Boyce, J., D. H Goodman, N. A Som, J. Alvarez, K. Hopkins, and A. Martin. 2020. Streamflow and Juvenile Salmonid Habitat Availability at Six Rehabilitation Sites on The Trinity River, California 2008-2017. Arcata Fisheries Technical Report TR 2020-39 for the Trinity River Restoration Program (TRRP). U.S. Fish and Wildlife Service, Arcata, California. Available: www.trrp.net/library/document?id=2468.
The Trinity River Restoration Program seeks to increase juvenile salmonid rearing habitat by implementing mechanical channel rehabilitation among other restoration actions. Effectiveness monitoring provides feedback to rehabilitation site designers to inform future restoration efforts and help facilitate adaptive management of the program. Recently, we documented increases in Chinook Salmon and Coho Salmon rearing habitat resulting from channel rehabilitation at summer base (12.7 m3/s) streamflow; however, a trend analysis found 53% (10 of 19) of sites had less rearing habitat at the most recent survey than they did at the first survey after construction. Here, we assessed the effect of channel rehabilitation and subsequent trends in rearing habitat at flows ranging between 9 and 57 m3/s at six sites by sampling just prior to construction, just after construction and during a revisit survey. Examples of constructed features included main channel meanders, split channels, side channels, alcoves, point bars and large wood jams. The area under the curve (AUC) of the streamflow to rearing habitat curves increased at five sites surveyed within a year before and after construction. Similar to the previous trend analysis, construction-related improvements were not sustained; four of six sites had lower AUC values at the most recent survey than they did at the post-construction survey. However, all sites had higher AUC values at the most recent survey than they did before construction indicating that, although diminished, construction related benefits persist at these sites. Reductions in bed relief, water surface elevation, channel sinuosity, surface area of constructed point bars and alcoves and flow entrainment at side channel entrances accounted for most of the observed habitat losses after construction; an unanticipated large increase in bed relief and water surface elevation at one site produced large increases in habitat. The Program should consider additional surveys at these sites to assess the stability of the habitat trajectories documented here.
First Posted: 2020-07-21 20:57:08
Post Updated: 2020-07-21 22:15:44