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The Great avulsion of Kosi on 18 August 2008


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The 18 August 2008 avulsion of the Kosi River draining the parts of north Bihar in eastern India may well be regarded as one of the greatest avulsions in a large river in recent years. The Kosi River shifted by ~120 km eastward, triggered by the breach of the eastern afflux bund at Kusaha in Nepal at a location 12 km upstream of the Kosi barrage. This event was widely perceived as a major flood in the media and scientific circles. Although a large area was indeed inundated after this event, it is important to appreciate that this inundation was different from a regular flooding event.
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CURRENT SCIENCE, VOL. 97, NO. 3, 10 AUGUST 2009 429
to detecting two spatially separated clusters of P. juliflora,
the L-band cross-polarized SAR was found to be best
suited as two distinct peaks were observed for it. Whereas
the C-band cross-polarized SAR could not give two dis-
tinct peaks corresponding to two tree clusters. Instead the
two clusters appeared as more or less as a single cluster
on the C-band cross-polarized SAR image. The X band
could not detect the presence of thin vegetation volume
for any of the three cases taken up in this study, as the
thin vegetation failed to have any impact on the X band
SAR in comparison to its surrounding features. Thus the
overall L-band cross-polarized SAR was found to be the
most suitable for detecting thin vegetation volume in the
present study.
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ACKNOWLEDGEMENTS. We thank Dr V. Jayaraman, Director,
National Remote Sensing Centre, Hyderabad for keen interest in this
study. H.S.S. and P.P. thank Dr Y. V. N. Krishnamurthy, Director,
Regional Remote Sensing Service Centre/National Natural Resources
Management System (RRSSC/NNMRS), ISRO Head Quarters, Banga-
lore; Dr J. S. Parihar, Deputy Director, Remote Sensing Applications
Area, Space Applications Centre, Ahmedabad; Dr K. P. Sharma, Head-
In-charge, RRSSC-Dehradun; Dr M. Chakraborty, Group Director,
Geo-Informatics and Techniques Development Group and Dr S.
Mohan, Head, Advance Techniques Development Division for support
and encouragement.
Received 4 September 2008; revised accepted 10 June 2009
The Great avulsion of Kosi on
18 August 2008
Rajiv Sinha
Engineering Geosciences Group, Department of Civil Engineering,
Indian Institute of Technology, Kanpur 208 016, India
The 18 August 2008 avulsion of the Kosi River drain-
ing the parts of north Bihar in eastern India may well
be regarded as one of the greatest avulsions in a large
river in recent years. The Kosi River shifted by ~120 km
eastward, triggered by the breach of the eastern afflux
bund at Kusaha in Nepal at a location 12 km upstream
of the Kosi barrage. This event was widely perceived
as a major flood in the media and scientific circles.
Although a large area was indeed inundated after this
event, it is important to appreciate that this inunda-
tion was different from a regular flooding event.
Keywords: Floods, Ganga plains, Kosi barrage, river
dynamics, river management.
RIVERS play a critical role in human society and history
as they are the major source of fresh water, transporta-
tion, and resources. However, this relationship is often
‘troubled’ because changes in river discharge (floods or
droughts) or position can play havoc with permanent set-
tlements. Such changes can be caused by natural forcing
as well as human interventions, or a combination of both.
Natural processes may include short-term changes in
sediment load or water volume as well as long-term
changes in relative sea level or climate change. The human
interventions impact changes in sediment load or run-off
through water resource management schemes such as
dams, barrages and embankments. Human alterations of
river systems can have many important consequences,
primarily because river systems are dynamic and highly
integrated systems and, any change in any part of the
river can easily propagate and affect the whole system.
The Kosi River is an important tributary of the Ganga
in the eastern India (Figure 1 a) and has distinctive hydro-
Figure 1. a, Location map showing the position of the Kosi River in eastern Ganga plains (G, Ganga; Y,
Yamuna; K, Kosi). b, The Kosi River has a large mountainous catchment in Nepal and a rather small alluvial area
in north Bihar giving rise to a large upland/alluvial (u/p) ratio; c, The historical records suggest a dominant west-
ward migration of the Kosi River during the last ~200 years before the river was embanked on both sides by
Table 1. Major hydrological and sediment transport characteristics of
the Kosi River. Note that the Kosi has a high sediment yield which has
to be accommodated in a rather small alluvial area (u/p ratio is 5.3,
see Figure 1 b)
Parameter Kosi Ganga Amazon
Catchment area (103 km2) 101 1073 7180
Total length (km) 1216 2700 6518
Average annual discharge (m3/s) 2036 15,000 480,000
Annual sediment load at 43 1670 1000
river mouth (mt/yr)
Discharge/area 20 14 25
Sediment yield (mt/y/km2) 0.43 1.56 0.14
logical and sediment transport characteristics (Table 1).
The dynamics of the Kosi River, generally described as
‘avulsive’ shifts, has been well documented by previous
workers1–3 and a preferentially westward movement of
150 km in the last 200 years has been recorded (Figure
1 c). Various explanations for this unidirectional shift of
the Kosi include sedimentation in a braided stream4, cone
building activity2, active tectonics5,6, and autocyclic and
stochastic movements3. Avulsion involves a sudden move-
ment around a nodal point (divergence point) and occurs
when an event of sufficient magnitude (usually a flood)
occurs along a river that is at or near avulsion threshold7
defined by the changing channel instability through time.
It also implies that avulsion may not always be triggered
by the largest flood in a given river, and that even a small
flood can trigger an avulsion if the river is close to avul-
sion threshold. One of the most common mechanisms of
avulsion is ‘channel reoccupation’ (rapid) when the new
channel occupies a pre-existing channel in the vicinity.
On the other hand, ‘crevasse splaying’ involves a gradual
process of breaching through the banks and development
of a new channel through time. Not just Kosi, several rivers
draining the plains of north Bihar are known for frequent
and rapid avulsions8–10 and the area is prone to fluvial
Unlike the previous westward avulsions (Figure 1 c),
the 18 August 2008 avulsion of the Kosi River recorded
an eastward jump of ~120 km which is an order of mag-
nitude higher than any single avulsive shift recorded in
historical times. The avulsion was triggered by a breach
in the eastern afflux bund of the Kosi at Kusaha, 12 km
upstream of the Kosi barrage (Figure 2 a and b). This
avulsed channel ‘reoccupied’ one of the palaeochannels
of the Kosi and 80–85% flow of the river was diverted
into the new course. Since the new course had a much
lower carrying capacity, the water flowed like a sheet,
15–20 km wide and 150 km long with a velocity of 1 m/s
at the time of breach. Interestingly, the new course did
not join back the Kosi nor did this find through-drainage
into the Ganga, as a result of which a very large area
remained inundated/waterlogged for more than four
months after the breach. This single event affected more
than 30 million people and there is still no reliable esti-
mate of loss of life and property.
