Geomorphological Manifestations of the Flood Hazard: A
Remote Sensing Based Approach
Vikrant Jain and R. Sinha
Engineering Geosciences Group, Department of Civil Engineering,
Indian Institute of Technology Kanpur, Kanpur - 208 016, India
Flood hazard is one of the most severe problems in the Himalayan river basins. Although floods are essentially
hydrological phenomenon, the uneven distribution of floods in the river basin highlights the control of geomorphological
and geological factors. A proper understanding of these factors is critical for a successful flood management
programme. Remote sensing data is of immense value in evaluating the geomorphological and geological controls in
flooding. The present paper highlights the control of geomorphology and neotectonics on flood hazard in north Bihar
Plains, eastern India. The Indian Remote Sensing (IRS) data has been used and a variety of image processing
techniques have been employed.
Introduction draining the interfan area between the Gandak and Kosi
megafans in north Bihar alluvial plains, eastern India (Fig.
The Indo-Gangetic Plains are drained by some of the 1). The total basin area of the river system is about 8848 km2.
largest river systems in the world. These plains are also Flooding in the Baghmati River basin is a regular
severely affected by frequently occurring disastrous floods
and are presently regarded as the worst flood affected region
in the world (Agarwal and Narain, 1996). Almost every
year, monsoon floods in the Indo-Gangetic Plains cause
countless misery to the inhabitants living on the floodplains.
The plains of north Bihar in eastern India have recorded the
highest number of floods in India in the last 30 years (Kale,
1997). In the last 5 decades, the flood management programs
on the rivers of Indo-Gangetic Plains have largely failed.
The available data suggest that during 1954-1990, more than
2700 billions of rupees were spent on the flood control
measures in India, but the annual flood damage increased
nearly 40 times and annual flood affected area increased 1.5
times in this period (Agarwal and Narain, 1996). These data
emphasize the need for a better understanding of the flood
hazard in these plains. The advent of satellite remote sensing
data has facilitated a fuller appreciation of geomorphological
and geological factors of floods apart from hydrological
understanding available from meteorological and
hydrological data. This paper demonstrates the use of satellite
remote sensing data for assessment of flood hazard in the
Baghmati river basin of north Bihar plains in eastern India
and, coupled with hydrological data and field observations,
provides some understanding of causative factors of flooding.
Study Area Description
The Baghmati River is a foothills-fed river (Sinha & Figure 1 Location map of the Baghmati River basin alongwith major
Friend, 1994) originating in Kathmandu area in Nepal and sub-surface faults (after GSI, 2000) .
Geocarto International, Vol. 18, No. 4, December 2003 E-mail: email@example.com 51
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phenomenon, inundating about 2370 km2 of area in the plains
(GFCC, 1991), and is responsible for extensive damage to lives
and property every year. Annual variation in flood hazard is quite
variable and unpredictable; however 5-yr average flood shows a
sharp increase from 1969 to 1973 (Fig. 2). Further, it is interesting
to note that the flood affected regions are not uniformly distributed
over the entire basin bur are localized to certain pockets (GFCC,
1991), which points to the control of geomorphological factors on
On the basis of the gravity data, seismic surveys and deep
drilling data from, some basement faults transverse to the Himalayan
faults have been demarcated in the Gangetic Plains by various
workers (Sastri, et al. 1971; Rao, 1973; Karunakaran and Rao,
1976; Valdiya, 1976; Agrawal, 1977; Dasgupta, et al., 1987;
Dasgupta, 1993, GSI, 2000). In the north Bihar region, the important
faults are Sitamarhi Fault (SF), West Patna Fault (WPF), East
Patna Fault (EPF) and the Monghyr-Saharsa Ridge Fault (MSRF)
(Fig. 1). The occurrence of recent earthquakes (1934, 1988) in this
region demonstrates that these faults are active and responsible for
neotectonic activity in the basin (Banghar, 1991). Several remote
sensing, hydrological and channel morphological evidences in the
Baghmati River basin also suggest that this basin is affected by
neotectonic activity (Jain, 2001).
