Simulated Effects of Water-Level Changes in the Mississippi River and Pokegama Reservoir on Ground-Water Levels, Grand Rapids Area, Minnesota

Simulated Effects of Water-Level Changes in the Mississippi River and Pokegama Reservoir on Ground-Water Levels, Grand Rapids Area, Minnesota

2005

The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, used an existing, three-dimensional, numerical ground-water flow model (referred to as the calibrated model) to assess the effects of water-level changes in the Mississippi River and Pokegama Reservoir on ground-water levels in adjacent glaciofluvial aquifers in the Grand Rapids area of north-central Minnesota. Pokegama Reservoir consists of Pokegama Lake, Little Jay Gould Lake, Jay Gould Lake, Cut-off Lake, and Blackwater Lake. Water levels in the Pokegama Reservoir are regulated at Pokegama Dam on the Mississippi River west of Grand Rapids. A steady-state model was used, and simulations represent "worse-case" scenarios for the effects of lowering or raising the river and lake water levels. The simulated ground-water levels represent levels that would result if the river and lake stages permanently declined or rose by the specified amounts. Eight hypothetical scenarios were simulated by varying water levels in the Mississippi River and Pokegama Reservoir from values used in the calibrated model. In the simulations, water levels for the Mississippi River, riverine wetlands of the Mississippi River, and lakes of the Pokegama Reservoir were raised and lowered uniformly by 0.50, 1.00, 2.00, and 3.00 feet from calibrated water levels. The extent of aquifer water-level changes resulting from these river, wetland, and lake water-level changes varied because of the complex hydrogeology of the study area. A 1.00-foot decline in reservoir/river water levels caused a maximum simulated ground-water-level decline in the middle aquifer near Jay Gould and Little Jay Gould Lakes of 1.09 feet and a maximum simulated ground-water-level decline of 1.00 foot in the lower aquifer near Cut-off and Blackwater Lakes. The amount and extent of ground-water-level changes in the middle and lower aquifers can be explained by the thickness, extent, and connectivity of the aquifers. Surface-water/ground-water interactions near wetlands and lakes with water levels unchanged from the calibrated model resulted in small water-table altitude differences among the simulations. Results of the ground-water modeling indicate that lowering of the reservoir and river water levels by 1.00 foot likely will not substantially affect water levels in the middle and lower aquifers.

Jones, Perry M.

US Geological Survey
US Department of the Interior

13

Groundwater
Surface Water

surface water
surface waters
surface-water
surface-waters
surfacewater
surfacewaters
reservoir
reservoirs
reservoires
water level
water levels
water-level
water-levels
groundwater
ground water
ground-water
groundwaters
groundwater level
groundwater levels
ground water level
ground-water level
ground water levels
ground-water levels
ground water - surface water interaction
ground water - surface water interactions
groundwater- surface water interaction
groundwater-surface water interactions

2000-2009

No

Public Domain

Minnesota Water Research Digital Library