Nelson Gulch Culvert Replacement

The Nelson Gulch culvert replacement project was the last part of Big River Haul Road Salmon Restoration project that the Mendocino Land Trust and State Parks were partnering to complete in the summer of 2014, under a State Rivers and Parkways grant awarded to Mendocino Land Trust. It included replacing several degraded and failing culverts along the main Big River haul road. These upgrades will allow young salmon to freely travel upstream and offer them safe passage while they grow and thrive.

The engineers and designers who partnered with Mendocino Land Trust and State Parks on this project had to account for the combined effects of extreme storm events and major tides when installing the fish passage and it has been functioning just as planned. It is located at Nelson Gulch, a side stream to Big River about 4 miles back along the main Big River Road.. The site sees a twice-daily impact by the tides.  These tides added additional challenge to the construction project…rising water in Big River over topped protective dams and inundated the construction site on more than one occasion. 

The restoration project is targeted at allowing coho salmon, an endangered species, free passage into this coastal tributary, a relatively short distance from the ocean, and a distance favored by coho.  The Nelson Gulch site contained an undersized, rusted out and broken pipe to pass water under the former Big River Main Haul Road.  The bottom of the new, extra-large “fish tube” is very large, 60 foot long, 15 foot wide, 10 ½ foot high and set below the average tide and the pipe itself is layered with river gravel to mimic a natural stream channel.

The sight of this huge 60-foot-long culvert hanging by straps from a giant crane was quite dramatic, but young fish that swim upstream through their new tunnel will never know the difference. The bottom of the new culvert will be filled with stream gravel so the fish will feel right at home. The enormous culvert was assembled at Big River from more than 50 metal plates that had to be bolted together on site.  It was so big that a 120 ton crane had to be brought in to lift it into place. With high tides, the water comes up several feet inside the buried pipe, allowing easy travel for migrating coho. This was a significant undertaking and will allow fish to migrate up and down Nelson Gulch, a small stream considered excellent salmon spawning habitat.

Watch the project time lapse video below to see this monumental project completed in a matter of minutes. If you’d like to see the newly installed culvert at Nelson Gulch, it is easily viewed in the Mendocino Headlands State Park at Big River traveling by bike, foot or horseback to Mile Marker 4.05 on the Big River Main Haul Road, nowadays called the Big River Trail.  Safe travels and enjoy the river!