Trees and water and levees -- a potentially dangerous mix?

I certainly don't claim to be a green thumb, but I did read today's Morning News story about the Army Corps of Engineers saying that trees planted in the side of the Trinity levees wouldn't increase the risk of a levee breach. The gist of the story is that the pro-tollroad people are showing drawings of lots and lots of trees around the tollroad, which is being built in the levee, meaning that lots of trees would be planted in the side of the levee to match all of the pretty pictures being shown around.

Which leads to two questions: Won't tree roots eventually weaken the levee walls as the trees grow, and knowing how hot the sun pounds down on open areas here in Texas, how are the trees going to be kept alive anyway?

The Corps says "no," but logic seems to dictate (at least to me) that the roots of a tree eventually are going to spread out, loosening soil, etc. At least, that's what the tree guy told me about a tree that was planted moderately close to my house. I'm sure it seemed like a good idea years ago long before I bought the house, but he told me that if I didn't get rid of it, sooner or later, it would start harming the home's foundation. Kind of a "seemed-like-a-good-idea-at-the-time" thing that became a problem only later, when the original decision-makers were no longer around, I guess.

The other question, to which I didn't see an answer in the story (if someone knows the answer, please post it here): Is there going to be some type of gigantic watering system implanted into the levee walls to keep all of this lush vegetation alive? If there is, won't the irrigation system weaken the levee walls all by itself? If there isn't, why bother to plant the trees in the first place, since they're just going to look like matches with burnt tips stuck in the ground by the end of the first summer anyway?

Comments

[David]

The Corps has consistently compromised their own standards on this thing. To make it worse, the NTTA is trying to get a waiver to keep the toll road designed to pre-Katrina standards. This entire fiasco has put that road ahead of everything-- flood safety, the environment, the will of the voters, you name it.

[Capitalist Pig (Aren)]

In your armchair quarterbacking, you reported a misconception.

Trees do not harm foundations in the absence of water drainage problems or foundation leaks. Roots only grow where there is water. Where there is no water, roots do not grow. So instead of blaming trees, let's keep foundations properly maintained and stop ignoring them until they break.

Some believe the silver maple is an exception. They allege that they wrecking foundations and driveways even outside the presence of water. I suspect that's really a communally reinforced misconception, but I don't know for sure.

I don't understand how trees will cause a breach. It's not like anyone is planting a forest. Isn't diverse vegetation is among the best ways to _prevent_ soil movement?

In the article, the Corps's stated reason not to have trees is to prevent impediments to service operations.

[Rick Wamre]

Here's some additional information about the idea of having trees planted in the side of a levee and whether that's a good idea.

The Morning News story has an interesting quote from Craig Holcomb, a pro-tollroad spokesman, who says "that top officials of the Corps of Engineers had reviewed the (pro-tollroad group's) promotional drawings and videos and 'they did not say yes or no' to the depictions of a heavily landscaped freeway. Mr. Holcomb, a former City Council member, acknowledged, though, that 'as a general rule' the corps won't allow trees to be planted in levees because the trees' root systems could undermine the integrity of those levees. He added, however, that 'under certain circumstances' there could be exceptions to that policy. 'And the corps has said they are willing to work with us,' he said." It's kind of a long, vague answer to what is really a pretty simple question. Anyway, here's the link to the News story:

http://www.dallasnews.com/sharedcontent/dws/news/politics/local/stories/DN-trinity_19met.ART0.State.Edition2.42a828e.html

And then an alert reader who preferred not to post this information sent a link to me from a newspaper in Monroe, La., where the Corps is actually tearing down 80-year-old trees that have grown in the levee there for reasons of the levee's structural integrity. So which is it?

http://www.thenewsstar.com/apps/pbcs.dll/article?AID=/20070917/NEWS01/709170316

Still no answer yet to my question about how the newly planted trees are going to stay alive without water, and if there is an irrigation system in the levee, why won't that cause a problem?

[vfl]

One way to keep trees alive without irrigation is a water truck. Ft. Worth has successfully used this method for years.

Usually 2 seasons with some nurturing will ensure stability.

[MJB]

All right. This is what the Corps of Engineers says (http://www.mvn.usace.army.mil/hps/tree_issues_Q&A.htm):

1. Why are trees a problem near levees and floodwalls?

Tree roots that have grown into the levees provide pathways for seepage, especially when the trees are dead. Root balls of trees that are blown over during a storm can create critical voids in the levees. These voids can worsen seepage and weaken stability. Large overturned trees can fall on floodwalls and damage them. Corps guidance is clear: Woody vegetation in and near levees, berms and floodwalls is prohibited.
. . .

4. Don’t trees actually help protect the levees?
We agree that forested areas can actually serve as buffers, or a valuable line of defense, when located on the flood side of levee systems. However, trees that are too close to the engineered structures that protect us (such as levees and floodwalls,) can undermine the stability and effectiveness of those structures.

[Rick Wamre]

Good point on the watering truck, vfl. But is that what is planned and budgeted for or simply what could happen?

[MJB]

The parenthesis and colon messed up the URL in the post above. This should work:

http://www.mvn.usace.army.mil/hps/tree_issues_Q&A.htm

[David]

The pro-toll road lobbyists don't have a lot of credibility when it comes to the pretty pictures they use in their advertising. In '98 it was lakes and sailboats, now it's this tree-lined "parkway." The Trinity Toll Road is not a parkway. Just like the George Bush Turnpike is not a parkway. Just like the Dallas North Toll Road is not a parkway.

We are not quite that stupid. Every time they use the term "parkway," they only shoot themselves in the foot. It's fun to watch!

[Norman Alston]

There are very large numbers of indigenous trees here that do just fine without an irrigation system.

[Bill Kennedy]

MJB... thanks for those excellent links -- you are entirely correct. You can follow my additional comments at this same topic in the Lake Highlands BackTalk. Bottom line = no trees on or near levees now. It all changed because of Katrina.

Now, if only we can get the Louisiana coastline back because the Corp "knew what they we doing with levees" there to! ;-)