tion. In circumstances where the situation is not deemed critical, and time
permits a systematically planned investigation, piezometers may be
installed to determine the local phreatic profile within a suspect location.
Where time is considered to be critical, and/or there is no clear evidence as
to the approximate location of a suspected seepage path, the use of fluo-
rescein dyes or radioactive tracers may provide a quick method of deter-
mining entrance and exit points and hence notional seepage path. More
sophisticated techniques which have proved successful in specific instances
include monitoring temperature and/or resistivity profiles within an
embankment (Johansson, 1996), and the use of fibre optics to monitor
temperature gradients and leakage (Aufleger et al., 2005). In the latter
instance anomalies in the temperature regime can relate to the presence of
internal seepage flows and may also highlight other negative aspects of
behaviour.
7.2.6 Instrumentation planningThe planning and specification of a comprehensive suite of instruments
involves a logical sequence of decisions:
- definition of the primary purpose and objectives;
- definition of observations appropriate to the dam considered;
- determination of the locations and numbers of measuring points for
the desired observations; - consideration of the time period to be spanned, i.e. long- or short-
term monitoring; - consideration of the optimum sensing mode in relation to the desired
rapidity of response, required accuracy, etc.; - selection of hardware appropriate to the task as defined under 1–5.
Step 3 is one of particular importance and sensitivity. Instruments must
cover known critical features of the dam, but for purposes of comparison
some should also be placed at locations where ‘normal’ behaviour may be
anticipated. In the case of a new dam at least two sections should be
instrumented, including the major section. It is good practice to draft an
ideal instrumentation plan in the first instance, and then to progressively
eliminate the less essential provisions until an adequate, balanced, and
affordable plan is determined.
At the installation and setting-to-work stage success is dependent
upon attention to detail. Points to be considered and resolved in advance
include procedures for the commissioning and proving of the instruments,
for the determination of ‘datum’ values and for the special training of
monitoring personnel. Detailed consideration must also be given at this