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‐m2grid. 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.