CREATION OF A MAP OF PALEOZOIC BEDROCK SPRINGSHEDS IN SOUTHEAST MINNESOTA Jeffrey A. Green Minnesota Department of Natural Resources, Division of Ecological & Water Resources, 3555 9th St. NW Suite 350, Rochester, MN, U.S.A., 55904,
[email protected] E. Calvin Alexander, Jr. Morse-Alumni Professor Emeritus, Earth Sciences Department, University of Minnesota, 310 Pillsbury Dr. SE, Minneapolis, MN 55455,
[email protected] Abstract hundreds-of-meters to kilometers-per-day range in all Springs are groundwater discharge points that serve of the bedrock aquifers tested. The width and duration as vital coldwater sources for streams in southeast of tails of breakthrough curves in these conduit flow Minnesota. The springs generally emanate from systems vary with the bedrock aquifers. The Galena Paleozoic carbonate and siliciclastic bedrock aquifers. Group has Full Widths at Half Maximums (FWHMs) of Use of systematic dye tracing began in the 1970s and a few hours and tails that are down to background in a continues through the present as a standard method for few days. The Prairie du Chien Group also has FWHMs investigating karst hydrology and to map springsheds. of hours but has tails that continue for weeks. The St. The work was accelerated in 2007 because of increased Lawrence and Lone Rock Formations have FWHMs of funding from the State of Minnesota’s Environment and months to years. Natural Resources Trust Fund. A compilation springshed map of dye traces conducted over the last several decades Introduction has been assembled for the region. Springs are natural discharge points for groundwater systems. They provide baseflow for streams and are In southeast Minnesota, the springs are the outlets of critical sources of cold, relatively constant-temperature conduit flow systems in both carbonate and siliciclastic water for trout streams.