Government of Western Australia
Department of Water
Farm Water Rebate Scheme
Design guidelines for on-farm water supply improvements – 2010
The adoption of best practice in the
design and implementation of on-farm water
supply infrastructure is strongly recommended by
the Department of Water to ensure future reliability of
water supply infrastructure constructed/installed under the
Farm Water Rebate Scheme.
You are urged to refer to the relevant design publications from the tables
within and consult a suitably qualified expert in the field before commencing
your on-farm water supply improvements.
In some areas mandatory application of design guidelines is required in order to
be eligible for the maximum rebate. Mandatory areas are indicated in the left hand
column of the relevant table.
Looking after all our water needs
Table 1
Dam site drilling guidelines
Department of Agriculture and Food Western Australia 2005, Bulletin 4609: Farm dams in
Western Australia, Western Australia
Dam site drilling
Table 2
Minimum five test holes, drilled to at least 1 metre below the proposed
dam depth.
Test holes should be drilled at least three days prior to construction to
allow for monitoring
12
Dam design and construction
Department of Agriculture and Food Western Australia 2005, Bulletin 4609: Farm dams in
Western Australia, Western Australia
Dam site
Page ref.
Page ref.
Dams located at least 300 m from boundary fences and at least 200 m
from roads
10, 16
Dams located away from valley floors or drainage lines
10
Silt pit
Temporary storage present in front of the dam (i.e. silt pit or wing bank)
7
Piped inlet
Piped inlet conveying water to the bottom of the dam to reduce erosion
and sedimentation
15, 18
Piped outlet
Piped outlet to avoid livestock accessing the dam
Spillway
Spillway directing overflow into a safe disposal area and composed of an
approach channel, exit channel and grassed spillway.
The spillway should have a level section, at least eight metres long.
11, 15
Spillway width should be calculated according to the following equation:
Q = 1.7W x H1.5
The spillway batter should be no steeper than 2:1
Mandatory: callback auditor will
be checking for
presence of spillway.
Emergency spillway designed to discharge water in excess of the main
spillway (particularly important if the dam is sited above buildings or shire
15
roads, linked to a roaded catchment larger than 5 ha or the dam is sited
in a natural drainage line)
Clay blanket
Clay blanket should be present on the base and sides of the dam and
should be thick enough to provide a seal (around 0.7 – 1 m thick)
5
Topsoiling external
batters
External dam batters should have top soil placed over them and seeded
with pasture grasses to encourage stabilisation.
14
Fencing
Dam should be fenced to exclude livestock
5, 14
Dam site drilling
Minimum five test holes, drilled to at least one metre below the proposed
dam depth.
12
Test holes should be drilled at least three days prior to construction to
allow for monitoring
Dam construction
Surveying and pegging of proposed sites prior to construction.
Overburden removed and stockpiled around the site.
Dam walls keyed in or attached to the underlying soil.
Compaction using a roller
16, 17
Silt traps should be cleaned out regularly
21
Maintenance
Table 3
Roaded catchment design and construction
Department of Agriculture and Food Western Australia 2005, Bulletin 4660: Roaded
catchments to improve reliability of farm dams, Western Australia
Site characteristics
Page ref.
Suitable areas are those where clay, clay loam or sandy clay loam is
close to the surface (<60 cm)
7
R/C sited up-slope and preferably within 500 m of the receiving dam
7
Area selected for R/C construction should have a slope of less than 5%
(steeper slopes require half-roads instead)
7
R/C area should be free of major obstacles (e.g. rocks, trees)
7
R/C site drilling to least 1 m depth should occur prior to construction
work to determine water-holding capability of the soil
9
Surveying and pegging should occur prior to construction work
9
Expert advice
Consultation with an expert for assistance with the R/C design
10
Design
Clay strength and road length will determine the appropriate grade of the
roads. The batters/side slopes shouldn’t be steeper than 1:5
14, 15
Roads are generally between 10 – 20 m wide from crest-to-crest and
between 100 – 500 m long
15
Collection channels should have grades less than 1:250. Stone concrete
or bitumen can be used to stabilise them if a steeper grade is necessary
14
Site investigation
Collecting channels should be parabolic in cross-section and of sufficient
17
capacity to handle large volumes of water safely
Road channels should not be cut below the dam’s full water level,
otherwise ponding of water at the outlet will occur
18
A clay layer of at least 75 mm is necessary if the site’s surface material is
unsuitable (e.g. sandy or gravelly)
14
The R/C must be compacted, preferably with a roller
20
Fencing
Livestock must be excluded from the R/C
10, 23
Maintenance
The R/C should be kept free of plant and organic matter
22
Receiving dam
design
Sediment trap should be present between R/C and the dam
10
An emergency spillway must be present on dam receiving R/C runoff if:
The roaded catchment exceeds 5 ha
The dam is sited in a natural drainage line
The dam is located above buildings or shire roads
10
Construction
Table 4
Grade bank design and construction
Department of Food and Agriculture Western Australia 2002,
Miscellaneous publications 27/2002: Grade Banks, Western Australia
Grade bank site
Design
Design
Page ref.
Grade banks should be constructed in the middle and upper parts of
landscapes.
