Environmental Engineering Reference
In-Depth Information
20
Monitoring and surveillance of embankment dams
20.1
WHAT IS MONITORING AND SURVEILLANCE?
ANCOLD (1976, 2003) give the following definitions:
Monitoring.
The observing of measuring devices that provide data from which can be
deduced the performance and behavioural trends of a dam and appurtenant structures,
and the recording of such data.
Surveillance.
The continuing examination of the condition of a dam and its appurtenant
structures and the review of operation, maintenance and monitoring procedures and results
in order to determine whether a hazardous trend is developing or appears likely to develop.
Monitoring and surveillance should be carried out during the construction, first filling
and operation of all large dams.
There is a generally accepted principle that the level of monitoring and surveillance
appropriate for a dam depends on the consequences of failure of the dam, whether the
dam is being filled for the first time or is in general operation, and whether abnormal
behaviour has been detected. This is discussed more in Section 20.3. The definitions of
consequence of failure ratings are given in Section 8.2.3.
It should be remembered that the consequence of failure rating can change during the life
of a dam. For example development downstream may raise the consequence of failure rating
from low to high.
20.2
WHY UNDERTAKE MONITORING AND SURVEILLANCE?
20.2.1
The objectives
The objectives of monitoring are (ANCOLD 1983):
-To provide confirmation of design assumptions and predictions of performance during
the construction phase and initial filling of the reservoir;
-To provide during the operation phase of the life of the dam an early warning of the
development of unsafe trends in behaviour;
-To provide data on behaviour of dams which may not conform with accepted modern
criteria and warrant continuous and close monitoring as a guide to the urgency for
introduction of remedial/stabilizing works or other measures;
- During raising or remedial/stabilizing works, which may of necessity be carried out
with the storage full, close monitoring of structural/seepage behaviour is warranted to
ensure that the additional loading introduced by the new works is applied in a manner
which will not adversely affect the safety of the dam.
In addition to this may be added:
-To satisfy legal obligations of the duty of care;
-To provide data to allow developments in dam engineering: through better measure-
ment of properties, e.g. rockfill modulus in CFRD, checking of analytical methods,