Dams, the most ancient of inventions, simple in design and efficient in operation, have allowed men to capture drinking water, control floods and practice agriculture for centuries. More recently, dams have also allowed humans to capture potential energy in stored water, turning it into safe, reliable electrical power. Today nineteen percent of the world’s electricity comes from hydroelectric sources . At a time when global demand for both water and energy is rising sharply, dams would appear to be a reasonable solution to providing water and renewable energy without burning dirty, nonrenewable fossil fuels. Dams, however, are anything but harmless.
Dams are every bit as destructive to the planet as fossil fuels, if not more so. The list of dam-driven woes is long and well-documented. The development of dams has left devastating effects on the surrounding land, ecosystems, fisheries and communities. Dams have destroyed rivers and the ecologies of entire river basins thereby altering the salinity of oceans and estuaries. They have disrupted and ruined whole human communities. Over time, they fill in with silt, making them even less reasonable and efficient. When they fail, they tend to have apocalyptic effects on any civilization downstream.
Dams have thus become swept up, just as fossil fuels have, into the global dilemma: Should the demands of the growing world population be given precedence over the preservation of our ecosystems? Where do we draw the line? What once seemed like a practical solution—the building of water storage units – now poses an ethical dilemma for engineers, environmentalists and politicians. Is dam-building, even if it provides huge benefits to the developing world, the right thing to do? While there are unquestionably economic benefits, as centuries of dam-building in the developed world have shown, there is simply no ignoring the destructive effects of dams on rivers, surrounding land, ecosystems, and human life, plus their short working life spans and the relocation of citizens. Equipped with this knowledge of dams and the history of environmental destruction caused by dams, we, as engineers, must strongly reconsider the construction of new dams in efforts to protect our planet and continue to look for alternative energy solutions that will not degrade ecosystems.
Today, the most common types of dams are arch, buttress, embankment and gravity dams. The majority of dams, regardless of the design, are single use, meaning that they only provide one service, such as irrigation (48%), hydropower (17%), water supply (13%), flood control (10%), recreation (5%) and a very small percentage for fish farming. (Multipurpose dams are, however, on the rise.)  These types of dams are all known as storage dams and are characterized by large hydraulic heads, storage volume and controlled release of water. Smaller dams, with small hydraulic heads and volume, where there is little control over the contained water, are known as run-of-river dams. The larger dams pose a more significant threat to the environment and therefore are often generally considered unethical. With the aid of recent technology, we are able to construct larger dams than ever before to harness more hydropower or store larger volumes of water. However, these new monstrous dams have had a much deadlier impact on the land, and specifically on the rivers.
To construct a dam the upstream river must first be diverted by digging or blasting a series of trenches away from the dam. Although rivers naturally meander and alter their course, the trenches disrupt that process and cause interruption for the river and aquatic ecosystems. Additionally, the residents of the surrounding area must be evacuated. China’s Three Gorges Dam, for example, caused the relocation of four million residents . Dams are built to help people by providing water and energy. But before the concrete is even poured, dams tear apart communities, displace natives, and disrupt rivers and aquatic life. The ends do not appear to justify the means. The initial phases of the dam construction are only the start of the environmental destruction and social interruption caused by dams.
Once the dam is erected, it blocks fish migrations both up and down stream. The low flows below Oregon’s Klamath Dam, for example, killed thousands of salmon in 2002 . This transformation of a natural, free-flowing river to a stagnant reservoir changes the surrounding physical river and fish populations as well as the chemical composition of the water.
The river, converted to a reservoir by the dam, now resembles a lake. Significant changes that affect aquatic life and water quality in the reservoir include temperature variation due to increased depth, limited sunlight and decreased dissolved oxygen levels caused by algae growth on the surface, and organic matter buildup . Dams also block sediment from being carried downstream. This buildup of the sediment not only disrupts the aquatic system in the reservoir and causes dam failure, it also starves the downstream river of nutrients and material replenishment from upstream that the river relies on. Free-flowing path disruption and sedimentation buildup are direct consequences of dams that have raised much concern.
