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Quaternary International 227 (2010) 81e86

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Quaternary International

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Shallow sub-surface stratigraphy of the Ganga basin, Himalayan foreland: Presentstatus and future perspectives

R. Sinha a,*, S.K. Tandon b, M.R. Gibling c

a Engineering Geosciences Group, Indian Institute of Technology Kanpur, Kanpur 208018, IndiabDepartment of Geology, University of Delhi, Delhi 110007, IndiacDepartment of Earth Sciences, Dalhousie University, Halifax NS, B3H 3J5 Canada

a r t i c l e i n f o

Article history:Available online 15 July 2010

* Corresponding author. Tel.: þ91 5122597317.E-mail address: rsinha@iitk.ac.in (R. Sinha).

1040-6182/$ e see front matter � 2010 Elsevier Ltd adoi:10.1016/j.quaint.2010.07.015

a b s t r a c t

The Ganga basin in northern India is one of the world’s largest fluvial basins and has attracted enor-mous attention from earth scientists across the globe with a view to understanding large riverprocesses and landforms. Despite the scarcity of hydrological data from the Ganga basin, someimportant studies have been carried out in the last several decades. However, the unavailability of deepsections in this vast alluvial tract has always limited understanding of the sub-surface stratigraphy ofthese plains. During the last decade, some important developments have taken place in integratingexposed cliff section data with the drill cores in pre-defined transects and with targeted geophysicalinvestigations. Additionally, new areas of the basin have been studied for understanding landscapeevolution including the effects of active tectonics. This special issue of Quaternary Internationalhighlights some of these developments from the stratigraphic archives of this large basin. Thiscollection of papers covers a wide gamut of subjects including terrace development in the frontal partsof the Ganga basin, resistivity-based mapping of sub-surface stratigraphy, micromorphology of soilsfrom plains drill-core samples, historical-scale avulsion of large dynamic system such as the Kosi,active tectonics and landform development in southern Ganga plains and finally some policy issues formanagement of dynamic river systems. This introductory paper provides a background and presentstatus of research in the Ganga basin. It attempts to summarise some of the recent research devel-opments in the Ganga basin research and highlights the unresolved issues, some of which have beenaddressed through the contributions in this special issue.

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1. Introduction

In order to improve our understanding of large river basins,a holistic approach is necessary, an approach that relies on multi-disciplinary analysis and synthesis of surface and sub-surface datathat includes geological, geophysical, pedological, mineralogical,geochemical, mineral magnetic and geomicrobiological results. TheGanga basin of northern India contains several kilometres of allu-vial strata and constitutes one of theworld’s most extensive alluvialplainse home to hundreds of millions of people, mostly dependenton agriculture. The plains constitute a fluvial region traversed bylarge rivers such as the Ganga (length: 2510 km; catchment area980,000 km2) and Yamuna (length 1376 km; catchment area366,223 km2) that are sourced in the Himalayan orogen, as well asrivers such as the Betwa, Chambal, Ken, and Son that are sourced in

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the central Indian Craton. Additionally, many smaller plains e fedrivers are sourced within the plains. The Ganga plains are of greatsignificance as they constitute an important link now and duringthe earlier Quaternary between the Himalayan Orogen and theIndian Ocean. Additionally, understanding the landforms of theGanga Plains e their origin, development and dynamic imprints eis of critical significance to plan effectively for sustainable devel-opment of the region. For comprehensive future strategies forutilization of the Ganga plains resources, it is necessary to study theplains to track changes in the alluvial landscape on different timescales e for example decadal, century, millennial and higher ordertime scales of 104e105 years. Multiple approaches must be adoptedthat combine modern process studies, Holocene environmentalchange, and alluvial stratigraphic development in the shallow sub-surface (w100 m depth).

