Water Resources

Important Definations

Tributaries:

A small river or stream join the main river is called a tributary. River Indus receives tributaries from the eastern and western bank. The eastern or left bank tributaries are Jehlum, Chenab, Ravi and Sutlej. From the western or right bank tributaries are river Gomal, river Tochi, river Kabul and river Kurram as its tributaries.

Discharge of a rivers:

The amount of water passing from a specific point of a river all around the year is called discharge of a river.

Irrigation:

There are two board categories of irrigation in Pakistan.

1. Traditional method of irrigation.2. Modern method of irrigation.

Traditional methods:

1. Simple lift irrigation:

It is mostly practiced in the remote and back ward villages of Pakistan. In this method people take out water from a shallow well with the help of a rope and bucket. Through this system formers can irrigate a small piece land, it is a time consuming method of irrigation.

2. Shaduf:(Dhenkli)

In the shaduf system water is drawn from a shallow well, river or canal by a bucket which is attached to a wooden pole on one side and weight (heavy racks) on the other side. A small area can be irrigated by this method. In some of the places people also use a pulley to take water out from a well.

3. Charsa:

In this method animal power is used to pull water from the well. In this method a bucket is suspended by a rope and with the help of animals, people take out water from slightly deep wells.

4. Persian wheel:

This is a system of continuous supply of water and irrigated a comparatively larger area. In this method a blind folded bullock is used to move a horizontal wooden wheel. This wheel is geared to a vertical wheel at the distant end the shaft. This carries the vertical metal attached to a chain of buckets. The buckets raise water from the well and spill their contents into the channels lending to the irrigation field.

5. Karez:

Karez system is practiced only in Baluchistan. Karez is a water tunnel or a narrow underground canal channel. It starts from the base of a hill or mountain where ground water is present. It runs for one or two kilometers before it emerges up the ground. Sometimes this underground water supply runs upto 10 kilometer. Throughout its length, the karez is dotted with vertical shafts which are used to clean and repair the canal in order to prevent any blocking in the flow of water.

6. Tank irrigation:

Tank irrigation is practiced by constructing mud banks across small stream to make a small reservoir which collect excess water during the rainy season. These reservoirs are sometimes covered with plastic and the water is used for irrigation, domestic purpose, livestock etc.

7. Seasonal canals:

These canals are only active during the rainy season. They are mostly in the old flood plains of Punjab and Sindh.

8. Inundated canals:

Long canals taken from large rivers are called inundation canals. They receive water when the river is high enough and especially when it is in floods.

Modern methods

i) Perennial canals:

These canals run throughout the year and are linked to dams and barrages for continuous supply. They irrigate large pieces land.

ii) Tubewell:

These are electrical or diesel powered machines which are used pull water from the depth of 92 meters or more to irrigate large fam lands. These also help in lowering the water table whereby protecting the land from water logging and salinity.

iii) Sprinklers or spray irrigation:

Sprinklers are devising attached to the public water supply. They are centrally located in the field to irrigate / water the plants; mainly in orchard and gardens. It is an efficient

method of irrigation as water is not wasted but at the time it is very expansive. This it is rarely used to irrigate agricultural crops.

iv) Tanker irrigation:

This is the most expensive method of irrigation. Tankers collect water from small water bodies (inland) and supply them to households in case of emergency.

Siltation:

The accumulation of sand and silt in dam reservoirs and canals is called siltation. When the rivers leave the foot hills of mountains they carry a large quantity of silt as result of deep erosion in the mountain areas. This silt is deposited in the dam reservoirs and canals.

Causes of siltation:

1. The foot hills of mountains are mostly made up of sedimentary types of rocks specially the sub- Himalayas. Rivers or stream can easily eroded these areas and deposit sand and silt in the dam reservoir.

2. Due to deforestation and overgrazing the land becomes unconsolidated and easily transported by wind and water to the rivers.

3. Most of the rivers come from the mountains areas. Due to steep slope and narrow channels rivers erode its bank bed. This eroded material is deposited in the dam.

Effects of siltation:

1. Blocked of canals because of silt accumulation.2. Weakens the foundation of dams and dam wall.3. Reduces the capacity of reservoirs. Less flow of water leads to reduction in

generation of H.E.P. it also result in availability of less water for irrigation. 4. Flow of flood water is hampered which may cause heavy damage to the dam

because of the heap of sediment which block the flow of water.

Controlling Method:

1. Encourage reforestation and a forestation specially is the foot hills of mountains.2. Lining of canal.3. Installation of silt trap before the water enters the dams and reservoir.4. Structural measures such as operating the reservoir at lower level during floods

and allowing free flow during low flow season to remove sediments from the reservoir.

Suggest ways to solve water logging and salinity:

o The Government started a lot of projects with the name of SCARPs (Salinity Control and Reclamation Projects) to control water logging and salinity in different areas of Pakistan. These projects are mainly working in Punjab and Sindh.

o They are planting trees around the water logged areas. The roots of trees suck up the water and it is evaporated through the leaves.

o Tubewells are being installed to lower the level of the water table.o With the help of fast flowing water (surface drain) flushing the first layer of soil to

remove salinity.o They are mixing gypsum with the saline soil to reduce the salinity and make the soil

cultivable. o They are lining the unlined canals to prevent what logging and salinity. o They are making canal closures to control the water and reduce the rate of seepage.o They are started desiltation of canal and also cleared the herbs, shrubs and bushes

from canal to increase the flow of water and reduce the rate of seepage.

Reference: Huma Naz Sethi pg. 44Fig. 3.24 pg 43Fig. 3.22 pg 42Pg 41 learns the link canals.