A Methodology for Rockwad Velocity and Predator Habitat

A continuous sequence of velocity and predator refugia is imperative to the survival of out-migrating juvenile salmonids on the Sacramento and San Joaquin Rivers. Gaps in habitat along the river corridor increase the risk of predation, fatigue, stress, and reduced growth rates, and therefore, necessitate mitigation actions. However, traditional habitat enhancement methods, such as side-channel restoration, are not applicable on all reaches or during all flow conditions. Areas confined by levees, steep banks, or other topographical constraints require new methods to supplement migration habitat where it is missing or insufficient. A rockwad is a tree trunk (with root cluster) anchored to a large boulder. The boulder and root mass provide velocity and predator refugia, and therefore, allow juveniles to safely rest and eat during their emigration. Through hydrodynamic simulations, physical modeling, and fish behavior algorithms, this project will determine the optimum quantity and placement patterns to achieve suitable migration habitat conditions. It is expected that the results from this research lead to design recommendations for future habitat projects.