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Irrigation System Performance Testing
Irrigation Systems
Supplementing rainfall with irrigation is important in agricultural production as it provides greater
management options, flexibility and the capacity to generate profit and better risk management.
Incorporating irrigation into the production system does, however, create a more complex
management environment and the effectiveness of irrigation must be measured to ensure a
reasonable return for input. The interaction and potential complexity between sub-system units and
irrigation management is represented in the following framework.
Framework for Water Use Efficiency
Barrett, Purcell and Associates, 1999
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Irrigation System Performance Testing
Measuring Irrigation System Performance
Water Use Indices
Water Use Indices (WUIs) are indicators of system performance that relate production to water use
and may be used to identify the efficiency of Economic, Agronomic and Volumetric water use. WUIs
are useful for assessment of overall farm water use as well as identification of problem areas within
the Water Use Efficiency Framework. Commonly used WUIs are presented below.
Water Use Efficiency:
Water Use Efficiency = volume of product  unit of water applied
Water use efficiency is usually expressed in terms of tonnes per megalitre
(i.e. grain, hay or fruit and vegetables) or litres per megalitre (i.e. milk) and
describes the combined efficiency of the irrigation system and crop
agronomics.
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Example of Commonly Applied Water Use Indices
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Background
Accurate measurement or estimation of water inputs and use/outputs is required in order to assess
overall farm water use. In-field irrigation performance is most commonly defined in terms of how
efficiently and uniformly a known volume of water is applied; these themes are discussed below.
Metering Irrigation Water
All sites where water is extracted for irrigation must have a water meter installed according to the
Natural Resources Management Act 2004. Water meters are important tools and provide information
that is fundamental to good irrigation management. Examples of different meters used in the South
East and tips on how to read and use your meter can be found in the “Irrigation Systems” section of
the “Water and Coast” tab on the “Natural Resources South East” website.
Irrigation Efficiency
Field Application Efficiency = crop water use  water delivered to irrigated field
Irrigation efficiency is defined as the ratio of water
used by (or available to) the plant to the water input
(i.e. the volume pumped). That is, application
efficiency of 85 % indicates that 85 % of the water
pumped was stored in the rootzone for use by the
crop and 15 % was ‘lost’.
The goal of irrigation design and management is
optimum efficiency, not necessarily maximum
efficiency, to deliver irrigation water in the target
range (see diagram at right).
Efficient water use at the whole farm scale may be
found by considering efficiency of the following subsystems:





