geomorphology of ganga basin

2. Content
● Geomorphology of ganga basin
● The ganga basin
● The ganga river
● Climate of the ganga basin
● Neotectonics of the ganga basin
● Geomorpholoogy of the ganga basin
● The upland terrace surface (t2)
● Marginal plain upland surface (mp)
● Megafan surface (f)
● Piedmont fan surface (pf)
● River valley terrace (t1 surface)
● Active floodplain surface (t0 surface)
● Geomorphological evolution of the ganga basin
● Refrence

3. Geomorphology of Ganga Basin
The Indo-Gangetic Basin is the largest alluvial tract in the world. Formed as a consequence of
collision between Indian and Asian plates, the basin evolved with progressive thrust sheet
building in the Himalaya. In response to the temporal thrust sheet loading in the Himalayan
Orogen, the foreland basin has been expanded southwards.
The last major event of basin expansion is considered ~500 ka when the Upper Siwalik
Sediments were raised by more than a kilometre and the basin shifted significantly Southwards.
Geophysical Surveys, deep drilling by ONGC and numerous shallow bore holes of CGWB
revealed that the basement of the Indo-Gangetic Basin is dissected by a number of lineaments,
Faults and structural highs that have controlled the basin fill through time. The basin is filled
with sediments eroded mainly from the Himalayas, though some sediment comes from the
Peninsular India. Similarly major water budget (about 70%) to basin is from the Himalayas and
rest is from craton side. From west to east, the Indo-Gangetic Basin is divisible into Punjab
Rajasthan Plain, Ganga Basin, Bengal Plain and Brahmaputra Plain, respectively.Centrally
located Ganga Basin is bounded by Aravalli-Delhi Ridge in the west to Rajmahal Hills in the
east; from Himalayan foothills in the north to the Bundelkhand-Vindhyan-Hajaribagh Plateau in
the south. It is highly diversified Showing alluvial geomorphic features of various scales formed
in response to climate and tectonic events during late Quaternary. Because of rich fauna and flora
and easy availability of water, the Ganga Basin has been the preferential habitat for the human
since the Stone Age. Large scale human migration took place between 3500-3000 BP, which
produced a pronounced effect on the land topography. Archaeological sites yielding vertebrate
faunal remains and artefacts have been recovered at different places along the River Ganga in
Kanpur, Banda, Jalaun, Allahabad and Varanasi districts of Uttar Pradesh and Bihar. In the
present study, the data is collected from Survey of India toposheets (in 1:50000 scale) and
satellite imageries which has been verified by extensive field checks. This exercise has been
utilized for the demarcation of geomorphic units in the Ganga Basin.
The Ganga Basin
Located between 77’- 88’ E longitudes and 24’- 30’ N latitudes, the Ganga Basin Occupies the
central position of the Indo-Gangetic Foreland Basin System. The Ganga Basin is about 1000 km
long in east-west direction, and 300-500 km wide normal to Himalayan strike in north-south
direction. Rather flat looking Ganga Basin has a gentle southeasterly slope followed by
numerous Himalayan and alluvium fed rivers. The Ganga Plains is densely populated and highly
cultivated. The deepest part of the Ganga Basin in the west is occupied by the Yamuna River.
River Ganga which is the trunk river of the basin before entering into Bay of Bengal forms the
largest Ganga-Brahmaputra delta. In the western Ganga Basin, Yamuna River acts as the axial
river up to Allahabad where it meets Ganga. In the eastern part, Ganga river is the axial river.
The Ganga River in the eastern Ganga Basin makes the water divide between the northern plains
formed of which is Himalayan derived grey coloured mica rich sediments, subgreywacke in
composition and southern plains produced by reddish coloured sediments derived from
Peninsular India, characterized by non-micaceous subarkosic sediments. The Ganga foreland

4. basin was filled by fluvial processes depositing huge sediment loads eroded from Himalayas in
the north and some sediments from peninsular Craton in the south.The sediment fill of the Ganga
Source : State Program Management Group(Namami Gange) Government Of Uttarakhand, Last Updated on 13-07-2021

