SACRAMENTO, Calif. – A U.S. Army Corps of Engineers Sacramento District project to plant willow poles along 30,000 feet of levees in the Sacramento and San Joaquin river systems is under way, designed to preserve habitat for threatened fish.
The work follows extensive environmental and engineering analysis to ensure that the small, native trees will provide maximum habitat benefit without harming the levees. Planting began Jan. 23 and is expected to conclude for the year by the end of February.
“Throughout these river systems, we’re trying to fix aging levees in a way that balances the environment and public safety,” said Paige Caldwell, the Sacramento District emergency manager. “Planting these willow poles is a great example of how we can preserve critical habitat without increasing the risk of living behind the levee.”
Corps policy generally prohibits trees on levees because they can destabilize levees and make it harder to inspect them or get to them in a flood. But where trees have critical environmental or cultural value, through the Corps levee safety program’s variance process, trees can stay when they can be shown not to increase the risk to public safety. The variance request process requires thorough engineering analysis to determine the impact of vegetation on levee stability. The Sacramento District is the first Corps district to receive a vegetation variance approval under the national policy.
The plantings will be allowed to grow naturally, but the agencies that maintain the levees will be required to trim the willow poles if they grow larger than 4 inches in diameter so they don’t inhibit inspection or threaten levee integrity.
The habitat project is the final step in completing emergency levee repairs the district began in 2007. Levees throughout the Sacramento and San Joaquin river systems in California’s Central Valley were heavily eroded by high river flows following winter storms in 2005 and 2006. Under the Corps’ levee safety program, levee systems that meet Corps maintenance requirements are eligible for federal help with repairing them if they’re damaged in a flood or storm. The district repaired the levees between 2007 and 2009 using large rock called rip rap, which strengthens the levee and inhibits future erosion.
But both river systems are home to a number of threatened fish species, and trees and shrubs lining their banks provide shaded habitat that is critical to their survival. Because erosion was repaired with rip rap, changing the makeup of the river bank, the plantings are needed to ensure their habitat is unharmed. The district designed the plantings in cooperation with the National Marine Fisheries Service and U.S. Fish and Wildlife Service.
A variance was required only for about 14,000 linear feet of plantings, where the only suitable planting location was closer to the levee than Corps policy generally allows, in what’s called the vegetation-free zone. The remaining 16,000 feet of plantings will be placed farther than 15 feet from the water side toe of the levee, where the Corps’ vegetation policy doesn’t apply. None of these plantings are being placed in the actual levee.
The district’s variance is the second variance the Corps has approved in California. In June 2009, the Corps approved a variance for the Sacramento Area Flood Control Agency and the Central Valley Flood Protection Board allowing trees to stay on nearly all of the 42 miles of levees surrounding Sacramento’s Natomas area. The extra-wide levees the Sacramento Area Flood Control Agency is building there make it safe for trees to stay on the old levee.
“We follow the exact same variance policy that we ask other levee managers to follow,” Caldwell said. “And that’s essential to making sure we all have a sound scientific and engineering basis for making judgments about whether or not trees are a risk.”
A $1.8 million contract for the willow poles project was awarded to Erick Ammon Incorporated in September 2012. About half of the total number of plantings are expected to be completed in February 2013, the end of the seasonal window in which the plantings will best survive. The rest are scheduled to be planted in 2014.