supply systems (i.e. pumping from
groundwater bores and on-farm storage dams
The Effect of Applied Water on Yield
or tanks)
storage systems (i.e. dams, tanks and ponds)
distribution systems (i.e. earthen channels and enclosed, pressurised pipes)
application systems (i.e. surface, spray and drip)
recycling systems (i.e. run-off / tailwater dams and wastewater reuse schemes)
Both the input and output water volume can be defined at a range of locations and over a range of
time scales within the overall irrigation system. Where and how the manager chooses to measure
these will vary according to system design and site characteristics.
Tip
Scheduling irrigating to replace crop water use requires that efficiency of the
irrigation system be considered in calculations. If distribution efficiency is poor (leaks,
atmospheric losses etc.), the volume of water pumped may need to be substantially
more than that required by the crop. If this is not accounted for, there is a risk of
under-irrigation throughout the season with resultant productivity losses.
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Distribution Uniformity (DU %)
Distribution Uniformity of an irrigation system is important for determining how efficiently, cost
effectively and productively we use water.
How evenly irrigation water is distributed to the field is of critical importance for plant water
availability, soil condition and irrigation scheduling and management. Accepted thresholds for
distribution uniformity vary according to irrigation method (see table below); however it is given that
no irrigation system spreads water with 100 % uniformity and this has implications for irrigation
management. For example, to ensure that the least well-watered area is sufficiently irrigated, the
volume of water applied may need to be greater than the calculated deficit. The only way to
determine this is by accurate monitoring. If DU % is very poor the additional irrigation required may
lead to waterlogging and/or drainage losses in other parts of the irrigated area.
Irrigation System
Drip Irrigation
Centre Pivot / Lateral Move
Travelling Irrigators
Surface Irrigation
Best Practice System Efficiencies (%)
90 – 95
85 – 90
60 – 65
50 – 65
EXAMPLES - Efficiency
Centre Pivot
Sprinkler systems that are positioned above the crop canopy and divide a stream of water into
streamlets or droplets will have some exposure to transmission losses; typically through a
combination of wind drift and evaporation. Sensitivity to atmospheric conditions thereby results in
variable efficiency in the delivery of irrigation water to the field. The example below is an excerpt
from a report on the results of a centre pivot evaluation. Although conducted under near-ideal
conditions the apparent loss between sprinklers and the ground (collectors) is 15 %.
Surface Irrigation
A typical surface irrigation system distributes water to the field via open channels formed from local
material. Conveyance losses in such channels can be attributed to evaporation, seepage, operational
losses and leakage; representing wasted effort and affecting irrigation performance by reducing
inflow at the field inlet. Seepage often contributes the greatest proportion of distribution losses and
can be measured by performing a pondage test in a representative section of the channel. Once
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seepage is calculated, the associated cost of water losses must be considered and plans for mitigation
put into place.
The following table shows the results of pondage tests performed before and after a channel was
lined with fine clay. Seepage losses of 1.05 ML/day were recorded for the original channel
configuration (representing almost 7.5 % of the total daily supply), reducing to 0.15 ML/day (less than
1.1 % of total daily supply). The volume saved, approximately 0.9 ML/day, represents approximately
1.5 hours pumping time per day.
Typical Supply
(ML/day)
Before Clay Lining
After Clay Lining
Measured Seepage
Loss (m3/d/m)
4.38
0.62
14.16
Total Seepage Loss
(m3/day)
1 051 (1.05 ML)
147.9 (0.15 ML)
EXAMPLES - Uniformity
Centre Pivot
Machines that operate with worn components or poor pressure supply are likely to display
unsatisfactory Distribution Uniformity. The following graph displays the results of an evaluation
where supply flow and pressure were below design specification and sprinklers components were
worn. Heavily undulating terrain only accentuated these problems.
Depth Variation Along Radial Length of Centre Pivot
Applied depth, di
Tower
Average Applied Depth
CU = 79.62
EXAMPLE #3
January, 2010
Dairy Pasture
Pivot speed - 80% (10mm)
Average wind speed - 4.8 ms-1
25.0
Application per pass, mm
20.0
15.0
10.0
5.0
0.0
0.0
100.0
200.0
300.0
400.0
500.0
Radial Distance, m
Above and Right: The effect of poor Distribution
Uniformity on pasture growth at a dairy in the
Lower Limestone Coast.
CONSIDER:
The efficiency of your irrigation system and agronomic efficiency of the crop
has a large bearing on the volume of water required. The following formula
600.0
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may be used to determine the volume of water required (ML) for a single
irrigation event or an entire season.
Total Flow Required = soil water volume (mm) x area (ha)  efficiency
Example: A 24 hectare stand of lucerne requires 45 mm of irrigation. The
surface irrigation system is assumed to operate at 40 % efficiency.
Total Flow Required
= 45 mm x 24 ha  40
= 27 ML
The minimum target efficiency for surface irrigation is 65 %. Consider what
this means in the context of the above scenario:
Total Flow Required
= 45 mm x 24 ha  65
= 16.6 ML
Irrigation System Performance Evaluation
Irrigation system evaluation should occur upon commissioning of the system and at regular intervals
thereafter. This is to ensure that the system has been installed according to design and provides a
benchmark to refer to over time.
This section provides an introduction to the methods and material used for testing performance of
the most common irrigation types. For more information or advice on your irrigation system, contact
your local irrigation designer or consultant.
Tools for System Testing
The following items of equipment will be sufficient for testing most aspects of centre pivot, drip and
surface irrigation systems:




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


pressure gauge which has been
tested for accuracy and capable of
operating up to 400 kPa
pitot tube attachment
watch or stopwatch capable of
measuring seconds
catch cans / collectors (number of
cans must cover entire wetted span
of the pivot plus a few extras to
allow for possible wind drift)
measuring cylinder
measuring Tape
marker pegs
anemometer (optional)
Important Information
When testing system performance it is
important to have at least some knowledge
of site and target crop(s) characteristics, as
these define the context in which system
performance should be judged. Meeting
Steps Required for Irrigation Systems Evaluation
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site and crop requirements is necessary for productive irrigation management.
Details considered useful include:
Soils (soil survey information, soil water holding capacity, totally available water, readily available
water, etc.)
Water (quality and test results, local observation well network information, drilling contractor
reports, pump supplier information, etc.)
Crop (crop water requirement, crop agronomy, etc.)
Pump Efficiency
The pump supplies pressure and flow for the irrigation system. An inefficient pump may have
substantially higher running costs and could affect crop yield. Pump performance evaluation requires
comparison of present pump (and motor) operation against the manufactured performance curve, as
follows:
Maintenance of pumping plant is essential for safe and reliable operation and ensures that equipment
continues to perform as designed. The level of maintenance required depends upon complexity of the
equipment and consequences of failure, such as:




