The closed irrigation system is an irrigation and drainage system the on-farm irrigation network of which is composed of pipelines. The irrigation network of the closed irrigation system is composed of main, distribution, and field pipelines.

Subject to their design, closed irrigation systems are divided into stationary, semi-stationary, and mobile. In stationary closed irrigation systems, the pipelines are permanent; their irrigation networks are laid under surface. Permanent hydrants are mounted on them, through which water is supplied to sprinkling and irrigating machines. In semi-stationary irrigation systems, the irrigation network consists of permanent subsurface and detachable surface pipelines, to which irrigating equipment is connected. In mobile closed irrigation systems, the irrigation network consists of detachable pipelines laid on surface. There are two types of closed irrigation systems: with pumping water supply, in which pressure needed for water to flow is produced by pumps; and gravity-pressure, in which water flows because of natural head generated due to site slope (i=0.003). Steel, cast-iron, aluminum, asbestos-cement, reinforced concrete, polyethylene, rigid PVC and other pipes are used for arrangement of permanent pipelines (at a depth of 0.8-1.25 m).

Detachable pipelines are made of steel, aluminum and polyethylene pipes. Closed irrigation systems can be of ring or dead type. According to their layout, there are three principal irrigation schemes of closed irrigation systems: Т-, E- and U-type. If the irrigated site adjoins a water source, T- and U-type schemes are applied; if the irrigated site is square-shaped, T-type scheme is used; if the site is extended along water source, E-type scheme would be more practical. Closed irrigation systems yield the highest efficiency factor (EF) and land use ratio (LUR) of irrigation systems, do not deteriorate land reclamation conditions, and allow automating water distribution over irrigated sites.

In recent years, closed irrigation systems with sprinkling irrigation are becoming more and more popular. In closed irrigation system, water is supplied through pipelines from an irrigation source to an irrigated area for watering crops. The required water pressure is provided by appropriate site slope or by means of a pump. The water-supply network consists of permanent subsurface pipelines. Regulating (distribution) network is composed of subsoil pipelines, portable spray hoses with water discharge to each row or of detachable pipelines with hydrants for water withdrawal by sprinkling machines or sprinkler systems. The combined irrigation system consists of permanent canals and mobile (more rarely stationary) pipelines supplying water to sprinkling machines. The general requirement for the arrangement of stationary canals on irrigated sites is creation of conditions not only for water application, but also for the use of machine-tractor aggregates during field works. This means that the sites are to be in the form of rectangles or rectangular trapezoids with the field width or length (depending on the direction of water application) multiple of the width of sprinkling machine grip. Within the boundary of the irrigated site, pipelines and temporary irrigation ditches are designed parallel to each other and laid at the interval equal to double wing length or sprinkling radius of the sprinkling machine; and from the site boundary, at the interval equal to wing length or sprinkling radius. Design pitches of closed irrigation network pipelines are determined proceeding from their optimal operating conditions. At that, provision of water discharge for the winter period is essential.

Source: Great Encyclopaedic Dictionary: Agriculture