To address Tucannon River restoration goals, CTUIR placed large wood in Project Area 3 (PA3; river miles 46.7-48.2) of the Tucannon River during the summer of 2014. This restoration treatment had four objectives: 1) establish two key pieces (> 6m long, > 0.3m diameter) of large wood per channel width,
(2) aggrade the channel, (3) reconnect the floodplain, and (4) increase channel complexity.
After the initial restoration project in 2014, the number of pools in the restoration reach decreased and the number of side channels increased, which indicated channel aggradation within the reach. The number of key pieces of large wood also decreased below the target quantity. In 2017, CTUIR used the River Complexity Index (Brown, 2002) as a relative indicator of floodplain connectivity and channel complexity to assess how habitat conditions were changing since the 2014 restoration treatment. The RCI for PA3 increased between 2014 and 2017. Given the observed channel aggradation we hypothesized that RCI could be further enhanced by adding additional large wood in an effort to meet wood loading objectives for PA3.
To complete the restoration design we used a vertol helicopter to add 350 whole trees with rootwads, 350 tree tops (racking material), and 30 ballast boulders. Large wood structures were designed to decrease stream velocities, aggrade the channel, and facilitate movement of surface water into existing paleochannels to increase floodplain connectivity. Using helicopters to place large wood in-stream reduced the time and money required to complete the restoration project, by decreasing costs for engineering design and permitting. As the river continues to work with the large wood structures over time, we anticipate additional increases in RCI (both in flood plain connectivity and channel complexity) which should result in habitat improvements for all life history stages of ESA-listed salmon species.
