CHAPTER -3 INDIA- DRAINAGE SYSTEM (BOOK II )

DRAINAGE SYSTEM

1. Define

Drainage :The flow of water through well-defined channels is known as ‘drainage’

Drainage system :The  network of well defined channels through which water flows  is called a ‘drainage system’.

Catchment area  : A river drains the water collected from a specific area,  is called its ‘catchment area’

Drainage Basin :  An area drained by a river and its tributaries is called a drainage basin

Water divide : . The boundary line separating one drainage basin from the other is known as the water divide

River basins  and Wtaer shed : . The catchments of large rivers are called river basins while those

of small rivulets and rills are often referred to as watersheds.

Watersheds are small in area while the basins cover larger areas.

2. What are the factors affecting the the drainage pattern of an area ?

 The drainage pattern of an area is the outcome of the geological time period, nature and structure of rocks, topography, slope, amount of water flowing and the periodicity of the flow.

3. What are the different drainage patterns formed by the rivers ? Explain

(i) The drainage pattern resembling the branches of a tree is known as “dendritic” the examples

of which are the rivers of northern plain.

(ii) When the rivers originate from a hill and flow in all directions, the drainage pattern is known

as ‘radial’. The rivers originating from the Amarkantak range present a good example of it.

(iii) When the primary tributaries of rivers flow parallel to each other and secondary tributaries

join them at right angles, the pattern is known as ‘trellis’.

(iv) When the rivers discharge their waters from all directions in a lake or depression, the

pattern is known as ‘centripetal’.

4. Classify Indian river system on the basis of discharge of water or orientations to the sea

On the basis of discharge of water (orientations to the sea), it may be grouped into:(i) the Arabian Sea drainage; and (ii) the Bay of Bengal drainage. They are separated from each other through the Delhi ridge, the Aravalis and the Sahyadris

Nearly 77 per cent of the drainage area consisting of the Ganga, the Brahmaputra, the Mahanadi, the Krishna, etc. is oriented towards the Bay of Bengal while 23 per cent comprising the Indus, the Narmada, the Tapi, the Mahi and the Periyar systems discharge their waters in the Arabian Sea.

5. Classify Indian river system on the basis of the size of the watershed,he drainage basins

: (i) Major river basins with more than 20,000 sq. km of catchment area.

It includes 14 drainage basins such as the Ganga, the Brahmaputra, the Krishna, theTapi, the Narmada, the Mahi, the Pennar, the Sabarmati, the Barak, etc.

(ii) Medium river basins with catchment area between 2,000-20,000 sq. km incorporating 44 river basins such as the Kalindi, the Periyar, the Meghna, etc.

 (iii) Minor river basins with catchment area of less than 2,000 sq. km include fairly good number of rivers flowing in the area of low rainfall.

6. Classify Indian river system on the basis of  the mode of origin, nature and characteristics,

Ans :  The Himalayan drainage and the Peninsular drainage.

7.State the characteristic features of the Himalayan drainage  

  1. These are fed both by melting of snow and precipitation,

  2. They  are perennial.

  3. These rivers pass through the giant gorges carved out by the erosional activity carried on simultaneously

      with the uplift of the Himalayas.

   4. Besides deep gorges, these rivers also form V-shaped valleys, rapids and waterfalls in their mountainous

       course.

   5.In the plains, they form depositional features like flat valleys, ox-bow lakes, flood plains, braided       

      channels, and deltas near the river mouth.

6. They also  display a strong meandering tendency and shift their  courses frequently.

8. Which river is known as the sorrow of Bihar and Why ?

River Kosi, is known  as the ‘sorrow of Bihar’, because it causes severe damage to the life and property of the people due to flood.

9.Describe the evolution of the Himalayan Rivers.

Geologists believe that a mighty river called Shiwalik or Indo-Brahma traversed the entire longitudinal extent of the Himalaya from Assam to Punjab and onwards to Sind, and finally discharged into the Gulf of Sind near lower Punjab during the Miocene period some 5-24 million years ago

The remarkable continuity of the Shiwalik and its lacustrine origin and alluvial deposits  consisting of sands, silt, clay, boulders and conglomerates support this viewpoint.

It is opined that in due course of time Indo–Brahma river was dismembered into three main drainage systems: (i) the Indus and its five tributaries in the western part; (ii) the Ganga and its Himalayan tributaries in the central part; and (iii) the stretch of the Brahmaputra in Assam and its Himalayan tributaries in the

eastern part.