A number of NE-SW and NW-SE trending faults have been
mapped in the Baghmati basin (GSI, 2000) (Fig.1). In the upstream
region, the area around Sheohar and Sitamarhi is uplifting, but due
to difference in the vertical movements along the SF and WPF, this
area is tilting in south-east direction. In the midstream region, the
area in between the WPF and EPF is tilting in NW direction due to
uplift along EPF but subsidence along WPF. In the downstream
region, the area in between EPF and MSRF falls in a graben area
i.e. it is subsiding. Vertical movements along these faults have
significantly affected the fluvial processes in general and flood
hazard in particular (discussed later).
Data used and approach
Hydrological data for two stations namely, Dhengbridge (u/s)
and Hayaghat (d/s) along the Baghmati River (see Fig. 1 for
location) are available from Center Water Commission (CWC)
and Ganga Flood Control Commission (GFCC), Government of
India. Discharge data is available for 20 years (1970-1989) for
upstream station and for 34 years (1956-89) for downstream station,
whereas the sediment load data is available for a period of 11 years
(1979-1989) for upstream station and 29 years (1961-1989) for
downstream station. Geomorphological study has been carried out
with the help of remote sensing data of IRS LISS II for 1989 and
2000 period (22-49B1, 22-49B2, 21-49A1, 21-49A2), topographic
sheets pertaining to the Baghmati River of 1:250,000 scale (72E,
72F, 72G and 72K) 1924 and 1986 and the corresponding toposheets
of 1:50,000 scale. The major emphasis of the remote sensing data
analysis has been to extract geomorphologic information through Figure 2 Flood damage trend in Baghmati River basin (a) Area
various image-processing techniques. affected due to flooding (b) population affected due to
Flood-prone windows in the Baghmati River basin lie in different flooding, (c) total flood damage in the basin area. Even
after implementation of several remedial measures, the
satellite images acquired during different passes of the satellite. As flood problem in the Baghmati River basin has not
a pre-processing step, these images were normalized through reduced in comparison to 1960s (Source: Ganga Flood
minimizing radiometric-striping effects (Malleswaran Rao and Control Commission, Patna).
Dookahatala, 1983). The right image was normalized with additional points and the root mean square error was obtained
respect to the left image using the equation, as 1.34 m. For a total height difference of 46 meters (from 94
meters to 48 meters) in the basin area, it gives an error of 3%.
g0′ = g0 ⋅ σ √σr + (ml - mr ⋅ σ √σr) (1) The DEM of the Baghmati River basin after density
slicing is shown in the Figure 4, which clearly depicts the
changes in basin slope from upstream to downstream. In
g′0 - normalized right image pixel grey value
general, the upstream basin area shows a regional slope in S
g0 = the right image input pixel grey value
direction with relatively steep gradient, whereas downstream
σl - standard deviation of the entire left image
basin area is characterised by SE slope. The overlaying of
σr - standard deviation of the entire right image
the Baghmati stream on the DEM indicates the relationship
ml - mean value of entire left image
between slope and the river flow direction. Barring a few
mr - mean value of the entire right image
exceptions, the channel follows the basin topography.
For normalization, the upper-left scene (22-49B1) was
taken as the base image for both 1989 and 2000 data and all Channel Morphology and Hydrology
the other images were normalized with respect to this image.
After normalization, the images were registered with respect The Baghmati basin falls in the interfan area bounded by
to the 1:250,000 scale toposheets of 1986 and were glued to the Gandak megafan in west and Kosi megafan in east. This
get a nearly complete basin of the Baghmati river (Fig. 3). interfan area is characterised by slightly concave at the
The present study has made use of band 4 (infrared) edges and gentler floodplain gradient (10 cm/yr) (Geddes,
image, standard False Colour Composite (FCC) and FCC 1960). The channel slope is also gentle in the alluvial plain
generated from Principal Component (PC) bands. The area and ranges from 53 cm/km to 11 cm/km from
standard (FCC) was prepared by assigning band 2, 3 and 4 Dhengbridge to Hayaghat (GFCC, 1991). Channel shifting
images to blue, green and red respectively and using linear is an important geomorphological process in the basin area
with saturation (2.5%) stretching. The PCA images of (Sinha, 1996) and detailed analysis of fluvial dynamics of
Baghmati River basin were generated using the multi spectral the Baghmati River using multi-date topographic sheets and
band 1, 2, 3 and 4 and a composite of PC-images was satellite images has indicated several major and minor
prepared by assigning the PC-1, PC-2 and PC-3 on red, avulsion events on a decadal scale (Jain & Sinha, 2003a, in
green and blue respectively. This PCA colour composite press). A summary of channel migration history for the
provides a better visualization of drainage network, period 1924-2000 shown in Figure 5 suggests eastward
abandoned channels and high moisture area. shifting of the river, which has also shifted the flood hazard
The alluvial plains of the Baghmati River have very low in the river basin from west to east. However, the enormity
relief and gentle slope. Therefore, the topographic contours of flood is not same all along the present course of the river
are not available on the toposheets of this region. A Digital and only few localities are severely affected.
