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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Land/Water Interfaces
STREAM GEOMORPHOLOGY, BED TOPOGRAPHY, AND IMPLICATIONS FOR PATTERNS IN HYPORHEIC EXCHANGE FLOW.
J.K. Anderson1 and S.M. Wondzell2. 1Department of Forest Science, Oregon State University, Corvallis, OR 97331, 2Pacific Northwest Research Station, Olympia Forestry Sciences Lab, Olympia, WA 98512
Pool-step and pool-riffle sequences drive patterns of upwelling and downwelling through bed sediments in mountain streams. Water surface slope, and dimensions were measured for channel units and steps in 12 randomly selected second-, third-, and fourth-order stream reaches in the Lookout Creek basin in Oregon. Regression models showed that the reach-averaged distance between breaks in stream gradient increases predictably with increasing watershed area. We hypothesize that patterns of upwelling and downwelling occur on a scale that is consistent with the pattern of breaks in the stream gradient, and that the longitudinal lengths of upwelling and downwelling areas will increase with increasing watershed area. We installed piezometers in a subsample of stream reaches to measure vertical hydraulic gradients and characterize patterns of upwelling and downwelling. The longitudinal length of downwelling areas is often consistent with the distance between steeply sloping channel units such as riffles and steps. Shorter upwelling areas occur within or immediately downstream from steeply sloping channel units. These results suggest that the pattern and scale of upwelling and downwelling areas can be predicted from patterns of breaks in stream gradient.
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