This week, Senator John Thune (R-SD) stated that the temporary levees now protecting Pierre, Fort Pierre, and Dakota Dunes, South Dakota, may need to be made permanent. Thune, a long-time climate change skeptic, admitted that those three communities could face similar flood events in the future. High, permanent levees would protect the residents of those towns from a larger, more voluminous future Missouri. Continue Reading »
One Man’s Levee is Another Man’s Loss
Notes from the Field, June 27, 2011, Back-Cutting at Big Bend Dam
Big Bend Dam, South Dakota. The Missouri is flowing through the emergency spillway at Big Bend Dam. The water shooting through the spillway gates is moving so fast and with such erosive power that it is back-cutting toward the earthen dam itself. Left unchecked, the water could threaten the structural integrity of the dam. Although at present, that scenario is highly unlikely. Nonetheless, the Army is concerned about the erosion. To address the issue, a dump truck hauled large blocks of quarried stone to the trouble spot. The Army plans on dropping the rock atop the eroded bank sections to halt the back-cutting. A civilian working for the Army acknowledged that the engineers did not expect to be in this predicament when they first opened the spillway gates to the Missouri’s floodwaters. The back-cutting caught the Army by surprise. But the military is on top of the problem, with tons of pink Sioux quartzite. Continue Reading »
Muddy Mo: Reservoir Siltation and the Flood of 2011
The Army closed Gavin’s Point Dam near Yankton, South Dakota in 1955. The reservoir behind the dam stretched upstream to the town of Niobrara, Nebraska, situated at the mouth of the Niobrara River. By the early 1970s, silt from the Niobrara River had created a shallow delta at the head of Lewis and Clark Lake. This accumulated silt did two things. First, it raised the water table at Niobrara. As a result, buildings in town suffered structural damage from water seepage. Second, it caused an increase in flooding in Niobrara when high flows came down either the Missouri or Niobrara rivers, struck the shallow delta, and then backed-up into residential and commercial areas. Because of the higher water table and the increasing likelihood of floods, the residents of Niobrara moved their town to higher ground in 1972. Continue Reading »