Evolutionary history of most landforms (mega- and mesoscale)in the Ganga Plains remains poorly understood because of themethodological difficulties associated with the study of sub-surfacedeposits. This aspect, notably the general non-availability of sub-

R. Sinha et al. / Quaternary International 227 (2010) 81e8682

surface geological data and drill cores, has been a serious impedi-ment in elucidating the history of alluvial plain sedimentation. TheDepartment of Science and Technology (DST), Government of Indiainitiated a research programme on the Science of Shallow Sub-surface (SSS) in 2005 with the objective of developing strategiesand a data base for the shallow sub-surface zone of different partsof India. This was an outcome of the long-felt realization that majorIndian river basins and deltas that support extensive agriculturalactivities should be studied on a priority basis. A coordinatedmulti-disciplinary program in several major river basins has emphasizedthe evolutionary history of mega- and mesoscale landforms thatrequire an integration of surface and sub-surface data. This specialissue of Quaternary International focuses on the Ganga basin andpresents a collection of papers dealing with new approaches tounderstand shallow sub-surface stratigraphy, surface processes andthe integration of the two.

This special issue is dedicated to Arthur Geddes who wasa Professor in Geography at Edinburgh, UK and contributedsignificantly to the advancement of physical as well as humangeography. He produced one of the first detailed geomorphic mapsof the Ganga plains along with topographic contours of themonotonously flat plains (Geddes, 1960). These maps provided thefirst perception of the major landscape elements of these plains. Hedescribed a series of ‘cones’ and ‘intercones’ across the entireGangetic plains. Although the terms cones and intercones have nowbeen replaced by fans and interfans in the geomorphic literature,the identification of these landscape-scale elements in the plainswas an important development which later led to more systematicinvestigations of these areas not just in terms of geomorphologyand landscape development but also in terms of understanding thealluvial stratigraphy below these plains. The following sectionshighlight some of the important recent developments in GangaBasin research.

2. Ganga basin research e where do we stand?

Academic interest in the Ganga basin has been focused alongfour major lines; (a) sediment discharge budgets (e.g., Metivier,1999), (b) description of the geomorphic and sedimentologicfeatures (e.g. Geddes,1960; Sinha and Friend,1994; Singh,1996), (c)geophysical prospecting to describe the sub-surface mainly forhydrocarbon exploration (e.g., Sastri et al., 1971; Raiverman et al.,1983), and (d) alluvial stratigraphic development (Gibling et al.,2005; Sinha et al., 2007, 2009). Fluvial geomorphology, sedimen-tation history and basement tectonics associated with the basinwere discussed extensively through to the 1990s (Geddes, 1960;Sastri et al., 1971; Joshi and Bhartiya, 1991, Raiverman et al., 1983;Sinha, 1995; Singh, 1996).

In tackling the complex geomorphic organization of the Gangabasin drainage, a fundamental point is the recognition of distincttypes of fluvial system, each characterized by different source areacharacteristics, viz. mountain-fed, foothills-fed and plains-fed(Sinha and Friend, 1994). Each of these “systems” has characteristicgeomorphic ‘units’ and these units themselves consist of differentgeomorphic ‘elements’. The mountain-fed rivers such as the Ganga,Gandak and the Kosi (Fig. 1) act as efficient conduits for thetransport of a great quantity of sediments, derived from theirsource areas of high relief, and consequently form large deposi-tional areas (fans, in some cases) in the plains. The foothills-fed (e.g.Baghmati, Rapti) and plains-fed (e.g. Burhi Gandak, Gomati) riversdrain the interfan areas and derive their sediments partly from thefoothills and mostly from within the plains, and a large proportionof this sediment is deposited back into the plains after localreworking. The interfan areas, therefore, essentially consist largelyof overbank sediments and represent mud-dominated intervals in

the Quaternary alluvium, although they locally include the depositsof rivers draining the interfluve surface such as the Baghmati (Sinhaet al., 2005a). Apart from developing a strongly ‘hierarchical’ sense,this approach allows examination of drainage and geomorphicheterogeneity from very large to small scales. This is a significantdeparture from previous work in which spatial homogeneity ingeomorphic development was implied, based on the inference thatcorrelatable geomorphic surfaces were present across vast regionsof the Ganga plains (Singh et al., 1990; Singh, 1996).

