Key Elements
Recreating a stream's alluvial character, channel/floodplain rehabilitation, restoring hydrograph variability, and managing the sediment budget (gravel augmentation, fines supply reduction).

Overview
The Trinity River Restoration Program is the first large-scale, leave-the-dam-in-place restoration project to be based on re-activating the below-dam stream’s natural fluvial processes as the principal means of restoring and maintaining productive fish habitat. As such, its successes and its lessons learned are of great interest to the Stream Restoration community. Use the links embedded in the text below or at right for more details on each aspect of the project. Other links at right will direct you to the project's own excellent web site and other related web resources.

Historical Context
The Trinity River has had a long history of major anthropomorphic “influences”. In the late nineteenth century, placer mining activities caused major alterations to the river, and in the early twentieth century, dredging activities turned the valley upside down as mining companies tried to find any remaining gold. Then, in the late 1950s,the government decided to dam the river for hydroelectric power and to divert a major portion of the flow to California’s Central Valley in response to agricultural and urban needs for water. Efforts to preserve the river’s salmon production, necessary for the culture and livelihoods of the Hoopa Valley and Yurok Indian Tribes whose reservations are downstream of the dam site, were based on “best practices” of the time, but failed, in large part because these studies assumed the habitat would stay constant despite significantly reduced flows. Standard habitat engineering and incremental flow fixes were attempted, but the changes that had already occurred to the river’s morphology and sediment regime, and therefore to the salmon habitat, were already substantial. Over the same time period, populations of naturally produced chinook salmon dropped to 1/4 of their pre-dam levels.

The Current Project
After extensive research by all parties and the support of the Hoopa Valley Tribe, the government came to believe that the best hope of restoring salmon populations (rather than maintaining the degraded status quo) was restoring the pre-dam fluvial processes that had created and maintained productive habitat in the first place, although at a smaller scale given that the dam had to remain in place. The current Trinity River Restoration Program is based on this principle, and has four major components:

1. Channel and floodplain rehabilitation  – re-enable the river to access to its floodplain and allow the alluvial portions of the river to regenerate.
2. Hydrograph management– restore most of the river’s natural discharge variability (albeit at reduced levels) which in turn will allow natural alluvial processes to maintain the physical habitat.
3. Sediment budget management – use gravel augmentation to replace the coarse fraction lost due to the dam, and watershed management to reduce the oversupply of fines.
4. Adaptive management – use predictive models in planning items (1) through (3) and closely monitor results as a way of both proving results and improving future river management.