Table of Contents
What is Irrigation?
Irrigation is the deliberate watering of an area of cultivation by artificial means. Irrigation systems have been used to cater to problems of shortages of water from the dawn of the practice of agriculture and agronomy (the science and technology of usage and improvement of agricultural output ) in ancient times till the various modern applications of today.
Definition of Irrigation Systems
Irrigation systems can be defined as the systems of artificial application of controlled quantities of moisture or water to an area of land for intended cultivation, already cultivated land, or growing crops to assist with the production of the crops by augmenting for non-existent or insufficient rainfall. These systems fall under the category of the water cycle and ecology.
Types of Irrigation Systems in Agriculture
Irrigation systems exist mainly in the two disciplines of medicine and agriculture. They both refer to beneficial water or moisture delivery systems. Irrigation in agriculture is called agricultural irrigation and that of medicine is called therapeutic irrigation (lavage). We will discuss the different types of irrigation systems in agriculture.
The agricultural irrigation system is the artificial watering of cultivated or agricultural land by man-made means to augment the naturally distributed moisture for the production of crops. Since its early use in pre-historic times, several methods and systems have been developed over millennia to make the artificial supply of water more efficient.
The application of hydraulic engineering (the application of the principles of fluid mechanics to the collection, regulation, transportation, measurement, distribution, and use of water) has greatly improved irrigation systems. Some of the main types are outlined below:
Surface/Flood Irrigation System
Surface irrigation is also known as flood, burrow, gravity, or level basin irrigation is most likely the oldest form of moisturizing an area of land that has been used since ancient times. It is also one of the simplest forms of irrigation systems since it requires very little modification other than simple ridges or channels in some instances, to guide the water to the desired areas.
The technique involved in surface irrigation is simply getting water to flow generously over the surface of a predetermined area of agricultural land. The water then percolates through the surface of the soil to the sub-surface layers. This movement is achieved by natural means like gravity or slope cultivation.
Surface irrigation can be subdivided into seven main types namely:
- Furrow Irrigation
- Basin Irrigation
- Border Strip Irrigation
- Wild Flooding
- Contour Ditch
- Contour Levee
In furrow or graded furrow irrigation, narrow parallel channels are dug all the way across the cultivated land with a gentle slope. This creates a raised ridge down the middle between the furrows or channels where the crop is planted. Water is applied to one end from where it travels down the furrow to the other end providing moisture for the crops planted on the ridges along the water’s path.
Dykes or levees (raised heaps of soil or other material built or placed along the edge of bodies of water to keep the water contained ) are built at the end of the land to prevent the water that travels down the furrows from spilling out of the land that has been designated for irrigation.
Furrow irrigation is suited for several types of crops but particularly row crops tree crops, and crops that are not suited to having their lower stems and roots inundated (submerged in water).
Corrugation Irrigation System
Corrugation irrigation is very similar to the furrow irrigation system but not as commonly deployed. The furrows or channeling in corrugation irrigation uses smaller furrows that instead of being straight, have a corrugated (having a series of loops, u, or v patterns ) shape tightly spaced. The water soaks into the soil along the tight, contoured furrows but also moves and moisturizes sideways.
Corrugation irrigation systems are most effective for use in fields with soil that has a tendency to be heated till the topsoil crusts over and is suited for uncultivated and sloping land. It is also suited for use where the soil is medium to heavy textured. It is an inexpensive and water-conserving system.
Close-growing and non-cultivated crops are suited to be irrigated by the corrugation method. Examples of some close-growing crops are; wheat, oats, and barley. Examples of non-cultivated crops are; Graptophyllum pictum, Amaranthus hybridus, Amaranthus triclor, Mangifera indica, and Deeringia polysperma. Forage crops like alfalfa (also called lucerne, Medicago sativa) that have been used as a medicine and to feed livestock for hundreds of years are also suited for the corrugated irrigation system.
Contour Furrow Irrigation Systems
Contour furrow irrigation is similar to the graded furrow method because it uses similar furrows. However, the contour furrow method allows for the movement of water across the field and not just down the slope due to the shallower furrows and lower ridge heaps that allow water over the top after controlled flooding.
The contour furrows are not straight but curved following the natural shape and contours of the land surface and have just sufficient gradation to channel the stream of flowing water. Head ditches or in some instances pipelines are run downhill and sometimes across the sloping field to supply the furrows independently.
Light sandy soils and those that have the type of texture that cracks from the effects of wetting and drying like clayey soil are some of the few types that are not suited for this method of watering.
Level Furrow Irrigation
The level furrow method is an irrigation system that utilizes small furrows running in parallel lines across the field. The main difference between this system and the graded furrow system is that the level furrow irrigation system has the absence of a slope in the land.
The field is flooded with water whose volume should be sufficient to flood the entire expanse of land where it is held stagnant due to the absence of a slope for the duration it will take for the soil to absorb it completely through percolation.
This system is mainly suited for soils that have moderate to slow moisture absorption or intake (2.0 or less). Border levees will generally be needed for areas and periods when the abundance of rainfall may cause the water contained in the cultivated furrowed land to overflow its boundaries.
Basin Irrigation System
The basin or level basin, irrigation systems are simple forms of irrigation that utilize mostly flat or level land surfaces that have thirty to fifty-centimeter (30cm-50cm) high dykes or levees built around the perimeter creating borders that hold the water within the land once it is flooded and prevents any run-off of the water. It can be used as a single whole field or be divided into individual level plots that are each bordered by the dykes.
This method is generally more suited to flat or level land but can also be employed for sloping land provided the soil is deep enough to be sufficiently leveled. Where sloping land is used, basins are constructed in steps or terraces in descending order keeping to the natural contour of the slope.
The width of the basins generally depends on the depth of the topsoil which requires a depth of about 30cm for healthy plant germination and growth. The bordering of the land can be in any shape and can vary in size depending on the soil type, flow rate, and availability of adequate water.
Provision for some level of drainage may be necessary for locations that receive intense rainfall to prevent the water from flowing over the levees. The flooding is usually done rapidly so that it is as evenly distributed and absorbed as possible. This system of irrigation is suitable for crops that can thrive despite long periods of inundation like rice and cotton and close-growing crops with deep roots like alfalfa and certain trees.
Border Strip Irrigation Systems
Border, border strip, graded border, bay, or border check irrigation is a system of watering crops that seems like a combination of furrow and basin irrigation systems and is very similar to the basin irrigation system but whose major difference is the typical presentation of a slope on the surface of the land and the entire space is divided into several bordered strips forming sections of land that may range between three and thirty meters (3m-30m) wide and roughly sixty to eight hundred meters (60m-800m) long. The height of the levees or borders should be twenty to twenty-five centimeters (20m-25m) high.
The water is introduced at the higher end of the slope and should be sufficient to be allowed to progressively flow throughout the bordered section to the end where a drainage channel may be required to evacuate excess water that is likely to accumulate there.
Each strip of bordered land is irrigated individually since the borders prevent any cross-flow of water. This type of irrigation is suited for crops like small grains, alfalfa, and grass.
Wild Flooding Irrigation Systems
Wild Flooding is a simple irrigation system used on steep land for low-income crops that do not strictly require uniform distribution of moisture and there is abundant water availability at a low cost.
