Felix Reinders
Agricultural Research Council-Institute for Agricultural Engineering
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T
he purpose of an in-field irrigation system is to
apply the right amount of water, at the correct application rate and distribution to all the
plants in the field, with as little non-beneficial
consumption or loss as possible. Consideration should
therefore be given to the land forming characteristics
of especially flood irrigation, as the application efficiency and distribution of water are dependent on
that.
The term flood or surface irrigation refers to irrigation
where water flows over the soil surface under controlled conditions with the purpose of allowing the
desired amount of water to infiltrate the soil. Although
the soil gradient is instrumental in setting the irrigation
water in motion, the gradient of the water surface itself is in fact what causes the water to flow over level
surfaces and gradient forming plays a vital role in the
performance of the water movement.
Flood irrigation makes out more than 80% of all irrigation methods used worldwide. There is evidence that
flood irrigation was in fact used about 5 000 years ago
in the Far East. In the Philippines, irrigation terraces
built 3 000 years ago are still in use to produce rice.
There are many types of flood irrigation and they may
be divided into three main categories, namely basin
irrigation, furrow irrigation and border irrigation. Every flood irrigation system consists of a source, convey-
ance and distribution component and the efficiency of
a flood irrigation systems is generally low but better
layout and design choices, improved soil preparation,
less water conveyance losses and more effective management systems will enhance its efficiency.
The design and management of flood irrigation systems are usually more complex than for other systems.
This may be because additional factors, such as soil
irregularities and gradients, play a determining role
with flood irrigation. The following interdependent
factors are crucial when water is flowing over soil and
infiltrating into the soil for irrigation purposes:
Soil type
Soil’s tendency to crust formation and resistance to
erosion
Limiting layers in the topsoil
Soil water level
Flow resistance due to crops
Weed density
Quality of water
Cultivation practices
Soil finish
Gradient
Soil preparation
Stream size
Contact time between water and soil