HR: 11:20h
AN: H42B-05    [Abstracts]
TI: Combining Electrical Techniques to map a Till Aquitard for Quantifying Lateral Flows and Improved Recharge Estimation
AU: * Thatcher, K E
EM: ket445@bham.ac.uk
AF: University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom
AU: Mackay, R
EM: r.mackay@bham.ac.uk
AF: University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom
AB: Where low permeability layers are present in the unsaturated zone, groundwater recharge can be significantly modified by lateral flows. To improve estimates of the magnitude and spatial distribution of lateral flows, a well defined model of the unsaturated zone hydraulic properties is required. Electromagnetic (EM) surveys, using Geonics EM31 and EM34, along with Electrical Resistivity Tomography (ERT) have been used in the Tern Catchment, Shropshire, UK to determine the distribution of Quaternary glacial deposits above the Triassic sandstone aquifer. The deposits are generally less than 10m thick and comprise low permeability lodgement till and high permeability outwash. Modelling studies have shown the depth and slope of the till surface to be key parameters controlling the magnitude of lateral flows with recharge focussed at the till edge. The distribution of permeability within the till is of secondary importance. The spatial extent of the till is well constrained by EM data and is shown to be continuous. ERT profiles provide data on the depth to the till surface in detailed 2D sections. Combining the two data sets has enabled the depth estimates from the ERT surveys to be extrapolated across a 2D map area. Recharge estimates based on the depth maps take into account lateral flows across the top of the till and show that these flows can contribute significantly to catchment recharge.
DE: 1804 Catchment
DE: 1835 Hydrogeophysics
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting