PLT32 - Smallwood Dam: Innovative Solutions for Phased Cofferdam Loading Challenges

Abstract Description: Smallwood Dam, constructed in the 1920s, has provided hydroelectric power to the Gladwin area for decades. Following historic flooding in 2020, the dam sustained severe damage to its structural integrity and earth embankment. The rehabilitation project posed unique challenges, as the new design had to be integrated with the existing structure while meeting modern state and federal regulatory requirements. Due to the dam’s remote location and the limited population around the reservoir, the project had to be cost-effective while still meeting all state and federal regulations for hydroelectric dam maintenance and flow requirements.

A key issue arose from the phased cofferdam sequencing, which imposed additional loads on the existing center pier (which separates primary spillway bays 1 and 2)—exceeding its original design capacities based on historical reinforcing drawings. While the center pier was adequate for original loading conditions, it was insufficient to withstand the increased forces during construction. Close collaboration between the contractor and engineering team led to an innovative, cost-effective solution: installing a 40’-0” tension anchor through the center pier down to the footings. This approach not only mitigated the load concerns but also avoided costly redesigns of the cofferdam bracing and prevented potential project delays. Additionally, to manage increased flow during phased construction, the contractor and design team worked together to also develop a siphon system capable of handling 70% of the historical flow capacity.

In addition to the structural challenges, construction access on top of the narrow center pier posed a critical obstacle. With limited space and the need for precise work, navigating the construction equipment and workers through this confined area was a major consideration in the design and execution of the retrofit. The team’s ability to efficiently address this issue was vital in maintaining the project schedule.

This presentation will discuss the technical challenges, innovative design solutions, and effective collaboration between the contractor and engineers that enabled the successful rehabilitation of Smallwood Dam. It will highlight the importance of addressing both structural integrity and logistical concerns in dam rehabilitation projects, demonstrating how creative solutions can meet complex regulatory and construction constraints.