Original Publication Date: June 14th, 2012
Republished with persmission from: Wahpeton Daily News
Exactly how much Red River Valley clay does it take to build a dam south of Fargo? The dam, which is rarely mentioned by its proponents, is part of a diversion project that will hold 200,000 acre-feet of water upstream of three cities.
Last week’s news described a landslide or “slumping” that shifted a 100-foot section of 32nd Street North in Fargo 13 1/2 feet. A year ago, shifting soils 27 feet beneath the approaches to a new bridge over Rose Coulee in south Fargo caused a $500,000 repair project.
One doesn’t have to be an old timer to remember what was going to be the Ski Hill at Bluemont Lakes in the 1980s. Earth excavated from the Bluemont Lakes development was going to be piled into a hill, but the pile started sinking into the soggy clay below, so instead the would-be mountain was hauled away for river dikes.
So, now the plan is to dig clay out of a diversion channel, and build a 15-foot-high dam from Comstock to Horace, and expect to provide protection for the metro area. But the problem is the clay under our black topsoil is expansive clay, which means it’s capable of absorbing large amounts of water. The more water it absorbs, the weaker it becomes. When it dries, it contracts and shrinks in size.
It is always changing. Already, the Corps has reduced the depth of the diversion channel due to the poor Breena clays below the surface, but these clays are still expected to support the dam structures, levees, or dam with large control gates. Roads, including I-29, will be raised 14 feet for 11 miles. The aqueducts and railroad raises are all subject to the soils’ weak properties.
The Minnesota DNR calls the proposed dam a “high hazard dam,” where failure is likely to cause loss of life. The proposed diversion is supposed to protect people from flood waters instead of putting them at risk with a false sense of security. History is a great teacher – just ask the folks at the Bluemont Ski Hill, which was an “ant hill” in comparison to this project.