Elevation Model (DEM) was prepared for the Baghmati Table 1 presents a summary of bankfull discharge, most
basin using 109 elevation points; following weighted-average probable flood, mean annual flood and 50-yr return period
technique. The height of each cell was determined by the flood for the Baghmati River based on flood frequency
average of 6 nearest control points of known height. The analysis. Higher values of the most probable flood and the
accuracy analysis was carried out with elevation data from 15 mean probable flood than the bankfull discharge indicate
Table 1 Discharge characteristics of Baghmati River
Station Probability Bankfull Maximum Most Mean 50-yr return
Distribution discharge Observed Discharge probable flood Annual flood period flood
(T=1.58 yrs) (T=2.33 yrs)
(m3/sec) (m3/sec) (m3/sec) (m3/sec) (m3/sec)
Dhengbridge Gumbel’s 1100 3033 1155 1473 3298
Log Pearson- 1334 1334 3048
Log-Normal 1342 1342 2986
Hayaghat Gumbel’s 870 2617 834 1076 2606
Log Pearson- 956 956 2460
Log-Normal 948 948 2525
that the river is flooded almost every year. Further, the peak Benibad to Hayaghat (all marked on the satellite image, Fig.
discharge of Baghmati River is quite variable and 3) and Badlaghat (outside the view of the satellite image,
unpredictable and ranges from 600 m3/sec to 3300 m3/sec shown in Fig. 1). These windows have been selected for
(Sinha and Jain, 1998). The Baghmati River also carries a detailed study following the reports of the Ganga Flood
significant sediment load, which varies from 10.4 million Control Commission (GFCC, 1991), our hydrological
tonnes/yr at upstream station (Dhengbridge) to 7.21 million modeling (Jain and Sinha, 2003 b) and repeated field visits.
tonnes/yr at downstream station (Hayaghat) (Table 2). Most A detailed description of flooding behaviour in these windows
of the coarser sediment load comes from upstream hilly and our understanding of the causative factors are presented
catchment area during the monsoon period but a major next.
fraction of the wash load is picked up by the river in the
plains itself (Jain, 2001). Due to flat gradient and less stream Window 1: Area Upstream of Bairgania Town
power (Table 2), extensive deposition occurs in the alluvial The left bank of the Lalbakeya River and the right bank of
plains area. The variation in total sediment load between the Baghmati River in the Indian territory spill frequently
upstream and downstream stations indicates deposition of during monsoon season upto Bairgania town (Fig. 6a), even
large amount of sediment load (≈ 3 mt/yr) in the midstream though both these rivers are embanked all along. Hydrological
basin area. data of the Baghmati River suggests that at Dhengbridge, the
mean annual flood discharge (1473 m /sec) is higher than
Window-wise Study of Flood Prone Area the bankfull discharge (1100 m /sec), which clearly explains
the frequent overspilling in the region. The satellite image of
Major flood-prone windows in the Baghmati river basin
include the areas around Bairgania, Sheohar, Katra, and
Figure 4 Digital Elevation Model (DEM) of the Baghmati River basin
prepared from point elevation data recorded from the toposheets.
The relief of this alluvial plain of Baghmati River basin varies
from 48 m to 94 m and the regional slope is in the S (in
upstream region) to SE (in downstream region) direction. Each
Figure 3 The Baghmati river basin as seen on satellite image (IRS LISS height range shown in the legend is further sub-divided into 8
II, band 4) of February 1989. Boxed area are flood-prone sub-classes with an interval of 2 m and is shown as different
windows (see text for details). shades.
