Caspar Creek Labyrinth Weir Fish Passage Restoration

Share on:

CalFire and the US Forest Service Pacific Southwest Research Station (PSW) worked cooperatively in a comprehensive paired watershed study at the Caspar Creek Experimental Watersheds in Jackson Demonstration State Forest, located in coastal Mendocino County, California. As part of the study, concrete dams equipped with precise flow measurement weirs were constructed providing an essential component of the scientific research. 

In 1964, a wooden fish ladder was built downstream of each weir. To avoid backwatering and submerging the measurement weir, which compromises its accuracy, tailwater levels were kept low requiring fish to leap over a two to three foot water surface drop at the weir. This precluded upstream passage of juvenile salmonids. During low-flow periods, leakage through the wooden fish ladder posed a significant risk of stranding and injury of juvenile salmonids.

In 2003, CalFire and PSW agreed to upgrade the facility and a number of agencies came together to make it happen, including the California Coastal Conservancy, the Five Counties Salmonid Conservation Program, National Marine Fisheries Service, and California Department of Fish & Game. GHD and Michael Love & Associates were tasked with developing the design of a fish passage facility that did not compromise ongoing data collection efforts. The project involved modifications of the dam, complete removal of the existing wooden fish ladder and replacement with a much more robust fish passage facility. The final design includes a pool-and-weir fishway with ten concrete weirs and four removable aluminum weirs. The spillway configuration and design of the weirs minimizes the required leap height while preventing submergence of the measurement weir under a range of flow conditions. Because operation varies under different seasons and different hydraulic conditions, the project included an operation and maintenance manual.

The facility incorporates features to support effectiveness monitoring and fish passage research. A remote wildlife time-lapse camera provides images and video illustrating how the facility is functioning at various flows. Two underwater viewing ports were installed in each fishway to allow for visual observation of juvenile salmonids, with the intent of improving our understanding of both their leaping abilities and behavior. During the final inspection of the project, a juvenile steelhead ascended the ladder in front of the project team, confirming that everyone’s efforts on this project were indeed worthwhile.

Aquatic Sciences


Our reliance on the ecosystem services provided by marine, freshwater and estuarine environments demands a proactive approach to our sustainable use of these assets.

Our aquatic sciences services integrate scientific knowledge with  engineering and economic services to provide innovative, cost-effective  management solutions.

Read More . . .



Our Environment team has earned a reputation for excellence by offering integrated, practical and innovative solutions to all levels of government, authorities and private organisations.

We draw on the skills of engineers, scientists, auditors and planners to deliver services in a number of critical areas:

Read More . . .

Related Projects
By Location
By Environment Sector
By Aquatic Sciences