The water is poured into simple ditches at the highest points of the field from where they flow down across the land in uneven distribution and no measures are taken to control or further direct the flow of the water. The frequent flow of water over uneven topography can lead to progressive erosion if not checked.
Wild flooding can be used for perennial forage grass and low-value permanent pasture crops that are close-growing and will aid in resisting erosion.
Contour Ditch Irrigation Systems
Contour ditch or the contour trench irrigation system is established by a system of ditches or dug-out depressions throughout the agricultural land along the contours of the sloping land. It has provision for flooding or overflow of water through the use of siphon tubes, controlled openings, or an appropriately flattened section of the ditch through which the water is channeled.
The water flows in an even sheet down the slope of the contour from one ditch over the cultivated land collecting in the next ditch. Temporary dams are used to accumulate and distribute the water so that when they are opened, sufficient water will spread across the expanse of the agricultural land and repeat the process throughout the land.
There are no dykes or levees to restrict the flow of water and any overflowing and run-off water applied in a uniform sheet is collected in the ditch below until the entire land is irrigated. The ditches are kept close together to allow for even distribution and the spacing is determined by the inclination of the slope, the irrigation water requirement, and the intake rate of the soil.
The contour ditch system of irrigation is suited for most close-growing non-cultivated crops except those that thrive in ponded water or inundated conditions. Crops like legumes, small grains, and grass are irrigated with this system.
Contour Levee Method
The contour levee irrigation system is similar to the level basin method but for a sloping field. The strips are leveled by grading and are bordered along the contours by small levees and cross levees at the lower ends of the strips.
The controlled flooding is applied at rates that notably exceed the intake rate of the soil where it moves across the field and is allowed to stand or stagnate until it infiltrates the soil reaching the required depth. This system is usually applied to land that has a slope gradient value greater than 2% but less than 4% and grading of the land would be expensive or not practical.
The excess water can be drained out soon after it has sufficiently percolated if the irrigation is for moisturizing purposes but can be left standing at a minimum depth of 3 inches and a maximum depth of 8 inches for up to 2 weeks at a time. The soil for the contour levee method should be medium to fine-textured with an intake rate of about 0.5.
Crops that are suited to the contour levee system are particularly rice and others that can endure having their roots and lower stems submerged in water for up to twelve hours at a time. Other crops that can be grown with this system are; soybeans, cotton, corn, small grains, pasture grass, and hay crops.
Terracing is an agricultural method that typically makes use of sloping or hilly land to cultivate and grow crops on a series of receding ridged platforms. The progressively extending surfaces of the land enable an easy, efficient, and conservative process of irrigation.
When the system is well set up, irrigation water travels down from one terrace to the next after the higher surface is flooded and can circulate downstream throughout the system without any additional input after the initial discharge.
The canal irrigation system is a surface irrigation system for the supply of water to cultivated land or crops with the use of artificially constructed channels to convey the water to the required location. It utilizes a set of gutters or canals that convey water from a source to the areas where it would otherwise be difficult to reach.
Lined Canal Irrigation Systems
Canals are generally built from and lined with cement, concrete, asphalt, flexible membrane, bentonite, prefabricated metal, shotcrete, stones, bricks, burnt bricks or clay, tiles, blocks, or some other durable material (lined canals) on their beds and banks to avoid detrimental problems that are associated with unlined canals.
Lined canals have the benefits of water conservation, far less maintenance requirement, further distances attainable, the reduced necessity for larger canal dimensions, and it can be used along with other forms of infrastructure like roads, bridges, or having valves or gates installed without incurring structural damage.
Chemical sealants are used to bond gaps between sections and coat areas that may be prone to seepage or corrosion. These chemical sealants are most effective if the surfaces they are applied to remain moist through most of the season. If the surface dries out, cracks in the soil can cause brittle breaks in the membrane formed by the sealant which may lead to water seepage from the cracks.
Some canals are sometimes dug and used without any of the above-mentioned hardware but consist of a single furrow dug into the natural soil sometimes heaping the extracted soil on both sides of the channel to limit the amount of material that falls in from the edges. This dirt channel runs from the source of the water to the supply area (unlined canals).
The benefits of unlined canals are the small number of materials required and the low cost of the entire undertaking especially in the short term and for smaller projects that may not be financially beneficial enough to spend significant capital executing.
Another benefit of the unlined canal irrigation system is the high level of fertility in terms of soluble soil nutrients that are contained in water that is passing over the soil leaching the nutrients as it moves along ultimately carrying it to the crops that are irrigated.
However, the problems of unlined canals are mainly issues with durability like erosion, structural integrity, and seeping out water not only from structural damage but any stagnation can lead to absorption and percolation into the surrounding soil.
The problem of ever-increasing vegetative growth of aquatic weeds that can accumulate debris and slow down and in unresolved cases completely impede the flow of water. Structural damage is easily caused by burrowing animals and human and animal traffic.
The canal irrigation systems can be broadly divided into a few different parts depending on their usage and how much water they convey, or discharge. The central part of the canal that is fed from the source and carries the most amount of water is the arterial or main canal.
The main, central, or arterial canal can also be described as an aqueduct or a waterway depending on the type of channeling that is used. It carries the largest volume of water in the system and may stretch long distances to convey water far from the sources which may include upstream rivers, dams, or reservoirs.
Aqueducts can be on the ground/surface level or elevated to clear unsuitable areas or take advantage of the pressure gravity provides but will generally have a slope system with or without a pump to ensure the continuous flow but does not feed directly to the crops or area to be irrigated but to smaller tributaries where the reduced pressure is more suited for irrigation.
The head discharge of the main canal is roughly 14 to 15 cumecs (an SI unit of volumetric rate of flow that is equal to a cubic meter per second). It is the superior channel of the system and supplies only to the branch canals.
Branch canals are next in overall significance and capacity to the arterial canals and can be channeled in different directions as needed. They have a head discharge rate of about 5 to 10 cumecs and also are not used to directly irrigate but are the feeder sources for major and minor distributaries.
Major Distributary Irrigation System
Major distributaries are fed from mainly the branch canals but occasionally from the main canal and typically have a head discharge rate of between 0.028 to 15 cumecs. They are termed significant distributaries and irrigation channels because they supply water directly to the field through a series of strategically located outlets. They feed water to the minor distributaries.
Minor distributaries are typically canals that discharge between 0.25 to 3 cumecs and are fed from the major distributaries. The water pressure is lower than the main and branch canals and major distributaries. It also has outlets dispersed along its course that feed into specific areas of the agricultural land.
Watercourses are generally defined as channels through which water flows and can be termed as such even during periods when they are dry provided water flows through the same channel periodically.
For this reason, the term watercourse is loosely used to describe virtually every type of furrow/gutter through which water regularly passes including field channels. Field channels are smaller tributaries of the canal irrigation system that are fed from the minor distributaries although can occasionally be branched off from the major distributary.
Field channels, unlike the other channels, are usually passed through the actual agricultural fields where they are flanked by the agricultural land for irrigation on both sides where they have outlets to feed into the land. The discharge rate here is less than 0.25 cumecs.
