HR: 1340h
AN: H33E-0513    [Abstracts]
TI: Combining Cross-Borehole Georadar and Electrical Resistance Tomography to Monitor Moisture Content and Pore Water Electrical Conductivity in the Vadose Zone
AU: * Looms, M C
EM: mcl@geol.ku.dk
AF: University of Copenhagen, Institute of Geology, Oester Voldgade 10, Copenhagen K, 1350 Denmark
AU: Nielsen, L
EM: ln@geol.ku.dk
AF: University of Copenhagen, Institute of Geology, Oester Voldgade 10, Copenhagen K, 1350 Denmark
AU: Jensen, K H
EM: khj@geol.ku.dk
AF: University of Copenhagen, Institute of Geology, Oester Voldgade 10, Copenhagen K, 1350 Denmark
AU: Thybo, H
EM: thybo@geol.ku.dk
AF: University of Copenhagen, Institute of Geology, Oester Voldgade 10, Copenhagen K, 1350 Denmark
AU: Binley, A
EM: a.binley@lancaster.ac.uk
AF: Lancaster University, Department of Environmental Science, Bailrigg, Lancaster, LA1 4YQ United Kingdom
AB: Cross-borehole georadar and electrical resistance tomography (ERT) measurements are being conducted at two field sites in Denmark to monitor spatial and temporal variation of moisture content and tracer transport. At both field sites the geology is characterised by a thick layer (i.e.~20-30 m) of unsaturated melt water sand and gravel. At one of the field sites, Hjelm Hede, a very simple setup was constructed. Four boreholes were drilled along a line to a depth of 12 m. The outer two boreholes (7 m apart) were equipped with ERT instrumented PVC-tubes (electrodes every 50 cm) while the inner boreholes (5 m apart) had access tubes for georadar installed. The estimated water content values collected by the two large-scale geophysical methods have at this locality been compared to water content values determined by a conventional method - TDR. During previous investigations a total of 7 one-meter-long TDR probes were installed horizontally at five depths, from 0.75 m to 6.00 m. The TDR probes were installed in a well located approximately 30 m from the test area. The use of TDR probes to determine water content represents the soil physical properties at small-scale. A comparison will therefore be appropriate when evaluating properties across different sampling scales. Initial field results based on georadar match TDR results within a few percent. The second field site, Arrenaes, is located by an artificial infiltration plant. Two identical field setups have been established each having four ERT and four georadar boreholes. The boreholes were drilled to form a cross consisting of two lines, each with the same geometry as was used at Hjelm Hede. The two setups are located 8.5 m apart enabling an evaluation of the spatial variability. In future tests one of the fields will, furthermore, be irrigated to accelerate flow. The setups provide the possibility of combining the water content images using cross-borehole georadar with the bulk conductivity images achieved from the cross-borehole ERT to monitor the variations in fluid conductivity. These changes may arise as a result of natural changes, i.e.~changes in temperature and/or rainfall conductivity, or artificial changes, such as an applied tracer.
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting