“ownership” of water is usually a contentious topic, which should be clearly and
definitively agreed as far as possible before any physical work starts. The issues are
often complex; sharing of water, both between different uses (domestic and/or irrigation
and/or livestock) and between different users with different claims, must be clearly
resolved as a first priority.
Water use committees may be established to decide who gets how much water and
on which days. Agencies that facilitate the organisation of such committees may make a
valuable contribution to food producers, sometimes more valuable than technical or
financial support.
Methods of Irrigation
There are three main types of irrigation systems: surface, overhead (sprinkler) and drip.
- Surface Irrigation
Again, there are three main types of surface irrigation;
- Flood irrigation—water covers the soil surface in a continuous sheet. In practice, it
is almost impossible to maintain uniform water coverage, so some parts of the field
always receive too much or too little water. - Furrow irrigation—water runs down furrows between rows of plants. Very labour
intensive, and also salts often accumulate in the crop beds between furrows. - Corrugation irrigation—water is applied in small furrows running down the slope.
Some overflowing of furrows normally occurs. Also labour intensive.
Surface irrigation normally requires the least amount of manmade materials, and the
water source may be cheap or even free, such as a river or water storage pond. There are
many ingenious ways of flooding fields, some of which are high above the water level.
These systems require the water to be lifted first, either with “cheap” human
powered devices such as bamboo pumps in Bangladesh and elsewhere, or with
diesel/petrol driven pumps.
Currently about 80% of the irrigated area around the world involves some form of
surface irrigation.
- Overhead or Sprinkler Irrigation
Normally powered by powerful machinery, but with sufficient ingenuity and head of
water gravity alone can sometimes provide enough power for simple systems. Water is
delivered through a main line from the source of supply to the lateral lines, then
discharged above the crop through sprinkler heads on riser pipes attached to the laterals.
Each sprinkler head supplies water to a circular area, the size of which depends on
the nozzle size, wind and the water pressure. To ensure uniform coverage, the patterns
are overlapped from 35% to 70%, depending on the type of sprinkler and the wind.
Advantages—compared with the other two irrigation systems, water is distributed more
evenly and in a more controlled way, so less water is needed for a given land area; land
preparation is reduced, and land on quite steep slopes can be irrigated; fertiliser can be