Different Types of Irrigation Systems Based on Delivery
Irrigation water conveyed to the head or upstream point of a field must be applied efficiently on the whole area such that the crops growing in the either fields gets water more or less uniformly. There are various types of irrigation techniques that differ in how the water is distributed within the field. These are:
1. Surface Irrigation
One of the most common and oldest methods of irrigation is surface irrigation. This method uses the force of gravity to distribute the water, which then seeps into the soil. It’s also known as flood irrigation because it simply allows water to flow into an area. Surface irrigation can be divided into furrow, border strip or basin irrigation. This method is not as efficient as other options because there is a tendency to use too much water in order to saturate the land.
The advantages of surface irrigation include:
(a) Requires less manual labour than hose spraying or shifting hose sprinklers.
(b) Better able to cover a large plot of land in a shorter amount of time.
(c) Not as negatively influenced by winds or sediments as other systems.
Drawbacks to surface irrigation include:
(a) Potential overwatering and wasteful runoff due to frequent erosions.
(b) If soil lacks proper sloping or doesn’t absorb readily, water can’t move through the field.
(c) Standing water can harm crops, mainly by reducing the respiration of the roots.
(d) Loss of water occurs due to percolation.
2. Sprinkler Irrigation
Sprinkler irrigation is a method of applying water to the land in a manner that mimics natural rainfall. Water is distributed through a system of pipes, usually by pumping, and is then sprayed into the air through sprinklers that break up the water into small drops that uniformly fall to the ground.
The advantages of sprinkler irrigation include:
(a) Suitable for varying sizes of land—both large and small plots
(b) Better able to direct water flow to specific areas of a property, avoiding water loss.
(c) Ability to administer fertilizers and chemical treatments through the system for even application.
(a) The initial cost is rather very high.
(b) Any cost of power to provide pressure must be added to the irrigation charges.
(c) Wind interferes with the distribution pattern, reducing spread or increasing application rate near lateral pipe.
(d) There is often trouble from clogged nozzle or the failure of sprinklers to revolve.
(e) It requires a dependable constant supply of water free from slit and suspended matter.
(f) It is suitable for high value crops.
3. Drip Irrigation
Drip irrigation, also known as trickle irrigation, functions as its name suggests. Water is delivered at or near the root zone of plants, drop by drop. This method can be the most water efficient method of irrigation, if managed properly, since evaporation and runoff are minimized. In modern agriculture, drip irrigation is often combined with plastic mulch, further reducing evaporation, and is also a means of delivery of fertilizer. The process is known as fertigation.
The Advantages of Drip Irrigation include:
(a) Saves time, money, labour and water because the system is so efficient.
(b) Prevents fungal disease by minimizing water contact with the leaves, stems, and fruit of plants.
(c) Discourages weed growth because water is only delivered where it’s needed
(d) Increases effectiveness on uneven ground.
(e) High efficiency in the use of fertilizers and no runoff of fertilizers into ground water.
The Disadvantages of Drip Irrigation are:
(a) Sensitivity to clogging
(b) Moisture distribution problem
(c) Salinity hazards.
(d) High cost compared to furrow.
(e) High skill is required for design, install and operation.
4. Subsurface Irrigation
Subsurface irrigation is similar to the drip/trickle method in that it distributes water through tubes and emitters. But in this method, the tubes are buried below the surface of the ground. Developed in the 1960s in Israel, where water tends to be scarce, this system works best for areas that are arid, hot, windy, or have sandy soil types.
The benefits of subsurface irrigation include:
(a) Saves water by eliminating surface water evaporation in hot and arid conditions.
(b) Reduces the number of weeds because water is not on the soil surface where most weed seeds germinate.
(c) Prevents damage from animals or machinery because the system is below ground.
(d) Prevents soil erosion which happens in surface irrigation.
5. Centre-Pivot Irrigation
Centre-pivot irrigation involves a self-propelled system in which a single pipeline supported by a row of mobile towers is suspended 2 to 4 meters above ground. Water is pumped into the central pipe and as the towers rotate slowly around the pivot point, a large circular area is irrigated. Sprinkler nozzles mounted on or suspended from the pipeline distribute water under pressure as the pipeline rotates. The nozzles are graduated small to large so that the faster moving outer circle receives the same amount of water as the slower moving ones on the inside.
(a) Uniformity of applied water
(b) No human labour required
(c) May operate at lower pressure, thus conserving energy
(d) Reduces the opportunity for surface runoff or deep percolation
(e) Provides opportunity for fertigation which allows the targeted application of small
quantities of nutrients, with a reasonable uniformity of application and less risk of nutrient losses.
(a) Relatively high capital cost compared to surface irrigation systems
(b) Require some form of energy source (electric or diesel) to operate
(c) Operation and maintenance of these systems require different skills than surface irrigation.
(d) Not suitable for irrigation of fields of rectangular or square shape.
6. Manual Irrigation
These systems have low requirements for infrastructure and technical equipment but need high labour inputs. Irrigation using buckets or watering cans is to be found, for example, in most rural areas and peri-urban agriculture around large cities.
Some Types of Storage Irrigation Systems
A dam is a hydraulic structure constructed across a river to store water on its upstream side. It is an impervious or fairly impervious barrier put across a natural stream so that a reservoir is formed. On the basis of structure, dams can be categorized as:-
(a) Gravity Dams: These dams are heavy and massive wall-like structures of concrete in which the whole weight acts vertically downwards. These dams resist the horizontal thrust of the water entirely by their own weight.
(b) Buttress Dam: is a gravity dam reinforced by structural supports. These dams have a solid, water-tight upstream side that is supported at intervals on the downstream side by a series of buttresses or supports.
(c) Earth Dams: They are trapezoidal in shape. Earth dams are constructed where the foundation or the underlying material or rocks are weak to support the masonry dam or where the suitable competent rocks are at greater depth.
(d) Arch Dams: These are designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, compressing and strengthening the
structure as it pushes into its foundation or abutments.
2. Spillways and energy dissipators
Spillway is a channel that carries excess water over or around a dam or other obstruction. An energy dissipator is a device that is used to convert concentrated storm water runoff to sheet flow and is constructed at the end of all storm sewers or channels that outfall into a buffer.
3. Sluices and outlets
A sluice is an artificial channel for conducting water, with a valve or gate to regulate the flow. An outlet is a small structure which admits water from the distributing channel to a water course of field channel. Thus an outlet is a sort of head regulator for the field channel delivering water to the irrigation fields.