Committee on Dam Decommissioning |
Terms of Reference
USSD Policy Statement on Dam DecommissioningDecommissioning is defined as the full or partial removal of an existing dam and its associated facilities or significant changes to the operations thereof. Dams were first built on the Nile River sometime before 4000 BC. Since that time, dams have been constructed to benefit mankind by providing water supply reservoirs, irrigation for agriculture, flood control, power, navigation and recreation. The oldest dams still in existence date back to the sixteenth century. Although the design of dams is typically based on a 50-year economic life, most appropriately designed dams are intended to last indefinitely with proper maintenance and periodic repairs. Without proper operation and maintenance, dams may deteriorate and can ultimately create public safety hazards, which must be corrected. Also, as societal values change some dams are considered undesirable from an economic, environmental, or other public interest or political standpoint. When any dam becomes a safety hazard that is uneconomical to repair or is deemed undesirable for other reasons, treatment alternatives may include decommissioning up to and including dam removal. The cost of decommissioning a dam can be very significant, especially the removal and disposal of contaminated reservoir sediments or replacement of lost hydropower generation. Each situation is different and must be considered on a case by case basis. Once a decision has been reached that decommissioning may be the best alternative, the actual dam removal must be carefully planned, giving full attention to the economic and environmental consequences of such removal. The incorporation of proper environmental protections must be an integral part of the removal plan.lanning for the removal process must include input by all affected stakeholders. Decommissioning of Dam Projects - Issues To Be Considered(Draft 8/14/01)IntroductionThe purpose of this paper is to introduce the issues associated with the decommissioning of dams. Decommissioning is defined as the full or partial removal of an existing dam and its associated facilities or significant changes to the operations. Dam decommissioning has not received much attention until recently, but is rapidly gaining momentum as societal priorities change. This paper is intended to create an awareness of the concept and stimulate thinking when dam decommissioning is being considered. The building of dams to provide for growth, development, and national security has been an important part of economic and social development of the United States. Thousands of existing dams now support a multitude of benefits. The most common uses of dams and reservoirs are the management of water for industrial and municipal supply, agricultural, flood control, recreation, and power generation purposes. Dams and reservoirs also provide for wildlife and fishery enhancement. Several changes have occurred in the past decade to limit the construction of new dams and to create more interest in the removal of existing dams:
Reasons for DecommissioningThere are many reasons for removing a dam - obsolescence, environmental concerns, economics, safety criteria, risk reduction, and operation and maintenance costs. Dam construction, repair, and operational costs of today far exceed those of even a decade past. Many older dams do not meet current safety criteria for floods or earthquakes. The benefits provided by the dam, such as hydropower production, may not justify repairing or rebuilding the dam. Along with keeping a dam compliant with existing safety criteria, legal liability in the event of a sudden uncontrolled release of water is an increasing concern. Dam failures, especially those with the potential for loss of human life, can be devastating in terms of economic and political impacts upon dam owners. Environmental ConsiderationsToday, one of the most common environmental considerations is fisheries habitat for selected species, especially salmonids and other migratory fish that are currently threatened or endangered. Dams without fish passage facilities prevent upstream migration of spawning adults, while inlet/outlet works and spillways of reservoirs may increase the mortality of juveniles as they migrate to sea. It seems intuitive that removal of dams would increase populations of threatened and endangered fish species, but it is a matter of continuing debate as to the impact of dam removals, especially in those areas where fish passage facilities are provided. A second common environmental issue is wetlands that are widely regarded as valuable ecological resources. Productive wetlands are sometimes inundated in reservoirs, but new wetlands and aquatic habitat are created in areas upstream. Similarly the flood protection provided by dams reduces the frequency of inundation in channels downstream as the geomorphology is altered. This tends to modify and move the area and nature of wetlands. Sediment accumulating and stored in reservoirs becomes an environmental concern when decommissioning is contemplated. The suspended solids contained in runoff tend to settle in the quiescent reservoir waters. In industrialized areas these sediments may contain contamination such as metals, oil and grease and many other chemicals. In rural areas these sediments may contain contaminants such as pesticides and herbicides from agricultural operations. The quantity and concentration of sediments, and the rate at which they will be returned to the fluvial system are also a major concern. Disposal of contaminated sediments that would be excavated or dredged prior to dam removal may be a significant issue. Impacts to upstream and downstream infrastructure may be of concern, since foundations for bridge piers and abutments, as well as any shallow pipelines or other utilities that cross the channel may be subjected to increased scour potential from higher flow velocities than they were designed for. Changes in flows may also impact piers, docks and other waterfront structures. Historical and/or archaeological impacts can be a significant issue, particularly where the dam or facilities associated with the dam are on national or state historic registers. At these facilities, removal of a dam may have historical and/or archaeological impacts if a site is altered. Additional considerations include recreational, visual and experiential values. River rafters, fly fisherman and others who use the river for recreation frequently express a desire to see a free flowing river. Dams and reservoirs are often located in relatively rural, natural settings. Many people have expressed distaste for manmade facilities in wild, scenic and natural conditions. It is not clear that dam removal or decommissioning would improve this situation. Economic ConsiderationsIf the dam owner can benefit substantially from ongoing operation of the dam and reservoir, it is normally feasible to maintain and upgrade the facilities to improve dam safety and comply with regulatory requirements. Where the benefits of the dam have been substantially reduced, there is often reluctance to invest in dam repairs, albeit with increased liability. In this case dam decommissioning may be considered for economic (and liability) reasons, as the long-term costs and risks for continued operation of the dam may very well exceed those for dam decommissioning. The economic considerations associated with decommissioning a dam are significant, as for operating and improving an aging dam. Careful advance planning is required, including analysis of alternatives, preliminary cost estimates, permitting requirements and consensus-building with concerned parties that must be identified. The economic losses due to discontinuing operation of the dam (i.e., flood control, irrigation, power generation, recreational uses) must be considered. Upon decision to pursue a dam decommissioning alternative, funding must be obtained. There are several national organizations that may provide funding assistance and/or other technical assistance for dam decommissioning. Funding from federal or state sources may also be available, however, appears to be limited at this juncture. The timing of availability of project funding is also an important factor. The environmental permitting process begins early, and may significantly impact costs for design, construction and maintenance of the decommissioned facility. Permits must be obtained from federal, state and local regulatory agencies, which sometimes take conflicting positions on a number of issues. Such situations may be excessively time-consuming and costly to resolve. Typically, all or most permits must be obtained prior to completion of final design and proceeding with construction of the decommissioning project. If one or more of the permits is denied, the project may not be able to proceed and the investment in decommissioning may be lost. Decommissioning ProcessPlanning a dam decommissioning project is much like the original construction project, except the end product is considerably different. All decommissioning projects are likely to be subject to National Environmental Policy Act mandates. Therefore, it is critical to identify all issues and obtain stakeholder concurrence early in the process. The process begins with the study of all alternatives including repair and upgrade and decommissioning. If decommissioning is the selected alternative, the process will likely follow the steps shown in the following flow chart.  ConclusionDecommissioning of dams is a reality that engineers and dam owners will be facing more and more in the next few decades. It is time to gather and begin to exchange ideas now. Costs associated with decommissioning can be many times the cost of repairs and upgrades. Much can be learned from reviewing the decision process from decommissioning case studies. Further information may be obtained by contacting the Committee Chairperson:
Thomas E. Hepler |