Morphology Changes of Ganga River over
Time at Varanasi
sabita madhvi singh1,*
1
Research Scholar, Department of Civil Engineering, Institute of Technology,
Banaras Hindu University, Varanasi, India

ABSTRACT
The morphology of a river can be viewed conveniently by
considering its long profile and cross profile. The degrees of
freedom of a river consist of the width, depth, channel slope,
bank slope and geo-morphological condition in the zone where
the river flows. As water flows along the channel of a river, its
long profile will be determined by several factors, which
include geological condition, different hydraulic structure
made in the channel, discharge and velocity. Alluvial rivers are
self-regulatory in that they adjust their characteristics in
response to any change in the environment. An alluvial river is
unconstrained, in the long term, in developing its stable width
to which the depth, slope, velocity, and flow resistance are
closely related. Meandering channels is a vast research field,
spanning a broad variety of time and space scales,
environmental domains, and conceptual and methodological
approaches. The present study has been carried out on the
river Ganga at Varanasi for calculating amount of meandering
in the form of change of sinuosity at two consecutive bends. For
this purpose 10 years of satellite imagery data has been
analysed of the Ganga River using Arc GIS combined with
historical data. The result shows that sinuosity varies from 1.66
to 1.26 and silt deposition of two bends varies from 4.52 to 3.14
and 3.4 to 2.42 respectively.
KEYWORDS
Arc GIS., River Ganga, Morphology, Meandering
INTRODUCTION
A
regime river is a system in dynamic equilibrium, or, to
be more precise, a system in quasi-equilibrium, for
which the sediment transport is balanced by the sediment
supply. The three main types of river patterns are braided,
meandering and straight, although there are rare straight
rivers. As the river precedes downstream the volume
*Corresponding Author: sabita madhvi singh
E-mail: [email protected]
Telephone Number:
Fax. Number:
increases and erosion gains momentum. The planform of
a river depends on both the size of the river and the part of
the fluvial system. The type of planform or pattern is key
interested for geo-morphologist and geologist. The
meandering of river depends on the hydraulics of flow, the
sediment transport and the potential for bank erosion that
closely related to distribution of sediment within the bend
and bed form with the channel. The distinct morphological
characteristic of any river shows that relationships for river
morphology are not continuous and that there exist several
apparent discontinuities between pattern states. The
conditions under which different river patterns and types
occur have been received interest by many scientists and
engineers.
The Ganga River is the longest river in India flowing
from Himalaya to Bay of Bengal and flow almost North
West to South East. The Ganga basin is largest river basin of
India, occupies about 26.3% of the total geographical area of
the country. During its course through plains of Uttar
Pradesh, the river flows in wide belt constantly changing its
course. Meandering of Ganga River observes in this plain
area of Uttar Pradesh from satellite images. Meandering
river channels are dynamic landforms that migrate over
floodplains. The migration of meandering rivers results from
interactions among flow, sediment transport, and channel
form that create complicated sedimentary structures and lead
to the evolution of channel plan form over time (Seminara,
2006). The morphodynamics of meandering river channels
play an important role in sedimentation patterns and
processes (e.g., Nanson and Beach, 1977; Howard, 1992;
Sun et al., 1996; Gilvear et al., 2000), and hydrological and
ecological processes (e.g., Salo et al., 1986; Ward et al.,
2002) in floodplain environments. Interest in the dynamics
of meandering river channels is scientific and includes
concerns related to river engineering and management, such
as flood control, navigation, bank erosion, and the protection
of land and infrastructure. Meandering river processes are
also important in the understanding of the functions of
river–floodplain ecosystem as well as human impacts on
these functions that can degrade water quality, disrupt river–
floodplain connectivity, and diminish aquatic-habitat health
and diversity (e.g., Brookes and Shields, 1996; Piégay et al.,
2005; Gurnell et al., 2006; Kondolf, 2006).
