water resources Flashcards
hydrological cycle
Water = natural resource
Water that reaches the ground from the atmosphere may fall as rain, snow or hail which are all included in the term precipitation.
Some of the water runs off the earth surface as rivers & streams draining into lakes and the sea. The rest is either utilized by plants or soaked into the ground
Water is returned to atmosphere as water vapors through evaporation from surface water and by transpiration from plants
As water vapor rises, it cools to form water droplets. This system is called ‘condensation’
This is the hydrological cycle
Most effective source of water in Pakistan are the rivers, esp river Indus and its tributaries.. Rainfall is scanty and its usefulness to farmers is limited, groundwater can only be utilized in areas where water tables are high, however water from rivers is available all year round thus they constitute the most important source of water supply
uses of water
Main uses of water: agricultural, domestic & industrial
Most important use of water in Pak is for agriculture
Present: over 69% of water used for irrigation purposes
Domestic uses of water:
Drinking
Cooking
Washing
Sanitation
Industrial uses of water:
Pharmaceutical industry:
Injections
Syrups
Drips
Chemical industry:
For making:
Acids
Liquid bleach
Solutions
Textile industry:
Washing
Bleaching
Dyeing
Printing
Water supply is one of the most important factors in location industry
Wet point locations (near to sea, lakes, rivers) are preferred for many types of industries
Many heavy industries in pak are located near rivers or close to arabian sea
Amount of water used varies from industry to industry i.e large amount of water is required to produce steel while pharmaceutical industries consume little water
Agricultural uses of water
Irrigation:
Irrigation is the artificial supply of water to the land to encourage plant growth
V important in arid regions but also used in humid regions to improve yields
In Pak 75% of cultivated area is under irrigation
Irrigation system of pak developed from traditional lift irrigation to complex canal system of today
Paks agriculture mainly depends on irrigation
why we need irrigation
most areas of Pak experience arid to semi-arid conditions with aridity incready from north to south
Ineffectiveness of rainfall:
High variability in distribution
Long dry spells
Rainfall in heavy showers increases surface run off
High variability in timings of rainfall
Small number of rainy days
High rate of evapo-transpiration
Low amount of rainfall
Monsoon winds bring most of the rainfall.
These rainfalls are extremely variable in timing and distribution
Rainfall mostly occurs in heavy showers → useless for farmers as the land either absorbs too much or the water drains away too quickly
After rainy season there are long and frequent dry spells
Such conditions demand a well developed irrigation system
Water stored behind dams and accumulates behind barrages on the river Indus and its tributaries to provide it to the crops throughout the year through perennial canals
Tube wells installed in some areas to make use of sub-soil water
Traditional irrigation methods i.e persian wheel, charsa and karez
shaduf system
Water is drawn from a well, river or canal by a bucket which is attached to a pole on one side and a weight on the other
Small area can be irrigated by this method
Shaduf system rarely used today
charsa system
Uses animal power to pull water from a well
Not used by many farmers now
persian wheel
Provides continuous supply of water
Irrigates larger area
Animal powered, turns a horizontal wooden wheel geared to a vertical wheel at the far end of a shaft. This carries a vertical metal wheel which is attached to a chain of pots. These raise water from the well and spill it into a channel that leads to the fields
karez system
Karez = horizontal underground canal in the foothills that brings underground water to the surface
Canal = several kilometers long
Dug by a group of people who then share the water for irrigating their crops
Vertical shafts dug down to the canal so that it can be cleared and repaired to prevent any blockage in the flow of water
This is an old system practiced only is Balochistan where water is scarce and rate of evaporation is high
By building the canal, evaporation losses are minimized
Inundation of canals
Long canals taken off from large rivers
Receive water when the river is high enough esp when it is in flood
diversion channels
Diversion channel is a narrow inundation canal
Common in highland areas, esp in northern mountains, where they divert river water often high up on valley sides, to small terraced fields.
tank irrigation
Practiced by constructing mud banks across small streams to make a small reservoir which collects excess water during rainy season
uses and effectiveness of conventional methods of irrigation
Have been used for centuries
Small-scale subsistence farms still use the charsa or persian wheel
Large farms = shift from conventional to modern methods
Disadvantages of conventional methods:
Irrigated limited areas as only a small amount of water can be obtained
Require manual labor or animals and are more time consuming
Difficult to build, maintain and use (i.e Karez)
Inundation canals only flow during rainy period or when water from melting snow and ice enters the rivers
modern systems
Perennial canals:
Linked to dams and barrages to provide water throughout the year
Irrigate a vast area
Extensively used in Pak
Initial cost is high but water is made available throughout the year
Schemes may provide for flood control and HEP development
Tube wells:
Are diesel or electrically operated pumps that can raise water from depths of 92 metres (300 ft) or more to irrigate farms of more than 1000 hectares
Help to lower the water table, protecting the land from waterlogging and salinity
Some modern tubes = solar powered
Indus Water Treaty
1947: with creation of Pak, province of Punjab was divided into east and west Punjab
Headworks of the canals of Sutlej and Rav remained in India as the share of India while the drained areas became part of Pak.
1948: India threatened to stop the water supply from these headworks, which would have endangered the prosperity of the Indus plain
Water dispute eventually resolved through the mediation of the world bank
Sept 1960: an agreement known as the “indus water treaty” was signed
Under this treaty: Pak received exclusive rights to the water of the three western rivers (Indus, Jhelum, Chenab) and India to that of the eastern rivers (Ravi, Beas, Sutlej).
During transitional period till 1973 India agreed to supply water to Pak
During transitional period Pak was expected to construct two storage dams, five barrages, one gated syphon and eight link canals
Construction cost was to be met by Australia, Canada, USA, UK, West Germany & New zealand
India was also expected to pay some of the cost
Remaining expenditure was to be met by Pak
WAPDA (water and power development authority) of Pak entrusted to supervise the projects
dams, barrages and link canals
Dams
Mangla dam
Tarbela dam
Barrages
Chashma barrage
Rasul barrage
Maraia barrage
Qadirabad barrage
Link canals
Marala - ravi
Rasul - qadirabad
Qadirabad - balloki
Balloki - Sulaimanki 1
Balloki - Sulaimanki 2
Mangla dam
Located on river jhelum
One of the longest earth-filled dams in the world (3100m at crest)
Multipurpose project designed to:
Control and conserve flood waters of Jhelum for irrigation
Generate hydroelectric power
Mangla lake:
Serves as a reservoir of the dam
Developed as a fishing centre and tourist resort
