Traverse City Record-Eagle

November 4, 2012

Are there safer ways to drain a reservoir? Yes

By Frank Christie

---- — What caused the Brown Bridge Dam failure?

As a semi-retired engineer who has specialized in dam and hydroelectric projects, I have been reading with much interest the articles about the recent failure of the Brown Bridge Dam.

The aerial photo that appeared in the Record-Eagle a couple of weeks ago tells a very compelling story about the failure. As someone who has designed, built and operated dams over the past 45 years, and has spent a good deal of time studying dam failures, I can attest that the driving of sheet piling through an earthen embankment is a very questionable practice.

The vibration resulting from the pile-driving operation loosens the soil on both sides of the piling wall and thus creates a path of low resistance to the flow of water. If the soil is not dense and well compacted, water will begin to seep through the soil along the smooth surface of the steel piling and create a path for an increasing amount of flow.

Once the flow of water increases to the point where it begins to flow out of the downstream face of the embankment, the erosion process begins. After the flow of water has developed along this path, the rate of erosion can increase dramatically and a failure can occur in a matter of minutes or hours, as was the case with the Brown Bridge Dam.

The proximity of a concrete retaining wall, if in fact that's what it was, would be of very little help since once started, the water would erode under the bottom of the wall and the wall would shift or fail allowing more water to pass.

Although the state and others say they will never absolutely know for sure what caused the failure, I would expect investigations will quite conclusively determine the failure scenario. Over the past 10 years or more there have been a number of dams removed in United States and much experience has been gained in the process. There are much safer ways to drain a reservoir.

About the author: Frank Christie of Onekama is a registered engineer and a member of the Association of State Dam Safety Officials. He has 45 years of experience in the design, construction and operation of dams and small hydroelectric facilities. He is currently managing the operations of four such facilities in central Michigan located on the Tittabawassee River.

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