Figure 1. Mountains create a ’rain-shadow’ effect increasing rain on windward side and decreasing on the leeward

Book One: Irrigation in New Zealand

This booklet is the first in a series of six providing a comprehensive training resource for irrigation managers and operators in New Zealand.

It introduces location, use and significance of irrigation to New Zealand, the types of irrigation systems in use and the common components of them.

Distribution of IrrigationNew Zealand stretches almost 1,500km from end to end. It is a long, narrow and mountainous island ridge situated between the Tasman Sea and Pacific Ocean.

New Zealand’s topography, coupled with its latitude and the prevailing westerly wind flow, determines the climate experienced in different regions.

Due to the mountains effects on climate, western regions of NZ tend to be wetter and eastern regions drier. The eastern dryness is especially so in summer, when drought is relatively common.

Fortunately, many of the eastern areas have surface water supplies from rivers originating in the mountains, were rainfall is high, and ground water from extensive aquifer systems.

As well as causing wet and dry variation, the mountain effects cause higher temperatures in the east.

Wet air loses temperature relatively slowly as it is lifted over the ranges. With water gone, the dry air warms faster as it drops again on the other side.

Further information: www.teara.govt.nz/en/irrigation-and-drainage/1/2Figure 2: Adiabatic cooling and heating increases air temperatures once water is removed from air

Source: explow.com

Figure 3 Distribution of irrigation by region

Source: Te Ara

Geographic distributionBecause of the climate effects, irrigation is predominantly found in the eastern regions; Canterbury, Otago, Hawke’s Bay and Marlborough.

Irrigation Type by RegionTable 1 shows Canterbury and Otago together have made the biggest investment in spray irrigation systems. There are also still areas of flood irrigation with flood being almost half the irrigated area of Otago.

There is no new flood irrigation being established in New Zealand. Conversion to spray irrigation increases farm business opportunities and improves water use efficiency. Spray systems such as centre pivot and linear (lateral move) irrigators now make up the majority of pastoral irrigation systems.

By contrast, drip or micro-irrigation makes up the majority of the irrigated area in Marlborough and about one third in Hawke’s Bay. This is a reflection on the importance of the wine industry, vineyards located on shallow and gravelly soils require little and frequent irrigation. Orchard production also utilises micro-irrigation with significant areas in Tasman and Hawke’s Bay. Spray irrigation is also in these regions and mainly used for vegetable cropping.

Increasingly the value of irrigation has been demonstrated in western areas to provide certainty of yield and quality. In the Waikato, the majority is spray irrigation for dairy production. Some is also related to the application of dairy effluent to land.

Table 1 also shows the irrigable land per region and also by system type. Note the dominance of Canterbury and Otago which together account for almost 80% of allocated water for irrigation.

Region Total area equipped for

Irrigable area by flood

Irrigable area by spray

Irrigable area by micro

Irrigable area systems

irrigation systems systems systems not specified

Hectares

Northland 8,714 R C 5,154 2,430 1,057

Auckland 6,256 R 29 4,880 R 880 R 630

Waikato 16,578 R 914 14,027 908 1,943

Bay of Plenty 9,986 R C 6,527 2,523 1,551

Gisborne 2,345 C 1,364 819 C

Hawke's Bay 25,165 R 413 17,318 6,887 1,733

Taranaki 3,414 R 303 2,764 134 C

Manawatu-Wanganui 11,730 R 152 9,007 361 2,629

Wellington 12,936 R 441 10,891 1,087 972

Total North Island 97,126 R 2,814 71,932 16,028 11,130

Tasman 10,712 R C 6,152 4,052 902

Nelson 342 - 260 C C

Marlborough 26,669 R 623 13,106 13,408 1,748

West Coast 560 C 586 C C

Canterbury 385,271 R 64,386 R 313,710 R 5,734 R 13,237

Otago 91,078 R 41,986 R 44,706 R 2,330 6,474

Southland 7,537 R 1,011 6,251 15 1,065

Chatham Islands - - - - -

Total South Island 522,168 R 108,103 R 384,773 R 25,629 23,524

Total New Zealand 619,293 R 110,917 R 456,705 R 41,657 34,653

Table 1: Irrigable Land by Region and Type - Year to June 2007i

Source: Statistics New Zealand

(1) Figures may not add to the totals due to rounding.(2) Land area could have been irrigated using existing resource consents and equipment on the farm.(3) Irrigable area may be irrigated by more than one system.(4) Some figures have been revised since the initial release of data in August 2008.Symbols: C = confidential; R = revised; - = nil or zero

