Electrical and visual monitoring of small scale three-dimensional experiments

Our objective is to describe two non-invasive monitoring techniques that could provide an alternative to traditional water sampling in small-scale tank experiments. Here, a dense plume was monitored both electrically and visually using probes emplaced in a three-dimensional sand tank. Long, clear glass-tubes, which were modified by the addition of conductive copper tapes and connecting wires, were installed in a vertical array in the tank. The plume was monitored using Rhodamine WT (RWT) as a tracer and a conductive solution of NaCl. Appropriate consideration for the confined boundaries is applied to the resistivity calculations. The resistivity measurements with the emplaced electrodes perform well in tracking the denser plume. The visual monitoring of the optical tracer was conducted using a flexible endoscope with a 90° mirror. The endoscope transmits the images through a CCD camera to a VCR. This visual monitoring system also provides an excellent capability to determine the location of the RWT plume. Results from both methods compare well with each other.