A contour canal is an artificially dug navigable channel for water whose course follows the natural contours of the land between the water source and the area for irrigation. There is no chiseling or boring through rocks or building of embankments or structural enhancements like viaducts (a typically elevated bridge-like structure for supporting systems), diversions, canal lock construction, or bridges.
Contour canals are easily identifiable from their meandering trajectory and absence of linear (straight line) channeling.
Watershed Canal Irrigation System
A watershed or ridge canal is established along a natural watershed, an area of land where water from natural precipitation flows through before being drained off into bodies below. The canal is established along the ridgeline where water passes naturally draining into the canal and ensures irrigation on both sides from gravity.
Side slope canal
Side slope canals are dug along the right angles of the natural contours like the sides and slopes of raised areas of land where the gravitational pull ensures a continuous flow. It runs parallel to the natural drainage and thus does not support cross drainage.
Maddu/Madda Irrigation Systems
Maddu or madda irrigation system is a centuries-old peculiar type of canal channeling or watercourse that is channeled from a dammed river to irrigate an area utilizing sticks and date palm leaves to line the shallow canal. This particular version is peculiar to the dammed Nai Gaj River of the Dadu District located in Sindh in Pakistan.
The Nai Gaj River which is ephemeral (existing for short periods due to being constituted by run-off from heavy precipitation) flows from Balochistan through the Kirthar Mountain area where locals use maddu water channels to divert some of the water to irrigate their mountainous crop fields located around high-altitude valleys as the river flows downwards to Sindh Province in Pakistan.
Spate Irrigation System
The spate irrigation system or floodwater harvesting is a surface flooding moisturizing technique that is achieved by diverting stormwater from mountain water catchments (an area of land typically bordered by mountains or hills through which water flows and collects after a storm or heavy downpour of rain) from surface runoff from valleys, rivers, riverbeds, and gullies with the movement aided by gravity, into channels, ditches, and sometimes canals for onward distribution to cultivated agricultural land and crops.
Spate irrigation is an ancient system that is centuries old and is mostly used in semi-arid or arid regions that are bordered by highlands. Spate is defined as a sudden and overwhelming outpouring.
This applies to the way the run-off water is generated and accumulated when there is a deluge (overflowing of water from intense rainfall) or heavy rainstorm and water that gathers in water catchments and previously dry river beds flows over and is channeled by either free intake (run-off water is allowed to spread across the intended irrigation area and to be absorbed without significant control measures), diversion spurs (also called groynes, spurs, or dykes are containment structures constructed on river banks normal to the dominant flow direction or at an angle inclining up or downstream to train the water in the desired direction), or bunds (a constructed retaining wall to contain or divert water flow).
Once the water reaches the field, four basic techniques of distribution are derived from two sets of related methods namely; field to field distribution/individual field distribution and extensive distribution/intensive distribution.
Field To Field Distribution Irrigation Systems
In field to field irrigation distribution, the water is diverted to a group of bunded fields that are configured in descending order. Only the upstream field is initially irrigated directly from the secondary or branch canal.
The water moves downfield and the typically earthen bund is opened either completely or partially to allow the water to flow into the adjoining fields for irrigation in a sequence that will progressively irrigate all the fields with water that has moved from the upstream field, the only one flooded directly from the source channel, through gaps in the field boundaries to all the other fields in the group.
Individual Field Distribution Irrigation Systems
Individual field irrigation distribution introduces water from the source distributary through inlets that feed into every individual field independently and unlike the field to field method, can discharge channeled water to several fields simultaneously.
This technique has the benefit of having more control over the water distribution and avoiding oversaturation or eroding of the upstream field from the heavy volume of water necessary to pass through the upstream field that would be sufficient to irrigate the downstream fields. Individual field distribution however requires more land area and capital for the construction of more channels of distribution.
In the extensive distribution method, a single irrigation system is used to moisturize a notably large area of agricultural land. An extensive channeling system is typically required and it is more expensive to establish but will usually require less frequency of operation.
Intensive Distribution Irrigation System
Intensive distribution is utilized for smaller areas of land and may require more than one or several applications to achieve the desired level of moisturization due to a limited distribution network. It is much less capital intensive than extensive distribution.
Lift irrigation is a method of irrigation in which water is conveyed to the intended areas for moisturization by mechanical means rather than the usual natural flow.
In most instances where this method is used, the descending velocity of the natural flow of water cannot be used because the intended areas for irrigation are located on a higher gradient than the available source of water.
Due to the absence of the possibility of using the natural flow and gravity to transport water to higher ground for irrigation, mechanical means such as older manual methods like the shaduf lever or pivot devices, various waterwheels, bucket chains, treadle pumps, endless screws, surge tanks, e.t.c., or modern ones like various electric-motor and other pumps must be employed to lift water from lower-lying sources.
The water must then be transported to the main delivery chamber from where it is distributed to the various irrigation zones. These zones are determined by their specific topography, size, and altitude.
The main challenge of the lift irrigation system beyond that of establishing an efficient water-lifting technique is the distribution to the agricultural zones which is largely dependent on the available hydraulic head (or piezometric head is a specific measurement of the pressure of a liquid when it’s above a vertical datum).
Each agricultural irrigation zone has to be catered for individually based on the contour plan that determines the soil type, water requirement, distance from the delivery chamber, and height of the zone. Field delivery chambers are then constructed at strategic points along the distribution pipes with valves fitted to control the flow rate.
The sprinkler system is the most similar irrigation system to rainfall and typically makes use of pressurized water and liquidized fertilizers from a pipe or rubber hose that is forced through a valve and in some instances a riser pipe (a vertical connecting pipe) into a dispensing device that applies the water to an area by uniform spraying.
The dispensing device usually consists of a rotating contraption made up of small perforated closed-off pipes or various other types of device heads with small holes to spray on crops or cultivated land. However, some systems use perforated closed-off pipes that sprinkle water from the holes along their length with the absence of a sprinkler head.
The rotating device can usually either be set to rotate slow (shorter distances), fast (longer distances), or to squirt or spray without rotating at all and has a head or a gun with a nozzle, small hole, or holes from which jets or sprayed water is dispersed over the crops or land in a uniform pattern at a rate lower than the intake rate of the soil to avoid oversaturation.
In the past, water pressure was crucial in enabling the system to squirt the water to reach other plants that are beyond the end of the hose. However, now there is a range of modern systems that use different means to achieve the required pressure. These include the use of mechanical and electric pumps, hydraulics, gravity-based systems, etc.
Micro-irrigation is a method of water application that uses a low-pressure and precision delivery to only the localized area of the plant or roots that avoids excess application of water and therefore excludes flooding.
Micro-irrigation is also referred to as low pressure, low flow rate, trickle, low volume, or localized irrigation. The water is distributed to each plant or root zone through a network of strategically configured pipes whose dispensing outlets correspond to the spacing and exact positioning of the crops to be irrigated.
Drip irrigation when carried out properly can be the most water-efficient irrigation system with an estimated efficiency of 80 to 90%. It is a type of micro-irrigation that uses a network of pipes to deliver water in a slow trickle or drops to individual plants below the upper stems. Drip irrigation can either be a surface or subsurface type of system.
