CS36C - Concurrent Session 36C: The Reconstruction of Clam Falls Dam: Upgrading and Repurposing a Century-Old Hydropower Facility to Meet Contemporary Demands

Abstract Description: Clam Falls Dam is located on the Clam River in Polk County in northwestern Wisconsin. The reservoir, Clam Falls Flowage, covers about 130 acres and has a storage volume of about 700 acre-feet at normal pool. The significant-hazard dam, owned by Polk County, consisted of an abandoned powerhouse and a severely undersized gated spillway.

Constructed in 1859 to support the local logging industry and rebuilt in 1915 to generate electricity, the dam played a large role in the development of the local economy. Power generation ceased in the 1980s due to increased maintenance costs, and ownership has changed several times since. Polk County established ownership in 2022 and was tasked with addressing Wisconsin Department of Natural Resources (WDNR) directives to bring the dam up to current safety standards: namely, either upgrade the dam to provide sufficient spillway capacity to pass the 500-yr flood or remove it completely.

Local residents lobbied strongly for the dam to be kept and upgraded, arguing that while the dam no longer generated power, it bolstered nearby property values and provided significant recreational and environmental benefits, including upstream wild rice habitat important to Tribal interests. This lobbying resulted in an appropriation of $2 million in the state budget and additional funding through grants from the WDNR and U.S. Army Corps of Engineers to upgrade the dam.

In 2022, Ayres was retained by Polk County to design modifications to upgrade the dam to the WDNR’s current safety standards. Challenges included: a remote site; a severe lack of information regarding the existing structure’s design and construction; the need to increase spillway capacity fivefold; greatly varying grades of foundational bedrock; the presence of a bridge immediately upstream of the dam; transforming the powerhouse from an abandoned building to a water-retaining structure built to today’s safety standards; and maintaining the recreational and environmental interests of the local community while working within a narrowly defined budget. The proposed design includes an uncontrolled ogee-crest spillway, three much larger gated spillway bays, and a non-overflow section built from the shell of the abandoned powerhouse and secured with post-tensioned rock anchors.

The new Clam Falls Dam was constructed in 2024-25 and was put into service in the spring of 2025. This presentation will describe the goals for dam replacement, including satisfying the interests of stakeholders and Tribes, the design process, and the construction of this unique improved dam.