risk to personal safety and environmental damage / crop loss
cost of emergency / contingency arrangements
cost of / access to emergency repairs
total loss of asset
Maintenance procedures can be based on time schedules (reactive maintenance – acting on a fault as
it occurs) or condition monitoring (proactive maintenance – planned repairs or overhauls at the most
convenient time). In reality, a good maintenance schedule is likely to contain both time and condition
based procedures.
De
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Bore Maintenance
There are a number of test that should be undertaken regularly to ensure protection of your
investment. Any change in the result may indicate a problem with the bore or the pump. Tests to
perform include:
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


measurement of the water level several times per
year for comparison with previous records
annual water sampling for salinity and any other
elements that might affect bore and pump
performance
bore capacity - flow rate and drawdown (see tip
below)
pump flow rate and pressure
Representation of Drawdown
Tip:
A Specific Capacity Test is the only reliable method for testing bore performance. The test
involves measuring depth to the watertable prior to pumping and measuring drawdown
water level at a given discharge rate after a standard pumping time. The following
calculation is then applied:
Specific Capacity
=
pumping rate (L/s)
corresponding drawdown (m)
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It is important that specific capacity be established early in the life of the bore and checked
at regular intervals thereafter so that any problems can be identified and remedied before
they become serious.
Water Meters
Water meters are critical for determining the supply component of all irrigation systems. Knowing the
volume and flow rate of your water supply will help you to estimate cropping area and the area that
can be irrigated in a given time.
Tip:
Depth of Irrigation (mm): Using a Flow Meter to Calculate Application
Depth =
Final Meter Reading (m3) - Start Meter Reading (m3)
Area (ha) x 10
Centre Pivot
Centre pivots are reliable irrigation machines that generally require lower labour input than surface or
travelling sprinkler systems. As with any other farm equipment, they do require regular checks and
maintenance for longevity and effective performance.
Regular System Checks
Several aspects of the centre pivot irrigation system should be checked regularly to ensure correct
operation. Performing these tasks regularly, say every 100 irrigation hours, allows the operator to
identify, locate and rectify any problems across the irrigation system. Things to look at include:


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


flow rate (meter readings)
supply pressure
end pressure
checks for damaged or blocked sprinklers
machine maintains alignment and tower drives engage and operate smoothly
signs of uneven crop development due to poor irrigation uniformity (donut patterns)
Centre Pivot Performance Evaluation
For a comprehensive evaluation of centre pivot design and performance, the following items need to
be measured and calculated:



pump efficiency
emitter pressure
speed of rotation/travel
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

depth of irrigation per pass
Average Application Rate (AAR)
Distribution Uniformity (%)
These can be divided into three parts:
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

System Capacity and Managed System Capacity (mm/day). Calculate flow rate (L/s) and
effective irrigated area (ha) to determine system capacity. Then determine Pump Utilisation
Ratio (PUR) and application efficiency (Ea %) to determine managed system capacity and see if
the system can match the daily crop water requirements.
Average Application Rate (AAR mm/h). Calculate AAR of the pivot and compare to the soil
infiltration rate. Problems with ponding and runoff can occur If AAR is far in excess of the soil
infiltration rate.
Distribution Uniformity (DU %). Calculate DU from irrigation water collected catch cans and
compare to ensure that sprinkler performance is suitable to promote uniform crop growth.
The correct procedure for taking measurements and recording an accurate assessment of sprinkler
performance can be found in the international standard ISO 11545:2001.
Layout of Collectors and Marker Pegs for Determination of Centre Pivot DU (%)
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4.3 Depth Variation Along Radial Length of Centre Pivot
Applied depth, di
Tower
Average Applied Depth
CU = 94.80
EXAMPLE
South East
December 22, 2009
Dairy Pasture
Pivot speed - 50% (mm)
Wind - Average 1.6 m/sec from
SE
18.0
16.0
Application per pass, mm
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
0.0
50.0
100.0
150.0
200.0
250.0
Radial Distance, m
Results of a Centre Pivot Performance Evaluation
300.0
350.0
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Field Recording Sheet Showing Catch Can Results and Calculated Distribution Uniformity
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The general test procedure for measuring centre pivot performance is:
1.
2.
Measure the length of the pivot arm
Set-out catch cans in a straight line, spaced 3 m apart and starting 33 m from the pivot centre.
Catch cans should be positioned so that they are not obstructed by the crop (make use of access
tracks if necessary) or collecting water when the pivot starts. Record the distance to each can or
position number
3. Note the pivot make and model, drive type (i.e. constant move or stop-start) and speed setting.
4. Note also sprinkler type, mounting height, nozzle range and pressure regulator setting(s) (if
fitted). Refer to the sprinkler chart supplied with the pivot by your retailer to check that
components are installed according to design.
5. Install a pressure gauge at the start of the pivot (on pipe work or above the pressure regulator on
the first sprinkler). Install a pressure gauge above the last sprinkler (above the pressure regulator
if fitted)
6. Place 2 marker pegs near the circumference of the pivot circle, within the last span, and at right
angles to the line of collectors. Measure the distance between the marker pegs (25 - 30 metres is
adequate). These will be used to measure the speed of rotation and wetted diameter.
7. Turn on the pivot
8. Record water meter, pressure gauges, the time at which water droplets start and stop wetting
marker pegs (time each marker peg separately and average the result) and the time the pivot
takes to pass between the marker pegs.
9. Make observations of the pivot in operation.
10. Once the pivot has passed over the collectors, measure the volume collected at each position and
record this on the field sheet in the column headed Volume (Vol.).
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Typical Sprinkler Design Chart Detailing Specification and Location of Centre Pivot Components
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Surface Irrigation
The term ‘Surface Irrigation’ refers to a category of irrigation systems in which water is distributed at
the field level via a free surface, overland flow regime. Surface irrigation methods are further defined
according to system configuration and management requirements as:



Border Check (top right)
Furrow (bottom right)
Basin
Border Check is by far the most
common
surface
irrigation
method in the South East.
Surface Irrigation Performance Evaluation
Surface irrigation performance testing will be considered in two subsystems: water delivery and field
application efficiency.
Conveyance / Distribution
Conveyance losses in channels can be attributed to evaporation, seepage, operational losses and
leakage; representing wasted effort and affecting irrigation performance by reducing inflow at the
field inlet. Seepage often contributes the greatest proportion of distribution losses and can be
measured by performing a pondage test in a representative section of the channel. Once seepage is
calculated, the associated cost of water losses must be considered and plans for mitigation put into
place.
The general procedure to conduct a pondage test is as follows:
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

Water is held in the channel and the rate at which the water level drops is measured. All sources
of inflow and outflow are minimised and measured wherever possible.
The section of channel to be tested must be identified and isolated from other sections of
channel. This is best done using existing control structures; but earth banks or tarpaulin stops can
be used to hold water in a specific section of channel (ensure these are well sealed).
The section of channel is filled to at least normal operating level before being sealed. Initial water
level is recorded and then at regular intervals as the water level recedes. This can be done using a
staff, hook gauge or water level recorder. Measurement of water level may be made at a single
point near the middle of the channel section or an average taken from each end of the channel.
Taking an average removes the influence of wind on water level along the channel.
Other measurements required and the formula used are as follows:
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Seepage
Where:
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





