The term Drainage describes the river system
of an area.
The area drained by a single river system is
called a drainage basin.
Any elevated area, such as a mountain or an
upland which separates two drainage basins,
is known as a water divide.
A drainage system is the pattern formed by the streams, rivers, and lakes in a particular
drainage basin. They are governed by the topography of the land, whether a particular
region is dominated by hard or soft rocks, and the gradient of the land.
Dendritic drainage systems are the most common form of drainage system. In a
dendritic system, there are many contributing streams (analogous to the twigs of a tree),
which are then joined together into the tributaries of the main river (the branches and the
trunk of the tree, respectively). They develop where the river channel follows the slope of
The geometry of a trellis drainage system is similar to that of a common garden trellis
used to grow vines. As the river flows along a strike valley, smaller tributaries feed into it
from the steep slopes on the sides of mountains. These tributaries enter the main river at
approximately 90 degree angles, causing a trellis-like appearance of the drainage
system. Trellis drainage is characteristic of folded mountains.
Rectangular drainage develops on rocks that are of approximately uniform resistance to
erosion, but which have two directions of jointing at approximately right angles. The joints
are usually less resistant to erosion than the bulk rock so erosion tends to preferentially
open the joints and streams eventually develop along the joints. The result is a stream
system in which streams consist mainly of straight line segments with right angle bends
and tributaries join larger streams at right angles.
In a Radial drainage system, the streams radiate outwards from a central high point.
Volcanos usually display excellent radial drainage. Other geological features on which
radial drainage commonly develops are domes and laccoliths. On these features the
drainage may exhibit a combination of radial and annular patterns.
Nature of flow – Himalayan rivers are Perennial as
receive water from rainfall as well as snow melting.
Catchment area - Very large basins
Erosion - Deep valleys and gorges in the Himalaya
due to intensive erosion
Nature of the course - Meandering course and
shifting beds in the Great plains
Other features - V-shaped valleys, high waterfalls and
Nature of flow - Seasonal dependent on rainfall alone
Catchment area – have shorter and shallower
courses as compared to Himalayan rivers
Erosion - Shallow graded valleys with little erosion
Nature of the course - Straight and linear course.
Other features - Shallow valleys, small waterfalls,
delta and estuaries
The Indus River System –
Rises in Tibet , near Lake Mansarowar, enters India in the Ladakh district of Jammu and
Tributaries in Kashmir are Zaskar, Nubra, Shyok and Hunza. Flows through Baltistan and
Gilgit, emerges from the mountains at Attock.
Satluj, Beas, Ravi, Chenab and Jhelum join together to enter the Indus near Mithnakot in
Pakistan, eventually reaches Arabian sea, east of Karachi.
Total length 2900 km. one of the longest rivers of the world.
Drainage basin covers, states of Jammu and Kashmir, Himachal Pradesh, Punjab and
the rest is in Pakistan.
The Ganga River System –
Bhagirathi is joined by Alaknanda at Devprayag in Uttranchal to form Ganga. At Haridwar
the Ganga emerges from the mountains on to the plains.
Tributaries from the Himalayas – Yamuna, Ghaghara, Gandak and Kosi Himalaya.
Chambal, Betwa and Son come from the Peninsular uplands.
The Ganga flows eastwards till Farakka in West Bengal. This is the northernmost point of
the Ganga delta. The river bifurcates here : Bhagirathi-Hooghly flows southwards.
Mainstream flows southwards into Bangladesh and is joined by the Brahmaputra. Here it is
knows as Meghna, finally flows into the Bay of Bengal before forming the Sunderban delta.
Length of Ganga is 2500 km. The plains from Ambala to Sunderbans is nearly 1800 km but
the fall in the slope is hardly 300 metres, resulting in large meanders.
The Brahmaputra River System –
Rises in Tiber east of Mansarowar lake, flows eastwards
parallel to the Himalayas, reaching Namcha Barwa (7757 m),
it takes a ‘U’ turn and enters India in ArunachalPradesh.
Is called Dihang, joined by Dibang, Lohit, Kenula and many
other tributaries to form the Brahmaputra in Assam.
In India it passes through a region of high rainfall, carries a
large volume of water and considerable amount of silt, has a
braided channel, forms many riverine islands.
During the rainy season, the river overflows its banks, causing
widespread devastation due to floods in Assam and
An estuary is a partly enclosed coastal body of
brackish water with one or more rivers or
streams flowing into it, and with a free
connection to the open sea.
