Post-Project Appraisal of Crocker Creek Dam Removal Project, Sonoma Co., California
Crocker Creek drains 3.3 mi2, flowing into the Russian River near Cloverdale, California. A 30-foot high dam built in the early 1900s had filled with sediment, and then experienced two structural failures in 1995 and 1997. In 2002, the Sonoma County Water Agency (SCWA) undertook a restoration project; the main objectives of the project were to restore anadromous salmonid (specifically steelhead trout) passage and stabilize adjacent stream banks. Activities performed by the SCWA include: removal of remaining parts of dam; regrading of steep banks to shallower slopes; revegetation of riparian corridor; and placement of geotextiles, rip-rap, and log structures along areas of the stream bank.
In 2005, we conducted a post-project appraisal involving visual observations, vegetation measurements, channel surveys, and interviews with the project engineer; our objective was to determine whether the project goals were achieved. We determined a pre-project longitudinal profile from construction documents; no longitudinal profile was surveyed after project completion. We measured post-project channel configuration through field surveys, including five channel cross-sections and a 1300-ft longitudinal profile. To evaluate the fish passage objective, we compared the pre-project channel profile to our post-project longitudinal profile and considered our visual observations; our analysis indicates this objective was successfully met. To evaluate the bank stabilization objective, we quantified the success rate of riparian revegetation effort and relied on visual observations. The revegetation effort was partially successful; our visual observations include areas of bank erosion and areas stabilized by rip-rap. We found this objective difficult to assess due to the lack of baseline data.