a network scale intermediate complexity model for simulating channel evolution over years to decades abstract excessive river erosion and sedimentation threatens critical infrastructure degrades aquatic habitat and impairs water quality tools for predicting the magnitude of erosion sedimentation and channel evolution processes are needed for effective mitigation and management we present a new numerical model that simulates coupled river bed and bank erosion at the watershed scale the model uses modified versions of bagnold s sediment transport equation to simulate bed erosion and aggradation as well as a simplified bank stability and toe erosion model bstem to simulate bank erosion processes the model is mechanistic and intermediate complexity accounting for the dominant channel evolution processes while limiting data requirements we apply the model to a generic test case of channel network response following a disturbance and the results match physical understanding of channel evolution the model was also tested on two field data sets below parker dam on the lower colorado river and the north fork toutle river nftr which responded dramatically to the 1980 eruption of mount st helens it accurately predicts observed channel incision and bed material coarsening on the colorado river as well as observations for the upstream 18 km of the nftr watershed the model does not include algorithms for extensive lateral migration and avulsions and therefore did not perform well in the lower nftr where the channel migrated across a wide valley bottom rem is parsimonious and useful for simulating network scale channel change in single thread systems responding to disturbance

modeling width adjustment in meandering channels widening in sinuous channels occurs when the retreat of the outer bank exceeds the advance of the opposite bank an analytical model is presented to simulate width adjustment in meandering channels of non cohesive bank material resulting from bank erosion of two interactive processes basal erosion and bank collapse bank collapse refers to the avalanche of non cohesive material in the upper part of bank above water surface resulting from over steepening of the bank surface due to basal erosion the rate of basal erosion including lateral erosion and bed degradation is calculated as a function of the longitudinal gradient of sediment transport rate and strength of secondary flow the transverse bed slope is treated as a variable that increases as channel sinuosity increases until the transverse bed slope reaches its maximum value by simplifying the bank collapse process for non cohesive materials the present study shows that the rate of bank line retreat is determined by lateral erosion rate near bank bed degradation rate sediment grain size and difference between flow depth and bank height the time dependent widening processes of two meandering channels in the laboratory are selected to test applicability of the model the result shows that the simulated bank lines at individual time intervals closely match the experimental measurements whether the sinuosity of a meandering channel will increase or decrease is primarily determined by didtribution of the lngitudinal gradient of sediment transport rate along the channel

fluvial processes and morphological response in the yellow and weihe rivers to closure and operation of sanmenxia dam abstract the fluvial and morphological processes induced by impoundment of the sanmenxia reservoir and relevant human activities on the yellow river and its tributaries are complex the long term annual sediment load of the yellow river was 1 6 billion tons ranking first of all the world s rivers in 1960 sanmenxia dam began filling sediment transport in the river then was greatly disturbed and a new cycle of the fluvial processes was induced first the dam caused not only anticipated sedimentation in the reservoir but also serious sedimentation in the largest tributary of the river the weihe river the response of fluvial process to the dam closure varies in space and time second the downstream reaches of the dam experienced erosion and resiltation changes of river pattern and development of meanders moreover the downstream reaches of the dam have experienced more and more water diversion which has induced readjustment of the longitudinal profile of the river the study reveals that sedimentation in the sanmenxia reservoir enhanced the bed elevation at tongguan where the weihe river flows into the yellow river the rising tongguan s elevation caused retrogressive siltation waves in the weihe river which propagated at a speed of about 10 km yr an equilibrium sedimentation model is proposed which agrees well with the data of sedimentation in the weihe river in the reaches below the dam the river changes from braided to wandering or from wandering braided to wandering meandering the discharge released to the downstream reaches has been regulated by the reservoir and it decreases along the course because the quantity of water diversions is more than the inflow from tributaries the reduction in discharge causes readjustment of the longitudinal bed profile by using the minimum stream power theory we prove that the riverbed profile is developing toward an s shape profile

