Thursday, September 01, 2011

Levee & Trees, Report & Guidance Letter

What the editorial from the Sacramento Bee fails to point out clearly, is that while the study finds that trees along the base of the levee can sometimes be helpful, the major problems are trees up the sides and tops of the levees and the access thus given to high or flood waters when dying or diseased.

The original policy is here.

The Army Corps published a Policy Guidance Letter February 9, 2010: Variance From Vegetation Standards for Levees and Floodwalls.

Levee denuding is a policy that makes sense, as we posted on before and the article quoted notes, “Worldwide, in countries such as the Netherlands and China, serious levee systems are cleared of trees”—though it does render some harm to the view field, the trade-off in increasing public safety trumps that.

An excerpt from the Bee editorial.

“When it comes to trees and levees, the U.S. Army Corps of Engineers needs to revise its one-chainsaw-fits-all policy.

“A new study by the Corps reveals why.

“The study, conducted by an Army Corps research unit in Mississippi, examined how trees affect flood-control levees in California, the Pacific Northwest, New Mexico and Mississippi.

“It found that trees actually strengthen levees in some situations. It also urged that engineers conduct site-specific evaluations to determine if trees on levees are harmful or beneficial, according to a report Saturday by The Bee's Matt Weiser.

“The Corps didn't need to commission a study to inject some common sense into this debate. But we are glad it did.

“Ever since Hurricane Katrina, the Corps has been rigidly enforcing a policy of no trees on levees, regardless of circumstance. If that policy were to stand, local flood agencies would have to spend millions removing trees in California. And people who have grown accustomed to see gorgeous old cottonwoods and other trees along waterways would have to encounter riverbanks denuded of shade and wildlife habitat.”