Several lines of evidence coupled with ground observa-
tions support that this event was a ‘mega-avulsion’ rather
than a regular flood.
CURRENT SCIENCE, VOL. 97, NO. 3, 10 AUGUST 2009 431
Figure 2. a, Google image showing the course of the Kosi River before avulsion and the breach point at Kusaha; b, Part
of the eastern afflux washed away after the breach and the river avulsed towards the east; c, Seepage channel outside the
eastern afflux bund causing significant toe erosion; d, The western side of river bed and the afflux bund – river bed is 4–
5 m higher than the adjoining flood plain.
Simulations for understanding the avulsion mechanism
suggest that avulsion points shift up-valley followed by
an abrupt down-valley shift as a result of continued
growth of alluvial ridges and increase in cross-valley
slope upstream of avulsion locations13. Specific simula-
tions for the Kosi also predicted the pseudo-nodal style of
the progressive westward shift and it was also suggested
that channel belt would start shifting towards the east
once the avulsing channel belts encounter a barrier created
by the depositional topography of the fan13. Although the
observational data from the Kosi2,3 show a down-valley
shift in avulsion sites through time, the river has a
tendency to periodically return to the upstream nodal
It has also been suggested that a decrease in inter-
avulsion period occurs through time7,13,14 because the
probability of avulsion increases due to decrease in over-
all channel belt slope. Data from Kosi shows a decrease
in inter-avulsion period7,14 between 1700 and 1955. A
sharp increase in the inter-avulsion period around 1955
coincides with the construction of embankments along
both banks of the Kosi which should have stabilized the
channel temporarily.
The breach at Kusaha occurred at a discharge of
144,000 cusecs which is much less than the design dis-
charge of 950,000 cusecs for the barrage upstream and
the afflux bunds. The river avulsed following the breach,
occupied one of its palaeochannels and inundated large areas
as the channel capacity of the new course was very small.
Repeated satellite images show that the Kosi River
around Kusaha was flowing very close to the eastern
afflux bund at least since 1999 and there are reports that a
couple of spurs upstream of the breach point were eroded
in the last few years. During the field visit, it was also
observed that a well-defined seepage channel (Figure 2 c)
outside and parallel to the eastern afflux bund formed
some years ago. This channel has also been causing signi-
ficant toe erosion of the afflux bund. Further, the afflux
bunds are more than 50 years old and have been poorly
maintained which may have facilitated the breach and the
In contrast, the channel has been aggrading on the
western side with an accelerated rate after the construc-
tion of embankment. This is not surprising as the Kosi is
among the highest sediment-laden river in the world15
(0.43 mt/y/km2; see Table 1). The river bed around the
western afflux bund was observed to be at least 4–5 m
higher than the surrounding floodplain level (Figure 2 d)
although no measurement of the rate of channel bed
aggradation is available at this stage. This suggests that
most of the sediment load was trapped within the em-
bankment and the river developed a ‘gradient advantage’
as the cross valley slope exceeded the down-valley slope
in this region (Figure 3). This made the eastern afflux
bund vulnerable to breach and pushed the river close to
‘avulsion threshold’.
This avulsion triggered by the breach, has once again
questioned the efficacy of the embankment strategy for
flood control. Even a casual look at the data and interac-
tions with local people in the Kosi region would reveal
that there has been no appreciable flood moderation in
the Kosi and other rivers of north Bihar even after the
construction of embankments and the barrage (designed
with a flood cushion). The embankment strategy for flood
control as well as several other human interventions such
as highways and railway embankments have also pro-
duced severe drainage congestion in the region which
results in longer inundation of large areas almost every
year. There is an urgent need to adopt an ‘integrated’
river basin management which requires a rigorous under-
standing of the physical processes by which river channels
are formed and maintained, and encompasses all physical
attributes of the earth’s surface involved in water cycle.
The 18 August avulsion of the Kosi triggered by the
breach at Kusaha occurred partly due to incorrect strate-
gies of river management and partly due to human negli-
gence and poor maintenance of the afflux bund for the
last several years. This means that this avulsion was partly
a ‘human disaster’ rather than regular flooding.
The Kosi River was diverted back into the old course
through the barrage on 26 January 2009 after restoring
about 2000 m long embankment which was breached on
18 August 2008. The big question now is: how long the
river will stay in this course and when will the next
breach/avulsion occur? The conditions which led to the
breach and avulsion of the river, i.e. aggraded river bed
within the poorly maintained embankment, remain as
they were before the avulsion. The sustenance of the
plugging of breach is questionable and the possibility of
another breach in the near future at other locations cannot
be ruled out. A good possibility should have been to use
the new course as a diversion channel for the excess water
Figure 3. Schematic model for the 18 August 2008 avulsion of the
Kosi River. a, Natural course of the river before embankment construc-
tion; large floods passed through the channel and avulsion threshold
was higher. b, River embanked on both sides resulting in accelerated
aggradation; frequent breaches through small floods, reduction in
stream power and lowering of avulsion threshold. c, Crossing of avul-
sion threshold triggered by ‘gradient advantage’ (increase in Sa/Se)
caused by aggradation.
during floods and to follow the age-old practice of ‘con-
trolled’ flooding. Perhaps a few other palaeochannels of
the Kosi can be surveyed and a system of channel net-
work can be developed as a long-term effort. The course
of the river through the barrage and within the embank-
ment would need significant channel improvement per-
haps through dredging in selected reaches. Till today, no
attempts have been made to improve the channel or
strengthen the embankment.
While a great deal of research needs to be done to find
a long-term solution to the Kosi avulsion and flooding, it
is important that a ‘system’ approach to river manage-
ment should be adopted keeping in view the dynamic
behaviour of the Kosi. Further, there has been a paradigm
shift globally from ‘river control’ primarily involving an
engineering approach addressing the ‘effect’ at a local
scale to ‘river management’ which emphasizes an inte-
grated approach at a crossover of scales and addresses the
‘cause’ rather than the effect16–19. Even though India is a
country bestowed with several large rivers, our river
management strategies are rather rudimentary and our
planners are yet to embrace modern approaches such as
satellite-based monitoring and multi-criteria decision
support system. Some efforts in this direction20,21 have
already shown encouraging results but a large-scale,
coordinated effort is needed to save a large population
from repeated miseries of fluvial hazards year after year.
A process-based understanding of the Kosi and the cou-
pling between river form and processes are needed to find
long-term solutions to river dynamics and floods.
1. Shillingfield, 1893; cited in Gole and Chitale, 1966 (see ref. 2).
2. Gole, C. V. and Chitale, S. V., Inland delta building activity of
Kosi River. J. Hydraul. Div., ASCE, 1966, 92, 111–126.
