shallow sub surface stratigraphy of the ganga basin himalayan foreland present status and future perspectives the ganga basin in northern india is one of the world s largest fluvial basins and has attracted enormous attention from earth scientists across the globe with a view to understanding large river processes and landforms despite the scarcity of hydrological data from the ganga basin some important studies have been carried out in the last several decades however the unavailability of deep sections in this vast alluvial tract has always limited understanding of the sub surface stratigraphy of these plains during the last decade some important developments have taken place in integrating exposed cliff section data with the drill cores in pre defined transects and with targeted geophysical investigations additionally new areas of the basin have been studied for understanding landscape evolution including the effects of active tectonics this special issue of quaternary international highlights some of these developments from the stratigraphic archives of this large basin this collection of papers covers a wide gamut of subjects including terrace development in the frontal parts of the ganga basin resistivity based mapping of sub surface stratigraphy micromorphology of soils from 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 for management of dynamic river systems this introductory paper provides a background and present status of research in the ganga basin it attempts to summarise some of the recent research developments in the ganga basin research and highlights the unresolved issues some of which have been addressed through the contributions in this special issue

sone megafan a non himalayan megafan of craton origin on the southern margin of the middle ganga basin india abstract researchers in the last few decades have focused on the fluvial megafans at the base of himalayan foothills in the ganga basin no major effort has so far been made to delineate any such large depositional environment at the base of the northern indian peninsular craton at the distal parts of the basin in this work for the first time we document a megafan unusually created by the cratonic sone river in the marginal plains south of the ganga the geomorphology of the megafan surface distribution of palaeochannels sedimentology and areal extent of the megafan are described the study also reconstructs the tectonic and palaeoclimatic conditions which might have helped in sediment supply from the cratonic catchment areas of the sone we suggest tectonic control over the sone river channel dynamics and development of the megafan the oval and fan shaped craton derived sediment body covers an area of around 12 000 km2 in the marginal plains and about 9000 km2 in the central alluvium north of the ganga river the megafan is around 190 km long and 240 km wide the mean slope of the megafan surface is 0 03 an onlap of himalayan sediments has occurred over the megafan at its toe parts caused by southward encroachment of the ganga during the holocene the megafan sediments comprise brownish yellow fine to coarse sand and gravels with an admixture of carbonaceous nodules kankars the thickness of the megafan sediment which directly overlies the precambrian basement varies from only a few meters in the south near the peninsular craton to 1000 m at the north in the central alluvial plain the granular zones form prolific aquifer systems in an otherwise poor hydrogeological setting of the marginal plains

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

causes of recent himalayan uplift deduced from deposited patterns in the ganges basin the hypothesis1 that late cenozoic uplift of many of the world s mountain ranges was a response to climate change rather than to tectonic processes is based on the premise that enhanced erosion in an altered climate led to a reduction in both the total mass of a mountain range and its mean elevation this reduction was coeval with increased regional relief and with passive isostatic uplift of the remaining summits the hypothesis is difficult to evaluate because both climate and tectonic forces affect uplift in many active ranges in the absence of sufficient denudational and uplift data from the mountains themselves depositional patterns in adjacent basins may sometimes be used to distinguish between uplift arising from erosional or from tectonic processes in foreland basins uplift of the proximal basin and a reduction or absence of asymmetric subsidence are predicted responses to erosionally driven uplift2 here i show that patterns of sediment accumulation and the position of major rivers in the neogene gangetic foreland basin seem to have changed markedly in plio pleistocene times these changes lend support to the hypothesis that the importance of erosional unloading has increased in the himalayas during the past 4 myr

