Wonderful structures with great power? Find out all about dams
What is a dam and what it used for?
Dams are man-made structures, artificial barriers built across bodies of water to interrupt or restrict flow, creating a reservoir. They were created and built over the natural course of rivers to ensure the survival and subsistence of countless communities. In the past, as in the present, by serving as a means to control water levels, dams prevent deluges and floods, and are also used to irrigate crops, thus ensuring food production. This seemingly simple invention has led to the construction of dams with greater potential than initially thought, leading to the discovery of power generation by harnessing water flows, key in the production of hydroelectric power and the transition to clean energy sources.
It is believed that the first dams were built in Mesopotamia nearly 2,500 years ago. Our ancestors used materials like rocks and clay to build these structures across rivers, a craft perfected by the Romans. With the “power” of being able to generate energy using the force of running water, in pre-industrial Europe and America small dams became a source of energy, powering machines used to saw logs or grind grain, for example.
Today, it is estimated that there 60,000+ dams around the world (so-called “big dams”, with a height of 15 metres or more), 3,000 of which are in Europe.
During the Industrial Revolution, bigger dams began to be built with the capacity to hold back more water and to power the large machines in factories and mines. From there they were quick to use the force of water to move turbines and generate electricity. In response to the growing demand for electricity, the early 20th century saw the emergence of big dams, especially in the US.
Built on the Colorado River between 1931 and 1936, Hoover Dam is one of the most famous dams in the world, with a height of 221 metres, a crest length of 379 metres, and a reservoir capacity of 37 billion cubic metres. It provides energy for the city of Las Vegas.
According to the International Energy Agency, hydropower is the main renewable energy source for electricity generation in 57 countries, and is expected to remain the largest renewable electricity source in 2028.
The structure of a dam
There are different types of dams (arch, earth, buttress…) and they can be built to fulfil different purposes simultaneously. That said, more than half of dams are single-purpose, with irrigation being the most common, followed by water supply and power generation. Normally, a dam has seven parts, each with a specific function.
Parts of a Dam:
- Crest: this is the top part, usually used for transportation from one end to the other.
- Parapet walls: protective walls on either side of the crest
- Heel: part which is in contact with the case of the water body on the upstream end.
- Toe: part of the dam in contact with the water body on the downstream end.
- Spillway: an outlet for water removal when its level rises more than the maximum value.
- Freeboard: space between the highest water level and the top of the dam.
- Dead storage level: the minimum level of water to be maintained inside a dam.
These are three examples of dams in Portugal, Poland, and Colombia.
The Alqueva Dam, in the Alentejo Region (inland Portugal), has created what is considered to be the largest artificial lake in Europe. It was commissioned in 2004 and, besides producing hydroelectric power, it supplies the water used for irrigation throughout the Alentejo. The dam was built on the Guadiana River, close to the Spanish border. Its banks span a length of 1,160 kilometres, more than the entire Atlantic coastline of mainland Portugal, impounding 250 km2 of water.
This dam is the tallest concrete dam and the largest structure of hydrotechnical engineering in Poland, standing nearly 82 metres tall and 664 metres long. The dam and Lake Solina, an artificial lake with 22 km2 formed after the construction, are one of the main tourist attractions of the region.
Located on the Sogamoso River, approximately 40 km from the town of Bucaramanga in the north-west of Colombia, this dam was inaugurated in January 2015. The project included the construction of a dam, 190 m high and 300 m long, and of an underground power station with a total installed power of 820 MW. The plant is the fourth largest in Colombia and supplies about 10% of the country’s annual energy requirement, playing an important role in generating the annual average of energy.
What are the benefits of a dam?
As an essential commodity, drinking water is an increasingly limited and unevenly distributed resource. In developing regions and countries, where the availability of drinking water is vital for the survival and development of communities, the importance of dams as a way of harnessing water resources is clear.
Rainfall fluctuations and irregular river flows prevent the storage and efficient and predictable harvesting of runoff water.
