- Over 470 dams have been removed in the United States, and a significant increase in dam removals has
occurred since the early 1990s. The aging of dams is often cited as the primary factor influencing removals;
as dams surpass their functional life span, safety hazards, economic costs, and environmental concerns can
increase significantly. However, the removal of dams has physical, economic, social, and political impacts
and the distribution of dam removals may be influenced by factors other than age. By analyzing this
distribution, this study aims to assess the various factors influencing the removals of dams. Understanding
these guiding factors ultimately will assist in the development of policies for future dam removals and
promote cooperation between the varied stakeholders in a particular region.
With the help of other researchers, I created a database of dam removals in order to analyze the
dam removal distribution in the United States. The database enabled an examination of three research
questions pertaining to the distribution of dam removals: 1) whether the age of dams influences distribution;
2) whether political boundaries influence distribution, through the presence of state dam statutes; and 3)
whether physical boundaries influence distribution, through the presence of coordinated river restoration
projects involving dam removal. The results of this study show a spatially and temporally uneven distribution
of dam removals in the United States. A weak trend toward removing older dams is apparent, suggesting
factors other than age controlling dam removals. Political, or state, boundaries appear to influence the
number of dam removals found within a particular region. These states that include provisions for dam
removals within a state statute have the highest number of dam removals, on average. Physical, or river basin,
boundaries also appear to influence dam removal distribution, although to a lesser degree. Several basins with
the most dam removals have coordinated ecosystem or river restoration efforts that include dam removal.
On average, the basins with coordinated restoration efforts have more recent dam removals compared to
dam removals nationally, suggesting a trend toward basin-level restoration efforts that include dam removal.
Other factors also appear to influence dam removal distribution as well, such as the presence of dam removal
organizations and agencies and state-supported funding for dam removal.