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Quantifying groundwater dependency of riparian surface hydrologic features using the exit gradient
Faulkner, Bart, S. Leibowitz, Tim Canfield, AND J. Groves. Quantifying groundwater dependency of riparian surface hydrologic features using the exit gradient. Hydrological Processes. John Wiley & Sons, Ltd., Indianapolis, IN, , 1-11, (2015).
Journal article to be submitted for review and publication in the journal Hydrological Processes in 2014. If accepted, it will probably print sometime in 2015.
This study examines groundwater exit gradients as a way to quantify groundwater interactions with surface water. We calibrated high resolution groundwater models for the basin fill sediments in the lower Calapooia watershed, Oregon, using data collected between 1928--2000. The exit gradient, often encountered in engineering analysis of structural stability of dams and levees, is a measure of upward potentiometric strength in effluent surface water. It can be simply defined as the ratio of the difference between computed head and the land surface elevation to the thickness of the uppermost layer, to which it applies. For the lower Calapooia 29% of the surface had exit gradients greater than zero in the wet season ranging up to about 0.3. During the dry season, 6% of the cells had exit gradients greater than zero, ranging up to about 0.2. Exit gradient maps reveal dry season groundwater inputs along the main stream channels supporting baseflow. Wet season groundwater inputs contribute to runoff along wide areas beyond the intermittent channels. This supports the notion of stream network expansion, potentially having a substantial effect on water quality in the lower Calapooia basin. The exit gradient is a simple, yet potentially effective measure of groundwater dependency.