Regional ground-water flow modeling of the Glacial Lake Agassiz Peatlands,Minnesota

Three-dimensional ground-water modeling experiments were done to test the h ypothesis that regional ground-water flow is an important component of the water budget in the Glacial Lake Agassiz Peatlands of northern Minnesota. P revious data collected from the Glacial Lake Agassiz Peatlands suggest that regional ground-water flow discharges to these peatlands, maintaining satu ration, controlling the peat pore-water chemistry, and driving ecological c hange. To test this hypothesis, steady-state MODFLOW models were constructe d that encompassed an area of 10,160 km(2). Data used in this modeling proj ect included surface-water and water-table elevations measured across the s tudy area, digital elevation data, and well logs from scientific test wells and domestic water wells drilled in the study area. Numerical simulations indicate that the Itasca Moraine, located to the south of the peatland, act s as a recharge area for regional ground-water flow. Ground water recharged at the Itasca Moraine did not discharge to the Red Lake Peatlands, but rat her was intercepted by the Red Lakes or adjacent rivers. Simulations sugges t that ground-water flow within the peatlands consists of local-flow system s with streamlines that are less than 10 km long and that ground water from distant recharge areas does not play a prominent role in the hydrology of these peatlands. Ground-water flow reversals previously observed in the Red Lake Peatlands are either the result of interactions between local and int ermediate-scale flow systems or the transient release of water stored in gl acial sediments when the watertable is lowered. (C) 2001 Elsevier Science B .V. All rights reserved.