Your Dam Your Responsibility (PDF~1.2MB)

7 Operation and Maintenance of Dams
(b) Embankment Settlement
On large dams, it is usual to have special level markers
to monitor embankment settlement. On small dams,
embankment settlement can be checked approximately
by monitoring the freeboard. The freeboard can be
estimated from the difference in height between full
water level and the top of the bank. Hard and fast rules
cannot be laid down but, as an indication, it should not
normally be less than about one fifth the height of the
embankment, but the important point is to examine
the records to see if settlement is still occurring or if it
has settled down. Checks should also be made to see
whether there is any development of transverse cracks in
the crest, and if so, professional advice should be sought.
(c) Surface Slips on Embankment
Slides are major structural defects. They normally require major remedial works such
as flattening of batter slopes; improved drainage or addition of rockfill as a stabilising
weight at the toe of a slope.
PHOTO COURTESY OF J WHITEWOOD
Longitudinal cracking along downstream
shoulder of embankment
Selection of an economical and effective
remedy normally requires expert
professional advice from a suitably
qualified engineer. In the short term it may
be necessary to drain or pump out the
stored water.
Classic surface slip
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7.5.8 Defects in Associated Structures
(a) Spillway Blockage
Debris, trees, shrubs, fences and tall grass should be regularly cleaned from all parts of
the spillway, including the approach area. These will tend to obstruct flow and also catch
any floating debris that would normally pass through the spillway. These obstructions can
lead to overtopping the embankment.
Note: If a spillway crest is raised as a means of increasing the storage capacity, there is
a high risk that the bank may overtop. It is a situation fraught with danger, and should
not be undertaken without professional advice.
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