Dams have been used to provide a store of water for agriculture, industrial uses, household uses for thousands of years. Hydroelectric dams, additionally, act as an alternative to non-renewable energy resources that constitutes the majority of the world’s energy . In the 20th century, over $2 trillion was spent on making dams around the world . However, dams have drastic damaging effects on the environment and on the populations that live near the dams and so have become the subject of great scrutiny, with organizations concerned with environmental health such as World Wildlife Fund (WWF) and International Rivers advocating the removal of old dams and the use of alternatives . Initiatives have been taken around the US to remove old, outdated dams . In this article, Mission 2017 looks into the uses of dams and ways of maximizing their efficiency and minimizing their environmental damage. The first part of the article looks into the details of dams and their problems and the second part deals with possible solutions to the problems.
Uses of Dams
Water Dams and Reservoirs have primarily been used to serve four functions :
- Irrigate crops
- Provide hydroelectric power
- Supply water
- Control flooding
Out of the 38,000 large scale dams registered by the International Commission on Large Dams (ICOLD), an international organization that sets the standards for dams, 50 percent are used for irrigation, 18 percent for hydropower, 12 percent for water supply and 10 percent for flood control and the rest for other functions 
The vast quantities of water in reservoirs allow them to act as effective and steady sources of water for irrigation with minimal seasonal fluctuations. 30 to 40 percent of the 271 million hectares that are irrigated worldwide rely on irrigation dams . A study done by the World Commission on Dams (WCD) , a commission organized by the World Bank and the World Conservation Union (IUCN) to assess the effectiveness of large dams, showed that dams built for irrigation typically are unable to provide water for the planned area of land initially, but the performance improves over time . According to the WCD, half of the 52 large water storage projects for irrigation it examined failed to meet the expected goals the dams had been initially planned for. However, the general trend shows irrigated area increasing from 70 percent in five years to 100 percent of the planned area in ten years .
The dams examined by the WCD that did not meet their initial goals often had failures at the management or organizational level rather than structural or engineering deficits.
These problems often included poor and insufficient water distribution networks, inefficiencies resulting from a centralized administrative system with unclear distribution of responsibilities, poor coordination within the system and lack of initiative to involve the local stakeholders (the farmers, etc.) . Involving those who run the dam and those in the community could greatly benefit the performance of the dam.
Dams can harvest gravitational potential energy to provide electrical power at low rates. Nineteen percent of world’s electricity supply comes from hydroelectric dams . Hydropower dams are able to reach their targets within five years, and around fifty percent of the hydropower dams worldwide actual exceed their targets .
As with irrigation dams, mistakes or changes at early points of project development are strongly correlated with delays in reaching anticipated power generation goals at the initial years of operation . The initial stages of project development are especially important, and improvements and organization at these phases could improve the ability of dams of attaining their set goals within their intended timeframe.
The water in the reservoirs can be sent to treatment plants to make it suitable for drinking. The reservoir already provides some filtration since silts and other particles settle to the base of the reservoir and algae and aerobic bacteria destroy harmful microorganisms . Water supply dams are not very good at reaching their intended levels of operation even after a decade of operation: 70 percent of the WCD’s 52 sample dams did not reach their targets even after long periods of time with around 25 percent of water supply dams have reached less than half their supply goals .
Inefficient taxation and pricing of the water is responsible for this issue. In WCD’s examined samples [SM3], 38 of 50 utilities used tariffs to fund their operational and maintenance costs. The funds generated from these tariffs were not high enough, and these dams will not be able to function properly. Studies have shown that even in underdeveloped nations, people are willing to pay to have a steady and good supply of water and sanitation services . For example, according to a study done by Ramnath Subbaraman and his colleagues in a slum in Mumbai, India, the residents paid 33 times more for water from informal vendors than residents in the surrounding areas who were provided with water supplied from the government. The residents told Subbaraman that they were willing to pay for improved water access . People are willing to pay for a stable water supply and better sanitation services provided that their money is used efficiently and effectively. Therefore, Mission 2017 proposes to increase taxation in this sector.
