Often, the best fish passage is none at all
Dam removals becoming increasingly popular
For residents along Pennsylvania’s Conestoga Creek, 1731 was the spring the shad didn’t show up. And they were irked. Each spring, they counted on the arrival of the silvery fish to help support their families. But that year, their nets went empty.
The culprit, they quickly discovered, was a downstream mill owner who had dammed the creek to power his operation. Enraged, upstream residents took their case to the Pennsylvania Assembly, demanding that the dam be torn out.
The assembly agreed to consider the action unless the mill owner could prove the dam wasn’t a problem. To head off action, he agreed to cut a 20-foot-wide passage in the dam. His concession wasn’t enough. Residents took matters into their own hands and ripped the dam down.
They were, however, fighting a losing battle.
In the following decades, dam construction would only escalate. Dams provided power for the Industrial Revolution, running mills and providing water to a vast network of canals. Later, they would provide electricity, city water supplies, flood prevention, recreation and a host of other services.
The result: There have been no unobstructed rivers linking the Bay to its mountain headwater areas since the mid-1800s. And the same is true for most major rivers on the East Coast. “Rivers that flow freely from the mountains to the sea are about the rarest feature left on the American landscape,” said Rebecca Wodder, president of American Rivers.
Nationwide, the government estimates there are 76,000 dams of 6 feet or more, and—altogether—they are capable of storing almost every drop of rainfall that hits the ground in a typical year. When all of the smaller dams are figured in, the total number is thought to be in the millions.
The numbers of dams in the Bay states is staggering. Pennsylvania’s official estimate is between 3,000 and 5,000. Maryland has 10,000. And Virginia has at least 3,000. Those figures are probably leaving out thousands of dams that were either built before records were kept, or are only a couple of feet high.
The obstructions have severed historic links between the ocean and freshwater streams, contributing to the steep drop in populations of American shad, blueback herring and alewife throughout the region.
The Bay Program has emphasized improving fish passages at dams—and thousands of other blockages, such as culverts and sewer pipes—to help reopen rivers to migratory fish. Those efforts have helped to reopen more than 1,300 miles of rivers to anadromous fish—those that live in the ocean but spawn in freshwater rivers. But many thousands of miles of spawning habitat remains off-limits.
Much of the focus has been on building ladders or other devises to help fish get past obstacles; some of the big dams on the Susquehanna River even have elevators.
But in February, when 650 pounds of explosives blew a 130-foot notch in Embrey Dam on the Rappahannock River, it provided a vivid example of something Conestoga Creek residents realized more than two centuries ago—the best fish passage is often none at all.
“What you get with a dam removal that you don’t get with a fish passage is you no longer have a barrier to fish migration,” said Sara Nicholas, associate director for dam programs with American Rivers’ Mid-Atlantic office. “A ladder usually has a target species in mind, like American shad, and is not always useful in terms of passing other types of fish.”
Some fish tend to move upstream along the riverbank, while others move in mid-channel. Where the fish ladder is built can determine which species benefits the most. Some species—such as sturgeon—are too big for ladders. And others, such as minnows and darters, generally don’t use them.
Also, manmade fish passages are not 100 percent effective, even for target species. On the Susquehanna River, only 4 percent of the American shad that pass Conowingo Dam—the first dam encountered on the river—make it past York Haven Dam, the fourth blockage.
Predation often increases in areas below the ladders as fish line up to get through. Even in the best cases, fish are delayed as they reach the dam and have to search for the ladder—or wait their turn to pass through if it’s crowded. That can be a particular problem for fish such as American shad, whose spawning is triggered in large part by water temperature.
“The more blockages you have, the more delays you have, and the less chance these fish have to get upstream before water temperatures make them do what they have to do physiologically—spawn,” said Scott Carney, a fisheries biologist with the Pennsylvania Fish and Boat Commission. “There is nothing more efficient than an open river system.”
As a result, Pennsylvania, prompted in part by Bay Program fish passage goals, has emphasized dam removal over other forms of passage.
In the past decade, Pennsylvania has removed 70 dams, 40 of which were in the Bay watershed. Since 1995, no state in the nation has removed more dams—something that no doubt would have pleased, belatedly, the irate residents of Conowingo Creek. Dozens of removals are in the planning stages.
The state has developed a streamlined permitting process to promote removals, and has earmarked both state and federal funds to help willing owners remove their dams. “It allows us to remove these dams at rock-bottom prices compared to the installation of permanent passage facilities,” Carney said.
Most of the dams removed in Pennsylvania are only a few feet high, and have often cost as little as $1,200 to $2,000 to take out, Carney said. The average removal cost has been about $30,000. In contrast, Carney said, it costs about $35,000 per vertical foot to build a fish passage. In addition, dam removals avoid the ongoing maintenance required to keep passages operating and free of debris.
Dam removal is often a good option for their owners.
Laws require dams to be maintained, which can be costly as they age. They can also create a liability for owners. “We’ve had some dams taken out where there have been multiple drownings,” Nicholas said. Often, they must be marked as a public safety hazard.
