The primary objective of a surveillance programme is to minimize
the possibility of catastrophic failure of the dam by the timely detection of
design inadequacies or regressive changes in behaviour. A further objec-
tive is to assist in the scheduling of routine maintenance or, when neces-
sary, of major remedial works.
Surveillance embraces the regular and frequent observation and
recording of all aspects of the service performance of a dam and its
reservoir. It includes routine observation and inspection, the monitoring
and assessment of seepage and instrumentation data and the recording
of all other relevant information, including hydrological records. Less
frequent but more rigorous statutory inspections by specialist engineers
are also carried out as part of a comprehensive surveillance programme
and may include a detailed investigation and complete reappraisal of
the dam.
Daily external observation of a large dam may be considered to rep-
resent the ideal; in practice, problems of access or of availability of person-
nel may render weekly or even monthly observation a more realistic
target. The surveillance procedures practised by two large UK dam-
owners are discussed in Beak (1992) and Robertshaw and Dyke (1990).
Routine inspection should cover all readily accessible parts of the
dam and of its associated components (e.g. spillways, gates, valves and
outlet works). Visual inspection should also extend to the area down-
stream of the dam, including the mitres and abutments, and to any parts of
the reservoir perimeter designated as requiring observation. Additional
effort may be directed at particular locations or to specific signs of
some possible deterioration, e.g. sources of suspected seepage or leakage
and, in the case of embankments, localized crest settlement and slope
SURVEILLANCE 305
Fig. 7.7 Representative monitoring plots: embankment dam