Studies on facies distribution of near-surface fluvial deposits inthe Ganga plains have concentrated mainly in the major channelareas (Singh, 1972; Singh and Kumar, 1974; Singh and Bhardwaj,1991; Shukla et al., 1999), as well as on channel dynamics of thenearby Brahmaputra river (Bristow, 1987; McLelland et al., 1999).Fewer studies have focused on megafan systems. Research on theKosi megafan in north Bihar plains (Singh et al., 1993) revealsa dominance of sandy facies in the plains with a very narrow zoneof gravel restricted to the reaches close to the mountain front(10e20 km downstream of the mountain front). Limited studies onsub-surface stratigraphy of themegafan deposits (Singh et al., 1993)suggest that they consist of multi-storied sand-sheets (generallygravel in upper reaches), interbedded with overbank muddy layers.In contrast to the channel deposits, which have received wideattention, the information available on the stratigraphy of theextensive interfluve areas, which form the overwhelming majorityof the Ganga plains surface, has until recently been very limited.Shallow alluvial architectural studies in the GandakeKosi interfluve(Sinha, 1995; Sinha et al., 1996; Jain and Sinha, 2003; Sinha et al.,2005a) showed that the top 2e3 m of the interfluve predomi-nantly consist of muddy sequences, with narrow sand bodiesdefining former channel positions and very minor sandy layersdefining crevasse splays. In the ShardaeGandak interfluve area, thetop 10e20 m of sediments are characterized by muddy sequencesalternating with thick medium-grained sand layers. The coarsesand layer was interpreted as a possible marker for a Rapti palae-ochannel with high-energy fluvial regime.

The GangaeYamuna interfluve in Uttar Pradesh has attractedmuch recent attention, and initial work on this area focused ongeomorphic mapping using aerial photos coupled with sub-surfaceanalysis based on water well data (Bajpai, 1989; Singh and Bajpai,1989). Singh et al. (1999) provided a brief description of theimportant Kalpi cliff section along the Yamuna river with evidence(worked bone artifacts) of human occupation of the region sincew30 ka. A provisional stratigraphic framework for the section anda small amount of chronological data was presented, and aninterplay of climate and tectonics was implied in the deposition ofthis 33 m thick section (Singh et al., 1999). Later research (Sinhaet al., 2002, 2005b; Gibling et al., 2005; Tandon et al., 2006) hasled to significantly different interpretations. Using an integratedapproach involving geomorphic analysis aided by remote sensing,and followed by rigorous stratigraphic and sedimentologic analysisof the exposures in cliff sections, these workers have recognizedprominent stratigraphic discontinuities. These discontinuities formthe basis for a stratigraphic framework that can be dated andcompared against proxy records for controlling factors (tectonics,climate, and relative sea-level). This work was followed up byraising a series of drill cores from the Ganga valley and the adjacentinterfluve to the south, which has further extended and improvedour understanding of the region (Sinha et al., 2007).

Some workers advocated the importance of preferentiallyaligned, tectonically-controlled lineaments on the channel patternof the Ganga river, and also suggested that lineaments have causedpreferential cliff incision along the southern bank near Kanpur(Singh and Rastogi, 1973; Singh et al., 1997, 1999; Srivastava et al.,2003). No support was provided for this argument from sub-

Fig. 1. The Ganga plains in the Himalayan foreland basin. The plains are fed by the rivers originating in the Himalaya to its north as well as the Craton to its south. The Ganga riverforms the axial drainage with a total length of 2510 km and catchment area 980,000 km2.

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surface data. Shallow sections below geomorphic surfaces nearKanpur were dated by Srivastava et al. (2003) and yielded earlyHolocene ages, although these surfaces are separated vertically byw10 m. In view of these dates, the suggestion of major tectonicactivity at w6 ka to trigger valley incision (Srivastava et al., 2003)does not seem plausible. On the contrary, a climatic control isstrongly supported by the regional distribution of incision events atsites across the Ganga plains and in western India, as well as bya general correlation with the available climatic proxy records forthe region (Sinha et al., 2002; Gibling et al., 2005; Tandon et al.,2006). The early to mid-Holocene was marked by high precipita-tion, and our own further work in this region using shallow drillcores suggests significant valley aggradation during these times(Sinha et al., 2007), as well as southward migration of the Gangariver. It has been argued that major phases of valley incision tookplace during transitions between humid and less humid conditions(for example, following the Last Glacial Maximum and during themid-Holocene). Conditions during such transitions are especiallyable to trigger incision due to changes in runoff intensity, as sug-gested by recent modelling (Rinaldo et al., 1995; Tucker andSlingerland, 1997).

