Investigation on dam failure complete

Flooding caused by the dam breach damaged 66 properties.

A state investigation has concluded that erosion caused the failure of a northern Michigan dam as it was being dismantled.

The breach occurred as the Brown Bridge Dam on the Boardman River near Traverse City was being removed in October 2012.

A pond created by the dam was supposed to be emptied gradually. Instead, a drawdown structure gave way and pond water cascaded into the river, causing flooding that damaged 66 properties.

Property owners have filed several lawsuits.

In a report Monday, the Michigan Department of Environmental Quality says water pressure destabilized subsurface soils. That led to erosion of foundation soils, release of water beneath the control structure and collapse of an earthen embankment beside part of the drawdown structure.

The city-owned dam was built for hydropower generation in 1921.