Natural Groundwater Recharge Response to Urbanization: Vermillion River Watershed, Minnesota

Abstract

Urban development of rural land can be a concern for water resources and wildlife. The quantity and quality of surface water runoff and groundwater recharge can be significantly affected by urbanization. Base flow in streams and cold-water habitat, e.g., for trout, depend on groundwater. If water recharge to aquifers is reduced, and surface runoff is increased, streamflow and cold-water habitat can be adversely affected. An investigation of the changes to groundwater recharge resulting from the urbanization of a rural/natural area in the Vermillion River watershed in Minnesota was conducted. Well established principles and relationships for the estimation of infiltration (Soil Conservation Service (SCS) and Green-Ampt (GA) methods] and evapotranspiration [Food and Agriculture Organization (FAO)-56 Penman-Monteith) were applied, and percolation or groundwater recharge was determined using a water budget approach. The relationships were assembled in three models called the FAO-SCS, the FAO-GA, and the GA models. Four scenarios of land development representing progressive stages of urbanization (past, present, plus 50years, and plus 100years) were developed and groundwater recharge was simulated for each scenario from predevelopment to fully developed. In 2005, about 60% of the 6.78km2(1,675acres) watershed of a tributary to the Vermillion River was undeveloped agricultural and natural land, and about 40% was developed urban residential and commercial land. Model estimates of groundwater recharge under the 2005 land-use conditions ranged from 12 to 24% of 829mm of annual precipitation. The full urban development of the study site would result in a decrease of groundwater recharge to a range of 9 to 14% of precipitation. To make this projection, the impervious areas were raised from an average of 18% for the present scenario to an average of 36%. The case study shows that the increase of 18% in impervious area may decrease the recharge by about 20 to 40% of its present value. A change of this magnitude will substantially affect the water supply to the aquifer which discharges into the Vermillion River which is classified as a cold-water (trout) stream.