Question

Which of the following is not a purpose to build dams?
A. To prevent flooding of the rivers in the area
B. To provide water for irrigation purposes
C. To generate hydroelectricity
D. None of the above

Answer 1

Hint: Recall that dams are not just barriers that check the flow of water but also come hinged to many other components like reservoirs, spillways, embankments and hydroelectric power plants. Think of how these structures prove to be useful and this will help in eliminating out the options in the question.

Complete answer:
Dams are barriers that are used to stop or restrict or direct the flow of water from water bodies. Dams are built with a reservoir that acts as a collecting unit for all inbound water. Thus, the reservoir acts like a storage unit or an impoundment that locks in water, ready to redirect the water for different purposes. Reservoirs are created by either controlling a watercourse that drains an existing water body, or by interrupting a watercourse to form an embayment with it or through excavation and adding retainer walls after.
Now, dams are usually built with floodgates and embankments that act as a spillway for excess water. Spillways are usually designed to direct the watercourse in the upstream to downstream direction. These floodgates direct excess flood water to extensions of the dam that are away from populated areas. Therefore, if a dam is built over a river, the barrier of the dam first checks the flow of water and in case the dam reservoir gets filled completely with flood water, the floodgates help redirect the water to safe spaces. Thus, dams prevent the implications that a flooding river has on surrounding populated areas.
Now, the reservoirs of dams have different channels through which different parts of the water from the main watercourse get directed. This is done to supply water to those regions that have no water sources to rely upon. Thus, water from reservoirs is extracted and directed through canals to provide water for irrigation purposes.
Now, hydroelectric power is a major source of electricity in the world. Hydroelectric power plants are stationed at dams to generate hydroelectric power. The potential energy of dammed water and the kinetic energy of flowing water through the plant drive a water turbine and a generator. A turbine converts the potential and kinetic energy of inbound water to mechanical energy, and the generator converts this motive work into electricity.
Since dams are used for all three purposes of handling floods, providing water for irrigation, and producing electricity, the correct option would be D. None of the above

Note:
In addition to the above three purposes, dams are also for the following:
1.Land reclamation: It is the process by which dams prevent ingress of water to an area that would otherwise be submerged, allowing its reclamation for human use.
2.Stabilize water flow: Dams are used to bring stability to the watercourse in case of rapid and dangerous waters, for both safety and agricultural purposes.
3.Navigation: The deep reservoir of dams can vary the flow of water downstream, making the watercourse more navigable.