Your Dam Your Responsibility (PDF~1.2MB)

Appendix A
A
and the resistance to penetration, it is easier to decide whether an area is saturated or
simply moist.
Pegging-stakes
The best way to find out if there is a leak is to check how fast water is disappearing
from a storage by marking the waterline with a peg at regular intervals, say, weekly.
If the storage is used for stock or irrigation, try to peg the waterline before and after
use. Alternatively measuring staff can be permanently set into the storage to level
measurement easier.
Measuring in this way is much better than simply guessing. A suspected leak, when
measured, may turn out to be only evaporation loss. Evaporation per day can easily be
five millimetres, and sometimes as much as ten millimetres in fine, dry, windy conditions.
Noting Slides and Signs of Surface Movement
Slides are often difficult to spot, because they do not always produce readily noticed
cracks at the surface. Their appearance is often subtle, since there may be less than
200mm of depression or bulging out at right angles to the slope in a distance of perhaps
ten metres. On the other hand, when the dam was finished, the bulldozer operator may
not have uniformly graded it, and in such a case the surface of the slope may have an
apparent bulge or concavity when in fact no slide is present. A good familiarity with how
the slope looked at the end of construction helps identify any slides.
A method of monitoring surface movement on the upstream or downstream slope is to
place a straight line of stakes down the slope with a string tape attached to the top of each
stake. The point at which a slide takes place will cause the uphill stakes to be pulled over,
whilst those just downhill of the movement would show a slackening of the string tape.
Noting Changes in Vegetation
The density or lushness of vegetation can also be an indication of extra moisture at a
particular location and the possibility of a leak. Probing the area will usually confirm
whether or not a problem is developing.
(f) Evaluation Of Observations
The record of observations taken at periodic inspections is used to develop a mental
picture of the dam’s performance. Accurate measurements pay off here because small
changes, which could go undetected if simply looked at rather than measured and
recorded, will show a pattern or trend.
Immediately following the inspection, the observations should be compared with previous
records to see if there is any condition, reading, or trend that may indicate a developing
problem. The owner can then begin to address any potential problem before it becomes a
threat to the dam. When a significant change is detected, any design drawings for the dam
should be examined carefully to see if an obvious reason for the change could be found.
If a questionable change of trend is noted, a suitably qualified engineer
experienced in the field of farm dam engineering should immediately be
engaged to determine if any action, such as increased monitoring or detailed
investigation of the condition, is required.
These actions will help ensure the safety, safe operation, and long, useful life of the dam.
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