The Morganza, Louisiana Spillway has been opened for the first time since 1973 in response to massive flooding in the Midwest.
I went looking for more information on this and reports were muddled, so I’ve put some maps and stats together to help people visualize this event.
Gotta give props to sphealey who has provided some excellent links to the back story behind this event.
Morganza Spillway inundation map with planned 21% open.
Morganza & vicinity - this is the area bounded by the small black box in the map above.
Google Earth image showing features. Red line is 3,900’ spillway. Yellow lines are 9 mile north levee and 16 mile south levee. South levee line terminates at Highway 190 - a clear landmark in other images.
They’re going to divert 150,000 cubic feet per second through the spillway. A common measure of water in the U.S. is an acre foot. This is 3.44 acre feet.
A foot ball field minus end zones is 1.1 acres. This is enough water to fill a football field waist deep passing every single second.
This is only 25% of the capacity of the spillway - it can do 600,000 cubic feet per second.
And here is what would happen if they didn’t open the spillway:
Massive flooding along the Mississippi
New Orleans would be toast, probably worse than when Katrina hit
Legend for colors on map
This was the scene yesterday - they’re opening it slowly so the waters rise in a natural fashion. The deer and black bear in the region can cope with rising water, but not if we slam the spillway open all at once.
As always, thanks to the Wiki fiddlers who produced Morganza Spillway, which provided the background for this piece and the fine predictive flooding maps.
A commentor asked about the opening happening because the Mississippi might change course. This is absolutely correct - just look at this image. See all the oxbow lakes? That's old riverbed that got left behind during a flood. We've artificially constrained the river with levees, which is part of why we have some of the troubles we do.
If they didn't open the spillway the river might just decide to cut its way around it anyway. If that happened there's a chance the primary channel could switch to being the Atchafalaya, which would be an awful mess due to the loss of all the barge shipping facilities on the current channel.
Local TV station WBRZ has a series of videos they've posted on Twitpic. The linked movie was shot standing above the open spillway.
And here's a great piece on Wunderground on the dangers faced due to the age of the Old River Control Structure. If we have any more rain ... well ... just look at this graph. The top line is the famous 1973 flood, and look at how crazy quick volume jumped this year. But climate change, it's a hoax, right?
sphealy has also provided a link to a great historical perspective on the flood control projects of the lower Mississippi, entitled Louisiana River Control.
Here's the final word - Morganza is the big letter A, the river wants to go straight south via the Atchafalaya, but we constrain it so that it goes east down the very long current course. It's entirely unnatural for the river to have such a long delta like that. Mother Nature, she's starting to chafe at our desire for river course stability in the region.