Dams are man-made barriers across a water body to control the flow or raise the level of water. Often this results in the creation of a reservoir upstream. Dam structures can be small-scale or large-scale infrastructure, with dam heights ranging from a few meters up to several hundred. The following content will focus on large dams.
Introduction to large dams
To date, an estimated 50,000 large dams have been built worldwide and, especially in developing and emerging countries, many more are being planned. The current context of climate change serves to highlight the relevance of dams. Hydropower plants help achieve climate change mitigation goals by generating clean renewable energy. Currently, 15% of all electricity worldwide and 75% of the total electricity from renewable sources is generated by hydropower. As climate change adaptation measures become more urgent, dams and reservoirs can increase the capacity to deal with extreme weather events. They offer run-off storage to regulate flooding in times of heavy rainfall and increase the capacity to harvest water that is needed in times of drought. It is estimated that, by 2025, up to 80% of additional food production will need to come from irrigated land.
Purposes of large dams
Dams and reservoirs are usually built to serve at least one of the following purposes:
- Hydropower generation: The most prominent use of large dams is for hydroelectric power generation, combined with a hydropower plant. Compared to other renewable sources, hydropower produces the most cost-efficient energy at costs as low as 2 US¢/kWh.
- Irrigation for agriculture: Water stored in a reservoir is used to irrigate agricultural crops. It is estimated that 30-40% of irrigated lands worldwide, which contribute 12-16% of global food production, rely on dams.
- Water supply: Especially in urban areas, reservoir storage capacities are used to supply drinking water or water for industrial purposes,.
- Flood control: As a positive side effect, dam structures often offer flood protection by regulating water discharge and balancing runoff differences.
- Inland navigation: The navigability of a water system enabled through the regulation by the dam may provide an impetus for trade and development. Inland navigation is the most cost effective and least polluting means of transportation.
- Recreation: Finally, the lakes created through water storage can additionally serve recreational and touristic purposes.
- Fisheries: Fish production is also feasible.
Large multi-purpose dams typically combine hydropower generation with water storage for irrigation or water supply. A combination with a flood-control function is also common in flood-prone areas. However, on a global scale, about 70% of large dams are still single-purpose. The complexity in planning, funding and implementing multi-purpose dams is a major challenge for the realization of multi-usage projects. Nonetheless, dams serving multiple purposes are gaining importance, especially for developing countries as they can provide several development benefits from a single investment. The ICOLD register of dams reveals that most dams worldwide have been built for irrigation pur¬poses, followed by hydropower generation, water supply and flood control.
Relevant international institutions
The International Commission on Large Dams (ICOLD) is the global umbrella organization for the profession of dam engineering, founded in 1928. Its main function is to serve as a forum for exchange of knowledge and experience with the aim of advancing technically safe, economically efficient and environmentally harmless large dams. Today, national committees on large dams in 82 countries form the membership of ICOLD.
The International Hydropower Association (IHA) is a hydropower industry association with members from more than 80 countries. It was established in 1995 under the auspices of UNESCO as a forum to promote and share good practice and further knowledge about hydropower. Today, IHA aims to advance the role of sustainable hydropower in meeting the world’s growing water and energy needs as a clean, renewable and sustainable technology.
The World Commission on Dams (WCD), initiated by the World Bank and the World Conservation Union (IUCN), was established in 1998 and existed until 2001 as an independent multi-stakeholder body comprising 12 members from governments, industries, NGOs, civil society and academia. Its mandate was to review the development effectiveness of large dams and to elaborate universal criteria, guidelines and standards for sustainable dam development. The result of the commission’s work is comprised in its report published in 2000.
Issues to consider regarding large multi-purpose dams
Large dam projects are subject to widespread criticism due to their social and environmental impacts. The construction of dams and the creation of reservoirs often lead to the resettlement of a high number of people, as well as to major changes in the river ecosystem. This criticism equally applies to multi-purpose dams.
Sustainable development of dams is therefore pivotal to ensure that dams provide true development benefits without worsening the overall situation of the population affected by the dam. Negative social and ecological impacts are to be mitigated or compensated; the participation of all relevant stakeholders, including the affected communities, at an early stage is an important prerequisite. Since the WCD published its report in 2000, its recommendations and guidelines for sustainable development of large dam projects serve as a point of reference for environmental and social NGOs and for the German Development Cooperation. The WCD process has had a significant influence on the development of other international standards for dam projects that have since evolved, such as the safeguard policies of the World Bank or the Hydropower Sustainability Assessment Protocol by the IHA.
For multi-purpose dams, careful consideration and coordination of the interests of the different users are additional prerequisites in order to avoid conflicts. While hydropower typically generates maximum output from maximum storage levels in the reservoir, it is necessary for flood protection to keep the water level low at certain times in the year. Further trade-offs between effectiveness and productivity may arise if irrigation or water supply is combined with hydropower when water levels are low.