To put it simply, Patrick McCully, Executive Director of International Rivers, stated, “Dams do not live forever.”  Despite their scale and seemingly permanent structure, dams often become inoperable, insufficient or unsafe. Dams primarily fail due to overtopping, sedimentation buildup, seepage from piping, and inadequate spillway capacity or age. Outdated and inefficient dams continue to harm our environment, swell in operation costs  and increase the risk of a catastrophic failure. Although the U.S. has been working to identify outdated dams and remove them, this is not occurring in other parts of the world. The American Society of Civil Engineers (ASCE) recently published guidelines for dam removal showing that it is an important issue and that measures should be taken to protect our rivers and land . However, there is still much unknown about best management practices for dismantling a large-scale dam.
In 2011, the largest dam removal began in Washington with the Elwha and Glines Canyon dams. When these dams were built back in the early 20th century, fish ladders, which help salmon navigate the dams, were not included in the design. However, due to the large population of salmon in the Elwha River, this became a significant issue. The dam prevented salmon from traveling upstream, which significantly reduced the habitat area, which in turn increased competition, causing food shortages and thus reducing the salmon population in the river.
Originally, there was resistance from the public to the removal of the dam. People were concerned about the landscape changes and the elimination of the power supply. People eventually realized how significant the environmental benefits of removing the dam would be, though, and so $351 million dollars and many years later, the dams are now completely gone . The Elwha river flows freely, carrying sediment and nutrients down the stream as vegetation flourishes and the salmon begin to recolonize the river . Although the Elwha River Restoration was successful, it was costly and spanned many years. Dams of a larger scale will cost even more to remove and will leave a much more significant environmental footprint. Unfortunately, we cannot change the past or undo damage caused by dams, but, moving forward, we can advocate for the removal of outdated dams with hope that the surrounding ecosystems can eventually return to their natural states.
So why then do we continue to erect dams if they are only destined to be removed decades later at an enormous expense? Is it really worth all of the environmental damage? Environmentalists believe that dams are a “man-made abomination” and are not worth the cost of destroying virgin land and diminishing rivers. Even politicians who believe that dams are essential to producing renewable energy, however, agree that environmental loss should be minimized.
Engineers, as natural problem solvers, find ourselves torn between the two sides. One issue is the increasing degradation of the natural resources and disruption of natural processes. The other problem is the exponential growth of the world’s population with its rising demand for water and energy. In the ASCE Code of Ethics, the first canon states, “Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties.” When considering the ethical issue of dams, this canon could be interpreted in multiple different ways. The health and welfare of the public depends on the access to clean water and energy. At the same time, a strong flourishing, natural environment means healthier and safer air, water and land. An engineer should be committed to “improving the environment…to enhance the quality of the general public.”  The absence of a clear, obvious solution to these problems created an inevitable ethical dilemma for engineers as well as everyone else.
Unfortunately, no single solution exists yet that significantly reduces environmental impact and provides sustainable energy and constant water supply. In 2009, the U.S. Secretary of Energy Steven Chu was reported saying that despite the lack of resolution to the energy crisis, “hydropower is clearly part of the solution and represents a major opportunity to create more clean energy jobs.”  However, the secretary failed to mention the horrifying negative side effects caused by dams to the planet. Now, almost ten years later, politicians are still debating the ethics of creating more dams.
Large-scale dam projects, specifically, have lost a lot of popular support due to their equally large costs, long building periods and the increasing public realization of the long-term negative effects dams have on the environment . A local poll reported that nearly 60% of the local population opposed the development of the dam in Patagonia, choosing their Aysen paradise over an improvement in infrastructure and increase in energy and water supply . To local citizens, it is not just the land that could be damaged; it is their homes and lives that are in danger. Chileans are not the only ones facing this problem. Many South American countries have untapped hydropower potential as well and are facing this dilemma. While these dams would significantly help these countries develop economically, the precious ecosystems around them would be forever altered and thousands would have to be evacuated. An engineer is held liable for public safety and welfare; therefore the public opinion regarding the construction or removal of dam must be strongly taken into consideration. However, this becomes very difficult when the public is divided on such a controversial topic.
