A multiscale radar‐stratigraphic analysis of fluvial aquifer heterogeneity

Abstract

The objective of this study is to use an integrated and multiscale exploration approach to quantify the geometrical parameters that are needed to predict block hydraulic conductivity tensors within fluvial deposits. We use 3-D ground-penetrating radar (GPR) data, electromagnetic (EM) surveys, resistivity soundings, and hand-augered borings to characterize the 3-D architecture of fluvial deposits on a floodplain of the Piscatiquis River, near South Sebec, Maine. Field-scale surveys made across the entire floodplain were used to map the depth to the glacially eroded bedrock surface and the thickness of the overlying sediments, which consist of glaciomarine clay, fluvial sands and silts, and overbank deposits. An EM conductivity anomaly in the center of the floodplain defines the position of a ridge in the glaciomarine clay deposit. This ridge separates horizontally bedded sand and silt deposits in the northern half of the floodplain from inclined point-bar sand and silt deposits in the southern half of the floodplain. The orientation and spacing of the lateral accretion surfaces (or bounding layers) within the point-bar deposits in the southern part of the floodplain were measured in a 3-D GPR survey conducted over a 50-m 2 grid. The geometrical parameters defining the internal architecture of the point-bar deposits are used to estimate anisotropy ratios for the principal components of the block hydraulic conductivity tensor. This integrated exploration approach establishes a framework for quantifying fluvial aquifer heterogeneity from local to regional scales. Geostatistical methods and geological models can be used to integrate the local-scale and field-scale surveys. With the addition of more local-scale surveys, geophysical logs, and high-resolution cores, this exploration approach can be used to develop a multiscale flow model for the entire floodplain.

Full-resolution 3D GPR imaging

“…Compared to imaging for oil/gas reservoir assessment and medical diagnosis, shallow subsurface imaging is still in its infancy. Manuscript Recently, 3D ground-penetrating radar (GPR) imaging has provided promising views of the shallow subsurface (Grasmueck, 1996;Beres et al, 1999;Lehmann and Green, 1999;Junck and Jol, 2000;Corbeanu et al, 2001;Szerbiak et al, 2001;Birken et al, 2002;Goodman et al, 2002;Grasmueck and Weger, 2002;Lesmes et al, 2002;Versteeg, 2002;Pipan et al, 2003). The problem is that many of these data sets are spatially aliased, so that a high degree of interpolation is required between parallel profiles.…”

Delineating Alluvial Aquifer Heterogeneity Using Resistivity and GPR Data

“…Geophysical studies may therefore contribute to producing an overall better subsurface model for ground water flow and contaminant transport. Electrical resistivity and ground penetrating radar (GPR), in particular, have become popular geophysical methods for characterizing subsurface hydrogeologic variations (Resistivity: e.g., Kelly 1977;Heigold et al 1979;Kelly and Frohlich 1985;Ahmed et al 1988;Cassiani and Medina 1997;Purvance and Andricevic 2000;Yeh et al 2002;Niwas and de Lima 2003; GPR: e.g., Hubbard et al 1997;Peretti et al 1999;Gloaguen et al 2001;Lesmes et al 2002), although uncertainties associated with data processing and interpretation do exist.…”

Integrated geophysical and geological investigation of a heterogeneous fluvial aquifer in Columbus Mississippi

“…GPR has been used extensively in shallow subsurface investigations in a wide variety of lithologies and stratigraphic settings (e.g., Jol and Smith, 1991;Cai and McMechan, 1995;Dominic et al, 1995;Greaves et al, 1996;McMechan et al, 1997;van Heteren et al, 1998;Peretti et al, 1999;Lesmes et al, 2002). Depths of penetration typically range from 9-20 m for antennae frequencies from 200-25 MHz, respectively (e.g.…”