Also, in Pennsylvania, the Fish and Boat Commission can require any owner of a dam to install a fish passage if it is blocking the migration of anadromous fish. “If you are given a choice of putting in a half-million-dollar fish ladder or letting groups like us and the state basically take over the cost of removing the dam, the economics usually argue in favor of removal,” Nicholas said.
That doesn’t mean everyone is pleased. In some cases, residents along impoundments have worried that their property values would go down if their “lake” were removed. Limited studies show that is not the case, Nicholas said. “Apparently, there are people who are just as willing to live next to a free-flowing stream as want to live next to an artificial lake.”
In fact, Carney said, most dams make poor lakes. Few reservoirs are big enough to mimic a lake ecosystem. The vast majority are small run-of-river dams that back up only small amounts of water. They end up slowing water movement, trapping nutrients and causing water temperatures to warm. The warm water temperatures and nutrient enrichment help to sap dissolved oxygen from the water.
They trap sediment which begins to build up on the bottom, smothering benthic life. It also covers the gravel and small rocks that provide feeding areas for other small fish and stream dwellers that are important to the food chain.
The result: Many small impoundments provide habitat only for the few species that are most tolerant of disturbance, often non-natives such as carp.
That can dramatically alter the population makeup in the stream, and it could have other impacts. For instance, freshwater mussels—one of the most threatened groups of water dwellers in the nation—have a parasitic life stage that attaches to darters. If the darter’s movement is blocked, so is the mussel’s.
And ironically, even as dams trap sediment upstream, they increase erosion downstream. A stream develops over time to handle a certain amount of sediment, which helps to establish its channel width and its twists and turns. When they become “sediment starved,” streams begin cutting deeper channels, exposing banks to erosion and creating a gap between the stream and terrestrial habitats.
“If you really want to resolve a lot of erosion problems,” Carney said, “tear a dam out.”
Those conditions are often quickly reversed after a dam is removed. When the state took a dam out on Lititz Run, the water temperature dropped 12 degrees in a single day, Carney said. That was critical to efforts to restore a cold-water trout fishery in the river.
Studies suggest that when dams are removed, biodiversity and population densities of native aquatic organisms increases. Even nonmigratory fish, such as darters, benefit because they gain access to local areas that had been off-limits. In some cases, populations of darters have increased four-fold.
“I have not seen anything that does more to restore stream habitat than a dam removal project,” Carney said. “It is unbelievable how you can turn things around and eliminate a lot of impacts.”
That doesn’t mean all dams should be removed. Many are well-maintained, fully functional, and provide electricity, water, or flood control.
“Some dams still serve a viable purpose,” Carney said. “Society needs them. We are not out to take out every dam. We are only focusing on those that don’t serve a valuable purpose, and that the owners want to take out.”
Indeed, many dams no longer serve any purpose. Some are the remnants of mills that rotted away decades ago, or canal long since overgrown by trees and weeds. Some dams are “orphans”—they are so old, no one owns them. Those dams, Carney said, are ripe for removal.
Larger dams can be more problematic than the small dams that Pennsylvania has focused on. Removals can cost millions of dollars—the full cost of the Embrey removal is expected to be about $10 million—especially if there are large amounts of sediment behind the structures which have to be removed. If that sediment has become contaminated with toxic chemicals, the problem can be even greater.
Efforts to remove dams are being stepped up. In Pennsylvania, American Rivers recently got an $767,000 grant in state Growing Greener funds to remove 30 dams in the next three years. The state is working on additional projects as well.
In the Bay watershed, 123 barriers to migration have been overcome, but mostly with fish ladders, not dam removals. Officials hope that mix changes in the future. “We’re trying to move toward dam removals,” said David Sutherland, a biologist with the U.S. Fish and Wildlife Services’ Chesapeake Bay Field Office, who chairs the Bay Program’s Fish Passage Work Group.
Although most of the action has been in Pennsylvania, he said officials in Maryland and Virginia are giving removals a closer look. “Embrey is a fine example,” he said.
It’s a message that has been gaining ground across the nation as well. In 1999, when the dismantling of Edwards Dam on Maine’s Kennebec River made headlines across the nation, a dam removal was a rare event.
The owners of the dam decided it was cheaper to remove the 24-foot-high, 917-foot-long structure than to spend $9 million to build a fish ladder. Then-Interior Secretary Bruce Babbitt showed up for the event and proclaimed, “this is the beginning of something that is going to affect this entire nation.”
Of the 460 dams (counting only those at least 6 feet high) removed in the past 40 years, more than 130 have come out since Edwards. Of those, the Embrey Dam was the largest.
The changing attitude toward dams, in fact, may have been best summed up by A. Thomas Embrey III, grandson of the man who built Embrey Dam.
Speaking at a ceremony before the demolition, Thomas Embrey hinted that the explosion was something his forefather would have approved had he realized the toll the dam would take on fish. His grandfather, the younger Embrey noted, was a fisherman, and had written of fish that were so numerous migrating up the Rappahannock they appeared “as a mass of molten silver moving against the water of the river.”
“He too would probably say, ‘let the river run free.’”
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