Fargo diversion and downstream river levels

A controversy has developed over whether the proposed Red river diversion at Fargo Moorhead will increase red river levels downstream in flood.  The corps state it could add 16 inches to the river level at the Thompson Bridge.

If the diversion is properly designed my view is that this is highly unlikely.

A letter from myself to the editor of the Grand Forks Herald was published  08/19/2010: -

LAPORTE, Minn. — I served on the mayor’s task force for flood protection for Grand Forks/East Grand Forks after the Flood of 1997. As part of our research, we studied the Winnipeg flood diversion project extensively. We also were advised by the engineers for the original Winnipeg diversion channel, Acres International. And, we had advice and counsel from the developer of the project, Ed Kuiper of Winnipeg.

Kuiper explained to me at length that a properly designed diversion channel does not raise river levels downstream. What it should do is channel the water that is out of the riverbank doing damage, to a safe channel where it does not do damage. The flow through the city in flood or the contained water in the channel should be the same.

The only river levels that change and are elevated are the levels upstream as the diversion channel is brought into operation. This is because as the gate is raised in the riverbed, the river level will rise to force the river over the lip of the diversion channel.

Richard Nelson, the late mayor of Warren, Minn., had a diversion for the Snake River designed not by the Corps of Engineers but by Acres International of Winnipeg. I discussed this project often with Nelson before his untimely death.

Warren had multiple floods every year. It has not flooded since completion of the diversion channel on the Snake River. I cannot find any data that suggests river levels increased on the Snake River downstream.

Having seen the workings of the Corps up close, I’m highly suspicious that they are touting these absurd rises in river levels to kill the Fargo-Moorhead diversion project. They killed the excellent Grand Forks diversion project by grossly inflating its cost.

Kuiper and others have pointed out that flood protection needs to protect against a 500-year event. Building to a 210-year event is totally inadequate. Remember, if you build for a 210-year event, you have a 1-in-210 chance of a flood each and every year. The figure does not mean you will get a flood every 210 years.

So, if you build to a 500-year event you have a 1-in-500 chance of a flood every year, which is much better odds.

It is no secret that I was opposed to the Grand Forks flood-protection project and regarded it as inadequate. Today, I’m of the view that because of the topography and hydrology in the Fargo-Moorhead area, a diversion project is the only way of providing flood protection to those cities.

If the Corps really believes its project will raise river levels 16 inches at the Thompson Bridge, then it also should build the diversion project to the west of Grand Forks — which it should have done and still needs to do anyway.

Mark Carter

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