Your Dam Your Responsibility (PDF~1.2MB)

4 Planning to Build a Dam
4.3 Types of Dams
There are many types of farm dams. Those built in a gully or waterway make use of the
natural formation to direct water to the dam and those built on sloping ground capture
surface run-off (often directed to the dam from contour drains).
Similar principles and problems apply to both dam types but gully dams are more at risk
of failure during heavy rainfall events. The focus here is on the more common gully and
hillside dams but comment is also made on other types of dam.
(a) Gully Dams
These are normally built from material
located within the storage area upstream of
the dam embankment if they are suitable
(Figure 4.2). Where possible, the outlet pipe
should be positioned to make use of all the
stored water. Gully dams are usually the
most economical form of storage and are
particularly suited to irrigation and domestic
and stock purposes.
Gully dams must have some way to
allow excess flood flows to pass downstream safely. This is usually done by excavating
a spillway channel into the adjacent hillside clear of the end (or abutment) of the
embankment. The floor level of the spillway adjacent to the embankment then sets
the maximum storage level in the dam and must be set some distance below the
embankment crest to prevent water overtopping the embankment.
Figure 4.2 – Gully Dam
Gully Dam
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PHOTO COURTESY OF SOUTHERN RURAL WATER
The design of the
embankment, outlet
works and spillway is
best left to a suitably
qualified engineer
who is aware of the
design parameters and
construction standards
required to provide an
adequate structure.
Note that a sound
design is of no avail if it
is not converted into a
sound structure by using
appropriate construction
techniques and
processes. The dam must
be matched to its site,
and for this reason it is
highly desirable that the
same engineer assesses
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