Big Muddy

[Botnst]

Gettin' bigger.

http://www.csmonitor.com/USA/2011/0508/Memphis-and-Baton-Rouge-brace-for-record-breaking-Mississippi-flood

Check your river gages here: http://waterdata.usgs.gov/nwis/rt

[The Swede]

As a kid, I jumped it.

[kerry]

"Mississippi could be flowing at 1.9 million cubic feet per second near the Morganza Spillway later this week."

That is an incredible amount of water. The most I've ever paddled on is probably around 40-50k cfs on the Liard River. Colorado in the Grand Canyon typically does not run about about 35k cfs.

[Botnst]

I attended a briefing hosted by the NOLA District, USACE. The colonel said their models indicate that this flood will exceed the 1973 flood by quite a bit. That was the flood that nearly changed the course of the Mississippi River and a complete re-engineering of the lower MS management system. Col also said that this one could rival or even exceed 1927 flood.

The 1927 flood extended from lower Illinois to New Orleans and from half-way across the state of Mississippi to half-way across the state of Louisiana. The 1927 flood is why we have Chicago blues -- the flood caused the largest single-event migration of Americans in history.

[Hatterasguy]

Rivers flood, this should do wonders for flood insurance.

[Botnst]

Paradoxically, much of Louisiana Louisiana is in severe drought.

[Kuan]

Is this going to be THE 100 year flood? I know further North it wasn't too bad. We crest here early and almost all of it is snowmelt. Parts of St. Paul were closed this year but have since reopened.

[cmac2012]

I hear reports about evacuating Memphis. What, all of Memphis or is there a lower riverside area?

On a trivial note, the Memphis NBA team enjoying unprecedented success in the playoffs. Not that the nation needs a reminder that Memphis is flooding, but games being moved, postponed whatever will no doubt bring it more to the attention of people who don't follow the news much.

[Botnst]

A lot of Memphis is low-lying. It is a river town. As Hattie alluded to, we as a nation fupped duck when we started leveeing to protect populations.Every leveed town means that the water must go somewhere else, which floods another town. Bam, 150 years later we have a river system between two levees. This helps to force the river to self-scour its bed which makes shipping safer for larger vessels.

However, instead of spreading over a large area and slowly receding, water is shunted immediately into the river system causing a huge bulge of water to zoom down the system. If the lower system is already saturated then the water has nowhere to go but up.

Also, the river scouring slowly moves upstream just as a waterfall etches the land upstream, receding higher into the elevation. This scouring proceeds up each tributary, too. This causes local bank erosion and then of course, screams for bank stabilization projects and channelization projects, further exacerbating the problem of increased velocity.

We have created a giant positive feedback loop and we cannot find a way out. Your congressmen love USACE projects in your district.

[Botnst]

Good description of the problem from a business perspective: http://online.wsj.com/article/SB10001424052748703864204576311493351900976.html

[cmac2012]

Where I'm in the dark is: does flooding of farmland with mega acre-feet of water help on some level, the way it did historically, or is water contaminated these days with various chemicals that were just not lying about in centuries past?

I was just reading again about the intentional breaching of the levee which will send much water onto Missouri farmland.

[Botnst]

Originally Posted by cmac2012

Where I'm in the dark is: does flooding of farmland with mega acre-feet of water help on some level, the way it did historically, or is water contaminated these days with various chemicals that were just not lying about in centuries past?

I was just reading again about the intentional breaching of the levee which will send much water onto Missouri farmland.

Normal overbank flooding by a river is a slow rise. Dynamiting a levee with 8-10 ft of head results in tremendous scouring as the water rushes over the farmland. The topsoil will be removed and deposited somewhere else. the farmland will be transformed from flat, easily tilled land to a corduroy landscape which the farmer will have to spend time and money re-leveling.

Had the USACE breached the levee before the flood level neared the top of the levee it would have still flooded the land but would not have scoured it. Indeed, overbank flooding is a great source of natural soil fertility and helps maintain a water table accessible to roots without having to irrigate. One silly thing in modern agriculture is to have a farm near a river using well irrigation. It is unbelievably common. That's a direct result of river management policy.

[t walgamuth]

Originally Posted by Botnst

A lot of Memphis is low-lying. It is a river town. As Hattie alluded to, we as a nation fupped duck when we started leveeing to protect populations.Every leveed town means that the water must go somewhere else, which floods another town. Bam, 150 years later we have a river system between two levees. This helps to force the river to self-scour its bed which makes shipping safer for larger vessels.

However, instead of spreading over a large area and slowly receding, water is shunted immediately into the river system causing a huge bulge of water to zoom down the system. If the lower system is already saturated then the water has nowhere to go but up.

Also, the river scouring slowly moves upstream just as a waterfall etches the land upstream, receding higher into the elevation. This scouring proceeds up each tributary, too. This causes local bank erosion and then of course, screams for bank stabilization projects and channelization projects, further exacerbating the problem of increased velocity.

We have created a giant positive feedback loop and we cannot find a way out. Your congressmen love USACE projects in your district.

This is an excellent easy to understand summary of the problem with the Mississippi.

[cmac2012]

Originally Posted by Botnst

Normal overbank flooding by a river is a slow rise. Dynamiting a levee with 8-10 ft of head results in tremendous scouring as the water rushes over the farmland. The topsoil will be removed and deposited somewhere else. the farmland will be transformed from flat, easily tilled land to a corduroy landscape which the farmer will have to spend time and money re-leveling.

Had the USACE breached the levee before the flood level neared the top of the levee it would have still flooded the land but would not have scoured it. Indeed, overbank flooding is a great source of natural soil fertility and helps maintain a water table accessible to roots without having to irrigate. One silly thing in modern agriculture is to have a farm near a river using well irrigation. It is unbelievably common. That's a direct result of river management policy.

Oh mah Ghod. An extra dimension added. No wonder they're pissed.

What I was uncertain about was whether water that likely flooded small bergs upstream picked up any and all petro distillate available and transferred that down to the floodplain. And then there's the drawback of one's buildings getting flooded. Prior to large permanent communities, regular flooding wouldn't have had as much downside, I can only imagine.

I mean just guessing, but I could see a calculation in value of topsoil added to value of building damaged. I mean of course I get the value of adding soil the way it's always been done in those regions, but I could see farmers having a different POV.

Sounds like a mess. I was working at a power plant on the Missouri River during the 1993 flood; failed levies, flooded roads, entire small towns underwater, etc. Not fun.