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Groundwater surface trends from ground penetrating radar (GPR) profiles taken across Late Holocene barriers and beach plains of the Columbia River littoral system, Pacific Northwest Coast, USA

By
Curt D. Peterson
Curt D. Peterson
Department of Geology, Portland State University, Portland, Oregon, 97207-0751, USA
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Harry M. Jol
Harry M. Jol
Department of Geography and Anthropology, University of Wisconsin–Eau Claire, Eau Claire, Wisconsin 54702-4004, USA
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David Percy
David Percy
Department of Geology, Portland State University, Portland, Oregon, 97207-0751, USA
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Eric L. Nielsen
Eric L. Nielsen
Department of Geology, Portland State University, Portland, Oregon, 97207-0751, USA
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Published:
January 01, 2007

Ground penetrating radar (GPR) records of groundwater surface (GWS) reflections have been analyzed from 40 across-barrier profiles, totaling 50 km in combined length, taken from barrier spits and beach plains of the Columbia River littoral system. The barriers and beach plains host shallow fresh-water aquifers in the prograded beach deposits and abandoned foredune ridges, totaling 10–30 m in thickness. Study results demonstrate that GWS reflections could be traced continuously at subsurface depths of 1–15 m with the GPR 100 MHz and 50 MHz antennae using 400 V and 1000 V transmitters. Boreholes (62 in number) and lake water levels (24 in number) provide ground-truthing of the across-barrier GWS trends interpreted from the GPR profiles. The GWS rises in elevation (4–8 m above base level) under high, broad foredune-ridges and drops under interdune ridge valleys (1–3 m above base level). Continuous profiles of GWS demonstrate that lakes, ponds, and bogs of the barriers and beach plains are “windows” into the shallow coastal aquifer. The GPR records demonstrate that the GWS slopes either to seaward (0.003–0.04 gradient) or to landward (0.001–0.05 gradient) from divides under the largest, shore-parallel dune ridges in the barriers. The GWS gradients indicate that subsurface contaminant transport from the developed dune ridges will be intercepted by intervening lakes and ponds in the interdune-ridge valleys. The GPR records also establish the effect of drainage ditches in lowering GWS elevations (1–2 m) in sensitive wetlands located 100s of meters in distance from the constructed ditches.

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Contents

GSA Special Papers

Stratigraphic Analyses Using GPR

Gregory S. Baker
Gregory S. Baker
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Harry M. Jol
Harry M. Jol
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Geological Society of America
Volume
432
ISBN print:
9780813724324
Publication date:
January 01, 2007

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