A Brief History of Dams
Dams are primarily built for water retention. A dam stops or limits the flow of water or underground streams by making use of obstructions. The first known dam was built somewhere around 2950-2750 BC in the ancient Egyptian civilization. Archaeologists have discovered many ancient dams, near Mesopotamia and middle east. Remnants of dams can be found across all the big rivers across the world like Tigris and Euphrates in Middle East or Ganges and Sindhu in the Indus Valley or Yangtze and Yellow River in China. The earlier dams were quite simplistic in construction and operation. As the science of dam building evolved, the dam sizes increased and the designs started becoming more refined as well as complex.
Why do we need Dams?
While water retention is the most common reason for which we build dams, it is not at all the only reason for which dams are built. Initially, dams were built for providing a lasting supply of water for human use as well as for irrigation. Over the years, dams were built for other aligned objectives like flood control, navigation, maintaining water quality, generating hydroelectricity etc.
Over the years, dams have emerged as a cornerstone asset for managing water basins and water resources therein. As the needs of human civilizations increase, instead of single purpose dams, multipurpose dams are becoming an option worth considering. A multi purpose dam fulfills two or more of the above mentioned purposes.
Multipurpose dams are a sought after asset especially by developing countries as they solve multiple domestic and economic problems in a single investment. Out of all dams in the world, around 48% are built primarily for the irrigation purpose. Roughly 17% dams cater to generating hydroelectricity, 13% for water supply, 10% for flood control, 5% for recreation and less than 1% for navigation and tourism.
Let us now have a closer look at how dams fulfill the above mentioned purposes.
Irrigation: As we have seen, almost half of the total dams in the world have irrigation as their prime objective. While the regions along the river basins are fertile and have ground water adequate for farming, across many regions of the world, the soil becomes so dry that the farming activities in it cannot sustain without irrigation. Dams prove to be an excellent storehouse for the water which can be released through canals as and when required. Normally, water is transported from dam to the users, under gravity.
Power Generation: As world migrates towards the renewable sources of energy, hydro-power is getting more and more popular. When dams are built for the purpose of power generation, the water is stored at location at higher altitude. The water is then fed in to turbines which are located at a lower height through long pipes, called as pen-stocks. These turbines, housed in a power station, convert the kinetic energy of moving water into the electrical energy.
Flood Prevention: Many rivers have basins of variable size which expand considerably during the rainy season. This expansion of basin poses the population living in the vicinity to the risk of flooding. A dam can be used to mitigate this risk. When it rains excessively, the water is first collected in the dam. When the dam is filled, water can be discharged in a regulated manner by opening one or more gates systematically.
Urban Water Supply or Industrial Usage: Many times, low elevation dams are built in river to maintain a certain minimum level of water in it. This water is then used to cater to a city nearby. Many such dams are also built on rivers in vicinity of industrial zones to supply water to the industry.
Navigation: Many rivers have shallow basins which make them unsuitable for ferrying and navigation. Sometime, the basin is deep enough but the water flow velocity is very high which makes it unsafe for navigation. A dam can be built at such locations to provide depth to the basin or to reduce the water flow or to achieve both of the above benefits. Many times, water level is sufficiently high during the rainy seasons but goes down in the summers. Building a dam can ensure a specific depth round the year. If region ahead of the dam dries, stipulated amount of water can be discharged.
Fishing and Culturing: Dams can also be used to create a water body where fishing, prawns culturing of pearl culturing can be done round the year providing stable income to the population in the vicinity.
In the next article in this series, we will have a closer look at how dams are classified based on different parameters and what are essential components of a dam.
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