sediment budget of the yangtze river the sediment budget is a method to study the distribution of sediment in different parts of a river basin this paper studies the sediment budget of the yangtze river by analyzing the data on soil erosion size distributions of sediment deposits sediment load and fluvial process a method to determine the sediment budget for the yangtze river is proposed in which the total soil erosion from the upstream reaches and tributaries is divided into two parts sediment load transported to the yichang station and sediment storage in the tributaries and gullies furthermore the sediment load is divided into three parts bed material load deposited in the middle and lower reaches for the fluvial process wash load transported to the estuary and sediment deposition in tongting lake the sediment transported into the estuary is further divided into two parts very fine sediment drifting to the ocean and sediment deposition in the estuary for land creation there is a large sediment demand for 1 the fluvial process to reach the minimum stream power in the middle and lower reaches 2 sediment mining for building material and 3 land creation in the estuary the riverbed profile in the middle and lower reaches is developing toward the equilibrium profile defined by the minimum stream power but the impoundment of the three gorges reservoir interrupts and modifies this fluvial process the annual sediment load in the yangtze river has reduced due to various human activities by about 100 x 10 6 t in the past 15 years thus there is a sediment shortage for land creation in the river mouth

a spatially distributed model for the long term suspended sediment discharge and delivery ratio of drainage basins 1 understanding and quantifying the long term suspended sediment discharge of drainage basins is a key goal of geomorphology with important implications for the study of water quality agricultural sustainability and the evolution of landscapes and sedimentary basins over geologic timescales previous studies have highlighted the importance of relief slope precipitation temperature vegetation and soil texture in controlling suspended sediment discharge in natural undisturbed landscapes however globally applicable models currently used to predict suspended sediment discharges are limited because they are based on basin averaged versions of these properties and do not incorporate all of the controlling variables into a single model in this paper i propose a spatially distributed globally applicable model for the long term suspended sediment discharge of drainage basins that includes all of the principal controls on suspended sediment discharge previously documented in the geomorphic literature the model explicitly distinguishes the detachment of sediment on hillslopes and in low order valleys from the transport of sediment in higher order alluvial channels the model uses slope soil texture mean monthly rainfall and mean monthly leaf area index as controlling parameters for the detachment component the transport component is modeled using a rouse number dependent transport criterion that explicitly includes the effects of slope and soil texture the model is capable of reproducing the long term sediment yield of 128 global rivers with a pearson correlation coefficient r value of 0 79 using just two free parameters the model also predicts sediment delivery ratios consistent with those measured in natural drainage basins

climatic variations and geomorphology of the indus river valley between nimo and batalik ladakh nw trans himalayas during late quaternary abstract the indus river valley is tectonically unstable exhibiting complex topography landscape relief and varied sedimentation the major geomorphic landforms are alluvial fans debris cones fluvio lacustrine deposits scree and talus cones in the present work a transect between nimo and batalik along the river was studied to consider the geomorphological landform evolution during the quaternary based on the distribution of the sediments along the valley mass movements catastrophic land sliding and tectonic activity transported material from steep slopes to valley bottoms which were responsible for forming lakes preserved as thick piles of fine sediment while the outburst floods redistributed sediment down valley three phases of lake formation are recorded in the 136 km stretch 35 000 26 000 bp lamayuru palaeolake 17 000 13 000 bp rizong palaeolake occupying 35 km of the valley length and 14 000 5000 bp khalsi saspol palaeolake 55 km in length and having the highest lake levels the lake formation is attributed to deglaciation after the last glacial maximum lgm and holocene warming tectonic activity seismites are concentrated only at 10 and 6 ka

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

determining sediment source areas in a tropical river basin costa rica abstract four hydrologic events were studied at three gauging stations in the pejibaye river basin costa rica the sediment sources were determined by comparing the timing of the sedigraph at the gauging station and the timing of rainfall in the catchment with addition of time for the new water to flow from different land use districts along the main rivers to the gauging stations the rainfall was recorded in the basin upstream of pejibaye gauging station which was therefore the only station where the sedigraph rainfall method could be properly used for determining sediment sources on three occasions the sediment discharges at the pejibaye station were of about equal height the sedigraph rainfall method indicated that on two of these occasions the sediment came mainly from the pasture and sugar districts and in one case from the forested middle basin on the fourth occasion rainfall amounts and intensities were locally high in the forested upper basin but water and sediment discharges were small re erosion of material deposited in the channel increased the width of clockwise sediment concentration discharge loops in one storm the concentration discharge loop changed from an eight shaped loop at the upper station to a counter clockwise loop at the downstream station explained by the lagging of the sediment after the water

