Restoration Activities:
Need for Action
Construction of dams, diversion of water, and reduction of flows in the Trinity River have impacted the river’s ecology, its fisheries, and its ability to recover from prior mining activities. In addition to the dams blocking salmon from the upper watershed, studies during the 1980′s and 1990′s revealed that weak flows resulted in channel simplification and a reduction of habitat for juvenile salmon.
This page gives a broad overview of TRRP restoration; more details are given on pages for each of TRRP’s restoration activities.
TRRP Restoration
The overall strategy of the Trinity River Flow Evaluation Final Report (TRFEFR) and the Trinity River Restoration Record of Decision (ROD) is to restore physical process and rescale the Trinity River as a foundation for fishery recovery. The ROD established the current Trinity River Restoration Program (TRRP) and specifies:
- Four modes of restoration:
- Plus:
- Infrastructure improvements to accommodate high flow releases
- Environmental Compliance (Riparian Vegetation, Wetlands, Turbidity, Water Temperatures)
- Science-based Adaptive Management to enable modifications to actions according to scientific feedback
High flow (6000 cfs release) activating floodplains, reworking bank vegetation, and building log jams (which provide excellent fish habitat).
Sawmill rehabilitation site during high flow (6000 cfs release). TRRP actions visible here include floodplains accessible to the river and young fish, greater channel complexity, and a wood-based habitat structure.
Gravel augmentation at the Lewiston ‘Weir Hole’ during spring high flow.
Hamilton ponds, constructed in 1980s to capture fine sediments from the decomposed granite that forms much of the Grass Valley Creek watershed. The ponds must be periodically cleared of sand and silt.
One of the bridges replaced by TRRP to accommodate dam releases up to 11,000 cfs.
Young coho salmon photographed during a study at Cemetery Hole (Lewiston).
