UNIT 4. IRRIGATION AND DRAINAGE

Watch this video about modern irrigation methods to introduce this unit:

DEFINITIONS

Supply: an amount or store of something (food, water, power, gas, electricity, etc.) that can be provided or used if necessary. (suministro)

Dams: a barrier to obstruct or control the flow of water, built across a stream or river (presa)

Reservoir /ˈrɛzəˌvwɑː/: a natural or artificial place where water is collected for use, supplying a community or region. (pantano)

Spillway: a passageway through which extra water escapes from a reservoir, lake, or the like. (desagüe, aliviadero)

Well: a hole drilled into the earth to obtain a natural deposit, as water or petroleum. (pozo)

Aquifer: any geological formation containing or conducting ground water, esp. one that supplies the water for wells, springs, etc. (acuífero)

Silt: earth carried by moving water and deposited as a sediment. (limo)

Dew: moisture condensed from the atmosphere, esp. at night, and deposited in the form of small drops upon any cool surface. (rocío)

Sewage  /ˈsuːɪdʒ/: waste matter from domestic or industrial establishments that is carried away in sewers (alcantarillado, cloaca) or drains (desagües) for dumping (vertido) or conversion into a form that is not toxic. (traducción: aguas residuales)

Weir  /wɪə/: a small dam in a river or stream. (azud)

A pump: an apparatus or machine for raising, driving, exhausting, or compressing fluids or gases by means of a piston, plunger (émbolo), or set of rotating vanes (aspas giratorias). (bomba)

To pump: to raise water with a pump.(bombear)

Sluice /sluːs/: water cannel.(canal)

Sprinkler: a device for sprinkling or scattering water, usually a perforated ring or small stand with a revolving nozzle (boquilla) to which a hose is attached for watering a lawn.(aspersor)

To drip: provide water drop by drop. (gotear)

Dripper: a device to provide water drop by drip.  (gotero)

To Flood or a flood: cover with water or a great amount of water that cover a surface. (inundar, inundación)

Drought /draʊt/: a long period of dry weather. (sequía)

Furrow: a narrow groove (ranura, canal) made in the ground, esp. by a plow (arado). (surco)

Pipeline: a route or channel along which supplies (water, gas, oil, etc.) pass. (tuberías)

Seepage: the amount of something that has leaked out. (filtración, fuga)

Irrigation and drainage. Definitions

-Irrigation is the artificial application of water to land.

-Drainage /dreɪnɪdʒ/ is the artificial removal of excess water from land.

Some land requires irrigation or drainage before it is possible to use it for any agricultural production; other land profits from either practice to increase production. Often both may be required together to assure sustained, high-level production of crops.

IRRIGATION

Water supply

The first consideration in planning an irrigation project is developing a water supply. Water supplies may be classified as surface or subsurface. Both surface and subsurface water come from precipitation such as rain or snow.

In planning a surface water supply, extensive studies must be made of the flow in the stream or river, including times of drought and flood. This information will determine the size of dams and spillways, as well as the seasonal storage needed.

The quality, as well as the quantity, of surface water is another important factor. The two most important considerations are the amount of silt carried and the kind and amount of salts dissolved in the water. If the silt content is high, sediment will be deposited in the reservoir, increasing maintenance costs and decreasing useful life periods. If the salt concentration is high, it may damage crops or accumulate in the soil and eventually render it unproductive.

Subsurface sources of water must be as carefully investigated as surface sources. We get water from aquifers through the use of wells. If a well is drilled in the right location, the pressure will cause it to flow on its own. If not, mechanical energy must be used to extract the ground water. In the past hand pumps were used. Modern wells use another energy source to pump the water, such as electricity.

Two sources of water not often thought of by the layman are dew and sewage. They are used mainly in arid regions.

In certain parts of the world, Israel and part of Australia, for example, where atmospheric conditions are right, sufficient dew may be trapped at night to provide water for irrigation.

The supply of waste water from some industries and municipalities is sufficient to irrigate relatively small plots. Sewage can be treated and reused for irrigation. This water contains high nutrient content that reduces or even eliminates the need for expensive chemical fertilizers. 

Transport systems

The type of transport system used for an irrigation project is often determined by the source of the water supply. If a surface water supply is used, a large canal or pipeline system is usually required to carry the water to the farms because the reservoir is likely to be distant from the point of use. If subsurface water drawn from wells is used, a much smaller transport system is needed, though canals or pipelines may be used. The transport system will depend as far as possible on gravity flow, supplemented if necessary by pumping.

Many auxiliary structures are required, including weirs (flow-diversion dams), sluices, and other types of dams. Canals are normally lined with concrete to prevent seepage losses.

Water application

Forrow irrigation

Flood irrigation

Drip irrigation

 

Sprinkler irrigation

After water reaches the farm it may be applied by surface, subsurface, or sprinkler-irrigation methods. Surface irrigation is normally used only where the land has been graded so that uniform slopes exist.

Surface irrigation systems are usually classed as either flood or furrow systems.

1.-In the flood system, water is applied at the edge of a field and allowed to move over the entire surface to the opposite side of the field. Grain and forage crops are quite often irrigated by flood techniques.

2.-The furrow system is used for row crops such as corn (maize), cotton, sugar beets, and potatoes. Furrows are plowed between crop rows and the water is run in the furrows.

Subirrigation is a less common method. An impermeable layer must be located below, but near, the root zone of the crop so that water is trapped in the root zone. If this condition exists, water is applied to the soil through tile drains or ditches.

In recent years sprinklers have been used increasingly to irrigate agricultural land. Little or no preparation is needed, application rates can be controlled, and the system may be used for frost protection and the application of chemicals. Sprinklers range from those that apply water in the form of a mist to those that apply an inch or more per hour.

DRAINAGE

Planning a drainage system

The type of drainage system designed depends on many factors, but the most important is the type of soil. Soils that have a high percentage of sand- and silt-size particles and a low percentage of clay-size particles usually will transmit water rapidly enough to make subsurface drainage feasible. Soils that are high in clay-size particles usually cannot be drained by subsurface improvements.

The topography or slope of the land is also important. If land is completely flat, drainage is more difficult.

Types of drainage systems

Drainage systems may be divided into two categories, surface and subsurface.