response of the ganges dispersal system to climate change a source to sink view since the last interstade the forcing of sediment dispersal systems by climate is widely accepted but there remains disagreement on the general responses to climate change such as how resulting signals propagate downstream and ultimately how they are preserved in the stratigraphic record towards a better understanding of these issues this paper presents a comprehensive overview of ganges dispersal system behavior since the last interstade which reveals major coeval responses to changes in the south asian monsoon at 3000 km from its mountain headwaters to deep sea fan the ganges dispersal system is immense and yet shows tight coupling between source area catchment basin and coastal and marine depocenters furthermore system wide responses and downstream transfer of the signal appear to occur at least as fast as current temporal resolution of 1 2 ky this tight linkage of source to sink components is considered a function of the southwest summer monsoon s overwhelming control on regional hydrology about 80 of the ganges discharge and 95 of its sediment load are delivered to the margin during only 4 months making the system extremely sensitive to this seasonal forcing in addition the regional scale and distribution of the monsoon weather system means that changes in atmospheric circulation affect the entire drainage basin rather than local subcomponents finally despite its present intensity strength of the summer monsoon has varied significantly over the past 150 ky under orbitally driven changes in insolation and global glacial boundary conditions the resulting changes in precipitation both well above and below modern values have forced system wide responses ranging from glacier advance retreat to sediment fluxes to the margin and deep sea fan the overall conclusions are 1 that this immense dispersal system responds to multimillennial scale 104 years climate change in a system wide and largely contemporaneous manner and 2 that major sedimentary signals can be transferred rapidly from source to sink with little apparent attenuation furthermore these acute responses to climate change have produced sedimentary stratigraphic features that diverge from traditional sequence models in their nature and timing

using local moran s i to identify contamination hotspots of rare earth elements in urban soils of london abstract rare earth elements rees in urban soils are receiving more attention because of their increased use in modern technology up to now there is little information about the spatial patterns of rees and their influencing factors in urban soils in this study based on the british geological survey london earth geochemical survey data containing a total of 6467 soil samples collected from the urban area of london the spatial distributions of ce la nd sc sm yb and y and their influencing factors were investigated the element sc is included in this study as related element urban samples were collected at a depth of 0 20 cm and total concentrations of 48 chemical elements were determined in the

late pleistocene holocene hydrologic changes in the interfluve areas of the central ganga plain india abstract abandoned channel belts ponds and point bar deposits of palaeochannels in the interfluve regions of the central ganga plain suggest changes in the morphohydrologic conditions during the latest pleistocene holocene stratigraphy of these ponds comprises channel sand at the base overlain by shell bearing clayey silt the contact of the two facies marks the phase when channels converted into standing water bodies point bar deposits of some palaeochannels are overlain by oxidised aeolian sand indicating that the channel abandonment possibly occurred due to the desiccation and aridity in the region optically stimulated luminescence osl chronometry of the pond sediments suggests that the deposition of the basal channel sand started before 13 ka and continued up to 8 ka the ponds formed around 8 6 ka when the channel activity ceased evidence from the point bar deposits also indicates that the fluvial activity in the region ended sometime during 7 5 ka this was followed by aeolian aggradation the present study thus suggests that the hydrologic conditions in the gangetic plains i e initiation of channels and their abandonment formation of microgeomorphologic features such as ponds and their eventual siltation were controlled largely by climatic changes i e monsoon changes supported by tectonic activity for the past 2 ka increasing human and related agricultural activity has substantially accentuated the natural siltation rate of ponds

