HR: 0800h
AN: H21A-1306    [Abstracts]
TI: On the Role of Hyporheic Exchange and Stream Flow Velocity in Driving Diurnal Fluctuations in Discharge During Baseflow Recession
AU: * Wondzell, S M
EM: swondzell@fs.fed.us
AF: USDA Forest Service, Pacific Northwest Research Station, Olympia Forestry Sciences Lab 3625 93rd Ave., S.W., Olympia, WA 98512 United States
AU: Gooseff, M N
EM: mgooseff@mines.edu
AF: Colorado School of Mines, Department of Geology and Geological Engineering, Golden, CO 80401 United States
AU: McGlynn, B L
EM: bmcglynn@montana.edu
AF: Montana State University, Dept. of Land Resources and Environmental Science, Bozeman, MT 59717-3120 United States
AB: Diurnal fluctuations in stream flow during baseflow discharge have been observed in many streams and is typically attributed to water losses from evapo-transpiration. However, there is no widely transferable conceptual model describing the response of hillslopes, riparian zones, and streams, and their interactions, that explains these diurnal variations in streamflow. Bond et al. (2002) proposed a conceptual model suggesting that diurnal streamflow variation during baseflow is, in part, due to groundwater-surface water interactions within the riparian corridor of a 2^nd-order stream in central Oregon. Their conceptual model is based on two critical observations: 1) that the amplitude in the diurnal fluctuations decreases with baseflow recession, and 2) that the time lag between maximum evapo-transpirational demand and minimum stream discharge increases with baseflow recession. We test Bond et al.'s (2002) conceptual model with data collected over the summer of 2004 from a previously-established network of piezometers and wells located at the site used by Bond et al. (2002) and with data from previous stream tracer experiments within the same reach. Our data do not support Bond et al.'s conceptual model. In fact, there is no evidence that evapo-transpirational drawdown of riparian aquifers generates diurnal fluctuations in stream discharge despite clear connections via hyporheic exchange flows. Our results do not shed light on questions about the location and physical mechanisms that generate diurnal fluctuations in discharge. Our results do suggest, however, that decreases in stream flow velocity with baseflow recession are important in influencing the amplitude and time lag of the observed diurnal fluctuations and that the hyporheic zone could act as a reservoir to dampen fluctuations in discharge generated higher in the watershed.
DE: 1818 Evapotranspiration
DE: 1830 Groundwater/surface water interaction
DE: 1860 Streamflow
SC: Hydrology [H]
MN: Fall Meeting 2005