A dam serves as catcher and store water in the rainy season when the river flows in large numbers and exceed the needs of both for irrigation, drinking water, industrial or otherwise. In contrast to the function of a weir that can not store water but only to raise the water level of the river and drain portion of existing water flow towards the edge of the right and / or left the river to drain into the channel through a building pengambilanjaringan irrigation.
By having such a large amount of capacity that exceeds the needs of river water can be stored in reservoirs and removable barn flows into the river again in accordance with the requirements hilimya alone at the required time.
Figure 23. dam or dam
A dam can be made from building materials mud land fill Minor to large sized stone or concrete. For example Jatiluhur dam in West Java and dam Asahan in North Sumatra. When the flow of river water pouring into the reservoir exceeds the water drained out of the reservoir in accordance with the needs, increasingly -makaisi reservoir is full and can transcend reneananya capacity, so that the water level in the reservoir will continue to rise and the end melimpas.
To Prevent the occurrence of runoff water in a dam, the water runoff was localized to the spillway building whose location is selected according to the best topography. Building long spillway discharge is calculated according to the plan of such that the reservoir water level will not rise higher than the center of the dam and even usually direneanakan that the reservoir water level is lower than the top of the dam minimum 5 meters.
Height difference varies from 5 meters to 20 meters. High dam varies from about 15 meters to hundreds of meters. The so-called high dam is the elevation difference between the top of the dam to the old riverbed. Along with advances in technology and construction methods were improved and efficient it opens now the possibility to plan and build a dam which reaches a height of 1000 feet or 330 meters, as it is being built on the river Vaksh in Russia.
According to historical records the first dam was built on the Nile of Egypt 4000 years BC., While the oldest dams that still exists and functions are bendungn Almanza in Spain over the age of 4 centuries. The basic concept of planning a dam usually do not stand alone but together with the planning of a weir, which are located within a few kilometers to tens km next hilimya. An example is Kedung Ombo dam with weir Sedadi at times Serang in Central and Jatiluhur dam with waterfall weir in the Citarum River in West Java.
Implementation of construction may overlap, but generally the weir is implemented first, and after the weir serves bertahuntahun and turned out the necessary additional water needs of a more reliable, only then can bendungn upstream implemented construction. For example Kedung Ombo dam with a capacity of 450 million M3 and a height of approximately 120 meters, carried out the construction of approximately 30 years after the weir Sedadi function.
With large storage capacity and a high water level of a dam in addition to regulate the flow of the river next hilimya to be more evenly sepanjag years, it can also function well as a means of effective flood control. In addition reservoir water level is high enough it can move the hydropower turbine before being used for other purposes as mentioned above. As an added benefit, the reservoir is also used for fishing.
So the main function is to stabilize a reservoir or equalize the flow of river water either by means of river water supply to accommodate changes throughout the year as well as to remove the pitcher water programmatically through custom-made water channel in the dam body as needed.