early to middle tertiary foreland basin development and the history of andean crustal shortening in bolivia a 2 5 km thick succession of tertiary strata in the eastern cordillera of southern central bolivia consists of predominantly fluvial and lacustrine deposits the age of the base of the succession is middle paleocene and its upper part which is erosionally truncated is probably late oligocene early miocene the lower 50 130 m of the succession consists of interbedded fluvial sandstone and mudstone including minor paleosols of the santa lucia formation these strata are overlain by up to 50 m of pervasively pedogenically altered mudstone and sandstone in the upper part of the santa lucia formation and lower part of the impora formation that may represent much of late paleocene eocene time above the paleosol zone is a thin zone 10 m of lacustrine carbonate and clastic rocks in the uppermost impora formation and this in turn is overlain by a 2000 m thick upward coarsening succession of clastic fluvial deposits in the cayara camargo and suticollo formations paleocurrent data indicate that fluvial channels that deposited the santa lucia impora and cayara formations flowed mainly westward whereas channels responsible for the camargo and suticollo formations flowed generally eastward modal sandstone petrographic data show a long term evolution from subarkosic during santa lucia deposition to quartz arenitic during impora and cayara deposition to sublitharenitic during camargo and suticollo deposition compositions we argue that the lithofacies and sediment accumulation history of this succession are most consistent with deposition in an eastward migrating foreland basin system e mail decelles geo arizona edu critical to this interpretation is the zone of extreme stratigraphic condensation in the lower impora formation the inferred upper paleocene eocene part of the succession the abrupt decrease in sediment accumulation represented by this zone is difficult to reconcile with the leading alternative model in which continuous postrift thermal subsidence resulted in a gradual continuous decay of early tertiary sediment accumulation rates stratigraphic condensation is however consistent with passage of the forebulge through the region an interpretation that also can be reconciled with the record of foreland basin development in the altiplano to the west and gross sediment accumulation patterns in the subandean zone and modern foreland basin to the east simple flexural modeling and palinspastic reconstruction of the complete cenozoic migration history of the foreland basin system suggest that 1000 km of foreland lithosphere has been underthrust westward beneath the andean orogenic belt at the latitude of southern bolivia the amount of middle and lower crust that would have been added to the andean infrastructure is sufficient to explain the present crustal thicknesses in bolivia

shallow sub surface stratigraphy of interfluves inferred from vertical electric soundings in western ganga plains india the application of geophysical surveys such as vertical electric sounding ves for inferring shallow subsurface stratigraphy in the vast alluvial tract of india has been under utilized this paper is aimed at demonstrating the potential of resistivity methods for mapping alluvial stratigraphy in parts of the ganga plains where the availability of exposed sections is scarce and bore logs are very limited data was generated from 40 vertical electrical resistivity soundings in a stretch of w150 km in the interfluve areas between the ganga and yamuna rivers and yamuna and betwa rivers in the western ganga plains based on the available lithological data from cliff sections along the major and minor rivers draining the study area and a series of 7 drill cores along the transect the resistivity sounding data was calibrated to interpret the sub surface stratigraphy the data shows the vertical extension of the valley fills and interfluve sequences down to w100 m a high resistivity layer runs quite extensively across the interfluves and below the valley fills interpreted as a calcrete layer that may mark a major discontinuity patches of very low resistivity layers in valley fills as well as interfluves suggest the presence of saline aquifers this study demonstrates significant sub surface heterogeneity across the interfluves which is a manifestation of variable fluvial activity over a period in excess of 100 ka lateral continuity of the sandy aquifers is often broken by muddy deposits of the floodplains which form a dominant component of the interfluve sequence except for the locations close to major valleys there are no major sand bodies in the upper w100 m of the interfluves which suggests that the modern configuration of the valleys and interfluves in this region is of late quaternary antiquity a few buried sand bodies however are comparable to the dimensions of the minor rivers draining the interfluve surfaces

late quaternary alluvial history of the northwestern deccan upland region continental and oceanic sediments from tropical africa australia and south america have recorded analogous changes in climate and stream behaviour during the late quaternary1 4 recently data from north central india have provided evidence for late quaternary changes in river regime in response to global changes in climate in the intertropical zone4 5 here we report evidence for late quaternary river metamorphosis6 from the northwestern deccan upland region of india radiocarbon dates combined with stratigraphic data have allowed the identification of major episodes of erosion and deposition7 8 supporting evidence from the arabian sea2 3 demonstrates that the successive phases of aggradation and incision are linked to late quaternary climatic changes7 8

extensional tectonic activity in the cratonward parts peripheral bulge of the ganga plain foreland basin india flexural subsidence of the indian lithosphere created the foreland basin in front of the emerging himalayan mountain belt the continued northward push of the indian plate and thrust sheet loading in the himalayan orogen caused an up warping along its cratonward margin in the form of a regional gentle bulge in the cratonward peripheral bulge small scale to moderate size deformation features e g gentle folds up arching of the sediment layers extensional normal faults and uplifted tilted blocks and incised river channels with 20 60 m high cliffs developed cliff sections of many rivers in this cratonward part of the foreland basin expose deposits of latest pleistocene holocene age and show evidences of active tectonics in the last few thousand years vertical uplift leading to deep incision of the river system development of prominent fractures cutting through the sedimentary succession bending and tilting of the strata and tilted blocks in the late quaternary relaxation phase of the himalayan orogen foreland there is increased vertical tectonic activity in the region of the peripheral bulge the vertical uplift in this part of the ganga plain foreland basin caused the rivers including the axial rivers to make further deep incision without shifting from their courses during periods of increased tectonic activity in the himalayan region i e the addition of thrust slices more rapidly probably caused the maximum down bending in the proximal part of the ganga plain foreland basin the high amplitude and asymmetric nature of this foreland basin is partly controlled by extensional tectonism

