As controversial as dams now are in the United States, their rise was driven by logical imperatives: flood control, fire protection, irrigation, water storage, and mechanical and hydroelectric power. Construction of new dams hit an all-time high in the United States between 1950 and 1970, deemed by some to be “the golden age of dam building.” In his campaign speeches of 1960, presidential candidate John F. Kennedy called on Americans to “harness our rivers,” and nearly 20,000 dams were built in the subsequent decade. The U.S. Army Corp of Engineers maintains an inventory of more than 87,000 dams in the United States. Yet in 2011 the U.S. demolished its thousandth dam, and 430 were removed just in the last decade. In the fifty-four years since Kennedy’s call, what has caused us to conclude that damming our waterways is a bad idea?
The ecological repercussions of damming waterways take more time to observe than, say, plumes of smoke billowing from a coal refinery. Plus, to appreciate how dams adversely affect rivers, it is necessary to understand how a healthy river works, from source to sea. That presents an extremely complex dynamic, often crossing or demarcating state or national boundaries. And then, every river is different. Unique spawning grounds, distinct species, rates of water flow, soil content, mineral content of bedrock—all of these factors figure into the impact a dam has on a particular riverine ecosystem. Now, given the demands on the U.S. power grid, which dams remain necessary, and, if one can rate the differences, which are the most environmentally destructive?
Since the 1970s, river ecologists have accumulated data and identified some underlying constants in the complex ecosystem of an undammed river. A free-flowing river slowly but inexorably erodes away the land through which it flows. Not surprisingly, headwater streams in the mountains and uplands tend to have a high gradient. Rushing water from steep slopes converts native rock into boulders, cobble, gravel, sand, and silt, and carries the particles downstream as “bedload” along the bottom of a river. As gradients decrease, water speed slows and that bedload starts falling out, the coarser material first, the finer material last. The river deposits its sediment and meanders through its floodplain. Eventually the remaining bedload gets carried to the sea, where the materials settle out to form deltas, beaches, and barrier islands.
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Although an undammed river flows continuously, different segments of the flow have distinct characteristics. Rapids and falls cause aeration. Cold water holds more oxygen than warm water. At lower elevations, water temperatures are higher, and dissolved oxygen content is often lower. Different species of fish have evolved and adapted to conditions in each of these segments. Brook trout in the eastern U.S., for example, and cutthroat trout in the West, breed and live their whole lives in cold and highly oxygenated headwater streams. Other species—Atlantic and Pacific salmon, American shad and other river herring, rainbow smelt, many species of sturgeon, sea lampreys, and striped bass—are anadromous: they breed in fresh water but live their adult life at sea. In a reverse pattern, American eels are catadromous; they are born in the Sargasso Sea in the mid-Atlantic Ocean and migrate as juveniles to freshwater rivers, where they grow to maturity. Regardless of where these species breed and then migrate, whether river or sea, both categories of fish are classified as diadromous and require the full run of a river.
Diadromous fish often migrate far upriver, probably to minimize competition or predation on themselves or their young. In an undammed river, Atlantic salmon and river herring can travel hundreds of miles to their destinations. Some Pacific salmon travel more than two thousand miles up the Yukon River in Alaska and the Yukon Territory. American eels grow to maturity high in mountain streams after lengthy upstream journeys. Diadromous fish bring nutrients from the ocean to rivers by way of their carcasses, feces, and unhatched eggs. In the well-known case of Pacific salmon, which all die after spawning, their bodies get recycled by invertebrates, amphibians, fish, birds, and bears. In the East, sea lampreys indigenous to the North Atlantic also die after spawning, thus contributing nutrients to rivers. Atlantic salmon and river herring are thought to play a similar role at a lower trophic level, because many survive spawning and return to the ocean.
As soon as a stream is dammed, it is broken into disconnected segments. The free-flowing sections are interrupted by slow water impoundments. The interruption of natural river flows has adverse biological, chemical, and physical consequences. The habitat within an impoundment created by a dam is compromised. The structure—the plants and animals that live there—and function of the resident communities of a free-flowing river are disturbed. Fish and invertebrates adapted to fast-flowing water become homeless. Reduced light penetration diminishes bottom-dwelling flora and the invertebrate fauna that feed on it and support predatory vertebrates. The rate of water exchange in an impoundment is greater than in a natural lake. It is measured in hours or days, whereas water exchange in natural lakes is measured in weeks or months. For this reason, the zooplankton community at the base of the food chain in natural lakes does not thrive in impoundments. Biologically, an impoundment works poorly as either a river or a lake.
