PWA worked with The Nature Conservancy and The Conservation Fund to provide a geomorphic assessment of Inman Creek in the Garcia River Forest in Mendocino County, California. Our work included a technical report summarizing geomorphic processes in Inman Creek, including the relationship between bar and pool morphologies, large woody debris accumulation and salmonid habitat. PWA performed a qualitative investigation to evaluate hydrologic and geomorphic processes associated with in-stream habitat quality, located and evaluated existing enhancement projects and developed recommendations for pilot projects focused on salmonid habitat enhancement.

Based on our findings, the team developed designs for unanchored woody debris structures, as well as recommendations for future management of the watershed--including a wood-loading program.

Key factors affecting the design:

Bedrock and large boulder elements, which govern the creation of bar and pool habitat utilized by multiple life stages of salmonids, affect how flows respond to channel geometry through scour and deposition. In turn, this influences sediment transport within the system. The persistence of large wood in the creek is directly related to the maturity and density of the forest canopy. Trees falling into the creek are a critical factor in retention of wood within the system. Further, channel width, large roughness elements and bedrock chutes all distinctly influence conveyance and accumulations of wood. The channel geometry is non-deformable over time scales relevant to the management of the creek; large roughness elements and boulders, which are persistent for geomorphically significant time periods (i.e. greater than 25-50 years), are the only occurrences that can offset the intense hydraulic conditions created by the confined channel. Finally, cable-anchored log elements have been installed throughout the lower reaches of Inman Creek – with mixed results. Severed and torn cables, as well as anchored log structures perched above the channel, are indicators of episodically extreme hydraulic conditions and an overall dynamic system. Future habitat enhancement actions must consider geomorphic and hydraulic conditions and principles in order to establish functional and persistent habitat features.

Implementation of the pilot enhancement projects and the wood augmentation program is anticipated in 2009.