Water Use for IrrigationGoldieii reviewed a 2006 Ministry for the Environment study iii of regional council water allocations for irrigation. Table 2 summarises the % of water used for irrigation per region

Council Volume of water used for irrigation (Mm3)

Percentageof total

Auckland Regional Council 9 0.2Environment Bay of Plenty 101 2.0Environment Canterbury 3,132 62.0Environment Southland 33 0.7Environment Waikato 53 1.1Gisborne District Council 21 0.4Greater Wellington Regional Council 191 3.8Hawkes Bay Regional Council 253 5.0Horizons Regional Council 57 1.1Marlborough District Council 160 3.2Nelson City Council 0 0.0Northland Regional Council 63 1.2Otago Regional Council 857 17.0Tasman District Council 98 1.9Taranaki Regional Council 13 0.3West Coast Regional Council 14 0.3Total 5,056Table 2: Water Allocated to Irrigation

Source: Robert Goldie, Clark Goldie Consultants. 2006

Farming Enterprises using IrrigationThe range of crops and activities for which irrigation is used are summarised by Statistics New Zealandiv in Table 3.This shows over one third of irrigation is for dairy production, and almost one third for other pastoral farming enterprises.

Farm type (ANZSIC96)

Total area equipped for irrigation

Irrigable area by flood systems

Irrigable area by spray systems

Irrigable area by micro systems

Irrigable area with systems not specified

Hectares

A011100 Plant nurseries 3,134 31 2,383 793 152

A011200 Cut flower and flower seed growing 536 28 226 339 56

A011300 Vegetable growing 33,760 75 31,577 867 1,652

A011400 Grape growing 27,127 378 6,213 19,501 2,296

A011500 Apple and pear growing 9,979 184 3,194 5,914 1,190

A011600 Stone fruit growing 2,436 394 1,337 1,035 124

A011700 Kiwifruit growing 5,302 47 1,860 3,367 450

A011910 Citrus growing 957 C 71 918 52

A011920 Berry fruit growing 1,598 C 839 720 151

A011990 Other fruit growing 3,647 97 1,218 2,473 259

A012100 Grain growing 28,854 1,278 27,315 C C

A012200 Grain-sheep grain-beef cattle farming 30,048 2,113 27,980 C 111

A012300 Sheep-beef cattle farming 18,238 4,285 12,937 120 1,618

A012400 Sheep farming 109,143 46,158 66,576 1,268 6,856

A012500 Beef cattle farming 30,987 4,462 25,108 275 1,889

A013000 Dairy cattle farming 234,619 37,406 187,697 1,777 11,775

A015100 Pig farming 2,845 388 2,397 C C

A015200 Horse farming 2,617 131 2,225 126 172

A015300 Deer farming 14,599 4,684 9,245 C 850

A015910 Mixed livestock 12,113 2,920 8,674 199 723

A015990 Livestock farming nec 1,153 75 1,054 38 49

A016910 Tobacco and hops growing 409 0 290 C C

A016990 Crop and plant growing nec 30,296 2,859 24,878 96 3,014

A021900 Services to agriculture nec 13,739 2,309 10,598 354 C

A030100 Forestry 897 C 621 175 46

Other 231 C 171 20 40

TOTAL New Zealand 619,293 110,917 456,705 41,657 34,653

Table 3:Irrigable Land by Farm Type

Source: ANZSIC96

(1) Figures may not add to the totals due to rounding.(2) Farm types are classified according to the Australian and New Zealand Standard Industrial Classification.

(3) Land area could have been irrigated using existing resource consents and equipment on the farm.(4) Irrigable area may be irrigated by more than one system. Symbols: C = confidential

The Economic Value of IrrigationThe relative economic value of irrigation varies widely by region, sector and season. It changes with weather and product prices. Irrigation development requires medium to long term investment, so longer term trends are better methods on which to assess value.

One of the more comprehensive assessments is The Economic Value of Irrigation in New Zealandv (Doak et al.) compiled by Ministry of Agriculture and Forestry in 2004.