spatial patterns and variation of suspended sediment yield in the upper indus river basin northern pakistan summary much of the flow of the indus originates in the mountainous regions of the karakoram and himalayas resulting in a high sediment yield that creates a number of operational and maintenance problems for downstream water use in pakistan analysis of the available hydro climatological data indicates that the upper indus basin can be subdivided into three characteristic regions based on whether runoff production is controlled by temperature region 1 upper glacierized sub basins precipitation caused by the monsoon and western disturbances region 3 lower sub basins or a combination of the two region 2 middle reach sub basins the runoff and sediment transport regimes for the shyok gilgit hunza and indus rivers in region 1 show the role of snow and ice melt in generating high runoff and 80 85 of the annual sediment load is transported in july and august the astore river at doyian in region 2 shows an early rise of the sediment yield starting in may due to the interaction of rainfall and snowmelt at lower elevations and a comparatively lower sediment yield in august indicating a lesser influence of glacier melt region 3 experiences two types of rainfall summer monsoons and the western disturbances in late winter and early spring consequently the gorband river at karora in region 3 exhibits two separate sediment yield peaks of equal height in april and july the runoff and sediment transport regime along the main stem of the indus river is dominated by the melt of snow and ice in its headwaters and consequently is similar to the regimes of the region 1 sub basins contrary to the conventional model the specific sediment yield increases markedly with drainage area along the indus river from 355 t km 2 yr 1 at kharmong to 1197 t km 2 yr 1 at besham qila likely because of the large number of small and relatively steep catchments discharging straight into the indus river analysis of the magnitude frequency characteristics of sediment transport for the tributaries shows that the effective discharge in the basin ranges from 1 5 2 0 to 5 5 6 0 times the average discharge and decreases downstream the main indus river however shows a consistent effective discharge of 2 5 3 0 times the average discharge

sediment supply versus local hydraulic controls on sediment transport and storage in a river with large sediment loads the rio grande in the big bend region of texas usa and chihuahua and coahuila mexico undergoes rapid geomorphic changes as a result of its large sediment supply and variable hydrology thus it is a useful natural laboratory to investigate the relative importance of flow strength and sediment supply in controlling alluvial channel change we analyzed a suite of sediment transport and geomorphic data to determine the cumulative influence of different flood types on changing channel form in this study physically based analyses suggest that channel change in the rio grande is controlled by both changes in flow strength and sediment supply over different spatial and temporal scales channel narrowing is primarily caused by substantial deposition of sediment supplied to the rio grande during tributary sourced flash floods tributary floods have large suspended sediment concentrations occur for short durations and attenuate rapidly downstream in the rio grande depositing much of their sediment in downstream reaches long duration floods on the mainstem have the capacity to enlarge the rio grande and these floods released from upstream dams can either erode or deposit sediment in the rio grande depending upon the antecedent in channel sediment supply and the magnitude and duration of the flood geomorphic and sediment transport analyses show that the locations and rates of sand erosion and deposition during long duration floods are most strongly controlled by spatial changes in flow strength largely through changes in channel slope however spatial differences in the in channel sediment supply regulate sediment evacuation or accumulation over time in long reaches greater than a kilometer

an assessment of sediment transport processes in the lower mekong river based on deposit grain sizes the cm technique and flow energy data abstract the lower mekong river has been an important research topic for at least 15 years notably in the fields of hydrology fluvial geomorphology and the impact of dams recent papers refer mostly to the impact of the lancang chain of hydroelectric dams constructed on the chinese section of the river among the pending scientific questions are 1 the upstream downstream variations in the concentration and yield of suspended sediment and 2 the relative importance of sand in the total yield the general consensus among the scientific community is that the relative importance of sand in suspended load is not the main scientific concern despite its extensive presence in the mekong river channel as noted by geomorphologists and despite its extreme importance for the stability of the delta shoreline in viet nam this paper contradicts the general consensus its objective is to present new information on the processes of sand transport in the lower mekong channel imagery field observations sampling on the river banks and grain size analysis of sand deposits have been carried out between chiang sean downstream of the chinese border and the delta the c m image technique served to discriminate between the various transport processes bedload and different types of suspension this technique helps in understanding the changing processes responsible for downstream sediment transfer in river channels the results of this study are the following 1 discrepancies in the values of annual suspended sediment load detected by different gauging stations have not yet been satisfactorily explained the cm image technique indicates that grain size and the quantity of sand transiting in suspension vs bedload vary from upstream to downstream 2 these upstream downstream differences may be related to the energy of floods energy helps to explain longitudinal variations in the relative importance of the different modes of transport and serves to distinguish between bedload graded and uniform suspension and wash load 3 the mekong is seen as a river carrying mostly silt and clay however the results suggest that sand plays a major role in downstream sediment transfer during floods this result is in line with the large amounts of sand present in the channel its relative importance in the total yield must be reassessed as suggested by walling 2005 2008 as may be expected the role of sand in the stability of the delta shoreline is of prime importance