discrete element modelling of hanging wall deformation along the d 1 fault system danish north sea with implications for gas chimney interpretations abstract this study uses 3d seismic mapping nncc attribute analysis and 2d sdem modelling of soft sediment deformation to analyse hanging wall deformation related to faulting across a listric fault detaching along the top of a major salt roller the computational model experiments used the overall fault and salt structure evolution as boundary conditions to predict the distribution of faults within the hanging wall the modelling successfully reproduced geometries similar to the syn and antithetic faults that are visible on seismics but it also showed the presence of well defined vertical deformation zones both in the hanging wall and the foot wall of the listric fault in the model salt movement controls the formation of the deformation zones the similarity of nncc inferred vertical chimneys and the modelled deformation zones suggests that the subtle vertical chimneys identified in the 3d seismic data might actually be related to vertical to sub vertical deformation zones caused by the presence and movement of the salt structure

historical geomorphology and pedology of the gandak megafan middle gangetic plains india the gandak megafan of eastern uttar pradesh and northwestern bihar lies in the middle gangetic plains the gandak river has shifted about 80 km to the east due to tilting in the last 5000 years this has created a soil chronoassociation similar to the chronosequences found on some flights of river terraces this chronoassociation has five members qgd1 5 they are distinguished on the basis of profile development clay mineralogy and calcium carbonate content chlorite transforms to vermiculite on a large scale from qgd1 to qgd3 and decreases drastically in member qgd4 kaolinite and interstratified kaolinite smectite are abundant in the older members of the chronoassociation the youngest soils qgd1 500 b p while qgd3 soils like those on the older gandak plain and old rapti plains date back to 2500 b p qgd4 soils like those on the oldest gandak plain are dated as 5000 years b p whilst the oldest qgd5 soils as on the old ghaghra plain and ganga ghaghra interfluve date back to 10000 b p these soils which include pedogenic calcite and a saline epipedon indicate a dry climatic spell during the period 9000 11000 b p faults developed on the megafan are not related to the basement structures

a note on the extent of glaciation throughout the himalaya during the global last glacial maximum abstract quantitative chronologies for the impressive glacial successions that occur throughout the himalaya have until recently been almost totally lacking within the last decade two new techniques have promised to remedy this situation these techniques optically stimulated luminescence and cosmogenic nuclide surface exposure dating enable the age of many glacial features to be determined and have allowed us to study the extent and timing of himalayan glaciation in the late quaternary new data show that the local last glacial maximum lgm occurred during the early part of the last glacial cycle in most areas during marine isotope stage 3 mis 3 mis 3 was a time of increased insolation when the south asian summer monsoon strengthened and penetrated further north into the himalaya the concomitant increased precipitation occurring as snow at high altitudes produced positive glacier mass balances thereby allowing glaciers to advance on the other hand during the global lgm 18 24 ka himalayan glaciation was very restricted in extent generally extending

active transverse features in the central portion of the himalaya abstract many transverse lineaments or faults across the himalaya are already known interpretation of satellite images of the central portion of the himalaya given here adds to that number and suggests their continuity from the himalaya to its foredeep several such faults appear to be seismically active their shear motion recognized from geologic data and focal mechanism solutions compares well with a classical stress model when applied to northward progress of india under the himalayan collision front