alluvial channel geometry theory and applications the downstream hydraulic geometry of alluvial channels in terms of bank full width average flow depth mean flow velocity and friction slope is examined from a three dimensional stability analysis of noncohesive particles under two dimensional flows four governing equations flow rate resistance to flow secondary flow and particle mobility are solved to analytically define the downstream hydraulic geometry of noncohesive alluvial channels as a function of water discharge sediment size shields number and streamline deviation angle the exponents of hydraulic geometry relationships change with relative submergence four exponent diagrams illustrate the good agreement with several empirical regime equations found in the literature the analytical formulations were tested with a comprehensive data set consisting of 835 field channels and 45 laboratory channels the data set covers a wide range of flow conditions from meandering to braided sand bed and gravel bed rivers with flow depths and channe

erosion of tephra from the 1980 eruption of mount st helens erosion of tephra on hillslopes north of mount st helens was measured at intervals of several months between 1980 and 1983 using large arrays of stakes rill erosion was initially greater than sheetwash but its importance decreased comparatively quickly both rill erosion and sheetwash decreased by one to two orders of magnitude over the three year period because a stable rill network developed and more permeable and less erodible substrates were created or exposed the decrease occurred prior to recovery of plants the causes for the rapid decline in erosion at mount st helens explain patterns of erosion following several other recent tephra eruptions basin wide annual rates of erosion were computed by mapping the surface cover the hillslope gradient and the texture and thickness of tephra and by using statistical relations developed between them and erosion rates annual erosion decreased from 26 mm between may 1980 and may 1981 to 1 8 mm between may 1982 and may 1983 projecting this rate of decline into the future indicated that only about one sixth of the tephra on hillslopes will be removed by water erosion before soil creep and other forms of mass wasting again dominate hillslope evolution

river channel adjustment to meander cutoffs on the river bollin and river dane northwest england morphological adjustment of a channel after cutoff should be expected but rarely has the mode and timescale of adjustment in natural channels been measured four natural cutoffs which have occurred since 1980 on two rivers in northwest england have been monitored from pre cutoff stage two of the cutoffs were neck cutoffs of large loops two were chute cutoffs in which significant bend curvature remained all the cutoffs were the terminal result of progressive bank erosion and or scour of the floodplain rather than overflow and all the cutoffs took place in peak flow events though two of these were of relatively low magnitude high frequency rapid widening and sedimentation took place within the straight channels produced by neck cutoffs immediately after breaching adjustment was mainly by formation of multiple riffles and bars producing a variable morphology in the first 2 4 years subsequently the morphology became more regular and in one case had stabilised within about eight years progressive steepening and acceleration of bank erosion appears to have been propagated upstream in one case but in the other cases erosion was very localised rates of vertical accretion at the entrances to the old channel were much higher than most quoted in the literature rates of change in all morphological sedimentary and biotic components exhibit an exponential decline with time but with slightly differing timescales on these active gravel bed streams major adjustment within the new channels may be completed within 6 12 years though lakes persist in the abandoned channels for much longer

theoretical regime equations for mobile gravel bed rivers with stable banks a system of rational regime equations is developed for gravel bed rivers with stable banks using the optimality theory ot the optimality theory is based on the premise that equilibrium river geometry is characterised by an optimum configuration defined here as maximum sediment transport efficiency theoretical dimensionless equations are derived for width depth slope width depth ratio and meandering braiding transition independent dimensionless variables comprise discharge sediment concentration and relative bank strength which is defined as the ratio of the critical shear stresses for the bank and bed sediments discharge exponents and general form of the equations agree well with previously developed empirical relations relative bank strength is used to parameterise the influence of riparian vegetation on bank strength and is evaluated by calibrating against observed width depth ratio once calibrated the hydraulic geometry of natural gravel rivers is well described by the theoretical equations including discrimination between meandering and braiding channels the results provide strong support for the assumption that equilibrium or regime river behavior is equivalent to an optimal state and underline the importance of bank strength and sediment load as controls on hydraulic geometry

a model of channel response in disturbed alluvial channels dredging and straightening of alluvial channels between 1959 and 1978 in west tennessee caused a series of morphologic changes along modified reaches and tributary streams degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed levels by as much as 6 1 m following degradation reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction aggradation downstream of the area of maximum disturbance reached 0 12 m per year with the greatest rates occurring near the stream mouths the adjustment of channel geometry and phases of channel evolution are characterized by six process oriented stages of morphologic development premodified constructed degradation threshold aggradation and restabilization down cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded threshold stage channel widening continues through the aggradation stage as the slough line develops as an initial site of lower bank stability the bank profile develops three dynamic elements 1 vertical face 70 to 90 2 upper bank 25 to 50 and 3 slough line 20 to 25 alternate channel bars form during the restabilization stage and represent incipient meandering of the channel

