Created by the construction of a dam in 1966, Cornwall Creek Flooding is a treasured water body for fishing, recreational use, and wildlife viewing in Northern Michigan’s Pigeon River Country State Forest. After a 2019 dam safety inspection by the Michigan Department of Environment, Great Lakes, and Energy (EGLE) rated the dam in poor condition, the Michigan Department of Natural Resources (DNR) Fisheries Division evaluated options to reduce the risk of potential failure. A combined effort between the DNR, nonprofit Huron Pines, and a “Save Cornwall” campaign raised enough funding from multiple sources to renovate the dam and preserve this pristine, 161-acre recreation destination. Wade Trim provided civil, structural, and hydraulic engineering design, survey, and construction engineering for the project.
In preparation to renovate the dam, which is approximately 33 feet high, Cornwall Creek Flooding was partially drawn down over several weeks in 2024 in compliance with EGLE regulations. Dewatering included the coring of 10-inch-diameter holes in the sides of the existing outlet structure to lower the water level by 6.5 feet. Efforts were undertaken to relocate protected freshwater mussels to deeper water as needed. During construction, an equestrian trail along the 583-foot-long embankment of the dam was rerouted and an access road leading to the boat launch area was closed and improved after completion.
The renovation design features a one-bay, sheet pile/concrete overflow control structure as the dam inlet and upsized outlet pipe to increase capacity to pass floodwaters. Based on a modified Puls routing analysis, a peak design flow was developed and hydraulic design for the spillway was verified using the HEC-RAS model to simulate minor losses in the system. The control structure in the middle of the dam features wing walls and a concrete headwall. The outlet pipe has drop manholes, a filter diaphragm, bank underdrains, armored slopes, and an energy dissipator channel. Aluminum stoplogs were added to better manage water level and improve safety for routine maintenance. The former water-control structure was demolished and the outlet was plugged.
Cornwall Creek Flooding has nearly returned to its full water surface elevation. The process of refilling allows water to flow downstream into Cornwall Creek to protect its aquatic resources and is estimated to be complete before the end of this summer.
All photos courtesy of Huron Pines