Table 2 Sediment transport characteristics of the Baghmati River window draped over DEM (Fig. 6b) illustrates the
topographic influence on flooding. The area in
Station Bankfull Channel Stream Annual Sediment
between the Baghmati River and Lalbakeya River
discharge Slope Power Sediment load yield
3 -2 is clearly low-lying and this induces overspilling
(m /sec.) (cm/km) (Wm ) (MT/yr) (T/km2/yr)
along the left bank of Lalbakeya River and right
Dhengbridge 1100 53 12.98 10.407 2745 bank of Baghmati River. The Bairgania town
Runisaidpur 300 18 6.54 - - lying in the Lalbakeya-Baghmati interfluve region
Benibad 350 15 7.25 - - is therefore flooded frequently.
Hayaghat 870 11 6.36 7.21 854
Window 2: Area in and around Sheohar District
The area around Sheohar district falls within
the anabranched reach of the Baghmati river (Fig.
1) and is known for extensive flooding almost
every year. The standard FCC of the area (Fig. 7a)
shows white coloured patches of channel sand
vouching for extensive overbank spilling in the
area. Presently, the right anabranch of the channel
lies abandoned (Fig. 7b) due to silting in the
upstream region, but is activated during the
monsoon period. Silting in the channel has reduced
the bankfull channel capacity, and therefore, this
channel is unable to carry increased discharges
during the monsoon. Further, the drape of the
satellite image over DEM (Fig. 7c) clearly depicts
that the floodplain slope is towards SE, which
accentuates the flooding effect in the area around
Sheohar. The FCC of the principal component
bands 3, 2, and 1 shows several other abandoned
channels as well (in blue) (Fig. 7b). Most of these
abandoned channels overspill during the monsoon
period and flood the adjoining areas, marked by
sandy patches on the satellite image. A photograph
of this area taken in September 1999 shows the
expanse of standing flood water (Fig. 7d) more
than a month later than peak monsoon.
Window 3: Area in and around Katra Town
This area in between the Lakhandei and
Baghmati rivers, shown in Fig. 8a, is one of the
worst flood affected regions in the Baghmati basin.
The Baghmati and Lakhandei rivers flow parallel
to each other for almost 13 kms separated by only
2-3 kms before finally meeting at Katra. During
monsoon season both the rivers carry very high
discharges and overspill both the banks. Figure 8a
is the FCC prepared from principal component
bands and clearly marks the high moisture zone
Figure 5 Summary of channel migration history for the last 76 years (1924-2000); an around Katra (in red) and yellow patches of fresh
eastward trend is apparent. sand interpreted as crevasse deposits bordering
the main channel. From a site immediately
this area shows that the Bhakuwa Nala is joining the Lalbakeya River to downstream of Katra (Nawada village), we have
its right bank and the Manusmaran River is joining the Baghmati River reported about 1m thick splay deposit, about 200
to its left bank upstream of Bairgania. Addition of discharge and m long and 100 m wide, invading an orchard
sediment load from these tributaries is a major reason of overspilling in formed in one single flood of September 1999
this region. A spill channel is also observed, which is originating from (Sinha et al, in press). Further, field observations
the Lalbakeya River and after flowing near the Bairgania town joining indicate that the Lakhandei channel is significantly
the Baghmati River in downstream reaches. The satellite image of this narrow and entrenched near Katra (Fig. 8b)
River system also joins the Baghmati River upstream of
Hayaghat. The channel plan form as seen on the satellite
image is highly sinuous with very sharp bends making the
channel prone to crevassing during high flows. The wide
areas upstream of confluence points show clear water
logging (in blue) and high moisture zones appear as red
patches on the principal components FCC (Fig. 9a). The
effect of tributaries is clearly reflected in peak discharge
data, which shows 3-4 times increase from Benibad (200-
600 m3/sec) to Hayaghat (500-2500 m3/sec).
Further, the Baghmati river channel has a very low
gradient (11 cm/km) in this reach (GFCC, 1991), which is
interpreted as a neotectonic effect. The East Patna Fault
(EPF) passes just south of Hayaghat with the upthrown
block in the NW direction (Fig. 1). This uplift has reduced
the channel gradient, making it prone to flooding and causes
several crevasse channels in the region (Fig. 9b). Our
systematic analysis of maps and satellite images has also
demonstrated that the confluence points of rivers in this
window have changed several times during the last ~ 76
years (Jain and Sinha, in press), mostly triggered by flood
Window 5: Area around Badlaghat
The area around Badlaghat lies in the downstream reaches
of the Baghmati river, close to its confluence with the Kosi
River. Besides extensive flooding, this region is severely
affected by water logging problem. The available satellite
Bairgania Dhengbridge imagery does not cover this area and therefore this window
has been analysed through available maps and field visits.