This report showed that irrigation contributed about 11% of farmgate GDP in 2002/03, yet accounted for less than 4% of farmed land. It noted variations between land uses and regions.

“Horticulture land uses, including viticulture and vegetables, contribute $550 million (60%) of the total, and dairy farming $270 million (29%).

Canterbury has 287,000 ha (60%) of irrigated land, which contributes $330 million (36%) of the total, or $1160/ha irrigated reflecting the generally lower value of land uses in that region.

Hawke’s Bay has 18,100 ha of irrigated land, with each hectare contributing on average $5,500 of farm gate GDP.” (Doak et al. 2004 p.2.)

In 2010 IrrigationNZ estimated irrigation contribution had risen to 19% of farmgate GDP and 1.5% of national GDP.

There is also considerable flow-on economic benefit to the wider community from irrigation. The Opuha Dam ex-post studyvi and the North Otago Irrigation Company studyvii show that farm expenditure, gross farm revenue and farm employment opportunities typically increase threefold when converting from dry land to irrigated agriculture.

Benefits of irrigationSome benefits of irrigation:

More certain and higher production levels. Increased land use opportunities for farm business. Increased profitability and improved return on investment. A more consistent income from year to year. Improved opportunity for family succession

Other considerations Investing in irrigation comes at a cost. Although the benefits of irrigation usually exceed costs over time there are costs and risks associated to be aware of.

High investment in plant and equipment. Increased debt loading. Additional farm staff and infrastructure (buildings, grain storage, etc) required. Need to up skill in a range of areas.

Substantial seasonal finance is often required. Changes in workload patterns.

The decision to irrigate or not is primarily an economic one but the personal, family and business implications also need to be factored in.

How irrigation adds value The way in which irrigation adds value is illustrated below in Figure 4Error: Reference source not found. The natural summer dry weather pattern (from spring to autumn) leads to reduced plant growth. Irrigation makes up the water deficit and enables production to be maximised throughout the season.

The general trend shown in Figure 4 is typical of a pastoral farming system. The actual impact varies by region, season and farm system. The effect on farm profit is further influenced by the farm management system and practices adopted.

Irrigation increases the efficiency of other inputs such as labour, energy, agrichemicals and fertiliser. Most of these inputs are required at the same level regardless of final yield. For example, irrigation effectively increases the benefit per litre of diesel, application of herbicide, and hour of work used in establishing crops.

Some farm systems can cope with periods of water deficit. Arable crops do not need water when drying off ready for harvest and grape crops are sometimes deliberately put under moisture stress.

Avoiding water stress induced production losses has flow on benefits. Processers require certainty from primary producers so their production and market commitments can be met. Irrigation gives them confidence to contract purchase and maximises their processing and marketing efficiencies.

Figure 4: Stylised Pasture Production Profile, Source: Doak et al. 2004)

Sources of Irrigation water

There are three water source categories

1. Surface water - rivers, streams and drains

2. Groundwater - bores accessing aquifers

3. Stored water - dams, lakes and ponds. Storage can be within natural lakes or manmade reservoirs.

Irrigation systems may use one or a combination of these to meet demand. The different sources are discussed in more detail in booklet six “Developing Irrigation”.

Enhancing Irrigation Water SuppliesIrrigation requires large volumes of water. In New Zealand a typical full cover crop or pasture will use about 30 mm per hectare per week in summer. Over a full season the irrigation required in addition to rainfall may be up to 600 mm per hectare. Water supplies need to be large and low cost to be economically viable.

In areas with high irrigation demand water resources are usually fully allocated – the quantity of water available for irrigation has been given out. Figure 5 shows the extent of surface water allocation in New Zealand for 2007 and 2012. Natural river systems flows are typically at their lowest during summer when the irrigation demand is highest. So while on an annual basis there is plenty of, water it is not always available when required.

Many community irrigation schemes use storage dams (both at the scheme and farm level) to harvest winter flows for release in summer. Other schemes use ‘run of river’ water as the supply for irrigation

New Irrigation SchemesThere were 22 prospective irrigation schemes known to the Ministry for Primary Industries (formally Ministry of Agriculture and Forestry) in 2008, both storage and non-storage based. A number of existing schemes are also undergoing modernisation, creating efficiency gains that allow them to expand their irrigated area. The locations of the prospective irrigation schemes is predominantly in Canterbury and Otago, however Tasman, Marlborough, Hawke's Bay, Wairarapa and the Bay of Plenty also have proposals underway. Figure 6 shows the area in Canterbury irrigated by existing and proposed schemes as at December 2008.