erosion history of the tibetan plateau since the last interglacial constraints from the first studies of cosmogenic 10be from tibetan bedrock abstract the cosmogenic 10be exposure histories of in situ bedrock surfaces from the tibetan plateau indicate low erosion rates of

the ganges and brahmaputra rivers in bangladesh basin denudation and sedimentation every year the ganges and brahmaputra rivers in bangladesh transport 316 and 721 million tonnes of sediment respectively these high loads of suspended sediment reflect the very high rate of denudation in their drainage basins the average mechanical denudation rate for the ganges and brahmaputra basins together is 365 mm 103 yr 1 however the rate is higher in the brahmaputra basin than that in the ganges basin several factors including mean trunk channel gradient relief ratio runoff basin lithology and recurring earthquakes are responsible for these high denudation rates of the total suspended sediment load i e 1037 million tonnes transported by these rivers only 525 million tonnes c 51 of the total load are delivered to the coastal area of bangladesh and the remaining 512 million tonnes are deposited within the lower basin offsetting the subsidence of the deposited load about 289 million tonnes about 28 of the total load are deposited on the floodplains of these rivers the remaining 223 million tonnes about 21 of the total load are deposited within the river channels resulting in aggradation of the channel bed at an average rate of about 3 9 cm yr 1 although the brahmaputra transports a higher sediment load than the ganges the channel bed aggradation rate is much higher for the ganges this study also documents a wide range of interannual seasonal and daily variation in suspended sediment transport and water discharge interannual variation in sediment deposition within the basin is also suggested copyright 1999 john wiley sons ltd

sediment load change in the yangtze river changjiang a review abstract extensive research into the changing sediment load throughout the yangtze river changjiang basin has been completed over recent years and it provides an ongoing example of how to evaluate the consequences of natural and anthropogenic impacts on sediment processing in a very large fluvial system this paper reviews these recent studies and critically assesses their findings regarding changes in sediment yield load both spatial and temporal variations grain size and rating curves as well as the morphodynamic response of the channel and delta we also discuss the factors driving these changes including climate change soil and water conservation measures dam construction and sand extraction and consider the likely future trends in sediment load based on a consideration of the major outcomes of and discrepancies between recent studies we conclude that sediment supply transport mobilization and deposition in this large river system are complicated by the heterogeneous nature of its morphology and climate as well as the progressive intensification of human activities therefore the identification and interpretation of hydrological and sedimentological changes in the yangtze basin can be difficult and an in depth study of the causal mechanisms of variations in sediment load and the impacts on the yangtze river system is urgently required

sediment supply and channel morphology in mountain river systems 1 relative importance of lithology topography and climate 1 quantifying landscape scale variations in sediment supply to streams and rivers is fundamental to our understanding of both denudational processes and stream channel morpho dynamics previous studies have linked a variety of sediment supply proxies to climatic topographic or geologic factors but few have connected these directly to the characteristics of fluvial systems draining these landscapes here we correlate landscape controls on sediment supply to observed sedimentology and channel patterns through direct measurements of water and sediment fluxes in over 80 drainage basins ranging in area from 1 4 to 35 000 km2 in the northern rocky mountains usa these data show that the relative sediment supply defined by the bankfull sediment concentration is dominated by basin lithology while exhibiting little correlation to factors such as relief mean basin slope and drainage density bankfull sediment concentrations bed load and suspended load increase as much as 100 fold as basin lithology becomes dominated by softer sedimentary and volcanic rocks relative to basins with more resistant lithologies as bed load concentrations increase stream beds become less armored and bed load grain size coarsens at very high sediment concentrations bed surface subsurface and bed load grain sizes converge and a transition from single thread to to braided channel patterns is commonly observed

