I previously listed flood control as a major benefit that the construction of the dams created. Prior to the construction of the dams, the Missouri River periodically overflowed its banks. Some of these floods were of major consequence, while others were minor. However, because of the wide spread effects of these floods, the congressional legislation which authorized and later funded these dams was titled “ The Flood Control Act of 1944”. Because of the length of the Missouri River, damage from these floods ranged from Montana downstream to the junction with the Mississippi River near St. Louis, Missouri, and then lent those flood waters to the Mississippi River, where damage continued on down the river to the Gulf of Mexico. These floods affected farm lands, urban areas, tore out bridges and roads, ruined houses and businesses, and destroyed lives and killed people.

The cost of these floods was enormous. The completion of these dams greatly alleviated these floods on the Missouri River. Recent floods on the Mississippi River are a reminder of how serious floods can be. These Mississippi River floods would have been much worse if the Missouri River dams had not provided flood control on the Missouri, therefore allowing the damming and storing of flood waters, and delaying their delivery into the already flooded Mississippi River valley downstream. Is it a perfect system? No. In order to build these dams, land had to be acquired for the dams and reservoirs. Much of this land had to be acquired under the right of eminent domain from unwilling land owners through condemnation. Many of these condemnation cases took years to settle, and many of the land owners were never truly satisfied with the final settlement. The land acquired generally extended beyond the high water mark of the reservoirs, often times to the top of the bluffs bordering the river. The line of acquisition is generally referred to as the “Take Line”. In South Dakota, the federal government acquired approximately 523,000 acres of land, most of it river bottom land which, when planted to crops, was highly productive. North Dakota was similarly affected.

So what has been the result of this massive construction program? As far as flood control goes, the results have been excellent. The Corps of Engineers estimates that, since completion of the system, flood damage savings have amounted to $24 billion dollars. That is 24 BILLION DOLLARS!! The Corps has also stated that the cost of the dams adjusted to 2002 dollars is $15 billion.  Averaged over the time since the completion of Fort Randall Dam, which was the first to begin storing water in 1955 and was completed in 1956, that amounts to three hundred seventy five million dollars per year in flood damage savings. In my humble opinion, that is a significant savings. It must be remembered that Fort Peck Dam in Montana was completed as a WPA project in the 1930’s, and was not a part of the Pick-Sloan Plan. However, some improvements to Fort Peck Dam were included in the Flood Control Act of 1944,and it does lend some flood control to the system.

These flood control benefits accumulate as the river progresses downstream. This is obvious. While Montana, North Dakota and South Dakota realize significant flood control from the dams, most of the benefits are realized in the downstream states. These benefits must not be lost. Will sediment accumulation destroy these benefits? Over the long term the benefits will be greatly diminished, but probably not totally lost. An example is Lewis and Clark Lake behind Gavins Point Dam. This dam and reservoir act as a power production and water release control dam. The reservoir does not fluctuate much in elevation, and could be termed as a “pass through dam”. It does not act as a major flood storage reservoir. This is also the reservoir most visibly affected by sediment, with large deltas and sand bars with aquatic vegetation growing on them.

The Corps of Engineers has estimated that in approximately 100 years the reservoir will be totally filled with sediment. Will this seriously affect the flood control benefits of this reservoir? No, as it was never designed as a flood storage unit. Lake Sharpe, the impoundment behind Big Bend Dam, serves a similar function, being primarily a power production unit, with irrigation water, domestic water and recreation also serving as primary functions. However, this reservoir has a narrow operating range, and flood control provided by this reservoir is not a significant factor.

This leaves the large reservoirs. How soon will they fill in and thereafter provide very little in the way of flood control? The only estimates I have heard estimates a thousand years as the fill in time. However, we are seeing some of the ill effects of sediment accumulation now. While this accumulation does not decrease flood water storage to any great degree, it does create a different type of flooding. That is the raising of ground water tables in some areas, with a resulting affect on crops , vegetation, and structures such as houses and businesses.

In the Williston, North Dakota area, the sediment plume from the Yellowstone River has raised the ground water level into the root zone of the crop area in the Buford-Trenton Irrigation District. This has flooded out crops, and has resulted in a federal buy-out of the district at a cost of 40 million dollars.

In the Pierre/Fort Pierre area of South Dakota, sediment deposits from the Bad River, coupled with winter icing conditions and the release of water from Oahe Dam upstream has raised ground water levels to the point of flooding and damaging basements. The federal government is in the process of buying out approximately 180 homes at a cost of 35 million dollars.

A similar situation is beginning to occur in Bismarck/Mandan area in North Dakota, With an estimated buy-out cost of 100 million dollars. So, while sediment accumulation has not resulted in significant loss of flood storage capability to date, sediment accumulation is obviously a problem. It must be addressed. The longer the sediment continues to accumulate, the more insurmountable the problem becomes, as the costs of attacking the problem will continue to rise. We must work now, to preserve as much as we can of the flood control benefits these dams and reservoirs provide. It is obvious to me that a benefit of 375 million dollars a year is significant. We can not afford to sit on our hands and wait for something to happen. We must begin now.