3. Unresolved issues and recent developments

The controls of alluvial architecture below the Ganga plainscontinue to be investigated, and the need for a comprehensive dataset on the sub-surface stratigraphy of the Ganga plains is enormous.Furthermore, the Ganga river system has experienced large fluctu-ations in discharge and sediment yield induced by variations overthe last 150,000 years in the strength of the monsoon (Goodbred,2003; Gibling et al., 2005), which is known from modelling andfield-based studies to have varied greatly over the past 100,000years and beyond (Prell and Kutzbach, 1987; Overpeck et al., 1996;Clemens and Prell, 2003). Some of the important questions which

remained unanswered over several decades of research in theGanga basin include: (a) how long have the axial Ganga and Yamunarivers been near their present positions, and have they ever inun-dated the interfluve between them? (b) how have the Himalayanand cratonic rivers competed in the geological past to generate theGanga plains stratigraphy? (c) is the modern geomorphic setting ofconsiderable antiquity, or have themajor rivers beenmoremobile inthe past and able tomigratemore freely? (d) what has been the rateof river migration and what has been the role of thrusting anddeformation along the Himalayan Front to the north in promotingriver avulsion? (e) how are variations in monsoonal intensityreflected in the sediment record of valleys and interfluves? (f) candistinctive stratigraphic patterns be used to test models of land-scape evolution across the vast expanse of the Ganga plains?

Most of these questions required an in-depth analysis of sub-surface stratigraphy which was not previously possible due tolimited exposures across the plains. Apart from the incised riversections in the western Ganga plains, there are few natural expo-sures that allow researchers to examine and understand spatial andtemporal variability in stratigraphy of the plains and link them toforcing functions. Systematic drilling and coring in this region hasbeen non-existent until recently. A major research programme wastherefore launched by us in 2000 and a decade of research hasinvolved cliff section stratigraphy, drill-core stratigraphy, resis-tivity-based sub-surface mapping, geochemistry, sedimentologyand magnetic mineralogy. These studies have added to ourunderstanding of the Ganga basin’s stratigraphic development, itsresponse to monsoonal forcings, and competition between Hima-layan and cratonic supply of sediments, among many importantissues. We summarise below some of the important contributionsand suggest some possible future lines of enquiry.

The stratigraphic record for the upper 50 m of the alluvial coverin the western Ganga plains has been studied through river-banksections (Gibling et al., 2005, 2008; Sinha et al., 2005b; Tandon

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et al., 2006) and drill cores (Sinha et al., 2007, 2009). These stratacover a period ofw100 ka, revealing a complex history of dynamicsof large and small river systems, and a strong climatic control. Amarked geomorphic diversity from north to south, as well as east towest across the Ganga plains (Sinha et al., 2005c), adds furthercomplexity in terms of the response of the river systems to externalforcing.

An important finding is the recognition of major discontinuitiesin the late Quaternary interfluve sequences (Gibling et al., 2005)separating aggradational sequences. Such discontinuities aremanifested as pedogenic events, gully fills, non-fluvial deposition,and carbonate cementation/calcrete development. The valley fillsof the Ganga record two major aggradational phases (pre-LGM andmiddle Holocene) in drill cores penetrating down to about 25 m(Sinha et al., 2007). Amajor river (paleo-Ganga) was located near itspresent position since at least 26 ka BP, with indications of south-ward migration between 11e6 ka. Our chronological work on thecliff sections and cores from the Ganga plains suggest that some‘aggradationedegradation rhythms’ follow monsoonal fluctuationsduring the Late Quaternary (Prell and Kutzbach, 1987, 1992;Clemens and Prell, 2003). Repeated cycles of valley aggradationoccurred particularly during transitions between humid and dryclimates, in accord with the available chronological and climaticproxy data and modelling results for the region. Where geochro-nological results are available, valleys in the western Ganga plainsmanifest late glacial/early Holocene incision in response tomonsoonal intensification, and this regional phase of incision wasprimarily responsible for generating the modern landscape in thisregion. Floodplain degradation and intra-valley floodplain accu-mulations mark the weak summer monsoon periods. High-reso-lution studies of lake sediments from the Ganga plains (Sharmaet al., 2004) have provided an important proxy record for climate,with which fluvial events may be compared.

