HR: 0830h
AN: H31B-0466    [PDF]
TI: Geophysical Techniques Applied to a Stream-Aquifer System
AU: Healey, J M
EM: john_healey@kgs.ku.edu
AF: Univ. of Kansas, Kansas Geological Survey 1930 Constant Ave., Lawrence, KS 66047 United States
AU: * Tsoflias, G P
EM: tsoflias@ku.edu
AF: Univ. of Kansas, Dept. of Geology 1475 Jayhawk Blvd., Lawrence, KS 66046
AU: Steeples, D W
EM: don@ku.edu
AF: Univ. of Kansas, Dept. of Geology 1475 Jayhawk Blvd., Lawrence, KS 66046
AU: Vincent, P
EM: pvincent@ku.edu
AF: Univ. of Kansas, Dept. of Geology 1475 Jayhawk Blvd., Lawrence, KS 66046
AU: Sloan, S D
EM: ssloan@ku.edu
AF: Univ. of Kansas, Dept. of Geology 1475 Jayhawk Blvd., Lawrence, KS 66046
AU: McElwee, C D
EM: cmcelwee@ku.edu
AF: Univ. of Kansas, Dept. of Geology 1475 Jayhawk Blvd., Lawrence, KS 66046
AB: In north central Kansas the Republican River and its associated alluvial sediments are important regional surface and groundwater supplies. A test site, adjacent to the Republican River (near Clay Center, KS), has been established within the porous alluvial sediments to study stream-aquifer interaction and aquifer heterogeneity. This is potentially important research for understanding how to maintain a desired stream flow in the presence of withdrawals from the stream and the aquifer. The site was prepared with seven observation wells oriented along a line perpendicular to the river channel and centered about a productive irrigation well. Several geophysical techniques, including direct-push electrical conductivity (EC), ground penetrating radar (GPR), and shallow seismic methods, have been used at this site to characterize the aquifer. The EC geophysical method of subsurface investigation is typically used for gross lithologic definition. When numerous direct-push EC profiles are completed, a general impression of vertical and lateral variation of subsurface lithology can be inferred. Recently, this technique has been used to extract more information concerning subsurface characteristics; based on the three main parameters controlling the electrical properties of soils, i.e. gross lithology, water content, and water chemistry. In unconfined water table aquifers consisting of coarse alluvial deposits there is typically a sharp boundary between the saturated and unsaturated sediment, which can be seen on an EC profile as an abrupt change or shift in electrical conductivity as the probe is advanced through the sediments. Performing this EC profiling at a number of locations can define gross features of the local lithology and define the general shape of the water table and this has been done at the current research site. Additional EC profiles can be taken during pumping periods to document the lowering of the water table at selected locations and corroborate or compliment water level measurements taken from nearby observation wells. High-resolution shallow seismic reflection data sets were collected to image the top of the saturated zone during and after a pumping event at the test site. Two identical common mid-point seismic surveys were conducted; the first survey at maximum drawdown during the second day of continuous pumping; the second survey in the recovery phase of the aquifer 18 hours after pumping ceased. Differences as well as similarities in the times and amplitudes of P-wave reflections are evident in the two data sets. Seismic data will be correlated with GPR data, EC profiles, and monitoring well water-level data to evaluate the presence of lithologic and/or water table reflectors. GPR reflection data were also acquired to investigate the hydrostratigraphy of the test site. Radar data collected at undisturbed hydrologic conditions imaged near-surface lithologic changes, also identified in EC profiles. Variations in the attenuation of the GPR signal showed close agreement with EC profiles at well locations. The imaging of shallow reflectors in both seismic and GPR data sets warrants further investigation of the combined use of the two methods for hydrogeophysical investigations at this site.
DE: 0925 Magnetic and electrical methods
DE: 0935 Seismic methods (3025)
DE: 1829 Groundwater hydrology
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting