Letter: Study Devils Lake flood risks before catastrophe strikes
Not many people are concerned about Devils Lake flooding potential, looking ahead to the spring of 2017. Since the Tolna Coulee Control Structure was built by the U.S. Army Corps of Engineers in 2012, the lake has dropped more than 4 feet.
But since drainage from the Upper Basin into Devils Lake continues unabated, a potential flooding problem still looms.
The problem: When Devils Lake overflows next time, the Tolna Coulee will be encouraged to erode. If the lake does overflow and if the coulee erodes, all of the water passing through and into the Sheyenne River will add to the flood potential downstream.
The Devils Lake Basin watershed will have been added to that of the Sheyenne, about doubling the flow in the river.
How much water could flood through an eroded coulee? If 2009 and 2011 are any indication, as much as 600,000 acre-feet could move through the coulee and into the Sheyenne. Corps’ figures indicate that as much as 3,000 cubic feet per second could flow from the lake into the river during an overflow.
And data about flows from the upper basin into Devils Lake show that as much as 7,000 cfs flow from the smaller coulees into the lake. That much water surging into the lake would effectively double the amount of water continuing on into the Sheyenne River.
The Corps’ operating plan for the control structure fails to indicate the possible downstream damage. Devils Lake could drop from an elevation of 1458 feet above mean sea level to 1446 feet msl. Those 12 feet on the lake hold more than 2 million acre-feet of water.
What would be their effect downstream along the Sheyenne? Hardly the Finding Of No Significant Impact the Corps claimed.
Before the control structure is allowed to operate as described, the Corps needs to do a thorough, scientific Environmental Impact Statement on Devils Lake flooding. Only then will deciders have enough information about this extremely important water issue to make the right decisions.
Valley City, N.D.