Ae. Springer et al., Spatial and temporal variability of hydraulic conductivity in active reattachment bars of the Colorado River, Grand Canyon, GROUND WATE, 37(3), 1999, pp. 338-344
Ground water/surface water interaction in rivers is dependent on the hydrau
lic conductivity of sediments lining the streambed, This study was designed
to determine the temporal and spatial variability of the hydraulic conduct
ivity of active sedimentary deposits lining the streambed of the Colorado R
iver in the Grand Canyon, These reattachment bars form aquifers and create
return-current channels that are critical for supporting terrestrial and aq
uatic ecosystems. Monitoring wells were placed in five separate reattachmen
t bars over a 200 mile long reach of the Colorado River below Glen Canyon D
am. Hydraulic conductivity was measured in all wells with the pneumatic slu
g test method. There is no significant difference in hydraulic conductivity
among the five reattachment bars in the Grand Canyon. Hydraulic conductivi
ty is bimodally distributed within a reattachment bar because of differing
sizes of sediments deposited under different eddy velocities. A major contr
olled release of water from Glen Canyon Dam in March 1996 redistributed the
sediments in the reattachment bars and compressed sediments deposited duri
ng previous floods, Hydraulic conductivity was significantly lower in these
sediments after the flood due to the increased effective stress from the n
ewly deposited sediment. A year later, after the sediments had drained and
some deflation had occurred, hydraulic conductivity of sand deposits return
ed to values similar to pre-flood values, whereas fine-grained sediments th
at compressed weren't able to elastically respond.