First off sorry for the delay between updates. Here’s a look at what’s been happening:
Temporary Dewatering Structure – Since my last update a great deal of work has been completed including the reconnection of the river to its historic channel where the powerhouse was located. Once that was done a team of investigators were able to inspect the temporary dewatering structure (TDS) to determine the cause of the breach. After inspectors gathered their information Molon crews began pulling sheet pile. As you can see from the attached pictures all the sheets have been pulled and the north bank is ready for shaping and grading.
Temporary Weir – After crews finished dredging the fine organic material (silt) that had accumulated in the relic river channel behind the dam a temporary weir (approx. 4-foot high) that helped retain some of the silt was removed. The need to remove this organic material was expected from the beginning of the project. The silt is much lighter than the heavier sand and gravel that settled out sooner, upstream in the sand delta area. The silt stays in suspension longer and was the source of the high turbidity (cloudiness) of the water while being actively dredged.
Turbidity – According to Andy Selle from Inter-Fluve, most of the turbidity now is being caused by passive cutting into this organic material. We will most likely see this turbidity continue at various levels for another month or two. Once this turbidity subsides to the point where we can see the bottom additional elements of the assessment on the extent of the impact of the breach downstream of Brown Bridge will continue.
Assessment – The Grand Traverse Band and other project partners including the Adams Chapter of Trout Unlimited volunteers, started to survey the river bottom (longitudinal profile) beginning at Brown Bridge. GTB had conducted a similar profile last summer. The two profiles will help assess the impact of the breach. Other assessment work that will begin once the river clears includes a fisheries population assessment below the dam at Brown Bridge Road, a habitat survey sponsored by the Adams Chapter, an erosion survey, and replication of an aquatic insect survey by the Au Sable Institute. Cross-section, velocity, and turbidity data continues to be collected on an ongoing basis. Additional assessments will occur as necessary.
New River Channel – Over 13,500 lineal feet of new river channel has been created with the removal of Brown Bridge dam. Nearly another mile of river upstream of the former impoundment is flowing more swiftly and clearing sand that had accumulated on the river bottom over the past several decades. Molon crews lead by Inter-Fluve and GTB staff have completed much of the shaping of the new river channel and floodplain in the upper end of project area. A beautiful gravel bed is emerging as the sand flushes down to the sand traps located closer to the former dam where it’s mechanically removed.
Public Access – Public access continues to be limited during construction. Last week the Brown Bridge Advisory Committee approved keeping the once temporary access road at the base of the steep north bank to serve as a permanent recreational trail. Final shaping and stabilization of the access road and other steep slopes will occur as weather allows. As people visit the area they are asked to stay off the newly exposed bottomlands for several reasons including to allow the native vegetation a chance to grow and for their own safety. Much of the bottomlands remain extremely soft. Individuals and pets may literally become stuck in the mud.
This is it for now….and, as always, please feel free to contact me anytime if you have questions.
– Steve Largent, Boardman River Program Coordinator