Flood safety rules requiring that trees be removed from more than 1,000 miles of California levees would be hugely expensive and environmentally destructive without providing significant safety benefits, state officials said.
California's top water and wildlife officials pleaded in a joint letter to the Army Corps of Engineers that the policy, which would require nothing more than grass on the nation's federal levees, be scrapped in California.
While it might make sense to keep shrubs and trees off new levees, they said many of California's levees are old and have for many decades provided some of the last remnants of riverside habitat.
"We are not aware of any levee failures in the Central Valley that were caused by woody vegetation on levees," Mark Cowin, Department of Water Resources director, and John McCamman, Department of Fish and Game director, wrote in an April 15 letter.
Most Delta levees would be unaffected. But some, particularly along the Sacramento River and around some developed areas such as Byron and Stockton, would be.
Rules discouraging vegetation on levees have been around since the 1940s, but after Hurricane Katrina the corps beefed up its levee inspections and enforcement, said Meegan Nagy, chief of the corps flood protection and navigation division in the Sacramento regional office.
Last year, the corps issued new guidance that prohibits trees and shrubs within 15 feet of a levee or on the levee
The proposal made clear the corps was going to be strict about implementing the vegetation rules. For example, even if an exception is granted, it would only allow vegetation on the lower two-thirds of a levee's water side.
"As a practical matter, it is not implementable," said Mike Inamine, the state water resources department's manager of levee repairs and evaluation. "It would not be a very good use of public funds to spend billions of dollars on an issue that is not a great risk to public safety."
Inamine said erosion, seepage and general stability problems are much greater threats to California's levees than trees.
And, he added, widespread cutting of trees along the state's rivers would trigger environmental reviews that would make such a program extremely difficult.
A lawyer for a reclamation district near Stockton that has federal levees said those reviews would likely result in requirements that agencies replant riverside forests elsewhere, a difficult and expensive prospect.
"It's going to be a big deal," said Dante Nomellini, lawyer for Reclamation District 17 in the Stockton area. "What we need is time to do it, and we need funding."
The rules apply to federal levees across the country. California has some 1,600 miles of such levees, but in Northern California most of them are upstream of the Delta.
In addition, local governments that have applied to be eligible for Corps' assistance in case of a flood would risk losing that aid if they do not comply with the rules. Relatively few reclamation districts in the Delta have applied for that program, Nagy said.
The regulations require clearing trees and shrubs from levees because of concern that water could infiltrate and weaken them through root zones when the roots rot, or when a tree topples over and pulls a chunk of dirt from the levee.
Nagy said that the new guidelines would not supercede ongoing meetings with state and local levee officials to develop ways to protect levees.
Mike Taugher covers the environment. Contact him at 925-943-8257. Staff writer Hannah Dreier contributed to this story.