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1.5 Irrigation hours per weekThese values are used to determine the required system discharge. The norms recommended byDWAF (1985) are accepted: 143 hours 143 hours 108 hours 60 hoursMicro and permanent sprinkler systemsCentre pivots systemsMoveable sprinkler and other movable systemsFlood irrigation systemsIt is also highly recommended that the ESKOM tariff structure applicable to the irrigation system istaken into account when determining the number of hours available for irrigation per week.1.6 Surveying and mappingThe map that will be used for the detailed design of the system should be drawn at an appropriatescale and contour interval, and it should be based on accurate data so that the irrigation system isdesigned correctly and all the design details can be legibly displayed.1.6.1 Recommended contour intervals and scales of mapsThe following scale and contour interval combinations are generally used:Table 5 Recommended scales and contour intervalsIrrigation systemsMicro irrigation (narrow row spacing: 3 m )Micro irrigation (wide row spacing: 3 m )Sprinkler irrigationCentre pivotsFlood irrigationContour interval0,5 m1,0 m1-2 m2-5 m0,5 mSmallest scale1: 5001: 1 0001: 2 0001 : 5 0001 : 1 0001.6.2 Use of GPS SystemsGlobal Positioning Systems (GPS) surveying is an evolving technology. As GPS hardware and processingsoftware are improved, new specifications will be developed and existing specifications will bechanged.GPS receivers can be divided into the following three categories:a) Recreational Grade GPS / GNSSRecreational grade GPS receivers are the least expensive and the simplest to use of the three types.These units have less functionality and are intended for recreational navigation uses. These units canbe expected to produce locations with accuracy of approximately 15-30 meters. This grade of GPS isnot advisable for data collection for irrigation design purposes.b) Mapping/Resource Grade GPS / GNSS11

Mapping or Resource Grade GPS collect positions with accuracies between 0.5 and 5 meters withdifferential corrections. These units have expanded functionality as well and can also record featuresas points, lines and polygons. These units also allow for loadable feature libraries designed toefficiently collect attribute information describing the feature.c) Survey Grade GPS / GNSSSurvey grade GPS tools are intended for tasks requiring a very high degree of accuracy - positionsdetermined by these receivers can be accurate to within less than a few centimeters. These systemsproduce data of the highest horizontal and vertical positional accuracy. They are relatively expensiveand complex, requiring specialized training and dedicated staff to oversee its use.The level of accuracy depends on the type of equipment you are using. In most cases for irrigation,the mapping (resource) grade receivers are adequate as some mapping grade receivers are evencapable of sub-meter accuracy and better, especially when differential correction is applied, real-timeor as post-processing.The following guidelines for the selection of GPS equipment are proposed:Table 6 Recommended GPS specificationsMinimum number of channelsUpdate rateCorrectionAccuracyMoving systems:Sprinkler systems:Micro and flood irrigation systems:AntennaOperating temperatureBattery lifePerformance2501 HzGlobal Real Time Differential Correction preferredAt a 95% confidence index: 2.5 m 1m 0.5 mExternal-20 C to 60 CMinimum 5 hours (8 hours preferred)Real Time Differential: 0.08m Horizontal, 0.16m VerticalRTK: 8mm 1ppmHorizontal, 15mm 1ppm VerticalProtectionEnclosure:IP65 (dust proof and 1m water quick submersion)Humidity:100% sealedDrop proof:Shock proof against 1m dropThe following user settings are recommended:Minimum number of satellites5PDOP 3Satellite filter angle10 Signal to noise ratio (SNR)6Other options recommendedInternal GSM for Network RTK (NTRIP) where available.Windows Mobile Data Logger with Survey/GIS software.Smart Voice Announcement System.System upgradeable to full RTK with base unit.12

