instrumentation is now frequently installed retrospectively to monitor
existing dams.
In the context of new dams, instrumentation data are interpreted in a
dual rôle: to provide some confirmation of the validity of design assump-
tions and also to establish an initial datum pattern of performance against
which subsequent observations can be assessed. With existing dams,
particularly elderly or less adequate structures, suites of instruments may
be installed to provide a measure of reassurance. In such instances they
serve to detect significant and abnormal deviations in the long-term
behaviour of the dam. In other applications to existing dams instruments
may be required to record specific parameters of behaviour in response to
an acknowledged or suspected design deficiency or behavioural problem.
The scope and degree of sophistication of individual suites of instru-
ments varies greatly. Careful attention to specification, design, and correct
installation of all but the simplest instrument arrays is critical to their satis-
factory performance. Responsibility for the planning and commissioning
of monitoring installations is therefore best retained at an experienced and
relatively senior level within an appropriate organization, e.g. the design
agency, owner, or state authority.
Suites of instruments may, for convenience, be classified according to
the primary function of the installation.
- Construction control:verification of critical design parameters with
immediate looped feedback to design and construction.
- Post-construction performance:validation of design; determination
of initial or datum behavioural pattern.
- Service performance/surveillance: reassurance as to structural
adequacy; detection of regressive change in established behavioural
pattern; investigation of identified or suspected problems.
- Research/development:academic research; equipment proving and
development.
Areas of possible overlap between certain of the functional classifications
are self-evident.
For construction control or research purposes absolute values of spe-
cific parameters and the observed trend in those parameters may be of
equal importance. This is less the case when the primary function of the
instrument array is to monitor long-term performance. Absolute values
may then be considered of secondary importance to the early detection of
changes and deviant trends in behavioural pattern which are not attribut-
able with absolute certainty to an observed change in loading régime, e.g.
in retained water level or other identifiable influence. Detection and
analysis of change in a previously established ‘normal’ cycle or pattern of
behaviour is the essential justification for all suites of instruments installed
primarily for surveillance purposes.
292 DAM SAFETY: INSTRUMENTATION AND SURVEILLANCE
