DETROIT – The U.S. Army Corps of Engineers, Detroit District, notifies the Traverse City community that a significant milestone on the Boardman Dam Removal and River Restoration project will begin soon.
A drawdown of part of the Boardman River, the impoundment, is scheduled to begin Friday June 23. The drawdown of the Boardman Dam impoundment through a temporary siphon system will be performed over the next month in preparation for the removal of the earthen dam and demolition of the powerhouse. This milestone will initiate river flow for the first time under the newly constructed Cass Road Bridge.
The public may notice an increase in the turbidity, or cloudy waters, of the river. The river flow is being diverted over the top of the dam rather than through the power house intake although flows are not increasing.
Right now turbidity levels are low (single digits for nephelometric turbidity unit, NTUs) and expected to remain low in the future. However, the Detroit District will monitor the turbidity levels to make sure they remain below 50 NTUs.
In order to safely dewater the Boardman Dam impoundment, a siphon system has been installed to pass the flow of the river over the dam in a contained system. Water will be discharged vertically through bladders or tubes at the outlets (located at the toe of the dam) in order to dissipate energy within the constructed stilling basin. This will provide a small “fountain” or “bubbling” effect within the stilling basin.
As the siphons are initiated, it is anticipated that the river below the dam may temporary become unclear as finer materials are washed out of the newly restored channel downstream. Some cloudy water could make its way as far as downtown Traverse City, to the mouth of the Boardman River, but eventually the water clarity will improve as flow continues downstream.
Although cloudy waters are expected, they will be temporary. The cloudy waters will disperse quickly and not have long term impacts on fish and wildlife resources. Because the Detroit District will be monitoring the turbidity levels, if they reach unexpected levels, construction activities within the river will be modified or suspended until the waters clear up.
The siphon system was installed with screens on the intakes of the pipes. This will minimize the passage of aquatic species (fish, turtles, etc.) and debris through the siphons. The screens were designed to maintain low enough velocities such that fish or other species can swim away and not become entrapped.
Project construction timing is best for trout life cycles. This year’s newly spawned trout are now juvenile fish and are mobile in stream, while new eggs will not be deposited until spawning in late fall after all in-stream work is complete.
For additional project information please contact U.S. Army Corps of Engineers, Detroit District employees Chris Schropp, civil engineer, (616) 842-5510 x25526 or Lynn Rose, chief of public affairs at (313) 226-4680.