3. Wells, N. A. and Dorr, J. A., Shifting of the Kosi River, northern
India. Geology, 1987, 15, 204–207.
4. Leopold, L. B. and Maddock, T., Flood control problems. J. Soil.
Water Conserv. India, 1955, 3, 169–173.
5. Arogyaswamy, R. N. P., Some geological factors influencing the
behaviour of the Kosi. Rec. Geol. Surv. India, 1971, 96, 42–52.
6. Agarwal, R. P. and Bhoj, R., Evolution of Kosi river fan, India:
structural implication and geomorphic significance. Int. J. Remote
Sensing, 1992, 13, 1891–1901.
7. Jones and Schumm, S. A., Causes of avulsion: an overview. In
Fluvial Sedimentology VI (eds Smith, N. D. and Rogers), Spl. Pub.
Int. Ass. Sedimentol., 1999, vol. 28, pp. 171–178.
8. Sinha, R., Channel avulsion and floodplain structure in the Gan-
dak–Kosi interfan, north Bihar plains, India. Z. Geomorph.,
Suppl.-Bd, 1996, 03, 249–268.
9. Jain, V. and Sinha, R., Fluvial dynamics of an anabranching river
system in Himalayan foreland basin, Baghmati River, north Bihar
plains, India. Geomorphology, 2004, 60, 147–170.
10. Jain, V. and Sinha, R., Hyperavulsive-anabranching Baghmati
river system, north Bihar Plains, eastern India. Z. Geomorph.,
2003, 47, 101–116.
11. Sinha, R. and Jain, V., Flood hazards of North Bihar Rivers, Indo-
Gangetic Plains. Mem. Geol. Soc. India, 1998, 41, 27–52.
12. Sinha, R., On the controls of fluvial hazards in the north Bihar
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13. Mackey, S. D. and Bridge, J. S., Three dimensional model of allu-
vial stratigraphy: theory and application. J. Sed. Res., 1995, 365,
14. Stouthamer, E. and Berendsen, H. J. A., Avulsion: the relative
roles of autogenic and allogenic processes. Sed. Geol., 2007, 198,
15. Sinha, R. and Friend, P. F., River systems and their sediment flux,
Indo-Gangetic plains, northern Bihar, India. Sedimentology, 1994,
41, 825–845.
16. Gilvear, D. J., Fluvial geomorphology and river engineering:
future role utilizing a fluvial hydrosystems framewok. Geomor-
phology, 1999, 31, 229–245.
17. Downs, P. W. and Gregory, K. J., River Channel Management,
Arnold Press, 2004, p. 395.
18. Brierley, G. J. and Fryirs, K., Geomorphology and River Man-
agement: Applications of the River Styles Framework, Blackwell
Publishing, Oxford, 2005, p. 398.
19. Brierley, G. J. and Fryirs, K., River Futures. An Integrative Scien-
tific Approach to River Repair, Island Press, Washington, 2005, p.
20. Bapalu, G. V. and Sinha, R., In Flood Hazard Mapping: A Case
Study of Kosi River Basin, GIS@Development online edition,
October 2005.
21. Sinha, R., Bapalu, G. V., Singh, L. K. and Rath, B., Flood risk
analysis in the Kosi river basin, north Bihar using multi-
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ACKNOWLEDGEMENTS. I thank Barh Jan Ayog Bihar for organiz-
ing a visit to the flood affected areas in Nepal and north Bihar includ-
ing the breach point at Kusaha. Discussions with several persons
namely, Dr Manas Bihari Verma, Dr Ajaya Dixit, Dr Deepak Gywali,
Mr Vijay Kumar, Narayajee and several others during the field excur-
sion helped immensely to develop the initial ideas in this paper.
Received 2 June 2009; accepted 7 July 2009
A novel nesting behaviour of a
treefrog, Rhacophorus lateralis in
the Western Ghats, India
S. D. Biju
Systematics Lab, Centre for Environmental Management of
Degraded Ecosystems, School of Environmental Studies,
University of Delhi, Delhi 110 007, India
Nest building by leaf folding is a rare behaviour in
anuran amphibians, with previous reports for only two
genera, the Subsaharan African Afrixalus, and Cen-
tral and South American Phyllomedusa. This commu-
nication reports a specialized nest building behaviour
of an Indian treefrog Rhacophorus lateralis, which was
observed in natural habitat at Kalpetta in Wayanad
District, Kerala. This behaviour of leaf folding is the
first report in the family Rhacophoridae, and in the
Asiatic amphibians. Nesting behaviour of R. lateralis is
unique among Rhacophorus a purse-like nest is
made over water by folding a single leaf around the
egg mass (embryos and translucent foam) by the
female alone after oviposition. The function of this
parental investment is to prevent desiccation of eggs in
open sunlight. This paper also documents the multiple
leaf nesting behaviour of other two species of this
genus, R. calcadensis and R. pseudomalabaricus, and
the previously documented nesting behaviour of R.
malabaricus using more than one leaf.
Keywords: Leaf folding, leaf nesting, Rhacophorus lat-
eralis, treefrog, Western Ghats.
IN addition to typical aquatic habitats, anuran amphibians
deposit eggs in a wide range of places including under-
ground1, arboreal foam nests2, tree holes3 and stream
banks4. Among the 262 anuran amphibians reported from
India5, above-ground nest construction using multiple leaf
is known only in Rhacophorus malabaricus6.
Rhacophorus lateralis is a small sized Rhacophorid
treefrog (snout to vent size-male: 28.6–30.1 mm, N = 5;
female: 33.5–34.8 mm, N = 3) having bright green or
light reddish-green dorsal colour with a prominent golden
yellowish streak from snout along the side of head to near
the vent. Scientific knowledge on R. lateralis is sparse
other than the original description based on a sole pre-
served animal7, followed by rediscovery after a gap of
more than 100 years from the Western Ghats of Kerala8
and Karnataka9. Rhacophorus lateralis is an endangered
species10, thus a better understanding of the breeding bio-
logy of this frog is critical for its conservation manage-
A breeding population of R. lateralis was observed
over two breeding seasons during which courtship, mating
and leaf nesting behaviour were studied. The primary ob-
jective of this communication is to document leaf nest
construction behaviour of R. lateralis and determine the
possible function of this behaviour based on field obser-
vations and laboratory studies. The complete sequence of
courtship and mating behaviour of this species is beyond
the scope of this communication. This study is based on
observation of 65 nests, including nine sequences from
pair detachment after oviposition to completion of leaf
The study was conducted during 2000 and 2005 breed-
ing seasons (June–September) at Kalpetta (11°36N,
76°05E; 980 m asl), Wayanad District, Kerala. Amplexed
pairs were located by active searching guided by choruses
or by making repeated observations of single females un-
til they mated. Amplexus is axillary and duration of egg
laying varies from 35 to 50 min (N = 9). Fieldwork was
undertaken at a natural breeding pool between 19:00 and
23:00 h using a dim or red flashlight. The pool was 3.2 m
wide and had a maximum depth of 0.9 m. Grasses, low
herbs (Ludwigia sp., Lantana sp., Chromolaena sp., etc.).
