The spatially continuous determination of groundwater flow to surface water bodies: Application to the Connecting Channels between Lakes Huron and Erie

The hydrogeophysical method to define the hydraulic properties of the sediments beneath a surface water body described by Taylor and Cherkauer is applied to a specific field site. Collection of electrical resistivity and seismic data long over 200 km of survey lines in the channels connecting Lakes Huron and Erie has allowed definition of the thickness, general composition and hydraulic properties of the sediment column. The geophysics provided a measurement of electrical longitudinal conductance of the sediment column at 40-m intervals along the survey line (> 5000 complete electrical soundings). This parameter has been empirically related to the hydraulic leakance (ratio of the hydraulic conductivity to the thickness of the unconsolidated materials) of the sediment column at discrete calibration points where seepage meters were installed. Groundwater discharges calculated using the geophysically derived hydraulic properties compare very favorably with those calculated directly from the seepage measurements and others calculated independently from analysis of stream gaging records. Convergence of three methods on a single answer is taken to indicate the validity of that answer and to confirm the reliability of the hydrogeophysical approach. The hydrogeophysical approach offers the advantage of higher resolution of lateral variations in hydraulic properties and relatively low monetary and time expenditures when compared with a drilling program. However, it cannot be utilized without calibration to direct hydraulic measurements; it is best run in conjunction with seepage meters and drilling or existing wells. Perhaps its greatest usefulness lies in its ability to rapidly and accurately define locations of high potential for interaction between surface water and groundwater.