HR: 1340h
AN: H53B-0472 [Abstracts]
TI: Simulating the Phreatic Surface Within new Sediments Deposited During the November 2004 High Flow Test
Along the Colorado River, Grand Canyon, Arizona
AU: * Sabol, T A
EM: thomas.sabol@nau.edu
AF: Northern Arizona University, Department of Geology
Box 4099, Flagstaff, AZ 86011
United States
AU: Springer, A E
EM: abe.springer@nau.edu
AF: Northern Arizona University, Department of Geology
Box 4099, Flagstaff, AZ 86011
United States
AB:
During the November 2004 High Flow Test experimental release from Glen Canyon Dam, 4,551 m3 of fine sediment was
deposited at river mile 30.4R. Following this beach building event, the newly deposited bar was instrumented with 16
screened wells and piezometers to observe how the phreatic surface of the bar responded to the return of diurnal
stage-fluctuation from Glen Canyon Dam operation. Values of hydraulic conductivity, obtained from slug tests, ranged from
0.15 to 3.05 m/day depending on the location of the screened interval.
A finite element groundwater model was used to investigate the dynamic relationship between stage fluctuation and the rate of
dewatering new sediments for sandbar 30.4R. The model was calibrated to hydrologic data collected from late November 2004
to early March 2005, during which the bar was subjected to multiple flow regimes from the operation of Glen Canyon Dam.
Preliminary data show that during periods of diurnal 0.84 m stage fluctuation, the phreatic surface within the bar decreases
as little as 0.27 m from peak to trough at select piezometer locations. Under these fluctuating conditions the bar can not
completely dewater before the rising limb of the Colorado River hydrograph begins to increase the phreatic surface in the
bar. The calibrated model was used as a predictive tool describing the relationship between stage fluctuations, the phreatic
surface in the sandbar, the rate of bar dewatering, and the observed instability of active seepage faces in sediment
deposited during the experimental release.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
SC: Hydrology [H]
MN: Fall Meeting 2005