The dismemberment was probably due to the Pleistocene upheaval in the western Himalayas, including the uplift of the Potwar Plateau (Delhi Ridge), which acted as the water divide between the Indus and Ganga drainage systems. Likewise, the downthrusting of the Malda gap area between the Rajmahal hills and the Meghalaya plateau during the mid-pleistocene period, diverted the Ganga and the Brahmaputra systems to flow towards the Bay of Bengal

10. What are the probable reasons for the dismemberment of the Indo-Brahm ?

The dismemberment was probably due to  :

1. the Pleistocene upheaval in the western Himalayas, including the uplift of the Potwar Plateau (Delhi Ridge), which acted as the water divide between the Indus and Ganga drainage systems.
2. The downthrusting of the Malda gap area between the Rajmahal hills and the Meghalaya plateau during the mid-pleistocene period, diverted the Ganga and the Brahmaputra systems to flow towards the Bay of Bengal

11. Which are the three main drainage system formed by the dismemberment of Indo-Brahm ?

(i)                  The Indus and its five tributaries in the western part;

(ii)                The Ganga and its Himalayan tributaries in the central part;

(iii)               The stretch of the Brahmaputra in Assam and its Himalayan tributaries in the eastern part.

12  State the characteristic features of the Peninsular rivers

      1. The Peninsular drainage system is older than the Himalayan one.

      2.  They are fed by the rain only.

3. They have broad, largely-graded shallow valleys,
4. They are characterised by fixed course, absence of meanders
5. They are non perennial
6. They do not form deep gorges

13    Name the peninsular rivers flowing westward

River Narmada, River Tapi

14 Which relief feature of the peninsular plateau  forms the waterdivide between the rivers flowing to the Bay of Bengal and the Arabian Sea. ?

Ans : Wester Ghats

15 Descibe the three geological events believed to have been responsible for the evolution of the Peninsular drainage .

Three major geological events in the distant past have shaped the present drainage systems of Peninsular India:

 (i) Subsidence of the western flank of the Peninsula leading to its submergence below the sea during the early tertiary period. Generally, it has disturbed the symmetrical plan of the river on either side of the original watershed.

(ii) Upheaval of the Himalayas when the northern flank of the Peninsular block was subjected to subsidence and the consequent trough faulting. The Narmada and The Tapi flow in trough faults and fill the original

cracks with their detritus materials. Hence,there is a lack of alluvial and deltaic deposits in these rivers.

(iii) Slight tilting of the Peninsular block from northwest to the southeastern direction gave orientation to the

entire drainage system towards the Bay of Bengal

16 Define River Regime

The pattern of flow of water in a river channel over a year is known as its regime.

17 Describe the River regimes of the Himalayan and  the Peninsular rivers.

The north Indian rivers originating from the Himalayas are perennial as they are fed by glaciers through

snow melt and also receive rainfall water during rainy season.

The rivers of South India do not originate from glaciers and their flow pattern witnesses fluctuations.

The flow increases considerably during monsoon rains. Thus, the regime of the rivers of South India is controlled

by rainfall which also varies from one part of the Peninsular plateau to the other.

The discharge is the volume of water flowing in a river measured over time. It is measured either in cusecs (cubic feet per second) or cumecs (cubic metres per second).

The Ganga has its minimum flow during the January-June period. The maximum flow is attained either in August or in September.After September, there is a steady fall in the flow. The river, thus, has a monsoon regime during the rainy season.

There are striking differences in the river regimes in the eastern and the western parts of the Ganga Basin. The Ganga maintains a sizeable flow in the early part of summer due to snow melt before the monsoon rains begin.

The mean maximum discharge of the Ganga at Farakka is about 55,000 cusecs while the mean minimum is only 1,300 cusecs.

The two Peninsular rivers display interesting differences in their regimes compared to the Himalayan rivers. The

Narmada has a very low volume of discharge from January to July but it suddenly rises in August when the maximum flow is attained. The fall in October is as spectacular as the rise in August. The flow of water in the Narmada, as recorded at Garudeshwar, shows that the maximum flow is of the order of 2,300 cusecs, while the minimum flow is only 15 cusecs.

The Godavari has the minimum discharge in May, and the maximum in July-August. After August, there is a sharp fall in water flow although the volume of flow in October and November is higher than that in any of the months from January to May. The mean maximum discharge of the Godavari at Polavaram is 3,200 cusecs while the mean minimum flow is only 50 cusecs..