A DC-resistivity (DCR) and ground penetrating radar (GPR) study was conducted on the floodplains and gravel bars at four sites along the Big River in eastern Missouri to determine if DCR and GPR measurements can be used to determine the sedimentological characteristics of the floodplains and gravel bars, thickness of the floodplain deposits and if these methods could determine the extent of contaminated sediments. GPR data were collected at 100 and 250 MHz along profiles perpendicular and parallel to the river to image sedimentary structures of different scale lengths. DCR measurements were collected on the floodplains using a Schlumberger array along the same profiles as the GPR profiles. Constrained by sediment cores along most of the profiles, GPR data were best at imaging the bottom of a silt-loam layer that occurred between 2 and 2.5 meters below the surface. The DCR measurements provided the most constraints on the nature of the floodplain deposits. DCR was able to image the thickness of the sediments at all sites except at St. Francois State Park. The floodplain core determined depth of 8.5 meters was beyond the depth that could be imaged with the system used. A more powerful system could easily image at this depth, so there was a limitation factor of the system used. Two-dimensional DCR models indicated that the resistivity of the floodplain sediments decreases downstream. At Morse Mill, Cedar Hill and Washington State Park, the floodplain sediments had electrical resistivities less than 50 ohm-m with thicknesses between 4 and 6 meters. St. Francois State Park was an exception with two areas of higher surface resistivities (~110 ohm-m) that were 2 meters thick and another area with thick (at least 8 meters) of higher electrical resistive material. These higher electrical resistivities may be indicative of more coarse grain material in an old channel fill deposit. The GPR and DCR methods used in this study could not delineate between the contaminated and uncontaminated sediments.

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Big River Mining Sediment Assessment Project
Funded by U.S. Fish and Wildlife Service Cooperative Ecosystems Studies Unit

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