... However, frequent breaches of the embankment have been occurringas many as nine since 1963 in both the eastern and western embankments (Fig. 11.5a), resulting in severe flooding (Mishra 2008;Sinha et al. 2014a). Although most of these breaches did not result in complete avulsions, the latest breachon 18 August 2008 at Kusaha (close to the fan apex) 12 km upstream of the Birpur barragemoved the main channel eastward by~60 km in a single avulsive shift (Sinha 2009;Chakraborty et al. 2010;Sinha et al. 2014a). The maximum shift to the east was recorded as~120 km (Sinha 2009). ...
... Although most of these breaches did not result in complete avulsions, the latest breachon 18 August 2008 at Kusaha (close to the fan apex) 12 km upstream of the Birpur barragemoved the main channel eastward by~60 km in a single avulsive shift (Sinha 2009;Chakraborty et al. 2010;Sinha et al. 2014a). The maximum shift to the east was recorded as~120 km (Sinha 2009). Several breaching points fall in the reaches marked as high and very high zones of siltation, and some in the moderate zone including Kusaha resulted in a major avulsion in 2008. ...
... Detailed analysis of the 2008 avulsion of the Kosi River at Kusaha by Sinha et al. (2014a) revealed that this breach occurred at relatively low flow, i.e., when discharge was only 4,078 m 3 /s, compared to the design discharge (26,901 m 3 /s) of the embankment (Sinha et al. 2013). It has been argued, therefore, that this avulsion occurred primarily because of large-scale aggradation that resulted in a 'superelevated' channel, thereby pushing the river close to the avulsion threshold at that point (Sinha 2009;Sinha et al. 2014a). ...
Megafans are partial cones of river sediment that reach unexpectedly large dimensions, with the largest on Earth being 700 km long. Due to recent developments in space-based observations, global mapping efforts have shown that modern megafan features cover vast landscapes on most continents. This book provides a new inventory of nearly 300 megafans across five continents. Chapters focus on regional studies of megafans from all continents barring North America and Antarctica. The major morphological attributes of megafans and multi-megafan landscapes are discussed, and the principal controls on megafan development are examined. The book also compares megafans with alluvial fans, deltas, floodplains and the recently recognised 'major avulsive fluvial system' (MAFS). The final part of the book discusses the application of megafan research to economic geology, aquifers and planetary geology including layered deposits on Mars. This is an invaluable reference for researchers in geomorphology, sedimentology and physical geography.
... However, the average avulsion frequency for the Kosi is known to be well below once in 24 years, and is thus among the highest in the world compared to, for example, up to 1400 years for the lower Mississippi River (Slingerland and Smith 2004). More recent work has also confirmed that the dynamics of the Kosi River is primarily controlled by local slope changes influenced by excessive sedimentation in the channel belt, and that the situation has become worse after the construction of embankments on both sides of the Kosi River (Sinha 2009;Sinha et al. 2014a). Figures 10.5b and c illustrate the typical down-fan slope profile and convex-up crossfan morphology. ...
... Similarly, sedimentary cores from the Kosi megafan down to a depth of~50 m have yielded the oldest OSL dates of~65 ka (Sinha et al. 2015). Even though the Kosi river is now embanked on both sides, frequent breaches such as that in August 2008 (Sinha 2009) have enabled opportunities for deposition on the fan surface. While more chronostratigraphic data may be required to constrain the antiquity of these megafans, it seems likely that those in the Gangetic plains have persisted since the late Pleistocene (MIS 3). ...
Megafans are partial cones of river sediment that reach unexpectedly large dimensions, with the largest on Earth being 700 km long. Due to recent developments in space-based observations, global mapping efforts have shown that modern megafan features cover vast landscapes on most continents. This book provides a new inventory of nearly 300 megafans across five continents. Chapters focus on regional studies of megafans from all continents barring North America and Antarctica. The major morphological attributes of megafans and multi-megafan landscapes are discussed, and the principal controls on megafan development are examined. The book also compares megafans with alluvial fans, deltas, floodplains and the recently recognised 'major avulsive fluvial system' (MAFS). The final part of the book discusses the application of megafan research to economic geology, aquifers and planetary geology including layered deposits on Mars. This is an invaluable reference for researchers in geomorphology, sedimentology and physical geography.
... But it has been experienced that, in most cases, flood management initiatives in this region failed in significant ways. In the meantime, the yearly flood damage increases > 40 times, and flood-affected regions grow > 1.5 times (Sinha, 2008). As this region contains a large and mightiest river network and a larger agglomeration of the population, it is not feasible to offer comprehensive protection to the people and their property from any flood, but effort should be done at the utmost level. ...
... However, when mega floods or dam breaches occur, the river diverts an enormous quantity of water into these channels, bringing havoc and calamity for the surrounding inhabitants. The same phenomenon was noticed in the previous decade in the Koshi river (Kale, 2008;Sinha, 2009). During the field study, we experienced a similar incident in the villages located on the right bank sides of the Rajepur, Harpalpur, and Sandi blocks. ...
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The Indo-Ganga–Brahmaputra plain is one of the world’s most vulnerable areas to catastrophic flood events. The severity and frequency of floods in this region have grown dramatically during the last few decades. As a result, an authentic map providing detailed spatial information on floods is required for reducing future flood disasters. This sort of map can be an invaluable tool for displaying flood-prone areas and determining the magnitude of flood risk. The Ramganga river (~ 200 km length) flowing in the western Gangetic plain was chosen for this investigation. This river is well known for its channel movement and flood hazards. The analytical hierarchy process model in GIS ambiance was used in this work to quantify and map flood risk in the lower Ramganga river basin. Six hazard-forming factors, namely relief, distance from active channel, slope, geomorphology, rainfall, and vegetation, and seven vulnerability factors, namely population density, household density, female density, road density, land use/land cover, female literacy, and total literacy, were chosen to determine flood risk zone (FRZ). According to the findings, about 35.29 per cent of the basin’s total area is in a high to very high flood risk zone, where flooding occurs at one- to three-year recurring intervals. The flood risk map has been validated using ground truth data, and the Kappa index has been computed, indicating a high degree of accuracy for the FRZ thematic classes.
