HR: 1340h
AN: H13D-1548    [Abstracts]
TI: Impacts of stream-aquifer connectedness on bank infiltration, seepage, and solute transport during semi-arid flooding
AU: * Desilets, S L
EM: seinloth@hwr.arizona.edu
AF: University of Arizona, 1133 East James E Rogers Way, Tucson, AZ 85721, United States
AU: Ferré, T P
EM: ty@hwr.arizona.edu
AF: University of Arizona, 1133 East James E Rogers Way, Tucson, AZ 85721, United States
AU: Troch, P A
EM: patroch@hwr.arizona.edu
AF: University of Arizona, 1133 East James E Rogers Way, Tucson, AZ 85721, United States
AB: Transient storage of flood water in stream banks during high flow conditions plays a unique role in semi-arid environments. In ephemeral streams, water infiltrated during flood events is a significant component of the water balance, is essential for sustaining low flows, and plays a critical role in sustaining a riparian habitat. This work examines the role of steam-aquifer connectedness in affecting differences of floodwater distribution in the stream banks. We consider a range of vadose zone depths from closely-connected streams, common to humid areas, to increasingly disconnected streams, common to semi-arid areas. Specifically, we address the question of how stream-aquifer connectedness affects infiltration rate, quantity of seepage, and distribution of solutes. We use the variable saturation code HYDRUS 2-D to simulate transient flow and solute transport. These simulations show a significant change in water distribution for a short change (5 m) in water table depth. In particular, during flooding, cumulative infiltration increases sharply with increasing depth of the water table. During recession, total bank seepage decreases sharply with increasing depth of the water table. Capture zones determined from particle tracking show that only a small area that extends laterally above and below the base of the stream contributes to seepage. Solute transport in connected systems is predominantly horizontal through the shallow root zone. However, for thick vadose zones, a small fraction of solutes in the area of the root zone will be affected by infiltrating water, and those that are mobilized will move predominantly toward the water table, rather than back toward the stream. The maximum transitional depth between humid-like connected behaviors and those in a disconnected system is only 5 m. This implies that riverine ecosystems under pressure from various water demands can expect significant changes in water distribution in the root zone area for even modest lowering of the water table.
DE: 1830 Groundwater/surface water interaction
DE: 1838 Infiltration
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting