HR: 0830h
AN: H21D-0871    [PDF]
TI: Heterogeneity and Stream-Aquifer Interaction in an Unconsolidated Aquifer
AU: * McElwee, C D
EM: cmcelwee@ku.edu
AF: Univ. of Kansas, Dept. of Geology 1475 Jayhawk Blvd., Lawrence, KS 66046 United States
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
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, 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 installation consists of seven observation wells located along a line perpendicular to the river channel and centered about a productive irrigation well. In addition to water level data, several geophysical techniques (direct push electrical conductivity, ground penetrating radar, and shallow seismic methods) have been used at this site to characterize the aquifer. The results of the geophysical methods are reported in another paper at this meeting. Water level data collected over a two-week period shows two consecutive irrigation cycles. Each cycle consists of two days of intensive pumping followed by five days of recovery. Several significant elements of stream-aquifer systems can be seen in the data. The water level data demonstrates a regional water level decline in the alluvium that mimics stream gage data located up and down stream from the site, thereby confirming stream-aquifer interaction. Most of the observation wells located symmetrically around the irrigation well show the normal asymmetry expected for a river acting as a specified head boundary. However, heterogeneity causes one pair of symmetric wells to behave differently. Hydraulic data analysis with an automated program (SuprPumpII) demonstrates a degree of heterogeneity within the alluvial sediments not evident from descriptive geologic drilling logs or geophysical logs. A time-drawdown plot of a symmetric pair of observation wells, 310W and 310E, shows an atypical response of the aquifer during early pumping times due to heterogeneous effects; the drawdown plots "cross-over" (transition point) and then behave in a more expected manner during latter pumping times. This "cross-over" phenomenon is an illustration of the interaction between heterogeneity and stream-aquifer influences. At later times the stream influences the observed drawdown to a greater degree than aquifer heterogeneity.
DE: 1829 Groundwater hydrology
DE: 1842 Irrigation
DE: 1884 Water supply
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting