Author: Explains

The Peninsular Drainage:

The Peninsular drainage system is older than the Himalayan one. This is evident from the broad, largely-graded shallow valleys, and the maturity of the rivers.

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

• 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 and left just the upper parts of west flowing rivers above the sea level.
• 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.
• Slight tilting of the Peninsular block from north-west to the southeastern direction gave orientation to the entire drainage system towards the Bay of Bengal during the same period.

River-Systems:

The peninsular river system can be categorised into the following sections:

• The East flowing rivers – the Mahanadi, the Godavari, the Krishna and the Cauvery flow eastwards and drain into the Bay of Bengal. These rivers make deltas at their mouths.
• The West flowing rivers:
  • Narmada and Tapi along with other small rivers originating from the Western Ghats and falling in the Arabian Sea form estuaries in place of deltas. This is due to the fact that these rivers, especially Narmada and Tapi, flow through hard rocks and are not able to form distributaries before they enter the sea.
  • Although these west flowing rivers of Sahyadri form only about 3% of the areal extent of basins of India, they contain about 18% of the country’s water resources.

Wondering what is the difference between a delta and an estuary? Let’s see:

• The Western Ghats running close to the western coast act as a water divide between the major Peninsular Rivers discharging their water in the Bay of Bengal and the small rivulets joining the Arabian Sea.
• The Chambal, the Sind, the Betwa, the Ken, the Son, originating in the northern part of the Peninsula belong to the Ganga river system.
• The Peninsular rivers are characterized by fixed courses, absence of meanders and non-perennial flow of water. The Narmada and the Tapi which flow through the rift valley are, however, exceptions.

A brief account of the major Peninsular river systems is given below:

Smaller rivers flowing Towards the West:

The rivers flowing towards the Arabian Sea have short courses ( Because their origins lie closer to the sea, and the Western Ghats act as a water divide). Several of these small rivers are important for the production of hydroelectricity because of steep slopes and waterfalls.

Gujarat:

• The Shetruniji – It rises near Dalkahwa in Amreli district.
• The Bhadra – It originates near Aniali village in Rajkot district.
• The Dhadhar rises near Ghantar village in Panchmahal district.
• Sabarmati
• Mahi

Maharashtra:

• The Vaitarna rises from the Trimbak hills in Nasik district
• The Kalinadi rises from Belgaum district and falls in the Karwar Bay.
• The source of Bedti river lies in Hubli Dharwar and traverses a course of 161 km.
• The Sharavati is another important river in Karnataka flowing towards the west. The Sharavati originates in Shimoga district of Karnataka and drains a catchment area of 2,209 sq. km. The famous Jog or Gersoppa Falls (289m) made by Sharavati river are the highest untiered waterfalls in India.

Goa:

• Mandovi
• Juari

Kerala:

• Bharathapuzha – It is the largest river of Kerala. It is also known as Ponnani. It originates from Annamalai hills and flows into the Arabian Sea at a place called Ponnani.
• The Periyar – It is the longest and the second largest river of Kerala. [Largeness of a river is related to its basin size and the volume of water flowing in the river. At the same time when we say that a river is the longest, it means that we are referring to its geographical length]
• The Pamba river – It falls in the Vembanad lake.

Small Rivers Flowing towards the East:

There are small rivers which join the Bay of Bengal, though small, these are important in their own right.

• The Subarnrekha
• the Baitarni
• the Brahmani
• the Vamsadhara
• the Penner
• the Palar
• the Vaigai

The Ganga River System

• The Ganga river system is the largest in India having a number of perennial and non-perennial rivers originating in the Himalayas in the north and the Peninsula in the south, respectively. It accounts for 26.3% of the geographical area of the country and is shared by ten states.
• Ambala is located on the water divide between Indus and Ganga.
• Origin: It rises in the Gangotri glacier near Gaumukh in the Uttarkashi district of Uttaranchal. Here, it is known as the Bhagirathi. At Devprayag, the Bhagirathi meets the Alaknanda; hereafter, it is known as the Ganga.

