Sediment Management during Low Dam Removal

Sediment management has become one of the key issues during the removal of dams, irregardless of whether the dam is removed because it is obsolete, unsafe, ecologically harmful, or simply unwanted. Many sediment management techniques have been used at low dams. The first step in removal is to assess potential downstream impacts and sediment transport to determine whether natural erosion of the sediment is tolerable and permitted by regulatory agencies. Active sediment management is appropriate along streams that are sensitive due to water supply sources, aquatic habitats, presence of rare and endangered species, recreation, contaminated sediment, or rivers with flood hazards. Sediment management options include use of excavated channels, headcut controls, partial sediment relocation, sediment removal, bypass channels, and partial breaches. Active sediment management helps to minimize the downstream impact of excessive sediment releases. In addition, it can aid the formation of a new upstream channel across the former pool area, provide fish passage, and accelerate aquatic and floodplain habitat restoration. In contrast, passive sediment management allows natural processes to readjust the sediment deposit and form a new channel that is proportional to water discharges and sediment loads.