Reservoirs can act to prevent floods downstream by holding and regulating the flow during major flood events. Reservoirs can also be used to balance flow during different weather conditions, such as decreasing the flow by holding water back during heavy rainfall and releasing more water during droughts .
Some dams combine two or more of the uses stated above, but a majority of large dams, as registered by ICOLD, are single purpose. Multi-purpose dams are complex and tend not to perform as well as single-function dams. Also, for certain combination of functions, a delicate balance has to be maintained For example, irrigation, hydroelectric and water supply dams require the reservoir to be at full capacity for efficient functioning while flood control requires water levels to be lower than maximum to hold the extra surging waters .
Environmental and Social Costs of Dams
Dams have many uses in the human community, but they also have large impacts on the environment and populations living close to the dams, which can be disastrous. The following discusses these effects.
Changing aquatic ecosystems
Habitat loss is the biggest cause of extinction. Freshwater habitats are thought to be the habitats face the highest loss of biodiversity . Building a dam in a river causes great changes within the river and leads to great changes in the river systems, leading to habitat loss. The structure of the dam itself acts as a barrier preventing fish populations from migrating along the river. The formation of a large still body of water in place of a small rapidly moving body of water changes the dynamics of the water system, which makes it less suitable for the original species to survive, which may lead to extinction . The temperature and chemical composition of water in the reservoir is also different from that of the flowing river. The reduced water flowing downstream causes the water downstream to be more saline, making it less suitable for certain fish nurseries and also enables predators to reach them. The water running off from the catchment areas upstream carry with them sediments and nutrients. Human activity upstream can increase the nutrient level in the reservoir with may lead to eutrophication, which eventually leads to the loss of most species in the reservoir .
For example, river dolphins of the Yangtze were lead to extinction after the Three Gorges Dam was built; the variety of fishes dolphins in the Mekong region are also at risk or extinction . The Glines Canyon Dams in the Elwha River in Washington, USA, has been responsible for almost wiping out the entire steelhead trout and salmon population .
This loss of fish populations can also lead to loss of economy from fisheries .
The decrease in water flow due to the reservoir leads to water losing the sediments it carries, to the bottom of the reservoir. This decreases the water storing potential of the reservoir and also decreases the silt and nutrients from being carried downstream, makes soil downstream less fertile, which harms the plants and animals that live and grow there, since the reduced fertility will reduce the number of plants and trees that can grow downstream and so, cause the number of animal habitat to drop, decreasing the biodiversity of the area. Because of the drop in the number of trees that can grow and hold soil together, the soil is more prone to erosion, meaning the structure of the soil is lost, making it less and less suitable for human or animal habitation .
Greenhouse gas emission
The condition at the base of the reservoir is anaerobic, meaning that vegetation under the reservoir are decomposed by anaerobic bacteria that give out greenhouse gases such as methane and carbon dioxide . According to the WDC, if the area being flooded during the reservoir filling is not cleared out, the amount of greenhouse gases produced could be higher for the same amount of energy produced by a coal powered station . However, power generation from the dams does not cause emission of gases such as sulfur dioxide, nitric oxide and carbon monoxide which are responsible for acid rain and blood poisoning, making them more eco-friendly in this sense than fossil fuels such as coal, which does produce these gases when burned .
Reservoirs have large open surfaces that facilitate water loss by evaporation, and much more water is lost in the same period of time from reservoirs than was originally lost from the river that flowed in its place. Even though the loss mainly depends on the climate of the area, it can also depend on the size, shape and depth of the reservoir, with reservoirs having smaller surfaces or larger depths losing less water . This added evaporation can affect the microclimate of the area as it reduces fluctuations in the extremes temperature  and may change the ecosystems that can exist there, since organisms suited to the two extremes of temperatures, or which need the fluctuation as part of their breeding cycles cannot survive.
It has been known that the filling of reservoirs of large dams has triggered seismic activity because of the physical change incurred in the area where the reservoir was filled, and the activity of the dam . Scientists have traced the cause of over 100 earthquakes worldwide to dams. In May 2008, the 7.9-magnitude earthquake in Sichuan killed 80,000 people has been linked to the construction of the Zipingpu Dam, and is possibly the most serious earthquake caused by a dam .