• The river-course:
  • The Ganga enters the plains at Haridwar.
  • From here, it flows first to the south, then to the south-east direction to reach Allahabad. Here it is joined by the Yamuna.
  • Further, near Rajmahal hills, Ganga turns south-east and bifurcates at Farakka into Bhagirathi – Hugli in West Bengal and as the Padma in Bangladesh.
  • The river finally discharges itself into the Bay of Bengal near the Sagar Island.

• Important left bank tributaries of the Ganga:
  • Ramganga
  • Gomati
  • Ghaghara
  • Gandak
  • Kosi
  • Mahananda
• Important right bank tributaries of the Ganga:
  • Son
  • Yamuna

Some important tributaries and their characteristic features:

The Brahmaputra River System:

• Origin: The Brahmaputra has its origin in the Chemayungdung glacier of the Kailash range near the Mansarovar lake. Mariam La separates the source of the Brahmaputra from the Manasarovar Lake.
• The river-course:
  • Most of the course of the Brahmaputra lies in Tibet, popularly known as Tsangpo. It flows eastwards parallel to the Himalayas. It receives a large number of tributaries in Tibet. The first major tributary is the Raga Tsangpo meeting the Tsangpo near Lhatse Dzong.
  • After reaching Namcha Barwa, it takes a “U” turn (also known as Hair Pin turn) and enters India west of Sadiya town in Arunachal Pradesh through the deep Dihang or Siang gorge of Himalayas. Here initially it is called as Siang and then as Dihang.
  • It is joined by Dibang, Lohit, Kenula and many other tributaries and finally forms the Brahmaputra in Assam.
  • It then enters into Bangladesh near Dhubri and flows southward. In Bangladesh, the Tista joins it on its right bank from where the river is known as the Jamuna. [Note: The Tista was a tributary of the Ganga prior to the floods of 1787 after which it diverted its course eastwards to join the Brahmaputra.]
  • The Jamuna and Ganga confluence at Goalundo and afterwards are called as the Padma. Further south, Padma is joined by Meghna (Barak river in India) and thence onward it is known as Meghna to finally merge in the Bay of Bengal.
• It is called:
  • The Tsangpo in Tibet ( Tsangpo = ‘the purifier.’)
  • The Brahmaputra in India
  • The Jamuna in Bangladesh
• Major left bank tributaries:
  • Burhi Dihing,
  • Dhansari (South)
  • Kalang
• Major right bank tributaries:
  • Subansiri ( It has its origin in Tibet and is an antecedent river.)
  • Kameng
  • Manas
  • Sankosh
• Characteristic Features:
  • River Brahmaputra is a little longer than the river Indus.
  • It forms a spectacular Grand Canyon – like canyon in Tibet.
  • The river is nearly 16 km wide at Dibrugarh and forms many islands, the most important of which is Majuli. Majuli is the world’s largest riverine island and India’s first island district.
  • The Brahmaputra has a braided channel. It carries a lot of silt and there is excessive meandering.
  • The Brahmaputra is well-known for floods, channel shifting and bank erosion. This is due to the fact that most of its tributaries are large, and bring large quantity of sediments owing to heavy rainfall in its catchment area.

The Indian Drainage System

The Indian drainage system consists of a large number of small and big rivers.

It is an outcome of:

• The evolutionary process of the three major physiographic units
• The nature and characteristics of precipitation.

Classification of Drainage Systems in India:

1. On the basis of discharge of water – the Arabian Sea drainage and the Bay of Bengal drainage:

On the basis of discharge of water (orientations to the sea), the drainage system of India may be grouped into:

• the Arabian Sea drainage
• the Bay of Bengal drainage

They are separated from each other by the Delhi ridge, the Aravalis and the Sahyadris (water divide is shown by a line in the following map).

