by Elizabeth Worzalla, M.S., Watershed Program Manager for the Ann Arbor, MI-based Huron River Watershed Council.
We have been as busy as beavers erecting dams on American rivers. Across the country, 2.5 million dams of all sizes block and harness rivers; of those, 80,000 dams are greater than 6 feet high and store a combined total of approximately 1 billion acre-feet – the equivalent to one year’s runoff (Graf, 1999). The 900 square mile watershed in Michigan that I call home has no fewer than 98 dams. Dams serve a wide range of purposes such as hydroelectric power, water supply and irrigation, recreation, shipping, and flood control, and have become integral to the identity of some communities.
Yet, dams have egregious impacts on rivers as they alter chemical, physical and biological processes. Downstream environmental costs of dams captured scientific attention only recently as obvious effects have resulted in the past 2 decades. Dams block free-flowing river systems and impede a river’s flushing function that enables transport of sediment and nutrients downstream; instead sediment builds up behind the dam. Dams fragment rivers and block movement of fish, mussels and other species. Dams have contributed to or caused many species to become threatened, endangered or extinct, in part, because they are located on prime spawning habitat. Many fish species require high gradient, well-oxygenated water and gravelly streambeds for spawning, which are the same parameters that provide a favorable dam site. Dams alter water temperatures, dissolved oxygen levels, turbidity and salinity both upstream and downstream of the structure. Essentially, dams prevent a river and its tributaries from fulfilling their most basic need – to flow.
Many dams across the country have aged beyond their planned life expectancy, causing safety risks for communities downstream. With most dams constructed since the 1950s, many are reaching the end of their typical 50-year design life. At present, about one-quarter of dams are more than 50 years old. The American Society of Civil Engineers estimates the figure to reach 85% by 2020. In many cases, owners are pursuing dam decommissioning as the best option for unsafe dams that are no longer economically viable and that no longer serve a purpose. Often, dam removal costs less than dam repair. Experience with dam removals in Wisconsin has found removal to be 3-5 times less expensive than reconstruction.
Three main factors are converging to change national dam policy from one of expansion to one of removal and maintenance. The dam building era has ended, economic effectiveness of dams has decreased, and safety concerns related to aging dams have placed significant liability burdens on owners. In addition, threatened and endangered species and the continuing evolution of watershed science are drivers in the shift toward river restoration. Certainly, dam removal is not appropriate for all dams as some are economically viable and, in some cases, environmental health could be worsened with removal. However, a significant number of dams in the Great Lakes basin are small dams that provide no economic benefit and serve no purpose, and are the most eligible for removal consideration.
Despite dozens of examples across the country, dam decommissioning still is an emerging field. While no uniform decision-making process exists to determine whether to remove a dam, several factors are essential for reaching a successful outcome. Identify stakeholders and key players and encourage their participation in the process early in the discussions about the dam’s future. Involve citizens by providing notice of meetings and opportunities to collect information to aid in decision-making. Dam ownership and dam regulation are two key factors that will need to be considered in the early stages. Many issues need to be reviewed including engineering, hydrology, hydraulics, ecology, water quality, fluvial morphology, socioeconomic factors and construction options. Even with these factors present, there is no guarantee that removal will happen. But without these factors, removal almost certainly will not happen. Engineering issues rarely prevent removal of a dam; more often individuals in opposition to a removal stymie the process and prevent a successful outcome. Each situation is unique and will require a particular set of economic, legal and environmental quality tools.
Myriad tools are in development to assist with dam decision-making. American Rivers, based in Washington, D.C., and River Alliance of Wisconsin are just two of many groups offering publications and videos to walk communities through the process. Numerous workshops with instructors experienced in dam removals are offered across the country for the concerned citizen, the state dam program manager, and everyone in between. A good place to start is “Dam Removal: A Citizen’s Guide to Restoring Rivers” created by the River Alliance and Trout Unlimited.
As more dams age, the nation will need comprehensive plans at state and national levels to handle dams. What to do about a dam is a question that will face increasing numbers of communities, dam owners and government agencies. Dam safety concerns will continue to drive assessments of a dam’s value. Dam removal experts identify tying dam removal to community redevelopment as a future trend as restoring rivers generally increases property values in the community. Also, removal will need to be placed more in the context of its role in water quality management, including evaluating dams in watershed management plans.
With watershed-level restoration gaining ground and public appreciation for rivers continuing to grow, our ability to remove dams that do not make sense will increase. And that’s very good news for our rivers.
Thank you to the Great Lakes Aquatic Habitat Network & Fund for helping to support community-based training in dam decommissioning.
The impacts of dams on the Great Lakes basin were described in a recent study that conducted a national census of dams based on the National Inventory of Dams. The Great Lakes basin has 2,075 dams that are 6 feet or higher with 66.3 acre feet/mile of storage area. There are 10,523 persons per dam, and storage per person is 1.14 acre feet/person.
Source: W. L. Graf. 1999. Dam nation: A geographic census of American dams and their large-scale hydrologic impacts. Water Resources Research, vol. 35, no. 4, pp 1305-1311.