InterFluve Inc., G. M. Kondolf, and SWCA Environmental and Engineering Inc. 2023. Trinity River Restoration Program phase II review. Report for the Trinity River Restoration Program (TRRP). TRRP, Hood River, Oregon. Available: https://www.trrp.net/library/document?id=2623.
The Trinity River Restoration Program (TRRP) was established in 2000 by the Department of Interior’s Trinity River Record of Decision (ROD). The ROD was the result of decades of studies described the impacts of the Trinity River dams and outlined the plan to restore the Trinity River and its fish and wildlife populations. This plan focused on five main categories of restoration actions: flow management, sediment management, watershed activities, channel rehabilitation, and adaptive environmental assessment and management.
To date, the program has been split into two phases: Phase 1 spanning from 2003 to 2011 and Phase 2 spanning from 2012 to 2022. Throughout both phases, changes have been made to both the program and to the management actions. These changes have reflected the knowledge that has been gained through extensive scientific inquiry and lessons learned from dozens of implemented projects. In Phase 2 (2012-2022), the TRRP has implemented 14 channel rehabilitation and 42 watershed restoration projects, implemented revised flow management strategies to better mimic natural winter month flow variation, and adjusted sediment augmentation methods to better align with flow releases and geomorphic processes in the Trinity River. Many different methods of evaluating project success have been conducted in the Trinity River since the ROD, but these have largely focused on biological monitoring of juvenile and adult salmonid presence in the reach, or the presence of physical habitat features that meet biological habitat criteria. In general, these results show that rehabilitated areas provide improved or equal juvenile salmonid rearing habitat compared to non-rehabilitated areas, though the overall geomorphologic setting of the project was also a large factor influencing rehabilitation project effectiveness (Cooper-Hertel et al. 2022).
The purpose of the review document is to summarize the TRRP’s channel rehabilitation, site revegetation, watershed projects, flow management, and gravel augmentation activities through 2021, with an emphasis on the channel rehabilitation projects implemented during Phase 2. The scope of the retrospective review is based upon group interviews, restoration site tours, and review of the existing available literature. This report builds upon an extensive body of literature produced in the TRRP, including lessons learned as part of the review of Phase 1 (Buffington et al. 2014).
This review further includes a discussion of: the perceived strengths and weaknesses of the design and design review process; the TRRP’s responsiveness to the actionable recommendations from the Phase 1 Review; the degree to which the projects as implemented meet the stated design objectives of the project; a critical review of the program’s overall approach to channel rehabilitation recommendations for Phase 3.