Defining Flood Recharge Processes: Lower Bill Williams River, Western Arizona

Monday, April 20, 2009: 11:50 a.m.
Joshua Tree (Hilton Tucson El Conquistador Golf & Tennis Resort )
Scott Simpson , Hydrology and Water Resources, University of Arizona, Tucson, AZ
Tom Meixner , Hydrology and Water Resources, University of Arizona, Tucson, AZ
James Hogan , Hydrology and Water Resources, University of Arizona, Tucson, AZ
River networks provide hydrologic connections between upland and headwater catchments and downstream reaches. In arid and semi-arid regions, full connectivity of a river system is rare and moments of connection may only occur during large flood events. Here we investigate the Bill Williams River, among the most arid river basins in the United States. The aridity of this system—and the associated lack of complicating hillslope processes adjacent to the river—provides a unique opportunity to study flood recharge processes in relative isolation. During all but the highest flows, the river infiltrates completely at the east end of Planet Valley and reemerges at the west end where it enters the Bill Williams River National Wildlife Refuge (NWR). Determining the sources of NWR baseflow and the residence time of this water in the groundwater system will provide insight into the dependence of streamflow on earlier recharge-inducing floods. Defining this dependence more clearly is the next step toward a detailed knowledge of the long-term, basin-scale impacts of floods on water quality and quantity.

To determine the impact of floods and the recharge they induce, surface and groundwater samples were collected during high and low flows throughout the basin from April 2007 through the present. Isotopic (18OH2O, 2HH2O) and chemical differences (most notably SO4) in streamflow and groundwater along the system indicate the importance of older groundwater in NWR baseflow—either in the form of prior flood recharge or influxes from local springs. Sulfate isotope analysis (34SSO4, 18OSO4) is pending for samples throughout the lower basin, which should allow streamflow sources to be defined and quantified. This study provides a better characterization of the hydrologic and hydrochemical behavior of a Basin and Range river, and allows the effects of flood recharge processes to be more clearly defined at the basin scale.