By Matt Weiser
Sacramento, CA (April 14, 2012)- The U.S. Army Corps of Engineers will plant more than 30,000 trees on Sacramento River levees next winter, a move that would seem to contradict its own policy calling for levees across the state to be stripped of their trees.
The Army Corps in 2007 advised California levee managers that trees and shrubs threaten levee stability and must be removed. The order, which has been put on hold while negotiations continue, would eliminate millions of trees from hundreds of miles of levee in the Central Valley.
It was the first time the national maintenance standard had been imposed in California, which has long operated under separate rules that permit trees. Those trees now compose most of the remaining riparian habitat in the region, providing vital food and cover for wildlife.
In a little-noticed exemption, however, the Corps in October granted itself permission to plant more trees. Officially called a “variance,” the move applies to 83 sites, mostly along the Sacramento River, where the Corps performed emergency erosion repairs after storms in 2006. Those repairs involved covering the eroded levees with giant hunks of rock, called riprap. Now the Corps will go back to those sites to plant willow trees and bushes to improve the habitat altered by the riprap.
The Sacramento District of the Corps sought the exemption from its headquarters in Washington, D.C. Claire Marie Turner, a project manager at the Sacramento district, called it evidence the policy can be flexible by allowing trees where they are needed for habitat and don’t harm levee safety.
“It provided us an avenue to say, ‘The policy doesn’t apply, and here’s why,’ ” Turner said. “We did examine this from a hydrologic and geotechnical perspective, and found that planting these willows will not impact levee integrity.”
The Army Corps policy allows nothing but grass to grow on levees. In light of the state’s objections, the agency has delayed enforcing the policy in California, and no trees have been removed from area levees. Instead, the Corps gave state officials until July of this year to propose an alternative. If the rule is ultimately imposed, local levee maintenance agencies that don’t comply would lose access to federal disaster recovery funds. The state’s proposed alternative, which has yet to be approved, would adhere to Corps policy on newly built levees – in other words, no tree planting – but trees would be allowed to remain on existing levees.
Unlike most of the nation, California’s levees were intentionally built close together in the wake of the Gold Rush in order to speed river flow to scour out mining sediment. It was a short-sighted decision. Among other things, the design eliminated natural floodplains between the levees where trees can grow. As a result, trees shading levees today provide virtually all of the riverside habitat that remains in the Central Valley. State officials and environmental groups have pressed the Corps to let these trees stay, arguing that they provide critical bird habitat and shade that keeps the water cool for migrating salmon.
Bob Wright, an attorney at Friends of the River in Sacramento, said the Corps exemption illustrates the policy’s flaws. He noted, for example, that it took a full year for the Sacramento District of the Army Corps to obtain the exemption, even though the entire process occurred within its own agency. It will have been nearly six years since the levees were stripped for repair, he said, until they are replanted.
“That’s a delay factor in which the people are deprived of the scenic beauty of the trees, and the fish and wildlife are deprived of the habitat,” Wright said. “When you think about the Corps having to seek a variance from itself to replant vegetation, that’s a bad joke.” Friends of the River is suing the Army Corps in an attempt to overturn the tree ban. The California Department of Fish and Game also has filed a notice of intent to sue.
On April 3 a bipartisan group of 35 House members from California, led by Rep. Doris Matsui, D-Sacramento, wrote the Corps to demand revisions. Rep. John Garamendi, D-Walnut Grove, said he is considering legislation that would exempt the entire state from the Corps policy. “The national policy makes no sense in California,” Garamendi said. “First is the expense of having to comply. Secondly, the levee districts are put in an impossible situation of having to destroy habitat.”
The Corps will plant trees at 83 sites on 5.6 miles of riverbank from Tehama to Lathrop. Many are in Garamendi’s own neighborhood in the Sacramento-San Joaquin Delta, including sites near Walnut Grove, Clarksburg and Hood. The variance allows two kinds of planting. On about half the sites, the Corps is allowing only shrub-sized willow species. This applies to locations where the levee is so narrow that there is no flat ground for planting. In such cases, shrubs will be planted on the levee slope at the water’s edge, also called the “toe” of the levee. Even these must be chopped off when the trunks grow to between 2 and 4 inches in diameter. On the other half of the sites, full-size willow trees will be allowed because there is flat ground available away from the toe.
Corps officials say the intent is to keep large roots out of the levee structure itself, also called the “prism,” to prevent roots from compromising the levee. “Basically, we wanted to create shaded riverine habitat with the least amount of impact to the levee prism as possible,” said Paige Caldwell, chief of readiness at the Army Corps Sacramento District.
The agency’s own research provides little justification for these limits and, in fact, contradicts it. A team of researchers at the Corps concluded in a study last year that trees planted at the toe actually increase levee safety because roots offer a reinforcing effect. The Corps aims to do the planting between December and March. It will hire a contractor, and does not yet have a cost estimate.