The northeastern corner of the region is still recovering from this year’s record flooding, even as they begin to move into fall and brace for the next winter, which will inevitably bring more moisture into the rivers and reservoirs.
The US Army Corp of Engineers is planning for next spring’s runoff and has some answers for the public about how they will handle it. One of the questions the Corp most frequently receives is about storage capacity. Essentially, the Missouri River system has a series of man-made reservoirs such as at the Fort Peck damn, that hold extra water. Questions from citizens have asked if the Corp should plan to find ways to incrase storage capacity for the next year.
Corp staff say the weather predictions will help shape their choices. 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 reservoirs 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.
The Corp says that for next year their 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.
Corp staff 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, assess 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 Corp says 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.