In the surface version of drip irrigation, the water is released to the area in drops that are discharged from an emitter (a small typically plastic device for regulating and dispensing water under low pressure in drops ). With this method of water application, water run-off, nearby weeds benefitting from excess flooding, water evaporation, and excessive wetting of foliage are eliminated.
There are drip irrigation systems that are inexpensive, low-tech, and use basic equipment making them more labor-intensive and there are those that are more capital intensive, high-tech, and employ the use of computerized and specialized equipment.
Water bubblers are a type of water dispensing device often used in drip irrigation that is a bit similar to sprinklers in design but does not rotate nor sprinkle water and operates under low pressure.
There are several design types for this device but they usually consist of a tube with a male-threaded base for fastening or screwing into the supply pipe and a head that has slot-like gaps around the top that water flows from forming a cascading sphere-like shower that resembles a bubble.
Water bubblers are usually deployed in drip irrigation but can also be used with the sprinkler system where they are sometimes set up near tree crops that are suited to slow steady moisturization.
Fertigation is the application of liquefied fertilizer to farmland, crops, or other plants, agricultural or cultivated land through an adapted irrigation system that dispenses the fertilizer in the same manner as it does the water.
The most commonly applied fertilizer component is nitrogen (N2) due to its high importance in plant development and for the fact that even though it is abundant in the atmosphere, it exists in nature as a diatomic molecule (molecules that are composed of only two atoms of either the same or different chemical elements although diatomic molecules like hydrogen are additionally termed homonuclear due to their two atoms having the same chemical elements ).
Most plants cannot consume the organic material that is in that form. For them to be able to process such material, it must be combined with other plant-absorbable compounds like ammonium nitrate, urea, and anhydrous ammonia and applied through irrigation systems.
Fertigation is closely related to chemigation (the application of chemical enhancements to agricultural land or crops through irrigation systems). Chemigation is, however, more controlled and regulated due to the potential hazard of applying too much of the chemical to the land and crops. The chemicals applied are typically fungicides, insecticides, and herbicides.
Sub irrigation (Subsurface drip irrigation)
Subirrigation, subsurface drip, or seepage irrigation is the artificial raising of the water table to saturate land or provide moisture for plants at their root zones by the underground application of water through seepage or trickling from underground-laid pipes or other channeling systems that causes an upward capillary action.
The subirrigation setup is usually a permanent system located in fields that can repeatedly be reused so it typically requires an efficient drainage system. It receives its water supply through a system of pumping stations, weirs (a kind of small scale dam built across a stream, river, or water channel to raise the water level on the upstream side), canals, and gates through which the water level in a network of ditches is regulated. This allows the system to determine the level of water in the area’s water table.
Greenhouse crops (crops grown in an insulated and controlled structure) that are cultivated in specially constructed synthetic tubes and certain pots often have a system in place where they are moisturized from subsurface tubes are also nourished by subirrigation and the excess water collected for recycling.
Sub-irrigated Planter/DIY Self Watering Planter
Sub-irrigated planters and self-watering planters are very similar because they both use the same fundamental working principles of subirrigation through upward capillary action.
A planter or appropriately adapted container with an opening at the bottom with a type of wick or similar absorbent material that will slowly soak up moisture passed through it and into another receptacle that acts as a reservoir over which the planter is placed.
Water or liquid fertilizer is introduced or poured into the larger container or reservoir that usually has a hole up near the planter to siphon out excess water. The wick hangs down from the planter into the water in the reservoir from which the water travels up the wick through capillary action and irrigates the soil in the planter around the root zone.
Some of these systems even have automated watering and advanced modern models have humidity condensers that trap water from the atmosphere and cycle it back through the system to the plant root zone.
A wicking bed irrigation system is very similar to the subirrigation planter system. It also uses the subirrigation method that supplies moisture from below and percolates upward with capillary action through a permeable medium like a wick to reach the plant root zone.
The main difference is while the planter system uses mostly pots and single plant containers, the wicking method uses plant beds that can accommodate several plants. The system is estimated to use about 50% less water than traditional methods. This extremely limited volume of water utilized and wasted makes wicking beds ideal for arid regions.
The wicking bed subirrigation system was developed by an Australian inventor named Colin Austin. It can be used in containers, on fields, or indoors in greenhouses. The system is basically containers for agricultural cultivation that are sub-irrigated through reservoirs at their base.
Subsurface Textile Irrigation Systems
Surface textile irrigation (SSTI) is a low pressure, high-efficiency, and specialized form of subsurface irrigation that was specifically developed to have the highest level of water conservation, the least amount of topographical damage, most efficient delivery system module, diminished necessity for fertilizer and herbicide application, and applicability to virtually all soil types.
The subsurface textile irrigation system usually consists of a base layer that is made of an impermeable material such as polyethylene or polypropylene which prevents moisture, nutrient, and soil-mass loss from below through gravitational percolation. A drip tube or line is run along the base layer to carry water all the way to its boundaries.
However, the number and spacing of emitters, extent of the pipe network, oversaturation, and other piped water delivery considerations are not important factors in subsurface textile irrigation due to the efficiency of the water distribution by the next layer which is made from a geotextile (permeable fabric made from polypropylene or polyester that typically comes either woven, needle-punched, or heat-bonded and is used in association with soil to filter, drain, separate, reinforce, or protect) material.
This geotextile layer sits on top of the drip line from where it absorbs and distributes the moisture which can move up to two meters or more from the emitter along the geotextile layer.
The final layer is another one using impermeable material that is established on top of the geotextile layer, although the top impermeable layer is narrower than the impermeable base layer. Water is gently delivered to the root zone without any disruption to the soil composition or percolation/capillary movement beyond the intended area for irrigation. This is why the usual drainage provisions typically required for even subsurface drip irrigation systems are not required in subsurface textile irrigation.
SSTI is the only irrigation system with which recycled or treated water can safely be used without the costly polishing (filtration of water to remove microscopic particulate material or low concentration of dissolved substances) that is typically necessary for surface methods of irrigation or those types where the water reaches the surface.
Generally, subsurface textile irrigation is established between fifteen to twenty centimeters (15cm-20cm) below the surface of the soil for commercial and residential applications and thirty to fifty centimeters (30cm-50cm) for agricultural applications.
Due to the movement of water restricted to soaking along the geotextile through mass flow and capillary action, the volume of water delivered can be controlled to a greater degree than any other irrigation system. This ensures the maximum conservation of water and the matching of the intake rate and capillary action of any soil type.
It also eliminates the need for any lingering moisture above and below the surface of the soil that can cause a host of problems for the crops. In conventional subsurface drip irrigation systems (SDI), water often discharges faster than the intake rate of the soil which causes structural damage to the soil around the emitters and creates anaerobic zones that are damaging to plant roots.
In some instances and topographical types, the moisture percolates upwards to the surface and accumulates into ponding when irrigated. This is eliminated with the SSTI system as the water is drawn from the geotextile layer upwards through capillary movement to the root zone keeping the stems and foliage dry and free from moisture-borne diseases.
Components or Parts of Irrigation Systems
Pumps For Irrigation
The pump is considered the heart of an irrigation system because it is responsible for the most important aspect of the whole endeavor which is the overall water distribution.
