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    Author(s): Lee H. MacDonald; Michael W. Miles; Shane Beach; Nicolas M. Harrison; Matthew R. House; Patrick Belmont; Ken L. Ferrier
    Date: 2017
    Source: Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 163-173
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (573.0 KB)

    Description

    A number of watersheds on the North Coast of California have been designated as sediment impaired under the Clean Water Act, including the 112 km2 upper Elk River watershed that flows into Humboldt Bay just south of Eureka. The objectives of this paper are to: 1) briefly explain the geomorphic context and anthropogenic uses of the Elk River watershed; 2) develop a process-based sediment budget for the upper watershed, including an explicit assessment of the uncertainties in each component; and 3) use the results to help guide future management and restoration. Natural (background) sediment inputs are believed to be relatively high due to high uplift rates, weak Miocene-Pliocene bedrock materials, steep slopes, high rainfall, and resulting high landslide frequency. The primary land use in the upper watershed is industrial timberlands, and intensive logging in the 1980s and 1990s greatly increased sediment production rates and downstream aggradation. Road improvements and major changes in forest practices have caused anthropogenic sediment inputs to drop by roughly an order of magnitude since the 1990s. Suspended sediment yields plotted against annual maximum peak flows indicate a decline since 2013, suggesting that the legacy pulse of sediment is now moving into the lower portions of the watershed and that improved management practices are having a beneficial effect. Recovery and restoration in the lower watershed is far more challenging as very low channel gradients cause sediment deposition, in addition to development of the floodplain for agricultural and residential use, forcing the river into a single-thread channel, and positive feedback loop between reduced flow velocities, aggradation, and dense vegetative growth in portions of the mainstem channels.

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    Citation

    MacDonald, Lee H.; Miles, Michael W.; Beach, Shane; Harrison, Nicolas M.; House, Matthew R.; Belmont, Patrick; Ferrier, Ken L. 2017. Development and implications of a sediment budget for the upper Elk River watershed, Humboldt County. In: Standiford, Richard B.; Valachovic, Yana, tech cords. Coast redwood science symposium—2016: Past successes and future direction. Proceedings of a workshop. Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 163-173.

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