A more recent work by Rahaman et al. (2009) has demonstratedthat the relative proportion of sediment supply from the Higherand Lesser Himalaya has varied through time in consequence ofmonsoonal fluctuations. In the 87Sr/86Sr and 3Nd profile froma Ganga plains core, two major excursions at w20 ka and w70 kawere identified, coinciding with periods of precipitation minimaand larger glacial cover. It was suggested that these excursionsresulted from a decrease in the proportion of sediment transportedfrom the Higher Himalaya due to decrease in monsoon precipita-tion and increase in glacial cover, which in turn are caused by lowersolar insolation.

Another important question tackled recently is the competitionbetween the Himalayan and cratonic sources of sediment togenerate a distinctive stratigraphic architecture below the plains(Sinha et al., 2009). Contrary to the general belief that the Hima-layas have been the dominant contributor of sediments in theGanga plains through most of the Quaternary (Burbank, 1992),Sinha et al. (2009) argued that the contribution from cratonicsources has been significant during the Late Quaternary. The sub-surface alluvial stratigraphy in the Gangetic plains reflects suchcompetition between the Himalayan and cratonic sources. Based onframework grains and dense minerals of drill-core sediments andmodern river sands, a wedge of cratonic sediment extended wellbeyond the modern line of the axial drainage in the southwesternpart of the foreland basin, at both shallow and deep levels. It wasconcluded that the dynamic cratonic rivers have been under-estimated as contributors to the Himalayan foreland basin. TheYamuna river may have occupied its present position in the Gangaplains only after w6 ka, prior to which cratonic rivers may havecontributed a considerable amount of sediment to the Ganga Riverand Bay of Bengal, although the Himalayan contribution hasprobably always predominated.

4. In this issue

The present issue has a set of seven papers including theintroductory paper which provides an overview of the Ganga plainsresearch. Sinha et al. focus on the stratigraphic sections alonga 50 km stretch of the Ganga valley in the frontal parts of theHimalaya. The authors recognize four levels of fluvial terraces, bothstrath and fills, and alluvial fans, and argue that these terracesdeveloped as a result of tectoniceclimate coupling during the LatePleistocene and Holocene. Based on OSL chronology, these terracesurfaces formed through river incision at w11 ka, 9.7 and 6.9 ka,andweremost probably climatically induced. The incision events atw11 ka and w7 ka are analogous to those recorded across theHimalaya and in the Ganga plains (Pratt et al., 2002; Goodbred,2003; Pratt-Situala et al., 2004; Tandon et al., 2006). The factthat, even in the tectonically active Himalayan mountain front,terrace formation is driven by climate is a significant input for thegeneral understanding of landform development in this region,although tectonics has influenced terrace elevation and gradient(Lavé and Avouac, 2000; Singh and Tandon, 2007).

Yadav et al. demonstrate the application of Vertical ElectricSounding (VES) for inferring shallow sub-surface stratigraphy inparts of the Ganga plain. This study fills a significant gap in terms ofreliable stratigraphic sections in an area where cliff sections arelimited and drill-core data is scarce. Resistivity sounding data fora stretch ofw150 km in the interfluve areas between the Ganga andYamuna rivers and Yamuna and Betwa rivers in the western Gangaplains clearly exhibit the vertical extension of the valley fills andinterfluve sequences down tow100 m. Apart from locating distinctboundaries between sandy and muddy strata, very high and verylow resistivity layers were interpreted as calcrete layers and salineaquifers, respectively. The study not only provides support for theinterfluve stratigraphy models proposed in earlier studies (Giblinget al., 2005; Sinha et al., 2007, 2009) but extends the stratigraphicdata to w100 m (w200 ka). The authors suggest that theGangaeYamuna interfluve is a stable and long-lived feature of theGanga plains and that the antiquity of the present valleyeinterfluveconfiguration extends to more than 200 ka. Significant sub-surfaceheterogeneity is noted across the valleyeinterfluve setting as wellas within the interfluves themselves.

