Spatial Variability of Constraints On Groundwater Usage Due to Potential Adverse Resource Impacts in the Great Lakes Basin

Groundwater pumping from aquifers in hydraulic connection with nearby streams is known to potentially cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. Attention to this issue is growing in the Great Lakes Basin, due primarily to the recent passage of legislation¹ that seeks to “protect, conserve, restore, improve and effectively manage the Waters and Water Dependent Natural Resources of the Basin.” In particular, the legislation requires the Great Lakes States to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts.  The response of streamflow to pumping depends on hydrogeologic parameters that are known to vary over orders of magnitude in space. Models ranging in complexity from simple analytical models to complex numerical models have been proposed and used to estimate streamflow depletion as a function of groundwater pumping rates and location.

This study examines the spatial variability of maximum allowable pumping rates, as defined by maximum streamflow depletions, across the Great Lakes Basin.  We use a simple analytical model to calculate streamflow depletion as a function of hypothetical, new groundwater pumping rates and locations. The model estimates rely on information such as aquifer characteristics, stream network locations, and streamflows compiled in a GIS database.  Using this technique, we assess the spatial variability of groundwater resource constraints in the Great Lakes Basin. We perform a sensitivity analysis to determine the impacts on the groundwater resource constraints, given a range of potential maximum streamflow depletion criteria and uncertainty in model input parameters.

¹ Great Lakes--St. Lawrence River Basin Water Resources Compact