5 different F-M flood diversion plans and a massive ring dike studied
WEST FARGO — The idea of putting ring dikes around Fargo-Moorhead is once more on the table as a replacement for the $2.2 billion flood diversion that Minnesota regulators have so far rejected.
Though diversion supporters consider diking unfeasible for such a large area, a team of technical experts, including regulators, meeting Tuesday, Nov. 14, at Cass County offices here agreed to take another look at ring dikes and five other alternatives that do involve a diversion.
"What we want to do is end up with some alternatives for the task force to consider," said Kent Lokkesmoe, an administrator with the Minnesota Department of Natural Resources. "You can have a no-dam alternative. The advantage of that is you don't need a Minnesota state permit."
He and five other engineers and planners make up the technical team advising the task force convened by North Dakota Gov. Doug Burgum and Minnesota Gov. Mark Dayton to figure out what kind of flood protection project would satisfy regulators.
Other alternatives include different variants of the diversion project with the diversion channel and dam elements shifted around and new features, such as an enormous earthen tub east of Horace to store flood water and hundreds of storage areas distributed throughout the Red River Basin.
Diversion opponents had urged the team to consider an alternative without the diversion channel or dam, such as fighting floods with levees only. They got their wish, though the DNR has already agreed with the U.S. Army Corps of Engineers that levees alone can't offer the flood protection required.
The task force came about as a result of a lawsuit brought by the DNR against the corps and Fargo-Moorhead Diversion Authority to enforce its decision to not issue a permit for the dam. The dam is needed to prevent the diversion from sending too much water to downstream communities, but DNR officials have said they feel it removes too much undeveloped land from the floodplain causing floodwater to be displaced upstream.
All of the alternatives being considered are meant to reduce the upstream impact one way or the other. Besides the ring dike here, are some others ideas considered:
- More flow through town: Build the diversion project as designed but with more water flowing down the Red through Fargo-Moorhead. This adds 2 to 4 feet to the river elevation, though the higher elevation would leave very little freeboard, the space between the top of a dike and the water surface. Freeboard is needed to prevent waves, ice jams and other unexpected changes in water level from overtopping the dikes. Nathan Boerboom, a Fargo city engineer and technical team member, said the cost of building higher levees would need to be considered because adding height with sandbags is unacceptable.
- Internal storage: Build the diversion project as designed but add water storage between Horace and Interstate 29. This would take the form of a ring dike that would contain water drawn from the dam, kind of like an above-ground pool, according to Cass County Engineer Jason Benson. The Diversion Authority had once considered this idea, calling it "Storage Area 1."
- More flow on Sheyenne and Maple rivers: Build the diversion project as designed but allow more flood water to flow upstream on the rivers. Presumably this would lead to more flooding in the area north of Fargo and West Fargo, since the Red River backs up in this area during the operation of the diversion project.
- Move the dam north by about 1.5 miles. The DNR had considered something like this as part of an environmental review and found that it results in less flooding upstream but protects fewer buildings.
- Move the dam north where the Wild Rice and Red rivers meet. This would be close to the edge of Fargo city limits, just south of Davies High School.
All alternatives considered will include some form of distributed storage, as agreed to by the task force Monday, Nov. 13. But because of the difficulty of getting FEMA certification for storage areas located far away from the metro, these areas are expected to play a supplemental role.