Jump-Starting Riparian Restoration in a Disturbed Riverscape: The Hammon Bar Riparian Enhancement Project on the Lower Yuba River

Summer 2014 Ecesis, Volume 24, Issue 2

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The lower Yuba River has been heavily altered by hydraulic mining debris, dredger mining, upstream dams and an altered flow regime. While over the last half century (following the control of hydraulic mining sediments and dredging), riparian vegetation cover has been increasing on the lower Yuba River floodplain, succession has not progressed and the vegetation is largely comprised of shrubby willow species. Large wood supply is severely limited with consequent limitations in habitat for salmon and other aquatic species. A more diverse supply of plant species, including an abundance of large trees such as Fremont cottonwood (Populus fremontii) and Gooddings willow (Salix gooddingii) would provide increased riparian biodiversity and multiple ecological benefits. 

In 2011 and 2012, the South Yuba River Citizens League (SYRCL) planted 6,389 Fremont cottonwood and willow cuttings to jumpstart riparian restoration by increasing vegetation cover and structural complexity. The long-term goal is to increase local production of large wood to enhance habitat for the salmon and trout populations that are at risk of extinction.
The five-acre, Bureau of Land Management-owned, riparian restoration area is located on an unvegetated portion of a cobble-dominated bar that ranges in maximum depth-to-groundwater from 3 to 11 feet and has a flood return interval of 1-5 years. Cuttings, harvested on nearby lands owned by Western Aggregates and Teichert Industries, were stripped to poles, 4-12’ in length, and soaked for 8-12 days before planting. Cuttings were planted with a species composition of 50% Fremont cottonwood, 13% Gooddings willow, 13% red willow (Salix laevigata), and 14% arroyo willow (Salix lasiolepis). Pod planting consisted of using a backhoe to dig holes down to water and plant 16 cuttings of mixed species per hole. Alternatively, a Stinger was used to plant single or paired cuttings less than 2” in diameter, to depths as low as 5 feet.

The pod and Stinger plantings have been monitored annually since 2011. Results show that survivorship is dependent on species and planting method. Willow cuttings planted in pods by a backhoe survived at higher rates after two years than single species cuttings planted by the Stinger after just one year. This difference is due to the larger size of cuttings planted in the backhoe-dug holes and may also be due to the lack of precision associated with using the Stinger in planting to groundwater depth. 

The plantings have caused increased deposition of fine sediment and accumulation of organic material on Hammon Bar, providing evidence that hydraulic interactions with the plantings promote floodplain heterogeneity. The project may also be helping to restore the natural processes of riparian recruitment and fisheries habitat formation that have been limited on the cobble-dominated bars of the Yuba River. 

John Bair of McBain Associates brought many years of experience from similar projects on the Trinity River to help design the Hammon Bar project. The Riparian Restoration session at SERCAL 2014 included an interesting discussion of why survivorship of plantings on Hammon Bar is higher than survivorship of similar plantings on the Trinity River. The active floodplain of the Yuba River is similar to the Trinity River in that the substrate is artificially course due to historic mining and dams. However, the substrate of Hammon Bar has been mobilized and deposited through fluvial processes, while the substrate at the Trinity River sites is more directly the result of mine tailings.

Monitoring of the Hammon Bar project — funded through the U.S. Fish and Wildlife Service (USFWS) — will continue through 2017 and will include monitoring fish habitat, invertebrate productivity, survivorship, and riparian vegetation. Meanwhile, SYRCL and cbec inc. eco-engineering have completed a plan for developing more restoration projects throughout 18 miles of the lower Yuba River, based on geomorphic analysis, riparian mapping, depth-to-water mapping and ecological flow modeling. Additionally, a study by the Yuba County Water Agency for the Federal Energy Regulatory Commission (FERC) has analyzed flow recession rates under current and historic hydrology. Ongoing analyses by SYRCL and other participants in the FERC re-licensing process are focused on opportunities for assisting the restoration of riparian condition through management of flows.

This project was funded by the Bella Vista Foundation, the USFWS and Pacific Gas & Electric Company. Results suggest that this type of riparian enhancement project is an economically feasible method of establishing additional riparian forest on the lower Yuba River. Monitoring of the project is expected to demonstrate the development of a structurally diverse riparian forest that interacts with hydraulic and biotic processes and creates complex floodplain habitat, pocket pools and log jams. This project is informing the planning of additional projects to improve salmon habitat and many other ecological benefits.

For more information and project reports, visit www.yubariver.org/restoration. — by Gary Reedy, Adele Rife, and Rachel Hutchinson, South Yuba River Citizens League