Thursday, April 10, 2008

Watching the Mississippi basin

Has anyone else been watching the USGS flood map this spring?

This is what it looks like today, April 10.



There are at least three things that scare me on this map.

1) All those black triangles represent places where the rivers are above flood stage. Look how many of them there are!

2) Some of the places above flood stage include the Mississippi River at Baton Rouge and the Atchafalaya River at Morgan City. (Recommended background reading: "Atchafalaya" in The Control of Nature by John McPhee. For anyone who hasn't read it: the Atchafalaya River would probably be the main course of the Mississippi River by now, if it weren't for some massive engineering. The Old River Control Structure, which tries to let just enough water into the Atchafalaya to prevent floods in Baton Rouge and New Orleans, nearly failed in the 70's. It's been strengthened since then, but it hasn't faced huge floods, either.) Both places have been a few feet above flood stage for a week, at least.

3) Of the big tributaries of the lower Mississippi, only the Ohio is currently above flood stage. But it's still snowing across the Rockies, the northern plains, and Minnesota:



The Missouri and upper Mississippi drain areas where the snow hasn't melted yet.

I was frantically writing my dissertation in 1993, and water data wasn't on the web for daily ogling. I remember some discussion that the 1993 floods on the upper Mississippi and Missouri didn't result in danger for Louisiana because the Ohio basin was fairly dry that summer.

I hope the Ohio goes down before the Missouri and upper Mississippi rise.

Edit: The National Weather Service flood warning for Natchez, Mississippi (above the Old River Control Structure) says the Mississippi should crest just below the level of floods in 1983:

THE FLOOD WARNING CONTINUES FOR THE MISSISSIPPI RIVER AT NATCHEZ
* UNTIL FURTHER NOTICE...OR UNTIL THE WARNING IS CANCELLED.
* AT 8:00 PM WEDNESDAY THE STAGE WAS 54.4 FEET.
* MODERATE FLOODING IS OCCURRING AND MODERATE FLOODING IS FORECAST.
* FLOOD STAGE IS 48.0 FEET.
* FORECAST...THE RIVER WILL CONTINUE RISING TO NEAR 55.5 FEET BY
TUESDAY MORNING.
* IMPACT...AT 55.0 FEET...FORT ADAMS POND ROAD IS FLOODED.
* FLOOD HISTORY...THIS CREST COMPARES TO A PREVIOUS CREST OF 55.7
FEET ON MAY 31 1983.

According to John McPhee (Control of Nature, p. 53), the 1983 flood was the 3rd largest of the 20th century. (1973 was the year the Old River Control Structure nearly failed.)

10 comments:

1&2 said...

The Atchafalaya is the tributary of the Mississippi that enters the Gulf to the west of the Mississippi's delta, isn't it? This is another reason why I like living inland, and a good bit above sea level.

I mis-wrote that first time around, so I deleted it.

Ron Schott said...

You bet I've been watching it, Kim. Especially since I posted Where on (Google) Earth #118. Knox Landing, LA is offline due to an equipment malfunction as I write, but it's been above flood stage and rising for days now. Natchez, Mississippi is the next station with available data above the Old River Control structure. Ominous...

I just wish I had some more time to seek out historical data to compare the real time measurements to. Since it's not in the national news yet, I presume we're not breaking any records... yet.

Kim said...

Now I've got "Atchafalaya" open in front of me. The Project Flood discharge is around 3 million cfs. Natchez has gauge height, but not discharge, so I can't tell how close we are to Really Bad News. (Six feet above flood stage would be a lot in most places, but the levees down there are immense.)

(And 1&2 - the Atchafalaya's a distributary, not a tributary. It would be a minor bit of terminology, except that the Atchafalaya is the main alternate route to the Gulf of Mexico for the Mississippi's water. It's the safety valve - it's the way the Army Corps of Engineers tries to keep the Mississippi River out of New Orleans and Baton Rouge. And if too much water goes down the Atchafalaya, it will become the new Mississippi, and the Mississippi will become a bayou.)

Elli said...

Well, I guess I should re-read not only "Cooling the Lava" tonight (my intro Volcanoes class is discussing it tomorrow), but also the Atchafalaya section. Good thing my freshman geology professor made us all read Control of Nature so I have a copy!

But the other surprising thing is that water levels are so high in eastern NY / Vermont & NH. Living in eastern NY, I haven't really seen any high streams...but I'm further south than the black triangles on the Hudson.

Kim said...

The Moose River in Victory, VT is running high, Elli. I bet it makes some pretty falls over the andalusite outcrops at Gallup Mills! (The Mad River is high, too - I'm also quite fond of that one.)

And it's a good thing you've always done what your freshman geology professor told you. ;)

Elli said...

Is Gallup Mills the locale with the stretched andalusites? I actually used that as a non-fossil discussion of how to measure extension in Structure last fall. But I don't have any pictures of the outcrop, so I had to rely on my "wonderful" drawings :)

Btw, have you seen "Days of Destruction"? Its about the Heimaey eruption and complements the John McPhee reading nicely. Our department had to order it directly from Iceland, but it was worth it.

Kim said...

I've got a big sample of the rock with the stretched andalusites. Maybe I'll take pictures of it next week, and use the thin section to practice making mosaics with our new camera.

I'll blog about it, and then send you high-res copies.

Elli said...

Thanks!

Eleanor said...

Interesting blog! Was referred over here from another geology blog. My husband is a agro-meteorology researcher at Purdue and I'm a scientific illustrator. We're both fans of geology and seisomology. The Wabash has been pretty high around here, but then, it's spring.

Earl said...

I'm originally from Louisiana and ever since reading John McFee's "Control of Nature," wonder when there's heavy flooding in the Mississippi River Valley if this will be the spring or summer when the Mississippi finally wins the battle with the Corp. The recent flooding upriver seems unprecedented. Could this be the "one?"