HEAT USED TO QUANTIFY SURFACE-WATER/GROUND-WATER EXCHANGES DURING HURRICANES KATRINA AND RITA IN THE BOGUE PHALIA, NORTHWESTERN MISSISSIPPI

In June 2005, three piezometers were installed in the Bogue Phalia, a stream located in northwestern Mississippi, to monitor streambed temperatures. The piezometers were installed laterally across the stream (approximately 43 meters wide) and equidistant from each other (approximately 10.5 meters apart from each other). Inside each piezometer was an array of four temperature loggers at 20 centimeters, 50 centimeters, 1 meter, and 2 meters below the sediment water interface. Variations in streambed temperature, along with stream temperature and stage, were used to determine surface-water/ ground-water exchanges during two major hurricanes, Katrina and Rita, which struck the Gulf Coast in late August and late September 2005, respectively. Precipitation in Mississippi was below normal prior to and between hurricanes Katrina and Rita. The temperature data, and other physical measurements, indicated that the Bogue Phalia was a gaining stream during these periods. Precipitation in conjunction with hurricanes Katrina and Rita created an almost instantaneous rise in stage in the Bogue Phalia. The temperature profiles indicated that the Bogue Phalia changed from a gaining stream to a losing stream in a short period of time, and returned to a gaining stream once the stage dropped below a critical threshold. As a quantitative tool, the U.S. Geological Survey heat and ground-water transport model, VS2DI, was used to develop two-dimensional simulations of water fluxes into and out of the streambed sediments. Inverse modeling fits of simulated-to-measured sediment temperatures yielded estimates of seepage fluxes across the streambed surface, which indicated that fluxes are highest on the west side and lowest in the center of the channel. Fluxes also increase as the stage increases and are higher when the stream is losing rather than gaining, indicating that surface water recharges the streambed faster than ground water discharges to the stream.