5. Basin is asymmetric decreasing in thickness from North to south. In the North at foothills near
the piedmont zone the alluvial fill is 3-7 km thick decreasing to about 0.5-1.0 km in the central
part; while in south near the craton it is just a few hundred to tens of metres thick apron
The rivers of northern Ganga Basin carrying Himalayan derived sediments have shifted towards
southern craton over the sediments deposited by rivers draining the craton.
The present geomorphic setup of the Ganga Basin is believed to have evolved under changing
conditions of climate, intra- and extra-basinal tectonics and sea-level induced base-level changes
during Quaternary.River systems of the Ganga Basin responded to these changes and evolved
differentially in time and space.Therefore, the sediments are important repository of Late
Quaternary changes in climate, neotectonics and base-level.
THE GANGA RIVER
Ganga River, about 2225 km long is the trunk river of the Ganga Basin, which emanates from
Gangotri glacier in the Himalayas and passing through vast alluvial plains makes a huge delta
system in the Bay of Bengal and supplies sediment load to the deep sea fan. Ganga gains its
name at Devprayag in the Uttaranchal Himalaya, where Bhagirathi and Alaknanda rivers meet to
form the main channel of this river. It drains a 10,60,000 km basin that covers over 25% of
Indiaís total surface area between Himalayan foothills in the north to Peninsular Craton in the
south (Rao, M.B.R., 1973). From its source to the sea the river is intimately related to civilization
since ancient times. Ganga River all along its length flows through a well-defined valley which is
generally 2-15 km wide. The active Ganga River and its narrow floodplain are incised in the
River Valley Terrace Surface developed within the river valley. Ganga River Valley margin is
well defined and bordered by cliffs of variable heights (8-30 m high). The Valley and the River
Ganga show distinctive changes in morphology, channel characteristics, hydraulic regime
sediment load along its length, and has been divided into seven segments. The region between
Allahabad toBuxar is designated as GRV ñ III. At Allahabad, the Yamuna, the largest tributary,
joins the Ganga on its southern bank and contributes a large volume of water and sediment load
collected mainly from discharge of several rivers of the Indian Peninsula flowing to northeast
direction. From Allahabad downstream, Ganga River becomes the axial river of the Ganga Basin
(Pl. II). Many important tributaries, namely Varuna, Gomti, Ghaghra, Gandak and Kosi from
north and Tons, Son, Punpun, Phalgu and many other rivers join the Ganga from south.

6. In the segment GRV ñ III, river valley is rather narrow, as it flows over the basement high
(Vindhyan
Plateau basement high) (Pl. II). At the beginning, the river flows east up to Chunar, where
basement rocks are exposed. Between Chunar and Buxar, the river flows NE, which is the
direction of basement lineament. The river channel is sinuous shifting from one margin of the
valley to the other. Mostly cliffs are present on both the margins of the valley; but in few areas
cliff is present only on southern side of the valley. The river makes huge point bars. On the River
Valley Terrace Surface, meander scars, ponds and minor channels are present (Pl. IIA).
At Varanasi the Ganga is flowing incised into its narrow valley (1-2 km wide) from south to
north direction (Pl. III). It makes a prominent meander loop with cut side towards Varanasi. On
the opposite side a wide point bar has developed followed by a vertical cliff along the valley
margin on which Ramnagar town is located (Pl. IVA). This cliff extends in NNE-SSW direction
and is partly located along the Ganga River as vertical scarp. At no point River Valley Terrace
Surface has developed.
CLIMATE OF THE GANGA BASIN
The Ganga Basin is located under subtropical humid climate and enjoys the credibility of three
seasons namely, rainy (monsoon) season (June-September/October), cold season

7. (NovemberñFebruary) and hot dry season (March-June). During monsoon season more than 80%
rainfall occurs due to southwest monsoon system. There is a gradual decrease in rainfall from
about 1500 mm in Bay of Bengal to 500 mm in western Uttar Pradesh. In response to rainfall,
river discharges varies from high in the monsoon season to very low in the other seasons.
Therefore, it is only the rainy season when large scale sediment transport occurs in rivers and for
rest of the months river channels become ponded or almost dry without any dynamic fluvial
activity. Through Quaternary times, the climate of the Ganga Basin seems to have had played an
influential role in shaping the morphology and human settlement behaviour in different parts of
the basin.