Surface water allocation 2007 and 2012

Figure 5: Surface water allocation 2007 and 2012 (

Source: New Zealand Business Council for Sustainable Development: www.nzbcsd.org.nz)

Figure 6: Canterbury irrigation schemes 2008

Source: National Infrastructure Unit

Irrigation System Types

Surface (Flood) Irrigation

Border DykeBorder dyke irrigation is common in older Canterbury and Otago irrigation scheme areas.

River water is carried by canal and race networks to head-races on farm. A series of gates in the head-race progressively hold water back, raising its level until it spills over a sill and on to graded land.

Furrow IrrigationCommon in some countries, furrow irrigation is practically unknown in New Zealand.

Border dyke control gate in raised position

Pressurised Irrigation

Solid SetSolid set irrigation systems are characterised by permanently fixed sprinklers on rigid riser pipes, usually arranged in a grid pattern. The spacing between sprinklers varies considerably and the sprinkler layout pattern may be either square or triangular.

Solid set sprinkler systems are commonly used for over-head frost protection and under-tree orchard irrigation. It is also used for nurseries and amenity irrigation including sports grounds and golf courses.

Regularly spaced fixed sprinklers apply water to prevent frost damage to grape vines

Micro-Irrigation (Drip and sprinkler)A micro-irrigation system consists of a network of lateral pipelines fitted with low discharge emitters or sprinklers. It encompasses a number of methods or concepts; such as drip, subsurface, bubbler and micro-spray irrigation.

In a drip system, water is discharged under low pressure from emitters mounted on or built into the laterals which may lie on or above the soil surface, or be buried below the ground in the crop root zone.

These systems are distinguished by the fact that water is delivered by the system to some point, for distribution laterally (and vertically) by the soil medium. Discharge rates are generally less than 8 litres / hour for point-source emitters and 12 litres / hour per metre for line-source emitters.

Micro-sprayer (micro-jet) and mini-sprinkler systems rely on aerial spread of water droplets to achieve significant lateral displacement before water enters the soil. There may be further lateral spread within the soil itself. Discharge rates are typically less than 60 L/h.

Micro-irrigation systems are potentially a very efficient way to irrigate. Water can be applied precisely to the point where it is required for crop growth, and not to inter-row or other non-beneficial areas.

The system is virtually unaffected by wind or surface evaporation. Because of the very low labour requirement per irrigation, such systems allow frequent light irrigations as needed to best fit crop water requirements and optimise production.

Spraylines

A sprayline irrigation system irrigates a field by sequentially moving a static line of sprinklers to predetermined parallel locations across a field. Water is discharged under pressure from the sprinklers which are set at even intervals along a lateral pipeline.

Irrigated strips overlap at the edges to ensure even coverage. The evenness of application across the irrigated strip, and the evenness of application along the length of the sprayline, both contribute to overall irrigation distribution uniformity.

Hand-move pipesHand-move pipes are typically aluminium lengths that clip together with quick couplings to fit field dimensions. A sprinkler is mounted on a riser at one end of each pipe section, so the sprinkler spacing is set.

Shifting is manual, with pipe sections separated, moved and rejoined at each position.

Side-roll systemsSide-roll systems consist of sprinklers mounted on aluminium or steel pipeline sections. Each section acts as the spindle of a centrally fitted wheel. Repeating units are joined to form the sprayline to fit field dimensions. The sprinklers are mounted on rotating couplings to ensure horizontal alignment regardless of spindle position. Sprinklers are mounted at pipeline height, and spacing is essentially set. Shifting is done by rolling the complete line sideways to the next position in the irrigation sequence.

Aluminium hand-shift pipes replace

Side Roll Sprayline irrigating lucerne

Towable spraylinesTowable spraylines consist of sprinklers fitted at set intervals on a polyethylene lateral. The sprayline length is generally set. Shifting is done by towing the complete sprayline by one end to the next position in the field.

