BONNET CARRE SPILLWAY: At the Bonnet Carre Spillway, two cranes are used to individually lift timbers from bays of the spillway and place them horizontally across the structure. A complete opening of all 7,000 timbers from the 350 bays in the spillway structure requires about 36 hours.
Image: COURTESY OF US ARMY CORPS OF ENGINEERS, VIA FLICKR
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Rain continues to fall (as it has for the past month) in record-breaking amounts across the middle Mississippi and Ohio river valleys, swelling the two waterways and their tributaries. As some residents evacuate and others await word on whether they must flee, the U.S. Army Corps of Engineers is considering its increasingly limited options for containing a major catastrophe already washing away homes and farmland.
Most of those options depend on the volume of water and the length of time that water stresses the man-made infrastructure of levees, dikes and spillways built along the Mississippi.
The Corps partially opened Louisiana's Bonnet Carre Spillway earlier this week to reduce the volume of water heading toward New Orleans. By the end of Friday a total of 264 spillway bays (out of 350) will be opened, according to the Corps, which plans to open additional bays as needed. They are also considering opening some portion of the 125 bays at Morganza Spillway near Baton Rouge as early as this weekend—for the first time in 38 years—to divert Mississippi River floodwaters heading down from the Midwest and Ohio River into the Atchafalaya River Delta, according to The Times-Picayune. If Morganza is opened even partially several thousand homes as well as farms, a wildlife refuge and a small oil refinery in the Atchafalaya Basin would be at risk of flooding in order to prevent a deluge from hitting densely populated Louisiana state capital Baton Rouge and New Orleans.
Heavy rains aside, the current flood conditions can be traced back to a number of factors, including the buildup of shallow flood barriers atop loose soil along the Mississippi and its tributaries over time that narrowed their pathways. This has led to more water running faster through narrower spaces, thereby placing more pressure on the region's levees.
To gain a better understanding of the precarious situation along the Mississippi as well as how such flooding might be mitigated in the future, Scientific American spoke with J. David Rogers, a professor of engineering at the Missouri University of Science and Technology, who also teaches flood control courses for the Corps. Whereas floods are inevitable, their impact can be mitigated through well-designed and constructed flood barriers, proper land management along major bodies of water, and a better understanding of how floods work, according to Rogers.
[An edited transcript of the interview follows.]
How serious is the situation facing communities along the Mississippi (in particular, Memphis, Vicksburg, Baton Rouge, New Orleans)?
The forecasted flows should be within the design capacity of the Mississippi River and Tributaries [MR&T] flood control project constructed by the Army Corps of Engineers between 1931 and 1980. That doesn't mean there won't be any levee failures or other problems, but that it should be within the design capacity to handle it.
Levees and other man-made attempts to regulate water levels often become an issue when the Mississippi threatens to flood its banks. Are such floods an inevitable fact of life along the river, or is it possible to protect all of the communities that have sprung up along the river over time?
We have probably diked off too much of the river's active flood plain; in many cases close to 90 percent of the historic flood plain. We probably shouldn't have diked off more than 75 percent, because the dikes located close to the low-flow channel (pdf) [designed to concentrate flows and increase channel velocity and depth during low-flow periods] are those most prone to foundation problems, due to under-seepage through pervious materials. Floods are an inevitability, and we would need 1,000 years of hydrographic records to accurately estimate a flood with a 100-year recurrence frequency. We have about 160 years of records, so there is a lot of guesswork involved.
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11 Comments
Add CommentSo what do the global warming deniers have to say now that the effects are being seen on the Mississippi River?
Reply | Report Abuse | Link to thisWithout denying or confirming global warming, waiting until the rivers crest has been proven to be not the way to go. If diversion had taken place when the rivers approached the spring melt and rain (which everyone knew was coming)might have been a better choice to open flood gates for gradual relief than waiting for the torrent. Once again I see the water flooding the plain could be used in drought areas that are suffering at the same time as the plains are flooding. Present technology can offer diversion techniques without flooding additional land while putting many many Americans to work building the diversion system. No doubt improvements to present technology could be accomplished but that would only put more people to work. Build conduits along the interstate system now to divert water from future floods and store it in resevoirs for the future global water shortages that have been forecast or route it to drought areas immediately as it is diverted. The Everglades are almost dry and other parts of the nation need water to save crops. Too late this time but not to avoid the next crisis.