9. NEOTECTONICS OF THE GANGA BASIN
The Ganga Basin is neotectonically very active and has been quick to respond to Renewed
tectonic activity in the Himalayas, peripheral craton and along its basement Highs and faults
through Quaternary. Additionally some newly formed faults Dissecting the alluvial fill are also
tectonically active. These faults have largely controlled the present day river courses and
thickness of alluvium and the overall geomorphic evolution of the Ganga Basin (Pl. II). The
Ganga Basin is divided into three regions, each characterized by specific tectonic setting and
geomorphic features indicating neotectonic activity.The Piedmont Plain, located adjacent to
Himalayan orogen shows E-W oriented Himalayan Frontal Fault (HFF), upliftment and tilting of
post-Siwalik deposits, conjugate system of strike slip faults in NNE-SSW and NW-SE directions,
linear ridges, undulating topography and incised rivers. The Central Alluvial Plain shows
preferred alignment of river channels with prominent tectonic trends of NW-SE and WNW-ESE .
Kilometre scale warping of the surface is prominent. The Marginal Alluvial plain exhibits
incision of river channels, conjugate set of fractures, bending, updoming tilted blocks, and
triangular facets in the cliff sections. Agarwal and his team argued that orogen part of the Ganga
Plains show contractional tectonics, while the cratonward margin faults and lineaments are
related to the activation of pre-existing lineaments in the cratonic basement. The existing
lineaments have largely controlled the river courses and are often occupied by the river valleys
(Pl. II). At least two tectonic events evidenced by liquefaction and deformation of the alluvial
strata are well documented from Kalpi and Varanasi area and are dated at about 45 ka BP and 7
ka BP respectively.
GEOMORPHOLOOGY OF THE GANGA BASIN
The Ganga Basin shows a number of geomorphic surfaces of regional extent, and Thus, are of
genetic significance (Figs. 2, 3). These surfaces have differences in spatial Distribution,
elevations, nature of sediment character and stratigraphic records. All these geomorphic surfaces
though were formed at different times during Quaternary, Are vertically accreting and have a few
metre thick Holocene sediment cover younger to their age of formation. Broadly Ganga Basin
can be divided into three basic Geomorphic subdivisions namely Piedmont zone at Himalayan
foothills in the north, Vast Central Alluvial Plain in the middle part and Marginal Alluvial Plain
south of Axial river near the Peninsular Craton forming the southern limit of the basin. Piedmont
zone is gravelly and central alluvial plains are sandy made up of Himalayan Derived sands and
sloping to SE whereas, marginal alluvial plains are northward Sloping and sandy but made up of
Craton derived material from south. Recently, based on toposheets in 1:50,000 scale and satellite
imageries in the Ganga Basin, at least six major geomorphic surfaces of regional extent have
been Identified, and based on morphostratigraphy, C14 and OSL dating methods, a relative
Hierarchy and chronological scheme for these geomorphic units have been proposed. A brief
description of all these Geomorphic units is given in the following sections.

10. THE UPLAND TERRACE SURFACE (T2)
The Upland Terrace Surface (T2) of the Ganga Basin is a flat surface with gentle slope (average
slope 5-10 cm/km) to southeast (Figs. 2, 3; Pl. IIA). This surface is often designated as Older
Alluvium (Varanasi Older Alluvium) or Bangar, which is made up of oxidized sediments,
showing evidence of incipient soil formation including calcretization and ferrugenization (Pl.
IVA). It shows a diversified microgeomorphology with areas of centripetal drainage. The Upland
Terrace Surface (T2) is considered to be the oldest formed between 128-74 ka BP, and acts as the
Basement for the deposition of the geomorphic surface. It is an accretionary surface with areas of
net erosion and net eedimentation. Numerous ponds, lakes, creeks, channels and vast sloping
areas with abandoned channel belts are characterictic features of this terrace surface (Pls. II, III).
All the major and minor rivers are deeply incised into this surface with their narrow floodplains.
This surface remains unaffected even by catastrophic floods in these rivers and independent
dynamics of sedimentation. Comprising fine-grained fine sand-silt and clay, the T2 Surface
deposits show strong mottling, extensive development of calcrete and lack reservation of
primary physical structures and organic matter (Pl. II). Sediment transfer and deposition on this
geomorphic surface is mainly by sheet flow processes during monsoon season. The deposits are
interpreted to have formed by interfluve (Doab) sedimentation.
MARGINAL PLAIN UPLAND SURFACE (MP)
Located south of axial river Ganga, the Marginal Plain Upland Surface (MP) is considered time
equivalent to T2 surface. It is made up of sediments derived from peninsular Craton by sheet
flow processes and gradually grades from gravelly deposits near the rocky exposures of craton to
thin sand wedge spreading to north.
The Marginal Plain Upland Surface (MP) shows extensive gulleying and ravine development (Pl.
IVB). It is drained by a few deeply incised rivers flowing to north And northeast. In the cliff
sections of the entrenched rivers mainly silty-sandy sediments Showing extensive development
of calcretes are exposed. Divisible into mottled silt, Interbedded silt and mud, channelized sand,