Displacement of People
An area to be flooded for use as a reservoir has to be cleared of human population . It is estimated that 40 to 80 million people have been displaced by dam construction worldwide . To mitigate relocation damage, such as loss of home and livelihood, governments need to protect both the populations that are being displaced and the ones that accept them. These efforts must be made in conjunction with affected peoples who live downstream. Affected peoples should be compensated. Compensation, however, often is rarely or poorly implemented . For example, in China, populations who were forced to resettle for dam construction became much poorer than they had been previously and worse off than those around them who did not move. Around 70 percent of all re-settlers were living in “extreme poverty” .
Human Health Risks
In tropical areas, reservoirs provide a perfect breeding ground for parasitic organisms, especially as mosquitoes . Larger reservoirs have a higher potential for breeding such parasites and spread disease to surrounding populations. Indirectly, infested water is used for irrigation and thus infects crops. If large numbers of people are relocated to areas near the reservoir during the reservoir formation, the increased density of people will make the spread of infectious disease more likely .
Now that the effects of dams on the environment and society has been looked at, the next section will deal with the possible solutions to these problems.
Steps that must be taken
The four major steps that need to be taken to in order to lessen the detrimental impacts of dams are as follows:
- Disassemble old, outdated dams
- Make existing hydroelectric dams more efficient
- Research on alternative sources of energy and efficient usage of water in agriculture and alternatives to new proposed dams
- Make sure new proposed dams are built at a site that result in the least amount of environmental and societal damage.
Timeline of implementation of solution
- (Short to mid term) Dismantle non-effective, old dams around the world, and improve functioning old ones and making sure proposed dams are efficient. The upper limit for each project is 3 years.
- (Mid to long term) Phase out dams in favor of more environmentally and socially friendly alternatives. This depends on increased efficiency in agricultural water uses, alternative sources, etc. For agriculture, water use efficiency can be attained by 2050.
- (Mid to long term, simultaneous to 2) Dismantle existing dams as efficiency gets better.
1. Disassemble old, outdated dams
There may be large numbers of dams around the world that, in addition to their environmental effects, no longer serve their purpose, for example, are silted up or are no longer producing hydroelectricity because the economic output of the dam has exceeded the input required in maintaining the dam , or have even started to pose threats to safety as failures in structure can lead to massive flooding . These dams can be totally or partially dismantled allowing the river to at least partly return to its original course so that ecosystems can start recovering in the river .
Disassembling old dams will be long and costly and will involve diverting rivers. Thus, removing outdated dams can take place over several years . The costs of disassembling dams is largely unknown, but may even exceed the cost of making a new dam  – however, studies have found that the costs of removing a dam could be up to 3 to 5 times less than the costs of maintaining it . To alleviate the financial burden, numerous financing options exist. Funding for larger projects could possibly be obtained from the World Bank since these projects deal with restoring the environmental health of a country. The WCD recommends dam owners to set aside funds for future dam decommissioning .
Decommissioning involves use of heavy equipment such as wrecking ball, backhoe,and hydraulic hammer, and explosives to dismantle the structure of the dam, along with river diversion . Since no advanced technology is required in the dismantling of the dam, and since river diversion is a component of the actual construction of a dam, a country that was capable of building the dam will have the technology required to demolish it. Decommissioning methods are highly specific to the dam and would depend on the size, type and location of the dam , however an upper limit of 3 years can be placed on it. The removal of the dams on the Elwha River, the largest dam removal project in US, is projected to take 3 years . So, typically such projects should take less than 3 years to complete.
2. Make Existing Dams More Efficient
There may be large numbers of dams around the world that, in addition to their environmental effects, no longer serve their original purpose or have even started to pose threats to safety. These dams can be totally or partially dismantled, allowing the river to at least partly return to its original course so that ecosystems can start recovering in the river . Hydropower dams can be made more efficient by replacing its turbines, as was done in Boulder Canyon Hydroelectric Facility in Boulder, Colorado, USA. Of the two turbines replaced in the Boulder Canyon dam, a single turbine was capable of producing 30 percent more energy than both the old turbines combined. The new, efficient turbines also cut electricity requirements to run the dam .
