The Unintended Benefits of Dams Should Be Considered Prior to Removal

Abstract

Dams provide multiple benefits; however, they also degrade rivers. Many dams no longer serve their intended purpose and are nearing the end of their operational lives. The aging of dams coupled with the cost of restoration and maintenance, regulation, and the ecologic impacts of dams has resulted in removal becoming a viable management alternative. Despite increased utilization, limited research and a lack of quantitative predictive capacity results in large amounts of uncertainty associated with impacts of dam removal. Additionally, dams which no longer serve their intended purpose may still have unintended positive benefits such as the prevention of the spread of invasive species, providing recreational opportunities, and the treatment of water pollution from upstream reaches. Failure to identify unintended benefits of dams can prevent accurate determinations of the potential consequences of removal. Therefore, identifying unintentional benefits of a dam is an essential step in determining the potential impacts of dam removal. The Mill Pond Dam in the Oak Creek Watershed is being considered for removal. The dam may be a barrier to invasive species, provide recreational opportunities, and improve downstream water quality. A fish passage survey was conducted at all stream crossings within the watershed to determine if the dam is a barrier to invasive species. A bathymetric survey was conducted and E. coli data was collected to determine if the dam provides recreational opportunities. A suite of water quality parameters was assessed weekly for 61 weeks at six sites upstream, within, and downstream of the impoundment to determine if the dam improved physical, chemical, or biological aspects of downstream water quality. The results of this study indicate that the Mill Pond Dam may have acted as a barrier to invasive species, the impoundment did not provide recreational opportunities, and the dam did not improve downstream water quality during the study period. The methods utilized in this study are transferable and could be used at other locations to improve the understanding of the potential consequences of dam removal.