SMALL DAMS PETITS BARRAGES

6.4 MONITORING SYSTEM
The present chapter only looks at aspects related to the design of a monitoring system
for small earthfill and rockfill dams, both new constructions and operating dams with no such
system.
However, it must always be remembered that visual inspection is as important as the
monitoring system as part of dam surveillance: that is often the means to detect problems and
anomalies that affect the dam. Monitoring is the quantitative method based on the use of
measuring instruments, selected and positioned to give information on how the dam behavior
changes. The monitoring system must therefore be designed according to the type, the
dimensions and the specific technical features of the dam and its foundation.
For small dams, the monitoring system should consist of simple, robust and easy to
install instruments.
6.4.1 Monitoring Instruments for Small Dams
Surveillance of a small dam is essentially intended to reveal, and if possible prevent any
deterioration, in order to keep the structure in good condition for safety and also apt to fulfill its
functions.
Monitoring should provide the means to detect anomalies, and evaluate how fast are
occurring and how they will probably end. The monitoring data will be very useful, helping the
engineer or entity responsible for the dam to decide on the nature and urgency of the required
remedial measures.
Reservoir Water Level
This measurement helps in meeting three objectives:
Improving reservoir management through continuous knowledge of the volumes of
water that are available;
Participating in dam monitoring by allowing examination of the influence of reservoir
water level on measurements taken by certain instruments (in particular flows and uplift
pressures);
Enriching hydrological data trough measurement of flood flows.
Leakage Measurement
Monitoring of seepage - both visually for any cloudiness or fines in the seepage water,
and for unusual changes in flow rates – is the most common method used to detect for internal
erosion and piping. Seepage rate is monitored by several methods, ranging from simple to
more technically complex. Some examples include:
collect seepage emerging from a toe drain or other collector pipe with a calibrated
catch container (bucket) and time the fill rate with a stopwatch (Fig. 6.1),
Parshall or other types of flumes installed in seepage collection trenches or manholes
Weirs installed in open channels (Fig. 6.2).
98