In a 2011 article regarding the protests following the hydroelectric dam project in Patagonia, Los Angeles Times journalists Fabiola Gutierrez and Chris Kraul wrote: “Chileans find themselves having to choose between conserving beauty and biodiversity and creating infrastructure to boost economic development.”  Although this proposed dam is estimated to increased electrical power supply by 15% by 2020, it will be destroying the pristine Aysen region of Patagonia, home to many rare creatures and a popular tourist spot. And of course its long-term efficiency is not guaranteed. As noted earlier, a majority of dams fail due to sedimentation build up over time. In the U.S. alone, more than 1,000 dams had been removed prior to 2012 due to their inoperable state , and by 2017 the number of dam removals had risen to over 1,200 .
Countries interested in the construction of dams for hydroelectric power and water supply must strongly consider the associated environmental loss, risk, relocation of citizens, life span of dams and possible future removal to determine if the economic benefit is worth it. A discouraging example of a newly constructed dam with low public support is the Three Gorges Dam in China. The largest dam in the world, the Three Gorges Dam cost roughly $180 billion to construct with additional relocation, environmental and maintenance costs. This dam was proposed to regulate the Yangtze’s frequent flooding, produce electricity to the increasing population and show China’s engineering prowess. However, the quality of the surrounding tributary rivers is rapidly decreasing, erosion of adjacent land is increasing and algae blooms are quickly forming as well . Due to the scale of this dam, policy makers must prevent an environmental catastrophe from occurring in addition to remediating any other negative environmental effects caused by the Three Gorges Dam.
As history has shown, dams have consistently been a topic of debate regarding potential failure, environmental impacts, economic benefit and cost. More recently, public opinion has been leaning against the construction of new dams and in favor of the removal of obsolete dams – just look at the failure that is the Three Gorges Dam in China. Not only has the Three Gorges Dam relocated millions of people and destroyed the Yangtze River, but due to the increase in pressure on the surrounding land, the Three Gorges Dam has also caused dozens of landslides leaving many dead in their wake . This leads people to consider the very real possibility of an earthquake caused by the dam and the damage that would result.
An engineer’s main obligation is to protect the public. The question is, though, protection from what? Protection from a contaminated, unhealthy environment, an energy crisis, or a shortage of clean water? Frankly, it depends on the specific country’s economic state and environmental conditions. Although it may be easy for people in the United States and other developed countries to advise third world countries against dam construction (just look at the dam removal movement going on in the U.S.), many citizens of developing countries are without access to clean water and are living in extreme poverty. These dams could provide constant water supply, flood control, water for irrigation, and hydroelectric power that would also boost the economy. The Katse dam, located on the Lesotho River in Africa, is one of the world’s largest concrete arch dams. However, this dam caused the relocation of 20,000 people and the demolition of a mountainous region, which included farmland and communal grazing grounds. Although the damage is unavoidable and cannot be ignored, the Katse Dam now provides 72 megawatts of electricity for Lesotho and earns Lesotho more than $2 million (USD) a month for supplying South Africa with water .
It is true that the Katse Dam resulted in wholesale destruction of the land, and it is also true that the dam has had very positive economic and social effects. The Katse Dam is just one of the many examples of dams that have yielded both positive and negative outcomes. Because of the controversial effects of dams, the building of dams remains disputed amongst engineers, governments, citizens and environmentalists. Although others may have alternative motives and responsibilities, as engineers, we are required to protect the public as well as the environment which makes the debate over dam-building that much more difficult.
By Margaret Gwynne, Viterbi School of Engineering, University of Southern California
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