Adaptation to climate change
Combined with political and institutional strategies, multi-purpose dams offer important solutions to climate change adaptation needs, especially in vulnerable regions. Though climate change predictions are still subject to a high degree of uncertainty on a local scale, rivers in dry areas of the tropical zone are expected to carry 10-30% less water in the future, while humid areas are predicted to contain 10-40% more water. Therefore, in regions likely to experience water stress, e.g. Southern Africa, increased water storage will make an important contribution to improve sustainable access to safe drinking water and sanitation (a target defined in the Millennium Development Goal #7). On the other hand, improved flood control is necessary to safeguard the lives of millions of people in regions with increased precipitation and runoff, e.g. parts of Southeast Asia.
Changing climatic and hydrological conditions are also challenging technical concepts of dam projects. If economic viability analyses rely only on the historical time series of annual water levels, then dams may fail to perform as desired when a water flow regime in the future substantially deviates from the past norms. In addition to technical solutions, information exchange and coordination between different institutions and sectors remains a key component for multi-purpose dams. To develop effective strategies to address climate change, it will not suffice to treat individual dams in an isolated way. Basin-wide coordinated approaches for all dams on a river system, although a challenging task, can be an important way to sustain ecosystems and the overall benefits generated by dams.
- From a macroeconomic perspective, multi-purpose dams provide multiple benefits from a single investment.
- While not as economically appealing to investors (see below), multi-purpose projects are often more attractive to international financial assistance.
- Multi-purpose dam projects may fit well into regional development programmes: e.g. to improve food production, electricity supply, and the general physical and social infrastructure in rural areas.
- Multi-purpose dams can complement strategies for climate change adaptation; for example, if hydropower generation is combined with increased water storage or flood regulation.
- Most multi-purpose dams are funded by governments, with possible international donor support. Attracting private investors to finance more multi-purpose projects is desirable but difficult due to the inherent complexity. Conflict of interests among the individual uses, e.g. hydropower requiring maximum storage levels and irrigation causing lower levels, result in complex and potentially vulnerable contract structures. Often, promoting a single purpose dam, such as hydropower, is more economically attractive as it promises secure returns on investment.
- Regulatory demands are more complex for multi-purpose dams as compared to projects serving only a single function. Water rights and allocation quotas have to be distributed among the users, with potentially competing demands and impacts usually spread over a large portion of the river basin. As a consequence, inter- and cross-sectoral coordination demands are much higher, requiring relatively strong institutional capacities.
- The impacts of climate change may further intensify competition among the different users as the overall water availability decreases.
Multi-purpose dams, if well planned and managed, provide an important option to meeting some of today’s major development challenges. By providing clean and reliable energy, storage volume to improve drinking water supply or agricultural food production, and enhanced flood control, they contribute to energy, water and food security -- and to human security in general. In vulnerable regions, multi-purpose dams can also be an appropriate response to the impacts of climate change. Yet, as many new multi-purpose projects are expected to be realized in the future, the sustainability of large dams and reservoirs will remain a key issue.
- ↑ According to the ICOLD (International Commission on Large Dams) definition, a ‚large dams‘ hasve a height of at least 15m or a reservoir volume of more than 3 million m³
- ↑ Despite some reservoirs emitting methane gas, the Special Report on Renewable Energy Sources and Climate Change Mitigation (SRREN 2011) by the IPCC declares emissions produced by hydropower reservoirs are still among the lowest of all forms of renewable energy, being of course dramatically lower than emissions produced by fossil fuel electricity generation.
- ↑ http://www.map.ren21.net/GSR/GSR2012.pdf
- ↑ http://www.icold-cigb.net/userfiles/files/World%20declaration/World%20Declaration-ENG.pdf
- ↑ http://www.irena.org/DocumentDownloads/Publications/RE_Technologies_Cost_Analysis-HYDROPOWER.pdf
- ↑ ftp://ftp.fao.org/agl/aglw/docs/Aquastat_Dams_Africa_070524.pdf
- ↑ http://www.icold-cigb.org
- ↑ http://www.hydropower.org/
- ↑ WCD (2000): Dams and Development: A New Framework for Decision-making. Earthscan Publications Ltd., London.
- ↑ http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter11.pdf
- ↑ E.g., see the SADC/GIZ project “Dam Synchronisation and Flood Release in the Zambezi River Basin”
- ↑ Ljung (2001): Trends in the Financing of Water and Energy Resources Projects. Thematic Review III.2 prepared for the World Commission on Dams. Cape Town, p. 55
SADC (2011): Dam Synchronisation and Flood Releases in the Zambezi River Basin Project. Final Report. Transboundary Water Management.