Your Dam Your Responsibility (PDF~1.2MB)

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Appendix B
Problem Possible Causes and
Potential Harm
Puddling on Crest –
Poor Drainage
Erosion Gully on Crest and
Downstream Slope
Cause:
1. Poor grading and improper
drainage of crest.
2. Localised consolidation soft
spots or settlement on crest
allows puddles to develop.
Harm:
1. Causes localised saturation
of the crest and loss of soil
strength.
2. Inhibits access to all portions
of the dam and crest.
3. Becomes progressively worse
if not corrected.
Cause:
1. Heavy rainfall.
2. Poor grading and improper
drainage of crest. Improper
drainage causes surface runoff
to collect and drain off
crest at low point in upstream
or down-stream shoulder.
3. Inadequate spillway capacity
which has caused dam to
overtop.
Harm:
1. Can reduce available
freeboard.
2. Reduces cross-sectional area
of dam.
3. If allowed to continue, can
lead to severe deterioration of
downstream slope and shorter
internal drainage path.
Action Required
Action:
1. Drain standing water from
puddles.
2. Regrade and re-compact
crest to restore integrity and
provide proper drainage
toward upstream slope.
3. Provide gravel or road-base
material to accommodate
traffic.
4. Perform periodic maintenance
and regrading to prevent
reformation of low areas.
Action:
1. Protect eroded areas with rock
or clay.
2. Regrade crest to provide
proper drainage of surface
run-off.
3. If gully was caused from
overtopping, provide
adequate spillway, which
meets current design
standards. This should be
done by a suitably qualified
engineer.
4. Re-establish protective cover.