TYPES OF IRRIGATION SYSTEMS
CATEGORIES OF IRRIGATION SYSTEMS
Irrigation systems can be designed to supply water for a wide range of irrigation applications, and many different types of irrigation are used around the world. Generally speaking, irrigation can be categorized into broad two categories:
- Gravity surface flooding systems (flood irrigation)
- Hillside flooding
- Border check
- Furrow irrigation
- Pressurised systems
- Sprinkler Irrigation – Hand move, side-roll and end-tow, long lateral, permanent sprinklers, travelling irrigators, low-level sprinklers, and Centre pivot and linear move
- Drip irrigation
- Micro-irrigation – micro-jets and mini-sprinklers.
These systems can also be described on the basis of whether they are surface or sub-surface irrigation systems.
Sub-surface irrigation – usually takes the form of dripper lines placed under the soil surface within the root-zone of the plants being irrigated. This form of irrigation is used in cropping enterprises, orchards etc, but is also useful for applications in amenity horticulture where soil disturbance is minimal or avoidable (e.g. lawns and beds for perennial plants).
Surface irrigation – takes the form of flooding cropping areas or the sprinkler application of water to the surface of the land. Rice production is a notable example of an agriculture form that uses flood surface irrigation. While some applications of this form of irrigation can have additional benefits such as weed control, it requires high volumes of water.
Crops such as soybeans can be watered by flood irrigation, but most crops could show a yield
decline if water stays on the crop too long or if the soil stays in a waterlogged condition for several days.
FLOOD IRRIGATION SYSTEMS
This involves flooding water into areas where the distribution of the water can be controlled, usually by having formed the earth into shapes which restrict the direction and extent of flow. Flood irrigation is used extensively in many countries throughout the world, primarily because it is inexpensive to develop and to operate.
Surface flood irrigation has traditionally made inefficient use of water (suffering a lot of wastage through seepage, evaporation etc), but those losses were outweighed by savings on manpower and equipment.
Relatively new developments in flood irrigation techniques have however greatly improved the efficiency of this type of irrigation.
Better land forming, and more accurate grading using laser levelling equipment, new design concepts, recycling of drainage water, better ‘dethridge’ wheels etc. all contribute to more efficient flood irrigation. (NB: A dethridge wheel is a device which moves and measures water taken from irrigation channels).
Border Check System
This may be used in orchards, vineyards, or for pastures, lucerne, and fodder crops.
This system involves creating a series of side by side bays, usually rectangular, which are fed water from a channel running along the high side of the line of bays.
Progressively, one at a time, an opening is made in the channel wall at the top of each bay, allowing that bay to flood. Once flooded, the opening is closed, and the next bay can have an opening made. The bays and channels are formed by mounded earth walls. The gradient across the bays must be carefully engineered to allow proper distribution of water.
Hillside Flooding
Also called “contour ditch irrigation”, this system is used in hilly country which is too steep to allow other forms of flood irrigation. This system can be used on land with slopes up to 1 in 10. A supply water channel runs along the top of a slope.
This channel is opened progressively, one point at a time, along its length, allowing water to spill down the slope. The slope may need earthworks to ensure an even surface gradient, hence an even distribution of the flooding water.
Furrow Irrigation
This is the most common flood system for orchards and vineyards, and is used in row cropping of cotton, corn, sunflowers and vegetables. Water is released from a supply channel on the high side of the area to be irrigated into furrows or channels. If vines or fruit trees are planted on mounds, a natural depression is made between the rows.
This can be ploughed to form the required furrows, or the depression as it exists may be used as a furrow. Irrigation water seeps into the bottom and sides of the furrow as it flows down the slope. The aim is to get a constant depth of wetness along the length of the furrow.
This is difficult to achieve in practice as lateral movement can be restricted by poorly structured soils, also excessive application of water can also occur at the head of the furrow in order to force an adequate amount of water towards the lower end of the furrow.
PRESSURISED IRRIGATION SYSTEMS
Drip irrigation is becoming increasingly common in many irrigation applications. It is particularly useful for the production of small-crops such as vegetables, and is also suitable for use in gardens and landscaping situations, as well as in nurseries.
Drip irrigation is conservative of water because water is applied to a localized area, directly on the soil surface. Some soils are less suitable for drip irrigation than other soils.
Drip irrigation systems are frequently based on pre-fabricated emitter piping and some planting schemes may make effective distribution to plants difficult.
Sprinkler irrigation is the most widespread form of irrigation in agricultural applications, from intensive vegetable production to broad-acre field crop production.
Sprinkler systems can effectively deliver water in many agricultural situations, although improper use can be wasteful of water and lead to additional problems such as erosion. Many types of sprinkler systems exist, suited to a range of water quality and pressure parameters. Examples of popular sprinkler irrigators are dealt with later in this lesson.
Sprinklers may have moving parts or non moving parts and they may be portable, permanent or semipermanent:
• Portable systems:…
