HR: 0830h
AN: H11G-0942    [PDF]
TI: Numerical Simulations Used to Test the Effects of Lithology and Recharge Rates on Temperature Profiles Beneath Ephemeral Streams in Southern Arizona
AU: * Thomasson, M J
EM: mjthomas@email.uncc.edu
AF: Department of Geography and Earth Science, University of North Carolina at Charlotte, Charlotte, NC 28223 United States
AU: Hoffmann, J P
EM: jphoffma@usgs.gov
AF: U.S. Geological Survey, 520 N. Park Avenue, Suite 221, Tucson, AZ 85719 United States
AU: Ferr\'{e}, P A
EM: ty@hwr.arizona.edu
AF: Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721 United States
AB: Recent studies conducted by the U.S. Geological Survey (USGS) have shown that deep temperature profiles, measured before and after controlled infiltration, can be used to determine infiltration rates within the unsaturated zone. In this investigation, we extend this method to deep-temperature profiles measured before and after streamflow events in two boreholes located in the channel of an ephemeral stream in southern Arizona to infer recharge rates from short-term flow events. The deep-temperature profiles were analyzed to determine vertical fluxes with the use of a one-dimensional, forward numerical computer model. Temperature profiles were collected in boreholes located in Rillito Creek, in Tucson, Arizona. The two sites are about 6 kilometers apart and were selected on the basis of their lithology and hydraulic characteristics. The lithology at the upstream site is primarily homogeneous coarse sand, and the water table is approximately 37 meters below land surface. The initial response of the water table lags the onset of streamflow by about 2 weeks, and the water-level changes are as much as a few meters depending on the magnitude of the streamflow. The lithology at the downstream site is primarily homogeneous sand, with the exception of a clay layer at 12 meters below land surface, and the water table is approximately 41 meters below land surface. The initial response of the water table at the downstream site is rapid, occurring within about a day of streamflow. The magnitude of the water table response, however, is typically less than a meter and usually on the order of a few centimeters. Basic hydrologic models were developed for each site using hydraulic and thermal properties inferred from borehole core samples and cuttings, and from laboratory-determined hydraulic parameters. Water-table elevations and stream stages were used to define hydrologic boundary conditions. Field-measured temperature profiles were used to calibrate the models. The basic numerical model constructed for each site was used to examine the effect lithology has on the recharge rate and deep-temperature profiles.
DE: 1829 Groundwater hydrology
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
DE: 1878 Water/energy interactions
SC: Hydrology [H]
MN: 2003 Fall Meeting