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Lecture-1 Introduction and water resources.pdf

  1.  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.
  2.  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.
  3.  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.
  4.  Four phases: 1) Storage and diversion. 2) Conveyance of irrigation water. 3) Distribution and application of irrigation water. 4) Drainage of excess water.
  5. ➢ 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.
  6.  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
  7.  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.
  8.  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
  9. ❖ 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.
  10.  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.
  11.  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.