river response to quaternary climatic fluctuations evidence from the son and belan valleys north central india abstract the last glacial period was cold and dry in peninsular india in north central india the interval from 39 9 to 16 3 ka was associated with widespread and prolonged aggradation in the son and belan valleys the aggradation ended with sustained vertical incision after 16 3 ka and reflects a return to warmer wetter conditions in this region it would appear that terminal pleistocene to holocene river incision was broadly synchronous with a strong summer monsoon regime and higher levels of river discharge and the preceding river aggradation with lower discharge and a weaker or more variable summer monsoon regime two older phases of prolonged aggradation followed by vertical incision are evident in the son and belan valleys before 39 ka one of these phases is centred towards 73 4 ka when ash from the toba mega eruption in sumatra was deposited across peninsular india the following phase of aggradation has yielded infrared stimulated luminescence ages of 58 6 and 45 12 ka the youngest phase of aggradation began towards 5 5 ka and seems to mark a return to a weaker summer monsoon regime

river systems and their sediment flux indo gangetic plains northern bihar india river systems of part of the himalayan foreland northern bihar plains india are described in terms of their channel morphology hydrology and suspended sediment characteristics a simple classification of the river systems based mainly on the source area characteristics is proposed i mountain fed ii foothills fed iii plains fed and iv mixed fed rivers distinct differences are noted between these classes of river systems most rivers show evidence of channel movement mainly by avulsion but cut offs also occur locally the mountain fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains fed rivers have relatively low discharge and high suspended sediment concentration the foothill fed rivers have moderate values of discharge and suspended sediment concentration the mountain fed rivers have built megafans of large extent whereas the foothills fed and plains fed rivers have formed muddy interfan areas semi quantitative estimates of water and sediment flux suggest that about 99 9 of the mass transfer into the plains is water with the remaining 0 1 being sediment and that 10 s of the latter 0 01 of the total is retained in the basin the remainder being transferred to the bengal fan

active tectonics and geomorphology in the sone ganga alluvial tract in mid ganga basin india active tectonics plays a major role in landscape evolution by bringing changes in topography and channel slopes the alluvial plains in ganga basin are divided into a number of tectonic blocks by several active subsurface faults the associated disturbances along these faults have given rise to a distinctive fluvial regime and geomorphology in the region in sone ganga alluvial plain in parts of south ganga plains in middle ganga basin the sone and ganga rivers have responded to the ongoing tectonic deformation in the area the study reports a classical example of tilt induced avulsion and channel migration during holocene from the parts of south ganga plains within the extensional half graben between east patna fault epf and west patna fault wpf the rate of lateral tilt appears to control the style of channel movement with gradual migration occurring at low tilt rates and avulsion at higher rates the river sone lying laterally close to the line of uplift has undergone avulsions at different times of tilting whereas the ganga river located at the lower parts of the tilting block away from the line of uplift has migrated in the down tilt direction various fluvial anomalies such as gradient reversals in the longitudinal profile of channels sinuosity variations channel incision frequency in the braid bar distribution and variation in the cross sectional parameters of the channels most probably created by tectonics have been studied satellite images and maps coupled with relative bank height measurements and other geomorphologic studies in field have helped in identifying such fluvial signatures and their relevance to tectonics the subsurface faults in the sone ganga plains cut across and also run parallel the river channels showing the effects of transverse and lateral tilting manifested in channel avulsions and migrations

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

shifting of the kosi river northern india 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

continental record of the southwest monsoon during the last 130 ka evidence from the southern margin of the thar desert india abstract field stratigraphy sedimentology and luminescence dating of the exposed fluvial and aeolian sequences from the southern desert margin were used to discern the pattern of southwest monsoon variability during the last 130 ka the sedimentary architecture and textural attributes of the sediments belonging to the period 130 120 ka suggests the existence of a meandering river system consequent to enhanced southwest monsoon conditions a shift from a meandering to a braided pattern during 120 100 ka indicates a phase of reduced precipitation presence of flood plain fines and bedded calcretes during 100 70 ka suggest a period of enhanced monsoon with seasonality following this a phase of weak monsoon activity was observed during 70 60 ka regional flood plain aggradation and pedogenesis during the period termination of a regional fluvial phase around 30 ka and incision of dunes dated to 20 11 ka suggest that the present rivers occupied their course between 11 ka drowned valleys in the estuarine zones suggest that the incision began during the low sea stand around 20 ka when the rivers were graded to the exposed shelf the incision intensified with the re establishment of monsoon during the early holocene

