Note:  Work described in this SOW is a progression of PA13 design Phase I, which was reviewed in 2020 (#74314 REL 65).  Phase I was completed in 2022 by WDFW under contract (#74314 REL 85).

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.

Project Area Summary:  Project Area 13 (PA-13) is located within the active river channel and floodplain of the Tucannon River, on public land from RM-40 (just upstream from the Tucannon Hatchery fish weir) to approximately RM-39 (just downstream of the hatchery bridge).  The Tucannon Conceptual Restoration Plan (Anchor QEA 2011) ranked PA-13 as a Tier I project for early implementation, citing this reach as being in poor condition and providing very little habitat for salmonid spawning or rearing.  The project is located adjacent to, and upstream from, the Tucannon Fish Hatchery and its essential infrastructure. The project restoration goals are to increase floodplain connectivity and channel complexity.

Site Description:  The project site has undergone significant disturbance historically, leading to channel conditions described as poor and restricted in the Conceptual Restoration Plan (Anchor QEA 2011). “The channel through PA-13 is characterized as a single-thread, plane-bed channel with forced pool-riffle and local rapid sections. The channel is typically straight, wide, and contains little complexity across much of the project length. Large levees confine the channel along the right bank from approximately RM 39.95 to 39.8, at RM 39.6, and from RM 39.5 to 39.2. The levees are typically heavily armored with large angular boulders.  No active side channels or off-channel areas exist in the project area.  The quality and availability of instream habitat is restricted by the lack of channel and hydraulic complexity. The straight and confined channel results in hydraulic conditions that create high velocities and high transport capacity. These conditions do not support the retention of LWD or bed-load, and therefore lack hydraulic complexity. A few downed logs and one log jam provide pools and cover in the actively eroding area near RM 39.7, but overall very few adequate pools for adult holding are available. The lack of side channels (except some apparent high-flow channels) limits the quantity of habitat for rearing juveniles” (Anchor QEA 2011).

Floodplain connectivity in this project area is affected by the presence of infrastructure, levees, and incision caused by channel straightening; as a result, little low-lying floodplain is present with the exception of the area near RM 39.8 and 39.3, which is disconnected by infrastructure.  Currently, there is very little difference in area wetted between the 2 year flood event and the 5 year flood event, indicating the severity of the incision and confinement.

Project Summary:  Enhancing and restoring instream habitat in this project area will be accomplished through a variety of treatment actions in the main channel, along the banks, and within the floodplain. These treatments include removal of river levees and rip-rap to reconnect disconnected floodplain and side channel areas, construction of a channel meander to reduce slope and increase length, construction of instream habitat features including engineered log jams to raise the river bed, and riparian plantings. The principal benefits of project implementation will be restoration of historic spring Chinook spawning, rearing, and migration corridor habitats. The associated treatment of riparian areas is expected to induce naturally occurring repair, restoration, and recovery of both floodplain and riparian zone function and processes.

The initial project reach was assessed for restoration alternatives in 2016 by WDFW and the Programmatic staff, as WDFW initiated designs for the reconfiguration of Rainbow Lake (part of the Tucannon Hatchery infrastructure). Refer to #74314 REL 85 for a description of the Rainbow Lake portion of this project, which removed over 700’ of river levee, reconnected 7.5 ac of low-lying floodplain, and created and connected 4,285’ of new perennial side channels and 1,050’ of new ephemeral channels.  To support channel shape and complexity, 20 LWD structures were placed in the channel and on the low floodplain.

Project Sequencing: PA-13 instream construction is being implemented in two phases, to accommodate funding cycles and limitations on site space for staging equipment and materials. Due to presence of the Tucannon Hatchery and critical infrastructure associated with the hatchery, several access and staging challenges are present.  Space at this site is limited for materials (i.e., trees, gravel and cobble) for placement in LWD structures.  Phase I was located at the downstream end of the project area: site preparation and staging began in 2021, and in-water work was done between July-September 2022.

Phase II and the work outlined in this SOW is scheduled to begin in 2023, with in-water work July 15th through August 25th. Implementation in Phase II is designed to reconnect >2,120’ of isolated side channel (~40/60 perennial-ephemeral) habitat through the removal of ~560’ of river levee and the placement of associated log jams. The removal of levees and placement of log jams will reconnect ~10.6 acres of floodplain, including 3.6 acres previously part of the Rainbow Lake impoundment footprint (refer to Phase 1 in #74314 REL 85), and improve connection on the 1.5 ac of existing connected floodplain within Phase II.  Phase II includes installation of ~15 ELJs and other additional LWD structures in the main channel to increase channel complexity over a 0.4-mile reach.  Additional unsecured mobile LWD will be placed in the main channel, side channels, and on the floodplain for complexity. Plantings will be done post-construction on adjacent floodplain and riparian areas, and construction access sites and staging areas will be re-vegetated. Planting efforts will emphasize an increase in pines and cottonwoods throughout the reach for the purpose of future LWD key piece recruitment.

Geomorphic Implications:  Reconnecting 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 LWD will initiate a geomorphic response resulting in bed scour and sorting of sediment, which forms critical habitat features (e.g., pools, cover, and spawning gravels).  The LWD structures will influence the development of additional pools and deposition areas in the plane-bed sections of the channel. 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 decreased instream velocities during high flows from better connectivity with the floodplain, and pool development and cover provided by the LWD placements. As the channel is able to establish a more complex plan form through the reconnected floodplain, more diverse habitat areas will be available to increase the carrying capacity for juvenile salmonids.  Deposition of sediment and formation of side channels will create additional spawning area. 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:  As in every implementation work-window we will be at the mercy of several factors out of our control, including delays caused by conditions that increase the risk of wildfire. Work delays can push implementation actions out of the designated work-window. This project is being planned in two phases to accommodate both funding allocations and the availability of space for construction activities and materials. Due to the presence of hatchery infrastructure, and the desire to minimize impacts to existing riparian habitat, we will only have room to mobilize half of the equipment and materials on-site at a time.