Elk River, the largest tributary to Humboldt Bay and natal stream to four species of anadromous salmonids, is undergoing intensive watershed-wide recovery efforts to remediate impacts associated with excessive channel sedimentation that occurred between 1986 and 1998. Resource agencies and stakeholders are resolving the complex ecological and social issues resulting from sediment impairment by implementing a multifaceted approach developed in tandem with the Total Maximum Daily Load Implementation and Monitoring Plan for Elk River. The approach includes: (1) Waste Discharge Requirements to reduce future sediment loads from timberlands, (2) a Recovery Assessment and Implementation Framework to alleviate existing sediment impairments and improve ecosystem function through mechanical channel rehabilitation, and (3) a Stewardship Program to coordinate stakeholder participation in recovery planning and implementation.
Stillwater Sciences and Northern Hydrology and Engineering, in partnership with California Trout and multiple state and federal agencies, are developing the Recovery Assessment and Implementation Framework. Underway since May 2014, the work involves defining existing and desired future conditions, identifying site-specific opportunities and constraints, and predicting system trajectory under existing and future sediment load and mechanical rehabilitation scenarios. Given the large amount of stored sediment that may be affected by recovery efforts, this overall approach is critical in addressing the potential effects of rehabilitation actions on sedimentation patterns and aquatic habitat within and between treated reaches. In 2012, the team developed a two-dimensional hydrodynamic and mobile-bed sediment transport model to assess sediment load reduction on channel recovery in a 2.5-mile pilot reach of Elk River. The Recovery Assessment and Implementation Framework is now expanding this modeling tool and associated field data collection to assess channel and aquatic habitat conditions and evaluate the effectiveness of potential restoration actions along 20 miles of the North Fork, South Fork, and mainstem Elk River. The approach will be used to assess reach-specific recovery rates, effects of restoration actions in treated and untreated reaches, and data collection priorities supporting adaptive management. This approach utilizing sediment transport models supported by targeted field data collection to predict geomorphic and aquatic habitat trajectories is gaining wide-spread use in restoration planning and is vital in large, complex projects where recovery is anticipated through a combination of treatments occurring at varying spatial and temporal scales and at significant cost.