Irrigation system and its components
Irrigation system means a land territory with the network of canals and other hydraulic and service facilities that provide irrigation of the area. In addition to a land territory, continuous-flow irrigation system includes:
- Head water-intake facility, which withdraws water from an irrigation source (river, reservoir, canal, well, etc.) and protects the system against sediment load, sludge ice/ice brash (frazil ice), trash;
- Irrigation network;
- Tail-water ditch;
- Collector and drainage network: lowers groundwater level and carries water and salts outside the irrigated area;
- Service facilities: roads, irrigated lands’ ameliorative condition supervision device, etc.;
- Forest belts; etc.
Irrigation systems can be of the following types: with gravity water intake (water inflows to canals from an irrigation source by gravity) and with mechanical water lift (water supply by a pumping station). In terms of design, they are divided into open, closed (piped), and mixed.
Open irrigation systems are the most common; they have earth/unlined canals (usually with waterproofing concrete protection, reinforced concrete, asphalt, synthetic materials) or flumes. Among open irrigation systems are rice-growing systems the entire area of which is divided by earth borders into plans, while the plans were divided into smaller lots, i.e. check plots (4-10 ha).
Disadvantages: low irrigation water use ratio (the majority of canals are unlined); difficulty with the automation of water distribution and delivery processes; continuously functioning operation service.
Closed irrigation systems are divided into permanent, semi-permanent, and mobile systems. There canals are replaced by pipelines (usually underground).
In permanent irrigation systems, all the links are stationary; the irrigation method is sprinkling irrigation (long-range and medium-range sprinklers that are fixed on irrigation pipelines). When irrigating cultivated permanent grasslands, the irrigation system can consist of a pumping station on the river or drill wells and a sprinkler, for example of the “Fregat” type.
Semi-permanent irrigation systems generally have fixed distribution and collapsible irrigation pipelines to which spray hoses or sprinkler laterals are connected.
In mobile systems, all the pipelines are collapsible.
Closed irrigation systems ensure high efficiency factor of the system (ratio of the water quantity supplied to a given irrigated area to the water quantity taken from an irrigation source); do not deteriorate the ameliorative condition of the irrigated land; enable economically using water; ensure high land use ratio as well as the use factor of the machines and mechanisms on fields; allow easily automating water distribution over land plots (programmable control) including those with complex relief. At the same time, closed irrigation systems are characterized by high construction cost; heavy operating costs, and more complex operation.
Large integrated irrigation systems are usually composed of open main canal and inter-farm water distributors, often with concrete channels and piped inter-farm irrigation network. Various irrigation methods are applied: sprinkling irrigation; furrow irrigation; etc. In addition to regular irrigation systems, there are liman (catchwork) irrigation systems and irrigation & water-distribution systems.
The design of irrigation systems is determined based on technical-and-economic comparison of the options for specific designing conditions. Operation of inter-farm systems is carried out by basin, provincial, or district water authorities and inter-district canal administrations; while on-farm systems are operated by hydraulic departments of sovkhozes or irrigation departments of kolkhozes.
Source: Great Soviet Encyclopedia
Irrigation network represents the network of permanent and temporary waterways (canals, pipelines) that supply water to irrigated lands from an irrigation source; it is the key component of the irrigation system. It consists of conducting and regulatory networks. It is equipped with the devices and facilities for water measurement (water gauges), rising of water level in canals, and control of water discharge (head regulators, checks), connection of canal reaches (check drops, chutes), retention of silt/debris (sediment tanks, guide systems), and so forth.
The conducting network in open irrigation systems includes a main canal, inter-farm, farm, and on-farm distribution canals (distributors) of different orders.
The main canal delivers water from a river, reservoir, well, etc. to inter-farm distributors which deliver water to particular farms or crop-rotation sites; on-farm distributors deliver water to crop rotation fields or irrigated sites.
In some cases, conducting networks have no full set of canal structures. Irrigation canals are arranged in the layout in such a way as to ensure the following at minimum construction and operation costs: water supply in sufficient quantity and in required time; highest efficiency of canals (ratio of the water discharge at the canal end to that at the head) and use ratio of irrigated area; efficient operation of canals and structures on them. The necessary condition of irrigation network operation consists in command of the main canal (exceeding of its water level over the water level in the canals of lower orders) over the irrigated area and higher-order canals over lower-order canals to provide gravity irrigation.
Irrigation canal routes should pass along the boundaries of farm crop-rotation sites, fields so that no to divide the irrigated area, main canal highest points of the irrigated area. Irrigation canals are divided into canals in cut, canals in cut-and-fill, and contour canals. To reduce seepage losses, the bottom and walls of canals are compacted, covered with concrete, reinforced concrete (cast in-situ reinforced concrete or prefabricated reinforced concrete) facing, screens made of clay and polymer films, reinforced concrete flumes.
In closed irrigation systems, the conductive network is composed of the main pipeline that delivers water from an irrigation source to distribution conduits laid 0.6-1.2 m deep and sometimes on the ground surface. The required head pressure is provided due to earth grade or by using a pumping station. In addition to full loss-free conditions, the closed irrigation network enables automating water distribution over the irrigated area, increases land use ratio, does not interfere with the operations of agricultural machines. It is especially effective in lift irrigation systems, at rugged topography.