Food security through agriculture is arguably the single most important human pursuance for the sustenance of life and is driven mainly by irrigation. From ancient times humans recognized the importance of irrigation and devised several means of conducting it over time. The main challenge was how to augment rainfall to increase the yield of crops, and how to transport water from a renewable source to the agricultural area.
Basic ways were devised with some of the techniques of antiquity so innovative that they are still being used today some with significant modern modifications and upgrades for larger-scale irrigation, while others are still being used as they were centuries ago or prehistorically.
Other than manually channeling accumulated rainwater to a nearby area or fetching water in some form of a container by hand and pouring it over an area of land, shaduf irrigation (a lifting contraption that uses a simple crane-like wooden beam or pole levered on a pivot similar to the configuration of a seesaw to lift an attached bag of water from a certain depth to the ground’s surface) is believed to be the oldest known form of irrigation by mechanical means. It was used by the Mesopotamians as early as 3000B.C.
From those early times when man used agronomical contraptions like the shaduf and early canal systems, there have been consistent progressive improvements. From the crudest forms to the Persian version of waterwheels (Raha) which is now considered to have been more of an early form of a pumping system than a manual lifting system.
Most contemporary large-scale and industrial irrigation is now carried out with the use of modern mechanical pumping systems that have the capacity to moisturize larger agricultural fields in a relatively short time. Most modern pumps use electric motors or internal combustion engines that run on fuel or are powered by alternative sources of energy.
The power is usually generated by converting electrical energy into hydraulic energy or mechanical thrust or suction to move a gas, liquid, or slurry (a mixture of water and small particles of a solid substance) from one place to another.
Pumps generally used for irrigation include centrifugal, deep well turbine, submersible, and propeller pumps. The turbine, submersible, and propeller pumps are all technically centrifugal pumps that are modified for different roles. High-speed centrifugal or turbine pumps are suitable for irrigation on individual surface fields. When the distance from the pump inlet to the surface of the water is less than eight meters the centrifugal pump is most suitable.
Deeper water sources like wells or reservoirs that are more than eight meters deep from the pump inlet to the surface of the water need a submersible pump (a pump that can be completely immersed in water).
Before selecting an irrigation pump a few key factors should be examined to determine its suitability for its intended role. They include:
- The source of water; (the distance and elevation from the source to the irrigation zones; the condition of the water).
- The necessary pumping flow rate. (The volume of water needed for adequate irrigation within a given time; requirement will be determined by the distance, height, and crop/soil conditions/requirement)
- Total suction head. (Pumps that operate above water surfaces use suction heads which comprise of vertical lift and losses of momentum through frictional contact with certain pipe fittings like diversionary joints and valves on the suction side of the pump that interfere with the seamless flow of the water).
- Total dynamic head. (The total sum of the static, pressure, friction, and velocity heads).
Head of Water
Head of water in irrigation systems is a term used to describe the maximum height that a water pump can lift liquid against the force of gravity.
The measurement of the total vertical distance that a pump must lift water to reach level ground. From a well, it would be the distance from the surface of the water to the ground’s surface plus the vertical distance the water must travel from the ground to its point of delivery. If pumping from a surface source, it will be the total vertical distance from the water source to the point of discharge.
The static head comprises two parts referred to as static lift, which measures the elevation difference between the water source and the pump; and static discharge which measures the elevation difference between the delivery point and the pump.
The pressure head of an irrigation pump is consistent with the definition in fluid mechanics which is given as the height of a liquid column that corresponds to a particular amount of pressure that is exerted by the liquid column on the base of its container.
It may be referred to as the static pressure head, or static head. The pressure head at any point on the system where a pressure gauge is located can be converted from PSI (pounds per square inch) to feet of head (a foot of head is a unit of pressure equal to about 2989.0669 pascals) by multiplying it by 2.31.
Friction head is defined as the energy lost and the resulting decrease in pressure of a liquid flowing in a closed system due to its contact and resistance with surfaces within its conduit. The degree of friction head in an irrigation system is dependent on the velocity of the moving water and the number of obstructing surfaces it makes contact with.
The velocity head is the pressure required to increase the kinetic energy or momentum of a flowing liquid. A partial vacuum can develop in the suction chamber due to a number of reasons including a drop in the pressure head. The amount of energy required to be expended for the liquid to resume or increase its flow is what is termed the velocity head.
Water Conveyance Structures For Irrigation Systems
image credit milbur plumbing – https://www.milburplumbing.com.au/
Transportation of water from available sources to the various locations that are intended for irrigation or other related uses can only be achieved through suitable mediums by which the water can be effectively carried and delivered.
These mediums are made from different materials and perform different functions depending on their suitability but are generally all geared towards the same ultimate aim of carrying out successful irrigation activity.
Some of the most important hardware and their functions used for water conveyance and drainage operations are outlined below:
- Inverted siphons
- Elevated ditches
- Weir/Drop spillway
- Energy dissipator
- Stilling basin
- Hydraulic jump
- Retaining wall/gabion wall/gabion basket
- Rain garden
- Retention ponds
- Drainage ditch
- Slide gate
- Division Box
- Turnout in Irrigation
- Siphon tubes
- Flexible gated pipe/Gated pipe
- Pipelines low/high pressure
- Sand trap
- Weep Holes
Flumes are constructed artificial channels that are supported by substructures that carry water across areas where the digging of ditches is not practical or would be too capital intensive.
Areas like steep rocky terrain, mountainous, hillsides, swale, or draw regions are topographically difficult to establish functional ditches. These are the type of areas where the construction of flumes is one of the few ways irrigation water can be transported across.
Flumes must be large and sturdy enough to contain and direct a sustained full discharge of a ditch, pipe, or channel without the substructure giving way. Open flumes (uncovered channel with only the base and sides) are typically built from materials that can produce durable, sturdy structures like timber, concrete, bricks, or metal. Pipes and concrete slabs can be used for closed flumes (covered channels with a base, sides, and roof) which may either be partially or completely insulated.
Reinforced concrete and metal flumes have the most long-term durability but are more expensive. Wooden flumes generally require treatment with preservatives to enhance their lifespan.
Inverted siphons are closed conduit pipes with raised ends that form a U-shape. They are used to convey water mostly under obstructions to an otherwise straight trajectory such as roads, depressions, drains, or other structures.
The u-shape helps to divert the flow to give room between the loops/raised ends for the obstructing structure without compromising its structural integrity or the flow of irrigation water.
They are typically constructed from corrugated, smooth metal, or concrete pipes, and sometimes reinforced concrete that is poured into a mold which is removed once the concrete has dried and set.
Inverted siphons are particularly suited to conveying water underneath roads, especially those that pass over culverts and other drainage and conveyance structures that require the passage of water above the ground’s surface. They are sometimes used in place of flumes particularly at locations where the water has to be conveyed over wide steep passes.
Although they both cross-drain water underneath roads and rail lines, inverted siphons differ from culverts in various ways; Culverts are single-unit cross-drainage channels that are not usually part of a comprehensive system. Inverted siphons are usually part of a comprehensive conveyance system.
Culverts are typically only partially submerged in the flowing water as only the bottom part makes constant contact with the water. inverted siphons are completely subsurface and carry a separate body of water. Being underground also protects inverted siphon pipes from the effects of flooding.