2. Irrigation systems2.1 Micro sprinkler irrigation2.1.1 Minimum gross application rateThe application rate should be equal to or greater than 3 mm/h on the wetted area (Lategan, 1995).Distribution tests can be done with the selected micro sprinkler on soils with poor water distributionability, to ensure that dry patches will not occur in the wetting area of the sprayer.2.1.2 Distribution Uniformitya) Emitter uniformity approachThe following minimum emitter uniformity (EU) values are proposed: Level terrain where slope 2%: EU 95%Undulating terrain or slopes 2%: EU 90%b) Conservative approachThe percentage emitter discharge variation should not exceed 10% of the design emitter discharge. Inthe case of emitters with a discharge exponent of 0.5, this will result in a maximum allowable pressurevariation of 20% of the design pressure.2.1.3 Flow velocity in lateralsA minimum flow velocity of 0,4 m/s at the lateral end point is required. (T-Tape, 1998)2.2 Drip Irrigation2.2.1 Distribution Uniformitya) Emitter uniformity approachThe following emitter uniformity (EU) values are recommended for pressure sensitive drip emitters:Table 7 Recommended EU Values of pressure sensitive drip irrigation systemsEmitter TypePoint applicationPoint applicationPoint applicationPoint applicationLine sourceLine sourceNumber ofemitters perplant 3 3 3 3AllAllTopography or slopeMin 2% 2%Undulating terrain or slope 2%Undulating terrain or slope 2% 2%Undulating terrain or slope 2%908585808080EU (%)Recommended959090909085If the EU value of 90% cannot be obtained with pressure sensitive emitters, it is strongly recommendedthat pressure compensating emitters should be used.13

b) Conservative approachThe percentage emitter discharge variation should not exceed 10% of the design emitter discharge. Inthe case of pressure sensitive emitters with a discharge exponent of 0.5, this will result in a maximumallowable pressure variation of 20% of the design pressure.c) Pressure compensating emittersIt is recommended that maximum allowable pressure variation (in m) will be within the followingsafety limits: Minimum design pressure the minimum working pressure at which compensation takesplace as per the manufacturer 3mMaximum design pressure the maximum working pressure at which compensation takesplace as per the manufacturer – 5m.Should the safety limits provided here result in a very narrow pressure band (for example in the caseof thin-walled drip laterals with a relatively low maximum working pressure), the limits can be reducedafter consulting with the manufacturer of the drippers.2.2.2 Flow velocity in laterals required for effective flushingThe following minimum flow velocity at the lateral end point is required (Netafim, 2013): Good quality water: 0.4 m/sAverage quality water: 0.5 m/sPoor quality water: 0.6 m/s2.2.3 Flushing of lateralsIf flushing manifolds are used, the pipe diameter of the laterals must be chosen correctly so that thefriction losses do not exceed 0.5m over the length of the manifold (Netafim, 2008).2.2.4 Flow velocity in manifoldsThe maximum allowable flow velocity in any section of the manifold should be 2 m/s (Keller & Bliesner,1990).2.2.5 Specific management systemsThere are several variations of the use of drip irrigation for which specialist knowledge and additionalinformation can be obtained, for example: Underground drip irrigation. The publication on “Engineering aspects of sub-surface dripirrigation systems” (Koegelenberg, F. 2005. ARC- Institute for Agricultural Engineers) can beconsulted.Open Hydroponics Systems and pulse irrigation. This system requires additional flow due toshort irrigation times, and steps must be taken to keep water from draining from the systembetween irrigation start-ups. The Irrigation Design Manual of the ARC can be consulted forany queries.14