The downstream reach of Baghmati River is characterized
by several low-lying areas (chaurs), ponds and some isolated
Spill channel channels, which act as the large lakes, e.g. Khabar Tal,
Goal Dhanaliya Jhil and several marshy lands (Fig. 10).
Several factors are responsible for flooding around
Badlaghat area. The most important factor is the structural
Figure 6 Window-1: Area around Bairgania (a) Stretched band 4 data,
control in this part of the river basin. The area lies in a
(b) Band 4 image draped over the DEM; note the low relief and
tributary influence upstream of Bairgania. graben bounded by East Patna Fault (EPF) in the west and
normal fault along Monghyr-Saharsa Ridge Fault (MSRF)
in the east. Because of these faults, this area is subsiding
reflecting a very low bankfull capacity. It has also been and hence the river gradient is very low near the confluence
observed that the Lakhandei river receives a significant amount of Kosi River. The occurrence of ponds/tals and low-lying
of backflow from the Baghmati river upstream of the areas are surface manifestation of the subsidence in this
confluence at Katra, the flood level of the Baghmati being region. Further, the base level of the Baghmati River is
higher, and this aggravates the flooding in the Lakhandei. controlled by the water level of the Kosi River, which does
not allow the Baghmati River to erode its riverbed and
Window 4: Area from Benibad to Hayaghat hence the pace with the subsidence can not be maintained,
The reach from Benibad to Hayaghat is another flood- which causes extensive flooding in the area during monsoon
prone area in the Baghmati basin. The flood problem is season. This subsidence in this block causes river-damming
particularly acute near Hayaghat area, which remains inundated effect, which in turn causes widespread flooding in this
for more than two months in a year. People living in this area region. Even the Kosi River backflows in the Baghmati
leave their homes during floods and return after the flood channel for a considerable length during monsoon season
recedes. (GFCC, 1991).
Fig. 9a shows three tributaries namely Siari River, Baghmati The area around Badlaghat is further influenced by
Nadi and Baghmati Nala joining the Baghmati River at embankments in the upstream reaches of the Baghmati
downstream of Benibad. Besides these tributaries, the Adhwara River. The Baghmati River is embanked from Hayaghat to
Figure 7 Window-2: Area in and around Sheohar (a) Standard FCC prepared from Feb. 1989 image (b)
FCC of Principal Component bands 3,2 and 1 coded on RGB prepared from image of Feb. 2000;
several abandoned channels (marked in blue colour) in the region are observed (c) DEM of the
area draped with standard FCC; the SE direction of floodplain slope is responsible for overbank
flooding around Sheohar area from the S flowing channel (d) Photograph of the area in
September1999; it is showing the effect of flood even after one month of the monsoon season.
Phuhiya at its left and upto Badlaghat at its right bank. Thus, hydrology and channel morphology with reference to
the area around Badlaghat receives the concentrated discharge overbank flooding, and (b) incorporating effects of basin
from the upstream area, which causes extensive overspilling geomorphology and neotectonics on fluvial processes in
in the region. general and flooding in particular. In the Baghmati basin,
hydrological characteristics such as variable peak discharge,
Discussion lower bankfull capacity than the mean annual flood discharge,
high sediment load and extensive sediment deposition due to
Hydrological response of a basin is governed by the basin decrease in stream power are the key factors which make the
geomorphology and hence, an integrated approach to flood basin area prone to flood hazard. Furthermore, the dynamic
studies should involve the geomorphological understanding behaviour of the Baghmati river system, which often renders
of the river basin. Floods have long been considered as the flood management programmes ineffective in many
purely hydrological phenomenon, and therefore, flood instances, has been identified as a long-term causative factor
management programmes have essentially focused on of flooding (Jain and Sinha, 2000). Remote sensing data, due
hydrological variations. This has been one of the major to their synoptic view and temporal resolutions have been
reasons for the failure of flood management efforts across demonstrated to be effective means to understand flooding
the globe including India. Historical data reveal that even behaviour and extent, in conjunction with topographic
after continuous efforts to control the floods, flood damages analysis such as DEM, and supported by ground visits. The
and flood-affected areas in India have increased with time eastward shifting of the Baghmati river (Fig. 4) has often
(Agarwal and Narain, 1996). At present, flood is one of the made the flood remedial measures useless along the old
most disastrous natural hazards in India and especially in channels and new areas prone to flooding have developed
north Bihar Plains. The failure of flood control measures in along the new course. Further, the avulsion of an old channel
the country suggests an urgent need of an integrated flood into a new one causes a sudden increase in discharge in the
analysis including the hydrological, geomorphological and newly formed channel with a low bankfull capacity causing
geological understanding of the river basin. The UNDP extensive overbank flooding. Since people are normally not
flood policy study also called for greatly increased research prepared for flooding along this newly formed channel, the
on river morphology, river training, mathematical modeling, damage due to flood is quite severe in such cases. Flood
and land and water management (Brammer, 1990). damage trend (Fig. 2) shows a 16 times increase in the
Our integrated approach to understand the flood hazard population affected by flood hazard after 1969 avulsion.
