Page 224 - Biosystems Engineering

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leading to the cooling effect. The plants will continue to photosynthe-
size under these cooler conditions.
Effluent Disposal
Irrigation systems have also been used as a means of disposing waste-
water from industrial processes and animal production operations.
The wastewater is initially treated in holding ponds, and the
supernatant water is pumped to different cells to achieve further
degradation. The water from the last treatment cell is used for
irrigating pastures as a means of disposal.

6.5 Irrigation Systems

6.5.1 Introduction
There are several different types of irrigation systems, which have
evolved over the years, depending on the complexity of the terrain
and the availability of water. The following sections describe the dif-
ferent systems and their applications. History is replete with evidence
of well-designed irrigation systems in use. The finding of major
ancient civilizations has also shown evidence of well-constructed
water storage reservoirs and canal delivery systems.
6.5.2 Types of Irrigation Systems
Irrigation systems can be broadly classified into surface irrigation,
sprinkler irrigation, drip irrigation, and subsurface irrigation, depend-
ing on how water is applied. The principles governing the design of
these systems also differ because of the differences in how water is
delivered to the root zone. It is important to understand the water-
saving features of these systems before selecting a particular system
for a given irrigation application.

6.5.3 Irrigation Efficiency
Irrigation efficiency is defined as the amount of water beneficially
stored within the plant root zone as a fraction of the applied quantity
of water. Generally, surface irrigation systems with 50 to 60 percent
efficiency have been in use in many parts of the world due to its sim-
plicity in design. Biosystems engineers have made advances in the
design of sprinkler irrigation systems, which have efficiencies as
high as 80 percent. Further advances in irrigation have been made
with the development of drip irrigation systems, which attained
90 to 95 percent efficiency (ASAE 1990).

6.5.4 Design of Irrigation Systems
Depending on soil type, land slope, and water availability, different
types of irrigation systems are used. The choice is also determined by