The water flowing through the inverted siphon has to be under pressure and the velocity at least as high as that of the ditch or channel that is feeding into the siphon to avoid sedimentation beneath the inside of the siphon.
Trash racks or debris screens are important features that must be added to prevent the frequent blockages from the accumulation of debris that is inevitable over time.
Elevated ditches are open conveyance channels built on heaps of compacted earth to carry water across shallow depressions or by an open ditch to a higher area of a field. The soil or filling material used for the elevation must compact readily but not crack when dry.
Elevated ditches are generally suitable for carrying large volumes of flow and can cost significantly less than alternatives like flumes, pipelines, or siphons. However, they tend to have problems like loss of water due to seepage (moisture loss from percolation of water through the soil), the accumulation of weeds, and patronage of wildlife with the resultant damage.
Culverts are structures that are built over waterways to allow cross traffic of vehicles above overflowing water below. The structure arches over the waterway with roads or rail lines and often both passing on top and water underneath and can sometimes be very similar to a small bridge and other times resemble a large pipe.
Culverts are usually partially embedded in the ground and must have sufficient cover or reinforcement and be sturdy enough to withstand vehicular traffic and flood water. They can be made from steel, reinforced concrete, stones, bricks, or other durable materials and are built in different shapes and sizes.
Bridges are high transit structures that are built to traverse a region and connect two elevated areas without hindering any thoroughfare or transit beneath it. In irrigation systems, bridges can be used to carry pipelines over all types of terrain that would otherwise be almost impossible to cross like ravines and gorges.
Bridges can be used for high-clearance crossings regardless of the elevation of the ditch and can be designed in a way that will incur little or no loss of head. Their design and placing also utilize the force of gravity as the water descends for optimal pressure levels.
A pipe drop or drop spillway in an irrigation system is a type of weir; A point along the watercourse where there is a sudden descent or drop in elevation that pours into a wider apron (an impermeable covering at the end of a water-retaining hydraulic engineering structure) and spilling basin (a deep and broader area that receives and contains high velocity falling water) area with a slant, or a slightly protruding surface at its far ridge.
The ditch velocity is controlled as the slant slightly slows the flow of water behind the point of elevation into a pool where it lingers before pouring over the top of the elevation in a slower more controlled sheet. From there it continues downstream through the rest of the conduit or channel system.
For small to intermediate drops (in terms of height), normal aprons and spilling basins will suffice. However, in higher drops, an energy dissipater (structure or device for reducing and controlling the velocity of flowing liquids) will be needed to control the velocity of the descending water.
Large open drop spillways are typically constructed of reinforced concrete whereas smaller ones can be constructed using concrete and other material like; bricks, rock masonry, or prefabricated steel and aluminum. Metal drops generally require an anti-corrosion coating.
Rot-resistant lumber can also be reinforced with suitable protective coatings and used. These include trees like redwood, cedar, fir, and creosoted pine. In areas where the soil has a higher than average chemical concentration that may speeden up the corrosion process, special cement, coatings, or alloys may be needed.
An energy dissipater is a structural device usually comprising of segmented surfaces and mechanical armoring placed or built at the outlets of high-velocity water conduits that protect downstream areas of an irrigation system by reducing the velocity of descending flowing water to acceptable levels that won’t cause harm to the soil, crops, or equipment.
This is usually achieved by the resistance energy dissipaters cause against the direction of the descending water by partially obstructing its flow thereby dissipating or releasing bits of the water’s kinetic energy to the surrounding.
Energy dissipaters were typically made from reinforced concrete but are now constructed from different sturdy materials including metals.
A stilling basin is a deep bowl-like structure in a water conduit system usually located at the base of a pipe or spillway drop that serves the function of controlling the velocity of the water flow.
It performs a similar task to the energy dissipator and is sometimes in conjunction with it as the dissipater is often placed in the basin either as a unit or as baffle piers (a series of blocks fixed in an intermediate position on the floor of the stilling basin ).
Chute blocks (a series of blocks at the opening of the stilling basin that breaks up the flow and lifts some of the water reducing its jump height) are also sometimes fixed across the entrance to the stilling basin. The end sill is the slanting elevation at the far end of the basin that slows the flow rate causing the water to pool there briefly before flowing the top.
The stilling basin and energy dissipater both reduce the momentum/kinetic energy by hydraulic jump (unstable abrupt spike or height and depth increase on the surface of flowing water that causes a decrease in the downstream flow velocity).
The difference between the energy dissipater and stilling basin is that the energy dissipater reduces water velocity by resistance from partial obstruction and can be installed at virtually any high-velocity discharge outlet or stilling basin. However, the stilling basin reduces water velocity by turbulence caused by hitting the bottom of the basin and is only installed below downstream discharge drops.
A hydraulic jump is the phenomenon of liquid suddenly rebounding back upwards increasing in height and slowing its flow rate as it hits the base of a drop after discharging from an elevated outlet higher velocity.
When the hydraulic jump occurs, the impact and resultant backward deflection increases the height of the water, causes the loss of some energy through heat discharge from the turbulence, and converts some of its initial kinetic energy to potential energy.
There are generally two main types of hydraulic jumps and a similar and related phenomenon namely:
- Stationary Hydraulic Jump
- Tidal Bore
Stationary Hydraulic Jump
Stationary hydraulic jump is the most frequently observed and usually occurs on rivers, outfalls, dams, and irrigation works. It is when liquid from a high-velocity outlet of flowing water discharges into an area of the channel or engineered structure that will only sustain lower flow rates.
It is referred to as stationary primarily because it is a continuous phenomenon that is constantly reoccurring at the same spot and not transiting from there.
A tidal bore is also referred to as a positive surge, hydraulic jump in translation, and moving, or dynamic hydraulic jump because it is usually formed by a tidal wave or waves that travel upstream against the direction of the current.
Like all hydraulic jumps in general, Bores can take on different forms depending on the conditions and level of the water. They can sometimes range between undulating wavefronts and shockwave-like walls of water.
A cascade is a wall or undulating wave of high volume and velocity water falling from an elevated surface and descending to lower stages as it flows downstream. It typically tumbles down in waves overtaking a shallower downstream flow and losing momentum as it makes contact with progressive surfaces as it descends.
Rip raps also termed rock armor, shot rocks, or rubble are man-made heavy breakwater (structures for controlling the damage from waves or moving water) objects with irregular shapes that are used for a similar function as energy dissipaters.
Heavily reinforced concrete, steel, or other durable material with rough surfaces (e.g. tetrapods: four-pronged solid structure ) are anchored to the ground.
They serve as fortifications against damage by water by placing them in the path of the water to protect an area or structure against scour (the removal of earth or ground material from around a structure that could compromise its integrity), and water, wave, or ice erosion.
Retaining Wall/Gabion Wall/Gabion Basket
A retaining wall is a long sturdy structure that is designed and built to hold in soil and moisture from being eroded or washed downstream by the action of draining runoff water from an irrigated land. Seawalls perform a similar but keep waterbodies from eroding inland soil.
Gabion walls and gabion baskets are modified versions of retaining walls adapted for use in more confined topographic irrigation locations or specific requirement areas.
