As more dams are constructed, more questions, topics and trends come along with them. Currently, managing aging infrastructure, using new technology, managing risk, and dealing with seismic issues are concerning and exciting dam owners and operators worldwide.
By Bethany Duarte
Dams serve as the lifeblood of communities and cities, helping to provide water for commercial and domestic use, irrigate agricultural land, and provide fuel for hydroelectric facilities. Advancement occurs every day in the design, construction and operation of dams and associated civil structures. In this article, we remind readers of the important roles dams play throughout the world, as well as provide a glimpse of some of the critical topics that are top-of-mind among the world's top civil experts.
Role of dams in today's world
According to the International Commission on Large Dams' (ICOLD) World Register of Dams (a non-comprehensive database created in 1958 as a resource on dams around the world, last updated in 2011), the demand for water as a natural resource is increasing internationally, with the potential to grow 2-3% per year over the coming decades.
"It is agreed today within the international community that there is a necessity to promote and ensure progress in water storage to address the world's challenges related to water security and global change," says Enrique Cifres, chairman of the ICOLD Dams and River Basin Management Committee. "Since 2000, [the industry] has seen a new impetus in promoting new infrastructure to meet the needs of countries in terms of water supply, energy and food, as well as the need to address the increasing occurrence of large floods and drought."
Dams are major players in meeting this demand, currently contributing an aggregate storage of 1.5 million hectares of water. To continue to meet the growing need for water, more dams need to be constructed to compensate for growing populations, seasonal variance and unevenly distributed water resources.
According to Cifres, the current trend of new growth is strong in developing countries "where local conditions allow funding from multilateral agencies." This along with increased new development in Europe and Asia is setting the pace for future development.
Purposes and use
Based on the 37,461 dams included in the World Register on Dams, the largest percentage of single-purpose dams, which make up more than 70% of dams worldwide, are designed for irrigation, providing a valuable asset to agricultural and rural regions. The second largest use (18%) of single-purpose dams is to impound water for hydroelectric power generation. Other smaller categories of use include water supply, flood control, recreation, navigation and fish farming.
In contrast, multi-purpose dams provide a more balanced distribution of purposes, with 24% being used for irrigation, 20% for flood control, 17% for water supply, and 16% for hydropower, among other uses. While they achieve a wider range of purposes, the number of multipurpose dams (9,321) is much smaller than that of single-purpose dams (26,938).
The USA boasts the largest number of dams in the register (9,265), with China and India following behind with 5,191 and 5,101, respectively. Japan ranks in the top four with 3,076. Canada, a country that produces the majority of its electricity using hydropower facilities, has 1,166 dams in the register. Also notable within the top ten are South Africa (1,114), Spain (987), Turkey (741), Brazil (684) and France (622). The countries with the smallest number of dams are Nepal, Latvia and Luxembourg with three apiece.
Type, size, capacity, and age
The main types of dams listed within the ICOLD register are earth, rock fill, gravity, buttress, barrage, arch and multiple arch. These types are widely distributed throughout the world. The highest of these dams (by type) are Rogun (earth and rock fill) in Tajikistan at 335 meters, Grande Dixence (gravity) in Switzerland at 285 meters, Itaipu (buttress) on the border of Brazil and Paraguay at 196 meters, Tongzihao (barrage) in China at 53 meters, Bakhtiyari (arch) in Iran at 315 meters and Deriner (multiple arch) in Turkey at 249 meters.
The register also classifies dams by spillway and reservoir capacity. According to Cifres, "records on height, installed power, discharges, etc. are reached continuously."
