Background on the Tucannon River:  The Tucannon River basin is located in Southeast Washington State in Columbia and Garfield counties. The system-wide restoration objective for the Tucannon River is to improve habitat conditions for Endangered Species Act (ESA) listed species (Snake River Spring Chinook and Steelhead) for all life history stages. It is expected that improved habitat conditions will lead to an increase in the abundance of listed species returning to the river. Increasing abundance is intended to contribute to de-listing of the species, which is the overall recovery goal for the system.  Previous efforts (CCD 2004; SRSRB 2006, 2011), have identified the habitat-limiting factors associated with the decline of ESA-listed populations, and the corrective restoration actions for implementation (Anchor QEA 2012, Anchor QEA 2021).

Project Area Summary:  The proposed project is planned to improve Tucannon River floodplain conditions in the WT Wooten Wildlife Area.  The project area previously was a campground adjacent to the Tucannon River, moved across the road in the late 1990’s.  Although the camp was moved, the landscape was not restored to a functional condition, based on the premises this would happen naturally, a reality that has not been observed.  There have been numerous attempts to establish riparian vegetation that have failed because the channel and water table were disconnected from the floodplain.  In 2015, a processed-based restoration project was completed and within a few years the water table and floodplain were starting to improve.  After the 2020 flood, the floodplain connection improved considerably, and the river upstream has aggraded enough to start flooding this reach at a one-year flow interval.  Impacts from the old campground footprint and other activities have disturbed the natural floodplain and currently the overflow has run into a ditch that flows along the Tucannon Road.  The project is designed to re-establish winter flooding into the historic channels and floodplain, and to plant riparian vegetation.  Additionally, the low area that is flooding along the road will be raised to eliminate river flows in the ditch.  The channels will include buried log jams to provide structure within the floodplain as the river reclaims this area and encourage flows/channels away from the road.  To realize the full benefits from the restoration, 6-7 powerlines will be moved out of the floodplain and across the road.  Upland trees (pine, elderberry) will be planted along the road on the river side and riparian trees (willows, cottonwood, water birch) will be planted throughout the newly flooded area.  The project will restore approximately 5 acres of floodplain and riparian habitat.

Site Description: The project site has undergone significant disturbance historically; a site-hardened campground was removed in the 1990’s. The site also contained channel and bank hardening to protect the campground, which led to incision. Channel conditions were described as poor and restricted in the Conceptual Restoration Plan (Anchor QEA 2011). In 2015, the reach was treated with LWD from RM 42.65 to ~40.7, at which time the majority of the 2-mile reach was incised and disconnected from the floodplain.  Following a 2017 high water event and the 2020 flooding event, some reaches of the stream channel have changed geomorphic character, from incised plain bed to anastomosing, gaining floodplain connectivity. The channel through PA-11.2 in the targeted reach (approximately RM 41.65 to 41.0) is currently characterized as an anastomosing channel, confined on the right bank by a high terrace and unconfined on the left bank.  The floodplain was burned severely in the 2005 wildfire and has only recovered in areas where annual floods have access and can support tree growth.  The reach extends on the left bank floodplain between the river and the Tucannon Rd. No LWD or mature trees exist on the floodplain, and although there are patches of riparian regeneration, floodplain conditions remain dysfunctional due to past land-shaping management activities.  

Project Summary: Enhancing and restoring instream habitat in this project area will be accomplished through a variety of treatment actions in the floodplain and along the banks.  The entirety of work proposed in this contract will occur in the floodplain, outside of the stream channel.  The treatments include removal of gravel and cobble previously placed to limit flooding of the floodplain, reconnect disconnected floodplain and side channel areas, construction of a channel meander to reduce slope and increase length, construction of floodplain roughness (LWD) features (including engineered log jams) to provide floodplain roughness and channel shape as highwater events create channels in the newly available floodplain, and riparian plantings. The principal benefits of project implementation will be in gaining floodplain and creation of function riparian. The associated treatment of riparian areas is expected to induce naturally occurring riparian restoration, and recovery of both floodplain and riparian zone function and processes.

Note: The initial project area was identified and prioritized in the Tucannon Restoration planning efforts as PA11 (Anchor QEA (2012)).  The project was assessed for restoration alternatives in 2013 by WDFW and the Programmatic staff; WDFW initiated LWD restoration treatments in 2015 by placing a combination of LWD ELJs and unanchored structures.  Following significant geomorphic change, a shift in improving floodplain character and quality has become the priority in this project reach.

Overview: As with other projects developed and implemented in the watershed, the design emphasis for the PA11.2 Floodplain Restoration project is reconnection of the floodplain throughout the project reach. The overall project is comprised of high priority restoration actions intended to address the multiple habitat structures, floodplain connection, infrastructure encroachments, and stream function deficiencies associated with this reach of the Tucannon River. The design focus is to increase floodplain connectivity and allow for increased channel complexity through side channel development, placement of floodplain roughness, and riparian planting. The primary objectives for habitat restoration actions in the project area are to: expand and sustain floodplain connection, increase in-channel shape complexity (LWD), increase perennial channel length through reconnecting historic flow paths and side channels, place LWD for cover or complexity, and reduce channel confinement through the placement of log jams.

The designs for PA11.2 may include components of the following measures to address spring Chinook and Steelhead limiting factors, and the prioritization goals for the watershed (outlined in the 2021 Tucannon Basin Geomorphic Assessment and Restoration Prioritization): 1) removing channel and floodplain confining features; 2) increasing large woody debris loading to promote floodplain roughness and habitat quality and complexity; 3) hydraulically reconnecting the river with its floodplain through side-channel construction (improved off-channel habitat, floodplain vegetation); and 5) restoring riparian forest vegetation to promote future large wood loading and summer water temperature reductions.

Geomorphic Implications: Improving floodplain roughness and making more side channel habitat will allow more connection to floodplain areas. Increased connectivity with the low-lying floodplain will lead to decreased channel velocities during high flows and dispersion of sediment across the floodplain.  Addition of flooding will initiate a geomorphic response resulting in less bed scour and increased sorting of sediment, which forms critical habitat features (e.g., pools, cover, and spawning gravels).  The LWD structures placed in dry side channels will influence the development of scour and deposition areas in new channels, minimizing the development of plane-bed channel in the floodplain. In addition, large wood structures will promote development of a more complex channel network by splitting flow, initiating gravel bar and island development, and promoting channel migration within the reconnected floodplain area.

Biological Benefits: Immediate biological benefits of the project include increase floodplain capacity and frequency of flooding.  It is anticipated that modifications to the floodplain will lead to inundation at the winter mean flows to increase inundation to greater than 90 days. This will reduce instream velocities during high flows.  Deposition of sediment and formation of side channels will create additional spawning/rearing areas. Over time, greater floodplain connectivity will also lead to a healthier riparian zone and, in turn, promote improved ecosystem processes and habitat function.  

Potential Challenges:  This project is not subject to typical constraints caused by wildfire or delays within the fish work window, because implementation will occur outside the wetted width and outside of the instream work window, allowing for adjustments to the schedule.  It is possible additional riparian planting may be necessary in 2027-28.

Anchor QEA (2021). Tucannon Basin Geomorphic Assessment and Restoration Prioritization; Habitat Restoration Prioritization and Conceptual Restoration Plans.