HR: 1340h
AN: H53A-0961    [Abstracts]
TI: Modelling Stream Aquifer Interactions During Floods and Baseflow Upper San Pedro River, Southeastern Arizona
AU: * Simpson, S C
EM: simpson@hwr.arizona.edu
AF: Department of Hydrology and Water Resources, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721, United States
AU: Meixner, T
EM: tmeixner@hwr.arizona.edu
AF: Department of Hydrology and Water Resources, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721, United States
AB: Streams and groundwaters may interact in distinctly different ways during flood versus base flow periods. Flooding periods may recharge riparian aquifer systems with this water destined to sustain baseflows in a river for long periods after the flood wave has passed. The riparian ecosystem along the Upper San Pedro River (southeastern Arizona) is one of only a few free flowing rivers in the Southwest. Recent research using isotopic and chemical data shows that (1) near-stream, or ‘riparian,' groundwater recharged during high streamflow periods is a major contributor to streamflow for the rest of the year, and (2) the amount of riparian groundwater derived from this flood recharge can vary widely (10-90%) along the river. Riparian groundwater in gaining reaches is almost entirely basin groundwater, whereas losing reaches are dominated by prior streamflow. The above results give rise to the questions of (1) how much flood recharge occurs at the river-scale, and (2) subsequently, what is the relative importance of flood recharge and basin groundwater in maintaining the hydrologic state of the entire riparian system. To address these questions, a coupled hydrologic-solute model was constructed for 45 Km of the riparian system. The model domain is divided into segments, with each segment representing a distinctly gaining or losing reach. Surface-subsurface water exchange is regulated by hydraulic properties of the system based on observed groundwater level response to flood waves. Daily discharge data at three points and chemical/isotopic river and groundwater data at various locations along the river were used to calibrate the model from 1995 to the present. Model results suggest good agreement between our model and the overall hydrologic and chemical/isotopic behavior patterns of the riparian system. Less than 51% of total summer flood recharge occurs in the upper two- thirds of the river, where gaining conditions dominate. However, recharge in this upper portion of the river on average accounts for more than 34% of the fall, winter and spring baseflow. Flood recharge along the lower losing reaches maintains the shallow water tables in the riparian aquifer that are essential to much of the vegetation composing the riparian forest.
DE: 1821 Floods
DE: 1830 Groundwater/surface water interaction
DE: 1847 Modeling
DE: 1860 Streamflow
SC: Hydrology [H]
MN: 2007 Fall Meeting