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US Fish & Wildlife Service FieldNotes

STOCKTON FWO: From Gold Mining to Salmon Habitat Merced River Ranch Restoration Makes a Splash

Region 8, November 20, 2013
Cobble and gravel restored to the Merced River for salmon spawning.
Cobble and gravel restored to the Merced River for salmon spawning. - Photo Credit: n/a
Adult salmon digging a redd in a restored strech of the Merced River.
Adult salmon digging a redd in a restored strech of the Merced River. - Photo Credit: n/a
4.5 acre flood plain to store increased fall and spring flows and to provide habitat for juvenile salmon.
4.5 acre flood plain to store increased fall and spring flows and to provide habitat for juvenile salmon. - Photo Credit: n/a
Large cobble dredge tailings left from gold mining on the river.
Large cobble dredge tailings left from gold mining on the river. - Photo Credit: n/a

By Cindy Sandoval, Michelle Workman and Zac Jackson

When the Merced River Ranch was first brought forward as a possible restoration site the original price tag was 26 million dollars. U.S. Fish and Wildlife Service (Service), California Department of Fish and Wildlife (CDFW) and partners worked to scale down the project into something they could manage and with the help of Cramer Fish Sciences the project was reduced to approximately 2.5 million dollars. The 318-acre Merced River Ranch property was purchased in 1998 by CDFW for its conservation and restoration potential on the Merced River. The property included large cobble dredge mounds that were removed from the river decades ago in the search for gold. This cobble is now being returned to the Merced River and serves as a source of gravel for salmon spawning restoration.

Prior to mining and dam construction the Merced River was a complex, multi-channel river system that began in the Sierra Nevada foothills and spread across the valley in river channels and flood plains. However, in the early to mid-1900s large mechanical dredges were used to excavate the river and valley floor. The dredges could move over 1.1 million cubic meters of dirt a year and some areas were excavated to the bedrock located 20 to 36 ft. under the top soil. After gold was removed the dirt and cobble was deposited in long rows. These rows or “tailings” left the river without the cobble needed for salmon spawning and raised the river’s banks with the tall cobble tailings.

The presence of large gravel rows made the Merced River Ranch site ideal for restoration because the restoration team could place the same gravel that had been removed by large dredges from the Merced River and place it back into the system without having to purchase and transport new gravel into the area. “When we increase habitat for Chinook salmon to spawn we generally have to introduce gravel, this property was full of dredger tails that were an easy on site source of gravel and it really brought down the cost of the project and gave us more bang for your buck” said Zac Jackson fisheries biologist for the Service.

Rhonda Reed with the National Marine Fisheries Service wrote the original grant for the project site and recalls a time when people asked “What are you going to do with a pile of rocks?” In total the Merced River Ranch Restoration partners placed 91,000 cubic yards of cobble back into the river, side channels and flood plain. The cobble tailings were sorted on site into different size categorizes and the fine sediment was placed in the flood plain to promote growth of vegetation that can provide food and cover for juvenile salmon and promote riparian recruitment to shade the river. The larger pieces were used to raise the river bed and cobbles used to provide material for salmon redds.

The project was completed in late summer of 2013 and during a site visit on November 15, salmon were seen digging redds and spawning in the restoration area. Along with increased spawning, an important aspect of the restoration project focused on increasing the survival of salmon fry and juveniles after they hatch. One way this was done was by designing a 4.5 acre floodplain that can store the increased fall and spring water pulses and provide habitat for small fish to avoid larger predators. “Because the floodplain water is shallow and moves slowly it gets more solar radiation so primary production is high and you get a lot of growth of food for juvenile salmon, as a result the salmon grow faster here then they would in the channel” explains Service fisheries biologist Michelle Workman. Studies have shown that faster growing fish survive better and have an increased chance of surviving to adulthood.

The partners for this restoration hope that the site will serve not only as habitat for salmon and other wildlife but that it can be an educational site as well. Recently local school children visited the site to plant trees near the new flood plain that was once covered in cobble and boulders. It is hoped that the Merced River Ranch Restoration project area can be linked with similar restored habitat on the river and create an extended corridor for salmon to spawn, grow and return to.

Cindy Sandoval is a Pathways intern in external affairs at the Pacific Southwest Regional Office in Sacramento, Calif.

Contact Info: Cynthia Sandoval, 916-978-6159, cynthia_d_sandoval@fws.gov