The power to create and restrain floods was once reserved for gods only. But once engineers figured out how to hold back the waters, way back in ancient Mesopotamia, it was only a matter of time before people started building dams all over the planet. Nearly 48,000 large dams (over about 50 feet high) exist today. Collectively, their artificial reservoirs hold several times more water than is contained in all the world’s rivers combined.
But the hubris of affronting the gods has its drawbacks (just ask Prometheus), and building a dam is very often a mistake. A March study from Oxford University on the economics of dam construction was utterly…damming. (Zing!) The researchers concluded that large dams cost far more than they are worth in energy savings.
The human costs are also high. In the last 60 years, dams have displaced between 40 million and 80 million people—usually indigenous communities or the rural poor. Around 200,000 Ethiopians may have to move from their tribal lands once the Gibe III dam is completed. Brazil’s Belo Monte dam, also under construction, will drive up to 20,000 people from their homes.
Although governments typically compensate those forced to resettle, the money doesn’t make up for the loss of an ancestral homeland. An August article in the New York Times told the story of anthropologist Thayer Scudder, a former dam enthusiast who no longer believes large dams can be built responsibly. Scudder documented what happened to the Tonga people of Zambia and Zimbabwe after the construction of the Kariba dam in 1956. It’s a disturbing tale of 50 years of disintegration, unemployment, and tragedy.
Environmental dam-age is also well documented. Dams have blocked fish migrations and put several species of salmon on the endangered list (see “Return of the Ghost Fish”). The endangered snail darter famously went up against Tennessee’s Tellico dam in the 1970s. The case went all the way to the Supreme Court. (The little fish lost.) Dams also trap nutrients behind their concrete, allowing algae and fish parasites to flourish in the stagnant waters of their reservoirs.
The United States has more than 75,000 dams over three feet in height, which is the equivalent of building a dam every day for more than 200 years. Most of them are little-known structures that have fallen into disrepair, but here are five of the most high-profile, environmentally destructive in America.
Glen Canyon Dam
Arizona’s Glen Canyon dam holds back so much of the Colorado River that its reservoir, Lake Powell, is the second-largest artificial lake in America. At 254 square miles and an average depth of 132 feet, Lake Powell took 17 years to fill after completion of the dam. The desert lake’s broad surface area encourages evaporation, and its sandstone basin absorbs water. In total, 8 percent of the Colorado River’s water—which already fails to meet the demands of the region’s population—is lost due to this faulty reservoir.
The dam, like many others, creates problems with sediment. Approximately 45 million tons piles up behind it every year, robbing fish downstream of needed nutrients and badly damaging the structure of the river. The clear, fast-moving water flowing through the dam erodes banks and destroys habitat for important riparian vegetation.
Grand Coulee Dam
On a good day, Washington’s Grand Coulee can generate 6,809 megawatts of electricity, making it the continent’s largest hydroelectric facility. Unfortunately, it has also helped shrink fish populations in the Columbia River to just 8 percent of their historical levels. With 12 million cubic yards of concrete, the dam is so massive that, during construction, planners didn’t even attempt to afford a passage for fish—they knew it was hopeless. Tens of thousands of large chinook once traveled through the area now blocked by the Grand Coulee. Since the dam was erected in 1937, salmon have been virtually gone from the waters above the dam.
Just before the Matilija dam was built in 1948, the number of southern steelhead traveling through California’s Ventura River was more than 5,000. By the end of the century, the population was down to 200. The dam’s fish ladder does not work, and the dam destroyed several beaches downstream. Sediment began accumulating almost immediately behind the structure, so much so that it has hampered the dam’s primary purpose (flood control). In 2000, its water retention was at 10 percent of the dam’s original capacity. For the Matilija, it may no longer be a question of if, but when the wrecking ball will come.
The Lower Snake River Dams
The Snake River begins in Wyoming and slithers between Idaho and Oregon before emptying into the Columbia River on its way to the Pacific Ocean. The four dams on the lower portion of the river—Ice Harbor, Lower Monumental, Little Goose, and Lower Granite—are among the most controversial dams in America.
The dams prevent juvenile salmon from swimming downstream and adult salmon from returning to their spawning grounds. The Snake River’s salmon population is at 3 percent its historic peak, and all four varieties—the Snake River sockeye, spring-summer chinook, fall-run Chinook, and the basin Steelhead—found in the river have been declared endangered. According to the documentary DamNation, in 1992 a single sockeye wonderfish somehow made the trip through Columbia’s dams, earning him local admiration and the nickname Lonesome Larry. In 1995 the Army Corps of Engineers began a seven-year study of how to improve fish stocks. The study rejected proposals to breach the dam, preferring instead to transport fish around the dams by truck and barge.
The Klamath River Dams
The Klamath River system runs from Oregon into California, draining nearly 13,000 square miles of land. The four hydropower dams along the river—Iron Gate, Copco 1, Copco 2, and JC Boyle—allow almost no fish passage. In addition to the usual fish migration problems, the large dams on the Klamath alter temperature patterns in the water so dramatically that a series of toxic algal blooms have spread through the river. Some samples contain several thousand times the concentration of algae necessary to raise human health concerns.
The Iron Gate dam in particular shouldered most of the blame for the deaths of 34,000 fish in the Lower Klamath in 2002. The Klamath River story, however, appears to be headed toward a happier ending. The utility company PacifiCorp, local farmers, indigenous tribal leaders, and state politicians all favor decommissioning the dams. The last hurdle, predictably, is the U.S. Congress, which is considering a bill to remove them.
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Local communities around the country are addressing the problem of out-of-date and environmentally damaging dams (though fishermen and native communities in Alaska continue to fight five new salmon-killing dams from being built as part of the Pebble Mine project). According to the riparian restoration group American Rivers, 51 dams were removed in 18 different states in 2013. That brings the total to 850 decommissioned dams over the past 20 years.
There’s more good news. A study published last month by Desiree Tullos of Oregon State University shows that rivers and their ecological communities can recover with amazing speed after dam removal.
“I just recently visited the site of the former Condit Dam, removed from the White Salmon River in 2011, and you really could not tell there was a 125-foot high dam there just three years ago,” says Tullos.
But as the five dams described above demonstrate, there is still much work to do. It’s not feasible to tear them all down today, but the environmental management of these concrete behemoths must improve if we are to protect the ecosystems they have so profoundly disrupted. Consider it God’s work.
onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.