A dam is a wall that is constructed to control water flow in a particular region. Apart from those that were built by people, dams also exist in nature with beavers being one of the most prolific dam builders in nature.
History of Dams
Dams are some of the oldest inventions of human societies as they date back to ancient Mesopotamian communities. Archaeological evidence indicates that one of the first dams constructed was located in present-day Jordan and is referred to as the Jawa Dam. The dam was interlinked with other dams indicating that ancient communities were well-versed in making use of water resources. The primary purpose of the Jawa dam was to conserve water to be used within the nearby community. Another ancient dam was located in Egypt and was referred to as the Sadd el-Kafara Dam. The dam had a tragic history as it was designed to control floods, but a flood destroyed it before construction could be completed. Other ancient societies such as the Romans also constructed dams for a variety of reasons such as supplying cities with water and irrigation. Over the years, technology improved which meant that dams could be constructed for many other reasons. The oldest dam still in operation is the Lake Homs Dam of Syria.
Purpose of Dams
The reason why dams are constructed is to store water for future use particularly in areas where the rainfall is unreliable. The water stored in the dams may be used for a variety of purposes. During the drier seasons, cities can be supplied with water stored in the dams ensuring that the residents have a constant supply of water. Some of the dams that store the highest quantity of water include the Kariba Dam which stores 43 cubic miles of water and the Bratsk Dam that stores 40.5 cubic miles of water.
One of the primary reasons for which dams are constructed is to supply water for supporting agriculture particularly in regions that receive limited rainfall. The concept of storing water for use in farming is an ancient concept; however, the construction of irrigation dams in the modern age makes excellent use of technology to store as much water as possible.
One of the dams that have had a significant impact on irrigation is the Aswan High Dam which was constructed in the 1960's. Due to Egypt's climate, agriculture is heavily dependent on irrigation. Data indicates that the dam releases 11 cubic miles of water into various irrigation canals which then directs the water into farms within the Nile valley and the Nile Delta. In these regions, nearly 130,000 square miles of land is under agriculture due to the influence of the dam. The large area under agriculture is vital to Egypt's food security.
Another region where dams play a significant role in irrigation is in Israel particularly the Tel-Yeruham Dam constructed on the Revivim Stream. The dam was completed in 1953 and has provided vast quantities of water for farming.
In the United States, one of the most famous dams used for irrigation is the Navajo Dam which was constructed in the 1960's. During the initial years after the dam's construction, the amount of water released depended on the agricultural requirements. The Navajo Dam is critical in the operations of the Navajo Indian Irrigation Project where almost 110 miles of land are used for agriculture.
Another reason why dams are built is to control floods in areas where they pose a high risk to communities. Floods are one of the most devastating natural disasters and they substantially affect communities that live along river banks. The River Nile was one of the rivers that caused tremendous flooding over the cause of its history. The flooding proved to be a significant issue for Egyptian governments even during the colonial period, and they tried to find methods to prevent the river from flooding. The government finally decided to construct the Aswan High Dam based on information provided by Harold Edwin Hurst. After the construction of the dam, the flooding of the Nile stopped. Dams are also present on the Mississippi River to control the level of water within the river after the great flood that occurred in 1927.
The construction of dams is also essential in the generation of hydroelectric power. Many of the world's nations are shifting their reliance from fossil fuels to renewable sources of energy such as hydroelectricity which increases the significance of several dams. One of the most important hydroelectric projects in the world, Itaipu Dam, is located along the Parana River. The dam gained international prominence in 2016 as it produced more hydroelectric power than any other project in the world at around 103,098,366 megawatt hours. The Paraguayan and Brazilian governments jointly manage the dam. The Three Gorges Dam, located on the Yangtze River, is another prominent hydroelectric project. The power station has a higher capacity than any other in the world, and in 2014 it set a global record in power generation as it produced 98,800,000 megawatt hours. In the US, the Grand Coulee Dam, located on the Columbia River, is one of the most important hydroelectric projects as it generates more than 20,000,000 megawatt hours annually.
Another reason why dams are constructed is to facilitate navigation along inland water bodies. The natural conditions on a river may change from time to time which makes it difficult to use the rivers for navigation consistently. Natural features on rivers such as rapids may also hinder navigation. Due to the numerous benefits of inland navigation, dams may be constructed to create optimum conditions for navigation. One of the dams that aid navigation is the McAlpine Locks and Dam built in Kentucky along the Ohio River. The presence of the Falls of Ohio hindered navigation along the river. After the project was completed, ships could comfortably navigate over the Ohio River.
Environmental Impact of Dams
Although dams play an important economic role, they cause significant environmental problems in the region where they are constructed. In malaria-prone regions of the world, dam reservoirs provide a breeding ground to mosquitoes which contribute to more instances of malaria. Another problem caused by the construction of dams is that it leads to soil erosion particularly in the downstream sections of the river. Dams sometimes interfere with the life cycle of some fish species which may lead to their eventual extinction. Dam failures are also extremely problematic as they cause loss of human and animal life. The 1975 Banqiao Reservoir Dam Failure in China, the world's deadliest dam failure, caused an estimated 171,000 deaths as well as the displacement of millions of people.