... The future prediction of precipitation from climatic models does show increased precipitation in the lower Kosi subbasin, especially in the area below the Nepal Himalaya both in Nepal and North BiharRajbhandari et al., 2018).The state of Bihar and the Kosi sub-basin of the Ganga River are an instance where floods affect millions. According to the Central Water Commission of India (CWC), the lower Kosi sub-basin located in north Bihar has experienced six major floods in the last two decades from 2001 to 2019 of which the years 2004 and 2008 were the most devastating in terms of damages done to people(Sinha, 2009). In the stretch of 310 km, the elevation gradient of river Kosi drops and flattens before joining the river Ganga at Kursela.Due to the low gradient, drainage congestion takes place and leads to an increase of permanently flooded areas in the lower Kosi sub-basin from Chatara to Kursela. ...
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The thesis starts by establishing the physical context of this interdisciplinary environmental justice study, focusing on the region of Bihar. I examine the impact of altering the natural flow of the intricate network of Himalayan rivers, including those fed by springs, snow, and rainfall, on the flood plains of north Bihar. The construction of embankments and barrages along the Kosi River in the context of the north Bihar flood plains has proven to be detrimental, resulting in the division of the region into three distinct landmasses: the area enclosed within the embankments, the area outside and adjacent to the embankments, and the area situated farther away from them. Conducting a secondary analysis of the geomorphological characteristics of the Kosi River, I investigate how these characteristics influence its capacity to carry water and render it susceptible to flooding. This forms the fundamental premise for reviewing existing literature on flood hazards and their disproportionate impact on marginalized groups. This study employs the theoretical framework of environmental justice and contextual vulnerability to investigate the unequal distribution of flood risks in north Bihar during the post-embankment period since the 1960s. It begins by examining the literature on historical events that have contributed to the landlessness experienced by marginalized communities such as the Musahar and Mallah. The study aims to shed light on how higher caste individuals and zamindars have systematically appropriated all the lands in the north Bihar region, pushing communities like the Musahar and Mallah to the margins. By analyzing these historical and socio-economic factors, the research seeks to understand the underlying causes of the disproportionate impact of floods on vulnerable communities in the region. The study begins by examining whether there has been an increase in flood frequency and intensity during the post-embankment period. A biophysical analysis uses precipitation data to understand precipitation trends within the Kosi sub-basin over time and how they impact the flood regime. The literature review focuses on the geomorphology of the Kosi River and its influence on its carrying capacity and drainage. Furthermore, a comprehensive review of the literature on the history of flood control interventions in India and their societal impact is undertaken. Quantitative data analysis examines the relationship between rainfall patterns and flooding events in two selected districts, namely Darbhanga and Saharsa. The findings indicate that while precipitation alone is not solely responsible for the increase in flooding events, the presence of embankments does reduce the occurrence of such events. However, more than biophysical analysis is needed to completely understand the situation. Quantitative data analysis from household interviews is conducted to complement and elucidate the nuances missed in the biophysical analysis. The data from these surveys suggest that flood frequency and intensity have increased in the post-embankment period. This assertion is further supported by the increased financial costs incurred by households in safeguarding their homes from flooding through measures like land elevation. The occasional breaches of embankments are found to be more devastating than annual flooding, catching communities off guard. In response to these challenges, local communities have adopted coping mechanisms in the post-embankment period. These include using detachable house parts, cultivating leguminous plants to protect agricultural fields against weeds, and raising home premises to protect against rising riverbeds caused by sediment accumulation. While these immediate proximate solutions have proved effective, communities are still seeking long-term and sustainable solutions to address the issue of floods. Regional disparities in Bihar are established by analyzing secondary literature on the socio-political dynamics of the north and south Bihar districts. The findings reveal that the north Bihar districts lag in development on various parameters, including agriculture, the service sector, education, and health, compared to the south and central Bihar districts. The north Bihar districts, particularly Darbhanga, rank highest regarding flood hazard index. Many flood-prone villages and blocks are categorized as having very high, high, and moderate flood risk in north Bihar. Consequently, both geographically and socio-economically, north Bihar has remained highly underdeveloped. These regional inequalities, coupled with poverty and the recurrent damages caused by floods, are examined within the framework of regional justice. The results of primary and secondary data analysis on flood risk, the geographical vulnerability of the Kosi communities, and their firsthand experiences with floods substantiate the case for regional environmental justice in the Kosi region. Additionally, the communities in this region are disproportionately exposed to flood risks due to their spatial location, and they bear the brunt of regular floods. As a result, they have developed physical and mental coping mechanisms, including adopting patriarchal Maithili worldviews, to deal with the consequences of flooding. The persistent exposure to recurring floods has compelled the communities to devise innovative disaster coping strategies. One such approach is the construction of detachable house parts using locally available materials such as tall grasses, manejara plants, and reusable cement pillars. These adaptable housing solutions enable the communities to disassemble and relocate their homes as needed during flood events. In the godforsaken countryside of Kosi, where floods test and trouble the residents every year, women play a vital role in ensuring that households continue to thrive. It is worth noting that women play a crucial role in ensuring the resilience of households in the challenging countryside of the Kosi region, where floods constantly threaten everyone each year. They take on significant responsibilities in managing household affairs and implementing flood preparedness measures. Their involvement in decision-making and resource management contributes to households’ overall resilience and survival in this flood-prone area. The study delves into the struggles faced by marginalized communities in coping with the impacts of floods, emphasizing the lengthy recovery process required after such disasters. It identifies embankments as critical factors that are pivotal in perpetuating regional environmental injustice by disproportionately distributing flood risks among communities. Examining inter-community differences reveals how these disparities affect the vulnerability of the Musahar and Mallah communities. Factors such as residency status, access to safe drinking water and sanitation, housing types, the cost of raising land, the safety of families at their current location, and community perceptions of flood frequency and intensity all indicate that the Musahar community tends to be more marginalized in most villages compared to the Mallah community. When analyzing intra-community vulnerability, gender is an essential determinant of flood vulnerability. Women, in particular, face unique challenges due to early marriage, which hinders their educational attainment and limits their ability to pursue economic independence. The low levels of education among both men and women in the Musahar and Mallah communities further exacerbate their vulnerability to floods. Overall, the study highlights the complex dynamics of vulnerability within and between communities, shedding light on the intersectionality of factors such as gender and education contributing to the disparities in flood impacts and resilience. The existing literature on inter-community inequality sheds light on how such inequality can disproportionately impact specific communities, such as the Musahar and Mallah communities, in their experience of flood risks within Kosi villages. These communities face multiple challenges due to their spatial, social, and economic circumstances, exacerbating the prevailing inequality. Inadequate access to suitable housing, sanitation, and toilets, coupled