Planning and implementing small dam removals: lessons learned from dam removals across the eastern United States

Abstract

We review and build on a growing literature assessing small dam removal outcomes to inform future dam removal planning. Small dams that have exceeded their expected duration of operation and are no longer being maintained are at risk of breach. The past two decades have seen a number of small dam removals, though many removals remain unstudied and poorly documented. We summarize socio-economic and biophysical lessons learned during the past two decades of accelerated activity regarding small dam removals throughout the United States. We present frameworks for planning and implementing removals developed by interdisciplinary engagement. Toward the goal of achieving thorough dam removal planning, we present outcomes from well-documented small dam removals covering ecological, chemical, and physical change in rivers post-dam removal, including field observation and modeling methodologies. Guiding principles of a dam removal process should include: (1) stakeholder engagement to navigate the complexity of watershed landuse, (2) an impacts assessment to inform the planning process, (3) pre-and post-dam removal observations of ecological, chemical and physical properties, (4) the expectation that there are short-and long-term ecological dynamics with population recovery depending on whether dam impacts were largely related to dispersion or to habitat destruction, (5) an expectation that changes in watershed chemistry are dependent on sediment type, sediment transport and watershed landuse, and 6) rigorous assessment of physical changes resulting from dam removal, understanding that alteration in hydrologic flows, sediment transport, and channel evolution will shape ecological and chemical dynamics, and shape how stakeholders engage with the watershed.

Fracturing dams, fractured data: Empirical trends and characteristics of existing and removed dams in the United States

“…These estimates of need will only increase over time, as federal funding for dam rehabilitation is currently not appropriated (ASCE, ). Given these very large ranges likely due to regional and project level factors (Tonitto & Riha, ; Whitelaw & MacMullan, ), our goal with these estimates is not to provide absolute certainty in rates and costs of future removal but to highlight the magnitude of trends, their economic relevance given other estimates of dam safety need, and make a case for more systematic data collection to refine our understanding and future projections.…”

Streambank Legacy Sediments in Surface Waters: Phosphorus Sources or Sinks?

“…This raises the question of how do the anoxic conditions influence the fate and release of P associated with millpond and streambank sediments? Moreover, dams are increasingly being removed across the mid-Atlantic and elsewhere [66][67][68][69]. An important question that is on the mind of many watershed managers and environmental agencies is how does the removal of the dams influence particulate and dissolved fractions of P stored upstream of the dams in the stream channel and along the banks?…”

Response of benthic macroinvertebrates to dam removal in the restoration of the Boardman River, Michigan, USA

“…Full restoration of species richness and densities, however, may take longer [21], and the macroinvertebrate community in the Boardman River will likely continue to shift as the stream habitat changes over the long term. Dams limit biota through impeding migration and altering habitat [5]. Such limitations and alterations are eliminated with dam removal.…”

“…Dams alter the downstream flow of nutrients, sediment, and organic matter, and limit macroinvertebrate drift [2,3]. Dams also create barriers to movement of aquatic organisms to upstream habitats, an effect most detrimental to fish populations, particularly diadromous fish species, because dams block these species' essential reproductive migrations and stop movement of juveniles to habitats required for optimal feeding and growth [4,5]. Additionally, dams reduce lateral connectivity in floodplain habitats and alter floodplain function by eliminating flooding [6].…”