Sprayline systems make irrigation feasible in many areas where other techniques are not suitable. Some types are easily transported between fields even over relatively long distances, and can be used to irrigate irregularly shaped areas. They are readily removed from the field to allow cultivation and other practices to be carried out unhindered.

Sprayline irrigation systems are usually arranged so that successive shifts create a grid pattern of sprinkler positions. The spacing between sprinklers may vary considerably. The sprinkler layout pattern that is achieved in practice may be either square, triangular or somewhere in between.

Multiple sprayline systems typically have smaller sized impact sprinklers. The laterals are connected to permanently buried mainlines and hydrants by a long polythene pipe. Each lateral is moved manually around 6- 14 positions.

Field with multiple spraylines running

Sprayline sprinkler in pod on towable lateral pipe

Long LateralLong-lateral (bike-shift or long-line) systems are a special case. Long-lateral systems typically have medium sized impact sprinklers mounted on a moveable stand, connected to permanently buried mainlines and hydrants by a long polythene pipe. Each sprinkler is moved manually around 6- 10 positions to cover 0.4 to 0.8 ha.

Long lateral sprinkler

Long laterals applying effluent on dairy farm

Travelling IrrigatorsA traveller irrigation machine irrigates a field sequentially, strip by strip by drawing a ‘gun-cart’ equipped with a water distribution system across a field.

Water is discharged under pressure from a water distribution system mounted on the cart as it travels across the field. A traveller is intended to be moved to, and operate from, several supply points established in advance in the field.

Irrigated strips overlap at the edges to ensure even coverage. The evenness of application across the irrigated strip, and the evenness of application as the traveller passes across the field both contribute to overall irrigation distribution uniformity.

Traveller irrigation machines are easily transported between fields. Compact booms and guns can be moved over relatively long distances, and used to irrigate irregularly shaped areas.

Three broad categories are recognised each having a structure that includes a reel, spool or winch and a travelling water distribution system.

In addition, there are three different water distribution mechanisms; big gun, fixed boom and rotating boom.

Traveller machines (soft hose)Soft hose traveller machines have a cable that is anchored at the run end. The water distribution system and a travelling winch are mounted on the gun-cart. The winch pulls the gun-cart along by coiling the cable on to the reel. The gun-cart drags the delivery hose across the field.

Rotating boom travellers winch themselves along wire rope anchored at paddock end

Small dairy effluent irrigator with rotating boom that winds cable on to a winch drum.

Reel machines (hard hose)Reel machines have a stationary reel anchored at the run end. The reel acts as a winch, coiling a delivery tube that both supplies water to the distribution system and drags the gun-cart along the field.

Hard-hose gun hose reel winds gun carriage in

Big gun sprays water up to 50m

Linear move irrigator with nutrient tank for fertigation

Linear (Lateral) Move

A linear move irrigation machine consists of a lateral pipeline supported above the field by a series of A-frame towers, each having two driven wheels at the base. The lateral traverses the field in a straight path creating a rectangular wetted area.

Water is discharged under pressure from sprinklers or sprayers mounted on the lateral as it sweeps across the field.

Evenness of application at points along the lateral, and the evenness of application as the lateral passes across the field both contribute to high overall irrigation uniformity.

Linear move irrigator demonstrating performance of different sprinkler types:

from left – rotators, sprays and spinners

Centre Pivot

A centre pivot machine consists of a lateral circulating around a fixed pivot point. The lateral is supported above the field by a series of A-frame towers, each having two driven wheels at the base. Depending on field layout, the pivot may complete a full circle or only part segments.

Water is discharged under pressure from sprinklers or sprayers mounted on the lateral as it sweeps across the field. As such, the evenness of application at points along the lateral, and the evenness of application as the lateral passes across the field both contribute to overall irrigation distribution uniformity.

Centre pivot irrigation machines are used on over half the sprinkler irrigated land in the United States and increasingly in New Zealand. They make irrigation feasible in many areas where other techniques are not suitable.

Because of the very low labour requirement per irrigation, centre pivots allow farmers to apply frequent light irrigations as needed to best fit crop water requirements and maximise production.

