How do dams impact watersheds and native wildlife?
-- M. Stoecker, Portola Valley, CA
The world of sustainability sometimes seems like it's divided into heroes and villains. Solar power good: fossil fuels bad. Organic kale good: genetically modified soybeans bad.
But understanding environmental impacts is rarely so simple, especially when it comes to dams. The scale of dams ranges from Stanford's Searsville Dam (one-quarter the height of Hoover Tower) and smaller, to enormous dams, such as the massive Kárahnjúkar Hydropower Plant in Iceland with a whopping three and a half times the volume capacity of the Hoover Dam. Their purposes range from as unassuming as providing irrigation water to a university's lawns, to as ambitious as singlehandedly increasing a country's energy output by 60 percent.
There is no litmus test for whether a dam is "good" or "bad." Ecological impacts might be tempered by the benefits of cleaner energy or opportunities for outdoor recreation. Let's look at these two very different dams, Searsville and Kárahnjúkar, to get a better grasp of the complexity of these man-made structures. In light of your question about specific impacts, let's recast the five W's into: Who, What, Why, Watersheds/Wildlife, and . . . so What?
Case 1: Kárahnjúkar Hydropower Plant, Reyðarfjörður, Iceland
Who?
Landsvirkjun, Iceland's largest energy producer, and Alcoa, an American company that is the world's third-largest producer of aluminum.
What?
In the late 2000s, Landsvirkjun's most recent hydropower project became embroiled in an environmental controversy, pitting those in support of new jobs and economic growth against those who saw nature areas being inundated in the name of industry.
Why?
Iceland is a land of waterfalls and geothermal hot spots. More than 75 percent of the country's energy (not counting transportation fuel) is produced domestically, from renewable hydropower and geothermal sources. It's an environmentally idyllic situation, by the sounds of it. But there's a catch: As more and more hydropower projects were built in the 1970s, more and more power-intensive industries flocked to the sparsely-populated island nation to take advantage of cheap energy prices. Aluminum refining takes huge amounts of electricity, so bauxite ore is shipped in to Iceland solely to take advantage of the cheap electricity. Now, more than half of Iceland's energy generation is not for personal consumption, but for aluminum production for international companies like Alcoa.
Landsvirkjun's most recent hydroelectric plant, built expressly to power an Alcoa aluminum smelter, was constructed in what had been the second-largest unspoiled wilderness area in Europe. Author Andri Snær Magnason describes the construction of Kárahnjúkar as a pivotal moment in Iceland's growing backlash against environmental destruction in his best-selling book and associated documentary Dreamland. At the same time, however, around 7 percent of Alcoa's vast supply of aluminum is now being produced using a renewable energy source, a preferred alternative to feeding our demand for the metal using fossil fuels.
Watersheds and Wildlife?
The rivers that feed the hydropower plant are fed themselves by one of Europe's largest glaciers. Since the dam and power plant were built, the paths of these highland rivers have changed. Valleys have been flooded by artificial lakes. Árni Finnsson, head of the Icelandic Nature Conservation Association, estimated that this single project would directly impact an area larger than San Francisco, and its indirect effects—from erosion to damage on delicate flora and fauna—would reach much farther. He foresaw extensive sediment buildup in reservoirs, with high winds blowing dust onto vegetation and into settled areas when water levels were low. The surrounding areas are important habitats for geese and wild reindeer, although project officers predicted only one percent of geese nests would be destroyed and that the biggest impact on reindeer would involve getting accustomed to heavier road traffic.
So What?
Iceland today is a charming mix of calmly pastoral and desolately alien landscapes. I spent three months there as an undergraduate, and passed several days backpacking through the Highlands. Cresting a ridge, I found myself looking down upon a soft, mossy landscape, the jewel in its crown a perfectly square lake beckoning to me in the distance. My body hummed with the energy of my surroundings, yet all was calm: calm with the knowledge that although the world is large and I was a tiny blip in its existence, at least for now I was an integral part of this place, at this time. A week later, my body hummed in the same jarring, yet strangely soothing fashion, as I stood sheltered within a massive hydrolectric plant. Earplugs and hardhat in place, I learned about the technology that allows humans to harness the power of nature without the massive climate change implications of fossil fuels. I struggle with the desire to preserve our natural areas, and the equal desire to ensure that our planet has a diverse, sustainable set of energy sources.
Case 2: Searsville Lake, Stanford, California
Who?
Stanford University and Jasper Ridge Biological Preserve.
What?
Searsville Dam stands in a stark contrast to Iceland's burgeoning industry of dam construction. Built in 1892 and acquired by Stanford University in 1919, for most of its lifetime its reservoir was used solely for recreational purposes. The dam was decommissioned in 1975, when it was absorbed into the Jasper Ridge Biological Preserve, although its water is still used for irrigation on campus. Today, there are several conflicting opinions on how to best handle the dam in its current state.
Why?
The Jasper Ridge Advisory Committee has determined that there are several possible courses of action, from allowing the reservoir to fill with sediment and become a vegetated area, to maintaining the reservoir with regular removal of sediment, to removing the dam entirely and allowing Corte Madera Creek to return to steelhead trout habitat.
Watersheds and Wildlife?
Over a century after its construction, Searsville Lake now is an integral part of its surrounding ecosystem, helping support nearby wetlands. The lake and wetlands are the territory of several threatened species, and provide a habitat and breeding ground for migratory birds. If any of the proposed actions were to be undertaken, significant changes in the current system would result. For example, allowing the reservoir to fill with sediment would mean the loss of habitat for species supported by the current lake and wetlands. Alternately, the reservoir could be maintained in its current state, requiring the regular removal of sediment. While dredging would mean increased traffic to the area, the ecosystem would remain largely unchanged and available for research and education. Finally, managers of the preserve could remove the dam and work to restore the river to its original state. Threatened steelhead trout would benefit, but at the expense of many other aquatic and land species.
So What?
Deconstructing dams to restore the natural flow of a river or stream may sound appealing, but it raises the hairy question of which "natural" state is preferable: The original that existed decades ago, or the current ecosystem that has developed? Philippe Cohen, administrative director of Jasper Ridge, notes that the freshwater wetlands sustained by the Searsville Dam are the last of their kind in Northern California. A century after significant human impact on the natural area, a new, but equally valuable biological resource has emerged.
What can we take away from these case studies?
For dams, the environmental tradeoffs vary location by location and use by use. Not all dams are created equal, and some are more justified than others. Dams built today, like Kárahnjúkar in Iceland, might destroy precious natural habitats in order to power the world in a more renewable way. A hundred years down the line, this dam might support another different, yet still precious ecosystem, as Stanford's Searsville Dam does now. So who is the hero and who is the villain in the world of dams? The answer is: we are them both.
TRACY MANDEL is a graduate student in civil and environmental engineering.
