Question about NOLA levees:

[karlrschneider]

They are reporting -one- has been breached but "others are okay". Wouldn't that just mean the RATE of flooding is lower than if, say several others were also compromised? Won't the "bowl" fill up just as full only a bit more slowly? I don't get it.

[NMDemDist2]

1. the Weather channel just reported 3 levee breaches n/t

[nashbridges]

2. It depends on

What kind of breach it is and where it is located. N.O. isn't just one big bowl, it's actually a few bowls kind of sitting together. If a levee fails parts of the city can get flooded but the water can't make it to the rest of the town.

If there are multiple breaches then the risk of flooding the entire city increases dramatically.

The rate of flooding depends on what kind of breach it is. If a levee ruptured all the way to the foundation, then eventually the entire lake would empty into the city. Since the breaches this time around seem to be happening because the water level is higher than the repairs in the levees, the water will stop once the level in the lake drops.

[karlrschneider]

3. But once "one" of the "bowls" fills up, won't the water spill over to the

next one(s)? What I'm asking is what would prevent the water from rising until an equilibrium with sea level is reached?

[CornField]

4. The pumps -- if any of them are working in the area

The pumps were supposed to be the fail-safe against the entire city flooding in case of an isolated breach. Unfortunately, they were not able to repair all the pumps prior to this storm hitting.

[karlrschneider]

5. Ah! Okay, I had assumed (not smart) the pumps all sucked from the

same (lowest) point. Do you know how the sewer system is arranged? I have no idea how that is handled...

[necso]

6. There are

distinct, separate low-lying areas (where flooding one does not necessarily mean flooding another) protected by levees. More central NO is in a different area (bowl) than some of the more eastern areas.

Here is a map that shows (some of) the eastern area: http://www.mvn.usace.army.mil.nyud.net:8090/pao/response/chalmette.asp

(Oh, the picture shows only some of the levees, specifically those for hurricane protection of this small eastern area. But if you imagine in the levees along the Mississippi, it gives a decent idea of one "bowl".)

Here is a better map:
http://www.kathryncramer.com.nyud.net:8090/./photos/uncategorized/map.jpg

With Katrina, some levees protecting the eastern area were basically overwhelmed (from Lake Borgne), while more central NO was effected by breaches that probably shouldn't have occurred. (Best data that I have at the moment.)

Most of the "reporting talent" (wherever it is found) has little or no idea of what they are talking about, and some on the administration side are trying to obscure important distinctions in order (to try) to support the "category four storm, levees -- never designed to meet this -- were overwhelmed" line that spins the damage as a no-fault situation, whereas much of the damage apparently resulted from (private contractor) work that wasn't up to specification (real shocker there). (The full category four effects were not felt in NO, and the levees protecting the more central areas should not have failed. -- Again, best data.)

Personally, at this time, I am waiting for some reliable information before trying to place the current data stream into context, separate it into fact and fiction, etc.

Here is a decent article that talks about Katrina damage. Hopefully, we will get similar data when this storm has passed... but I ain't countin' on it.

(The article doesn't seem to talk much about a barge(s) ramming levees and breaching them.)

[karlrschneider]

7. Thanks for the very informative post!

:-)

[necso]

8. More properly, the area encompassing

St Bernard Parish would appear to be three smaller bowls (as shown in the second pic). But my point (with the first linked pic-in-page) was the separation of "central" NO in terms of flooding from other areas. (The first pic also better shows the proximity of Lake Borgne.) The correct url is: http://www.mvn.usace.army.mil/pao/response/chalmette.asp

The second pic shows the importance of the breach in the Industrial Canal levee, because there is an intermediate structure (with pumps) between much of the parish and Lake Borgne, which structure may have stopped the storm surge. (Note the deliberate breaches in this structure and elsewhere.)

However, even with the better map in the second picture, there are still areas where the source of flooding appears unclear, and so one awaits some impartial study.

...

On another note, I am happy to see that picture caching place (.nyud.net:8090) doesn't eat non-picture URLs that careless people stick in.

Editing is such a drudgery... and I get bored so easily.