A swale is a natural or artificial sunken marshy gently-sloped shallow depression or channel that accumulates runoff rain or irrigation water and sometimes acts as an infiltration basin (a contain/disbursement structure that helps runoff water percolate through permeable soils into the groundwater aquifer), drought reservoir, or a flood drain.
Bioswales are artificial channels built to accumulate and transport stormwater runoff to reservoirs, back to the downstream supply system, or the drainage while removing debris and pollution. Bioswales also help to recharge groundwater.
A rain garden is a type of bioretention (the process through which contaminants and sedimentation are removed from stormwater runoff) facility consisting of a gentle depression built into the landscape just downstream from an irrigation zone. It utilizes plants that help to reduce the flow rate, total quantity, and pollution load of runoff from upstream irrigation areas.
Rain gardens use water absorbent plants and natural or engineered soils to retain rain and irrigation runoff water and optimize its infiltration by increasing its stagnant lag time while remediating and filtering.
Retention ponds, also known as detention basins, wet ponds, or stormwater management ponds, are natural or artificial depressions for accumulating and retaining runoff water slightly downstream from an irrigation zone or naturally drained land that is established to reduce the eroding effect and loss of water from runoff.
Retention ponds are similar to but distinguished from swales, bioswales, and rain gardens by their additional water holding capacity.
A drainage ditch is a water containment channel that is typically established in low-lying areas downstream from elevated irrigated or water catchment areas. Its secondary function is to retain and subsequently distribute water for irrigation.
Chutes in irrigation or drainage systems are conveyance structures that consist of an inclined channel that may be in form of either a trough, tube, or shaft that conveys water from a higher to a lower surface.
They are typically designed and built to be sturdy and able to withstand high velocity and often precede drops and stilling basins.
A headgate is a regulating device or valve that controls the water supplied from a conveyance structure into a containment area or other receptacle.
Headgates are usually used to divert irrigation water from the supply source to the farm field ditches. Weirs measuring devices may sometimes be built into headgates to measure the flow of water into field ditches.
Slidegates and sluice gates are manual or automatic control devices that consist of a flat slab made from metal, plastic, wood, synthetic, or other material that slides on grooves in a pipe or some other water conveyance system to open or shut off the water supply.
A division box is a conveyance junction facility built at a strategic point in an irrigation system where water is diverted or redirected between two ditches without compromising its overall flow.
Division boxes are usually sturdy structures with inlet and outlet spaces or holes opening towards the necessary direction for the passage of water and have gate valves to regulate the flow rate. There is typically one inlet from the source but one or more outlets.
Checks in irrigation systems are adjustable regulating structures that are placed or built into water containment ditches forming retaining walls that act as dams and can be adjusted to retain or release its flow.
The daming of the water by the check controls the water level and surface elevation upstream so that it can be distributed to different respective downstream channels. Checks can be either portable or permanent.
An upstream apron or apron slab in irrigation is an impermeable upstream structure built to cover the base of a water-retaining hydraulic engineering structure such as a reservoir for irrigation systems.
The purpose of the apron is to lengthen the path of water that seeps out from beneath the receptacle channeling it away from the topographic surroundings to reduce uplift at the bottom of the structure and prevent erosion from the seepage.
Turnout In Irrigation
A turnout, offtake, or delivery gate in irrigation is similar to a headgate because they both control and regulate the passage of irrigation water between two areas. Turnouts, in particular, are an established point where the control of the water flow changes from the supply district to the distribution and reception areas.
A turnout has the following functions; opening and closing the flow of water, flow rate control with the aid of a valve, a gauge for flow rate measurement, and one for volumetric measurement.
Siphon Tubes For Irrigation
Siphon tubes are simple and efficient water conduits in form of tubes or pipes typically made of rubber, plastic, or some other flexible synthetic material that are used to conveniently carry water over difficult-to-cross obstacles like rock outcrops or embankments.
Siphon tubes are indispensable on different forms of unlevel terrain due to their flexibility and ability to lift water above the surface of a reservoir and convey it to the point of discharge without a pump or any mechanical input.
They use the shape of the tube, the presence of a vacuum, gravity, and the siphon principle (simply put, is that a liquid can be lifted above the surface of an upstream reservoir over an expanse and to a downstream reservoir or point of discharge using a looped tube) to lift, convey, and discharge the water.
Flexible Gated Pipe/Gated Pipe
A gated pipe is a sectionalized portable metal pipe that is typically made of aluminum and has a series of water outlets along one side similar to lateral lines. The outlets have controllable covers (gates) that can be opened to irrigate corrugations or furrows or closed as needed.
The gates on the outlets can be independently adjusted to regulate the discharge rate of each outlet which can also be spaced to correspond with the furrow spacing. The pipes are designed to be lightweight and can be used with other sections that can easily be coupled and uncoupled.
Gated pipes can be used in conjunction with, or in the place of head ditches on top of fields or instead of intermediate head ditches on fields that are too vast to be irrigated in one length.
Flexible gated pipes are similar to gated pipes in being sectionalized, portable, and having outlets along one side but differ from them by being made from flexible materials like rubber, plastic, canvas, or some other flexible material.
Due to the flexibility of these pipes, they can be used on rougher terrain than the metal types and can be rolled up for transportation and storage easily but are not as durable.
Spiles in irrigation are small outlets sometimes made with short pipes that are opened up on the lower part of ditches or channel embankments that allow water to flow into the irrigation field. Some spiles have the provision to shut them off with gates or plugs.
Pipelines are the main closed conduits or conveyance structures for moving water throughout irrigation systems. They can be installed both on the surface and below the surface and are effective at preventing the loss of water by seepage.
Pipelines are generally either flexible or rigid and there are two basic types of pipelines that are generally used namely:
- Low-pressure pipelines
- High-pressure pipelines
Low-pressure pipelines are typically used only in surface irrigation and utilize open channels and operating heads of less than twenty pounds per square inch (20 psi).
Concrete is generally used for low-pressure buried pipelines but other materials like steel, wrapped aluminum, fiber, asbestos cement, plastic, or synthetics are also used.
Concrete pipes are built with tongue and groove joints which are sealed with rubber gaskets or filled with cement mortar. They are either precast or cast in place.
Low-pressure pipelines can be permanent, semi-portable, or portable.
Permanent low-pressure pipelines usually have buried supply and distribution lines. Semi-portable low-pressure pipelines utilize buried pipes for field supply lines and portable easy-to-couple metal or flexible pipes are laid on the surface for water distribution. Portable low-pressure pipelines utilize metal and flexible pipes for both supply and distribution.
High-pressure pipelines are conveyance structures that transport water through irrigation systems that need a pressurized supply for their optimal operation. Establishments like sprinkler systems require up to forty pounds per square inch (40 psi) to function properly and require high-pressure pipes.
The supply and main lines for high-pressure systems may either be permanently buried or surface lines. Buried lines can be established from the water source all the way to the fields and surface pipes used for the field main and lateral lines.
This limits damage to the supply lines from moving equipment. Buried lines are more expensive to install in the short term but require less overall maintenance.