Meandering rivers have drawn considerable attention
from a large group of researchers in various fields, ranging
from fluvial geomorphology (e.g., Leopold and Wolman,
1960) to fluid mechanics and morphodynamics (e.g., Ikeda
et al., 1981); from river engineering (e.g., Jansen et al.,
1979; Elliot, 1984) to petroleum engineering (e.g.,Henriquez
et al., 1990; Swanson, 1993) to landscape ecology and river
restoration. The scope of research also encompasses a broad
range of spatial scales, from the detailed studies off low
properties at the scale of turbulent eddies (e.g., Blanckaert
and de Vriend, 2003) to investigations of the evolution of
meander trains (i.e., series of meander bends) over the entire
length of an alluvial floodplain (e.g., Gautier et al., 2007).
Similarly, studies on river meandering vary in temporal
scale, ranging from the response to a single channel-forming
event (Hooke, 2004) to the evolution of floodplains over
millennia (e.g., Howard, 1992). Although substantive
progress has been made, further research is required to
achieve a comprehensive understanding of the biomorphodynamics governing the evolution of meandering
channels at different scales and in a variety of environmental
domains. Spatial variability in the erosional resistance of
floodplain environments is an important external factor that
influences the dynamics of meandering (Güneralp and
Rhoads, 2011), including the effects of riparian vegetation
(e.g., Perucca et al., 2007), the sedimentology of river
deposits (e.g., Hudson and Kesel, 2000) and the geological
structure of the floodplain landscape (e.g., Nicoll and
Hickin, 2010).
Meandering patterns similar to those of rivers are also
observed in depositional submarine fans at or beyond the
base of the continental slope formed by turbidity currents
(Abreu et al., 2003) and on other planetary environments
(Bray et al., 2007; Howard, 2009). Meandering channels in
submarine and extra-terrestrial environments drew the
attention of the scientific community later than the terrestrial
counterparts. Growing interest in submarine meandering
channels, since the beginning of 21th, century can be
attributed mainly to the increasing availability of extensive
high resolution data produced by new oceanographic
bathymetric mapping technologies.
In the present study, the course of River Ganga at Varanasi
is studied for last 10 years satellite image available in
Google Earth. The picture reveals that the morphology of
the Ganga River has been changed in last few years in terms
of sinuosity and silt deposition. Sinuosity and morphology
are interrelated and it needs attention to study the planform
of a river and its historic change of course.
DESCRIPTION OF STUDY AREA
The Ganga River is the longest river in India. . It is the
longest river in India and flows for around 1,569 miles
(2,525 km) from the Himalayan Mountains to the Bay of
Bengal. The geographical map shown in the Figure 1 shows
the political and morphological state of the River Ganga in
India.
Figure 1a: The River Ganga basin
Figure 1b: The River Ganga with tributaries
The Ganga River emerges from Himalayan mountains
and flow into the Indo-Gangetic plain of Uttar Pradesh,
Bihar and West Bengal end at Bay of Bengal. The study
area Varanasi is located in the middle Ganga valley of North
India, in the Eastern part of the state of Uttar Pradesh, along
the left crescent-shaped bank of the Ganga River. Being
located in the Indo-Gangetic Plains of North India, the land
is very fertile because low level floods in the Ganges
continually replenish the soil. On a local level, Varanasi is
located on a higher ground between rivers Ganga and
Varuna, the mean elevation being 80.71 m.
The Ganges River is extremely important to the people
of India as most of the people living on its banks use it for
daily needs such as bathing and fishing. It is also significant
to Hindus as they consider it their most sacred river. The
hydrologic cycle in the Ganges basin is governed by the
Southwest Monsoon. About 84% of the total rainfall occurs
in the monsoon from June to September. This strong
seasonal variation underlies many problems of land and
water resource development in the region. The seasonality
of flow is so acute it can cause both drought and floods.
The satellite image of the Ganga River upstream and
downstream of Varanasi city is shown in the Figure 2 taking
from Google earth. The outer radius of the Ganga River near
Varanasi is 4925 m and the range of this curvature varies
from 4399m to 4927m. The inner radius of curvature is
around 4393m and its value varies from 3840 m to 4509m.
Some sections of the river are already completely dry.
Around Varanasi the river once had an average depth of 60
metres (200 ft), but in some places it is now only 10 metres
(33 ft).
