Assessing Hydrologic Changes in the St. Louis River Basin from Past Land Uses

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Resource managers can use assessments of past and future land use to make science-based decisions.  This project characterizes how changes in land use can change groundwater and surface-water flows in the St. Louis River Basin, MN. The USGS is constructing a set of groundwater models to simulate groundwater/surface-water interactions and evaluate how water flows have changed.

St. Louis River, looking downstream from County Highway 52 bridge crossing.

Photo of the St. Louis River, looking downstream from County Hwy 52 bridge crossing. (Credit: Anna Baker, USGS)

Effective stewardship of the St. Louis River Basin requires that tribal resource managers have tools to assess how past and future land uses in the Basin may change groundwater and surface-water flows.  In cooperation with the Fond du Lac Band of Lake Superior Chippewa (FDLB), the Bois Forte Band of Chippewa, the Mille Lacs Band of Ojibwe, the Leech Lake Band of Ojibwe, and the Minnesota Chippewa Tribe, the U.S. Geological Survey is constructing a set of groundwater models to simulate groundwater-surface water interactions and evaluate how water flows have changed because of human activities in and near the St. Louis River Basin.

Treating groundwater and surface water in the basin as a single interconnected resource, this study characterizes and quantifies flow broadly across the St. Louis River Basin with a two-dimensional analytic element GFLOW model (Haitjema Software), and at higher resolution with a three-dimensional finite-difference MODFLOW model focused on the Mesabi Iron Range and the northern half of the St. Louis River Basin. The three-dimensional model will be used to estimate the hydrologic state of the basin before mining began and to compare flows from pre-mining against current conditions.  Further refinement is also being undertaken for site specific three-dimensional models, in particular for the Second Creek area northeast of Aurora, Minnesota.

A nested approach, beginning with a broad, basin-scale model, provides information about the regional flow system that is translated for use in smaller-scale inset models.  At all scales, these models use measurements of streamflow under baseflow conditions to estimate flows between groundwater and surface-water.  Collectively, these models serve to:

  • Describe the general distribution, direction, and rate of groundwater flow and of groundwater-surface water interactions across the basin. 
  • Identify locations where the collection of additional hydrologic data is most efficient for identified forecasts of interest.
  • Evaluate the hydrologic effects of historical land-use changes within the basin.
  • Produce a detailed estimate the hydrologic effects of current human activities within the basin

Results from this study will provide a scientific foundation for decisions that will help tribal partners manage water resources, understand hydrologic changes, and assess possible trade-offs of proposed activity throughout a large part of the area of their treaty rights.

 

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