=
W x L x {(d1 – d2) – E – D + I}
t2 – t1
W = average surface width between t1 and t2 (m)
L = length of channel, m
d1 = depth of water at t1, m
d2 = depth of water at t2, m
E = evaporation rate over area of channel, m/day
D = diversions, m/day (stock water, leaking outlets)
I = inflows, m/day (rainfall, over area of channel)
t1 = time at first measurement
t2 = time at subsequent measurements
t1 - t2 = elapsed time (h)
Note: Time is measure in hours and all other measurements in metres (evaporation and rainfall are
usually measured in mm, divide this by 1000). Seepage is expressed as m3/h over the length of the
channel and can be converted to m3/day by multiplying by 24. This value can be divided by channel
length to express seepage as m3/day per metre or kilometre of channel length (enables comparison of
different channel lengths and construction materials), or divided by the pump flow rate to determine
% seepage.
Example:
The following table shows the results of pondage tests performed before and after a channel was
lined with fine clay. Seepage losses of 1.05 ML/day were recorded for the original channel
configuration (representing almost 7.5 % of the total daily supply), reducing to 0.15 ML/day (less than
1.1 % of total daily supply). The volume saved, approximately 0.9 ML/day, represents approximately
1.5 hours pumping time per day.
Typical Supply
(ML/day)
Before Clay Lining
After Clay Lining
14.16
Difference
Measured Seepage
Loss (m3/d/m)
4.38
0.62
3.76
Total Seepage Loss
(m3/day)
1 051 (1.05 ML)
147.9 (0.15 ML)
903.1 (0.9 ML)
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Another important attribute of the conveyance system is that it should maintain head and provide for
adequate command over the irrigated field.
Head
Head is the energy that moves water through an irrigation system and is a measure of the pressure on
water due to elevation. Head is expressed in metres (m) or kilopascals (kPa) such that:
1 m head = 9.806 kPa = 1.42 psi
In a channel delivery system head is directly related to the elevation of various features of the system,
with water flowing from high to low points. However, head loss can limit the speed of flow through an
irrigation system even when elevation dictates that water should flow from point A to point B.
Head loss occurs because of friction, as water passes along channels and through various structures or
other obstructions in the system. Some head loss is inevitable, but can be excessive in poorly
designed and maintained systems. This has a detrimental impact on irrigation performance. Excessive
head loss can be caused by a range of issues:
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
Undersized channels
Silting up of channels
Undersized structures (i.e. bay inlets)
Too many bends
Rough channel surface
Weed growth in the channel
Identification of Head Loss Through a Channel Delivery System
Command
Command is essential for surface irrigation and refers to the elevation difference between the
irrigation water supply level and field surface. Clearly, the water supply must be higher than the field
surface otherwise water cannot flow onto the land.
A rule-of-thumb recommendation is for at least 250 mm command. That is, the highest level of the
field should be at least 250 mm below the supply level in the delivery channel
Illustrating How Command is Derived
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Head loss is important for command. Head loss reduces water level in the supply channel and
therefore reduces the area of land that may be commanded.
No Command = No Flow = No Irrigation
To calculate command over a particular field, head loss in the supply channel must be estimated and
relative levels must be determined for the start of the supply channel and the irrigated area (i.e.
upper end of all bays).
It is important to maintain the distribution system so that properties of head and command are as
designed. Some things to consider are:
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
Can you measure the water supply? Do you regularly measure or obtain the flow rate?
Is head-loss in the system acceptable?
Does the channel have adequate freeboard above the normal operating level? As a ruleof-thumb, at least 200 mm of freeboard is desirable.
Are channels free of weeds and other obstructions?
Are flow-control structures installed correctly? Are there signs of leaking, erosion or
silting around these structures?
Do all bays irrigate evenly? Do bays away from the supply irrigate as easily as those that
are near?
Does the channel drain completely at the end of irrigation?
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Trees Planted on Channel Bank – Seepage is Likely to be Very High Unless the
Channel is Lined
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Field Application Efficiency
For the majority, most benefit will be gained testing field application; that is, the manner in which
water is distributed in irrigation bays.
Seven key factors govern surface irrigation performance in the field, some of which are fixed and
some that can be adjusted through design or management. These provide a basis for our field testing
procedures.
Variable
Impact on
Advance
Impact on
Performance
Variable Type
Comments
Soil infiltration
characteristic
***
***
Fixed
High infiltration soil – slow
advance & rapid recession
Inflow
***
***
Design &
Management
High flow rate – fast advance
rate, potential tail water losses
Surface roughness
*
*
Fixed
Rough surface / high crop density
– slower advance
Field slope
**
**
Design
Steeper slope – faster recession
& potentially faster advance
Length of field
-
**
Design
High efficiency & uniformity
difficult on long fields
Time to cut-off
-
***
Management
Final determinant of opportunity
time & tail water
Desired depth of
application
-
**
Management
High efficiency is easier
achieve with large deficits
Inflow
An important variable in the surface irrigation process and second only to infiltration, inflow affects
advance but has little impact on the rate of recession. Provided all other factors are held constant,
increasing the rate of inflow yields more rapid advance.
Inflow is expressed as litres per second per metre width (L/sec/m), providing a common unit which
enables comparison between different scenarios and system designs. It is found by dividing the rate
of flow through the bay inlet by bay width, as follows:
Inflow = flow rate (L/sec)  bay width (m)
Example:
Bay width:
Flow rate:
22.5 m
157 L/sec
Inflow = 157  22.5
Inflow = 6.98 L/sec/m
Bay width:
Flow rate:
30 m
157 L/sec
Inflow = 157  30
Inflow = 5.2 L/sec/m
Inflow of around 2 L/sec/m is common, although up to 7 L/sec/m has
been recorded at case study sites.
to
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As illustrated, increasing inflow does not necessarily require larger supply capacity. Varying bay width
can produce a similar result, but must be done with consideration for other farm activities (i.e.
machinery width, number of check-banks and outlet structures etc.)
Slope
The longitudinal slope of the field influences both advance and recession, whereby increasing slope
increases the rates of advance and recession. Experience in the South East suggests that a greater
degree of slope (around 0.2 % or 20 cm per 100 m) is desirable for soils characterised by high
saturated hydraulic conductivity. It should be noted that higher degrees of slope and uniformity are
more difficult to achieve with increasing field length.
Laser-levelling is now widely practised and helps to achieve a more accurate and even finished
surface. Even so, performing a survey on completion of earthworks is worthwhile to ensure that the
final product is as designed. This is of particular importance when the field surface is relatively flat, as
shallow gradients are more sensitive to surface variations and more prone to uneven irrigation and
drainage.
Example Survey
North Bay
Total Fall: 1.891m Length: 440m Width: 22.5 Area: 0.99ha
Section 1 (0-250) - 0.7236%
Section 2 (250-400) - 0.0287%
Section 3 (400-440) - 0.0975%
Bay Slope Cross-Section
100.50
Inlet
100.00
Relative Level (m)
99.50
99.00
End of Field
98.50
98.00
97.50
0
50
100
150
200
250
300
350
400
450
Distance Along Bay (m)
Field Slope Obtained for a Surface System (Border-Check) Completed in 2008
Significant changes in slope (see example above) can have a
detrimental effect on irrigation performance and crop
health. These field conditions usually promote slow
advance and poor drainage, yield excessive application
depth and restrict plant growth through prolonged periods
of soil saturation (picture, right).
Tip:
When measuring irrigation advance, position
markers at changes in slope to capture any effect
this variable may have on performance.
Infiltration Opportunity Time (IOT)
Infiltration occurs when water is on soil surface; therefore, Infiltration Opportunity Time (IOT) is a
product of irrigation advance and recession (surface drainage). To apply the correct depth of water
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across the field, advance and recession curves should be parallel and separated by a distance (time)
equal to the required opportunity time.
Depth of irrigation increases with greater IOT and the appropriate length of time for any given
irrigation event is determined by the soil infiltration characteristic and soil moisture deficit. It is
typical for soils with high infiltration rates or low water holding capacity to require short irrigation
times and soils with low infiltration rates or high water holding capacity to require longer irrigation
times.
Advance and Recession Curves
Site #1b, November 14, 2007
480
420
Recession
Time (Minutes)
360
300
Infiltration Opportunity Time
240
180
Advance
120
60
0
0
50
100
150
200
250
300
350
400
450
Distance Along Bay (m)
Advance and recession, along with methods used to measure and assess both, are described below:
Irrigation Advance
When irrigation is applied to the field, water advances across the surface until it covers the entire
area. Under border check irrigation, water will directly wet the entire surface as the whole bay area is
designed as the flow path.
The rate of irrigation advance is expected to slow during an irrigation event as the area over which
infiltration is occurring increases with time; therefore a smaller proportion of inflow contributes to
advance over time. The soil infiltration characteristic and inflow are important as they are the primary
determinants for the rate of change.
Advance can be measured simply, as follows:
1.
2.
3.
4.
5.
Record the time at which the bay inlet is opened.
Return to the bay at regular intervals (i.e. hourly) and place a marker at the leading edge of
the wetted front. Alternatively, you can place markers at known distances prior to irrigation
and note the times at which the wetted front passes each point.
Mark the final position prior to closing the inlet and record the time at which the inlet is
closed.
When irrigation is complete, measure the distance between each marker position.
Draw a graph with distance (m) along the x-axis and time (h) along the y-axis. Plot the
numbers recorded in the field to see the ‘shape’ of irrigation advance.
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Use the advance curve to judge how appropriate inflow is for the bay length. A curve that becomes near-vertical ind
Recession (Surface Drainage)
The volume of water on the soil begins to decline following cut-off, either draining as run-off or
infiltrating into the soil; therefore drainage is considered in vertical and horizontal phases.