changes in sediment yield of the yellow river basin of china during the holocene this research reconstructs the changes in sediment yield of the yellow river based mainly on a large number of 14 c dates collected from the literature the total volume of sediment yield of the basin during the holocene is estimated to be 8 0 x 10 12 tons the annual sediment yield had an increasing trend over the holocene from 0 68 0 72 0 79 to 1 0 1 x 10 9 tons over each 2500 year period from the early holocene to the present the changes in sediment yield are ascribed to both natural and anthropogenic reasons in which the latter became important in the late holocene the mean rate of increase in natural sediment yield throughout the holocene is estimated to be about 0 027 x 10 6 ton year and the natural annual sediment yield is projected to be 0 95 x 10 9 tons at the present the increasing trend of natural sediment yield is reasoned to be the consequence of evolution of landforms enhanced by tectonic movement and climatic change in the loess plateau the principal sediment source of the river towards a condition favorable to soil erosion comparing the estimated annual natural sediment yield with the current annual sediment load of 1 6 x 10 9 tons of the river it is clear that human activities have augmented natural soil erosion by about 41 in the yellow river basin furthermore an estimate of the overall pattern of anthropogenic sediment yield shows an accelerated increasing trend which is approximately correspondent with that of population in the loess plateau area c 2002 elsevier science b v all rights reserved

spatiotemporal variations of suspended sediment transport in the upstream and midstream of the yarlung tsangpo river the upper brahmaputra china the yarlung tsangpo river which flows from west to east across the southern part of the tibetan plateau is the longest river on the plateau and an important center for human habitation in tibet suspended sediment in the river can be used as an important proxy for evaluating regional soil erosion and ecological and environmental conditions however sediment transport in the river is rarely reported due to data scarcity results from this study based on a daily dataset of 3 years from four main stream gauging stations confirmed the existence of great spatiotemporal variability in suspended sediment transport in the yarlung tsangpo river under interactions of monsoon climate and topographical variability temporally sediment transport or deposition mainly occurred during the summer months from july to september accounting for 79 to 93 of annual gross sediment load this coincided with the rainy season from june to august that accounted for 51 to 80 of annual gross precipitation and the flood period from july to september that accounted for approximately 60 of annual gross discharge the highest specific sediment yield of 177 6 t km2 yr occurred in the upper midstream with the highest erosion intensity the lower midstream was dominated by deposition trapping approximately 40 of total sediment input from its upstream area sediment load transported to the midstream terminus was 10 43 mt yr with a basin average specific sediment yield of 54 t km2 yr comparison with other plateau originated rivers like the upper yellow river the upper yangtze river the upper indus river and the mekong river indicated that sediment contribution from the studied area was very low the results provided fundamental information for future studies on soil and water conservation and for the river basin management copyright 2017 john wiley sons ltd

influence of the three gorges dam on downstream delivery of sediment and its environmental implications yangtze river 1 water and sediment supplies from ungauged areas were calculated and combined with datasets from gauging stations to establish sediment budgets using sediment budgets and regression relationships the influence of the three gorges dam tgd on downstream delivery of sediment was quantified we found that 151 mt yr 1 mt 10 6 tons of sediment has been retained by tgd since it began operation 2003 2005 in response to this significant erosion has occurred in the downstream riverbed this erosion did not offset the sediment lost in the reservoir and the sediment flux into the estuary decreased by 85 mt yr 31 this decrease has lead to conversion from progradation to recession in the delta front in combination with other anthropogenic impacts tgd was expected to decrease the sediment flux into the estuary for centuries which is of great importance for delta ecosystem and human development citation yang s l j zhang and x j xu 2007 influence of the three gorges dam on downstream delivery of sediment and its environmental implications yangtze river geophys res lett 34 l10401

