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Missouri River Flood 2011 Vulnerabilities Assessment Report. Volume 2 - Technical Report

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The duration and magnitude of the 2011 Missouri River runoff event exceeded all other events in the recorded gage history of the river. The thaw of an unusually heavy snowpack coincided with heavy rain throughout the upper and middle portions of the basin. Almost a years average precipitation fell in 2 weeks in May, in the upper basin. This combination and continuing rainfall raised pool levels at the mainstem reservoirs, reaching record elevations at three reservoirs, and requiring record releases from all six dams from late May through late September. Discharges reached 150,000 cfs cubic feet per second 201cfs202 at Gavins Point Dam June 1, 2011 and continued through September, peaking at 160,700 cfs June 27. Emergency spillways were operated at all the dams except Oahe, and flood tunnels were used at 3 dams. The inflows exceeded those estimated for the design storm by 20 percent. Total inflow would have exceeded the entire storage capacity of the Corps reservoir system if it had started empty. Flows peaked in the Omaha area at 217,000 cfs. Fortunately for the reach downstream of Gavins Point Dam, the runoff occurred upstream of the dams and had to pass through the dam system, allowing prevention of much greater peak flows in the river 201examples include 313,100 cfs at Omaha and 338,000 cfs at Rulo, Nebraska202 and prevention of more disastrous damages. In managing the record runoff of more than 61 Million Acre-Feet in 2011 and record releases from Corps Projects, the Corps flood risk management facilities and actions were effective. The handling of inflow and the releases in preventing even more damage than occurred, but the facilities themselves were damaged but still intact and fully functional. While many key repairs have been accomplished and many more will be complete within a year, other vulnerabilities in facilities and operations will take longer to address.

Subject Categories:

  • Hydrology, Limnology and Potamology
  • Civil Engineering

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