deformation. The inspecting engineer must be alert to change, whether
favourable or unfavourable, between successive visits.
The conduct of second-level inspections, i.e. the relatively infrequent
but rigorous inspections carried out to comply with imposed statutory or
other obligations, lies beyond the scope of this text. Inspection routines
and procedures, including comprehensive checklists appropriate to differ-
ent types of dam, are detailed in the SEED Manual (USBR, 1983), John-
stonet al.(1999) and Kennard, Owens and Reader (1996).
7.4 Dam safety legislation
7.4.1 Legislative patterns
Legislation to cover the construction and safe long-term operation of dams
has assumed greater importance as the number and size of dams at risk
has steadily increased. The situation is dynamic rather than static, and
most countries have introduced or reviewed national legislation in the
wake of catastrophic disasters such as those identified in Table 7.1.
National legislation falls into one of two generic patterns. In the first,
the legislation is precise and detailed, and is operated through some
measure of direct state control. It may adopt a detailed, prescriptive
approach to design standards, to construction and to inspection and sur-
veillance. In such cases supervision and periodic inspection may be the
responsibility of a state authority or inspectorate. The second pattern of
legislation adopts a much less prescriptive approach. State involvement is
minimal, with most responsibility devolved to nominated agencies or
authorities. An example of the first pattern is provided by French legisla-
tion, while the second, but with responsibility placed in the hands of nomi-
nated individual engineers, is exemplified in the British approach outlined
under Section 7.4.3.
Advantages and disadvantages are apparent in either approach. A
centralized inspectorate or design bureau has the merit of ensuring unifor-
mity of standards, but may prove to be insufficiently flexible and respon-
sive to specific situations and to the peculiarities of individual dams. A
system which minimizes state prescription and devolves responsibility is,
however, open to the counter-criticism of possible variation in the stand-
ards applied. In reviewing legislation it is also important to appreciate that
legislative provision does not, of itself, guarantee safety. Legislation is only
as effective in operation as the associated administrative structure will
allow. It must be considered in context with the national perspective
regarding numbers, age, type, size and ownership of the dam population.
The applicability of any legislation must be clearly defined. This is
generally prescribed in terms of a minimum reservoir storage capacity
306 DAM SAFETY: INSTRUMENTATION AND SURVEILLANCE
