nrmirrigation Irrigation System Performance Testing Irrigation Systems

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1 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

2 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.

3 Example of Commonly Applied Water Use Indices

4 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 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 or tanks) The Effect of Applied Water on Yield 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.

5 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 Best Practice System Efficiencies (%) Drip Irrigation Centre Pivot / Lateral Move Travelling Irrigators Surface Irrigation 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

6 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) Measured Seepage Loss (m 3 /d/m) Total Seepage Loss (m 3 /day) Before Clay Lining (1.05 ML) After Clay Lining (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 Average Applied Depth Tower CU = EXAMPLE #3 January, 2010 Dairy Pasture Pivot speed - 80% (10mm) Average wind speed ms Application per pass, mm 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

7 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: 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

8 De nrmirrigation 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.

9 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: 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)

10 Water Meters 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 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 (m 3 ) - Start Meter Reading (m 3 ) 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: 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

11 depth of irrigation per pass Average Application Rate (AAR) Distribution Uniformity (%) These can be divided into three parts: 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 (%)

12 Depth Variation Along Radial Length of Centre Pivot Applied depth, di Average Applied Depth Tower CU = EXAMPLE South East December 22, 2009 Dairy Pasture Pivot speed - 50% (mm) Wind - Average 1.6 m/sec from SE Application per pass, mm Radial Distance, m Results of a Centre Pivot Performance Evaluation

13 Field Recording Sheet Showing Catch Can Results and Calculated Distribution Uniformity

14 The general test procedure for measuring centre pivot performance is: 1. Measure the length of the pivot arm 2. 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.).

15 Typical Sprinkler Design Chart Detailing Specification and Location of Centre Pivot Components

16 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: 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:

17 Seepage = W x L x {(d 1 d 2) E D + I} t 2 t 1 Where: 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 m 3 /h over the length of the channel and can be converted to m 3 /day by multiplying by 24. This value can be divided by channel length to express seepage as m 3 /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) Measured Seepage Loss (m 3 /d/m) Total Seepage Loss (m 3 /day) Before Clay Lining (1.05 ML) After Clay Lining (0.15 ML) Difference (0.9 ML)

18 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 = 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: 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

19 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: 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?

20 Trees Planted on Channel Bank Seepage is Likely to be Very High Unless the Channel is Lined

21 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 Field slope ** ** Design Length of field - ** Design Time to cut-off - *** Management Rough surface / high crop density slower advance Steeper slope faster recession & potentially faster advance High efficiency & uniformity difficult on long fields Final determinant of opportunity time & tail water Desired depth of application - ** Management High efficiency is easier to 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: 22.5 m Bay width: 30 m Flow rate: 157 L/sec Flow rate: 157 L/sec Inflow = Inflow = Inflow = 6.98 L/sec/m 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.

22 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. Bay Slope Cross-Section Example Survey North Bay Total Fall: 1.891m Length: 440m Width: 22.5 Area: 0.99ha Section 1 (0-250) % Section 2 ( ) % Section 3 ( ) % Inlet Relative Level (m) End of Field 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

23 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. 480 Advance and Recession Curves Site #1b, November 14, Recession 360 Time (Minutes) Infiltration Opportunity Time Advance 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. Record the time at which the bay inlet is opened. 2. 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. 3. Mark the final position prior to closing the inlet and record the time at which the inlet is closed. 4. When irrigation is complete, measure the distance between each marker position. 5. 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.

24 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.

25 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) = 1.06 Depth applied = {430 x 6} x 10 = = 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 = x 10 = = 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.

26 Specialised Measuring Equipment The Irrimate TM Suite of Tools Irrimate TM 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 Irrimate TM 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 Irrimate TM 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.

27 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

28 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 (m 3 /m), Outflow (m 3 /m) and Infiltrated Volume (m 3 /m) Screen Image of SIRMOD II Simulation Output

29 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

30 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 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

31 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