Sahu et al. have investigated the parts of theMiddle Ganga valleyinBiharplains and report a classical exampleof tilt-inducedavulsionand channel migration during the Holocene. The study focuses onone of the important southern tributaries of the Ganga, the SonRiver, and parts of the GangaeSon confluence. Although tilting ofalluvial surfaces has been documented in the tectonically activeregion of north Bihar (Jain and Sinha, 2005), this is the first detaileddocumentation of active tectonics and its influence on landscapeevolution from a region south of the Ganga river. Although severalactive sub-surface faults reported from the northernpart (Dasgupta,1993; Jain andSinha, 2005)havebeen thought toextend southof theGanga, their influence on river morphology and processes hasremainedunknown. The authorshave identified9avulsionevents inthe Son river and have attributed these to high lateral tilt related toits proximity to one of the important faults, the East Patna Fault(EPF). The Ganga river is located in the lowered part of the tiltedblock away from the line of uplift, and hasmigrated in the down-tiltdirection. Various fluvial anomalies such as gradient reversals in thelongitudinal profile of channels, sinuosity variations, channel inci-sion, frequency of braid-bar distribution, and variation in the cross-sectional parameters of the channels were identified on satelliteimages and using topographic data to reconstruct the tectonichistory. The authors conclude that the rate of lateral tilt hascontrolled the style of channel movement, with gradual migrationoccurring at low tilt rates, and avulsion at higher rates.

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Srivastava et al. have presented a detailed documentation of soilmicromorphology of core sediments from the GangaeYamunainterfluve in the Himalayan foreland basin. Two cores,w50 mdeep,were used for this study, one each from the northern (IITK core) andsouthern (Bhognipur core) parts of the interfluve. Despite the coresbeing separated by only w60 km, they show significant variabilityin terms of distribution and nature of paleosols, and are charac-terized by a set of micromorphological features that includemicrostructures, rhizocretions, FeeMn features, pedogeniccarbonate, illuvial clay coatings and relict pedofeatures. Thesepaleosols range in character from simple ones having weaklydeveloped pedofeatures to mature paleosols with strongly devel-oped pedofeatures, and are similar to modern Entisols, Inceptisols,Alfisols and Vertisols of the Ganga Plains. The authors notea significant difference in the pedosedimentary evolution in thetwo cores representing northern and southern interfluves in termsof stratigraphic stacking of paleosols, types of paleosols, andheterogeneous nature of sediments. In the northern part (IITKcore), a thickmature paleosol with a strongly developed argillic (Bt)horizon at 41e45 m depth is striking, while the remaining core hasonly weakly developed paleosols. In the southern part (Bhognipurcore), a mature palaeosol with well-developed argillic (Bt) andvertic (Bss) horizons is noted at a shallower depth (10e14 m). Themature paleosol is interpreted to represent a major discontinuityduring MIS 5e4 transition when prolonged pedogenic activity tookplace following regional degradation and local gullying in responseto climate change from sub-humid to semi-arid conditions. Theauthors conclude that the pedosedimentary evolution of theinterfluve was controlled by climatic transitions from humid todrier phases and also by supply and availability of sediments.

The Kosi river in the eastern Ganga plains is one of the mostavulsive river systems in theworld and has often generated interestamong geomorphologists and stratigraphers alike, the former interms of understanding the avulsion process (Wells and Dorr, 1987;Sinha et al., 2009) and the latter in terms of a distinctive alluvialarchitecture below the Kosi megafan (Singh et al., 1993). Chakra-borty et al. have revisited the Kosi river and have examined thehistorical records to question the hypothesis of unidirectionalwestward migration of the Kosi River over the last two centuries.On the contrary, the Kosi channels have occupied a narrow zone inthe east-central part of the megafan. The channel position did,however, oscillate randomly within this zone. Further, the authorsargue that, based on examination of the upper 2e3 m of successionin the north-central part of the megafan, there is an overwhelmingdominance of meandering stream deposits across the fan surfaceand not deposits characteristic of a sweeping braided river. Threeaccretionary lobes identified on the fan surface and their relativechronology, determined from channel discordances between lobes,suggest avulsive behaviour of the trunk channel which is in linewith other fans across the world such as the Tista in the easternGanga-Brahmaputra plains and Taquari in Pantnal wetland, Brazil.Themost recent avulsion of the Kosi river byw120 km to the east inAugust 2008 (Sinha et al., 2009) is also in line with the avulsivebehaviour of the Kosi. The authors reiterate the inefficacy of engi-neering solutions for large rivers through high embankments andlarge dams, and argue that these measures have enhanced theavulsive tendency of the river. Co-existence with floods and avul-sions and an integrated catchment management may be betterstrategies than a ‘command and control’ approach.

