Geomorphology, hydrology, and aquatic vegetation drive seasonal hyporheic flow patterns across a gravel-dominated floodplain

Authors

  • Krista L. Jones,

    Corresponding author
    1. Eco-metrics, Inc. 2520 Pine Lake Road, Tucker, GA 30084, USA
    • Eco-metrics, Inc. 2520 Pine Lake Road, Tucker, GA 30084, USA.
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  • Geoffrey C. Poole,

    1. Eco-metrics, Inc. 2520 Pine Lake Road, Tucker, GA 30084, USA
    2. Institute of Ecology, University of Georgia, Athens, GA 30602, USA
    3. Flathead Lake Biological Station, University of Montana, Polson, MT 59860, USA
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  • William W. Woessner,

    1. Department of Geosciences, University of Montana, Missoula, MT 59812, USA
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  • Matt V. Vitale,

    1. Eco-metrics, Inc. 2520 Pine Lake Road, Tucker, GA 30084, USA
    Current affiliation:
    1. Water Management Consultants, Inc. 1005 Terminal Way, Suite 220 Reno, NV 89502, USA.
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  • Brian R. Boer,

    1. Department of Geosciences, University of Montana, Missoula, MT 59812, USA
    Current affiliation:
    1. CH2M HILL, 155 Grand Avenue, Suite 1000, Oakland, CA 94612, USA.
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  • Scott J. O'Daniel,

    1. Confederated Tribes of the Umatilla Indian Reservation, PO Box 638, Pendleton, OR 97801, USA
    2. Institute for Computational System Science and Geography Department, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
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  • Steven A. Thomas,

    1. Eco-metrics, Inc. 2520 Pine Lake Road, Tucker, GA 30084, USA
    Current affiliation:
    1. School of Natural Resources, University of Nebraska, Lincoln, NE 68583-0995, USA.
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  • Brook A. Geffen

    1. Eco-metrics, Inc. 2520 Pine Lake Road, Tucker, GA 30084, USA
    Current affiliation:
    1. Oregon Water Resources Department, 725 Summer Street, NE Suite A, Salem, OR 97301, USA
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Abstract

Across 1·7 km2 of the Umatilla River floodplain (Oregon, USA), we investigated the influences of an ephemeral tributary and perennial ‘spring channel’ (fed only by upwelling groundwater) on hyporheic hydrology. We derived maps of winter and summer water-table elevations from data collected at 46 monitoring wells and 19 stage gauges and used resulting maps to infer groundwater flow direction. Groundwater flow direction varied seasonally across the floodplain and was influenced by main channel stage, flooding, the tributary creek, and the location and direction of hyporheic exchange in the spring channel. Hyporheic exchange in the spring channel was evaluated with a geochemical mixing model, which confirmed patterns of floodplain groundwater movement inferred from water-table maps and showed that the spring channel was fed predominantly by hyporheic water from the floodplain aquifer (87% during winter, 80% during summer), with its remaining flow supplied by upslope groundwater from the adjacent catchment aquifer. Summertime growth of aquatic macrophytes in the spring channel also influenced patterns of hyporheic exchange and groundwater flow direction in the alluvial aquifer by increasing flow resistance in the spring channel, locally raising surface water stage and adjacent water-table elevation, and thereby altering the slope of the water-table in the hyporheic zone. The Umatilla River floodplain is larger than most sites where hyporheic hydrology has been investigated in detail. Yet, our results corroborate other research that has identified off-channel geomorphic features as important drivers of hyporheic hydrology, including previously published modeling efforts from a similar river and field observations from smaller streams. Copyright © 2007 John Wiley & Sons, Ltd.

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