embankment utilized locally available and untreated materials. As the
embankment dam evolved it has proved to be increasingly adaptable to a
wide range of site circumstances. In contrast, concrete dams and their
masonry predecessors are more demanding in relation to foundation con-
ditions. Historically, they have also proved to be dependent upon relat-
ively advanced and expensive construction skills and plant.
1.2.2 Statistical perspectiveStatistics are not available to confirm the total number of dams in service
worldwide. Accurate statistical data are confined to ‘large’ dams entered
under national listings in the World Register of Dams, published by the
International Commission on Large Dams.
ICOLD is a non-governmental but influential organization repre-
sentative of some 80 major dam-building nations. It exists to promote the
interchange of ideas and experience in all areas of dam design, construc-
tion, and operation, including related environmental issues. Large dams
are defined by ICOLD as dams exceeding 15 m in height or, in the case of
dams of 10–15 m height, satisfying one of certain other criteria, e.g. a
storage volume in excess of 1 106 m^3 or a flood discharge capacity of over
2000 m^3 s^1 etc. The World Register of 1998 (ICOLD, 1998) reported
41 413 large dams completed or under construction. Of this total, which
excluded separately registered industrial tailings dams, over 19 000 were
claimed by China and over 6000 by the US. These figures may be com-
pared with a worldwide total of 5196 large dams recorded in 1950.
The 1998 edition of the World Register restricted the number of
entries for certain countries, notably China, in the interests of saving
space. This was achieved by listing only dams of 30 m height and above, a
total of 25 410 dams.
Few reliable estimates of national totals of dams of all sizes have
been published. Estimated total numbers for the UK and for the US are
available, however, following national surveys. They are presented along-
side the corresponding national figures for large dams in Table 1.2. From
these statistics it may reasonably be inferred that the total number of dams
in existence worldwide exceeds 300 000.
INTRODUCTORY PERSPECTIVES 5
Table 1.2 Summary of numbers of British, US and Chinese dams (1998)
Large dams Estimated total dams Dams subject to national
(national surveys) safety legislationUK 0535 0 5500 2650
USA 6375 75000 N.K.
China c. 19100 90000 N.K.