Jump to content

Causeway Vulnerable?

Recommended Posts

We've seen in Pensacola and Slidell that 1960s-era causeway structures are highly vulnerable to storm surges. Loss of the causeway would be disastrous for Galveston. So the questions are: could the Galveston Causeway survive a category 4 storm surge? Is the new causeway any better?

I think the answer is that the existing causeway is vulnerable but not as vulnerable as I-10 in Pensacola or Slidell. If we get something like Katrina or stronger (highly unlikely), there is cause for concern. Otherwise, at least the northbound structure should survive.

In terms of height above the water, it appears to be comparable to Pensacola and Slidell. Definitely a minus. These photos show that the bridge is rather low to the water


However, it is somewhat sheltered from wave action, whereas both Pensacola and Slidell were more exposed.

More importantly, the northbound structure built in 1938 is mostly cast-in-place concrete so it is not vulnerable to being lifted up. But the high-level span over the intracoastal waterway is precast beam construction. The structure is most vulnerable at the transition points from precast beam to cast-in-place concrete, where there is at least one low precast beam section at each end. I'm not aware of any provisions to tie down precast bridge deck sections.

The entire southbound structure is vulnerable since it is entirely precast beam and has been having structural problems for years.

In terms of the new causeway being built, there appears to be no special anti-storm-surge provisions (but I can't speak for TxDOT engineering - they would need to answer that question). The design effort was mostly focused on protecting the bridge against barge impact, but since construction began there have been two causeway failures due to storm surge. Slidell apparently had design characteristics that made it especially vulnerable: closed-off ends which allowed air to be trapped underneath the bridge deck, and short independent sections between piers which were easily lifted. The new Galveston causeway reportedly will not trap air and has much longer interconnected sections which should be more resistant to lifting. Furthermore, I don't know the exact height but it looks to be in the neighborhood of at least strong category 4 surge.

So, no cause for alarm but big risks justify extra caution.

Link to comment
Share on other sites

  • 2 weeks later...

The storm surge can still come in through the back of the bay. However, the causeway looks to be built high enough not to get hit by one. Certainly, a head on surge from the Gulf would be stopped by the island, as kjb suggested.

Welcome back, kjb, BTW. I hope your family did OK in the latest storm.

Link to comment
Share on other sites

Thanks Red.

In Katrina, they didn't get much rain but a lot of wind. Just some tree limbs and a few shingles messed up. They were on the West side of the storm in Thibodaux. Power was out for about three days. Andrew was much worse eventhough it was a smaller storm since the east side of the eyewall passed fairly close.

My parents lost power from Rita for about 12 hours and got about 6 inches of rain in the gauge in their backyard. The winds weren't as strong though.

I felt bad because I didn't lose power or cable throughout the storm. Although the trees nearby look like they were going to break at any time.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...