with caste discrimination, further marginalize these communities and leave them without support or mechanisms for recovery when facing floods. The loss of cultivable land affects landowners and has a profound impact on Musahar agricultural labourers and Mallah sharecroppers, who are landless and depend on others for wage labour. Additionally, these marginalized communities lack sufficient livestock, fixed and movable assets to aid in their recovery from floods, unlike the higher caste communities who possess more resources. Both the Musahar and Mallah communities perceive an increase in flood frequency, intensity, and duration in their villages, further highlighting their vulnerability. Moreover, the absence of early warning systems and limited social networks among the Musahar and Mallah communities exacerbate their suffering when sudden floods occur. The relief camps established for displaced communities have proven problematic, particularly for marginalized groups such as women. These camps often subject them to exploitation and discrimination, rendering girls and women from the Musahar and Mallah communities even more vulnerable to flooding and its negative impacts, including displacement. The biophysical context of the Kosi villages perpetuates a cycle of constant flight from the perils of floods, with the communities becoming accustomed to the trauma of temporary displacement as a result. These communities’ enduring challenges highlight the urgent need for comprehensive measures to address the underlying inequality and support marginalized groups in their resilience-building efforts. However, the socioeconomic conditions of households play a significant role in determining the outcomes mentioned above. Affluent households tend to avoid seeking shelter in relief camps, thus avoiding the shame of leaving home and living as refugees. On the other hand, marginalized castes like Musahar and Mallah have no choice but to reside on embankments in relief camps, compromising their dignity temporarily. Another noteworthy social change resulting from the division caused by embankments is evident in bridal preferences. Communities residing in flood-prone villages prefer brides from similar areas while marrying off their daughters to non-flood-prone villages, even if it means paying higher dowries. Consequently, there is a direct impact on the marital relationships between community members living inside and outside the Kosi embankments in the post-embankment period. Additionally, the embankments affect flood exposure, disproportionately exposing communities living inside or close to the embankments to higher flood risks than others. This excessive flood exposure signifies environmental injustice across the Kosi floodplains, directly impacting these communities’ physical and mental well-being and necessitating adaptations to the altered conditions. Findings from oral history interviews and focus group discussions with women's groups indicate a disparity in risk based on spatial location, caste, class, and gender in the Kosi floodplains. The presence of a regressive and dominant patriarchal system places women at greater risk. Their roles are typically limited to domestic responsibilities, such as caring for children and managing household chores, leaving them with limited agency in making economic decisions. However, the experience of floods does play a crucial role in acquiring the skills necessary for coping with them, becoming pivotal in the lives of individuals in the floodplains. Individuals remain mentally prepared for floods and utilize their social capital and networks to address recurring flood situations. Gender and the community members' worldview also play significant roles in dealing with flood-related losses. They draw inspiration from Sita, the courageous daughter of Mithila, who has overcome numerous challenges and achieved success in her life. As a result, gender has emerged as a significant theme in flood recovery efforts within Kosi villages. Nonetheless, early marriages often lead to larger family sizes and increased child malnutrition. The migration of young males from the area burdens women, as they are left to contend with floods and provide for their families. Nevertheless, women exhibit adaptability and quick learning from their flood experiences. Those from flood-prone villages display exceptional skills in dealing with floods and displacement compared to those from non-flood-prone villages. Annual flooding and temporary displacement primarily affect women, as seeking shelter in relief camps on embankments makes them more vulnerable to human trafficking and compromises their dignity. Particularly for young girls and women, the situation becomes precarious as they face objectification and rely on government-provided rations. Community members generally hold negative views towards embankments, as they believe it has created a permanent division between communities residing inside and outside of the embankments. The daily struggle of households, especially women, to secure food, fodder, and fuel for their families is a harsh reality‒the communities' worldview and experiential learning aid in coping with floods. Remittances from outmigration, along with household social capital and cash reserves, are crucial elements in recovering from floods. Among Kosi villages, women from Musahar and Mallah communities suffer the most due to environmental and social factors, including floods, land erosion, sand casting, crop damage, loss of lives, inadequate education and healthcare facilities, and prevailing patriarchal norms and worldviews. These factors severely restrict their opportunities and subject them to the vulnerabilities posed by both society and nature.
... 3 of 22 Avulsions can occur abruptly over a period of days to weeks (Qian, 1990;Sinha, 2009;N. D. Smith et al., 1989) or take decades to centuries to complete (Fisk, 1944;Jones & Harper, 1998;Schumm et al., 1996;Stouthamer & Berendsen, 2001;Tornqvist, 1994). ...
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Avulsions change river courses and transport water and sediment to new channels impacting infrastructure, floodplain evolution, and ecosystems. Abrupt avulsion events (occurring over days to weeks) are potentially catastrophic to society and thus receive more attention than slow avulsions, which develop over decades to centuries and can be challenging to identify. Here, we examine gradual channel changes of the Peace‐Athabasca River Delta (PAD), Canada using in situ measurements and 37 years of Landsat satellite imagery. A developing avulsion of the Athabasca River is apparent along the Embarras River–Mamawi Creek (EM) distributary. Its opening and gradual enlargement since 1982 are evident from multiple lines of observation: Between 1984 and 2021 the discharge ratio between the EM and the Athabasca River more than doubled, increasing from 9% to 21%. The EM has widened by +53% since 1984, whereas the Athabasca River channel width has remained stable. The downstream Mamawi Creek delta is growing at a discharge‐normalized rate roughly twice that of the Athabasca River delta in surface area. Longitudinal global navigation satellite systems field surveys of water surface elevation reveal the EM possesses a ∼2X slope advantage (8 × 10⁻⁵ vs. 4 × 10⁻⁵) over the Athabasca River, and unit stream power and bed shear stress suggest enhanced sediment transport and erosional capacity through the evolving flow path. Our findings: (a) indicate that a slow avulsion of the Athabasca River is underway with potentially long‐term implications for inundation patterns, ecosystems, and human use of the PAD; and (b) demonstrate an observational approach for identifying other slow avulsions at river bifurcations globally.
... recent and significant breach observed in the eastern embankment occurred at Kusaha in Nepal, 12 km upstream of the Birpur Kosi Barrage. This caused a major shift of the Kosi River by ∼120 km eastward, and globally, it was one of the significant avulsions in a big river in recent years (Sinha, 2009a;Chakraborty et al., 2010;Sinha et al., 2014). ...
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Flood is one of the most significant natural hazards, and people living in flood zone always face the event of flood during monsoon in India. This paper assesses the historical impacts of Koshi flood, particularly 'The Killed' and 'The Billed', in Northern Bihar. The aftermath of severe floods in the past has been assessed with the help of quantitative methods. The study is based on the secondary database. Lack of services, fragile living, and disadvantaged groups make people vulnerable to flood in the Koshi region of Bihar. The present study also tries to analyses the geographical problem of River Koshi in the northern plain of Bihar. This study will help realistic assessment of flood impact in the region. The focus area comprises of Madhubani,
... This is a result of frequent avulsions of the Kosi River channels. In the last three centuries, the Kosi River has migrated about 150 km [56][57][58][59] . During the process of migration, the river has deposited its sediments and built a large fan like structure. ...