Making hydroelectric dams more efficient reduces the operating costs of the dam and reduces the need to construct new dams.
Sedimentation buildup decreases dam capacity. Sediment flushing can prevent large buildups of sedimentation in dam reservoirs. Large gates should be built into the base of dams and opened when the flow rate is high. This allows sediment that had been collecting at the bottom of the dam to flow downriver, thus improving reservoir yield.
Sediment flushing is usually employed in reservoirs that are located in narrow valleys that are supplied by monsoon rains, such as the Himalayas. However, sediment flushing has been found to be extendable to other areas, with benefits seen in the Sefid-Rud reservoir in Iran.
3. Transitioning to Alternative Solutions in the Stead of Dams
Investigations into alternatives should be included in proposals for new dams. Mission 2017 proposes that a small research group be formed by the government or an interested organization in the country where the dam is proposed and undergo a detailed research on the effects of a new dam and alternatives that could serve the same purpose. If the proposed dam is a hydropower dam, it should be investigated if alternative sources of electricity, such as solar power or wind energy, can be used instead; or if there is an older dam already in the area, if increasing the efficiency of the dam can be increased to satisfy the increased energy demand.
If the proposed dam is an irrigation (or water supply) dam, investigations should be done to see if the agricultural water use can be reduced instead. Large quantities of water are lost due to poor, inefficient irrigation methods. Irrigation is responsible for 70 percent of all water usage in the world, so reduction in water usage in this sector will also allow more water to be allocated to other sectors. The WWF suggests the following practices to reduce water use :
- Improving management of surface irrigation systems.
- Implementing better field application practices, such as ‘bed and furrow’ irrigation or drip irrigation.
- Encouraging a cropping pattern adjusted to the local climatic conditions, for instance growing sorghum instead of rice or wheat in drought prone areas.
- Enhancing local water storage in ponds or lakes through small structures, connecting channels, and measures to encourage groundwater recharge, such as the traditional ‘tank’ system in Southern India.
Adopting water harvesting techniques.
Water harvesting, one of the techniques suggested by the WWF, can come in many forms. One technique that had been developed two thousand years ago is the sand dam. Sand dams consist of a wall made of concrete with sand-reservoir behind it. This sand collects rain and acts as a filter so that freshwater is stored at the bottom. The water can be extracted months later by inserting pipes. The benefits of sand dams, other than water collection and purification, are that it reduces evaporation and does not allow parasites such as mosquitoes to breed, unlike reservoirs . The rainwater harvesting techniques article discusses this in more depth.
Some other methods of reducing water demand, as suggested by American Rivers, include :
- Reuse: Also known as water recycling or reclamation, water reuse refers to the use of treated sewage, graywater, or stormwater for non-potable purposes such as irrigation, industrial processes, fire protection, toilet flushing, among others. Drawbacks of this option can include costs associated with a municipal scale dual distribution system, and water that would have otherwise returned to the source river/water body once treated is now designated for a consumptive use, in the case of irrigation, that will not return to the river and may result in decreased flows.
- Groundwater recharge: This involves recharging underground water sources during a wet year or a season (often winter) when water is available. Drawbacks of this option can include costs associated with pumping and piping infrastructure, and the effect on instream flows when water is pumped from a river.
- Re-operation of existing dams: Changing the way an existing dam is used is typically cheaper and less environmentally harmful than building a new dam, and in some cases re-operating a dam can provide water for cities, farms, and fish during critical times of year without major environmental, energy-production, or flood protection drawbacks.
Since agriculture is the largest consumer of water worldwide, with 70 percent of the world’s water usage , reducing agricultural water usage will have the biggest impact. Agricultural efficiency is expected to increase within 30 years. If the suggestions provided by Mission 2017 are implemented within the coming years, efficiency goals can be attained by 2050.
