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Smart water management
By DAVID EAST
UILDING a farm dam is not a
case of digging a hole and wait-
ing for it to fill with water --
many dams fail because they were
not planned or built properly.
Most farm dams are compacted
earth structures built at depressions,
gullies or hillsides, and they should
be planned and built with the same
care you would apply to building a
There are several things to consider
in planning, which can limit the size
of the dam that can be built without
a licence, or can impact on its loca-
• Government regulations that
apply to your dam, including the
maximum allowable size.
• Size of your dam, allowing for
farm water needs and evaporation
• Where to build it.
There are also several other things
to consider when building a farm
dam, such as who should build the
dam, preparation of the site and dam
Generally farm dams can be built
on minor watercourses (lower order
streams) but not on larger streams,
unless the appropriate local and State
Government approvals are sought.
The State Government has been
reforming water management since
the 1990s and has introduced a range
of changes that may impact on the
size and location of a new farm dam,
and some local councils require a
development application for every
dam built in their area.
What size dam is required?
When determining what size to
build, consideration must be given to
the whole of the farm water require-
ments, which will vary considerably
with geographic location, annual
average rainfall, irrigated crop types
intended, stock types and numbers.
For example, pastures and other
crops grown in the Adelaide Hills and
Fleurieu regions generally will
require less irrigation water than sim-
ilar crops grown elsewhere.
Similarly, 100 sheep will need less
water than 100 cows.
If the dam is to be used for irriga-
tion it will increase the required size
considerably, depending on the pro-
portion of the crop's needs against all
the other requirements.
As a guide, indicative average
annual irrigated water requirements
can range from:
Pastures: 4-6 megalitres a hectare a
Vines: 2-3 mgL/ha a year
Vegetables: 3-5 mgL/ha a year
Stone fruit: 3-4 mgL/ha a year.
Evaporation loss must also be con-
sidered when determining the stor-
age capacity and this loss will not be
constant but will vary from month to
month and from location to location.
Average evaporation losses can be
as low as 1400 millimetres a year
near the coast and as high as 3600
This equates to annual evaporation
losses of around 14-36 mgL/ha of
There are several options available
for the reduction of evaporation loss-
es from farm storages. Initially the
most desirable is to make the storage
as deep as possible to reduce its sur-
Once it has been estimated how
much water is required, the next
thing is to establish where to put the
dam, remembering that the site cho-
sen will determine its success or oth-
erwise. A gully is usually a good place
because it reduces the amount of
earthworks and the overall cost,
however, not everyone has the
advantage of a gully site on their
property, so many farm dams are
built on hillsides.
Two important considerations here
are the catchment yield and the soil
type at the site.
Unless the dam fills from a spring
or by pumping from a river or bore,
the main source of water will be rain-
fall that runs off the catchment, and
generally the bigger the catchment
area, the greater the volume of water
run-off will be.
The catchment can be natural from
the ground run-off or it can be artifi-
cial, from roads and roofs.
The amount of run-off also
depends on several other factors,
including ground slope, rainfall
intensity, type of ground cover, soil
type and existing drainage patterns.
More to dams than digging
A number of factors
Council approval required
Consider farm'e entire water
Allow for evaporation loss when
Drip irrigation saves with efficiency
WATER management is one of the most critical aspects facing all
What to do with the land -- run livestock, grow crops, establish an
orchard or vineyard are just some of the options but whatever the
decision, water and its availability are probably the two biggest hur-
dles that have to be overcome.
Control of moisture within the root zone of plants is the main factor
which makes drip irrigation more effective than other systems of irriga-
tion, however, to achieve these efficiencies, growers need to under-
stand three important criteria:
• The water holding capacity of the soil profile to the depth of the
• How weather conditions affect crop water use
• The application rate (mm/hr) and efficiency of the irrigation system
Perhaps the one extra cost with drip irrigation is a good water filtration
system, the type and size of which will depend on the water source.
The spacings between the drippers or 'emitters', is generally deter-
mined by the plant spacings and the soil's water holding capacity.
An efficient drip system
No need to drain or rebuild
Cost effective and easy to apply
Can be applied to full or partially full dams
Building a Dam
Failure to hold water is the most common problem for farm dams.
Repairing a Dam
Structural repairs are expensive and not always successful. Sealant
treatments normally require you to empty your dam.
An Easy Solution
To create a permanent plug to seal the area where the water is being
lost. Water$ave Plug is a unique blend in powdered form when applied to
a dam that is leaking will get sucked into those problem areas where your
water is being lost. WaterSave Plug will expand creating a permanent
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Well I'll be buggered. IT WORKS! After about three days, there was a marked decrease in the loss rate,
and after two weeks, the dam wall is bone dry. I must admit, I was amazed. Thanks for the product, and
for the prompt professional service. Graham, Bywong, NSW.
Seal it with ease using WaterSave Plug
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