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We propose a new architecture based on a fully connected feed-forward Artificial Neural Network (ANN) model to estimate surface soil moisture from satellite images on a large alluvial fan of the Kosi River in the Himalayan Foreland. We have extracted nine different features from Sentinel-1 (dual-polarised radar backscatter), Sentinel-2 (red and near-infrared bands), and Shuttle Radar Topographic Mission (digital elevation model) satellite products by leveraging the linear data fusion and graphical indicators. We performed a feature importance analysis by using the regression ensemble tree approach and also feature sensitivity to evaluate the impact of each feature on the response variable. For training and assessing the model performance, we conducted two field campaigns on the Kosi Fan in December 11–19, 2019 and March 01–06, 2022. We used a calibrated TDR probe to measure surface soil moisture at 224 different locations distributed throughout the fan surface. We used input features to train, validate, and test the performance of the feed-forward ANN model in a 60:10:30 ratio, respectively. We compared the performance of ANN model with ten different machine learning algorithms [i.e., Generalised Regression Neural Network (GRNN), Radial Basis Network (RBN), Exact RBN (ERBN), Gaussian Process Regression (GPR), Support Vector Regression (SVR), Random Forest (RF), Boosting Ensemble Learning (Boosting EL), Recurrent Neural Network (RNN), Binary Decision Tree (BDT), and Automated Machine Learning (AutoML)]. We observed that the ANN model accurately predicts the soil moisture and outperforms all the benchmark algorithms with correlation coefficient (R = 0.80), Root Mean Square Error (RMSE = 0.040 m3/m3), and bias = 0.004 m3/m3. Finally, for an unbiased and robust conclusion, we performed spatial distribution analysis by creating thirty different sets of training-validation-testing datasets. We observed that the performance remains consistent in all thirty scenarios. The outcomes of this study will foster new and existing applications of soil moisture.
... Therefore, it becomes necessary to prepare better layout for such regions to minimize the losses during and after the flood events. A number of studies focusing on the physical aspects i.e. river morphometry, grain size analysis, flood mapping, geomorphological study, streamflow analysis etc. were conducted on the Kosi region (Bhatt et al. 2010;Kale 2002;Kattelmann 1993;Mishra & Sinha 2019;Sinha 2009). The region has become a prime location for field-based investigation for geomorphic study and prediction of floods using different statistical models. ...
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The present work focuses on the comparison between Analytical Hierarchy Process (AHP), the most commonly used Multi-Criteria-Decision-Analysis (MCDA) model, and three bivariate models: Evidential Belief Function (EBF), Weights of Evidence (WoE) and Frequency Ratio (FR) to predict the flood susceptible areas in the Lower Kosi River Basin of the Ganga River Basin. Twelve flood conditioning factors, topographic (altitude, slope, aspect, curvature, and geomorphology), hydrologic (rainfall, TWI, river density), anthropogenic (LULC, distance from road), and others (distance from river, soil) have been utilized for the spatial modelling. The results suggest that geomorphology, TWI, land-use, and river density are the most dominating factors. Area-under-Receiver-Operating-Characteristic (AUROC) method was used for validation of the used models. The value of the AUROC curve for AHP is found 0.837, outstands the bivariate models- FR (0.807), EBF (0.820) and WoE (0.787), suggests the MCDA model is more accurate in predicting the flood lands than bivariate models in the plains of Ganga River Basin.
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The Kosi River, draining through Nepal and north Bihar, India, has been known for excessive sediment (commonly called silt) deposition—a primary cause of several hazards. However, there are still no good estimates of the volume of silt accumulated in the Kosi River channel, which makes removal and utilization of silt a major challenge, both technically as well as economically. In this work, we first present a novel method to estimate sediment volume on a reach scale using hydrological and channel planform data mapped from satellite images. We then identify various commercial uses of the Kosi River sediments such as embankment construction, backfilling, land reclamation, landscaping, agricultural applications, industrial applications, and geotextile silt walls. In consultation with various stakeholders, backfilling and embankment construction were identified as potentially the best solutions shortlisted for the development of a business case and investment model. Therefore, we prepared an investment model based on economic viability, cost-to-benefit ratio, and stakeholder consultations for two districts. We performed a SWOT analysis by breaking down the opportunities and risks into political, economic, social, technological, environmental, and legal (PEST-EL) factors to identify the pros and cons within the sector and of the ecosystem in which the stakeholders operate.
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This scientific venture to understand the nature and impact of channel hydrological fluctuations on channel sedimentation of the Torsa River has utilised daily discharge, water level and periodic channel cross-sections provided by the Central Water Commission of Govt. of India. The flood-frequency analysis and prediction of extreme flood discharge of the Torsa River was conducted using the Gumbel’s extreme value, log-Pearson’s III and log-normal method. Higher flood volume and greater flashiness of flood discharge with lower channel water residence time is evident on the piedmont surface compared with the northern plains in the Torsa River catchment located on the Himalayan foothills of West Bengal, India. The Peak Over Threshold (PoT) or the vulnerable river discharge at Hasimara is measured 2856 m3 s−1, and at Ghughumari, it is 2954 m3 s−1. The mean flash flood magnitude between 1990 and 2015 was found 1.60 and 1.38 at Hasimara (representative of Piedmont surface) and Ghughumari (representative of the Northern plains), respectively. The higher accumulation of sediment during any flood period is evident throughout the course, but the intensity of channel aggradation decreases downstream as the piedmont surface acts as the depo-centre of channel deposits brought down from the Himalayan terrain. The correlation coefficient between the channel bar width and ratio of peak discharge and long-term mean peak discharge was found 0.45 and 0.34 at Reach I (roughly covering the Piedmont) and Reach II (covering the Northern plains), respectively. The sensitiveness of channel bed modification to annual flood discharges is found higher at Hasimara in comparison with Ghughumari. The correlation coefficient between channel Bed Roughness Index and ratio of peak discharge and long-term mean peak discharge was measured 0.54 and 0.46 at Hasimara and Ghughumari, respectively. Even the temporal difference in channel mean elevation during the pre-monsoon and post-monsoon period and corresponding annual peak discharge was measured at 0.80 and 0.46 at Hasimara and Ghughumari, respectively. This study carries a concerned level of significance to regional planners and institutes responsible for flood forecasting and framing flood protection measures.
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A long historical record of channel migration of the Baghmati river system draining the Himalayan foreland basin is presented. Reconstruction of the migration history carried out by maps and satellite imageries reflects a very high frequency of avulsion events (8 major and several minor events in 230 years). Hydrological characteristics, sedimentological readjustments and neotectonic tilting are the important factors triggering avulsions and thereby influencing the development of anabranching. © 2003 Gebrüder Borntraeger, D-14129 Berlin · D-70176 Stuttgart.
