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 »