The Flood of 2011 on the Lower Mississippi is draining away into the Gulf of Mexico. Save for the fact that all that good mud, which could nourish the Louisiana wetlands in Breton Sound and the Barataria Basin, has gone sailing off into the Gulf of Mexico, the Corps of Engineers management of the flood has been deemed a success. The reservoirs on the tributaries of the Mississippi retained water in the uplands until the big river could handle it; the spillways, the New Madrid, the Morganza, and the Bonnet Carre siphoned floodwater off the river and eliminated the possibility of flooding in Cairo, Illinois and New Orleans. The severe drought along the Louisiana coast and in the Atchafalaya Basin dried out the land, and lessened the damage to the land, to homeowners in the protected towns in the Atchafalaya Basin and Western Terrebonne Basin. In short the dry land soaked up the flood that spilled out of the Morganza Floodway.
Which brings us to Act 2 of the Great Flood of 2011: the Missouri River. The St. Louis Post-Dispatch has had a series of articles on flood control on the Missouri River in the last week.
Remember that during the Flood of 1993 both the Missouri and the Upper Mississippi flooded simultaneously, leading to the collapse of the levee systems on both rivers. During the 2008 flood on the Upper Mississippi, farmers on the American Bottom were grateful that the Missouri was not also in flood, because water was seeping under the levee that broke in 1993.
Well, this year we have serial flooding first from the Upper Mississippi and then the Missouri. So unless we have lots of rain in Minnesota, Iowa, and Wisconsin, we will not have both rivers in flood at the same time below St. Louis.
In the old days, before the construction of the six dams on the upper Missouri river, the river tended to flood twice each year, once in April when snow melted on the prairies and washed into the river and the second time in June when the snow-pack in the Rockies melted and streamed into the river. The Flood of 1881 inundated Niobrara, Nebraska, and the town moved to higher ground. The Flood of 1927 had eased off in the late spring, only to reassert itself with the June rise on the Missouri.
The dams were designed to solve to dual annual floods on the Missouri and for the most part they did. Folks who live along the river put its floodplain to other uses: corn and soybean fields, industrial plants, or starter castles on the banks of the river. All of these are threatened by the June flood rolling down the Missouri. The only creatures who will benefit are the birds and the fish and the people who care about their survival. The flood will enhance the work the Corps of Engineers has done to restore sandbars to the Missouri, sandbars, which provide nesting sites for the endangered Piping Plover and the Least Tern, and side channels for the endangered pallid sturgeon. The birds may have a hard time this year while their sandbars are under water, but next year, should the dams do the work they were designed to do, should be great.
It’s the management of the reservoirs to mimic the dual floods that once streamed down the Missouri that is causing the flooding problems this year. The reservoirs were almost full in preparation for the “spring rise” before a heavy rain soaked the Missouri River watershed, which filled them to capacity. Now the engineers have to release excessive amounts of water from the reservoirs. That will keep the flood going through August.
Which brings us to the dams, which also may be endangered. They are old; they are hydraullic fill-read earthen-dams; their floodgates have seldom been opened or have never been opened; the reservoirs behind them are full. And they are holding back a tremendous amount of water. “Earthen dams when overtopped by floodwater, do not stand.” Should the first one go–the Fort Peck Dam, which three miles long–the other five could follow. The Corps of Engineers has expressed confidence in the viability of the dams.
All that mud that comes down the Missouri has been deposited behind the dams. So much so that the cattails grow in the still shallow waters behind the Gavins Point Dam at Yankton, South Dakota, where the Niobrara River has deposited sand from its watershed. After the completion of the dam in 1957, the water table at Niobrara rose, flooding basements. In 1969, the town decided to move again. The Federal Government helped pay for the move.
The problems Niobrara experienced after completion of the Gavins Point Dam are roughly analogous to the problems the Corps of Engineers is experiencing behind Lock and Dam 26 at Alton, Illinois on the Mississippi. Construction of the dam raised the water table and water began seeping under the levee, putting stress on the levee.
When I was writing The Mississippi: A Visual Biography, I tried to figure out why these dams were built. What was their purpose? They were built because the Corps of Engineers could and Congress supplied the funds. They are an extension of the Mississippi River and Tributaries Project, designed to retain floodwaters upstream until the Lower Missouri and the Mississippi could handle them. The Fort Peck Dam and its reservoir are used to produce hydroelectric power, to reduce floods, to enhance navigation, to protect fish and wildlife, to create opportunities for recreation–boating, to irrigated the surrounding prairies, to supply the public with water, and to improve water quality. It’s a tall order.