Fish habitat in the Yankee Fork River has been drastically altered as a result of historical land use in the Yankee Fork drainage, particularly where dredge mining occurred.  Dredging occurred intermittently between 1940 and 1952 and obliterated the Yankee Fork stream channel, eliminating or substantially reducing the floodplain.  The new channel that formed was often trapped between dredge tailings and the valley hillside, where it was unable to re-establish a natural meander pattern. Further, flood-flows contained between the hillside and dredge tailings resulted in increased stream energy, which mobilized spawning gravels and wood out of the reach. The inability for this area to naturally recover has also been exacerbated by past removal of trees from the landscape, especially the riparian areas.  

Timber harvest began occurring in the Yankee Fork in the mid-1800s and was conducted primarily to support mining.  By approximately 1904, the hills for miles around the town of Custer (on the Yankee Fork River above the current restoration sites) were denuded of trees, as huge quantities of wood had been used for homebuilding, mine supports, and mills.  This timber harvest was followed, in the dredged area, by clearing to facilitate additional dredging.

Over the past several years, partner agencies and conservation groups that make up the Yankee Fork ID Team (e.g., Trout Unlimited, Shoshone-Bannock Tribes, U.S. Forest Service, Bureau of Reclamation, BPA) have partnered to implement several projects (e.g,. West Fork Yankee Fork Confluence, Preacher's Cove) throughout the dredged reach. Building on the progress made in past years' restoration work, the ID Team believes that the Bonanza City reach of the Yankee Fork has the potential to be improved substantially through removal of dredge tailings to form a flood-plain, construction of a new channel within that flood-plain, and additions of large wood in the reaches up and downstream from that area.

The goal of the three-phase Bonanza project is to return the mainstem Yankee Fork River in the project reach to more natural hydraulic and complex habitat conditions. Habitat restoration in this reach was designed to enhance fish habitat for all life-stages of migratory and resident fish, provide cover during high and low flows, provide winter habitat for juvenile salmonids, and provide spawning areas for all salmonids. Salmonids that will benefit from this project include spring/summer Chinook salmon, summer steelhead, bull trout, and westslope cutthroat trout.  

Bonanza Phases I-III were contracted under previous contracts (79310, 81598, and 84695). During Phase III of the project (in 2020), water from the Yankee Fork was moved from the straight, armored, plain-bed channel, where it had been left following dredging, to its historic location from which dredge tailings had been removed to form a meandering channel and floodplain.  This new channel that was built over unconsolidated dredge tailings was porous and substantial amounts of water seeped through the permeable gravel and cobble channel and then re-entered the channel as springs further downstream within the project area.  As flows declined in the fall of 2020, flow rates eventually decreased below seepage rates, resulting in three constructed riffle sections going dry within the project area for several weeks. The project reach was surveyed for migrating Chinook, steelhead, and bull trout in fall 2020, and fish were captured and moved past the dry sections as needed. Flows have been monitored continuously since the fall of 2020 to determine timing and extent of the dry reaches of the project area.

In 2021, Trout Unlimited is working with Yankee Fork basin partners to address passage limitations for upstream migration of adult Chinook salmon and downstream migration of juvenile Chinook salmon and steelhead, and juvenile and adult bull trout. The "Bonanza City Floodplain Restoration Project Fish Migration Impacts Mitigation Plan for 2021", attached to this contract, outlines measures for addressing fish passage under flow restrictions.  Trout Unlimited will coordinate installation and operation of a fish weir and trap at the head of the downstream most pool that maintains perennial flow (see also the "Draft Weir Operating Plan" attached to this contract).  Trapping in this location will allow Chinook Salmon and Bull Trout to utilize this pool and spawn in the riffle downstream from this pool, as happened with Chinook Salmon during 2020, but to be captured and moved if they attempt to migrate upstream from this pool.  Trapped adult fish will be transported upstream from the dewatered project sections and released above Jordan Creek, where they can continue their migration.  

Trapping will begin when flows in the project area reach the point that 0.4 ft water depth in the channel is not maintained through project area riffles.  This is expected to happen at about 100 cfs at the Yankee Fork gauge (which amounts to about 50 cfs at the trap location).  Intermittent precipitation events may increase water flow at the trap area but flows in excess of 100 cfs are not anticipated.