application of lidar and discriminant analysis to determine landscape characteristics for different types of slope failures in heavily vegetated steep terrain horseshoe run watershed west virginia abstract a landslide inventory map was created for horseshoe run watershed west virginia using high resolution topographic data obtained from airborne lidar a total of 152 landslides were remotely mapped and classified as planar slides rotational slumps debris flows debris fans debris slides and active slopes based on morphologic characteristics interpreted from lidar derived shaded relief maps with field verification at several locations seven landscape variables were calculated for the watershed from the high resolution 0 5 m topographic data elevation slope angle slope aspect distance from roads distance from streams plan curvature and profile curvature statistical analyses were conducted to determine the mean and standard deviations for each variable and corresponding slope failure type discriminant analyses were conducted on the different types of failed slopes with a maximum 86 accuracy level to determine which landscape characteristics contribute to each type of landslide results from the discriminant analyses indicate that statistically significant differences exist between the failure classes mapped within the watershed and that slope angle slope aspect and landscape curvature are important variables influencing the type of process the results from this study have important implications for predicting where certain types of slope failures may occur based on landscape characteristics

mathematical modeling of graded river profiles numerical modeling of the longitudinal profiles of rivers at grade is accomplished using the basic equations of open channel flow sediment transport equations and empirical relations for downstream variation in flow discharge sediment discharge sediment caliber and channel width only in some cases are the computed stream profiles fit exactly by any one of the commonly supported mathematical function analogs to graded profile form exponential logarithmic or power function but in most cases any of these functions can provide a fit with a degree of error smaller than would be noted in treating field data profiles dominated by spatial change in fluid and sediment discharge are distinctly power functions while profiles dominated by sediment size reduction are not necessarily exponential in form other important controls on profile shape are the degree of downstream width change in response to increasing discharge and the general range of sediment size a dynamic model of a river s approach to grade

air photo based change in channel width in the minnesota river basin modes of adjustment and implications for sediment budget abstract the minnesota river and major tributaries have experienced large increases in discharge over the past century aerial photograph based measurements of channel width were made for the 1938 2015 period at 16 multibend subreaches by digitizing the area between vegetation lines and dividing by centerline length results show considerable increases in width for the main stem 0 62 0 10 y and major tributaries 0 31 0 08 y but are inconclusive for smaller channels width

influence of sand on hydraulics and gravel transport in a braided gravel bed river measurements in a braided reach of the proglacial white river washington are used to compare the bed load capacity and competence of flow over the predominant gravel bed and over a narrow ribbon of mobile sand which extended alongside the talweg analysis of 144 velocity profiles and 222 bed load samples shows that shear stress and roughness height were significantly lower over sand than gravel but maximum bed load diameter and total gravel transport rate significantly higher as were transport rates of given size fractions at similar shear stresses these differences in competence and capacity are explained by relative size effects on the threshold shear stress for entrainment the influence on gravel transport of local variation in bed material size may explain the self sorting of bed load sheets described by other workers however in channels like that described here the continuous longitudinal ribbon of sand allows the flow to develop a lower shear stress over the smoother bed which partly offsets the relative size effects on competence and capacity

channel processes following land use changes in a degrading steep headwater stream in north island new zealand abstract in headwater streams in steep land settings narrow and steep valley floors provide closely coupled relationships between geomorphic components including hillslopes tributary fans and channel reaches these relationships together with small catchment sizes result in episodic changes to the amount of stored sediment in channels major sediment inputs follow high magnitude events subsequent exponential losses via removal of material can be represented by a relaxation curve the influence of hillslope and tributary processes on relaxation curves and that of altered coupling relations between components were investigated along a 1 3 km reach of a degrading channel in the 4 8 km2 weraamaia catchment new zealand extensive deforestation in the late 19th and early 20th centuries followed by invasion of scrubs and reforestation induced changes to major erosion types from gully complexes to shallow landslides changes in the size and pattern of sediment slugs from 1938 to 2002 were analysed from air photographs tied to detailed field measurement the rate and calibre of sediment flux changed progressively following substantive hillslope input in a storm in 1938 subsequently the channel narrowed and incised decoupling tributary fans from the main stem thereby scaling down the size of sediment slugs as a consequence the dominant influence on the behaviour of sediment slugs and associated relaxation processes changed from tributary fans to the type and distribution of bedrock outcrops along the reach

