A floating electrode array for continuous geoelectrical imaging

Abstract

Hydraulic connectivity between watercourses and aquifers can be rapidly imaged in great detail using a floating electrode array. Below watercourses, the salinity contrast between rising groundwater and sinking surface water is clear on electrical conductivity images. Interpretation is complicated by conductivity variations related to clay percentages and sediment porosity. A new robust floating electrode array design (``Blue Eel') using air filled layflat tubing addresses many of the problems that have previously prevented productive surveying of watercourses most of which contain many navigation hazards. A modified dipole-dipole array with exponentially spaced and sized receiver dipoles can provide optimal signal levels and depth resolution. Additional data from a GPS receiver and sonar depth profiler are important for managing the large volume of data acquired. The data acquired can be presented as a vertical 2D inverted conductivity image with a water depth trace overlain. Because watercourses generally meander, this image is best wrapped like a ribbon along the track of the watercourse. If the ribbon is presented in orthographic projection, it can be overlain easily on airphotos and map layers.