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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Hyporheic Processes
INFLUENCE OF CHANNEL MORPHOLOGY ON HYPORHEIC ZONES IN MOUNTAIN STREAMS.
S.M. Wondzell1 and T. Kasahara2. 1Pacific Northwest Research Station, USDA Forest Service, Olympia WA 98512, 2Department of Geography, York University, Toronto, Ontario, Canada M3J-1L1
We used groundwater simulation models to examine how channel morphology controls hyporheic exchange flows in small mountain streams. We made comparisons among stream reaches to examine the influence of stream size (2nd-order vs. 5th-order) and channel constraint. Within stream reaches, we examined the influence of channel longitudinal gradient, changes in gradient across pool-step or pool-riffle sequences, channel sinuosity, and the influence of secondary channels and channel splits. Our results showed that the way in which channel morphology controlled exchange flows differed with stream size. These differences can be explained by dissimilarities in valley-floor morphology between the two sizes of streams. We also found differences between the 2nd-order and 5th-order streams in the degree to which channel constraint influenced hyporheic exchange flows. Our results show that surface-visible valley-floor and channel morphologic features control the development of the hyporheic zone in small mountain streams, controlling both the volume of hyporheic exchange flow and the residence time distribution of stream water in the subsurface.
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