Dam Information

What is a dam?
A dam is defined as a barrier or structure across a stream, river or waterway to confine and then control the flow of water. Dams vary in size from small earth embankments, often for farm use, to high massive concrete structures generally used for water supply, hydropower and irrigation.

Dams and reservoirs are essential structures that are critical for providing us with some of our basic needs. Dams are structures built to retain water by forming a reservoir behind the structure. These are usually built across, or near, naturally flowing water to manage the water for human use.

How old are Dams?
Simple earth dams and networks of canals were constructed as far back as 2000 BC. The Romans built an elaborate system of low dams for water supply. The most famous was the Cornalbo earth dam in southern Spain which had a height of 24 meters (78 feet) and a length of 185 meters (606 feet).

The building of the Marib dam in Yemen began around 750 BC and took 100 years to complete. It consisted of an earth embankment 4 meters in height and stone sluices to regulate discharges for irrigation and domestic use. In 1986, the existing dam was raised to 38 meters that created a reservoir of 398 Mm3.
The Sayamaike dam, one of the oldest dams in Japan, was built in the early 7th century and after several modifications and a heightening is still in use today.

In the UK the oldest dam is purportedly Castle Pond, Pembroke, which was given by King John in 1199 to the Knights Templar of St. John of Jerusalem.

On this page you will find general information about dams providing an introduction to dams and some of the issues associated with them.

Arch dam


Some of the different types of dams


How dams are used

Spillways & Outlets

What spillways & outlets do


Professionals who design dams


Methods of building dams

People and Environment

How people and environment are affected by dams


How dam safety is checked


Links to other interesting web-sites


Additional photographs were kindly provided by Malcolm Dunstan, Halcrow Water, Andy Hughes, Jim Millmore, HR Wallingford, John Sawyer and Scottish and Southern Energy plc.