In spillway capacity, India boasts the largest projects with Nagarjunasagar Tail Pond (1,600,000 m3/s), Ukai Dam (1,125,000 m3/s), the Mid Manair Project (508,000 m3/s), Mohini Pick-up Weir (265,400 m3/s), and Maudaha (111,328 m3/s ) all in the top six. China also ranks high in this category with Sanxia Dam, which has a spillway capacity of 124,300 m3/s. Rounding off the top 10 are Brazil's Tucurui with 100,000 m3/s, the Democratic Republic of Congo's Inga II dam with 96,000 m3/s, Canada's Kootenay Canal with 95,600 m3/s, and Paraguay and Argentina's Yacyreta with 95,000 m3/s.
|Three Gorges Dam is a larger-than-life example of the colossal impact civil works and hydropower generation have on a particular region.|
In terms of the size of a dam, reservoir capacity is an additional vital measurement. The three largest dams with regard to reservoir capacity are Kariba in Zimbabwe/Zambia with 180.6 billion m3, Bratsk dam in Russia with 169 billion m3, and High Aswan dam in Egypt with 162 billion m3. The top 10 show incredible regional diversity, including dams from Ghana (Kpong Dam/Dykes and Akosombo Dam), Canada (Daniel Johnson Dam, Manic 5 and Bennett W.A.C), Russia (Krasnoyarsk Dam and Zeya Dam), and Brazil (Lajeado Dam).
Well-built dams are known for being able to stand the test of time, and a number of dams in Spain, Japan and India have proven the long-term value of dams. Proserpina in Spain was construction in AD 130, with an age of 1,883 years. Japan boasts 10 dams considered to be some of the oldest in the world, ranging from 885 to 1,613 years. India's Thonnur Tank dam is also one of the oldest with an age of 1,013 years.
Installed hydroelectric power capacity
A considerable percentage of large dams impound water for hydroelectric power generation. Some of the largest dams in the world also produce the most electricity. The final generating unit at Three Gorges Dam on the Yangtze River in China was completed and brought online in 2012. This colossal project has an installed capacity of 22,500 MW, making it the largest hydroelectric plant in terms of capacity in the world.
While it is smaller in terms of capacity with 14,000 MW, Itaipu Dam on the Parana River in Brazil and Paraguay actually produces more electricity annually than Three Gorges (98.3 TWh compared to 98.1 TWh). Other top plants in terms of capacity include 12,630 MW Sanxia, 12,600 MW Wangjiahe and 12,600 MW Xiluodu in China. Guri hydropower project on the Caroni River (10,200 MW/53.41 TWh) in Venezuela, the Tucurui project on the Tocantins river in Brazil (8,370 MW/41.43 TWh), and Grand Coulee Dam on the Columbia River in the USA (6,809 MW/20 Twh) also boast large installed capacities.
Hot topics and trends
So what are the trends and topics currently being discussed with regard to dams and other civil structures?
With as many sources as there are out there to address this topic, there are probably just as many diverse answers.
One way to identify these trends is to examine the topics coming to the forefront at two international events: HydroVision International, held in July in Denver, Colorado, USA, and ICOLD's 81st Annual Meeting, held in August in Seattle, Washington, USA.
Conference content at these two events clearly points to a focus on four important trends:
Managing aging infrastructure
As the age of the world's infrastructure increases, additional technical approaches and strategies for managing and extending the life of these dams are essential, as is determining when and how to decommission dams when they reach the end of their lifespan, or if they can be successfully rehabilitated.
Both HydroVision Inter-national and the ICOLD meeting include sessions on this topic, demonstrating its current importance in the industry.
As the largest hydropower event in the world, HydroVision International has a wide range of tracks and sessions but focuses one entire seven-session track on the topic of Civil Works and Dam Safety. A number of the sessions at HydroVision International 2013 touched on this topic, including one regarding the importance of monitoring and maintaining gate operation and another identifying the factors that can impact and extend the useful life of a dam, primary causes of dam failure, and how to use risk-informed decision making on remedial projects. Technical papers were also presented on this topic, including case studies on repairs and modifications to extend the life of dams.
