Tucannon PA 13 Habitat Enhancement

The project restored 1 mile of Tucannon River in Project Are 13. The project was constructed in two phases during the 2022 and 2023 summer in-water work windows. The main focus of the project was to reconnect floodplain throughout the project reach. This was done by removing levees, adding channel length, reconnected relic channels, raising the channel in key areas, and augmenting gravel throughout the project reach. 35 large wood structures were added to the new channel configuration to improve channel complexity and increase the habitat diversity.

Floodplain connectivity and channel complexity were measured using three rapid habitat surveys conducted during base flow (<130 cfs) during the summers of 2020 & 2021 (pre-project) and 2023 post implementation. These surveys in combination with pre-project remote sensing spatial data (2017 & 2020 bathymetric LiDAR) were the source for physical habitat data used to conduct implementation and change detection monitoring for this project. Metrics are summarized for the entire project reach (1.26 km) each year.

Installation of LWD structures and racking materials increased the overall number of LWD key pieces from 0.31 to 4.43 key pieces per bankful width exceeding the objective of 2 per bankful width. Fifty-eight percent of log jam construction was associated with pool formation increasing pool frequency from 8 to 25, with a mean maximum depth of >1 m, overall pool area increased by 84%. The placement of logjams reconnected > 17 acres of low floodplain increasing connectivity by 50% at the 2 yr. return flow or less.

Channel habitat units were estimated in the field by the CHaMP program in 2016 at two habitat control sites surveying ~ 50% of the overall project length. In 2016, 59% of the surveyed area was categorized as turbulent riffle or rapids and only 7% as slow deep-water pools, with fast water non-turbulent glides making up the remainder. Post project Channel habitat units show significant (70%) increase in frequency, with decrease from riffle/rapid habitat types to glides, pools and side channels, and improved channel unit diversity. Large planar rifles were targeted for conversion to glides and pools for the purpose of increasing deeper lower velocity Spring Chinook rearing habitats. The project also reconnected >1.6 km of isolated side channel habitat through the placement of associated log jams and designed channel plugs.

Beginning in the winter of 2022-23, riparian planting was initiated and will be ongoing as the site shapes up and fine sediments are deposited on cobbles exposed during levee removal and site access. It is anticipated that riparian planting and weed control will be ongoing as floodplain connectivity and river process advance over the next 5-10 years.

The project aims to enhance river complexity and floodplain connectivity to improve adult holding, spawning, and rearing habitat conditions for Snake River ESU spring Chinook and steelhead. This enhancement will be accomplished by removing levees, introducing wood, and releasing gravels that have been confined by man-made structures.