Stillwater Sciences is working with The Nature Conservancy (TNC) to restore habitat for endangered Central California Coast (CCC) coho salmon in the Ten Mile River basin in Mendocino County, California. TNC and its partners are establishing conservation easements over nearly 4,000 acres encompassing 10 miles of the lower river channel and floodplains. Habitat restoration within these protected areas of the Ten Mile River is particularly important to CCC coho salmon recovery because the basin supports a functionally independent population within a NOAA core recovery area with high restoration potential. Restoration efforts in Ten Mile River are the cornerstone of a TNC program to recover coho salmon in coastal California watersheds.
Stillwater Sciences identified winter rearing habitat availability as a key factor limiting the coho salmon population in the Ten Mile River basin. Coho salmon recovery in the basin will require improving winter habitat for juvenile refuge, foraging, and rearing by increasing in-channel habitat complexity and hydraulically reconnecting relict off-channel and floodplain areas during winter high flow events.
We developed a scientifically-based framework for coho salmon habitat restoration in lower Ten Mile River that defines winter rearing habitat restoration goals, approaches, and potential project areas. The framework integrates information about historical and current winter rearing habitat, channel confinement and morphology, sediment dynamics, flow magnitude and duration, and floodplain connectivity. Three inundation surfaces were mapped to inform where winter habitat for juvenile salmonids occurs in off-channel areas during target flows and to identify relict floodplain features that provide opportunities for winter habitat enhancement.
The Project demonstrates the importance of integrating analyses of hydrogeomorphic processes and factors limiting fish production as the basis for restoring floodplain and off-channel coho habitat in coastal California streams.