CA Water-Info

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Surface irrigation

At surface irrigation, distribution of irrigation water occurs over the soil surface. When selecting the type of surface irrigation the following should be taken into consideration: biological characteristics of the crop; relief and slope of the irrigated field; water-physical and chemical properties of the soil (water-absorbing capacity, water permeability, salinity), cultivation technology as well as irrigators labour productivity. In terms of the way of water distribution over the field, surface irrigation can be broken down into the following types: border ditch irrigation, flooding irrigation, and furrow irrigation.

Surface irrigation is the most ancient and to date the most widely used method, because it is simple and fail-safe, requires almost no energy consumption for water application, allows irrigating in windy weather, and ensures ample penetration to the soil at water-charging (off-season) irrigation. Water is supplied from a source to the highest point of the irrigated area either through the no-load part of the main conduit (in case of river-canal (damless) or dam water intake), or through a pipeline (in case of water intake by a pumping station). The water from there comes to the irrigation network than consists of the main canal, inter-farm, on-farm, stationary delivery irrigation ditches (distributors), and temporary irrigation ditches. Then by using irrigation furrows or irrigation ditches, from the movement state water is converted into the soil moisture state. All the canals should be arranged in conformity with the relief, pass the sufficient quantity of water, and ensure water delivery to any section of the irrigated area.

The main purpose of water application is to supply a certain water amount to the irrigated site in the required time, distribute it uniformly over the area, and ensure water absorption by the soil. At that, the irrigation practice must ensure preservation of the soil structure, high ratio of the use of the irrigated area, possibility of widespread mechanization of labour and high labour productivity.

At surface irrigation, water is supplied to the field surface. Uniform distribution of irrigation stream over the site and its inflow to the soil (absorption) are determined by the three following factors: stream rate (discharge), water velocity, and rate of its inflow to the soil.

Depending on the combination of these factors, the following water application methods are applied at surface irrigation: dead and through flooded and unflooded furrow irrigation; border ditch irrigation; check irrigation.

At the same time, surface irrigation, especially gravity irrigation, has a number of drawbacks: low labour productivity; low water application quality; degradation of soil structure and emergence of erosion; uneconomical use of irrigation water; low land use ratio because of the installation of open distribution and irrigation system; risk of waterlogging and secondary salinization; in many cases, necessity to carry out large-scale leveling works.

The rationalization of irrigation practice (technology) at surface irrigation method should be considered in close relation to the structure of the irrigation and drainage network, irrigation and leaching regimes, as well as with environmental and economic conditions of the zone where such irrigation method is applied.