has followed two levels of analyses: (a) understanding of Therefore, the understanding of avulsion mechanism will
Figure 8 Window-3: Area around Katra (a) FCC of Principal Figure 9 Window - 4: Area from Benibad to Hayaghat (a) FCC of Principal
Component bands 3,2 and 1 coded on RGB prepared from Component bands 3,2 and 1 coded on RGB prepared from image
image of Feb. 2000; note large flood-prone areas around of Feb. 2000; note a large number of tributaries joining between
Katra marked by water logged areas (blue) and high moisture Benibad and Hayaghat and the angular drainage pattern. Area
area (red); large areas of crevasse deposits (yellow) are also upstream of confluence points show water-logging and high
seen upstream of Katra (b) photograph showing the moisture zones (b) A small crevasse channel near Benibad
entrenched, narrow (low w/d) channel of Lakhandei River; damaging the road during flood in September 1999.
during flood season the water level rises upto the road level
(seen on the upper right corner of the photograph).
have an important bearing on flood studies and management. 1998). In recent years, large lengths (3,400 km.) of
Further, basin-scale geomorphologic and neotectonic embankments have been constructed in Bihar particularly
studies aided by remote sensing data and coupled with after the devastating floods of 1954 (Agarwal and Narain,
DEM analysis have provided insight towards long-term 1996). Even after the construction of embankments along all
causative factors of flooding to supplement the the north Bihar rivers, the inundation by spilling still continues
understanding of local factors through hydrological analysis. in most parts through the gaps in the embankments and
Our studies indicate that the factors such as tributary breaching of embankments (GFCC, 1991). In the Baghmati
influences, topographic variations resulting through River basin, the flood control measures were initiated from
neotectonic movements, and tectonically-triggered 1942. Since then, 466 kilometers of embankments have been
avulsions are important enough to be considered for any constructed/under construction. Initially, embankments in the
flood management program in the region. downstream reaches worked effectively. However, after the
We now turn our attention to flood control measures in construction of embankments in upstream region, the flood
the Baghmati river basin. Out of a range of flood control peak in the Baghmati River downstream of Hayaghat increased.
measures available such as embankments, reservoir dams, Hence, the embankments along Baghmati River just
watershed management through afforestation in the basin downstream of Hayaghat were frequently breached and did
area, channel improvement, upstream storage, detention not help much in quick drainage. In this way, the artificial
basins within flood plains, artificial drawdown of embankments have merely transferred the trouble from one
groundwater to absorb excess monsoon rainfall and place to another and have given a false security to the people
floodwater, diversion of flood water in an abandoned living in the area (Sinha, 1998). Moreover, these embankments
channel or in a canal and small scale irrigation strategies, interfere with natural fluvial processes of the rivers. In areas
the embankments have been the most popular flood where the land is protected from spilling, water logging and
management strategy in India for several decades (Sinha, salinity problems have developed. The drainage congestion is
Figure 10 Flood affected area-5: Area around Badlaghat; this region falls in a graben area bounded by East Patna Fault
and Monghyr-Saharsa Ridge (see Fig. 1). Presence of several muddy areas and lakes in the region also indicate
the subsidence in the region. During monsoon season, this area receives concentrated flow of the Baghmati
River from embanked upstream channels and backflow from the Kosi River.
