Nov. 2002: Oahe Delta Grows in South Bismarck, Mandan
By Andy Mork, Chairman of the BOMMM Joint Water Resource Board, Bismarck

The Oahe delta has not developed as fast as the deltas in the other Pick-Sloan reservoirs.  A delta forms where the silt borne rivers meet the still water of the lakes.  Since the Oahe reservoir levels fluctuate greatly, the delta there is distributed over several miles.

However, the delta is growing and the end result will be the same.  A recently completed FEMA re-study of the Bismarck/Mandan area indicates about a one-foot rise of the hundred year flood level.  Winter hydro releases at Garrison are the maximum possible because of higher value of power then.  Because of the rise of the river bottom this has been reduced from 33,000 cfs twenty years ago to 22,000 cfs now with great loss to revenue.  Also the possibility of ice jam flooding during fall freeze-up and spring break-up is more probable as the delta increases.

The U.S. Geological Survey indicates that 94% of the silt load come from the eroding banks and the bottom of the river with only 6 percent from the Heart and Knife Rivers and other tributaries.  It is obvious that rip-rapping the eroding banks where needed will greatly reduce and delay of the delta.

A survey in 1997 by the North Dakota Water Commission indicated that 30 percent of the banks are now protected and only 10 percent more need protection, leaving 60 percent natural. 

The BOMMM Joint Board is attempting to complete the needed bank protection, but is obstructed by U.S. Federal Fish and Wildlife Administration and other preservationist groups that want to keep the river “natural.” A recent alarming development is that a private owner who wanted to save his banks at this own expense was required to mitigate his project by extensively developing and maintaining a sand bar habitat for the plovers and terns!

The Corps of Engineers in its cost/benefit studies include only the market value of the land and refuse to include loss of habitat, delta formation and other obvious benefits.

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