New corps report shows Minnesota, North Dakota diversions meet cost-benefit analysis
FARGO - A feasibility study released today by the Army Corps of Engineers shows a North Dakota-side flood diversion would meet the standard for federal funding but would require a significantly larger local share than a Minnesota-side diversion.
With contingency funds included, a North Dakota diversion that would carry 35,000 cubic feet per second would cost nearly $1.3 billion and hold the Red River level through Fargo-Moorhead at about 35 feet during a 500-year flood. The river crested at 40.84 feet last spring, which was a 125-year flood event, the corps says.
A Minnesota-side diversion that would do the same thing would cost $1.14 billion with a local share of $631 million, compared with a local share of $783 million for the North Dakota diversion.
The corps is meeting with local leaders this morning to discuss the study's findings and wants them to choose a locally preferred plan by April 15.
The contingency funds cover areas of risk that could impact the cost and schedule of the project, such as environmental concerns and uncertainty with ground conditions.
Without those funds included, the estimated costs are reduced to $1.049 billion for the Minnesota diversion, with a local share of $537 million, and $1.168 billion for the North Dakota diversion, with a local share of $656 million.
The corps also studied three smaller diversion options in Minnesota: Without contingency funds, it would cost $787 million for a 20,000-cfs diversion, $892 million for a 25,000-cfs diversion and $959 for a 30,000-cfs diversion. A 30,000-cfs diversion on the North Dakota side is estimated at $1.109 billion.
All of the diversions meet the corps' cost-benefit ratio of 1.0, meaning for every dollar spent on the project there would be a dollar of savings resulting from the flood protection.
The 20,000-cfs Minnesota diversion has the highest ratio, at 1.59. The 35,000-cfs diversions have ratios of 1.37 in Minnesota and 1.29 in North Dakota, without contingency funds.
The study also estimated the diversions' impacts on the Red River north of Fargo-Moorhead, which is a concern for downstream communities.
During a 100-year flood event, a 35,000-cfs Minnesota diversion would raise the river level 3.7 to 4.6 inches at Halstad, Minn., 6.8 to 9.4 inches near Hendrum, 4.2 to 6.0 inches at Perley and 5.3 to 7.7 inches at Georgetown.
A 35,000-cfs North Dakota diversion would raise levels 4.4 to 5.3 inches at Halstad, 7.9 to 10.4 inches near Hendrum, 3.6 to 5.4 inches at Perley and 5.2 to 7.6 inches at Georgetown.
A North Dakota diversion channel would be 36 miles long, compared with 25 miles on the Minnesota side, and take 8½ years to build, compared with 6½ years in Minnesota, the corps estimated. However, the west-side option also would require only 3.3 miles of tieback levees, compared with 9.9 miles on the Minnesota side.
A timeline included in today's report shows construction starting in April 2012.