HGS RESEARCH HIGHLIGHT – Investigating groundwater-lake interactions in the Laurentian Great Lakes with a fully-integrated surface water-groundwater model
bmcneill last edited by bmcneill
AUTHORS: Shu Xu, S.K. Frey, A.R. Erler, , O. Khader, S.J. Berg, H.T. Hwang, M.V. Callaghan, J.H. Davison, E.A. Sudicky
This study used HydroGeoSphere to quantify groundwater exchange with the five Great Lakes under monthly average climate inputs calculated using historical data from 1981–2010. The results indicate that groundwater discharge provides a relatively small component of positive basin supply, with significant seasonal fluctuations due to changes in lake levels and groundwater elevations. Another interesting result is the spatial variability in groundwater exchange, with the the 4-kilometer-wide nearshore lakebed area making a much larger contribution to groundwater/lake exchange than the remaining inner portion of the lakebed area.
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Modelling groundwater-surface water (GW-SW) interactions at scales of large river basins is a difficult challenge. In this study, a fully-integrated surface water-groundwater model accounting for hydrologic seasonality is developed for the 766,000 km2 Laurentian Great Lakes basin, and applied towards the characterization of groundwater-lake (GW-lake) interactions in the five Great Lakes under monthly normal climatology.
The simulated annual average rates of direct groundwater discharge to Lakes Superior, Michigan, Huron, Erie and Ontario through the combined lakebed and 8 km wide band of shoreline surrounding each lake are 29.0, 38.6, 24.5, 11.9, and 11.6 m3/s, respectively. Thus, direct groundwater discharge accounts for a small component of positive basin supply; ranging from 0.6% for Lake Ontario to 1.3% for Lake Michigan, with an overall average of 0.8% for all lakes combined.
Simulation results demonstrate that GW-lake interactions are strongest nearshore, and vary temporally in response to seasonal fluctuations in both lake levels and terrestrial groundwater levels in nearshore regions. In winter, direct groundwater discharge dominates the GW-lake interactions in both the distal and nearshore lakebed areas. In summer, the combined effects of rising lake levels and lowering terrestrial groundwater levels lead to notable reductions in direct groundwater discharge through nearshore areas. Direct groundwater discharge is also shown to vary spatially, with highest rates associated with areas containing thick Phanerozoic hydrostratigraphy, as opposed to Precambrian basement rock. The results from this study indicate that the Great Lakes primarily act as groundwater receivers, gaining considerable amounts of water directly from the basin’s groundwater system.