To spawn, salmon need clean gravel that they can move and put their eggs in between. They also need cold water.
Salmon find cold water in the Sacramento River just downstream of Shasta Dam and, as has been done since the late 1980s, the Bureau of Reclamation through their Central Valley Project Improvement Act provide the gravel. In 2015, the Western Shasta RCD took on management of the gravel “injections” and have completed two injections just below Keswick Dam and one at Market Street Bridge. Both in Redding, CA.
At the Keswick Dam site there have been 20 gravel injections since 1997. In September 2016 the Western Shasta RCD worked with partners and local gravel companies to dump 20,000 tons of spawning gravel down a 100-foot high terrace over a 5 week period. Within 6 months all the gravel was mobilized by the high flows of 2016 and in March 2017, 14,000 tons of gravel was dumped over a 3 week period that was mobilized by the river within 1 week. Check out this video.
Shown below is a picture taken February 2018 below Keswick Dam where a spawning riffle created from the Keswick gravel injections can be seen.
At Market Street Bridge the Sacramento River Technical Advisory Committee decided to replicate a highly successful spawning gravel project completed in the early 1990's. This is gravel that can be used immediately by returning Chinook Salmon. In March 2016 with a donation of services from the Glenn-Colusa Irrigation District, over 15,000 tons of gravel was placed into the Sacramento River at this site over a three week period.
Check out this video provided by John Hannon. Shown in the picture below (taken February 2018 at low flows) there is still gravel for salmon to spawn in despite the 2016-17 record precipitation and flows in the river.
Why Add Spawning Gravel? Section 3406 (b)(13) of the Central Valley Project Improvement Act mandates spawning gravel additions to the upper Sacramento River to mitigate for impacts to anadromous fish habitat resulting from the construction Shasta and Keswick Dams. Gravel gets trapped behind the dams, thus becoming inaccessible to salmon below the dams.
Where Does It Go? Mobilized by high winter flows and scheduled dam releases, quality gravel moves downstream, ideally settling out in areas accessible for returning adult Chinook to use for spawning redds. From observations in early 2018, the supply of gravel just downstream of Keswick Dam site appears relatively abundant.
Next Steps: To determine how much and where gravel might be needed in the near future, the US Bureau of Reclamation, with assistance from our Sacramento River Restoration Team, has plans to update a gravel budget. This will be done with support from past studies, new LIDAR and hyperspectral imagery paid for by a CDFW grant, and aerial observations during CDFW monitoring surveys.