There are many rumors circulating in regard to the historic flood that we experienced in the summer of 2011. This letter is submitted to provide property owners and public officials with data to make informed judgments regarding future actions that are so important to preventing the reoccurrence of this event.
First: We accept the local flood stage of the river to be 16 feet.
Second: We accept that the current capacity of the river at flood stage (16 feet) is 85,000 cubic feet per second. This value is based on records obtained from the North Dakota State Water Commission.
These numbers enabled me to flood-route the actual flows in the Missouri River during the 2011 flood period. It showed that had releases on April 1 been increased to 85,000 cfs, and having had the Garrison reservoir drawn down to 1,931.37, there would not have been a flood for those who are protected to river stage 16 feet.
March 28 through
April 30, the average discharge for the Garrison reservoir was 14,755 cfs. I ask you, does this sound like sound management that is preparing for snowpack that is 116 percent of normal annual snowfall on April 1? This is with two months of the snow season left. This is when the releases should have been increased at Garrison to provide for flood stage. The snow depth increased to 149 percent of normal annual snowfall by May 1, with another 30 days of snow accumulation left.
Third: The pool elevation on April 1 was 1,840.2. Does this appear to be a pool management scenario that is preparing for the above-average snowpack? Does this sound like a competent engineering decision?
Fourth: On July 28, the inflow to the Garrison reservoir dropped to
78,000 cfs (7,000 cfs below flood stage at Bismarck-Mandan) and its inflow continued to decrease.
Fifth: Discharges at Garrison did not fall below 85,000 cfs until Aug. 24. This resulted in the extension of the flood event for Bismarck-Mandan for a period of 28 days. Does this sound like competent engineering management? Should we trust this management for the 2012 runoff period?
These are numbers that are based on what actually occurred during the 2011 flood event. What it shows me is that we may not need additional protection for people who are protected for flooding to river stage 16 feet. What it does show me is that competent engineering management is needed to manage the Garrison Dam for the purposes for which it was designed and constructed.