RI-22 Regional Approach to Estimating the Ground-Water Resources of Minnesota

Abstract

The feasibility of making regional estimates of ground-water resources has been demonstrated in Minnesota. Average annual ground-water recharge rates were used as an indicator of groundwater resources. Ground-water resources are defined here as the amount of ground water that can be withdrawn from water-table aquifers for a long period of time without irreversible depletion of the ground-water reservoir. In contrast ground-water reserves are a function of the areal extent, thickness and hydrogeologic parameters of the aquifers and confining beds. Data from three research approaches were used to estimate ground-water resources: ( 1) ground-water contribution to the streamflow; (2) 3D-day lowflow characteristics of Minnesota streams; (3) ground-water hydrographs. Comparison of results of the three methods shows that values derived from ground-water hydrographs and data on groundwater contribution to streams are relatively close. Values derived from low-flow data, however, were consistently smaller. This discrepancy is related to two factors: (1) the limited time for which records of low-flow measurements were available; (2) the severely limited accuracy of low-flow estimates. However, the use of all three methods in conjunction does provide meaningful estimates of ground-water resources; The study shows regional distribution of ground-water resources in the 39 watersheds in Minnesota. The general distribution of ground-water resources is due to three major factors -- hydrogeologic environment, geomorphology and climate. The general trend is a decrease in ground-water resources from southeast to west and north in Minnesota.