This topic is discussed at the one-day ICOLD Symposium: Changing Times: Infrastructure Development to Infrastructure Management, as well as during two ICOLD technical workshops. Technical approaches and strategies for managing aging infrastructure; new technology advances in dam safety; security, monitoring, and risk management; and sustainable hydropower development are all key components concerning dam owners and operators today that are being discussed at the ICOLD event.
Additionally, workshops are planned to cover the aging and life extension technologies for concrete dams, which indicates a growing need for knowledge and technological advances to keep these dams safe and operating reliably as they age.
Using new technology
Based on the discussion of challenges faced by dam owners and operators, the availability of new, state-of-the-art technology for dam, risk and levee management are essential to a constructive dialogue about the future of the industry. Utilization of technology can help extend the life and efficacy of a dam, improve best practices for dam safety management, improve current practices in levee and embankment management, and provide seismic analysis to help manage embankment dams.
One HydroVision International presentation in particular discussed a method of using steel-rod breaking excitation to identify instability of tainter gates. Additional technical paper sessions cover the instrumentation and controls technology for dams with a hydroelectric component and total condition monitoring systems.
An ICOLD workshop also covers new technologies on an important topic: monitoring dams and levees. The discussion includes perspectives and case studies on the use of laser scanning, geophysical methods, and GPS for measurement; fiber optic temperature and strain sensing; as well as advances and improvements made on more traditional instruments and tools, such as piezometers.
While no owner likes to consider the damages and consequences that follow a dam failure, the best safeguard is having all bases covered in case of a failure. This includes evaluating the construction and development; considering rehabilitation as a preventative measure; quantifying and identifying environmental impact, economic, and life losses; and handling insurance coverage. An important component of this process is also determining the real risk of a catastrophic event or dam failure, whether it be a mechanical fault or an external natural disaster such as an earthquake. From a technical perspective, identifying the importance of sound mechanics and failure mode analysis are also vital components in handling the possibility of dam failure.
The trends in this field are moving towards improved design techniques and monitoring during dam operation, according to Cifres. "The newest dam safety techniques are used to optimize the safety of the structure to minimize plant damages," in spite of the natural and unnatural forces placing them at risk.
Understanding the threats and being able to filter through predictions and forecasts is a vital component to a risk management plan, as seen by the emphasis placed on risk management at HydroVision International. Peter Amos of Damwatch Services in New Zealand took part in a panel presentation session to discuss just how real the risks can be, how to analyze flood frequency and seismic hazard, as well as what to do with load uncertainty and the impacts such threats have on dam design.
An ICOLD workshop on risk-informed dam safety management sheds a light on how dam safety has transformed to rely on risk-informed decisions through examples from public and private dam safety regulators. This practical workshop focuses on how this concept is implemented and the difference it can make in protecting an asset. Dam safety is a major issue and one of the targeted goals determined by ICOLD, reflecting "the concern of scoiety and thus, the dam engineering community" as well.
Addressing seismic issues
Seismic issues grow ever more important as we depend heavily on infrastructure for irrigation, flood control, hydropower and more. The threat of a dam collapse or cracks due to an earthquake or tremor is very real throughout the world and is one that must be planned for.
This concern was shared by the speakers at HydroVision International, particularly in regards to the grid stability of hydropower. As seismic events can damage dams and the hydroelectric plants that they power, the stability of the energy grid requires precautionary measures and constant seismic analysis. Additionally, probabilistic seismic hazard analysis was also discussed.
ICOLD addresses this concerning topic in a Technical Workshop format, with experts discussing the seismic analysis of embankment dams specifically. The workshop will break down the framework of seismic analysis and also discuss dynamic response analysis, liquefaction and post-earthquake stability through practical case study analysis and application.
Keeping up to date
The top concerns and topics of the industry can change as quickly as a river current. To stay up to date on what's happening in the industry, bookmark the Dams and Civil Structures Topic Center at http://www.HydroWorld.com www.HydroWorld.com, where the news is updated daily to keep you informed and on top of the latest trends.
Bethany Duarte is associate editor of HRW-Hydro Review Worldwide.