Santa Cruz, CA
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  Portland, OR
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Mill Creek Dam Removal

lowerdam webClient: Sempervirons Fund and Peninsula Open Space Trust

Mill Creek is the largest tributary of San Vicente Creek, in Santa Cruz County, an important stream for steelhead and coho salmon on the central California coast. Mill Creek drains a small, steep watershed containing a localized area of granitic rocks within the highly erosive marine sediments that dominate the Coast Range. Because of this, Mill Creek is an important source of resistant spawning gravel, which is limiting for fish in many watersheds in the central Coast Range. Within the recently-acquired San Vicente Redwoods Preserve, two dams on lower Mill Creek impound gravel and prevent fish passage.

Waterways was hired by the landowners - Sempervirens Fund and the Peninsula Open Space Trust – to evaluate existing conditions, opportunities and constraints; perform a risk evaluation; develop the dam removal approach; produce engineering designs; assist with permitting and outreach; oversee construction; and contribute to the post-project monitoring and adaptive management program. The Existing Conditions Assessment identified the geomorphic context and considerations for various dam removal options. Through an Alternatives Analysis it was determined that the preferred option was to remove the downstream dam, which is larger and structurally impaired, while leaving the upper dam in place. Dam removal will eliminate a passage barrier on lower Mill Creek, reduce risk, liability, and maintenance for the landowner, and provide a pulse of resistant spawning size gravel to enhance recently built restoration projects downstream in San Vicente Creek. The dam removal designs were developed to maximize the downstream delivery of spawning-size gravel while reducing the chances for developing fish passage barriers after removal. Dam removal will occur in fall of 2022.