numerical modelling of erosion processes in the himalayas of nepal effects of spatial variations of rock strength and precipitation the interplay between tectonics and erosion has a predominant control on the evolution of the morphology of mountain belts here we investigate the modalities of deformation in central nepal on a c 100 ka time scale in response to tectonic and external forcings through the use of a finite element thermomechanical model coupled with an integrative denudation formulation that accounts for fluvial incision and hillslope landsliding we study the complex coupling existing between tectonics and erosion with special emphasis on the influences of rock strength and rainfall distributions our results underline the key role played by lithologic variations in the elevation of both rivers and mean topography we show that the location of the main frontal thrust is mainly controlled by the low erodability of the unconsolidated sandstone in the siwaliks hills as previously suspected burbank et al 2003 our simulations demonstrate that the pattern of uplift in nepal is mainly dependent on both erodability and fault geometry rather than on rainfall distribution

first 40ar 39ar dating of intense late palaeogene lateritic weathering in peninsular india lateritic surface processes have shaped large platform and cratons of the tropical belt constraining the timing of such processes is crucial to decipher their role in cratonic morphogenesis and their response to long term climatic change and lithospheric deformation weathering histories have been documented for south america africa and australia but precise time constraints of the lateritic weathering processes in south india are still lacking we present 40ar 39ar ages of supergene cryptomelane k mn oxide formed in the sandur mn ore deposits exposed on the highest lateritic paleolandsurface that once covered the mysore plateau and the adjacent deccan traps significant 40ar 39ar ages are estimated between 36 and 26 ma from well defined plateaus in step heating 39ar release spectra and from best fitted inverse isochrones these ages constitute firm time constraints that document intense late eocene oligocene lateritic weathering over peninsular india under the influence of warm and wet climate comparable to that prevailing in tropical humid forests these results imply that southern india was weathered between 36 and 26 ma and may have been dissected mostly in the neogene

climatic and morphologic relationships of rivers implications of sea level fluctuations on river loads the characteristics of 279 rivers that discharge into the world oceans are analyzed in terms of their basin hydrology river discharge morphometry basin slope and area river length extension of the continental shelf seaward of the river mouth and climate precipitation statistically reliable relationships are found between discharge and basin area and between sediment load and a combined function of basin area and slope these functions are used to demonstrate how river hydrologic features would be strongly influenced by sea level fluctuations particularly under the influence of continental shelf emergence a fall in sea level toward a glacioeustatic lowstand would induce the merging of rivers on the subaerial continental shelf thereby allowing giant rivers to form for example rivers of western europe would reorganize themselves into two or three very large rivers sediment concentration carried by these mega rivers would decrease and thus the number of hyperpycnal plumes generated at river

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

aquifer system response to intensive pumping in urban areas of the gangetic plains india the case study of patna a significant component of domestic demand for water of urban areas located in the gangetic plains is met by heavy pumping of groundwater the present study is focused on the patna municipal area inhabited by 17 million people and spanning over 134 km2 where entire urban water demand is catered from pumping by wells of various capacities and designs the present study examines the nature of the aquifer system within the urban area the temporal changes in the water piezometric level and the recharge mechanism of the deeper aquifers the aquifer system is made up of medium to coarse unconsolidated sand lying under a 40 m thick predominantly argillaceous unit holding 8 to 13 m thick localised sand layers and continues up to 220 m below ground groundwater occurs under semi confined condition with transmissivity of aquifers in 5 500 9 200 m2 day 1 range hydraulic head of the deeper aquifer remains in 9 19 m range below ground in contrast to 1 9 m range of that of the upper aquitard zone the estimated annual groundwater extraction from the deeper aquifer is 212 0 million m3 which has created a decline of 3 9 m in the piezometric level of the deeper aquifer during the past 30 years unregulated construction of deep tube wells with mushrooming of apartment culture may further exacerbate the problem the sand layers within the aquitard zone are experiencing an annual extraction of 14 5 million m3 and have exhibited stable water level trend for past one and half decades this unit is recharged from monsoon rainfall besides contribution from water supply pipe line leakage and seepage from unlined storm water drains

