August 15, 2011
This week, the topic addressed is how the Corps is getting ready for the 2012 runoff season.
Won’t adding more flood control storage better prepare the basin for 2012 runoff? Wouldn’t more storage have prevented the 2011 floods in the first place?
The current 2012 weather forecast predicts a 66.6 percent chance of normal or below normal precipitation and a 33.3 percent chance of wetter than normal conditions. However, the forecast for the fall of 2011 is that conditions will be wetter than normal. Both of these predications contributed to the drawdown decision. Further consideration was given to the low probability of the 2011 amount recurring (a 0.2 percent chance) again in 2012.
The Missouri River Mainstem Reservoir System is designed to manage runoff in order to provide time for downstream communities to prepare for high water. Adding more flood control storage to the system prior to the 2012 runoff season would keep water releases high throughout the fall in order to lower the reser voirs below the base of the annual flood control pool storage of 56.8 million acre feet. That would mean high water on temporary and permanent levees and in the floodplain longer. This would not provide enough time to inspect, assess and repair infrastructure throughout the basin before the 2012 runoff season and would increase the potential for damages and overtoppings and breaches. No options can ensure 100 percent flood-risk reduction.
Our foremost priority is reducing the risk of further damages and getting affected homeowners, farmers and businesses back on their properties to begin repair and recovery efforts as quickly as possible.
What went into the Corps’ drawdown analysis, and how was that option determined?
Our staff experts looked at eight different drawdown options and carefully considered how each strategy impacted multiple criteria. These factors include: weather forecasting; additional flood control storage; federal and non-federal levee conditions; other authorized purposes; Tribal concerns; funding; contractor capability; construction during the winter; the inspection, design and repair process and how to safely evacuate the floodplains.
All of these criteria were analyzed through the context of "how best to be ready for 2012." It was determined that too fast of a drawdown could increase risk of damage to permanent and temporary flood-risk reduction structures and might cause riverbank erosion. Too slow of a drawdown would maintain high releases and high water in floodplains and on temporary and permanent levees too long and would not provide adequate time to inspect, asse ss and repair damages throughout the basin. The strategy has two operational aspects: one to help evacuate the reservoirs out of their exclusive flood control storage zone and another that will allow time to assess the drawdown strategy.
The goal is to evacuate these historic and unprecedented floodwaters as safely and responsibly as possible and bring the entire system back to its full annual flood control capacity of 16.3 million acre feet by March 1 - the date, generally thought to be the start of the spring 2012 runoff season. This will put the flood control pool at a system storage level of 56.8 million acre feet.
If the Corps won’t increase flood control storage for 2012, will it in the future?We have begun a post-flood assessment that, among other things, will analyze how dam and levee infrastructure performed during the 2011 Flood and whether additional flood control storage is necessary. Due to sheer size of the basin and the complexities of the dam/reservoir system - as well as the need to fully determine possible impacts to the other authorized purposes - these studies will take no little time. However, the Corps is fully committed to work closely with its stakeholders in collectively determining the path forward for the optimal operation of the Missouri River Mainstem Reservoir System.
It is a very important fact to note, however, that prior to the Flood of 2011, and since 1881, 16.3 million acre feet have been adequate to capture spring runoff and manage water flow through the system.
What will releases look like from Gavins Point and the other dams for the rest of the year?
As always, the release strategy is subject to change based on daily conditions and alternations in the forecast. Providing for slightly higher-than-normal fall precipitation, releases out of Gavins Point will hold at 150,000 cubic feet per second until Aug. 18. On Aug. 19, releases will be at 145,000 cfs, and then they will continue to drop by 5,000 cfs every day until reaching 90,000 cfs on Aug. 30. Releases will hold for two weeks during inspection of dam infrastructure and continue to drop by 10,000 cfs every two days until reaching a more normal fall release rate of 40,000 cfs around Sept. 30.
Refer to the online resource for specific dates and drawdown schedule, as the releases are subject to change based on actual weather condi tions: http://www.nwd-mr.usace.army.mil/rcc/reports/twout.html
Releases of 85,000 cfs, the estimated release to get flows inside the channel at Bismarck, ND and Pierre SD, will be reached at Garrison around Aug. 17 and at Oahe around Aug. 27, based on this release schedule.
Will flood control again become the number one priority when managing the river?
To view the components of the release strategy, visit: http://www.nwo.usace.army.mil/html/op-e/flood2011/ReservoirRelease/reservoirstrategy.html