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The rivers of the north Bihar plains, eastern India, pose three major fluvial hazards: rapid lateral migration, frequent flooding and extensive bank erosion. Lateral shifting of the Kosi, Gandak and several other rivers in the area has been attributed mainly to neotectonic tilting and subsidence of the area, and to some extent, local topography and sedimentological readjustments in the basin. Overbank flooding is a perennial problem, with most of the rivers of the north Bihar plains causing the rivers is only a short-term solution to mitigate floods not only because of frequent breaches in the embankment due to extremely high discharges during high flows but also because of the fact that these rivers carry a high sediment load causing rapid siltation and thereby raising the water level in a few years' time. Severe bank erosion takes place during the lateral shifting of rivers as well as during high flows. Efforts to prevent these fluvial hazards in the area have largely failed as the geological and geomorphological considerations have not been taken into account.
The rivers d.aining the plains of nonh Bihar, eastem India have been investigated for their flooding behaviour A geomorphological study of floods has been advocated in the paper (o develop a better understanding of flooding characterislics of these rivers which record the highest flooding events in the country. Alongwith a detailed analysis of hydrological data, geomorphological factors influencing the overbank spilling of these rivers have been discussed. Other fluvial processes such as bank erosion, channel morphological changes and sediment load variations have also bcen discussed in relation to overbank flooding.
Fluvial processes operating in an area of rapid subsidence and neotectonic activities have been studied. Investigations through remote sensing data and field observations in the interfan between the Gandak and Kosi megafans in the north Bihar plains, eastern India indicate that channel migration through avulsion and cut-offs, and extensive overbank flooding are the most important factors controlling the floodplain structure in the study area. The utility of satellite images offering a synoptic view in the study of regional as well as local geomorphic features has been re-emphasised. A dominance of vertical accretion overbank deposits over the lateral accretion point bar deposits in the interfan area is clearly established which seems to be linked to the sediment load characteristics of the river and the considerable magnitude and frequency of overbank flooding.
This book outlines a generic set of procedures, termed the River Styles Framework, which provides a set of tools for interpreting river character, behavior, condition, and recovery potential. Applications of the framework generate a coherent package of geomorphic information, providing a physical template for river rehabilitation activities. management and restoration of rivers is a rapidly growing topic for environmental scientists, geologists and ecologists - this book provides a learning tool with which to approach geomorphic applications to river management describes the essential geomorphological principles underlying river behaviour and evolution demonstrates how the River Styles Framework can turn geomorphic theory into practice, to develop workable strategies for restoration and management based on real case studies and authors extensive experience applicable to river systems worldwide synthesises fluvial geomorphology, ecology and management.
A three-dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution, proportion, and connectedness of coarse-grained channel-belt deposits in alluvial strata as a function of channel-belt width, floodplain width, bankfull channel depth, channel-belt and overbank sedimentation rates, avulsion location and period, compaction, and tectonism (tilting and faulting). In this model, a floodplain surface of variable width and length is occupied by a single channel belt. Changes in floodplain topography are produced by spatial and temporal variation of channel-belt and floodplain deposition rates and by compaction and local or regional tectonism. The location and timing of avulsions are determined by local changes in floodplain slope relative to channel-b lt slope and by flood magnitude and frequency. The diverted channel belt follows the locus of maximum floodplain slope. At the end of each simulation, architectural parameters are calculated, including channel-deposit proportion and connectedness and the dimensions of channel-belt sandstone bodies. Three-dimensional perspective diagrams, mesh surfaces, and two-dimensional stratigraphic sections can be plotted to illustrate depositional surfaces (time planes) and the location and geometry of coarse-grained channel-belt deposits within finer-grained overbank deposits. The model predicts that channel-belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross-section orientation. Upstream from avulsion points, sandstone bodies have low width/thickness ratios because of aggradation in a fixed channel belt. Immediately downstream from avulsion points, channel belts tend to be connected, resulting in sandstone bodies with high width/thickness ratios. Avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period. Such sequences may produce successions in which channel-belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years. Down-valley increases in aggradation rate or down-valley decreases in floodplain slope (for example, associated with a rise in base level) may result in an increase in channel-belt proportion and connectedness because of high avulsion frequencies in down-valley regions of the floodplain. Down-valley decreases in aggradation rate (as in alluvial fans, foreland basins, and during base-level fall) may result in high avulsion frequencies in up-valley parts of the floodplain. Tectonic tilting and faulting locally increase avulsion probabilities, and channel belts generally shift toward areas of maximum subsidence. Under certain conditions, however, depositional topography may cause channels to shift away from areas of maximum subsidence. Channel-deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain, but distribution (clustering) of channel belts may not be a reliable indicator of fault geometry or displacement. Models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified. The three-dimensional model presented here predicts many of the features of channel behavior observed in modern rivers, but there is a pressing need for better models and adequate natural data to test them.
The Kosi River shifts laterally over the Himalaya foreland plain by continual minor cutoffs and bank cutting and by episodic major shifts across watersheds, by moving into and then out of preexisting, adjacent, less actively aggrading streams. Migration is unidirectional because after a channel is filled to instability, floodwater will drain preferentially into a new adjacent low rather than across it to the next watershed or back to the last abandoned channel. Major shifts seem stochastic and autocyclic; they do not correlate with the many severe quakes and floods that undoubtedly helped prime the system for shifts.
Palaeohydrology has continued to develop during the GLOCOPH period (1991-2003) so that it is now appropriate to consider how its research contributions can relate to global change. Palaeohydrology is just one multidisciplinary research field that can make a contribution to the study of global change, achieved through deriving data, elucidating the mechanics of change; identifying spatial contrasts; assisting the coupling of global change models to hydrological models, and eventually providing new models of palaeohydrological change. Palaeohydrology can contribute to river channel management, which has now progressed from hard engineering, to ecological and thence to sustainable approaches. Inputs from palaeohydrology can inform river channel hazards, although necessarily varying according to the engineering, working with the river, or sustainable approaches. Research on temporal change can provide information for river management to complement periods of continuous instrumental records. Contributions can be made from palaeohydrology for the elaboration of flow records, especially of palaeofloods; demonstration of the sensitivity of reaches and their role within a basin context; provision of hydrological and sedimentological histories to provide a temporal context; and elucidating the question of what is 'natural'. It is possible to extend protocols for river channel management by a provisional protocol from palaeohydrology. Although palaeohydrology may not readily provide analogues for future sequences it can provide insight into the scenarios and mechanisms that may occur, and offers experience that requires river management to be undertaken within the framework of a long-term perspective.