Centre pivots can cover relative steep terrain

Capital Invest Construction

Hydrant Pressure

kPaReliability Labour

RequireIrrigation Practice

Run Length

m

Shift Timemins

MovementApplic Rate

mm/hr

Applic Depth

mm

Distributn Uniformit

yProblems

Centre Pivot - fixed

Medium / high

Bow string self propelled spans, fixed at centre

Low, 200-300

Excellent if maintain

Extremely low

Complete circles in up to 35 hrs 60-1000 N/A N/A 15-75 5-100 Very high

Shelter, farm shape, corners missed, water supply

Centre Pivot - towable

Low / medium

Bow string self propelled spans, fixed at centre

Low, 200-300

Good if maintain

Low, 1 shift per2-3days

Complete circles in up to 35 hrs 60-1000 Slow

60-90 Tractor towed 15-50 5-100 Excellent

Flat tow path, shelter, farm shape, corners, water supply

Linear Move (Lateral Move)

Medium / high

Bow string self propelled spans <800m

Low, 200-400

Good if maintain

Low, 1-2 shifts/day

Irrigation shifts <400m, hose dragged behind drive unit

200-400

Quick 15-20 –slow 5-6 hours

Run to next shift or pivot for return run

25-40 5-100 Very high Farm shape, shelter, flat land

Hard Hose Guns

Medium - high

Poly pipe, gun carriage

High, 600-1200

Good if maintain

Low, 1-2 shifts/day

Irrigation lanes up to 90m, gun pulled to reel

< 400Mod quick15-20

Towed by tractor to next shift

10-20 10-100Average, poor in wind

Wind, crop damage

Soft Hose Guns

Medium - high

Soft layflat hose, gun carriage

High, 600-1200

Good if maintain

Low, 1-2 shifts/day

Irrigation lanes up to 90m, gun carriage pulled on wire rope

< 400

Moderately quick, 20-30

Towed by tractor to next shift after hose wound up

10-15 10-100Average, poor in wind

Wind, crop damage (hose and water)

Rotating Boom

Medium - high

Rotating boom with end nozzles, some mid, on carriage

Medium, 400-600

Good if maintain

Low, 1-2 shifts/day

Irrigation lanes up to 100m, gun carriage pulled in on wire rope

< 600 Moderate30-60

Towed by tractor to next shift

15-25 30-80Average, poor in wind

Wind, crop damage (hose and water), miss corners

Fixed Boom Medium - high

Fixed boom on carriage

Medium, 400-700

Good if maintain

Low, 1-2 shifts/day

Irrigation lanes up to 100m, gun carriage pulled in on wire rope

< 600 Moderate 30-60

Towed by tractor to next shift

20 - 50 10-100Good, vulnerable in wind

Wind, crop damage (hose and water), unwieldy shifting

Side Roll Sprayline Low

Aluminium pipes on carriage wheels

Medium, 300-500

Good if maintain

High, <3 shifts/day

Series of set positions <400

Slow if not well planned

Rolled by motor unit to next position

7-15 5-100 Average Shelter, fences, wind

Hand-shift Sprayline Low

Aluminium pipes clip together

Medium, 300-500 Good High,

demandingSeries of set positions <250 Slow if

many

Move each pipe section by hand, reconnect

7-15 5-100 Good

Danger of powerline arc when shifting, muddy working conditions

Multiple Lateral Sprayline

Low / medium

Poly pipe, pods, sprinklers

Low medium, 250-350

Average Medium high

Diagonal shift to next set position <250

Slow for many lines

Towed, 4Wbike or ute

3-8 50-80 Very poor / poor

Poor uniformity, limited crops, wind

Long lateral sprinklers Medium

Polypipe, sprinkler on stand

Medium, 400-500

Good / average

Medium high

Multiple positions around multiple hydrants

Individ hydrantssprinklrs

Slow for many lines

Drag to next position, 2 or 4W bike

7-15 35 + Average Wind, limited crops

Micro Spray, Dripline

High / very high

Low density polypipe, PVC mains

Low, 200-400

Good / very good Very low Automated series

of blocksLaterals < 300m None None 3-6 5-30 Good /

very good

Water quality, damage (equipment, pests)

Comparison of Irrigation System Types Adapted from Davoren

Irrigation System Components

PumpsThere are two basic groups of pumps, positive displacement and centrifugal.

Positive displacement pumps move a fixed amount of liquid for every movement of the shaft. The shaft moves a piston or diaphragm. Flow rate is determined by the speed the pump is driven at. A common application where irrigators may use this type of pump is in fertigation units.