response of active tectonics on the alluvial baghmati river himalayan foreland basin eastern india active tectonics in a basin plays an important role in controlling a fluvial system through the change in channel slope the baghmati an anabranching foothills fed river system draining the plains of north bihar in eastern india has responded to ongoing tectonic deformation in the basin the relatively flat alluvial plains are traversed by several active subsurface faults which divide the area in four tectonic blocks each tectonic block is characterized by association of fluvial anomalies viz compressed meanders knick point in longitudinal profiles channel incision anomalous sinuosity variations sudden change in river flow direction river flow against the local gradient and distribution of overbank flooding lakes and waterlogged area such fluvial anomalies have been identified on the repetitive satellite images and maps and interpreted through dem and field observations to understand the nature of vertical movements in the area the sub surface faults in the baghmati plains cut across the river channel and also run parallel which have allowed us to observe the effects of longitudinal and lateral tilting manifested in avulsions and morphological changes

alluvial fans formed by channelized fluvial and sheet flow i theory alluvial fans and fan deltas are of three basic types those built up primarily by the action of constantly avulsing river and stream channels those constructed by sheet flows and those resulting from the successive deposition of debris flows the present analysis is directed toward the first two types a mechanistic formulation of flow and sediment transport through river channels is combined with a simple quantification of the overall effect of frequent avulsion to derive relations describing the temporal and spatial evolution of mean i e averaged over many avulsions bed slope and elevation in an axially symmetric fan an example of a fan formed predominantly by the deposition of sand is compared to a similar one formed predominantly by the deposition of gravel in each example the case of channelized flow is compared to the case of sheet flow the model is applied to the tailings basin of a mine in the companion paper

sedimentology of the narmada alluvial fan western india abstract the narmada alluvial fan is one of the world s largest with an axial length of 23 km the architecture is dominated by debris flow deposits gms facies matrix support a clay content of 3 and clast contact indicate that the clast support mechanism resulted from a combination of buoyancy and dispersive pressure the other faci facies gsh planar cross stratified gravel facies gp1 and gp2 sand sheet facies sm and trough cross stratified sand facies st gms gsh and sm facies are debris flow and sheet flow deposits that aggraded the fan whereas gp1 and st are channel bars and channel fills that dominated the fan between major flood events the fan is characterised by subrounded to rounded clasts the rounding is due to the elongated catchment area upstream of the fan apex as clasts are rounded during prolonged bed load transport and are temporarily arrested upstream of the fan apex as channel bars these clasts are remobilized and entrained in debris flows on the fan during events of anomalous discharge storm events the basalt clasts show a progressive fall in maximum clast size from 150 cm to 10 cm away from the fan apex the narmada river exhibits discharges of up to 60 000 m3 s but due to reconfinement of the feeder channel resulting from tectonic reactivation of pre existing lineaments during the late pleistocene this does not aggrade the fan tectonism has influenced the location of the depositional site has provided the necessary physiographic contrast and has played an important role in the erosion of the fan whereas climate controlled primary and secondary processes have determined the nature of alluvial architecture

characterization of recharge processes in shallow and deeper aquifers using isotopic signatures and geochemical behavior of groundwater in an arsenic enriched part of the ganga plain abstract arsenic concentrations in groundwater extracted from shallow aquifers in some areas of the ganga plain in the states of bihar and uttar pradesh exceed 50 g l 1 and locally reach levels in the 400 g l 1 range the study covered 535 km2 of active flood plain of the river ganga in bihar where a two tier aquifer system has been delineated in a multi cyclic sequence of quaternary sand clay sandy clay and silty clay all 250 m below ground surface the research used isotopic signatures 18o 2 3h 14c and major chemical constituents hco 3 so 4 2 no 3 cl ca 2 mg 2 na k as total of groundwater to understand the recharge processes and groundwater circulation in the aquifers values of 18o and 2 combined with 3h data indicate that the recharge to the as enriched top 40 m of the deposits is modern