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Skokomish River Basin Ecosystem Restoration Project, Mason County, Washington, 25 August 2015

Skokomish GI Basin OverviewABSTRACT:  The Skokomish River Basin Ecosystem Restoration Project addresses severe ecosystem degradation in the Skokomish River Basin, located in the Olympic Peninsula of Washington State.  The non-Federal sponsors for the study are the Skokomish Indian Tribe and Mason County.

The Skokomish River Basin is located on Hood Canal, a natural fjord-like arm of the Puget Sound.  The Skokomish River is the largest source of freshwater to Hood Canal as it flows into Annas Bay and is of critical importance in the overall health of Hood Canal and Puget Sound.

The river collects flow from steep, mountainous basins and drains into a flat, alluvial plain known as the Skokomish Valley.  The study area is approximately 11 square miles comprised of the lower Skokomish watershed, the Skokomish Valley and Skokomish River estuary.

The primary concern to be addressed in this study is ecosystem degradation in the Skokomish River Basin, which includes the Skokomish Indian Reservation.  Historically, the Skokomish River system produced the largest runs of salmon and steelhead in Hood Canal.  Since the settlement of the Skokomish Valley in the 1850s by European and American settlers, human activities have altered the Skokomish River’s hydraulic and geomorphic processes and reduced the fisheries resource, resulting in the listing of four anadromous fish species (Chinook salmon, chum salmon, steelhead and bull trout) under the Endangered Species Act (ESA).  In addition, two runs of salmon are already extinct from the Skokomish River system.

Degradation includes reduced quality and complexity of channel habitats (e.g., reduced frequency and depth of pools); loss of riparian cover and large woody debris; and limited connection to floodplain, wetland and side channel habitats.  High sediment load, reduced flows and encroachment on the floodplain by man-made structures are causing continued degradation of natural ecosystem structures, functions and processes necessary to support critical fish and wildlife habitat throughout the basin.  A key problem this project intends to address is ongoing aggradation, which causes areas of flow to run subsurface during summer months, completely blocking fish migration during this time (see figure at right). The impaired ecosystem has adversely affected riverine, wetland and estuarine habitats that are critical to nationally significant resources, and is detrimental to salmon survival and migration.Summer low-flow -- fish migration blocked

The recommended plan is the National Ecosystem Restoration Plan and consists of several restoration actions at five sites.  Removal of a levee near the confluence of the North Fork and South Fork Skokomish River will allow for year-round fish passage, alleviating a channel constriction that is more than a mile long.  This action will remove a blockage to upstream and downstream fish passage and allow salmon access to spawning grounds.  Installation of large woody debris and engineered log jams will create pools for spawning, rearing and refuge habitat for juvenile and adult salmon, providing critical habitat types for their survival and productivity.  Reconnection of a historic side channel will provide refuge and rearing habitat for fish as well as expand the prey base for birds and mammals.  Finally, wetland restoration at two sites to reconnect and restore floodplain habitat will improve productivity of all riverine life stages of salmonids by increasing available spawning, incubation, rearing and over-wintering habitats.

The recommended plan will restore approximately 277 acres of degraded habitat and produce 187 average annual habitat units.  Based on an October 2014 price level, the total estimated project first cost of the recommended plan is $19.3 million.  The Federal share of the cost is $12.5 million and the non-Federal sponsors’ share is $6.8 million.  Minimal operations, maintenance, repair, rehabilitation and replacement (OMRR&R) expenses are estimated to be $10,000 per year, and will be a non-Federal responsibility.

The overall cumulative effects of the recommended plan would be synergistic benefits to all aquatic species through process-based restoration in the lower Skokomish River.  The benefits of increasing the number and size of in-channel pools, placing enough large woody debris to mimic quantities in nearby more natural rivers and reconnecting aquatic habitats in the adjacent floodplain will provide substantial benefits to fish and wildlife habitat, especially for four ESA-listed salmon species in the Skokomish River Basin.

REPORT DOCUMENTATION:  Pertinent documentation on the project, the results of the Civil Works Review Board, and subsequent Washington-Level Review Actions are listed below (items not linked will be provided when available):