The regulatory network in open irrigation systems consists of temporary irrigation ditches, auxiliary ditches from which water flows into the irrigating network, i.e. to furrows and beds (see Surface Irrigation), or taken by sprinkling and irrigating machines. The regulatory network is trenched every year before starting irrigation and leveled upon completion of the irrigation and during every post-irrigation cultivation process.
In closed irrigation systems, temporary irrigation ditches and auxiliary ditches are usually replaced by underground pipelines, movable spray hoses (with discharge outlets to every irrigation furrow) or collapsible pipelines with hydrants for water extraction by sprinkling and irrigating machines.
Source: Great Soviet Encyclopedia
Sources of water for irrigation can be represented by:
- rivers in natural and regulated regimes;
- local surface flow coming to estuaries (coastal lakes) and pools;
- groundwater taken from dug-out (pit) wells, bore wells, water captation structures.
In addition, industrial and household wastewater, mine water, and system wastewater, and in some cases seawater can be used for irrigation.
The requirements applicable to water sources are as follows: water must be usable for crop irrigation; water reserves and flow rate in the source must always and ideally fully satisfy the needs for water; the source should be located close and upstream to a given irrigated area so that to ensure water delivery by gravity at low cost of the construction of a water intake facility and irrigation system.
The requirements applicable to the quality of irrigation water are as follows: at irrigation, it must improve the mechanical, chemical, biological, and temperature soil regimes; possibly not silt irrigation canals; be applicable for irrigation by using the available equipment and mechanisms.
Irrigation water quality depends on the temperature, quantity, and fineness of suspended particles, salinity (quantity and composition of the dissolved salts and chemical elements in the water).
At low temperature of soil and air, irrigation water should heat it and, therefore, its temperature is advisable to be within the range of 25…40° Ñ. If the water being in natural state is of low temperature, it is heated. When using cold underground and glacier waters, they construct pools where the waters can be heated. Irrigation by heated water, especially in northern areas, accelerates ripening of vegetables, fruit, berry-like, and other crops, increases their yield and improves their quality.
The photosynthesis of spring wheat ceases at temperatures above 21° Ñ and that of cotton ceases at 30° Ñ. Therefore, drop of soil and air temperature in such cases leads to the enhancement of plant growth and development. The quantity of suspended sediments per gram in one liter of water means water turbidity. The water turbidity in lakes, ponds, lowland rivers, and groundwater is little. For example, turbidity of the Amudarya river water is great and ranges from 5 to 0.4 g/l.
Fine suspended particles contain nutrients and, therefore, irrigation by using such water not only wets but also fertilizes the soil. Small particles at water transportation by canals do not settle and come to fields, while big ones settle, silting up canals, pipes, flumes. So, to prevent their silting, sediment tanks are constructed, where coarse suspension settles. At surface irrigation, it is advisable that the water should not have coarse suspended sediments.
When irrigating by sprinkling machines, water should not contain debris and suspension larger than 0.5 mm so that not to clog the filter installed on the pipe before the hydraulic cylinder; when irrigating by using hose pipes, water turbidity should not be higher than 1…1.5 g/l; when irrigating from underground pipelines, it should not be higher than 3…4 g/l. Depending on water turbidity, they establish an appropriate mode for flushing hose pipelines and underground pipelines.
With subsoil and drip irrigation, there must be no suspension in the water. Therefore, the irrigation water is pretreated being infiltrated.
Water salinity is determined mainly in terms of dissolved solids, expressed in g/l, (total soluble salts) as well as its chemical composition.
For most plants, irrigation water with a salinity of up to 1…1.5 g/l is harmless, and for salt-tolerant plants it is 5…8 g/l. Water is considered toxic the concentration of soluble salts in it is 15… 20 g/l. Therefore, in some cases even sea water can be used for irrigation, the salinity of which near to river mouths reduces because of inflow of fresh river water.
When irrigating by saline water under washing irrigation regime on light drained soils not much salts accumulate in the soils and resalinization does not take place. On heavy-textured poor-drained soils, irrigation by sea water inevitably leads repeated salinization. Sea was can be used for irrigation of horticultural crops, forest belts, roadside decorative plantations and shrubbery in seacoast areas, perennial grasses, and winter cereals. The microelements contained in the seawater highly reduce the harmful effect of sodium on water & physical properties of the soil.
To use wastewater of agricultural and industrial enterprises, chemical analysis is carried out with the view of identifying nutritive (nitrogen, phosphorus, potassium) and harmful (tar, soda, phenols, petroleum products, lead, fluorine, etc.) substances in it, and compare the quantity with permissible concentrations. If their content is less than the respective permissible concentrations, water is deemed usable for irrigation, and unusable if it is more than the respective permissible concentrations.
Usability of saline water for irrigation depends on the interaction of a number of factors: climate; drainage conditions in the area; texture and chemical content of the soil; irrigation practice; agricultural technology; and salt tolerance of crops.
There are no recommendations on the quality of saline water usable for irrigation yet; therefore, relevant studies are conducted in every particular case.
Source: Mse-Online.Ru