Another method of moving away from hydroelectric dams is the use of alternative sources of energy. Energy sources such as wind, solar power and biofuels are experiencing increasing use worldwide. However, the subsidies for fossil fuels worldwide is 5 times higher than that for renewable sources, according to the International Energy Agency (IEA) . A potential way to increase the interest in alternative sources is to persuade countries to allow higher subsidies and incentives towards research on making these alternative sources more efficient and viable. For agriculture, the irrigation article discusses way in which the efficiency in irrigation can be increased and ways in which the discussed methods can be implemented.
Other alternatives to large dams could be as follows:
Underground/Groundwater Recharge Dams: Groundwater dams store water in permeable alluvial deposits below riverbeds. They intercept sub-surface water flow, slowing the flow of water away from high demand areas. This allows more water to trickle down into the water table, raising groundwater levels, and increasing the ease of water access at wells.
Groundwater dams have been used successfully in parts of Africa and the Middle East .
Small Community Dams: In areas where the ground is composed of a sand layer on top of a rock layer, communities can build small dams to increase their water overall water supply and access. A village in Katuthia in Kenya built a small dam in 15 days that was able to hold enough water to supply the community members for up to three months .
Mission 2017 proposes the commission of a small research group to look into the site of the proposed dam and analyze what alternatives could be placed there to serve the same purpose. Governments can appoint and fund the research group.
4. Make sure new proposed dams are built at a site that result in the least amount of damage
The factors responsible for dam inefficiencies (as outlined in the “Uses of Dams” section of this article) should be taken into account, and measures taken to prevent them from happening so that the new dams can function as effectively as possible.
Mitigating environmental and social effects of functioning dams
The following are ways to minimize the environmental and social effects of dams that cannot be altogether removed. For one, to reduce the eutrophication in reservoirs, “floating islands” can be used. A floating island consists of a small buoyant frame on which plants grow. These floating islands can be put into the reservoir where they will compete with algae for the excess nutrients. They can act to remove excess nutrients from the water which will prevent algal bloom and hence water oxygen levels will not be depleted. Floating islands can reduce biochemical and chemical oxygen demands of the water by 80 and 60 percent respectively. They can also provide habitats for fish and nesting sites for birds. Since they can float, they will not be affected by the changing water levels in reservoirs .
One way to mitigate the social effects of dams is to add doctors’ clinics around the reservoir area to increase treatment of mosquito related diseases such as malaria .
Factors that should be considered when building dams
Dams should be situated at a site which has the least environmental impacts, where, for example, there is no danger of an endangered species dying out. The dimensions of the dam and reservoirs should also be taken into account. Dams should minimize surface area and maximize depth so as to reduce evaporation and the rate of siltation. Thus it is preferable to situate dams in deep gorges that will require little or no flooding of forests, to prevent decay and hence, carbon dioxide and methane production and eutrophication . Simulations should be done by the research group suggested my Mission 2017 or the project developers to project the effects of the dam on the numbers of organisms originally living in the river and also the effects on the people living near the site. The project only approved if it is predicted that the affected individuals will be able to tackle the effect of the dam.
The hydroelectric power article also discusses possible ways in which dams can be made more efficient while being more environmentally friendly.
Ensuring that new dams are built in the least environmentally harmful site will be difficult, since the most environmentally friendly may not be the most economical (this article goes into more details about why this is so). International, environmentally-minded standards need to be developed that requires sites for new dams to meet certain criteria, such as the rarity of the species of fish found in the river, which will help reduce the effects of the dam on the environment.
The implementation article discusses methods by which any changes made as solutions to the water problem can be made sustainable and work in an integrated way, at the international level.
Dams and reservoirs, though effective sources of water and electricity, are immensely detrimental to the environment. To allay concern over the environment, Mission 2017 proposes to reduce the numbers of dams in the rivers and allow rivers to flow naturally to preserve the environment and biodiversity. At present, it is not possible to eliminate all dams. Still, there must be efforts to take down old, outdated dams and to return as many rivers to their natural state as possible. Mission 2017 also proposes to reduce the number of new proposed projects to the minimum to conserve as many natural river systems as possible.
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