The Effects of Restoration Actions on Juvenile Salmonid Rearing Habitat in the Trinity River Restoration Reach at an Index Streamflow, 2009–2017

In the Trinity River, Chinook Salmon population sizes have been hypothesized to be limited by the availability of age-0 rearing habitat. Restoring rearing habitat is the focus of a large-scale effort that has been ongoing for the last two decades through streamflow management, channel rehabilitation, and sediment augmentation among other actions. The effects of restoration actions and channel configuration on rearing habitat and changes in rearing habitat were estimated over a 64-km restoration reach between 2009 and 2017. Rearing habitats were mapped at sample units by field measurements of water depth, average flow velocity, and proximity to in-water escape cover. All data were collected at an index streamflow of 12.7 m³/s, which is similar to discharge in the restoration reach during the critical winter and early spring rearing period under contemporary flow management. A 7.9% increase in total habitat was found where amounts of rearing habitat were best predicted by channel rehabilitation, wetted area, distance from Lewiston Dam, and channel complexity. Change in amount of rearing habitat was best approximated by channel rehabilitation and changes in wetted edge length.