The last paper by K. Rudra deals with the science-policy inter-action of river dynamics with special reference to the Ganga inWest Bengal. This stretch of the Ganga river is perhaps the leaststudied stretch and there is very little understanding ofthe processes controlling river dynamics. Almost no data exists onthe sub-surface stratigraphy of the alluvial plains in this region. The

author has compiled the data on historical movements of the Gangariver in West Bengal since the second half of the 18th century fromrather inaccessible sources of maps. Reconstruction from sequen-tial maps suggests that the Farakka barrage, since its constructionin 1971, has influenced the morphology and position of the GangaRiver in a major way. The Ganga has migrated eastward appreciablysince 1971 and has formed a mighty bend upstream of the barrage.The impact of the barrage on the river flow and morphologyextended tomore than 150 km upstream of the barrage. The authorargues that river aggradation upstream of the barrage has been theprimary factor influencing the change. Downstream of the Farakkabarrage, the river has been unstable and bank erosion has beena serious problem. Several villages have shifted to the oppositebanks due to rapid channel migration. Apart from causing damageto the local people, such rapid migration has serious politicalimplications at interstate as well as international level. Adjoiningthe Ganga river, the state of West Bengal shares its boundaries withBihar and Jharkhand states and Bangladesh; the river migration ata decadal scale has posed problems such as land reallocation,population displacement, and border disputes. These issues needserious policy interventions, and the existing laws and constitu-tional amendments are not adequate to handle these problems,neither at interstate nor at international level. The author hasemphasized that, “...the river management in India was guided bya colonial legacy and a ‘business-as-usual’ engineering approachwithout any concern for holistic eco-hydrology. A paradigm shift isneeded from a narrow sectoral outlook of ongoing river managementstrategy to the ecological engineering approach.”

5. Future perspectives

Having evolved strategies for geomorphic mapping of someparts of the Ganga plains, these need to be applied uniformlythrough the entire length of the dispersal system from the Hima-layan Orogen to the ocean sink(s). This is imperative for under-standing the landscape connectivity in conjunction withhydrological and sediment connectivity. The assessment andanalysis of the connectivity structure(s) in a multi-scale contextwill serve as a pre-requisite for exploring ideas related to the timescales of propagation of signals at different scales, both in spatialand temporal contexts, across the length of the dispersal system.

Yet another gap in the holistic understanding of the Gangasource-to-sink dispersal system is insufficient surface and sub-surface data in the downstream reaches of the Ganga (south andeast of the Kosi river). Such data would eventually enable a betterunderstanding of the stratigraphic development of the Gangaplains as governed by the interaction of fluvial and marineprocesses.

The geomorphic diversity and heterogeneity in landscapecompartments of the Ganga plains needs to be explored further.Such data need to be collected particularly in the landscapecompartments occurring to the south of the axial rivers, in additionto intensifying efforts in all the other compartments as well. Finally,good practices in river management depend strongly on an inte-gration of rigorous geomorphological, hydrological and ecologicaldata collected at different scales. Such experimental studies need tobe undertaken in strategically chosen reaches. Results from thesestudies could then be of general applicability not only formanagement of the Ganga river but also for the optimal manage-ment of the natural resources of the river basin.

Acknowledgements

Several studies reported in this special issue were supportedthrough a large programme on the Science of Shallow Subsurface

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(SSS) funded by the Department of Science and Technology (DST),Government of India. We sincerely thank DST for their generoussupport for this programme.Wewould also like to thank all authorswho contributed to this special issue and have waited patiently forthe issue to be finalized. This research is a contribution to IGCP 582on Tropical Rivers.

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