Estuaries form a transition zone between river
environments and ocean environments and
are subject to both marine influences, such as
tides, waves, and the influx of saline water;
and riverine influences, such as flows of fresh
water and sediment. The inflows of both sea
water and fresh water provide high levels of
nutrients in both the water column and
sediment, making estuaries among the most
productive natural habitats in the world
A river delta is a landform that is formed at the
mouth of a river, where the river flows into an
ocean, sea, estuary, lake, or reservoir. Deltas
are formed from the deposition of the
sediment carried by the river as the flow
leaves the mouth of the river. Over long
periods of time, this deposition builds the
characteristic geographic pattern of a river
The Peninsular River –
The main water divide in
Peninsular India is formed by
the Western Ghats.
West flowing river
Narmada and Tapi are the
west flowing rivers of
These rivers make estuaries
at their mouth
These rivers drain into
East flowing river
Mahanadi, Godavari, Krishna
and Kaveri are the east
flowing rivers of peninsular
These rivers make deltas at
These rivers drain into Bay
Drainage basins are
comparatively small in size
The Narmada Basin –
Rises in the Amarkantak hills in Madhya Pradesh, flows west in a rift valley, creates many
‘Marble rocks’, near Jabalpur and the ‘Dhuadhar falls’ are some of the notable ones.
Narmada basin covers parts of Madhya Pradesh and Gujarat.
The Tapi Basin –
Rises in the Satpura ranges, in the Betul district of Madhya Pradesh. Flows in a rift
valley parallel to the Narmada, but it is much shorter in length. Basin covers parts of
Madhya Prdesh, Gujarat and Maharashtra.
The Godavari Basin –
Largest Peninsular river, rises from the slopes of the Western Ghats in the Nashik district
Length about 1500 km, drains into the Bay of Bengal, largest drainage basin amongst
peninsular river, covers parts of Maharashtra, Madhya Pradesh, Orissa and Andhra
Tributaries – Purna, Wardha, Pranhita, Manjra, Wainganga and the Painganga.
Becouse of its length and area it covers, is also known as ‘Dakshin Ganga’.
The Mahanadi Basin –
Rises in the highlands of Chattisgarh
Flows through Orissa to reach Bay of Bengal, length about 860 km.
Drainage basin is shared by Maharashtra, Chhattisgarh, Jharkhand and Orissa.
The Krishna Basin –
Rises from a spring near Mahabaleshwar, flows for about 1400 km, reaches the Bay of
Tributaries – Tungabhadra, Koyana, Ghatprabha, Musi and the Bhima Drainage basin is
shared by Maharashtra, Karnataka and Andhra Pradesh.
The Kaveri Basin –
Rises in the Brahmagri range of the Western Ghats, reaches the Bay of Bengal in south
of Cuddalore, in Tamil Nadu.
Total length is about 760 km, drrains parts of Karnataka, Kerala and Tamil Nadu.
Tributaries are Amravati, Bhavani, Hemavati and Kabini.
Lakes differ from each other in size and characterstics. Most lakes are permanent, some
contain water only during the rainy season, some of the lakes are the result of the action
of glaciers and ice sheets, some are formed by wind, river action and human activities.
Meandering river forms cut-offs that later develop into ox-bow lakes. Spits and bars from
lagoons in the coastal areas, e.g. the Chilika Lake, the Puliket lake, the Kolleru Lake.
Lakes in the region of inland drainage are sometimes seasonal, the Sambhar lake in
Rajasthan is a salt water lake.
Most of the fresh water lakes are in the Himalayan region. They are of glacial origin. The
Wular lake (the largest freshwater lake in India) in Jammu and Kashmir is the result of
tectonic activity. Dal Lake, Bhimtal, Nainital, Loktak and Barapani are some other
important fresh water lakes.
The damming of the rivers for the generation of hydel power has also led to the formation
of Lakes such as Guru Gobind Sagar (Bhakra Nangal Project).
Importance of Lakes –
Helps to regulate the flow of a river, prevents
flooding during heavy rainfall and during the dry
season helps to maintain even flow of water, can
be used for developing hydel power, moderate the
climate of the surroundings, maintain the aquatic
ecosystem, enhance natural beauty, helps develop
tourism and provide recreation.
Role of Rivers in the Economy
Water from the rivers is a basic natural resource
The river banks have attracted settlers from
ancient times, many have developed as big cities
Using rivers for irrigation, navigation, hydro-power
generation is of special significance
The growing domestic, municipal, industrial and
agricultural demand for water from rivers naturally
affects the quality of water. As a result, more and
more water is being drained out of the rivers
reducing their volume. On the other hand, a heavy
load of untreated sewage and industrial effluents
are emptied into the rivers. This affects not only the
quality of water but also the self-cleansing capacity
of the river. But the increasing urbanization and
industrialization do not allow it to happen and the
pollution level of many rivers has been rising.
Concern over rising pollution in our rivers led to the
launching of various action plans to clean the rivers.