Characterizing lakebed seepage and geologic heterogeneity using resistivity imaging and temperature measurements

Abstract

The contribution of groundwater-surface water exchange to lake budgets is poorly understood and depends in part on lakebed heterogeneities. These heterogeneities are difficult to characterize using traditional point sampling methods. The goal of this project was to use electrical resistivity to identify potential zones of groundwater discharge and recharge, providing focus for point measurements. Multiple resistivity surveys were conducted at Lake Lacawac, a small, glacially-formed lake in northeastern Pennsylvania. Two types of resistivity surveys were conducted. In a continuous resistivity profile, a multi-electrode cable was towed parallel to shore to look for spatial variability in resistivity around the lake. Two parallel to shore surveys were conducted, an inner and outer loop, to help characterize the lateral extent of sediment types. The results of these surveys suggested lithology changes both along the shoreline and with distance from shore. Follow-up resistivity data were collected using cables laid along the lake bottom perpendicular to the shoreline to look for finer scale zonation that affects seepage as a function of distance from shore.Follow-up seepage measurements showed that seepage rates are very low, which is consistent with the resistivity data from which we concluded that most of Lake Lacawac is lined with glacial clay and that the lake is essentially perched above the groundwater flow system, with just minor amounts of seepage in a few locations where fingers of sandy sediments extend a short distance from the shore. Discontinuities in these patches of transmissive sediments can result in reversals in the direction of seepage at nearby locations.We conclude that towed resistivity is useful as a rapid reconnaissance tool for mapping geologic heterogeneity. The results can be used to guide the more time-consuming but higher-resolution, lake bottom resistivity measurements, which in turn can guide the placement of seepage meters.

Riverbed Clogging Associated with a California Riverbank Filtration System: An Assessment of Mechanisms and Monitoring Approaches

“…ERT has been successfully used to investigate geologic features controlling seepage into lakes and rivers (Mitchell et al, 2008, Nyquist et al, 2009, contaminant seepage to a river (Slater et al, (Miller et al, 2008). To our knowledge, ERT has not been used to investigate hydrodynamics associated with RBF-related clogging.…”

Delineating a road-salt plume in lakebed sediments using electrical resistivity, piezometers, and seepage meters at Mirror Lake, New Hampshire, U.S.A

“…Geophysical methods have been used in hydrologic characterization to avoid problems associated with point-source measurements by providing more detailed subsurface mapping ͑reviewed in Robinson et al, 2008͒. Geophysical applications in hydrologic studies include acoustic profiling ͑Cherkauer, 1991͒, radar ͑Day- Lewis et al, 2004͒, electromagnetic methods ͑Paillet et al, 1999Robinson et al, 2008͒, induced polarization ͑Titov et al, 2005͒, spontaneous potential ͑Nyquist and Corry, 2002͒, and resistivity ͑Belavel et al, 2003Manheim et al, 2004;Allen and Merrick, 2005;Day-Lewis et al, 2006;Mansoor and Slater, 2007;Swarzenski et al, 2007;Stieglitz et al, 2008;Nyquist et al, 2009͒. Resistivity, a measure of the resistance to electrical flow in a medium, is commonly used to locate and map contaminants and tracers in groundwater, to characterize groundwater flow through fractures, to determine the saltwater-freshwater interface in coastal areas, and to target zones of groundwater seepage ͑Cherkauer, 1991; Day-Lewis et al, 2006;Nyquist et al, 2008͒. Cherkauer ͑1991͒ uses a combination of marine resistivity surveys and seismic soundings to identify zones likely to have groundwater in-seepage in the river connecting Lake Huron and Lake Erie.…”

Underwater ERT surveying in water with resistivity layering with example of application to site investigation for a rock tunnel in central Stockholm

“…The effectiveness of ERT as a tool for assessing groundwater or surface water interactions within streams was investigated by Nyquist, Freyer and Toran (2008), who concluded that patterns of ground water discharge can be mapped at a detailed scale. Nyquist, Heaney and Toran (2009) concluded that towed resistivity is useful as a rapid reconnaissance tool for mapping geologic heterogeneity. The results can be used to position more time-consuming but higher-resolution lake-bottom resistivity measurements, which in turn can guide the placement a low-resistivity anomaly at vertical dike location to about 12 m below the sea bottom ( Figure 2b).…”