Depletion (vertical drainage): The depletion phase is the period in which depth of water at the
upstream end falls to zero.
Recession (horizontal drainage): The recession phase begins at the point of depletion and
continues until the surface is drained.
The receding edge is not always apparent due to several factors (slope, crop density etc) and
recession is often a notional phase - but the field surface must always drain.
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Depth applied
Average depth applied is calculated as below:
Depth Applied (mm) = {flow rate (KL/h) x time (h)} – runoff (KL)
area of field (ha) x 10
Runoff may only be an estimate if it cannot be measured, but all other
parameters should be measured, as has been described earlier. Remember
that this assumes even distribution.
Depth applied can be compared to the estimated soil water deficit (or target application) to assess
application efficiency. If irrigation is far in excess of the deficit (or water holding capacity of the
rootzone), there is increased likelihood of soil saturation and losses to deep drainage.
Example:
Irrigation is applied to a 425 x 25 m bay for 6 hours at 430 KL/h. No run-off is
observed.
Bay Area (ha)
= (425 x 25)  10 000
= 1.06
Depth applied
= {430 x 6} – 0
1.06 x 10
= 2 580 – 0
10.6
= 243 mm
Irrigation is applied to two 1.3 hectare bays for 12 hours at 385 KL/h. Run-off from
the two bays is estimated at 200 KL.
Depth applied
= {385 x 12} – 200
(2 x 1.3) x 10
= 4 620 – 200
2.6 x 10
= 4 420
26
= 170 mm
Surface Irrigation Simulation and Performance
Modelling
While it is possible to make an estimate of
surface irrigation performance and efficiency,
measuring distribution uniformity is more
difficult. A rough idea can be gleaned by testing
resistance across the field to a push-probe (see
picture), but more detailed assessment requires
specialist equipment.
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Specialised Measuring Equipment – The IrrimateTM Suite of Tools
IrrimateTM is the commercial name within Australia given to a package for surface irrigation evaluation
and optimisation. The package consists of hardware for in-field measurement and software to
translate field measurements into objective performance figures.
Hardware components of the IrrimateTM package include a flume gauge, calibrated meter and set of
data-loggers. These items enable measurement of such irrigation parameters as instantaneous inflow
rate, total volume of water applied and advance rate along the bay or furrow.
Specially Designed and Calibrated Flume Attaches to the Bay Inlet to Measure Inflow
Data Logger Used for Measuring Irrigation Advance
Software components of the IrrimateTM package include Infiltv5, IPARM and SIRMOD II. Infiltv5 and
IPARM calculate soil infiltration parameters from field data and SIRMOD II is a modelling tool used to
find optimum surface irrigation design and management conditions.
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Infiltv5
Infiltv5 is a tool designed to calculate the soil infiltration parameters (Kostiakov-Lewis equation) by
using measured advance data. Infilt employs a volume balance model using optimisation to minimise
the error between the predicted and measured advance. Average cross sectional area of flow and the
final infiltration rate are treated as fitted parameters and need not be measured – although the
quality of results is improved when using more comprehensive input data.
IPARM
IPARM is an acronym for Infiltration Parameters from Advance and Runoff Model and is based on the
Infiltv5 software package - drawing from the optimisation techniques used in Infiltv5. IPARM offers
many advantages over the traditional inverse solution using advance data such as:



Using advance and runoff data – accuracy increases where run-off measurement is reliable
Ability to use either a single constant inflow rate or a series of varying inflow rates – better
matching observed irrigation conditions
More options to calculate surface storage
SIRMOD II
SIRMOD II is an irrigation model that simulates the hydraulics of surface irrigation (border, basin and
furrow) at the field scale. The principle role of SIRMOD II is the evaluation of alternative field layouts
(field length and slope) and management practices (application rate and cut-off time). The ability of
SIRMOD II to accurately assess furrow and border system performance has been well established and
confirmed under Australian conditions.
Screen Image of IPARM Data Output
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Surface and Subsurface Flow Profile,
indicating:
- Desired Depth of Application (1)
- Potential Drainage Fraction (2)
(1)
(2)
Simulation Results, including:
- Irrigation Advance (mins)
- Application Efficiency (%)
- Distribution Uniformity (%)
- Inflow (m3/m), Outflow (m3/m) and
Infiltrated Volume (m3/m)
Screen Image of SIRMOD II Simulation Output
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Drip Irrigation
Every component that makes up the irrigation system is equally important, so it is vital that the
system is designed, installed correctly and maintained correctly.
Once the system is operational a regular program should be in place to ensure efficient ongoing
performance. This checking or audit procedure starts at the pump and ends at the emitter, as follows:






