Sandy beaches may be what dreamy travel magazines are made of, but sand was the downfall of a Traverse City Dam removal that failed nearly two years ago.
The state has released a report detailing the investigation of the Brown Bridge Dam. It says internal erosion of a temporary dewatering structure was the most likely cause. That erosion, the report said was the result of unstable subsurface soil.
The dam failure spilled more than 600 million gallons of water into the surrounding areas.
Bill Creal is the water resources division chief with the Michigan Department of Environmental Quality (DEQ). He said public safety needs to be assured when dams are removed.
“When we are looking at dam removals in the future we’re making sure that we take a closer look at this specific instance so we don’t have this piping occur underneath dams,” Creal said, “So we’re going to make sure what kind of soil of soil types we have under the dams the proper width of the dam and the proper control structures in place so we don’t have this situation occur again.”
Creal said originally the DEQ issued the city of Traverse City a violation. He said the state also issued an order to restore the river area and the city took action to remove sediments downstream of the release and that the original goal was to remove the dam water in a controlled way but the soil conditions created a problem.
“What happened was it turned out that there was sand underneath there,” Creal said “And the the water pressure and water movement through that narrower pathway eroded out the sand underneath the structure and basically formed a conduit like a pipe underneath there that allowed all the water to then flow out in a period of six hours instead of what we were going to do over a period of weeks.”
Creal said the river is looking normal now, but the DEQ needs to do additional studies to verify a complete recovery of wildlife.
He added that the DEQ continues to support dam removal, but it needs to be done in a way that supports public and environmental safety.
Currently the state is discussing the violation with the city.
ON THE WEB
Brown Bridge Dam Failure Report