Sand Trap/Sediment Filter/Debris Screen
Sand traps and sediment filters are filtration devices that are installed in irrigation conduits or conveyance structures to collect sand and other debris that is usually carried in flowing water and can accumulate and cause serious obstructions or outright blockages to the flow of water and operation of the system.
Valves are regulating devices that are installed in irrigation systems to control the flow rate and pressure of water in the system by opening, closing, or partially obstructing the flow of water or air in the conveyance structure.
There are several types of valves that perform various functions that are generally related to the flow rate and pressure of the water. Some valves are manually operated, while others are automated.
Weep holes, weeps, and weep bricks are small outlets made at the bottom area of water and soil containment structures such as retaining walls to allow water to drain from the assembly or structure.
The weep holes help to overcome the surface tension (properties of the surface of a liquid that makes it resist an external force due to the cohesive nature of its molecules) and thus reduce the hydrostatic load (the pressure a contained liquid exerts on the structure in which it is contained) the water contained in the structure will exert on it.
Weep holes are similar to spiles in being outlets along the base of conveyance or containment structures but differ in being primarily for drainage of irrigation water, whereas spiles are primarily for irrigation.
Automotive water pumps also usually have weep holes to protect their bearings by discharging water that sometimes leaks and accumulates beyond the seals.
Drainage In Irrigation Systems
Drainage in agriculture or irrigation is the removal of water from the surface, subsurface, or plant root zone of agricultural land to enhance the production of crops. It involves the control of erosion and the water table, and the proper channeling and control of stormwater and irrigation runoffs.
There are two basic types of drainage systems which are surface drainage and subsurface drainage systems which can be further subdivided into natural drainage and artificial drainage systems.
Surface drainage is the removal of excess water, usually by utilizing gravity, from the surface of agricultural land and washing it down to low-lying bodies of water.
In natural surface drainage, the process begins naturally as soon as there is flooding from a substantial amount of rainfall or irrigation. The water will flow down topographic inclinations and repeated runoff stormwater forges shallow and deep channels in the ground.
This is done by eroding surface soil along descending routes it follows as it drains downstream. The channels get deeper and wider with time and become regular paths for draining water.
Artificial surface drainage utilizes a series of shallow ditches or open drains that are dug at strategic spots to collect the water. These shallow ditches then discharge the water into larger collection drains where it can either be recharged and fed back into the irrigation or ecosystem.
Fields that do not have a sufficient enough slope to achieve optimum drainage with the aid of gravity have to be modified by land grading.
Subsurface drainage is the removal of excess water from under the surface of the ground or the root zone with the aid of gravity. The water is sometimes washed into underground systems or can emerge and collect on the surface.
Natural subsurface drainage utilizes previously established underground channels to travel down to underground water bodies, percolate into the water table, or emerge with ascending water as spring water.
Artificial subsurface drainage is manmade and makes use of deep open drains or buried pipe drains.
Deep open drains are narrow deep channels or ditches that are dug into the soil along the sides of an agricultural field. The ditch has to be deep enough to reach the saturated soil below the level of the root zone.
The water in the ditches is channeled away from the root zone and will typically feed into a larger downstream ditch where it can be processed and redistributed.
Buried Pipe Drains are buried pipes that are designed with openings at the ends that are immersed in the saturated soil and collect water that is transported to a collection drain for further utility.
Frequently Asked Questions
What is an Irrigator?
An irrigator can be defined as any one of three notably similar meanings. It can be a person or farmer who carries out the process of watering on agricultural land. An irrigator can also be the machines or equipment from irrigation systems used to irrigate the land. It can also be used to describe the water and solution dispensing devices that are used in therapeutic lavages (medical irrigation).
What are the means of irrigation?
Means of irrigation simply refers to the ways and methods through which irrigation can be carried out. For example, manual irrigation, flooding irrigation, or mechanized irrigation.
What is a Watering Station?
A watering station is a term used to describe a specific point in an irrigation or water supply system where a provision or outlet for dispensing water has been installed.
How to adjust a Sprinkler Head
Adjustments of sprinkler heads are often necessary to either increase or reduce the reach (distance covered) of the water’s trajectory or the direction of the spray and radius covered to suit the specific dimensions of the area intended for irrigation.
The adjustment of most sprinklers and sprinkler heads is easy and only requires the loosening or tightening of a small screw located on the sprinkler head. Turning the screw clockwise with a small screwdriver will usually reduce the pressure with which the water will be thrust from the nozzle or nozzles. Screwing anticlockwise will increase the pressure and the reach of the spray.
A screw can also be loosened or tightened to change the direction of the spray. Simple and clear instructions are stated in bold writing on the sprinkler heads.
How To Adjust Rainbird Sprinkler Heads
Rainbird sprinklers are a relatively reliable type of irrigation sprinkler that is commonly used. However, there seem to be many who have difficulty adjusting these particular sprinklers to suit their specific requirements. The following is an outline of the adjustment procedure:
Changing The Nozzle Head
- Remove the previous nozzle head by turning it anticlockwise by hand.
- Take out the filter screen below the nozzle.
- Insert a new replacement filter screen in the same position as the previous one.
- Gently screw on the new nozzle by turning the head clockwise until it can’t turn any further.
Adjusting The Watering Direction
The water spraying direction can be adjusted manually by rotating the stem by hand to aim the slots where the pressurized water is squirted towards the desired direction for irrigation.
Adjusting The Spray Distance
Changing the squirting distance is done by adjusting a screw located at the center of the sprinkler head with a flat screwdriver. Turning the screw clockwise will reduce the pressure and distance sprayed. While turning the screw anticlockwise will increase the pressure and distance of the spray.
Adjusting The Spray Pattern
Adjusting the spray pattern can only be done on certain models with this option like the 12/15/18, and 2SA, 42SA, 42SA+, or 52SA series. The adjustable spray radius ranges from 0° to 360°.
To adjust the spray pattern, twist the threaded collar to the right or left while the system is turned on to see and produce the desired spraying patterns.
What is Irrigation Timing?
Irrigation timing is the suitable period when irrigation should be carried out. It also refers to the amount of time or how long a given area should be irrigated.
Some irrigation systems are designed to work with an irrigation controller which can be programmed to regulate different functions of an automated irrigation system like frequency, sensors for soil analysis, pre-set timing for starting, intensity, and duration so that the system shuts itself off automatically when the timer reaches the stipulated length of time that was set for cessation of the application.
These systems usually use solenoid valves (electromechanically operated valves) designed to be controlled automatically and remotely. This timing facility is only available for high-tech automated systems.
Where to get Irrigation Supplies
Standard and specialized irrigation system supplies are available in several hardware stores across the U.S. and many nations all over the world, however, it is now possible to select, order, and receive irrigation supplies from numerous vendors that now have online facilities. A few are listed below:
- Sprinkler Warehouse
- Sprinkler Supply Store
- Drip works
- The Home Depot
- Ewing Irrigation and Landscape Supply
Specific irrigation system equipment such as Hunter sprinkler heads and Rain bird sprinklers can be obtained from the stores listed above or at their specific brand outlets listed below:
- Hunter Sprinkler Heads/Hunter Sprinklers
- Rain Bird Sprinklers/Rain Bird Sprinkler Heads/Rain Bird Controls