Dams : Types of Dam

 Dam

Dam is an obstruction or a barrier constructed across a river or stream to create a reservoir on its upstream side for impounding water for various purposes like Irrigation, Hydropower, Water-supply, Flood Control, Navigation, Fishing and Recreation.

The side on which water gets collected is called upstream side, and the other side of the barrier is called downstream side. And the lake or pool formed on upstream side is called a reservoir.

Dams and weirs are primarily intended to divert the river flow into the water conveyance system leading to the power house. It also produce additional head and provide storage capacity. Hence it fulfills the two fundamental function:

a.       Develop a reservoir which has a capacity to store water

b.        Builds up head and thus potential for river water.

Various types of dams:

Dams can be classified in various ways depending upon the purpose of the classifications. But most usual ways of classification of dams are mentioned below:

Classification according to Materials used

Rigid Dam : Rigid dam are those which are constructed of rigid materials such as masonry , concrete , steel or timber . Rigid dams may be further classified as follows :

a.       Solid masonry or concrete gravity dam

b.       Arched masonry or concrete dam

c.       Concrete Buttress dam

d.       Steel dam

e.       Timber dam.

  Non Rigid dam: Non rigid dams are those which are constructed of non rigid materials such as earth , and rockfill. The most common type of non rigid dam are :

a.       Earth dam

b.       Rockfill dam

c.       Combined earth and rockfill dam

Classification According to Use

Storage Dams : This is the most common type of dam normally constructed . Storage dam is constructed to impound water to its upstream side during thr period of access supply in the river and use in the period of deficit supply. Behind such a dam a reservoir or lake is formed. The storage dam may be constructed for various purposes such as for irrigation, water power generation or for water supply for public health purposes or it may be for a multipurpose project .A storage dam may be constructed of wild variety of materials such as stones , concrete , earth and rock fill etc

Diversion Dams : The purpose of diversion dam is essentially different. While a storage dam stores water at its upstream for future uses, a diversion dam simply rises water level slightly in the river and thus provides head for carrying or diverting water into ditches, canal, or other conveyance system to the place of use. A diversion dam is therefore of small height and no reservoir is formed. The common examples of diversion dam are weirs and Barrage. A diversion dam may be constructed for irrigation or municipal or industrial use.

The detention Dams: A detention dam is constructed to store water during floods and releases it gradually at a safe rate, when the flood recedes . There are usually two types of detention dam .In the first type, water is temporarily stored and released through a suitable outlet structure. In the other type of detention dam water is not released and no outlet structure is provided. Instead water is held in the reservoir as long as ii possible. In a multipurpose river valley project, the dam may serve the purpose of storage, flood protection and recreation. The store water may also be use for irrigation water power generation municipal and industrial supply and other purposes

Classification According to Hydraulic Designs

Overflow Dams : An overflow dam is the one which is design to carry surplus discharge over its crest.Its crest level os kept lower then the top of the other portion of the dam . Since water glides over its downstream face it should be made of such a materials which is not easily eroded by flowing water. Such dams are generally made up of concrete or masonry . An overflow dam is commonly known as spill way. Very often , in a river valley project, the two types of dam are combined. The main dam is kept as non over flow dam made of either rigid materials such as masonry or concrete or non rigid materials such as earth and rockfill and some portion of the dam is kept as overflow dam at some suitable location around the main dam.

Non-Overflow Dams : A non over flow dam is the one in which the top of the dam is kept at a high elevation the the maximum expected high flood level. Water is not permitted to over top the dam. Hence a non over flow dam may be constructed of wide variety of materials , such as earth, rockfill,masonry,concrete.