Figure 2: Satellite image of River Ganga near Varanasi with movements of
meander bend
River meandering
The rate of bank erosion is related to the near-bank flow
velocity and rates of bank migration are related to the
physical processes, such as hydraulic erosion and mass
failure. The natural bank profile and different soil layers in
the profile are interplay between the channel hydrodynamics
that are varying near-bank shear stress–and the spatial
variation of bank properties–expressed through the critical
bank shear stress and the erosion-rate coefficient. The
variability in the bank-erosion associated with bank shear
stress, soil composition, vegetation density and flow
turbulence. Active meandering rivers are some of the most
dynamic and sensitive parts of the landscape. Important
questions remain to be answered relating to mechanisms of
change in dynamic river reaches, the extent to which
changes are propagated both upstream and downstream, and
the timescales and variability of change. These questions are
important because the answers have implications for
understanding river movement at human lifetime scales; for
management of rivers, where these dynamic rivers pose
particular challenges; for habitat management, conservation
and diversity; and for understanding the evolution of river
channels and floodplains.
Analysis of planform changes over historical timescales,
mainly using historical maps has increased enormously
since early applications (Hooke and Kain, 1982), especially
with the developments in GIS (e.g. Gurnell et al., 1994;
Leys and Werritty, 1999). Other studies have examined
changes in short reaches over short timescales, particularly
monitoring changes in bars, processes of bank erosion or
configuration of flow patterns (e.g. Frothingham and
Rhoads, 2003). The specific effects and role of vegetation
and large woody debris in channel change have received
much attention (e.g. Brooks et al., 2003). Many researchers
have examined the morphological impacts of floods (e.g.
Cohen and Brierley, 2000; Heritage et al., 2004) and a few
studies of channel instability have combined timescales.
Much literature is concerned with the impact of land-use
changes, in catchments, mainly through alterations of runoff
and sediment load (e.g. Kondolf et al., 2002) or the
responses to dams (e.g. Shields et al., 2000) or to
channelisation (e.g. Talbot and Lapointe, 2002).
Freely meandering rivers have attracted a great deal of
attention from river scientists and engineers over the last
century. We now know a great deal more about meanderplanform geometry, bend flow, bend-migration dynamics,
and lateral accretion sedimentology than we understood
early last century (Knighton, 1998). That understanding has
come to us in part because of carefully designed but
selective laboratory and field studies of meandering so
structured as to avoid the complicating vagaries of nature
(the special cases). But as a result, however, we still know
relatively little about one of those special cases: that of
confined meanders.
Confined meanders are those that are unable to fully
develop the planform geometry of free meanders because
their lateral migration is constrained by the walls of the
relatively narrow valleys through which they flow. Meander
bends laterally migrate into the valley walls; and the
potentially sinuous channel loops are truncated to form
sharp right-angled bends, producing the distinctively
asymmetric saw tooth array of river bends that are uniquely
associated with meander confinement. Relationships for
river morphology are not continuous and that there exist
several apparent thresholds or discontinuities between
pattern states.
Study on meandering of Ganga River near Varanasi
Main sources of data and evidence on the morphological
changes have been used in the analysis of the spatial
patterns and interactions of change in the meander bends.
The historical evidence of maps and aerial photographs (Fig.
2) are used. These were previously compiled at large-scale,
digitised and analysed quantitatively, enabling detailed
measurements of rate and locations of change and patterns
of evolution of the meanders. Each bend or loop between
points of inflection has been numbered sequentially
downstream and these are used to reference location along
the course (Figure 2). All the bends were previously
classified according to morphology and type of change.
The study area is the river Ganga in Varanasi. The holy river
Ganga is the largest river in India and having the strategic
importance in India. The two bends are selected for analysis
of meandering of river Ganga. Figure 3 shows the study area
with two consecutive bends bend1 and bend 2 respectively.
ecological zones with varying vegetation types, preventing
the use of the same boundary criteria at all sites. Photo
quality and therefore the ability to delineate exposed bars
accurately also vary between photos.