factors controlling specific sediment yield in the upper indus river basin northern pakistan estimates of sediment yield are essential in water resources analysis modelling and engineering in investigations of continental denudation rates and in studies of drainage basin response to changes in climate and land use the availability of high resolution global environmental datasets offers an opportunity to examine the relationships between specific sediment yield sysp and drainage basin attributes in a geographical information system gis environment this study examines sysp at 14 long term gauging stations within the upper indus river basin twenty nine environmental variables were derived from global datasets the majority with a 1 1 km resolution the sysp ranges from 194 to 1302 t km 2 yr 1 for sub basins ranging from 567 to 212 447 km2 the high degree of scatter in sysp is greatly reduced when the stations are divided into three groups upper glacierized sub basins lower monsoon sub basins and the main indus river percentage snow ice cover lcs emerges as the single major land cover control for sysp in the high mountainous upper indus river basin a regression model with percentage snow ice cover lcs as the single independent variable explains 73 4 of the variance in sysp for the whole indus basin a combination of percentage snow ice cover lcs relief and climate variables explains 98 5 of the variance for the upper glacierized sub basins for the lower monsoon region a regression model with only mean annual precipitation p explains 99 4 of the variance along the main indus river a regression model including just basin relief r explains 92 4 of the variance in sysp based on the r2adj and p value statistics the variables used are capable of explaining the majority of variance in the upper indus river basin copyright 2007 john wiley sons ltd

quantifying periglacial erosion insights on a glacial sediment budget matanuska glacier alaska glacial erosion rates are estimated to be among the highest in the world few studies have attempted however to quantify the flux of sediment from the periglacial landscape to a glacier here erosion rates from the nonglacial landscape above the matanuska glacier alaska are presented and compare with an 8 yr record of proglacial suspended sediment yield non glacial lowering rates range from 1 8 0 5 mm yr 1 to 8 5 3 4 mm yr 1 from estimates of rock fall and debris flow fan volumes an average erosion rate of 0 08 0 04 mm yr 1 from eight convex up ridge crests was determined using in situ produced cosmogenic 10be extrapolating these rates based on landscape morphometry to the matanuska basin 58 ice cover it was found that nonglacial processes account for an annual sediment flux of 2 3 1 0 106 t suspended sediment data for 8 years and an assumed bedload to estimate the annual sediment yield at the matanuska terminus to be 2 9 1 0 106 t corresponding to an erosion rate of 1 8 0 6 mm yr 1 nonglacial sources therefore account for 80 45 of the proglacial yield a similar set of analyses were used for a small tributary sub basin 32 ice cover to determine an erosion rate of 12 1 6 9 mm yr 1 based on proglacial sediment yield with the nonglacial sediment flux equal to 10 7 of the proglacial yield it is suggested that erosion rates by nonglacial processes are similar to inferred subglacial rates such that the ice free regions of a glaciated landscape contribute significantly to the glacial sediment budget the similar magnitude of nonglacial and glacial rates implies that partially glaciated landscapes will respond rapidly to changes in climate and base level through a rapid nonglacial response to glacially driven incision copyright 2009 john wiley sons ltd

sediment supply and channel morphology in mountain river systems 2 single thread to braided transitions differences in sediment supply between single thread and braided channel types provide a long recognized though difficult to quantify pattern discrimination building on the results from our preceding paper we present a multiscale assessment of the sediment supply geomorphology and sediment transport characteristics of braided gravel bedded reaches in the northern rocky mountains usa first we present a quantitative theoretically based discriminant function that stratifies single thread and braided reaches on the basis of variations in bankfull sediment concentration and dimensionless discharge following the work of millar 2005 and eaton et al 2010 this function correctly classifies 50 of the 53 channel types where bed load concentrations are known second while channel pattern transitions are often linked to changes in slope field studies along sunlight creek wyoming show that downstream transitions between single thread and braided reaches are instead caused by valley constrictions and changes in the grain size of sediment from tributaries finally we demonstrate that the two dimensional variability in flow properties in braided reaches produces locally high values of shear stress and bed load transport yet bed load measurements and sediment transport calculations also show that sediment transport rates between adjoining braided and single thread reaches may be approximately equal where channels are near the pattern threshold and downstream variations in bank fortitude and channel constriction force pattern transitions taken together these results indicate that high bed load concentrations are fundamental to the braided channel planform and that braided channels likely reflect a quasi equilibrium state within watersheds with persistent high sediment supply

