Lowhead dams are short (<7.5m) constructed barriers that bisect streams, but allow uninhibited discharge of water over the top of the dam. Due to the alteration of stream habitat and flow, these dams significantly impact a stream’s geomorphic, chemical, and biological processes. Lowhead dams disrupt the transportation of sediment in a stream, creating sediment traps in upstream reaches and causing erosion and instability in downstream reaches that are deprived of their sediment load. These changes in geomorphology, along with other factors such as disrupted flow regimes and altered chemical compositions, negatively affect stream communities as many organisms are left without suitable habitat.
Throughout the contiguous United States, there are over 45,000 registered lowhead dams (US Army Corp of Engineers, 2016). The actual number of lowhead dams is estimated to be far greater. The removal of these dams is an increasingly common management practice as many lowhead dams are reaching the end of their functional lifespan, requiring costly repairs and creating safety hazards. Over the past century, more than 1000 dams have been removed in the United States and the rate of dam removals has been increasing (O’Connor et al., 2015). One such dam that was removed as it reached the end of its lifespan was the 5th Avenue Dam in Columbus, Ohio. The 5th Avenue Dam, a lowhead dam on the Olentangy River, was constructed in 1935 in order to create a water source for cooling the Ohio State power plant. After the water source was no longer needed, the removal of the dam was recommended by the Friends of the Lower Olentangy Watershed as a means to improve water and stream habitat quality. The 5th Avenue Dam was removed in late summer 2012 following an agreement between the City of Columbus and the Ohio Environmental Protection Agency. Shortly after in fall 2013, the Main Street Dam, located on the Scioto River in Columbus, Ohio, was removed as part of the City of Columbus’s Scioto Greenways Project. The Scioto Greenways project aimed to expand and improve park space alongside the Scioto River in downtown Columbus. Like the removal of the 5th Avenue Dam, the removal of the Main Street Dam was part of an effort to improve water quality and restore aquatic habitat.
(Figure reprinted from Dorobek et al., 2015)
The removal of the 5th Avenue and Main Street Dams provides an excellent opportunity for a large-scale, experiment of ecosystem responses to lowhead dam removal. The Dam Removal Project is an ongoing study of ecosystem responses on varying temporal and spatial scales. Data collection has been conducted from 2011 (pre-dam removal) to present at seven reaches located both upstream and downstream of the removed dams, as well as control sites located upstream and downstream of intact lowhead dams. Data collection includes geomorphic variables (bathymetry and sedimentation), biological surveys (including fish, birds, insects, spiders, and vegetation), and measures of water quality (nutrients, heavy metals, and pesticides). The objective of this study is to examine stream responses to dam removal, with particular focus on changes in the physical structure of the rivers and the surrounding areas, shifts in biodiversity of flora and fauna, and shifts in food web interactions (both within-stream and between aquatic and terrestrial ecosystems). In addition to contributing to the emerging science of dam removal, these findings will aid in informing future land management and stream restoration practices.
Funding for this project has been provided by the National Science Foundation, Ohio Water Development Authority, Ohio Division of Wildlife through the Ohio Biodiversity Conservation Partnership, and United State Geological Survey
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