Planform geometry variables such as wavelength, bankfull
width, meander–belt width, sinuosity, and radius of
curvature were measured on the most recent set of aerial
photos for each bend. Bankfull width is measured at
meander inflection points and taken to be the distance across
the channel between vegetation boundaries. The arithmetic
averages of several measurements are used for analysis. To
calculate meander wavelength, a line defining the valley
axis is split at each crossing of the channel centreline. The
length for each line segment is multiplied by 2, and the
average of these calculations is taken to be the meander
wavelength for that study reach. Sinuosity is calculated in
much the same way with the channel centreline split into
segments at each crossing of the cross section. The length of
each segment of the channel centreline is multiplied by 2 to
give equivalence of the channel length over one wavelength
then divided by the average wavelength of the reach; the
arithmetic average of all calculated sinuosity values is used
for analysis. The historical change of the river course with
time is shown in the Figure 4.
Figure 3: Movement of the meander bends of the river Ganga at Varanasi
[2002-2013].
Measurement of planform geometry and migration rate for
the Ganga Rivers in this study is completed through GIS
analysis of historical aerial photography, a technique well
established in the literature (Nanson and Hickin, 1986; Petts,
1989; Gurnell, 1997; Wellmeyer et al., 2005). The number
of time periods examined for each bends of river reach
varies according to the availability of suitable air photos.
Air photo prints were georectified using the georeferencing
tools available in ArcGIS 9.1. The ground control points
(GCPs) used for rectification were either collected through
GPS survey in the field or obtained from topographic maps.
The most recent photography for each study site was
georeferenced using the GCPs.
Measurements of planform geometry were conducted in GIS
using ArcGIS 9.1 software. Channel outlines were digitized
using the water boundary to denote the edge of the channel
because it is clearly defined in the aerial photography.
Although several other studies use the limit of vegetation or
change in vegetation type to denote channel boundaries,
initial overview of the sites indicated that this approach is
difficult to adopt here. The study sites span a large
geographical area and therefore include markedly different
Figure 4: Historical and recent courses of the River Ganga, 1988–2013.
A summary of all environmental, planform geometry and
migration data for the study area of two bends are shown in
Table 1. The sinuosity values and sand deposition are found
from satellite imagery data using Arc GIS.
Table1: Variation of sinuosity and sand deposition from 2002 to
2013.
Sand Deposition (Km2)
Year
Sinuosity
Bend 1
Bend 2
2002
1.66
4.2
2.42
2003
1.62
4.12
3.20
2005
1.51
3.14
2.65
2006
1.49
3.24
2.75
2008
1.40
2.45
2.89
2010
1.34
4.52
3.14
2011
1.30
3.145
2.95
2012
1.28
3.425
2.94
2013
1.26
3.215
2.84
Examination of the pattern of meander migration over
the photo period reveals that the river meanders generally
tend to translate downstream as a package and cutoffs are
relatively uncommon compared to the case of freely
meandering rivers. Bend over tightening commonly
proceeds the generation of a cutoff in meandering rivers,
leading to a decrease in the channel curvature. As this
process appears to be relatively rare on these confined
rivers, the corresponding reduction in l/w and rm/w does not
occur. As the bends migrate downstream, the inflection
points move with the bend and the bend curvature remains
relatively constant. Furthermore, although these confined
meanders have very sharp bends at the point of impingement
on the valley wall, most of each meander is comparatively
open. The comparison of sand deposition in two consecutive
bends is shown in the Figure 5.
landscape denudation, and topographic uplift. The inner and
outer mean radius of curvature of the bend is 4925m and
4393m are respectively in the River Ganga at Varanasi. The
sinuosity in the River Ganga decreases from 1.66 to 1.26 in
last 10 years and sand deposition also changes over time.
This implies that the channel morphology of River is
changing continuously. The erosion and deposition also
depends on the manmade obstruction in the river course
which influence the river dynamic. It is observed from
sinuosity data that sand deposition varies year to year that
may depends on the discharge and flow velocity change due
to climate change. Such changes distort the natural quasiequilibrium of a river; in the process of restoring the
equilibrium, the river will adjust to the new conditions by
changing its slope, roughness, bed material size, crosssectional shape, or meandering pattern.
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