In the 1960s, the peak period of dam construction, the United States built the equivalent of five large dams a day. The National Inventory of Dams (NID) catalogues these dams and many others built since then. By 2020, 85 percent of the approximately 79,000 dams currently catalogued by the NID will have exceeded their 50-year life span.
The NID categorizes dams as those that are: (a) 6 feet or higher and impound at least 50 acre-feet of water, (b) 25 feet high and impound at least 15 acre-feet of water, or (c) a potential serious hazard to people downstream. The decision to remove or take a dam out of commission occurs for a number of reasons.
Often, the cost of maintenance and environmental compliance outweigh power revenue. For instance, many of the dams built in the 1960s and after were granted 50-year license agreements by the Federal Energy Regulatory Commission. As these permits come up for relicensing, the dam owners must meet new, more stringent environmental regulations.
Those owners along the Pacific Rim have the added concern of seismic activity. Dams that pose a potential hazard to downstream communities must undergo renovation to meet current seismic standards. In other cases, the original purpose of the dam — water storage, hydroelectric production, flood control, et cetera — is no longer applicable.
The funds to remove a dam can come from a variety of sources. The American Recovery and Reinvestment Act (ARRA) is helping fund the National Park Services for the removal of the Elwha and Glines Canyon dams in Washington. The Bureau of Reclamation is using ARRA funds to study the removal of four dams on the Klamath River in California and Oregon. In another case, the National Oceanic and Atmospheric Administration (NOAA) used its stimulus funds to help Jackson County, Ore., remove the Gold Ray Dam and hydroelectric facilities as part of NOAA’s habitat restoration program. Funding can also come from congressional earmarks and state watershed enhancement board grants.
Once funding is available, the engineering expertise to remove a dam and its related infrastructure is straightforward. It often includes the removal of spillways, the powerhouse, flow lines, and surge tanks, as well as the reservoir piers and docks. However, the consequences created by the dam removal require careful attention and are often complex. Environmental challenges are common, particularly when the dam removal is driven by fishery issues, and sediment management is critical to restoring the watershed.
Fundamentally, there are three stages to removing a dam: early feasibility assessment, final design just prior to breach, and removal/restoration. The feasibility study should include sediment characterization; assessment of impacts to fisheries, water quality, cultural resources, and manmade facilities; and regulatory requirements as defined by federal, state, and local agencies. Once a conceptual design approach is developed, the plans must be refined to include sediment management plans, aquatic protection, woody debris management, re-vegetation, and recreation changes, as well as traditional construction management processes that range from traffic control and public safety to the transport of hazardous materials.
The United States has removed 20 to 50 dams annually during the last 10 years — only 1 percent of the total dams in the NID inventory. There are many more to go as we transition through this age of dam repair, removal, and decommissioning.
Links to online resources
Peter L. Stroud, CEG, is a principal engineering geologist for Kleinfelder. He can be reached at email@example.com.