2.3 Sprinkler Irrigation2.3.1 Sprinkler selectionThe operating pressure, sprinkler application, wetted diameter and spacing of the sprinklers allinfluence the performance of the specific sprinkler and nozzle combination. The Christiansen’suniformity coefficient (CU) is used to determine the water application in a laboratory. The sprinklerwith the best CU value must be selected. The following norms for the selection of sprinklers based onthe laboratory-tested CU values are recommended: (Keller, 1990): CU 85% for vegetable crops75% CU 85% for deep rooted crops e.g. lucernCU 70% for tree cropsWhen applying chemicals through the system, the CU should be 80%.2.3.2 Sprinkler spacingThe maximum sprinkler/lateral spacing is calculated as a percentage of the wetted diameter of thechosen sprinkler for the average wind speed as displayed in Table 8 (Rainbird, 1998):Table 8 Sprinkler spacing according to average wind speedAverage Wind speed(km/h)Maximum spacing between sprinkler/lateral in wind conditions displayedas a percentage of the wetted diameter of the chosen sprinkler. 1010 - 15 15Between sprinklers (%)404030Between Laterals (%)656050If the chosen sprinkler spacing surpasses the maximum allowable spacing for wind still conditions,then the spacing must be calculated according to the CU standards for wind still situations.2.3.3 Minimum gross application rateThe following minimum gross application rates are recommended: Moveable systemsPermanent systems 5 mm/h 4 mm/h2.3.4 Maximum pressure variationThe diameter of a lateral should be designed so that the pressure variation between differentsprinklers irrigating simultaneously is not more than 20% of the design pressure (Jensen 1983).15

2.4 Centre Pivot2.4.1 Maximum irrigation time vs. soil infiltration rateThe design of a centre pivot should ensure that the application rate does not exceed the soil’sinfiltration rate, especially at the end of the machine.2.4.2 Christiansen uniformity coefficient (CU)It is recommended that the CU as calculated by the supplier for the selected nozzle package should be 95%. In the field a 85% CU value can be expected.2.4.3 Friction through centre pivot 3,6% (m/100m) of the total centre pivot length.2.4.4 Effective radius of end gun50% of the wetted radius of the end gun.2.5 Travelling irrigators2.5.1 Pressure variation over the length of the travelling pathThe moving direction must be such that the pressure difference between the upper and lower endsof a strip does not exceed 20% of the working pressure.2.5.2 Speed variationThe maximum speed variation allowed between the fastest and slowest speed is 10%.2.5.3 SiteIt is recommended that cross slopes over the strips be limited to less than 5% during system lay-out.A pressure regulator is recommended for travelling irrigators on steep slopes to ensure a constantflow rate.2.5.4 Flow rateThe design flow rate must be increased by 2.5 m3/h to allow for driving water when a hydraulicallydriven travelling irrigator is used. Confirmation of this value must be insured by the specific supplier.2.5.5 Sprinkler choiceThe type of sprinkler and pressure may be selected from the manufacturer's catalogue. Big gunsprinklers with a high jet angle ( 23 degrees) are only recommended for low wind areas. Thefollowing minimum working pressures are recommended to limit droplet size: 300 kPa for 12 mm nozzles400 kPa for 14 mm and 16 mm nozzles500 kPa for 18 mm and 20 mm nozzles16

2.5.6 Strip widthStrips should be set out perpendicular to prevailing winds if possible. Manufacturer's manuals shouldbe used in choosing strip widths. Because of the influence of wind on travelling irrigators, mostmanufacturers recommend strip widths for different wind velocities as follows:Table 9 Reduction factors for travelling irrigator strip widths to allow for windy conditionsWind velocity [km/h]Strip width [% of wetted diameter]0-88 - 16 1670%60%50%2.6 Flood irrigationAlthough flood irrigation appears to be a relatively simple system, it requires various designinformation to ensure a well-designed scheme. The infiltration rate of the soil must be thoroughlyinvestigated and the results thereof taken into account during the planning phase of the system. Awater runoff control plan must be implemented to ensure that rainwater is kept away from theirrigation area.The following norms are recommended:2.6.1 Slope of bedsSlope along the length of the field must be 0,7% to prevent erosion unless an in situ test is done. Theslope across the width must be 0% for basin and border irrigation.2.6.2 Allowable flow depth in beds50 mm fl

The SABI design norms serve to guide the designer in calculations and decision-making in the planning and design of agricultural irrigation systems. The norms are presented under the following four main headings: System planning Irrigation systems Water supply systems Greenhouses and tunnels