Mirror Lake Dam Rebuild:
Engineering & Infrastructure Narrative

Problem; A earthen private dam was built in the forties to create a 12 acre lake, it eventually failed in the sixties when over washed in a storm and was haphazardly rebuilt. The dam was again leaking and engineers determined to be again close to failure potentially creating downstream flooding and threatening a substantial highway bridge.

At the clients request our engineers submitted all design and permit drawings to EGLE and a permit was fairly rapidly issued due to the risk factor. Our crews fused together and installed two 12” diameter by 150’ long HDPE pipe siphons with fish screens and control valves to direct discharge water around the dam and lowered the lake water level approximately 5’ to facilitate the dam repair and bank/shoreline contouring. Our crews began installing 300’ linear sheet of heavy sheet piling (projected 120 year life span) as designed down the dam center, created a new adjustable sheet piling spillway adjacent to the existing old cement spillway structure, removed the old cement spillway structure, and finalized the sheet piling installation. The sheet piling top cab was set to the maximum dam water level over run elevation, which qualified as a emergency spillway, saving the client the extensive additional expense of a separate emergency spillway. The downstream driveway paralell to the dam was also raised approximately 5’ including the installation of a new box culvert exceeding all 120 year emergency flow capacity’s, replacing the former double undersized failing drive culverts, excess dredge spoils were installed between the  driveway and dam contoured to direct any potential emergency overflows to the correctly sized driveway box culvert. We also furnished a long reach excavator that operated concurrently with the dam rebuild construction to take advantage of the lowered water level and recontoured several stretches of shoreline to allow foot travel along the shoreline for fishing and recreation. The siphons were then shut off and removed allowing the lake level to rise to design levels and any disturbed earth on the entire site was seeded with historical  native grasses after final grading.