2. Irrigation is the controlled application of
water to soil to supplement the deficient rain
fall to provide moisture for plant growth.
Only about 1/3rd of the earth surface
receives enough precipitation in a normal
year to mature food crops and much of the
area is unsuited for agriculture. Adequate
food supplies which are essential for national
prosperity cannot therefore be produced
without irrigation.
3. Benefits
1) Cooling the soil and atmosphere and thereby
creating a favourable environments.
2) Washing out and diluting undesirable salts in
the soil.
3) Reducing the hazard of soil piping.
4) Softening the land for better tillage.
4. IRRIGATION:
Irrigation is the art of applying
water to the land by artificial means to fulfil the
water requirements of crops in areas where
rainfall is insufficient.
5. Four phases:
1) Storage and diversion.
2) Conveyance of irrigation water.
3) Distribution and application of irrigation
water.
4) Drainage of excess water.
6. ➢ Arid and semi arid climate
➢ Aridity increase from North to South
➢ Ineffectiveness of rainfall
➢ Annual rainfall is less than 250 mm
➢ Number of rainy days is less than 10 especially in South of
Pakistan
➢ Balochistan receives very low amount of rainfall
➢ Spells of high temperatures increase the rate of evapo-
transpiration
➢ Monsoon winds are main source of rainfall but they are of
pulsating nature
➢ Rains occur heavily and land absorb small amount of water
➢ Long and frequent dry spell
➢ Lack of well – developed irrigation system.
7. A Land division w.r.t rainfall
1) Arid Zones: For such zone annual rainfall
is less than 15" and an irrigation system is
necessary.
2) Semi-Arid Zones: In these areas,
precipitation (annual rainfall) ranges from
15"-30" and an irrigation system is
desirable.
3) Humid Zones: For these zones the annual
rainfall is more than 30". Therefore an
irrigation system is beneficial.
B Food Demand and population
8. The water supply available to agriculture is
from three main sources:-
1) Rainfall which occurs directly on the crop
areas.
2) Surface water from rivers or storage tanks.
3) Ground water from aquifers.
9. Two irrigation methods are used in Pakistan
Lift Irrigation / Artificial Irrigation
1) Shaduf
2) Persian Wheel
3) Charsa
4) Tube wells
Canal Irrigation
1) Inundation / Flood Canals
2) Perennial Canals
3) Link Canals
4) Karez
10.
11.
12. ❖ Inundation Canal/ Flood Canal
They flow during flood season
➢ Perennial Canal
a) They have been dug out from head works/ barrages and
dams.
b) They flow through out the year.
c) They supply water to agriculture fields.
➢ Link Canals
The link canals were constructed to meet
the deficiency of water in Eastern Rivers occurred after
Indus Basin Treaty 1960.
13. In this method, underground tunnels are
constructed to gather subsoil water,
through gravitational pull, at the foot of
hills. This water is then either taken to the
fields and villages through vertical shafts
which are sunk underground, or it is drawn
out at the foot of the hill where it has been
gathered.
14. The ancient Karez system is comprised of a
series of wells and linking underground
channels that uses gravity to bring ground
water to the surface, usually far from the
source. Originally ancient towns used to
depend on the streams and rivers nearby
into which glaciers in far-off mountains
used to feed. As the time passed the
glaciers gradually shrank over the centuries,
the streams they fed likewise diminished,
resulting in less water flowing downwards.