11. variegated clayey silt and cross-bedded calcretelithogies, the succession represents sedimentation
in sloping topographic depressions; small sandy-gravelly ephemeral channels reworking the
Marginal Plains
MEGAFAN SURFACE (F)
Considered to have formed during middle Late Pleistocene (74-35 Ka BP), the Megafan Surface
(F), resting over the oldest T2 surface, is largely sandy and represents sedimentation under
conditions of higher sediment-water discharge and higher regional slopes than today (Fig. 3)
(Singh, I.B., 1996; Shukla, U.K. et al., 2001). Megafans occupy large areas of the Ganga Basin,
and were deposited by snow fed Major rivers such as Ganga, Kosi, Gandak and Ghaghara rivers,
emanating from the glaciated terrains of the Himalayas. They are large, and marked by low relief
relict features presently being modified by surface processes. The Ganga and Yamuna rivers
formed Ganga Megafan and presently they are deeply incised into the fan deposits. Their valleys
are several tens of kilometre wide (10-20 km) and show development of river Valley Terrace (T1
Surface) into which present active channel and its narrow floodplains are entrenched for 5-10 m
(Fig. 7). On the Megafan Surface, Ganga-Yamuna interfluves (Daob region) shows abandoned
channel belts of varied dimension and morphology. The megafan deposits are represented by
channelized fine to medium grained grey coloured mica rich sands of Himalayan origin and
subordinate representation of gravelly deposits in the proximal and muddy deposits in the distal
parts, respectively (Pl. IVC). The sandy fan deposits are covered by a few metre thick grey to red
coloured muddy deposits formed in abandoned channels and present day sheet flow processes
effectively redistributing the sediments during the rains.
PIEDMONT FAN SURFACE (PF)
Developed adjacent to Himalayan front all along its length from east to west, the piedmont Fan
Surface (PF) considered to have formed around latest Pleistocene-Holocene (25-10 Ka BP) often
overlaps the Megafan Surface and is gravely in nature. Piedmont Fan Surface is 10 km to more
than 50 km wide and shows differential development along its depositional strike. Where ever
the megafan development has not taken place, the PF rests directly over the Upland Terrace
Surface (T2).

12. The Piedmont Surface shows gentle slope gradient decreasing away from the mountain front,
low drainage density and an uneven topography. The gravelly proximal part of the Piedmont
(Bhabar region) exhibits uneven topography with a surface relief of 1ñ2 m (Pl. IVD). The distal
Terai belt is sandy and swampy with low-lying waterlogged conditions and extensive
development of ponds, lakes and abandoned channel belts. The surface processes are
continuously modifying the Piedmont Surface. During the rains, sheet flows become operative
and redistribute the fine-grained sediments across the surface piedmont surface shows a
sub-parallel to radiating drainage pattern with low drainage density. Numerous abandoned
channel belts are present on the fan surfaces. All the active river channels draining the Piedmont
zone are incised into the fan surface for 5 to 15 m exposing vertical cliff sections for tens of
kilometres (Pl. IVD). The river valleys are 80 m to 2 km wide, and show development of distinct
terrace surfaces. They are gravel bed rivers and braided in character. The rivers bring the
sediments from Lesser Himalayan terrain, Siwalik hills and also cannibalize the piedmont
surface. Most of the rivers are ephemeral, and get activated during rainy season. Away from the
mountain front, in Terai, they meet with the water bodies and disappear. At present, these rivers,
however, are not contributing any sediment load to the Piedmont surface, but rather, are filling
up their valleys. Outcrop and bore hole data (from Irrigation Department) reveal that the
piedmont deposits are constituted of gravels with quartzite, mica schist, gneiss, spilitic basalt,
dolomite, silty shale and fine to medium-grained sandstone belonging to Lesser Himalayan and
Siwalik succession. Sand and mud deposits are present in the distal parts of the fan only.
Deposits are mostly channelized, though interbedded mudflow deposits are also common (Pl.
IVD).
RIVER VALLEY TERRACE (T1 SURFACE)
Developed within the broad river valleys which in turn are entrenched into T2 , MP and MF
surfaces, the T1 Surface is believed to have formed during Late Pleistocene (35-25 Ka BP),
under the conditions of high rainfall and sediment input as compared To modern times.
It is also referred to Khadar or Newer Alluvium. The active rivers are incised in to this surface
up to a level of 4-8 m. The surface is seldom flooded by channels overtopping of the active
channels. On surface it shows network of abandoned channels, meander cut-offs, lakes, ponds
and linear sand ridges (Pl. II, III). The T1 surface is characterized by rippled and cross-bedded
silt, sand and lensoid units of silty mud. The sand of T1 Surface is coarser than what is being
carried by the present day rivers like Ganga and others (Pl. IVE).
ACTIVE FLOODPLAIN SURFACE (T0 SURFACE)
The rivers of Ganga Basin (T0 surface) are flowing incised into the T1 surface, and have narrow
valleys (Fig. 3; Pl. IVA-B). This is the youngest geomorphic surface of The Ganga Basin (10 Ka
BP) carved from older surfaces. The rivers show varied channel patterns ranging from
meandering to braided and straight reaches in different parts of the basin. These channels have a
restricted lateral movement within their valleys and their associated floodplains are rather
narrow, a few tens of metres to kilometre wide, which is muddy and used for cultivation of
seasonal crops (Pl. IVE). The rivers carry mainly silt and fine sand forming huge channel bars
and floodplain-levee sequences. The Himalayan rivers carry grey coloured and micaceous silt

