Though it was a whimper, and not a roar, when the Kennebec River hydroelectric dam came down last week in Augusta, Maine, scientists and environmentalists stood at attention.
This was the first time in United States history that the federal government had deemed a dam's environmental damage greater than its economic benefit and refused to renew its license. The precedent may open the floodgates for more dam removals.
With the dam-building era long past, scientists are now learning of the environmental damage dams wreak on river ecosystems. This includes burying fish-spawning areas with silt and debris, blocking fish migration, and preventing the natural spread of plants and nutrients.
Dams have also contributed to the extinction of 106 native salmon and trout stocks in four Western states, despite hatching programs and fish passages.
Added to this, dams all over the US are crumbling. One-quarter of the nearly 75,000 around the country are more than 50 years old, their average life expectancy, according to American Rivers, an environmental group in Washington, D.C.
But until recently, dam removal was unthought-of, and scientists could only speculate about how rivers would respond to a release of their penned-up waters.
A blossoming movement to restore rivers across the country to their natural, free-flowing state is, at last, starting to give scientists their chance to study the ecological effects of dam removal.
"There are a lot of important questions that scientists are grappling with, and we are just recently being given the opportunity to do the much-needed research," says LeRoy Poff, a professor of biology at Colorado State University in Fort Collins.
The Edwards Dam on the Kennebec will offer one such case study. After 162 years of feeding power to local industry, the 25-foot-high dam was breached with backhoes July 1 and will be fully removed by Thanksgiving.
The Kennebec, the second largest river in Maine, and the Androscoggin River share the ecologically unique Merymeeting Bay, one of the largest freshwater tidal estuaries in the US. Now that the Edwards Dam has been breached, scientists believe freshwater from the river will have a much greater influence on the estuary.
Jim Stahlnecker, leader of the Kennebec River Restoration Project for the Maine Department of Marine Resources, has been collecting data in an effort to make a before-and-after assessment of dam removal.
Using historic survey reports of the river conducted by the Army Corps of Engineers before construction of the dam, the Maine Department of Marine Resources has developed a scheme of how the Kennebec may adjust now that the dam is gone.
According to Mr. Stahlnecker, the predictions are elegantly simple. The river's natural flow will be restored, providing a friendlier environment for native species of plants and animals.
At least 10 migratory fish species will have unimpeded access to 17 miles of the Kennebec, the longest stretch of their habitat north of the Hudson River.
Although the river may restore itself quickly, the battle to remove the dam took 10 years. It finally came down to an environmental impact statement that declared relicensing the dam would cost almost two times as much as removing it.
The power it generated (1/10th of 1 percent of Maine's total use) did not justify the environmental damage.
When repair is not worth it
Edwards is not unique. In many cases, the cost of repairing dams outweighs their economic benefit. Since 1993, when the first of these older dams came up for license renewal, the public and governmental agencies have used the Federal Energy Regulatory Commission relicensing process as an opportunity to push for dam removal. The FERC licenses about 2,000 privately owned hydroelectric dams.
Now hundreds of FERC dams are coming up for license renewal. The FERC-licensed Condit dam, on the White Salmon River in Washington State, could be the next in line for removal.
But the FERC relicensing process is not the only way dams are being slated for removal. For the first time, a dam will be removed following a collaborative effort between a utility company and the government
In an unprecedented case, Oregon Governor John Kitzhaber announced last month the removal of two dams in the Sandy River Basin, about 30 miles east of Portland.
The Edwards Dam is not the first dam to be removed, but it's the first not to have its license renewed. A handful of small dam removals across the country have already illustrated the promise for successful river restoration.
In 1998, the Natural Resources Conservation Service of Maine removed the Grist Mill Dam, a small hydropower dam that had blocked fish from swimming up the Souadabscook Stream, a major tributary of the Penobscot River, for two centuries.
Less than four months after removal, the US Fish and Wildlife Service spotted Atlantic salmon spawning sites upstream from the removed dam. Other species of fish that swim up river to spawn, such as smelt and alewives, quickly returned.
"We just let mother nature run its course and watched to see what needed to be done," says Bob Wengrzynek, a biologist for the Natural Resources Conservation Service of Maine. "Our experience has been very successful."
Other small dams have been removed in North Carolina, Wisconsin, California, Idaho, and Oregon. But rivers respond differently, depending on their size, location, and climate. Each river ecosystem is unique and may require more or less restoration efforts by ecologists.
How not to shock the river
One of the major short-term environmental impacts of dam removal is the release of sediments that have collected behind the dam and may contain toxic wastes. Suddenly releasing large amounts of sediment and water can shock the river's system.
Fortunately, the Edwards Dam had little sediment buildup. The dam's porous material and its sloped design increased the velocity of the water as the river approached the dam, sucking up most fine sediments.
Some coarser, sand-like sediment may interfere with spawning. But Stahlnecker says that spring flooding will move these sediments and scour them out of that segment of the river.
Timing of dam removal is key in minimizing the impact on fish. It is no coincidence that Edwards Dam came down the first week in July, the end of spawning season.
Nonaquatic plant and animal populations may also be affected by the dam's removal. Bald eagles, for example, nest not too far up and downstream from the Edwards Dam.
"The last thing you want to do when you remove a dam is lose a population that has established itself in the area," says Emily Stanley, professor of zoology at the University of Wisconsin-Madison. "We have to carefully assess the area to minimize the loss of habitat."
The impact dam removal has on the local community is equally critical, she adds. "It's really important to realize how this affects people."
Many residents use and enjoy the reservoirs created by dams. Removing the barrier may leave homes along the reservoir with dried up beaches and lost recreational opportunities.
But not all dams are removable, especially the bigger dams in the Western US. Alternative methods for bringing rivers to a healthier state need to be pursued also.
Professor Poff of Colorado State University says one of the ways dammed rivers can gradually be restored is by mimicking the river's natural flow.
He mentions as an example the controlled flooding of the Glen Canyon Dam on the Colorado River in 1996. For seven days, the river ran free, with a water flow that scientists estimate was only 35 percent of an average spring flood in pre-dam history. Nevertheless, the river responded immediately by broadening its flow onto the sandy banks, which in the past had provided a rich environment for plants and fish.
Restoration as a river runs its course
Natural flow restoration efforts elsewhere have also shown that rivers can gradually recover. An artificial increase in the water flow of Virginia's Roanoke River (which has been altered by a hydroelectric dam) has increased the number of native striped bass.
In the Pecos River of New Mexico, short surges that mimic the historical floods produced by summer thunderstorms have significantly benefited a native species of fish.
Scientific information is one of the keys to successful river restoration. Fortunately, the science of dam removal is coming of age.
"It's an emerging science that nobody paid attention to in the past," says Ms. Bowman. "But as more and more dams come down, dam removal will certainly become an area of great interest to scientists."