The major areas that require monitoring are,
- For concrete dams: leakage, deformation, uplift and response to earthquakes
- For embankment dams: leakage, deformation, pore pressure (seepage line) and response to earthquakes.
Instruments that are used for monitoring the following parameters:
- Leakage or seepage losses: V-notch weirs, drainage holes;
- Deformation (concrete): plumb lines and external reference points;
- Deformation (embankment): differential settlement gauges and external reference points;
- Uplift pressure: piezometer
- Earthquake: seismograph
The most important parameter for monitoring is leakage from the foundation rock. Following the initial filling of a newly constructed dam and when the dam level has stabilised at a constant level, then leakage is considered to be stable if the rate of leakage decreases gradually. If the rate of leakage is observed to gradually increase then the cause must be investigated. If the leakage rate increases abruptly, then this must trigger urgent investigation.
The greatest risk of dam failure is during the first filling of the dam. It is during this period that leakage rate must be monitored and scrutinised continually for abnormal leakage rate.
Monitoring Leakage Trends
Plot a graph of dam level vs measured leakage. Where dam level data is on the vertical axis and the measured leakage data is on the horizontal axis. Such a graph can assist with detecting any abrupt increases in leakage rate.
Apart from leakage rate, the turbidity of the leaked water is also a critical indicator of possible leakage failure in the rock foundation or dam body.