a major problem in the downstream part of the Baghmati and in the different part of sub-basin area will reduce
River basin particularly in the low-lying areas, locally called the influence of tributaries and hence will reduce the
‘chaurs’. flooding problem at the confluence point of the channel
The embankment strategy has lately been questioned at with main river. Because of their small size, these
the international level citing the failure in Mississippi and check dams will be environment friendly and also cost-
three major Chinese rivers (Rogers et al., 1989; Shu and effective. Further, as most of the sediment load comes
Finlayson, 1993) and alternative methods such as small from the upstream basin area, and not from the
scale irrigation strategies are now favored flood control downstream tributaries, these check dams will not be
measures in many flood-prone countries such as Bangladesh affected by the high silt load in the main Baghmati
(Brammer, 1990). In the Baghmati basin as well some River.
alternative methods besides embankments, have been (c) The proposal for diverting the floodwater at Belwa
considered by GFCC (1991) e.g. construction of dam in the village to the south flowing anabranch of the Baghmati
upstream reach flood regulator at Belwa village, channel river needs closer scrutiny keeping in view the
improvement, watershed management and underground neotectonic situation in the region. The south flowing
storage reservoir. Computations show that there will be no channel crosses the Sitamarhi Fault at Sheohar and
appreciable flood moderation in the middle and lower reaches uplift of the NE block will continuously decrease the
of the river even after the construction of dam and there will channel gradient. Therefore, regular channel
be very little effect (0.1-0.2 m) on the stage at Hayaghat maintenance may be required to maintain the flow.
(GFCC, 1991). Further, the large amount of silt load from Further, the eastward trend of channel migration will
the upstream basin area will also reduce the age of the require continuous monitoring of the left bank for
proposed dam. Based on our study, some suggestions for crevassing.
improving the flood management programs can be made.
(a) High sediment load is a major problem in Baghmati Conclusions
River and has been cited as a major cause of avulsion
and flooding due to rapid channel aggradation and An integrated approach employing remote sensing data
reduction in bankfull capacity. Our analysis suggests coupled with DEM, hydrological study and field observations
that a major proportion of the sediment load comes is recommended to understand the causative factors of
from the upstream basin area. An extensive afforestation flooding using the example of the Baghmati river basin in
work in the upstream basin area will help to reduce the eastern India. The study has shown that the tributary influence,
sediment load in the Baghmati River topographic control, abandonment of channels and
(b) Small check dams at the outlet of different tributaries neotectonics in the basin area are the major reasons for the
flooding in the study area. The remedial measures such as Jain, V. (2001) Fluvial Geomorphological analysis with special
small check dams and afforestation work in the upstream reference to flood hazard, Baghmati River basin, north Bihar,
India, Unpublished Ph.D. Thesis, Indian Institute of Technology,
basin area may be more effective in reducing the flood
hazard in the region.
Jain V. and Sinha, R. (2003a) Hyperavulsive-anabranching Baghmati
river system, north Bihar plains, eastern India, Zeitschrift für
Acknowledgement Geomorphologie (Annals of Geomorphology), 47 (1):101-116.
Jain, V. and Sinha, R. (2003b) Derivation of Unit hydrograph from
The work presented in this paper is a part of the doctoral GIUH analysis for a Himalayan river, Water Resources
thesis of the senior author (VJ) at the Indian Institute of Management, 17: 355-375.
Technology Kanpur and the Institute Fellowship for the
Jain, V. and Sinha, R. (in press) Fluvial dynamics of an anabranching
same is thankfully acknowledged. The Central Water river system in Himalayan foreland basin, north Bihar plains,
Commission and the Ganga Flood Control Commission, India, Geomorphology.
both Government of India organizations, are thanked for Kale, V.S. (1997) Flood studies in India: A brief review. Journal of the
providing the hydrological data. VJ was supported through a Geological Society of India, 49: 359-370.
sponsored project from Dalhousie University, Canada and
Karunakaran, C. and Rao, A. R. (1976) Status of exploration for
Research Associate Fellowship from CSIR, India when this hydrocarbons in the Himalayan region-contributions to stratigraphy
paper was written. We thank Prof. Martin Gibling for the and structure. Geological Survey of India Miscellaneous Publication,
financial assistance as well as his valuable suggestions. 41 (5): 1-66.
Malleswaran Rao, T. Ch. and B. I. Dookahatala (1983) Techniques for
References minimizing radiometric striping effects in Landsat data.
