Assessment of Electrical Resistivity Method to Map Groundwater Seepage Zones in Heterogeneous Sediments

Abstract

Underwater electrical-resistivity data were collected along the southwest shore of Mirror Lake, NH, as part of a multi-year assessment of the utility of geophysics for mapping groundwater seepage beneath lakes. We found that resistivity could locate shoreline sections where water is seeping out of the lake. A resistivity line along the lake bottom starting 27-m off shore and continuing 27-m on shore (1-m electrode spacing) showed the water table dipping away from the lake, the gradient indicative of lake discharge in this area. Resistivity could also broadly delineate high-seepage zones. An 80-m line run parallel to shore using a 0.5-m electrode spacing was compared with measurements collected the previous year using 1-m electrode spacing. Both data sets showed the transition from high-seepage glacial outwash, to low-seepage glacial till, demonstrating reproducibility. However, even the finer 0.5m electrode spacing was insufficient to resolve the heterogeneity well enough to predict seepage variability within each zone. For example, over a 12.5-m stretch where seepage varied from 1-38 cm/day, resistivity varied horizontally from 700-3900 ohm-m and vertically in the top 2-m from 900-4000 ohm-m without apparent correlation with seepage. In two sections along this 80-m line, one over glacial outwash, the other over till, we collected 14 parallel lines of resistivity, 13.5 m long spaced 1 m apart to form a 13.5 x 13 m data grid. These lines were inverted individually using a 2-D inversion program and then interpolated to create a 3-D volume. Examination of resistivity slices through this volume highlights the heterogeneity of both these materials, suggesting groundwater flow takes sinuous flow paths. In such heterogeneous materials the goal of predicting the precise location of high-seepage points remains elusive.

Effect of surficial disturbance on exchange between groundwater and surface water in nearshore margins

“…Hydraulic conductivity averaged 13.8 m/d based on constant head permeameter measurements of 11 shallow cores collected along this shoreline. Geophysical [ Gagliano et al , 2009; Mitchell et al , 2008] and well‐log [ Winter , 1984] data indicate that the sand‐and‐gravel unit exists beneath the shoreline reach from about 5 to about 55 m northwestward from an arbitrary origin near a swim beach on the southern shore (Figure 2). Artificial disturbance of the surface of the sediment bed associated with a previous study resulted in increases in seepage that ranged from 45% to 110% [ Rosenberry and Morin , 2004], making this site a good candidate for more thoroughly testing the effects of bed disturbance associated with measuring seepage in shallow, nearshore sediments.…”

Sedimentary architecture beneath lakes subjected to storms: Control by turbidity current bypass and turbidite armouring, interpreted from ground‐penetrating radar images

“…Glacial till was inferred to underlie all of the lake‐bottom silt (Rosenberry & Winter, ; Shapiro et al ., ), which will be shown to be partially correct. Its σ is at least an order of magnitude less than that of the water (Mitchell et al ., ; Gagliano et al ., ; Toran et al ., ). Henceforth till as it appears in profiles is termed ‘diamicton’, meaning a wide range of grain sizes, because minor stratification indicates that the till has been reworked.…”

Limitations and considerations for electrical resistivity and induced polarization imaging of riverbed sediments: Observations from laboratory, field, and synthetic experiments

“…Clifford and Binley, 2010;Crook et al, 2008;Colombero et al, 2014), and locate zones of GW up-welling (e.g. Mitchell et al, 2008;Gagliano et al, 2009). Additionally, IP methods have been used to characterize structure (e.g.…”