As of Fall 2019, the RCD has completed the Alpine Creek Fish Passage project in the San Gregorio watershed! This project restores three miles of habitat for fish like steelhead and coho salmon by modifying a culvert, removing a fish ladder and failing weirs, and reconstructing 425 feet of stream channel.


Biologists first relocated over 300 steelhead from the project area. Most of these fish were “young of the year” meaning they were only a couple months old. The fish within the project area were netted and relocated outside of the project area beyond exclusion nets that were placed along the upstream and downstream ends of the project area to prevent fish from swimming back into the site.

Once the project area was cleared of fish, the creek was temporarily diverted into a big pipe so work could be carried out in a dry environment without disturbing aquatic species. Dewatering a creek is tough, and the construction crew, Hanford ARC, installed sheet pilings across the channel to hold the water back.

Below, from left to right: 1) Black pipe diverting creek flow 2) Sandbag dams created individual pools that could be drained 3) A sheet pile dam was installed across the culvert to isolate the work area from flow.  

With a dry streambed, work began to remove old, unfunctional features limiting fish passage including weir pools, a defunct fish ladder, and the concrete base of the arch culvert. The streambed was then carefully and methodically reformed at a 4% grade (perfect for fish) with engineered streambed material to optimize streambed shape, roughness, and longevity. Engineered streambed material is a technical way of saying “a bunch of rock”: various rock sizes from pebbles to boulders were mixed onsite to achieve desired gradation and then placed within the streambed and set with fine material to form a tight structure.

The base of the arch culvert was also reformed. A concrete crew prepared formwork and rebar in preparation for two concrete pours to reshape the base of the culvert to allow for fish passage. The previous base of the culvert and fish ladder were too high above the creek (eight and three feet, respectively). The ladder was removed, the base of the culvert was lowered, and features were added to provide stability and catch excess sediment. Rock for engineered streambed material was placed in the arch culvert as well to form a natural streambed surface above the concrete structure. Engineers from Waterways Consulting inspect the construction process at each phase to ensure designs are met.

 Following completion of the streambed, the temporary diversion dam was removed on October 8 and water once again flows in the creek channel. With the final touches to restore the access hillslope, the project is officially complete. Now we just wait for spawning season and welcome fish back to the creek this winter!

Image of the Alpine Creek Crossing at Pescadero Creek Road before the project.
Image of the Alpine Creek Crossing at Pescadero Creek Road after the project.

This project was funded by the Fisheries Restoration Grant Program through the California Department of Fish and Wildlife.