Army Corps of Engineers: "Five Flood Facts (II)" - KTIV News 4 Sioux City IA: News, Weather and Sports

Army Corps of Engineers: "Five Flood Facts (II)"

Five Flood Facts (II)

Daily, the U.S. Army Corps of Engineers, Omaha District, Missouri River Joint Information Center receives flood questions through a variety of communication venues ranging from phone calls and e-mails, through Facebook to simple Tweets via Twitter.

In an effort to better assist the public in understanding the scope and extent of this unprecedented Missouri River basin flooding, the following answers to commonly asked questions are provided. These focus on the very core of the Corps flood mitigation efforts – its dams and reservoirs.

Where are the dams/reservoirs that comprise this system?

The mainstem reservoir system is composed of six Corps dams on the Missouri River: Fort Peck in eastern Montana; Garrison in central North Dakota; Oahe, Big Bend and Fort Randall in South Dakota and Gavins Point along the South Dakota/Nebraska border.

The approximate total flood control storage of these facilities is as follows: Fort Peck: 3.6 million Acre Feet; Garrison: 5.7 million acre feet; Oahe: 4.3 million acre feet; Big Bend: 177,000 acre feet ; Fort Randall: 2.3 million acre feet; and, Gavins Point: 108,000 acre feet.

How are the dams operated?

The Missouri River Mainstem Reservoir System is multiuse and is operated through the difficult challenge of balancing eight, diverse, Congressionally-authorized purposes. Flood risk management is but one of these mandates which direct that the reservoirs capture spring and summer runoff and allow the Corps to manage releases throughout the year in order to accommodate the other seven authorized purposes: navigation, irrigation, water supply, hydropower, fish and wildlife, recreation, and water quality.

To manage this the Corps follows the directions of the Missouri River Mainstem System Master Water Control Manual. This Master Manual is a water control plan that helps guide how much water should be released, when, and for how long from the six reservoirs for the benefit of the entire Missouri River Basin. The Master Manual hydrology (runoff volume, timing, shape of watersheds, etc) is based on over 100 years of historical runoff records (1898-2004).

The Corps revised the Master Manual in 2004 following a 14-year period of public involvement to balance all the competing uses for the Missouri River. Deriving input from residents and farmers who live along the Missouri River, in addition to local, State and federal elected officials, hundreds upon hundreds of alternatives were analyzed and considered during this process. The Corps made every effort to create this document based upon input from all manner of stakeholders throughout the entire basin on how to optimize the reservoir system to serve all the purposes for which it was authorized and constructed.

Each year, an annual operating plan is developed to make necessary adjustments to the reservoir operations based on current and projected annual conditions, such as: amount of water received the previous year, rainfall events, plains snow pack and mountain snow pack. The annual plan is circulated every fall, and public meetings are held through the Missouri River Basin to gain input from the public and tribes. In addition, the actual operation is reviewed and, if required, adjusted on a daily basis depending on current and forecast conditions. In light of this flooding, it is important to note that, in 2011, the dams have been operating solely for flood risk reduction.

During this natural disaster, have the dams ever been in jeopardy of failing?

No, the dams are safe. The Corps has a vigilant dam safety program. The dams are routinely inspected and maintained on a rigid schedule and are well-prepared to handle the flood water. This is what they were designed to do. Our dams are structurally sound and are not experiencing any signs that indicate impending failure.

Has this system worked as planned and what would have happened if this system had not of existed?

The mainstem reservoir system provides flood control by capturing runoff during period of high inflows and releasing at a later time in a controlled manner. Record inflows have been recorded in the Missouri Basin this summer. June was the wettest single month on record and May was the third wettest month on record. Runoff during this period has exceeded the reservoir design flood; however the system continues to provide flood risk reduction despite the record inflows and releases.

If this system were not in place, flows on the Missouri River would have been considerably higher than those experienced during this event. Studies are ongoing to determine what the flows would have been had the system not been in place and we will release that information as soon as it becomes available.

Could more reservoir-held water have been evacuated earlier this year?

At no time prior to the repeated rounds of heavy rain in the upper basin in May did we have reason to evacuate water at a higher rate. Operation of the reservoir system is based on the best available information at the time, not on hunches or long range forecasts which are notoriously inaccurate. We closely monitor the snowpack on the plains and in the mountains throughout the system, and we were well positioned to handle the expected runoff with normal to above normal rainfall; however, there was no way to predict the record rains that fell over the eastern half of Montana, the western Dakotas and northern Wyoming in May.

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