RI-06 Ground-Water Contribution to Streamflow and Its Relation to Basin Characteristics in Minnesota

Abstract

Estimates of annual ground-water contribution to streamflow in 38 drainage basins of Minnesota by use of standard streamflow hydrograph separation methods permit determination of relations between ground-water runoff and such basin characteristics as geologic environment, precipitation and temperature, and percentage of lake and wetland cover. Generalized conclusions derived from analysis of the data are that ground-water runoff is (1) least from glaciated basins that have surficial lake bed sediments or gray-drift ground moraine immediately underlain by relatively impermeable bedrock and (2) greatest from glaciated basins that have surficial depos its immediately underlain by permeable bedrock or that have thick surficial loess deposits immediately underlain by permeable bedrock. Ground-water runoff is much greater from glaciated basins having red drift than from basins having gray drift. The rate of ground-water increases as annual precipitation increases. Lakes and wetlands sustain and regulate streamflow during rainless periods; if they were absent sustained streamflow from northern parts of the state would be greatly reduced. Recharge to aquifers in the state is difficult to ascertain. Because many aquifers are deeply buried by glacial materials of varying characteristics, not all ground-water runoff can be diverted into cones of depression, for there is some lateral as well as vertical movement of water in surficial deposits. Data on ground-water runoff can be useful in estimating the rate of recharge to aquifers and in evaluating the potential yields of ground-water reservoirs. However, no simple re- 1ation exists between ground-water runoff and ground-water recharge or the potential yields of aquifers. Studies of basin characteristics were handicapped because of a lack of detailed geologic information. Collection and study of data intended to describe the dimensions and water -yielding properties of unconsolidated deposits in the basins of the state are urgently needed to support hydrologic studies involving ground-water development and management decisions.