downstream patterns of suspended sediment transport in a high arctic river influenced by permafrost disturbance and recent climate change abstract spatially and temporally variable suspended sediment transport from upstream sources was investigated in the west river unofficial name at the cape bounty arctic watershed observatory cbawo on melville island nunavut 74 55 n 109 35 w a river with nearly a decade of hydrological and sediment transport research in the canadian arctic and subject to recent permafrost disturbances such as soil skin flows on slopes massive ground ice melt in the channel and substantial climate change during the 2012 season a survey was undertaken during the nival period to identify areas of the river where the flow was isolated from the channel bed by snow and where it progressively reached the bed during the nival period and throughout the rest of the season suspended sediment transport data were collected from a primary outlet station and six upstream locations to identify the sources and sinks of sediment in the various reaches of the west river an inferred sediment budget approach was used to identify the storage and release dynamics in each reach nival event scale hysteresis and seasonal diurnal hysteresis patterns for 2012 were primarily anticlockwise suggesting that sources of sediment were not readily available for transport during peak flows but became available as discharge waned analysis of diurnal hysteresis relationships for the years 2004 2012 excluding 2011 signals a shift in daily sediment discharge hysteresis from primarily clockwise to anticlockwise following an episode of permafrost disturbance and enhanced erosion in 2007 consistent sediment storage in the upper catchment from this disturbance is interpreted to have contributed to the shift to anticlockwise daily hysteresis results provide insights into the fluvial and geomorphological response to changes in sediment availability in arctic rivers and how these changes in turn affect sediment transport in these environments

yangtze river of china historical analysis of discharge variability and sediment flux hydrological records covering a 100 year period from the upper middle and lower yangtze river were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin the yangtze discharge as expected increases from the upper drainage basin downstream only an estimated 50 of the discharge is derived from the upper yangtze with the rest being derived from the numerous tributaries of the middle and lower course however the distribution of sediment load along the yangtze is the reverse of that observed for discharge with most of the sediment being derived from the upper basin a dramatic reduction in sediment load by 0 8 108 tons year occurs in the middle yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper yangtze rock sections considerable siltation also occurs in the middle yangtze drainage basin as the river cuts through a large interior dongting lake system sediment load in the lower yangtze while significantly less than that of the upper river is somewhat higher than the middle yangtze because of additional load contributed by adjacent tributaries a strong correlation exists between the discharge and sediment load along the yangtze drainage basin during the dry season as lower flows carry lower sediment concentration during the wet season a strong correlation is also present in the upper yangtze owing to the high flow velocity that suspends sand on the bed however a negative to poor correlation occurs in the middle and lower yangtze because the flow velocity in these reaches is unable to keep sand in suspension transporting only fine grained particles downstream hydrological data are treated for 30 years 1950 1980 when numerous dams were constructed in the upper yangtze drainage basin at yichang and hankou hydrological stations records revealed a decreasing trend in annual sediment load along with slightly reduced annual discharge at the same stations this can be interpreted as the result of water diversion primarily for agriculture sediment load at datong further downstream is quite stable and not influenced by slightly reduced discharge furthermore sediment concentration at the three hydrological stations increased which can be attributed to sediment loss in association with intensifying human activity especially in the upper drainage basin such as deforestation and construction of numerous dams mean monthly sediment load of these 30 years pulses about 2 months behind discharge implying dam released sediment transport along the entire river basin during the high water stage

post speleogenetic biogenic modification of gomantong caves sabah borneo article i nfo the gomantong cave system of eastern sabah malaysia is well known as an important site for harvesting edible bird nests and more recently as a tourist attraction although the biology of the gomantong system has been repeatedly studied very little attention has been given to the geomorphology here we report on the impact of geobiological modification in the development of the modern aspect of the cave an important but little recognized feature of tropical caves basic modeling of the metabolic outputs from bats and birds co2 h2o heat reveals that post speleogenetic biogenic corrosion can erode bedrock by between 3 0 mm ka 1 m 300 ka and 4 6 mm ka 1 m 200 ka modeling at high densities of bats yields rates of corrosion of 34 mm ka or 1 m 30 ka sub aerial corrosion creates a previously undescribed speleological feature the apse flute which is semicircular in cross section and 80 cm wide it is vertical regardless of rock properties developing in parallel but apparently completely independently and often unbroken from roof to floor they end at a blind hemi spherical top with no extraneous water source half dome ceiling conch pockets are remnants of previous apse fluting sub cutaneous corrosion creates the floor level guano notch formed by organic acid dissolution of bedrock in contact with guano speleogenetic assessment suggests that as much as 70 95 of the total volume of the modern cave may have been opened by direct subaerial biogenic dissolution and biogenically induced collapse and by sub cutaneous removal of limestone over a timescale of 1 2 ma 2011 elsevier b v all rights reserved

