Keeps on Rolling - but where.
Is this the year Ole Miss decides to break loose?
Back in '08 I noted that conditions were lining up for a risk of the Mississippi breaking out of its path, but that it was a low probability scenario/
Well, 2011 is looking much worse and there is now low probability that the lower Mississippi will not break out of its historic path...
So, the issue is the Atchafalaya River, a distributary of the Mississippi, which is tangent to the Mississippi at Red River Landing.
The Mississippi would like to break out of its current channel and move west to a shorter path to the Gulf, ie along the Atchafalaya river channel, coming out 100+ km west of New Orleans.
This would be inconvenient, to say the least, and for decades the Army Corps of Engineers has been making sure it won't happen, in particular through the Old River Control Structure a set of three dams at Red River Landing, which controls the amount of water going from the upstream Mississippi to the Atchafalaya.
Old River Control Structure (click to embiggen)
The problem is the pulse of water from heavy rains coming down from the Mississippi/Ohio River junction up at Cairo, IL, currently headed for Memphis TN.
It is looking to cause second highest flood level in recorded history on that part of the Mississippi, and all time record flooding on the lower Mississippi, particularly at the Old River Control Structure.
Mid-river is closed to barge traffic because Corps of Engineers is concerned that barge wakes could overtop levees in places near peak flooding - gates and spillways are near maximum flood capacity.
That is if there is no more rain before then... then being roughly May 23rd
(hey, group velocity and dispersion of flood water in river channel would make a really good candidacy question...)
Of course the forecast is for unsettled weather in the south-central US with gulf moisture moving up into lower western Mississippi drainage basin.
Those dams will probably have flood water bypassing them, and possibly be overtopped, and it is not clear they will hold, the lateral forces will be large and there is a risk of the damns being undermined.
If they give, the Mississippi is moving most of its water west, and it may not come back.
As before River Watch at NOAA has the gory details...
65+' at Red River Landing May 23/24
Current forecast, assuming no rain, has the flood at 6" below the levee tops when it gets to New Orleans later, according to the wunderblog.
Gonna be interesting...
MODIS Mississippi (click to embiggen)
MODIS imaging at NASA of Cairo IL -> Memphis TN stretch of Mississippi
Jeff Master's Wunderblog has good summary
Jeff is planning a more detailed discussion and scenario evaluation closer to peak flood
another good summary at John A Weeks III structures geek webpage
very good background discussion at Americas Wetland Resources
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In retrospect, maybe Congress should have used Katrina as opportunity to walk before the River makes it run.
Sooner or later, the Mississippi is going to jump. The best time to abandon New Orleans would have been, you know, when it was already abandoned.
I've always found this topic fascinating. Thanks.
Classic discussion of the ORCS in John McPhee's "The Control of Nature"
@beowulf: There is a reason New Orleans was not abandoned after Katrina: the port. Lots of stuff (e.g., grain from large areas of the Midwest) moves by barge along the Mississippi River and its larger tributaries. Much of that is exported (imported) and has to be transferred to (from) an ocean-going vessel somewhere. Currently, New Orleans is that somewhere. If the Mississippi jumps, there will be a period of at least several years where there won't be a somewhere--I would assume that the new path won't be fully established right away even if the jump does happen. That would be bad news for the US economy since we don't have anywhere near enough transport capacity to move it any other way--and bad for the world as well, since cheap US grain won't be available outside North America until a new port can be constructed on the Atchafalaya.
AWR has some useful diagrams, but reads like government propaganda.
This seems like another short-sighted and ill-fated attempt to "control nature" for the benefit of entrenched interests. (When I was growing up, we were supposed to be grateful that the forest service was preventing all forest fires. That didn't turn out so well.). Even when the river jumps, there will still be a significant amount of flow to the current MS river. With a little work and inconvenience, people will adapt. Yes, some towns along the two river may be adversely affected. But I'm guessing that the longer we postpone the inevitable, the most inconvenient and costly it will be to adapt.
This sounds like a good example of how a government jobs program could provide short term jobs while investing in infrastructure that will pay long-term benefits. Too bad stimulus is a bad word this year.
"...there is a risk of the damns being undermined."
Damn! (Or is it "Dam"!?)