I posted this under "surveying" to see if anyone has any experience surveying major flood control levees. A levee broke along the Missouri River yesterday in southwest Iowa. One of the biggest concerns I've heard from Corps of Engineer people is that the earth levees are continually at the mercy of badgers or other burrowing animals. I've heard the Corps doesn't even want rebar driven into the levees for control points.
The Missouri River flood is just beginning and predictions are that this will continue all summer or even into fall at levels several feet above what is now happening. The Corps is taking a lot of heat because the dams in the Dakotas were supposedly too full to handle the spring rains and upcoming snow melt. Flood control measures took a backseat to recreation and environmental issues in the minds of many people now affected. They have to release the water from all the dams because if one of those would give, it would be a chain reaction. Lewis and Clark's river is certainly being unruly.
Here is a link to flood pictures from the Kansas City Star.
http://www.kansascity.com/2011/06/13/2948373/missouri-river-flooding.html
The LSU Center for GeoInformatics (C4G) has surveyed ALL of the flood control levees in South Louisiana as well as ALL of the Hurricane Evacuation Route highways. We have accomplished that with our GPS Real Time Network of 60+ Continuously Operating Reference Stations networked into a cellphone correction system. The New Orleans District Corps of Engineers has employed our system since after Hurricane Katrina.
Crevasses commonly occur AFTER a sudden drop in water levels, more often than during a flood stage event.
I don't know what the recent crevasse was caused by, though.
I have surveyed various levees for the COE in SE LA for years. Crevasses, slides, sand boils etc.
Various levee failures are the result of poor soils here. From the look of your pictures, the levees look like they have a very loamy soil. The land is agricultural and the borrow pit may have been in close proximity.
The levees look similar to some "ring" levees that are built here along the Lower Mississippi.
One of the big fears of major California flooding is the fact of the network of agricultural levees that are in place. Subsequent land development are risky.
Survey baseline control is set along the C/L of the levee at determined distances and at determined stationing and all PIs etc. pipes/caps.
field survey (x-sec) & traverse control - buried 60d nails
Here in SE LA , the nutria rat causes a lot of damage to levees.
One of the local SWAT teams shoots them in the early morning hours for practice even.
IMO, a good levee is made of good soil, based on erosion fabrics along with flood side rip-rap in addition to native flora to absorb and and diffuse flooding.
http://www.houmatoday.com/article/20100421/ARTICLES/100429838
http://www.houmatoday.com/article/20100831/ARTICLES/100839852
here are a few pic that I took about a month after Katrina on the MRGO levee below New Orleans.
We were tasked with providing a new baseline for emergency construction.
There Is No Such Thing As A Flood Control Levee
There are only river or flood confinement levees. The narrower you channel the flow the higher the flood elevation, thus allowing a smaller flood the oportunity to top the levee.
A proper flood control levee must allow the river an adequate floodway. That generally means you start your levees at least a mile from top of the 1 year floodway, generally equal to the top of bank. That makes that 1 mile strip only suitable for farming of certain crops, corn not being one of them. With this years rainfall that area could easily be under water for 3 months.
The current levees do not have to be completely removed, just lowered to the 10 or 25 year level. Then they should construct cross levees from the river side to the 1 mile levee at the same elevation or slightly lower as the riverside levees. These segments should be at least 10 miles long. There should be armored overtopping chutes at the upstream end and on the cross levees with a flood control discharge dam to the river at the lower end. Provisions should be made at the dams for portable pumps, but permanent pumps to be at municipal or state expense.
Existing small towns may be allowed to remain within that 1 mile zone but no flood insurance will be sold for new construction and only 1 reconstruction for existing structures allowed but not at a full reimbursement level.
Special studies must be down for cities. For instance Saint Louis could remain but a 2 mile overflow to the West must be created for a Missouri River cutoff plus the 1 mile on the Ilinois side must be widened from 1 to 2 miles for the Mississippi. That just might equal the stream width we saw leaving Saint Louis in 1993 a day or two after the rivers peaked there. An alternative might be an even wider cutoff from Peruque on the Mississippi to the Missouri West of Saint Charles and back to the Mississippi near Arnold. They best have a whole lot of shovels ready.
Paul in PA
There Is No Such Thing As A Flood Control Levee
Our levees parallel the river and its major contributors. The levees aren't the problem. People are the problem.
First, we have the popular notion that flood control dams must also be recreational hot spots in order to achieve the alleged benefit to cost ratio required for funding. They are viewed as revenue generators rather than strictly flood-based projects. The result is that the rivers never have what a historian would call 'normal' flow. The flow is 'managed' to provide the best lake levels for the 'revenue generating' side of things. Then when Mother Nature comes knocking loudly, it is too late.