Still-water ponds at the heads of dams host warm-water predators that ravage juvenile migratory fish moving downstream. Drawdown of storage impoundments creates biological deserts, unfit for either aquatic or terrestrial life. Lack of aeration and warming of water lowers dissolved oxygen levels, as do bacteria that consume organic material in sediments. Anoxic bottom waters occur when impoundments stratify. Many impoundments were never cleared of trees before flooding. Decaying vegetation consumes oxygen, generates carbon dioxide, and creates a weird chemical stew as organic compounds are released. Retention of pollutants and nutrients brings growth of undesirable vegetation and mats of often-toxic algae. Retention of sediments reduces the storage capacity of impoundments. Many become useless in just a few decades. At the same time, downstream regions are starved of replacement material. Altered seasonal flow patterns interfere with formation of pools and riffles.
Loss of water by evaporation reduces flow significantly, particularly in the arid and currently drought-stricken West. It is estimated that the cumulative loss on the Colorado River from evaporation at Lake Powell (formed by the Glen Canyon Dam), Lake Mead (formed by the Hoover Dam), and other dams is 20 percent of annual river flow.
The single most negative effect of dams is disruption of fish migration. Both river-resident and diadromous fish breed in some stream reaches, feed in others, and overwinter in still others. Dams without fish passage are an absolute barrier to migration. Of those that have fish passage, even the best-designed fishways cannot compete with the efficiency of an undammed stream.
A frequently cited rule of thumb is that a well-designed fishway will allow about 90 percent of fish to proceed upriver. In a multi-dam system, the cumulative effect can be great. On the Connecticut River, the largest in New England, almost 400,000 American shad arrived in 2013 at the lowermost dam in Holyoke, Massachusetts. Less than 10 percent of those arrived at the next upstream dam at Turner’s Falls, Massachusetts, less than 5 percent at the dam above that at Vernon, Vermont, and none at all at Bellows Falls, Vermont, the fourth upstream dam, even though there are fish passage facilities at all of the dams.
Many species either cannot or will not use fishways. Large fish—such as the black drum, blue and channel catfish, paddlefish, and sturgeon native to the Ohio, Missouri, Tennessee, and other rivers of the Mississippi Basin—require specialized fishways. Some species are weak swimmers, and cannot move upstream against the flow. Others are too nervous to enter. American shad are notoriously finicky. Adult anadromous fish returning in the spring face delay when they encounter high water and cannot find the fishway entrance. By the time flows have dropped, water temperature has often increased. The fish must then swim through a head pond with poor oxygenation and high temperature, increasing their stress.
Loss of post-spawn adults and juvenile fish migrating downstream is another problem. Many dams have no downstream passage. In those that do, it is usually an afterthought, such as a tube or a slot cut into the dam. It is frequently located near the turbine intakes, and can be difficult for downstream migrants to find. Some fish are killed passing through turbines; some are caught in racks meant to snag trash; and some spill over the top of the dam and are dashed on rocks below. Cumulative losses of migrating fish at multiple dams can reduce overall survival dramatically. Not all of these negative effects exist at every dam, but every dam has some of them. As John Waldman, a professor of biology at Queens College, New York, sums it up: “A dam is the most profound affront to the ecological health of a river.”
European settlers arriving in North America started by building milldams. The fall line of the Piedmont, where the eastern foothills of the Appalachian Mountains meet the Atlantic Coastal Plain, stretches southwesterly for 900 miles through dozens of large and small industrial towns, running from Paterson, New Jersey, through Richmond, Virginia, to Columbus, Georgia. All of these towns were founded to take advantage of water power. Concern for fish passage was minimal. The nineteenth century brought larger dams for hydromechanical power that used turbines instead of waterwheels. Typical was the 917-foot-long and 24-foot-high Edwards Dam, built in 1837 on the Kennebec River in Augusta, Maine to power sawmills and later a textile mill. (It was converted to hydroelectric generation in 1913.)
Few rivers escaped this fate. Henry David Thoreau addressed blocked fish passage in his 1849 book, A Week on the Concord and Merrimack Rivers, which recounted his 1839 trip with his brother John in their homemade dory. The following passages refer to the dam in the town of Billerica, Massachusetts, just above where the Concord River enters the Merrimac at Lowell.
Salmon, Shad, and Alewives were formerly abundant here, and taken in weirs by the Indians, who taught this method to the whites, by whom they were used as food and as manure, until the dam . . . at Billerica . . . put an end to their migration hitherward . . . . It is said, to account for the destruction of the fishery, that those who at that time represented the interests of the fishermen and the fishes, remembering between what dates they were accustomed to take the grown shad, stipulated, that the dams should be left open for that season only, and the fry, which go down a month later, were consequently stopped and destroyed by myriads. Others say that the fish-ways were not properly constructed. Perchance, after a few thousands of years, if the fishes will be patient, and pass their summers elsewhere . . . nature will have levelled the Billerica dam . . . and the Grass-ground River run clear again, to be explored by new migratory shoals.
