Engineering considerations for large dam removals

The removal of a large dam requires special engineering considerations not normally required for the removal of smaller dams. Large dams generally provide greater project benefits, but they represent a higher downstream hazard in the event of failure and greater challenges to fish passage. The reservoirs associated with large dams can impound more sediment and affect downstream water quality to a greater degree. The environmental compliance and decision-making process for a large dam removal project can take many years and will normally require the evaluation of a full range of project alternatives with estimated costs, the performance of a comprehensive environmental impact analysis, and the identification and implementation of extensive mitigation measures. Streamflow diversion and demolition plans for the removal of a large dam must ensure acceptable construction risks from start to finish, and produce reservoir drawdown at a controlled rate for sediment management purposes and to prevent instability of natural or embankment slopes. Large dams require more time for removal, at a higher cost, and contain greater volumes of materials for which disposal sites must be found. © 2013 Geological Society of America. All rights reserved.