This past week, the “Sioux Falls Argus Leader” and the Gannett Washington Bureau acquired thousands of Army Corps of Engineers e-mails related to the Missouri River flood of 2011. The e-mails confirm that Brigadier General John McMahon and Jody Farhat have been concerned about media criticism of the Army’s management of the reservoirs this past winter and spring. The e-mails also indicate that officials have sought to lessen criticism of the Army’s actions along the river by framing the flood as a consequence of extreme weather. The Army wants the public to believe that neither the Army’s management of the upstream reservoirs nor its flood-prone navigation channel south of Ponca, Nebraska, caused the Great Flood of 2011. One unnamed official urged his/her colleagues to continually emphasize to the media that the flood was an unprecedented event that resulted entirely from excessive precipitation. He/she stated in an e-mail, “It is important that we keep pounding that message with the locals….” Since May, Army officials have stayed consistently “on message.” No one within the Army has said a word about how reservoir operations and the navigation channel contributed to the flood. Many media outlets have accepted the Army’s interpretation of the causes of the flood, especially those located in the state of Missouri. Continue Reading »
Today, the Army announced its management plan for the Missouri River reservoir system for the remainder of 2011 and early 2012. In preparation for the 2012 runoff season, the Army will drop the water volume in the reservoirs to 56.8 MAF (million acre feet) by March 1, 2012. That level will free up 22% of the reservoir system’s available storage for next year’s runoff. Surprisingly, that is the same amount of reservoir storage space that existed at the start of this year’s runoff season. We now know that 22% was not enough to stop the Great Flood of 2011. Had the reservoir system had available 30% or 40% of storage this past spring, the flood of 2011 would have been sharply curtailed or wholly contained by the Dakota and Montana dams. The lack of adequate reservoir storage was a primary cause of this year’s flood. Continue Reading »
Sioux City, Iowa. The persistent high water of the Missouri is beginning to take a toll on the trees lining the stream’s banks. The saturated soil around the roots of the trees no longer provides a strong base of support. Thus, when high winds or strong river currents strike the vulnerable trees, they easily tumble over into the floodwater. Dozens of large and small trees are lying on their sides in the engorged Missouri just a mile downstream from its juncture with the Big Sioux River at Sioux City, Iowa. The number of downed trees is going to increase exponentially as the summer moves toward fall and the Army keeps the discharge rate out of Gavin’s Point Dam at 160,000 cubic feet per second. The loss of bankline timber will increase runoff into the Missouri for years to come. Healthy timber tracts halt or slow runoff by storing water in root systems, trunks, and leaves. Once the trees are dead and gone, rain will hit the valley floor and more quickly drain into the Missouri. River edge trees also act as a natural means of bank stabilization. Trees slow down erosive currents, deflect water from the bankline, and keep valley soils from rapidly washing away. The absence of trees along the river will lead to intensified bank erosion. Additionally, the loss of timber strips adjacent to the river means that agricultural chemicals, feedlot fecal matter, and urban storm water (which contains automobile lubricants) will readily find its way to the Missouri. The destruction of river side timber will have serious negative repercussions for the health of the Missouri River ecosystem.
Prior to European-American agricultural settlement, the eastern Dakotas contained vast prairies of big bluestem grass. The region also held thousands upon thousands of sloughs and potholes. Not surprisingly, the area became known as the prairie-pothole region. The prairie grass held snowmelt and rainfall in its extensive root systems. The potholes acted as natural reservoirs, storing meltwater and rain. When full, the wetlands also attracted fish, ducks, geese, muskrats, frogs, toads, and beaver. The sloughs also brought bison to their edges. Bison went to the sloughs on hot summer days, drinking in their fresh water to cool their wooly bodies. Since the 19th century, agriculturalists have drained the wetlands with ditches or tiles to acquire additional acres for crop production. The loss of the wetlands, and their natural reservoir storage, is one of the reasons rivers across the northern plains experience higher flood stages and more frequent floods today than in the past. Continue Reading »
Garrison Dam, North Dakota. The 70-mile Missouri River reach from Garrison Dam to the outskirts of Bismarck is wide and unchannelized. In a manner similar to the unchannelized reach from Yankton, South Dakota, to Ponca, Nebraska, the Missouri’s high flows remain largely within its banks along this section. Because it is able to enter its former floodplain, the Missouri’s channel area absorbs the bulk of the floodwater exiting the spillway and tunnels at Garrison Dam. But on the northern edge of the state capital, riprap and housing developments encroach on the river’s meander belt. The river’s narrowed channel area cannot carry the floodwaters safely past Bismarck. When the water flows down from the dam above, it hits the confined channel and rises. Once again, simple observation makes it apparent that suburban housing construction in the floodplain exacerbates flooding.