bed load transport in bedrock rivers the role of sediment cover in grain entrainment translation and deposition 1 bedrock rivers exert a critical control over landscape evolution yet little is known about the sediment transport processes that affect their incision we present theoretical analyses and field data that demonstrate how grain entrainment translation and deposition are affected by the degree of sediment cover in a bedrock channel theoretical considerations of grain entrainment mechanics and sediment continuity each demonstrate that areas of exposed bedrock and thin sediment depths cause sediment transport to be size independent albeit excluding extreme grain sizes we report gravel and cobble magnetic tracer data from three rivers with contrasting sediment cover the bedrock river calder 20 cover the bedrock south fork eel river 80 and the alluvial allt dubhaig 100 these data sets show that 1 transport distances in the river calder are controlled by sediment patch location whereas in the other rivers transport distances are described by gamma distributions representing local dispersion 2 river calder transport distances are size independent across all recorded shear stresses whereas the other rivers display size selectivity 3 river calder tracers are entrained at a dimensionless shear stress of 0 038 which is relatively low compared to alluvial rivers and 4 virtual grain velocities in the river calder are higher than in a comparable reach of the allt dubhaig these contrasts result from differences in the thicknesses and spatial distribution of sediment in the three rivers and support the theoretical analysis sediment processes in bedrock rivers systematically vary along a continuum between bedrock and alluvial end members citation hodge r a t b hoey and l s sklar 2011 bed load transport in bedrock rivers the role of sediment cover in grain entrainment translation and deposition j geophys res 116 f04028 doi 10 1029 2011jf002032

a neoarchean paleomagnetic pole from the kisii series of western kenya implications for crustal mobility abstract the kisii series lavas of western kenya were the target of a paleomagnetic study the kisii series is a volcano sedimentary sequence dated to 2531 3 ma u pb that rests unconformably over the mesoarchean neoarchean nyanzian and kavirondian series the paleomagnetic study reported in this paper expands on an earlier study by brock et al 1972 using modern demagnetization and analysis techniques in spite of the advanced methods the results of both our new study and the previous study are statistically indistinguishable we therefore combine the results of both investigations to arrive at a grand mean pole at 7 s 166 e a95 8 due to the relatively minor tilt corrections a fold test is inconclusive however the dual polarity magnetization passes a reversal test we argue for a primary remanence on the basis of a comparison to other paleomagnetic data in kenya and tanzania and geological information we examine the relationships between age equivalent paleomagnetic poles from the tanzanian zimbabwe and kaapvaal cratons based on this limited dataset we cannot conclude whether or not the observed apparent polar wander was due to true polar wander or modern style plate tectonics such as would be implied by the variable apparent polar wander path segments we favor the latter explanation based on the disparate lengths of the zimbabwe versus tanzanian apparent polar wander paths during the 2700 2500 ma interval the protopangea model is not consistent with paleomagnetic data from these three cratons

erosion and sediment transport in the ganges river basin india abstract based on sampling of the entire region of the ganges basin chemical and sediment load supplied at various parts of the basin have been computed annual flux of materials from sub basin into the main basin and input to the hoogly estuary have been calculated and compared to major river systems of the world the total annual load at calcutta mouth of the river was calculated as 411 10 6 t 328 10 6 t sediment load 83 10 6 t chemical load erosion rate 549 t km 2 yr 1 is among the highest in this river system and controlling factors on a global scale such as basin area are discussed in detail annual decrease in basin elevation indicates a rapid process of denudation and such rates have a bearing on rates of shelf sediment accumulation

multimineral fingerprinting of modern sand generated from the tethys himalaya nianchu river tibet abstract the nianchu as the largest southern tributary of the middle yarlung tsangpo upper brahmaputra river in southern tibet drains mainly sedimentary rocks of the tethys himalaya and subordinately metamorphic and igneous rocks of the greater himalaya kangmar gneiss dome and indus yarlung ophiolitic suture zone this study presents the first detailed compositional fingerprinting of detritus released from the tethys himalaya in southern tibet sand carried by the nianchu and by its major tributaries range from quartzo lithic to litho quartzose sedimentaclastic with a few metamorphic volcanic and ultramafic lithic grains reflecting dominant erosion of tethys himalayan strata transparent heavy mineral assemblages are moderately poor they include a mixed recycled assemblage with amphibole tourmaline and rounded zircon together with first cycle sillimanite and garnet grains from the greater himalaya young titanite and monazite grains from either the greater himalaya or the kangmar dome chloritoid from the low grade metapelites surrounding the kangmar dome and clinopyroxene olivine and enstatite grains shed from forearc ophiolites forward mixing models indicate that 80 of nianchu sand is recycled from the tethys himalaya which is roughly the same percentage as the corresponding exposure area based on previous geochronological and provenance studies and on available suspended load data from the nianchu lhasa and yarlung tsangpo rivers we assess the average erosion rate in the nianchu catchment as 0 10 mm a 1 about twice as that in the middle yarlung tsangpo catchment 0 05 mm a 1 and about five times as that of the lhasa river catchment 0 02 mm a 1 this marked difference is principally ascribed to the higher erodibility of tethys himalayan sedimentary strata within the nianchu basin low precipitation in the rain shadow of the high himalayan range may explain a lower erosion rate in the headwaters 0 07 mm a 1 than in the less steep lower reaches 0 14 mm a 1

