseflow from cold groundwater sources. The average annual estimates were found to compare well with results of previous studies (Baker et al. 1979, Ruhl et al. 2002, Lorenz and Delin 2007).