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.