Photonirvachak, Journal of Indian Society of Photo Interpretation
Agarwal, A. and Narain, S. (1996) Floods, Floodplains and and Remote Sensing, 11 (1): 31-36.
Environmental Myths. State of India’s Environment: A Citizen Rao, M. B. R. (1973) The subsurface geology of the Indogangetic
Report, Centre for Science and Environment, New Delhi. Plains. Journal of the Geological Society of India, 14: 217-242.
Agrawal, R. K. (1977) Structure and tectonics of Indo-Gangetic Plains. Rogers, P., Lydon, P. and Seckler, D. (1989) Eastern waters study:
In: Bhimsankarau, V. L. S. and Gaur, V. K. (eds.) Geophysical Strategies to manage flood and draught in the Ganga-Brahmaputra
Case Histories of India, AEG Seminar, Hyderabad, I: 29-46. basin. ISPAN, USAID, Washington.
Banghar, A. R. (1991) Mechanism solution of Nepal-Bihar earthquake Sastri, V. V., Bhandari, L. L., Raju, A. T. R. and Dutta, A. K. (1971)
of August 20, 1988. Journal of the Geological Society of India, 37: Tectonic framework and subsurface stratigraphy of the Ganga
25-30. Basin. Journal of the Geological Society of India, 12: 223-233.
Brammer, H. (1990) Floods in Bangladesh: II, Flood mitigation and Shu, L. and Finlayson, B. (1993) Flood management on the lower
environmental aspects. The Geographical Journal, 156 (2): 158- Yellow River: Hydrological and geomorphological perspectives.
165. Sedimentary Geology, 85: 285-296.
Dasgupta, S. (1993) Tectono-geologic framework of the eastern Sinha, R. (1996). Channel avulsion and floodplain structure in the
Gangetic foredeep. Bihar-Nepal Earthquake, August 20, 1988, Gandak-Kosi interfan, north Bihar plains, India, Zeitschrift für
Geological Survey of India Special Publication, 31: 61-69. Geomorphologie N.F., Suppl.-Bd, 103: 249-268.
Sinha, R. (1998) On the controls of fluvial hazards in the north Bihar
Dasgupta, S., Mukhopadhyay, M. and Nandy, D. R. (1987) Active
Plains, eastern India. In: Maund, J. G. and Eddleston, M. (eds.)
transverse features in the central portions of the Himalaya.
Geohazards in Engineering Geology, Geological Society, London,
Tectonophysics, 136: 255-264.
Engineering Geology Special Publications, 15: 35-40.
Geddes, A. (1960) The alluvial morphology of the Indo-Gangetic Sinha, R. and Friend, P. F. (1994). River systems and their sediment
Plain: Its mapping and geographical significance. Transactions of flux, Indo-Gangetic plains, northern Bihar, India, Sedimentology,
the Institute of British Geographers Publications, 28: 253-277. 41: 825-845.
GFCC (1991) Comprehensive plan of flood management for the Ganga Sinha, R., Gibling, M.R., Jain, V. & Tandon, S.K. (in press) Floodplain
sub-basin, Part II/9 - The Baghmati River system. (Unpublished), processes and sedimentation in a hyperavulsive anabranching river
Ganga Flood Control Commission, Ministry of Water Resources, system in the Himalayan foreland basin, India. In: Fluvial
Government of India. Sedimentology (eds. Blum, M. and Marriott, S.), Special publication
of the International Association of Sedimentologists.
GSI (2000) Eastern Nepal Himalaya and Indo-Gangetic Plains of
Bihar; In: Narula, P. L., Acharyya, S. K. and Banerjee, J. (eds.) Sinha, R. and Jain, V. (1998) Flood hazards of north Bihar rivers,
Seismotectonics Atlas of India and its Environs; Geological Survey Indo-Gangetic Plains. In: Kale, V. S. (ed.) Flood Studies in India,
of India, 26-27. Geological Society of India Memoir, 41: 27-52.
Jain, V. and Sinha, R. (2000) Monitoring fluvial hazard from space: a Valdiya, K. S. (1976) Himalayan transverse faults and folds and their
case study from north-Bihar plains, India; In: Muralikrishna, I. (ed) parallelism with subsurface structures of north Indian Plains.
Proceeding, International Conference on Remote Sensing and GIS, Tectonophysics, 32: 353-386.
Hyderabad, 2: 11-16.