The present edition of the Register take into account 37641 dams. Circular letter 1443 specifies the criteria for inclusion. Basic requirement is a structural dam height above foundation not less than 15 metres.

The World Register is widely recognized as the best data basis on dams worldwide. But despite all our efforts, some data are lacking. In using the data basis for calculations, you should stay aware that those calculations are made on the basis of the available data. Therefore, the dams for which the data are lacking are ignored.

Purposes of dams

Runoff waters are a natural resource for nations. For developing countries, storing water is often vital and in any case, the only means to develop economically this natural resource.

Number and Purposes of registered dams

Demand for water is steadily increasing and would reach 2-3 per cent per year over the coming decades. With their present aggregate storage of about 15 501 km³, dams clearly make a significant contribution to the efficient management of finite water resources that are unevenly distributed and subject to large seasonal fluctuations. Many more dams need to be built to ensure proper use of this resource, in accordance with ICOLD policy set out in the "Position Paper Dams and Environment".

Referenced dams can be broken in two main categories :

• single-purpose dams (26 938) or 71,6 % dams.
• multipurpose dams (9 321) or 24,8 % dams.

a) single - purpose dams :

The distribution for each purpose lead to the folowing results :

b) multipurposes dams :

The distribution for purposes lead to the following results :

Dam types

Earth dams predominate for some 63 % of all reported dams. This is of course the oldest type and there are traces or earth dams in the remains of the most ancient civilisations. Furthermore this type of dam can accommodate a wide range of different foundations. The world's second highest dam is Nurek dam in Tajikistan (300 m high).