Project Name

Crooked River Valley Rehabilitation (NEW)

River, Stream and Wetland Restoration
Client / Agency
U.S. Forest Service - Nez Perce National Forest
Nez Perce Tribe
South Fork Clearwater River, Idaho
Project Description
During the mid-1900s the lower Crooked River Valley was heavily impacted by dredge mining, leaving behind large tailing piles and deep ponds throughout the valley bottom. Gold and silver mining affected over 6 miles of the river and approximately 200 acres of the valley bottom. Physical changes to the valley bottom altered stream and riparian processes, and affected aquatic and terrestrial habitat conditions, resulting in degraded ecosystem conditions relative to historical conditions. The U.S. Forest Service Nez Perce National Forest and Nez Perce Tribe are leading efforts to improve ecosystem conditions in the lower Crooked River by re-grading the tailing piles and re-constructing the river and floodplain.

In 2013 RDG provided assessment and design services in for development of final design products including a final design report, final design drawings, cost estimates and technical specifications. RDG completed bathymetric surveys, habitat surveys and geomorphic investigations in support of evaluating limiting factors and providing criteria for the design. RDG worked collaboratively with the stakeholders and subcontractors to develop project phasing plans that met construction budget expectations and permitting requirements. Project design performance was evaluated using multi-dimensional hydraulic models. Model output was used to map aquatic habitat scenarios representing preferred habitat conditions for focal fish species including steelhead, Chinook salmon, bull trout and westslope cutthroat trout. Project implementation is scheduled for 2015-2016.
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Typical dredge mining impacts in the lower Crooked River valley resulting in degraded riparian conditions and impaired aquatic habitat for steelhead, Chinook salmon and bull trout.
Floodplain connection exhibit comparing existing valley bottom elevations to observed bankfull/floodplain indicators. The exhibit illustrates a lack of floodplain connection whereby existing surfaces within the valley bottom are either too high or too low to support development of woody riparian vegetation needed for establishing desired aquatic habitat conditions.
2D hydraulic model output showing velocity for existing and proposed conditions. Proposed project conditions will improve hydraulic complexity by providing a greater range of depth, velocity and substrate conditions within the project area.
2D hydraulic model output showing availability of spawning habitat for proposed conditions. Criteria for spawning habitat was derived from estimated bed mobility for preferred spawning substrates ranging from 50 to 75 millimeters.
2D model output showing proposed condition depth at 10-year discharge. The map illustrates floodplain connection in the valley bottom for proposed conditions.
2D model output showing proposed bed mobility conditions at bankfull discharge.
RDG prepared a final design report for addressing dredge mining impacts in the Crooked River valley bottom.
RDG prepared final design drawings, cost estimates and technical specifications for rehabilitating two miles of the Crooked River valley bottom.