13. and fine sands in comparison to rivers originating incartonward side and carry mainly fine to
coarse grained pink coloured sand rich in feldspars and lacking mica content (Pl. X). Since the
last 18,000 years, the incised rivers are aggrading filling up their valleys. Different rivers show
variable valley widths ranging from less than 1 km to more than 20 km. It seems that the major
rivers like Ganga, Yamuna etc., have survived in their valleys for a few thousands to
at least 4,00,000 years and have had faced a number of climatic and neotectonic
turnovers.
GEOMORPHOLOGICAL EVOLUTION OF THE GANGA
BASIN
The Ganga Basin is a peripheral foreland basin where fluvial sedimentation is taking place since
Quaternary. Several well-defined geomorphic surfaces have been identified and considered to
have formed in response to climatic and base-level changes during the late Quaternary (Fig. 3).
The Ganga Basin receives most of its discharge from Indian Summer Monsoon and hence the
geomorphic imprints of this basin are closely associated with the monsoonal strength. All the
geomorphic surfaces are depositional and have a sediment muddy cover younger to the timing of
their formation. The Upland Terrace Surface (T2) and the marginal plain Surface (MP) are the
oldest forming extensive interfluve (Doab) areas, beyond the reachs of the river channel flooding
(Pl. IVA-B). The dominant process of sedimentation on these surfaces is the sheet flow during
monsoon rains. Hundreds of kilometre wide interfluve (Doab) areas, which are beyond the reach
of flooding by major river channels of the basin are vertically accreting by sedimentation in
ponds, lakes, creeks and channels building up mud-dominant successions with specific facies
association, quite distinct from channel related deposits of overbank-floodplain. These interfluve
surfaces are the oldest and rest of the geomorphic elements are developed over them. The Megan
fans (MF) resting over the Upland Terrace Surface (T2) were formed under humid climate and
increased water budget in the rivers coupled with repeated tectonic turnovers in the Himalayas.
The distal parts of the MF surface merge with the T2 surface and presently represent a relict
surface continuously being modified by the surface processes (Fig. 3; Pl. IVC). After the
formation of megafans most of the drainage shows tendency of incision forming broad river
valleys. These river valleys were subsequently filled by river processes forming the River Valley
Terrace (T1 surface) under high rainfall and humid climate. The T1 surface is occasionally
inundated by catastrophic floods in the channels cutting and flowing through this surface
forming T0 surface (Fig. 3; Pl. II, IVE). The evolution of Piedmont Surface seems largely related
to neotectonic activities taking place along various faults of outer Himalaya. It was formed at the
Himalayan foothills by prograding gravelly alluvial fans involving fluvial and debris flow
processes. It is believed that Piedmont Surface developed due to low rainfall and reduced
sediment budget during 25-10 Ka BP. The incision of rivers in the Ganga Basin is primarily
related to climate related base level changes; though at places tectonics seems to have plaid
overwhelming role. Large-scale incision appears to have started in Last Glacial Maxima (LGM)
during 20-18 Ka BP. Rivers were deeply incised due to lowered base level changes. The next
phase of incision started with beginning of Holocene approximately 11-7 Ka BP, which also is a
phase of tectonic instability in the Ganga Basin. It appears that this later phase of channel
incision is essentially related to tectonics, whereas the role of the climate would have been

14. subordinate. Because of incision along the river courses, cliffs of 10-20 (sometimes 25 m) are
exposed laterally for several kilometres. The differentially geomorphic evolution of the Ganga
Basin through Pleistocene-Holocene provided a differential topography comprising raised and
low-lying areas, and flat lying sloping surfaces. This uneven topography of the Ganga Basin has
been judiciously used by man since palaeolithic times.

15. Refrence
Geomorphology of Ganga Basin, January 2016, Uma Kant Shukla. Banaras Hindu University
https://www.researchgate.net/publication/306039512
Source : State Program Management Group(Namami Gange) Government Of Uttarakhand, Last
Updated on 13-07-2021
https://spmguttarakhand.uk.gov.in/pages/display/87-course-of-ganga