The history of the Billerica Dam is a study in controversy. Every East Coast colonial and state archive holds hundreds of petitions to state authorities from angry citizens deprived of access to historic fisheries. Dam owners usually had the economic and political clout to fend off petitioners. In 1871, Spencer Fullerton Baird, the first U.S. Commissioner of Fish and Fisheries, surmised that the collapse of marine groundfish stocks in southern New England was due to impassable dams.[media:node/2688 caption vertical medium right]
While dams raised the water level to drive mills, loggers also relied upon the power of water to move their product. Logs harvested in the winter were drawn by teams of oxen or horses on sleds over snow or ice to the nearest river. In the spring, the logs were pushed into the stream to travel to sawmills. Dams collected runoff from snowmelt and stored sufficient water to drive logs for long distances. The water was released a little at a time, keeping the logs moving while holding back enough water for later in the season. The mass of moving wood plowed up the streambed, ruining miles of habitat. Thousands of abandoned and deteriorated logging dams impact stream flow to this day.
The final third of the twentieth century brought a sea change, so to speak, in the public’s understanding of the negative impact on the environment of longstanding commercial and government practices. A prerequisite to the concept of dam removal was a series of epic environmental fights over dam construction that took place in the 1960s and 1970s. With changing public attitudes, organized protesters successfully blocked the construction of major dam projects in the Colorado, Delaware, Tennessee, and St. John rivers. The flavor of that era is captured in John McPhee’s 1971 book, Encounters with the Archdruid, relating the struggle between David Brower of the Sierra Club and Floyd Dominy of the Bureau of Reclamation. Had those battles not been won by dam opponents, the regulatory landscape in which dam removal is recognized as a serious option would not look nearly as robust as it does today.
Even so, preventing the construction of a new dam was not the same as removing an existing dam. Well into the late twentieth century, the concept of dam removal was difficult to grasp. In 1976 the Edwards Dam on Maine’s Kennebec River was breached in a flood. A few isolated voices called for removal of the remnants to open the way for migratory fish, but the dam was rebuilt.
The mind-set began to change as the negative impact of dams became increasingly apparent in the Pacific Northwest. Crashes of Pacific salmon populations led to the loss of thousands of jobs in the fishing industry. The near extinction of important subpopulations resulted in listings under the Endangered Species Act. The destruction of food resources was a violation of treaty rights with Northwest tribes and nations. Efforts to compensate by producing fish in hatcheries, and by such costly and bizarre procedures as trapping migrating juveniles and barging them downstream through miles of dead-water head ponds, are recognized as ineffective attempts to compensate through technology for the destruction of natural processes. On the Atlantic Coast, the memory of lost resources was not as strong as on the West Coast. But there were those who perceived dams as a major impediment to the restoration of migratory sea-run fish.
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In the State of Maine, open clashes between restoration of sea-run fish and dam owners began in the 1980s and resonate to this day. After passage and refinement of the Anadromous Fish Conservation Act, with its federal staff support and federal dollars, Maine began to work with the U.S. Fish and Wildlife Service (USFWS) and the National Marine Fisheries Service (NMFS) to restore migratory sea-run fish. Maine’s two largest rivers, Penobscot and Kennebec, became targets for restoration because of the ecological, economic, and sociological benefits.
Under the Federal Power Act, the Federal Energy Regulatory Commission (FERC) has exclusive authority over hydroelectric generation. Dams are licensed for periods ranging from thirty to fifty years. Licensing or relicensing a dam is a complex process, carried out over five years or longer. In the early 1980s, Maine had developed a restoration plan for the lower Kennebec River that called for removal of the Edwards Dam, and in 1986, Congress made that possible by amending the Federal Power Act to require consideration of environmental values and state plans when licensing power facilities. But when the Edwards Dam came up for relicensing in 1993, the owner wanted to preserve the status quo—no fish passage, just trap and truck of river herring for the duration of another thirty-year licensing cycle. Federal and state fishery agencies, and a consortium of nonprofit environmental groups organized as the Kennebec Coalition, thought otherwise. Biological and economic studies predicted that restored sea-run fisheries would far exceed in value the amount of electricity the dam produced. Through a decade of contentious proceedings, two successive Maine administrations supported removal of the Edwards Dam. In 1997 a historic first-ever-in-the-nation decision was made to decommission and remove the dam. It was taken out in 1999. A seventeen-mile section of flat water was transformed into a vibrant river with rapids, riffles, pools, and gravel bars. The biological results were spectacular—all the predictions for recovery of sea-run fish were borne out. Millions of alewives soon appeared at the Fort Halifax Dam, twenty miles upriver. [for more on Maine river restoration, visit www.mainerivers.org.]
