What is Dam ?

The Kallanai is constructed of unhewn stone, over 300 m (980 ft) long, 4.5 m (15 ft) high and 20 m (66 ft) wide, across the main stream of the Kaveri river in Tamil Nadu, South India.

This arrangement would, however, require bracing and this will increase the cost. These are quite costly and are subjected to corrosion. These dams are almost obsolete. Steel dams are sometimes used as temporary coffer dams during the construction of the permanent dams.

Embankment dams typically are constructed of compacted earth, rock, or both, making them less expensive than others that are constructed of concrete. Consequently, more than 80 percent of all large dams are of this type. Embankment dams have a triangular-shaped profile and typically are used to retain water across broad rivers.

Steel coffer dams are supplemented with timber or earthfill on the inner side to make them water tight. The area between the coffer dams is dewatered so that the construction may be done in dry for the permanent dam.

Early dam building took place in Mesopotamia and the Middle East. Dams were used to control the water level, for Mesopotamia's weather affected the Tigris and Euphrates rivers, and could be quite unpredictable.

The basic structure dates to the 2nd century AD and is considered one of the oldest water-diversion or water-regulator structures in the world which is still in use

Examples of Steel Dam: Redridge Steel Dam (USA) and Ashfork-Bainbridge Steel Dam (USA)

The earliest known dam is the Jawa Dam in Jordan, 100 kilometres (62 mi) northeast of the capital Amman. This gravity dam featured an originally 9 m (30 ft) high and 1 m (3 ft 3 in) wide stone wall, supported by a 50 m (160 ft) wide earth rampart. The structure is dated to 3000 BC.

The purpose of the dam was to divert the waters of the Kaveri across the fertile delta region for irrigation via canals.

Main load-carrying structural elements of timber dam are made of wood, primarily coniferous varieties such as pine and fir.

Their sheer dimension and immense capacity have this humbling effect on anyone that would come across this structure. It's literally like standing in front of a calm, reassuring giant staring at you in all its glory

Du Jiang Yan is the oldest surviving irrigation system in China that included a dam that directed waterflow. It was finished in 251 BC.

The Ancient Egyptian Sadd-el-Kafara Dam at Wadi Al-Garawi, located about 25 km (16 mi) south of Cairo, was 102 m (335 ft) long at its base and 87 m (285 ft) wide. The structure was built around 2800 or 2600 BC. as a diversion dam for flood control, but was destroyed by heavy rain during construction or shortly afterwards.

Timber dams are made for small heads (2-4 m or, rarely, 4-8 m) and usually have sluices; according to the design of the apron they are divided into pile, crib, pile-crib, and buttressed dam

First on my list of fascinating dams would have to be the Contra Dam or most commonly known as the Verzasca Dam in Ticino, Switzerland. It is perhaps most famous for its 1995 epic appearance in the opening scene of the James Bond movie GoldenEye.

During the XIIth dynasty in the 19th century BC, the Pharaohs Senosert III, Amenemhat III and Amenmehat IV dug a canal 16 km long linking the Fayum Depression to the Nile in Middle Egypt.

A large earthen dam, made by Sunshu Ao, the prime minister of Chu (state), flooded a valley in modern-day northern Anhui province that created an enormous irrigation reservoir (100 km (62 mi) in circumference), a reservoir that is still present today.

The openings of timber dams are restricted by abutments; where the sluice is very long it is divided into several openings by intermediate supports: piers, buttresses, and posts. The openings are covered by wooden shields, usually several in a row one above the other.

Contra Dam is a slender concrete arch dam standing at a height of 220 m with a crest length of 380 m. Because of the dam's slender design, the volume of concrete required to construct it was reduced and consequently cutting down the cost of the infrastructure.

Two dams called Ha-Uar running east-west were built to retain water during the annual flood and then release it to surrounding lands. The lake called "Mer-wer" or Lake Moeris covered 1700 square kilometers and is known today as Berkat Qaroun.

Roman dam construction was characterized by "the Romans' ability to plan and organize engineering construction on a grand scale.

Simple hoists—permanent or mobile winches—are used to raise and lower the shields.

The dam's base is 28 m in width and gradually tapers up to 7 m at the crest. Two spillways were incorporated at each side of the structure, which has a maximum discharge capacity of 1,300 cubic meters per second.

Roman planners introduced the then-novel concept of large reservoir dams which could secure a permanent water supply for urban settlements over the dry season

By the mid-late 3rd century BC, an intricate water-management system within Dholavira in modern day India, was built. The system included 16 reservoirs, dams and various channels for collecting water and storing it.