ZIMSEC O Level Geography Notes:Agriculture:Farming types in Africa:Irrigation Farming:Types of Irrigation
- irrigation may be divided into two groups namely:
- traditional forms of irrigation and
- modern ones.
Traditional forms of irrigation
- Under traditional methods, there’s the water wheel moved by draught power or humans, the shaduf (popular in the Lower Nile), the Archimedes screw and flood or basin irrigation.
- A water wheel is a machine for converting the energy of free-flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim which carry the water onto the irrigation land.
- Shaduf, also spelled Shadoof, hand-operated device for lifting water, invented in ancient times and still used in India, Egypt, and some other countries to irrigate land. Typically it consists of a long, tapering, nearly horizontal pole mounted like a seesaw.
- A shaduf is a large pole balanced on a crossbeam, a rope and bucket on one end and a heavy counter weight at the other.
- By pulling the rope it lowers the bucket into the canal. The farmer then raises the bucket of water by pulling down on the weight.
- The Archimedes screw, also called the Archimedes’ screw or screw pump, is a machine historically used for transferring water from a low-lying body of water into irrigation ditches.
- Water is pumped by turning a screw-shaped surface inside a pipe.
- Surface irrigation has evolved into an extensive array of configurations which can be broadly classified as: (1) basin irrigation; (2) border irrigation; (3) furrow irrigation; and (4) uncontrolled flooding.
- This is when the irrigation water either runs off the field or begins by being placed into a pond on the surface, transferred to the irrigation land.
Modern forms of irrigation
- For modern types, there’s the use of windmills to pump the water, diesel and electric pumps, overhead sprinkler irrigation, use of siphons, boom irrigation methods (central pivot system) and the bouzer and trickle technique.
- In both groups of irrigation methods water is drawn from either perennial rivers or dams/lakes or smaller rivers or night storage dams or from tanks or from underground aquifers.
- Canals or pipes may carry the water over vast distances into irrigated fields.
- A windmill is a mill that converts the energy of wind into rotational energy by means of vanes called sails or blades.
- Centuries ago, windmills usually were used to mill grain, pump water, or both. Thus they often were gristmills, windpumps, or both.
- A diesel pump is the device that pumps diesel (as the fuel) into the cylinders of a diesel engine, this may produce electricity which then is used to pump water into irrigation pipes an water the crops.
- Overhead sprinkler irrigation is a pressurized irrigation system where water is distributed through pipes to the field and applied through a variety of sprinkler heads or nozzles.
- Pressure is used to spread water droplets above the crop canopy to simulate rainfall.
- Siphoning is common in irrigated fields to transfer a controlled amount of water from a ditch, over higher elevated sections of land.
- A boom system consists of one or more pipes containing nozzles that apply water as the system moves over the plants.
- Drip irrigation is sometimes called trickle irrigation and involves dripping water onto the soil at very low rates (2-20 litres/hour) from a system of small diameter plastic pipes fitted with outlets called emitters or drippers.
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