Reply | Report Abuse | Link to thisI'm not a dedicated global warming denier; although, I question some of the so-called proof. The Mississippi has flooded for hundreds of years during our occupation of North America. Recent floods have been exacerbated by poor engineering decisions made since 1927. As more people inhabit the area, the floods will become more and more disasterous. But to say the the current flood is caused by GW is a real stretch.
Reply | Report Abuse | Link to thisAlso, by your reasoning, the coldest April on record in the Northwest poinst to global cooling and an imminent Ice Age.
Reply | Report Abuse | Link to thisThey don't wait for the crest. The ACOE uses a trigger flow rate, then opens the gates. This is well before the crest occurs.
Reply | Report Abuse | Link to thisIt will be interesting to see if the flooded farm land produces better after the nutrients and sediments are deposited...maybe flood gates should be built that can flood certain areas in one year and other areas in another year...replenishing used/extracted nutrients...
Reply | Report Abuse | Link to thisJust a couple of observations stewie;
Reply | Report Abuse | Link to thisa) Tectonic activity makes your idea of subteranian cities really silly.
b) Rumor has it that you are mentally ill.
It is nice to see that someone has the ability to think rationally. Flood plains that flood regularly are some of the most fertile in the world. Flood plains that are prevented from flooding have significant drops in productivity over time. Too bad the powers that be don't have that much mental capacity. This A.C.E. guy makes more sense than most but still isn't quite there yet.
Reply | Report Abuse | Link to thisThere's not much can be done about the rivers' flooding. But there's alot to be done to save property:
Reply | Report Abuse | Link to thisThe gov't should require [through insurance companies, FEMA, or other] that all new building in floodplanes shall be mounted on steel barges. Instead of basements, homes shall be built atop a steel or re-enforced concrete buoyant platform. They shall have sloped sides like the bow of typical river barges. They shall be anchored, in four directions, with buried mushroom anchors and heavy chains painted with rubberized epoxy paint. The "barges" may be inset into the ground. When the flood comes the building will simply float up and not drift away. Perhaps the four corners of each building should have retractable/extendable legs, like a PU camper shell, so that after the flood the house can be held aloft and prevented from resettling into its hole until such time and the hole is re-excavated to it's original shape, and the house can be lowered back down.
The added cost can be somewhat amortized by reduced insurance premiums, perhaps in a plan administered by the Federal Government and financed by 0.5% bonds sold to rich Republicans and rendered invisible to the poor blokes who can't afford to live on hillsides.
Perhaps there should be pre-planned designated areas to be flooded, like as you say, during low stages ahead of the crest. This should be done, to varying degrees, most years, during spring floods. Rotate designated areas succeeding years.
Reply | Report Abuse | Link to thisAlso flood large areas and retain the water, not let it drain back into the river after flood stage. These areas could be an agricultural reserve. Also, if large enough in areal extent would have a significant effect on the weather; retaining a wetter atmosphere in the center of the continent later in the year, thus encouraging more reforestation and enabling crops higher in carbon content downwind of the "flood plains".
So, the farther west [ie: upwind] water can be captured the better.
Not an imminent ice age, simply a reordering of weather patterns due to a steepening temperature gradient with altitude [warmer near the ground, and cooler near the stratosphere] due to the increasing "foggy" appearance of the atmosphere as would be seen in the infrared if we could see in the infrared.
Reply | Report Abuse | Link to thisMost areas of the globe are warming, fewer areas are cooling. Various computer climate models showed this would happen even back in the 80's. Remember, higher temperature at the ground -> greater evaporation -> more cloud cover downwind -> cooler daytime ground temperature there -> change in surface wind patterns, etc. This is why we pay smart people to figger it out!