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Salmon Creek Restoration

SalmonCreekRestoration2011 512Aerial photo of the restored meandering channel and oxbows of salmon creek.

History 

 
Salmon Creek is the third largest tributary to Humboldt Bay. As the name implies, Salmon Creek historically supported large runs of Coho and Chinook salmon as well as steelhead and coastal cutthroat trout.  
 
Salmon Creek within the Refuge boundaries was historically tidal salt marsh with complex slough channels.  However, these lands were reclaimed for grazing during the early 1900’s through construction of dikes and levees, draining of salt marshes, straightening or relocation of stream channels, and installation of tide-gates to eliminate tidal influence.  After these lands were acquired by Humboldt Bay NWR, management plans identified Salmon Creek as needing habitat improvements to reestablish estuarine and off-channel habitat.  Off-channel habitat consists of  sloughs, ponds and oxbows adjacent to the main channel that naturally would have slower water velocities, moderately higher temperatures and more large wood and food where fish (especially salmonids) can spend time while they make the physiological transition from a freshwater animal to saltwater animal.  In comparison to pre-1900’s conditions, almost all rearing habitat in the lower portion of Salmon Creek has been lost. 
 
 

 SalmonCreek1870and2009 502  

Pictures: The left picture shows what the Salmon Creek delta looked like in 1870. The aerial photo to the right shows what the Salmon Creek delta looked like in 2009. If you look closely, you can see that there is very little evidence left of the historical channel.   

 
The Refuge initiated efforts to improve fish access and habitat for Salmon Creek in the early 1990’s. One of the first projects was adding a small opening (“fish door”) to one of the flaps on the tide gates. This slightly improved fish passage and allowed some minor tidal exchange upstream of the tidegate, creating a small estuary inside the levees.  In 1993, the refuge dug a new channel, re-establishing channel sinuosity and complexity to replace a portion of the lower channel that had been ditched and straightened.  While this improved habitat, further restoration was needed to increase tidal circulation, improve fish access, and enlarge estuarine rearing habitat for salmonids.  

Restoration 

 
In 2006-2007, Phase I of the project increased Salmon Creek’s tidal prism, tidal connectivity, and tidal influence by replacing an existing tide gate structure, constructing a new tide gate structure in the Salmon Creek overflow area, and re-connecting several off-channel ponds to the stream. 
 
TideGatesTogether 508 
  Pictures: The tidegate to the left restricted movement of brackish water into the salmon creek channel. These were replaced with the tidegate shown in the picture to the right, which allows the movement of brackish water into the upstream reaches of Salmon Creek, reflecting historic estuarine conditions.  

 



  

With increased tidal inundation, Phase II of the project focused on construction of 4,200 feet of new estuarine channel with a larger capacity and increased sinuosity.  Much of this channel followed the alignment of slough channels through the historic marsh.  Connection to the former ditched channel was maintained to allow it to serve as a backwater habitat.  Five off-channel habitat features were also constructed to provide freshwater rearing habitat for salmonids in winter.  A connection channel between Salmon Creek and Cattail Creek was excavated to improve seasonal freshwater habitat and fish movement between the two systems.  To further enhance this restored habitat, large log structures were added to the channels and ponds to provide resting and hiding places for fish and to add complexity to the stream hydrology.  Over 200 logs of various sizes were anchored within banks to provide a diversity of habitat for fish.  In the fall following construction, 12 different species of native trees and shrubs were planted adjacent to the channel and ponds to create a riparian component to this effort.
 
ExcavateandWood 510
 Pictures: The left picture channel shows two excavators digging the new channel. To the right is a newly connected channel with woody debris added for salmon and steelhead habitat. 
 
The excavation of the channel and ponds generated over 40,000 cubic yards of fill.  Rather than dispose of this off site, the Refuge used this material to raise the elevation of the subsided Overflow Area of mudflat to create tidal salt marsh.  Due to the subsidence, this area was too low to sustain salt marsh vegetation.  This effort provides a habitat type that is lacking around the bay, as over 90% of salt marsh habitat in Humboldt Bay has been lost in the last 150 years.  Within two years after addition of the fill, this area was dominated by native plants, especially pickleweed (Salicornia virginica).  
  
SalmonCreekChannelandOxbow 512  
Picture: A section of the newly constructed Salmon Creek channel land an oxbow pond. 

Fish Response 

 
Almost immediately after restoration was completed, fish monitoring conducted by our partners with California Department of Fish and Wildlife yielded some interesting results.  Within the first year post-construction juvenile salmonids, tidewater goby, long-finned smelt, and multiple other estuarine species of fish were detected.  In fact, more juvenile coho salmon were captured during 2011-2012 sampling season than in all previous sampling years combined.  In addition, four endangered fish species were captured in a single pond during one sampling day.  This effort is ongoing and will be used to continually track fish response to the restoration efforts.  

Partners 

 
Restoration projects like these are happening all over the west coast and indeed the country, but as is generally the case, it is hard and expensive to repair damaged ecosystems and it can’t be done without many partners.  This project has had many partners both public and private including Pacific Coast Fish, Wildlife and Wetlands Restoration Association, USFWS Coastal Program, CA Dept. of Fish and Wildlife, CA Conservation Corps, Ducks Unlimited, and National Fish and Wildlife Foundation among others.  
 
Last Updated: Feb 26, 2013
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