Pump
Filtration
Mainlines
Valves
Laterals and emitters
Flushing devices
Filtration System Evaluation
Filtration systems are an integral component of
modern pressure irrigation systems and serve to
prevent suspended material blocking irrigation
emitters.
A range of filtration systems are available, from
relatively simple manual screen filters to self-cleaning
disc and media filters.
Filter performance can be measured by finding the
pressure differential (pressure loss) between entry and
discharge points of the filter assembly. This should be
done directly after filter flushing and the results
compared to manufacturer specifications (also use
these to find test points, pressure set-point for autoclean cycle activation and flushing time).
As a guide, pressure loss is greatest through media
filters and lowest through punched screen filters – in
accord with the amount and type of suspended
material removed.
Tip
If the pressure differential remains high after
cleaning (or is always low) then the filter
should be dismantled and inspected for
breakage or excessive material deposits.
Above and Below: Automatic Self-Cleaning
Disc Filtration System and Associated
Pressure Loss Graph – source
www.amiad.com
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Mainline Evaluation
In a correctly designed irrigation system, mainline evaluation should not be required. When a problem
is found it is often low pressure associated with larger than expected friction loss. In the event that
this is suspected, the following method is used to investigate:




Tip:
Pipe friction loss is calculated on flow rate and internal pipe diameter, so the class, size and
length of pipe to be measured must be determined (this should be provided in the design)
Insert tapping points at each end of the mainline and attach pressure gauges
Use a water meter to measure flow into the mainline and measure elevation if required
Compare the actual change in pressure recorded with the gauges to calculated pressure loss
indicated on the pipe friction loss graph
This method can be applied for any section of pipe (main or submain) that has a
constant flow rate along its length
Pipe Friction Loss Graph – source www.toro.com.au
Valve Evaluation
Valves control the rate of flow through a section of pipe and,
like filters, range from simple manual units to automated and
regulated assemblies. Several checks should be performed to
ensure that the valve is performing as desired, including:



Check that valve controllers are working – automated
systems that rely on hydraulic or electric actuation
require regular inspection
If a pressure regulating pilot is fitted, measure
downstream pressure and check against design
specification. If necessary, adjust the pilot to set the
correct pressure
Undersize valves and fittings yield excessive pressure
loss. In the event that this is suspected, test pressure loss
across the valve unit using the method described for
mainlines (above). The valve must be fully open and flow
rate known during the test, then compare results to
manufacturer specifications
Pressure Reducing and Pressure
Sustaining Valves – source
www.tycoflowcontrol-pc.com
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Emitter Evaluation
The term emitter refers to a suite of irrigation water discharge devices (such as drippers, micro jets
and sprinklers) available in various shapes, sizes and configurations. All components of the irrigation
system are designed to ensure that emitters discharge water at a uniform rate across an entire valve
area (described as a valve unit) so that all plants receive the same volume of water.
Regular maintenance will help to ensure reliable and efficient performance. The maintenance
program should include:





Replace any emitters that are not functioning properly (in-line emitters may require a section of
pipe to be replaced or addition of button drippers to the pipe)
Repair any leaks in HDPE lines or other pipes
Flush filters and check pressure loss across filter assemblies (see Filter Evaluation above).
Flush the system – flushing points on mains and sub-mains should be opened to allow any
sediment or rubbish to clear out (micro and drip system HDPE lines should be opened until the
water runs clean)
Now that the system is checked and flushed, other system checks can be completed to see how
well the system performs