Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
LODI FWO: Re-establishing the Merced River’s Henderson Park for a New Generation
California-Nevada Offices , January 8, 2016
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Henderson Park November 2015
Henderson Park November 2015 - Photo Credit: Steve Martarano/USFWS
An aerial view of the restored site, December 2015
An aerial view of the restored site, December 2015 - Photo Credit: Jesse Anderson, Sr., Cramer Fish Sciences for USFWS
Sisters of some of the Cub Scouts Troop helped out by spreading grass seeds and collecting acorns for planting.
Sisters of some of the Cub Scouts Troop helped out by spreading grass seeds and collecting acorns for planting. - Photo Credit: Laura Heironimus/USFWS
A Cub Scout hard at work, digging holes in the newly constructed floodplain
A Cub Scout hard at work, digging holes in the newly constructed floodplain - Photo Credit: Laura Heironimus/USFWS

By Laura Heironimus and Zac Jackson
Lodi Fish and Wildlife Office 

The Merced River was historically a complex, multi-channel river system that began in the Sierra Nevada foothills and spread across the California Central Valley in river channels and floodplains. However, in the early to mid-1900s large mechanical dredges were used to excavate the river and valley floor in search of gold. The dredges could move over a million cubic meters of natural material each year, impacting large amounts of habitat as they worked. This left the river without the gravel and cobble needed for salmon spawning and raised the river’s banks so much that the floodplain was no longer functional.

Today, Henderson Park, the restored area situated along the north bank of the Merced River in eastern Merced County, offers opportunities for picnicking, fishing, and other river recreation. In the early 2000’s, the U.S. Fish and Wildlife Service teamed with Merced County, Cramer Fish Sciences, and the local community of Snelling to restore channel form and function on the Merced River at Henderson Park.

The primary goal of the project was to mitigate decades of gold mining and river regulation through floodplain and channel restoration to support Chinook salmon and steelhead populations. The project addressed these issues by improving spawning areas, providing more seasonal rearing habitat through side channel and floodplain creation, and reducing predator habitat by filling deep glides and increasing water speed through the site.

One feature in particular that made the Henderson Park site ideal for restoration was the proximity of the dredger tailings to the river. When there’s habitat for Chinook salmon to spawn, gravel is usually brought in from another area. Henderson Park, however, already had an easy on-site source of gravel that lowered the overall cost of the project. The restoration team could place gravel and cobble from the tailings back into the Merced River without having to purchase and transport new gravel into the area. 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 covered with gravels and smaller cobbles to provide material for salmon redds. In total, the Henderson Park Restoration partners placed about 70,000 cubic yards of cobble and gravel back into the river.

Over the course of a few years, Henderson Park was transformed from a barren rock field back to a more natural looking and functioning environment where native grasses and other vegetation have already begun to take root.

Site construction was completed last October. One feature of the site includes the reclamation and re-grading of mine tailings to rehabilitate approximately 15 acres of floodplains. Also, lateral bars and islands within the main channel that improved almost 8 acres of spawning habitat were created.

As a result, Chinook salmon are already responding to the project and spawning in areas that they haven’t been able to utilize in over 80 years. Along with increased spawning, an important aspect of the project focused on increasing the survival of salmon fry and juveniles after hatching. One way this was done was by designing a floodplain that can store the increased fall and spring water flows or releases and provide habitat for small fish to avoid larger predators. Primary production is high in shallow floodplain areas, providing food for juvenile salmon which helps them grow faster than in the main channel. Studies have shown that faster growing fish survive better and have an increased chance of surviving to adulthood.

In November, a local Cub Scouts troop assisted by family members helped rebuild the newly constructed floodplain. Everyone worked together to collect acorns, spread mulch along the hillsides to prevent erosion, as well as to plant oak trees and native grasses that will one day bring life to the floodplain. The scouts and family members worked a long day, taking breaks only to identify animal tracks and splash around in the shallow side channels.

Long-term goals for the restoration site include continuing public recreational opportunities by providing an easily accessible restored area which offers mutual benefits to fish resources and the local community.

Contact Info: Steve Martarano, 916-930-5643, steve_martarano@fws.gov
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