existing at time of installation, possibly many years after completion of the
dam. This renders interpretation of the significance of an observed change
in behavioural pattern more difficult than in the case of a dam which has
been routinely monitored since construction and first impounding. The
desirable minimum installation for retrospective instrumentation is once
again provision for monitoring seepage flows and, on embankments, crest
settlement and deformation. It may in some instances be appropriate to
make further provision for monitoring local piezometric and/or deforma-
tion profiles, e.g. where culverts and similar works run transversely
through the body of the embankment.
Initial impounding and the first few years of operation represent the
most critical phase for a new dam, as foundation and structure interact and
progressively adjust to the imposed loadings. Failings in design or con-
struction which impinge upon structural integrity and safety will generally
become apparent at this early stage, given that an appropriate monitoring
regime is in operation. First impounding should consequently take place at
a controlled and modest rate, with the response of dam and foundation
particularly closely monitored during filling and over the critical first few
years.
The procurement and installation of all but the most basic level of
instrumentation, i.e. provision for monitoring seepage and settlement,
requires care in planning and execution. In the case of the more extensive
instrumentation arrays common for larger dams it is always advisable to
plan in consultation with the specialist manufacturers and suppliers. Con-
siderable advantage is to be derived from entering an appropriate contrac-
tual arrangement with the selected provider to cover procurement,
installation, setting-to-work and proving of the instrumentation. The con-
tract may also be extended to include training of the technical staff who
will subsequently take responsibility for in-service monitoring.
The level of instrumentation provided on embankment dams is
almost invariably more comprehensive and more complex than that for
concrete dams of similar size, where only seepage flows and alignment
may be provided for. The instrumentation of embankment dams, from
selection through installation to data processing, is discussed in the context
of surveillance in Penman, Saxena and Sharma, 1999.
7.2.7 Data acquisition and managementLogical planning of data acquisition and processing is essential if the
purpose of an instrumentation programme is to be fully realized. Unless
observations are reliable and the information is interpreted quickly, the
value of a programme will be severely diminished. Operating procedures
must be carefully defined and the individual responsibilities of personnel