By Mike Cherry, PE, and Martin Weber, PEWAVERLY DAM REPLACEMENT
Owner: City of Waverly, Iowa, Public Works
Engineering and design: Stanley Consultants Inc., Des Moines, Iowa
Gate supplier: Obermeyer Hydro Inc., Fort Collins, Colo.
Contractor: Peterson Contractors Inc., Reinbeck, Iowa
Cost: $4.4 million
Funding: U.S. Economic Development Administration (75%); Community Development Block Grant (25%)
For more than 150 years, the Waverly Dam has been an integral part of picturesque Waverly, Iowa; population 10,000.
In 1853 city founder William Harmon built his family a cabin on the Cedar River's heavily wooded east side and a dam of stone and timbers to power his sawmill, which would provide lumber for the growing town. Additional water-powered mills followed, including a flour mill and a woolen mill. By the 1880s entrepreneurs had built a more uniform and durable crib dam to harness the river's power for industrial use. The crib dam was constructed using large timbers connected with steel spikes to form “cribs,” then hand-filled with stone to add weight.
Waverly boasts the oldest operating hydroelectric plant in the state (circa 1908), which annually saves the city $100,000 on electricity. Over the years the river's value to the city's industrial and economic development led to extended development on the adjacent floodplain and a need for more power.
In 1915, the original crib dam was replaced with a concrete dam and elevated spillway. Unfortunately, the new structure plagued residents with decades of persistent and regular flooding. Memorable flood events occurred in 1917, 1933, 1945, 1948, 1961, 1965 (twice), and 1993 (twice). A 100-year flood hit in 1999 and a 500-year flood struck in 2008, destroying hundreds of homes and businesses.
After the 100-year flood of 1999, Waverly's Department of Public Works retained Stanley Consultants Inc., which had designed improvements to the dam in the 1940s, to perform a flood protection study. The engineering firm identified two methods of flood protection: levees or an “inflatable” dam.
Surprisingly, at public forums the inflatable dam concept held the popular appeal with residents. Despite the hardship it has caused, most embrace the Cedar River as a recreational and aesthetic asset and feel their city should be “one with the river.” They considered levees to be the equivalent of turning their back on this resource and creating a visual obstruction that would put the community at odds with it. An inflatable dam, on the other hand, would maintain recreational opportunities and hydroelectric functions while also preserving the community's historical look and feel.