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Dam Decommissioning and Sediment Management
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The integrity of aging structures is a recurrent global issue, including in the United States.

Of particular interest are the number of aging dams in the United States, the average age of which is 56 years. In addition, more than 2,000 of them are at least 120 years old. Many of these dams have outlasted their life-cycle, hence when performing a life-cycle analysis of them, decommissioning is usually an option considered. Multiple drivers affect the dam removal decision process, including cost-benefit of maintenance and repairs versus removal, energy production, recreation, possible mobilization of contaminated sediments, and cultural and ecological benefits. Regardless of the reasons for decommissioning a given dam, evaluation of the following aspects is necessary: engineering, hydrology and hydraulics, environmental restoration of the pool area, riverbank erodibility downstream, habitat restoration, etc. Among those aspects, sediment management is key to the success of the decommissioning process, and it is critical to understand the contaminants, quantities, method of sediment transport, as well as habitat created or modified, and the future of water quality in the river system.

Some questions to be answered include what is the applicable regulatory framework for sediment management in decommissioning, what are the considerations for sediment fate and transport when a dam is decommissioned, and how can the quality and quantity of sediments be assessed most effectively and efficiently to quantify potential contamination and the risks and costs associated with sediment removal and final disposal.

This paper explores these topics and presents a case study involving a sediment characterization, field investigation, and data analysis to support dam decommissioning for two reservoirs in California. The case study also addresses a feasibility study featuring model predictions of how the sediment will be evacuated from the reservoir under different notching/demolition options.

Publication Summary

  • Geosyntec Authors: Rob Annear, Anju Wicke
  • All Authors: Rob Annear, Anju Wicke
  • Title: United States Society on Dams (USSD) 2022 Annual Conference
  • Event or Publication: Event
  • Practice Areas: Dams; Dam Safety
  • Citation: United States Society on Dams (USSD) 2022 Annual Conference and Exhibition at the Town and Country Resort in San Diego, California on April 11 through 14, 2022.
  • Date: Wednesday, April 13 at 10:30 a.m. PDT
  • Location: San Diego, California
  • Publication Type: Platform Presentation