recent changes in sediment delivery by the huanghe yellow river to the sea causes and environmental implications in its estuary summary over the past 60 years climate change and human activities in the huanghe yellow river basin have changed the river system in particular construction of large reservoirs and soil conservation practices within the river basin have reduced sediment flux to the sea by 90 and increased the grain size of suspended sediment delivered to the sea 30 m now versus 18 m before in median grain size scouring of the channel in the lower reaches has added a new sediment source to those derived from the loess region of the middle reaches before construction of the xiaolangdi reservoir at the downstream end of the middle reaches suspended sediment concentrations at station lijin the last hydrographic station before the river enters the sea were high enough 35 kg m 3 in the flood season to offset the density contrast between freshwater and ambient seawater thus hyperpycnal flows developed along the subaqueous slope at the river mouth during the flood season observations from two cruises near the huanghe river mouth one before and one after the operations of the xiaolangdi reservoir suggest that buoyant hypopycnal plumes rather than hyperpycnal plumes have occurred at the river mouth since the dramatic changes in concentration and grain size of suspended sediment discharged to the sea the rapid decrease of sediment discharge to the sea and the increase of grain size of suspended sediments not only changed the sediment dispersal pattern at the river mouth but also modified the shoreline and subaqueous slope the effects of climate change and human activities in the river basin have been transferred along the hydrological pathway to the estuary and delta and have changed estuarine sediment dynamics and delta morphology the huanghe presents an illustrative example of river basin coastal zone interactions in the context of climate change and human activities

neoproterozoic oceanic crustal thinning emergence of continents and origin of the phanerozoic ecosystem a model ophiolites emplaced in collisional orogens prior to 1 ga generally have a thicker magmatic crust than younger complexes this fact suggests a model in which mesoproterozoic oceanic crust was two or three times as thick as at present possibly owing to partial melting of a more fertile mantle earth had less continental freeboard and 90 95 marine inundation producing a much more uniform worldwide temperature distribution neoproterozoic oceanic crust thinning increased ocean basin volume and continental freeboard and caused a drop of average sea level relative to the level of the continents the resultant increased erosion sediment deposition upwelling and consequent biological productivity and burial led to increased atmospheric oxygen which permitted the evolutionary development of animals

millennial lag times in the himalayan sediment routing system abstract any understanding of sediment routing from mountain belts to their forelands and offshore sinks remains incomplete without estimates of intermediate storage that decisively buffers sediment yields from erosion rates attenuates water and sediment fluxes and protects underlying bedrock from incision we quantify for the first time the sediment stored in 38 000 mainly postglacial himalayan valley fills based on an empirical volume area scaling of valley fill outlines automatically extracted from digital topographic data the estimated total volume of 690 242 452 km 3 is mostly contained in few large valley fills 1 km 3 while catastrophic mass wasting adds another 177 31 km 3 sediment storage volumes are highly disparate along the strike of the orogen much of the himalaya s stock of sediment is sequestered in glacially scoured valleys that provide accommodation space for 44 of the total volume upstream of the rapidly exhuming and incising syntaxes conversely the step like long wave topography of the central himalayas limits glacier extent and thus any significant glacier derived storage of sediment away from tectonic basins we show that exclusive removal of himalayan valley fills could nourish contemporary sediment flux from the indus and brahmaputra basins for 1 kyr though individual fills may attain residence times of 100 kyr these millennial lag times in the himalayan sediment routing system may sufficiently buffer signals of short term seismic as well as climatic disturbances thus complicating simple correlation and interpretation of sedimentary archives from the himalayan orogen its foreland and its submarine fan systems