The Fort Halifax Dam, with no fish passage, then stood a short distance above the mouth of the Sebasticook River, the largest tributary of the Kennebec. The Sebasticook’s headwater lakes are ideal spawning habitat for alewives. When the Fort Halifax Dam came up for relicensing, the public utility that owned it concluded that the dam could never generate enough electricity to repay the cost of installing fish passage, so it applied to FERC for authority to decommission and remove the dam. At the eleventh hour, however, landowners, who realized their riverfront properties were about to be profoundly changed, banded together to oppose removal of the dam. After many hearings and court appeals, common sense prevailed and the Fort Halifax Dam was removed in 2008.
In the mid-1980s the lower Penobscot River had four dams. When a fifth was proposed, the Basin Mills project by Bangor Hydro-Electric Company, the USFWS concluded that yet another dam would doom the fish restoration that had been underway for two decades. Federal and state fishery agencies, the Penobscot Indian Nation—which has treaty rights to fish for food and ceremonial purposes—and citizens led by the Atlantic Salmon Federation spent the next decade battling the Basin Mills proposal. Eventually, the proposal was terminated, and two more dams were removed: the Great Works Dam was demolished in 2012, followed by the Veazie Dam in 2013. After almost three decades of effort and the expenditure of more than $60 million, one thousand miles of spawning and rearing habitat is available to sea-run fish.
In California, the 106-foot-high San Clemente Dam on the Carmel River south of Monterey Bay is being dismantled in the largest dam removal project in California history. The dam was built in 1921 for water storage. By 2002, the impoundment had filled with 2.5 million cubic yards of sediment and gravel, reducing its capacity by 95 percent and making it useless as a reservoir. The project, begun in 2013, will take three years and cost $84 million. Restoration of Pacific salmon and steelhead trout is the goal. Beach nourishment along the central California coast is anticipated to be a collateral benefit as sediments that once would have been trapped in the impoundment are carried to the sea.
Also on the Pacific Coast, the largest dam removal project in the nation to date took place on the Elwha River in Washington State’s Olympic Peninsula in 2012. The 105-foot-high Elwha and 210-foot-high Glines Canyon Dams were removed. The beneficiaries will be Pacific salmon and steelhead trout. The dams had become obsolete in less than a century because the impoundments silted up. As removal has progressed, the amount of sediment, originally estimated at 18 million cubic yards, has turned out to be almost double that much.
Nationwide, efforts are ongoing to remove dams that have outlived their usefulness or that produce less in value than the benefits that would accrue from their removal. The opportunity to remove a dam doesn’t happen in a vacuum. Usually a specific event prompts the decision. It may be that in the process of FERC relicensing it becomes evident that the expense of installing required fish passage would be economically unfeasible. The dam may have become unsafe. Dams need constant maintenance, such as periodic removal of debris that has floated down from upriver. As a dam ages, repair costs increase. A neglected dam poses a threat to the life and property of those living downstream. Liability insurance, if obtainable, can be ruinously costly.
Removing a dam can actually be of economic benefit for a community. After engineers have figured out the best plan of action, breaking up and removing a dam becomes a construction project. Contrary to popular belief, dynamite is seldom the tool of choice. Instead, new temporary, coffer dams are built to divert river flow. Access roads for heavy equipment are then constructed in the riverbed below the dam. Hydraulic rams attack the downstream dam face, and rubble is removed. Then the roads and coffer dams are removed, all the while trying to minimize any environmental disruption.
The federal government provides the majority of the funding for these costly projects. NMFS and USFWS both receive annual appropriations from Congress for this purpose. The National Fish and Wildlife Foundation and other federal agencies also receive funds. Other funders range from state agencies to foundations and private donors. Money is distributed through a variety of methods to the organizations that do the boots-on-the-ground grunt work of planning and permitting, engaging contractors, supervising the work, and reporting back to the funding and permitting agencies once the removal has been completed. These groups include state agencies and private sector entities. Organizations managing distribution of federal funds to smaller groups include American Rivers, Trout Unlimited, and the FishAmerica Foundation.
What is the future of dam removal? Not all dams are candidates for removal. Dams that are large electricity producers, furnish drinking or irrigation water, control floods, or support barge transportation are less likely to be removed. Drums have been beating for years to remove four dams on the Snake River in Idaho, a major tributary of the Columbia River, and four dams on the Klamath River in California. But there is support from agricultural and transportation interests for keeping them. Those proposals will not play out for years or even decades. Nonetheless, it seems probable that if alternative energy sources can be tapped, dams will likely outlive their purpose, and the trend of dam removal will continue.