Linear and Centre Pivot
Laterals and pivots have a main pipeline supported above the field by a series of A-frame towers, each having two driven wheels at the base that keep the machines travelling in a straight formation. Water is discharged under pressure from sprinklers or sprayers mounted along the pipeline.
Laterals traverse the field in a straight path creating a rectangular wetted area. Water is supplied from a drag hose connected to a series of hydrants off a mainline.
A centre pivot machine consists of a lateral circulating around a fixed pivot point. Depending on the field layout, the pivot may complete the full circle or only a segment. The inside of the pivot covers less area than the outside of the pivot. The model assumes that water discharge is tailored accordingly to ensure the rate of application per unit area is the same along the length of the pivot.
Controlled Flood
Water is directed to areas of land via a network of channels and ditches. This method utilises the natural contours and fall of the land to distribute the water. It is common only in older Central Otago schemes. Furrow irrigation is practically unknown in New Zealand but if practiced should be included under controlled flood.
Solid Set
Solid set irrigation systems are characterised by permanently fixed sprinklers on rigid supports. They are typically arranged in a triangular or rectangular grid pattern with spacing dependent on sprinkler throw capacity.
Solid set sprinkler systems are commonly used for over-head frost protection and under tree orchard irrigation. They are also used for nurseries and amenity irrigation including sports grounds and golf courses. Pastoral applications are increasing.
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; 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 the 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 litres/hour
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. There are four basic types; hand-move pipes, side-roll systems, towable systems and long lateral systems.
- Hand-move pipes are typically aluminium lengths that clip together with quick couplings to fit field dimensions. Shifting is manual, with pipe sections separated, moved and re-joined at each position. A sprinkler is mounted on a riser at one end of each pipe section, so the sprinkler spacing is set.
- Side-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.
- Towable spraylines consist of smaller sized impact sprinklers fitted at set intervals on a alkathene pipe. The laterals are connected to hydrants off buried mainlines. The sprayline length is set. Shifting is by towing the complete sprayline by one end to the next position in the field. Each lateral is moved manually around 6-14 positions.
- Long-lateral systems have medium sized impact sprinklers mounted on a moveable stand on the end of a length of alkathene pipe. The pipe is connected to hydrants off buried mainlines. The pipe length is typically 60-80 metres long and each sprinkler is moved manually usually by motorbike around 6-10 positions to cover an average 0.8 ha.
Sprayline irrigation systems are typically arranged so 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 shifts over time overlap to water all of the area.
Travelling Irrigator
There are three categories of travelling irrigators; either gun, fixed boom and rotating boom. Each consists of two parts:
- a winch mechanism with a reel or spool
- a gun-cart carrying the water distribution system.
A travelling irrigator moves across a field sequentially, strip by strip drawing the gun-cart. It is connected to successive hydrants along a buried mainline.
Travelling irrigators are characterised by either a soft hose or hard hose. Soft hose travelling irrigators have a wire rope anchored at the end of the run. The water distribution system and a winch are mounted on the gun-cart. The winch pulls the gun cart along by coiling the rope on to the reel. The hose, pulled by the gun cart, drags behind. At the end of each run the hose is flattened and coiled onto a drum when moving to the next position. Hard hose travellers have a large 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.
Border dyke
Water is carried by canal and race networks to head-races on the 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 contained within borders. The gates are controlled by clocks connected to a release mechanism to ensure and they fall at set intervals along the race.