Main benefits of dams:
- Water storage: dams create a reservoir to store water for human consumption, irrigation and industrial use, and ensure supply during periods of lower water availability.
- Flood control: by acting as a barrier, dams help control the flow of rivers, preventing flooding.
- Ecosystem preservation: by trapping water collected during rainy periods, dams help maintain a minimum flow of water in rivers during dry periods.
- “Clean” energy production: many dams, especially the larger ones, have hydroelectric power stations that enable the production of electricity from a renewable source. This energy helps to reduce dependence on fossil fuels, thereby helping to minimise the impact of climate change.
- Crop production: by helping to irrigate areas that might otherwise face water shortages, dams have a direct impact on agricultural output, ensuring food availability.
- Safety and navigation: dams create routes for the safe transport of people and goods in areas that were once impossible to navigate.
- Tourism and leisure: river beaches can often be found along dam reservoirs, used for leisure activities and water sports. They can be major tourist attractions and promote economic development for communities.
The role of hydropower in the energy transition
Generating energy and electricity using the flow of water? This is called hydroelectric power, the product of large dams.
Typically, a hydroelectric power station has three parts: a power plant, where the electricity is produced, a dam to control the flow of water, and a reservoir to store the water. The water flows through an intake “hidden” behind the dam wall, which pushes against the blades of a turbine coupled to a generator to produce electricity. This energy is then transported through high-voltage electric lines.
Dams can also serve as an energy reservoir, as some are equipped with pumps that return some of the water to the reservoir, allowing the same water to be used more than once to generate power. In many of these cases, the pumps are powered by wind turbines during off-peak hours, times of the day when there is less electricity consumption.
By 2023, hydropower will account for about 14.3% of all electricity produced worldwide. China produces the most electricity from hydroelectric power.
What are the negative impacts of a dam?
- People and their livelihoods are affected when the areas where they live and work are flooded. In some cases, tens of thousands of people have been forced to leave their homes and have been displaced, breaking up existing communities.
- Dams disrupt the natural balance of a river and affect animal and plant life. When a river valley begins to flood, animals are forced to leave the area and the plants and trees die.
- A dam can block fish species from migrating upstream, such as salmon. As a workaround, the dam should include passageways so that adult fish can swim upstream to spawn and later return to the sea.
- When the river flow enters a reservoir, the current velocity decreases and sediment can be deposited on the reservoir bed. If too much sediment is stored, the natural balance of the river downstream can change, affecting people, animals and plants as far away as the river estuary.
- Water quality can deteriorate. Not only can oxygen levels in the water decrease, but pesticides from farms and toxic materials from factories can increase water pollution in the reservoir.
- Throughout history, people have settled in river valleys. This means that many of the archaeological sites and historical monuments are in areas close to the rivers. This heritage could be lost forever if a dam bursts.
Did you now?
1. The oldest dam in the world is 2,500 years old.
The Jawa Dam, in Jordan, is the oldest known dam. It was built around 400 BC. Today only ruins remain.
2. The largest dams in the world are in Asia and Africa.
The tallest dam in the world is Jinping-I, in China, standing at 305 metres. China is also the home of the Three Gorges Dam, which has the largest electricity generating plant in the world (around 22,500 megawatts). The Three Gorges Dam was built on the Yangtze, China’s main river and the third largest in the world. The Kariba dam has the largest reservoir, built on the Zambezi River between Zambia and Zimbabwe, holding around 185 km³ of water.
3. China is the country with the most dams in the world.
There are more than 20,000 dams in China. In second place is the US, with around 9,000 dams. All over 15 metres in height.
4. The oldest working dam is in Spain.
The Cornalvo Dam, in Badajoz province, is the oldest operational dam. It was built by the Romans between the 1st and 2nd centuries.
5. If not for dams, the Netherlands could disappear.
Some cities in the Netherlands lie below sea level, with the lowest point at seven metres below sea level. The country relies on structures such as dams and dykes to protect certain areas from flooding.