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

1. Rivers of the inland drainage basin (endorheic basin): When a river does not reach the sea but disappears into the sand, such a region is called an area of inland drainage. Inland drainage streams are ephemeral streams (short-lived). E.g.:

• The Ghaggar river in Haryana, which is supposed to be remnant of the proverbial ancient Saraswati river, gets lost in dry sands near Hanumangarh in Rajasthan.
• The Luni river in Rajasthan originates near Ajmer and after flowing through Thar desert gets lost in the Rann of Kutch.
• The Aksai Chin region in Ladakh too has some inland drainage.

2. On the basis of the size of the watershed:

• 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, the Tapi, the Narmada, the Mahi, the Pennar, the Sabarmati, the Barak, etc.
• 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.
• Minor river basins – with catchment area of less than 2,000 sq. Km, these include 55 river basins.

3. On the basis of the mode of origin, nature and characteristics:

• The Himalayan drainage, and
• The Peninsular drainage.

There is no clear-cut line of demarcation between these two drainage systems, as many of the peninsular rivers like the Chambal, Betwa, Sind, Ken and Son are much older in age and origin than the Himalayan rivers.

Let’s follow this line of classification and look at the drainage system of India in detail. We begin with the Himalayan drainage.

The Himalayan Drainage system:

• It consists of the rivers originating in the Himalayan and trans-Himalayan region. It further consists of three river systems namely:
  • the Ganga,
  • the Indus, and
  • the Brahmaputra river systems.
• Since these are fed both by the melting of snow and precipitation, rivers of this system are perennial.
• The various geographical features made by the Himalayan rivers are:
  • In upper reaches (Youthful stage): Gorges, V-shaped valleys, rapids, waterfalls, truncated spurs etc.
  • In plain areas or middle part (Mature stage): While entering the plains, they form depositional features like flat valleys, ox-bow lakes, flood plains, braided channels, and deltas near the river mouth. Over the plains, they display a strong meandering tendency and shift their courses frequently.

Evolution of the Himalayan Drainage System:

There is a difference of opinion about the evolution of the Himalayan Rivers. However, geologists believe that:

1. 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.

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

2. It is opined that in due course of time Indo–Brahma river was dismembered into three main drainage systems:

• the Indus and its five tributaries in the western part;
• the Ganga and its Himalayan tributaries in the central part; and
• 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.

Let’s take up the three major river systems of the Himalayan drainage individually:

1. The Indus River System

• It is one of the largest river basins of the world. A little over one-third of the Indus basin is located in India; in the states of Jammu & Kashmir, Himachal Pradesh and Punjab. The rest of the portion is in Pakistan.
• The Indus also known as the Sindhu, is the westernmost of the Himalayan rivers in India.
• Origin: It originates from a glacier near Bokhar Chu in the Kailash Mountain range (Tibetan region). In Tibet, it is known as ‘Singi Khamban; or Lion’s mouth.
• The river-course:
  • The Indus cuts through Himalayas and enters India near Damchok.
  • flows in India only through the Leh district in Jammu and Kashmir.
  • It enters into Pakistan near Chillar in the Dardistan region through a deep gorge near the hair-pin bend of Nanga Parbat.
  • It finally discharges into the Arabian Sea, east of Karachi.
• The right-bank tributaries of Indus:
  • Shyok
  • Gilgit
  • Hunza
  • Nubra
  • Kabul
  • Khurram
  • Tochi
  • Gomal
  • Sangar
  • Kunar
• The left-bank tributaries of Indus:
  • Zaskar
  • ‘Panjnad’ joins Indus a little above Mithankot). The Panjnad is the name given to the five rivers of Punjab, namely:
    • Satluj
    • Beas
    • Ravi
    • Chenab
    • Jhelum
  • Chief Characteristics:
    • The Indus drains the largest number of glaciers of Himalayas, Ladakh, Zaskar, and Kailash.
    • The Indus plain has a very gentle slope.

Let’s look at some important tributaries of Indus:

The Indus water treaty: The waters of the Indus river system are shared by India and Pakistan according to the Indus Water Treaty signed between the two countries on 19th September 1960. According to this treaty, India can utilise only 20 percent of its total discharge of water. The Indus water treaty was recently in news. Remember why? Read here!