Drawdown of Cornwall Flooding to start renovation project

CHEBOYGAN — The effort to repair an aging dam in a popular Cheboygan County recreation area is scheduled to start on Aug. 12.

Cornwall Creek Flooding will be lowered by approximately six feet to comply with a state safety order and prepare for dam renovations to preserve the impoundment for recreation and wildlife.

Cornwall Impoundment, better known locally as Cornwall Flooding, is located approximately 15 miles east of Wolverine in southern Cheboygan County. Cornwall was built in 1966 to create the 295-acre Cornwall Creek Flooding in the heart of the Pigeon River Country State Forest, which is managed by the Michigan Department of Natural Resources. Outdoor enthusiasts have used the area for fishing, hiking, horseback riding, hunting and kayaking for many years.

Regional environmental organization Huron Pines has been selected to manage the project by the DNR.

"The ultimate goal is to renovate the structure next year that will address the safety concerns so we can rebuild the impoundment. We are hopeful we have enough funding for the repair work," said Josh Leisen, senior project manager for Huron Pines.

Cornwall Dam is one of 62 such structures in Michigan that are owned by the DNR Fisheries Division, many of which are reaching the end of their projected life span. Because funds available for dam renovation are limited, Huron Pines brought together several stakeholders to raise the estimated $1.5 million needed to repair the dam and maintain the flooding.

"Right now we have raised $1.5 million but until we see the bids there is some uncertainty about the cost," Leisen said.

Built in 1966, the earthen dam impounds Cornwall Creek, a small tributary of the Pigeon River. A 2019 safety inspection by the Michigan Department of Environment, Great Lakes, and Energy (EGLE) rated the dam and its water control infrastructure in poor condition. Past and recent engineering inspections indicate the partial drawdown is necessary to reduce the risk of a potential failure until problems with the dam can be addressed.

For the drawdown, contractors will modify the dam’s existing water intake structure to gradually lower the flooding over the course of up to 90 days and at a rate of no more than six inches per day. This controlled, permitted and irreversible drawdown will allow time for exposed bottomlands to stabilize while minimizing sediment input into Cornwall Creek and the Pigeon River.

The DNR believes the six-foot drawdown will reduce the amount of habitat available for fish and some mortality may be expected, particularly during the winter. Some water will remain in the impoundment, which is 25 feet at its deepest.

Once the drawdown is completed, Huron Pines will seek bids on removing the existing concrete river structure and outlet pipe, which will be replaced by a new water intake structure.

"We will also install some some drainage on the downstream embankment to address the seepage issues," said Leisen.

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Usually Huron Pine advocates for removing dams, but Leisen said Cornwall has some unusual characteristics.

"Cornwall is unique as it has a small upstream catchment area, so removing the dam would only have marginal improvement for fish passage. We are aware of the added benefits of Cornwall Flooding for recreation and wildlife and we feel these outweigh the dam’s comparatively low negative impacts on Cornwall Creek and the Pigeon River," said Leisen.

Public access via Tin Bridge Road will remain open during the project but access to the water will become increasingly difficult or impossible as it recedes. Exposed soils will be very soft and may be dangerous for people attempting to reach the water. The Shore-to-Shore equestrian trail, which crosses over the dam, will be closed and a detour will be implemented.

If the project bids match the cost estimate of $1.5 million, work should begin by the spring of 2025 with completion by the fall, according to Leisen.

— Contact Paul Welitzkin at pwelitzkin@gaylordheraldtimes.com .

This article originally appeared on The Petoskey News-Review: Drawdown of Cornwall Flooding to start renovation project