Dams are artificial barriers that can impound water or any liquid for the purpose of storing or controlling water. Dams have been in existence for many thousand years. They were erected by early civilizations in ancient China, Mesopotamia, Persia, Egypt and India. Dams, as well as dikes (long walls of earth), are also used for defending habitats and land from river floods, i.e. for disaster risk reduction.
Besides their traditional role in irrigation, dams bring great benefits to mankind in important domains such as:
i. Water supply for domestic and industrial use
A reliable source of water is needed both to sustain existing civilization and to support future growth. Dams contribute significantly to fulfilling our water supply requirements. To accommodate variations in the hydrologic cycle and avoid the complete disappearance of groundwater, dams and reservoirs are needed to store water and subsequently provide more consistent supplies during shortages.
ii. Agricultural demand for irrigation and food supply
“Food grows where water flows” is a well-known saying in many regions of the world. According to estimations, 80% of the additional food production required by the year 2025 will have to come from irrigated land.
iii. Flood control
Dams and reservoirs can be effectively used to regulate river levels and flooding downstream of the dam by temporarily storing the flood volume and releasing it later. Lowering of the reservoir level to create more storage before the rainy season eliminates the risk of flooding.
iv. Hydropower
Water has been used since ancient times to drive water wheels for various mechanical processes, such as grinding corn, sawing timber or driving textile mills. From the mid-19th century water power was used to produce electricity. Since water is the source, hydropower is a renewable and widely used source of electricity. What is very important is that it is a clean source of power, as it does not involve burning fuel and therefore does not pollute the environment.
v. Other purposes
Recreation, navigation improvement, fish breeding.
A dam needs several components in order to operate properly: the reservoir (lake) that stores water, the spillway (structure over or through which flow is discharged from a reservoir in order to prevent dam overflow), the outlet works and a control facility. Under normal operating conditions the water level is managed by the control facility which regulates discharges in the outlet works, consisting of a large tunnel or conduit with control gates. Under flood conditions the reservoir level is maintained by both the spillway and the outlet works.
Consequently, a dam-related emergency is a situation when the main use of dams (namely retaining water) is no longer ensured.