Grade banks are usually constructed on land with a slope between 2%
and 10%
2
Prior to construction the slope of the land for the grade bank should be
determined
3
Cross section – should be trapezoidal with a 3 m to 3.5 m wide flat
bottomed channel
3
Side slopes – for land slopes up to 5%, channel’s uphill side slope and
bank’s uphill and downhill side slope are approximately the same length
as the channel width. For land slopes over 5% all three side slopes are
shorter, at approximately 2.5 m
3
Channel depth – for land slopes of about 2%, 0.4 m from max. water
level to floor of channel. For land slopes between 2 and 5%, depth
should be 0.5 m. Depth should be 0.6 m for land slopes over 5%
3
Freeboard on bank height – 0.2 m above max. water level
3
Spacing – refer to graph in Misc. Publ. 27/2002 to determine appropriate
spacing
Design
Channel grades – grade should be between 0.2% and 0.5% depending
on topography
3
Bank length – length should not exceed 1 km
3
Grade banks should feed into storage dams with sufficient storage
capacity and appropriate overflows
4
Department of Agriculture and Food Western Australia 2005, Bulletin 4660: Roaded
catchments to improve reliability of farm dams, Western Australia
Compaction
Table 5
Page ref.
A clay layer of at least 75 mm is necessary if the site’s surface material is
unsuitable (e.g. sandy or gravelly)
14
The grade bank must be compacted, preferably with a roller
20
Guttering
Department of Health 2005, Country Rainwater Collection, Western Australia
Cleaning
Roofs, gutters and down pipes should be kept clean and clear of leaves
Material
The guttering should be composed of material that complies with Australian
Standards
Table 6
Polyethylene pipe distribution system
Must be fit for purpose-Refer to manufacturers specifications for further system and installation
requirements
Mandatory: Callback auditor will
check that pipe is
buried.
Must be buried or covered at a minimum depth of 30 cm (45 cm if under and
unsealed road/track or 75 cm if buried under a heavily used road/track).
Piping should be buried with sand and not in coarse rocky soils.
Piping under roadways should be laid in a concrete pipe or culvert
Mandatory: Callback auditor will
check for release
valve on gravity fed
systems.
Pipes running downhill from storage point must have an air release valve at the
storage point or the delivery point to prevent the pipe from being sucked flat
Table 7
Developing production bores
Drilling production
bore
Drillers should be registered with the Australian Drilling Industry Association
Mandatory:
Call-back auditor
will ask for date and
details of contact
with regional office.
The nearest regional office of the Department of Water MUST be consulted prior to
drilling
All bores drilled into confined aquifers require licensing by the Department of Water
Call-back auditor will Borehole must be gravel packed, cased, have screens installed, be developed to
sight water quality
remove fines and attain a consistent flow rate
results and view drill
A pump test must be conducted on each bore
logs and results of
pump.
A water quality test must be performed on each bore with results provided to the
Department of Water
Bores must be equipped with a pumping device
Table 8
Pump-testing bores
Department of Water 2007, Rural Water Note 5: Simple pumping test for farm water bores,
Western Australia
Page ref.
Carrying out a pump
test
Pump testing should occur for a minimum of eight hours
1
Measurement of draw-down should occur every five minutes for the first
half hour, every half hour for the next two hours and hourly for the rest of
the test
1
A correct pumping rate should be able to be maintained without using
more than 2/3 of the available draw-down
1
Determining safe
yield
Requirements not related to published guidelines
Mandatory: Callback auditor will be
checking the pump
test results.
To claim a rebate for Pump testing it must be carried out by a contractor
Table 9
Tanks
Department of Food and Agriculture Western Australia 2004, Farmnote 64/2004: Rainwater Page ref.
Tanks, Western Australia
Installation
Mandatory: Callback auditor will
check to see that
inflow of debris is
restricted.
Installation of the tank should include an effective means of keeping
organic matter and animals out of both the intake and overflow
3
A device to divert the first 10 litres of run-off from each storm
3
Maintenance
Gutters and the inlet strainer should be cleaned whenever necessary
3
De-sludge tank every year
3
Department of Health 2005, Country Rainwater Collection, Western Australia
Installation
Install a tightly fitting manhole cover for cleaning and inspection purposes
Make sure all materials in contact with drinking water are Australian
Standards approved
Table 10
Troughs and trough/ tank combinations
Tank size and
specifications
Tanks and troughs must be new and fit for purpose
Tank capacity for use with stock trough must be between 5 kL and 22 kL
The total capacity of the tank must be enough to supply the dependent stock for at
least five (5) days in the event of source failure
Tank must be directly connected to stock trough
Tank/troughs must be connected to a reliable water source with appropriate
sized pipe
Copies of the publications listed in this brochure can be obtained by contacting
Rural Water Planning on 1800 780 300, your Farm Water Supply Auditor, or by
referring to the publisher directly.
Emergency farmland water response plans
Emergency farmland water response plans
are currently available for the following shires:
Gnowangerup, Kent, Kondinin, Kulin, Lake Grace,
Narembeen, Ravensthorpe, Yilgarn. These and
subsequent emergency response plans can be
accessed at <www.water.wa.gov.au>.
Strategic water assets mentioned in the
emergency response plans are available for
landholders in times of on-farm water deficiency.
© Department of Water 2010
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concerning reproduction and rights should be addressed to the
Department of Water.
Department of Water
168 St Georges Terrace, Perth, Western Australia
PO Box K822 Perth Western Australia 6842
Phone: 08 6364 7600
Fax: 08 6364 7601
www.water.wa.gov.au