Centrifugal pumps are commonly used to pump the water in an irrigation system. These pumps work using an impellor which gives velocity energy to the water and this in turn is converted into pressure head by the shape of the pump casing. These pumps come in a number of configurations as shown below (explain). All of the pumps use impellors. If increased pressure is needed, such as in bore pumps, impellors can be stacked one on top of the other.

Name & better pictures

FiltersFilters are used to prevent blockages in the irrigation system. The type and grade of filtration is dependent on nozzle or emitter size. Filters in agriculture are generally screen or disc types. Screen filters provide a simple barrier to particles entering the irrigation system while disc filters have a depth of filtration with a convoluted pathway for particles to pass through. Filters can be automatically controlled and back flushed based on the pressure difference across the filter. The two types are shown below:

Water MetersRegulation stipulates that water meters are to be installed on irrigation takes greater than 5 l/sec., however it is recommended all irrigation systems fit one. Meters should not only be thought of as a compliance necessity but also a useful management tool. An accurate measurement of flow rate allows the irrigator to audit the performance of the irrigation system and determine if all of the allocated water is reaching the crop. Meters are supplied in a number of formats including electromagnetic, mechanical, and ultrasonic – each has its advantages and disadvantages. It is recommended that the best quality meter that is affordable be used on the irrigation scheme to ensure accuracy of the data collected.

Pictures and ellaborate

ValvesValves are used for a number of purposes within an irrigation system. There are generally three categories of valve. The categories of include; manual valves, such as gate or butterfly valves; automatic control valves, frequently used to operate drip-micro systems; regulatory valves, such as pressure regulators. Samples of these are shown below:

Name & better pictures

Pressure GaugesPressure gauges and test points are an essential management tool for irrigation systems. They can be used to give an evaluation of what is happening when water is moving through the system.

A pressure gauge, or pressure gauge test point, should be installed near to the pump in the headworks. When used in conjunction with the water meter, an indication of the pumps

performance may be gained. If a filter is present a second gauge should be installed after it. The difference between the two gauge readings will give an indication of how dirty the filter is - whether it needs cleaning.

Pressure test points should also be installed at key points in the irrigation system, hydrants and field valves for example. Importantly they should also be fitted on the furthest points of the irrigation system, the end sprinkler on a centre pivot or linear move, on the gun or boom carriage, or for drip-micro systems on the ends of the furthest laterals from the valve.

Fitting and regularly using pressure test points will show whether the irrigation systems operating pressure is as per the design specifications and thus whether it is applying the right amount of water – whether the irrigation system working correctly.

Pressure can also be measured at the sprinkler outlets with the use of a pitot tube as shown opposite.

Add pictures

SprinklersSprinklers may take many forms but are essentially a nozzle and a method of distributing the water. The size of the nozzle, when combined with the system operating pressure, determines how much water is applied by the sprinkler, and the distribution device will influence the area and pattern over which the water is distributed. Some examples of sprinklers are shown below:

Essential

Name sprinklers above

The uniformity of distribution is determined by the sprinkler spacing and pressure. Sprinkler manufacturers have software programs to aid in selecting suitable nozzle, distribution and spacing combinations.

Add drip emitters

References

i Source Statistics New Zealand: http://www.stats.govt.nz/browse_for_stats/industry_sectors/agriculture-horticulture-forestry/2007-agricultural-census-tables/land-treatments.aspx

ii Goldie, R. 2011. Clarke Goldie Consultants, Canterbury. Pers.Com

iii Snapshot of Water Allocation. Ministry for the Environment. 2006 via: http://www.mfe.govt.nz/publications/ser/snapshot-water-allocation-nov06/html/page1.html

iv Irrigable Land by Farm Type. Statistics New Zealand. 2007. Via http://www.stats.govt.nz/browse_for_stats/industry_sectors/agriculture-horticulture-forestry/2007-agricultural-census-tables/land-treatments.aspx#Irrigation

v Doak et al. 2004). The Economic Value of Irrigation in New Zealand. MAF Technical Paper No: 04/01.

vi The Opuha Dam: An ex post study of its impacts on the provincial economy and community, Aoraki Development Trust, 2006

vii The Economic Benefit to the Community of the North Otago Irrigation Scheme, Waitaki Development Board 2010