3d imaging of subducting and fragmenting indian continental lithosphere beneath southern and central tibet using body wave finite frequency tomography abstract we perform a finite frequency tomographic inversion to image 3d velocity structures beneath southern and central tibet using teleseismic body wave data recorded by the tibet 31n passive seismic array as well as waveforms from previous temporary seismic arrays high velocity bodies dip 40 northward beneath the himalaya and the lhasa terrane we interpret these high velocity anomalies as subducting indian continental lithosphere icl the icl appears to extend further north in central tibet than in eastern tibet reaching 350 km depth at 31 n along 85 e but at 30 n along 91 e low p and s wave velocity anomalies extend from the lower crust to 180 km depth beneath the tangra yum co rift yadong gulu rift and the cona rift suggesting that rifting in southern tibet may involve the entire lithosphere the anomaly beneath tangra yum co rift extends down to about 180 km whereas the anomalies west of the yadong gulu rift and east of the cona rift extend to more than 300 km depth the low velocity upper mantle west of the yadong gulu rift extends furthest north and appears to connect with the extensive upper mantle low velocity region beneath central tibet thus the northward subducting indian plate is fragmented along north south breaks that permit or induce asthenospheric upwellings indistinguishable from the upper mantle of northern tibet

fluvial sediment transport and deposition following the 1991 eruption of mount pinatubo the 1991 eruption of mount pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows bedload sampling in the pasig potrero river one of the most heavily impacted rivers revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth fine grained bed dimensionless bedload transport rates in the pasig potrero river differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments the similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply in arid rivers this is attributed to a flashy hydrograph whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery this work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced d 2002 elsevier science b v all rights reserved

channel adjustment of an unstable coarse grained stream opposing trends of boundary and critical shear stress and the applicability of extremal hypotheses channel adjustments in the north fork toutle river and the toutle river main stem were initiated by deposition of a 2 5 km3 debris avalanche and associated lahars that accompanied the catastrophic eruption of mount st helens washington on 18 may 1980 channel widening was the dominant process in combination adjustments caused average boundary shear stress to decrease non linearly with time and critical shear stress to increase non linearly with time at the discharge that is equalled or exceeded 1 per cent of the time these trends converged by 1991 1992 so that excess shear stress approached minimum values extremal hypotheses such as minimization of unit stream power and minimization of the rate of energy dissipation minimum stream power are shown to be applicable to dynamic adjustments of the toutle river system maximization of the darcy weisbach friction factor did not occur but increases in relative bed roughness caused by the concomitant reduction in hydraulic depths and bed material coarsening were documented predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991 1992 geometries and bed material characteristics measured in the field it is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision retreat of stream side hummocks and establishment of riparian vegetation to limit the destabilizing effects of large floods further prediction of energy slope and consequently stream power by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained sand and gravel bank materials relative to the coarsened channel bed from bank retreat and from upstream terrace erosion

river responses to the 2010 major eruption of the merapi volcano central java indonesia abstract this study examines the fluvial readjustment of a javanese river impacted by the major eruption of the merapi volcano indonesia in october and november 2010 the basin of the opak river located on the southern flank of the merapi was subject to substantial sediment input related to massive pyroclastic deposits that were remobilized by numerous lahars during the year after the eruption two study sites were equipped in order to evaluate the morphodynamic evolution of the riverbed of the opak river topographic surveys bedload particle marking and suspended sediment sampling revealed an important sediment mobilization during efficient flash floods surprisingly no bed aggradation related to the progradation of a sediment wave was observed two years after the eruptive event marked bed incision was observed the opak river readjustment differs from that of other fluvial systems affected by massive eruptions in two ways firstly local population extracted the sand and blocks injected by the eruption as they represent a valuable economic resource secondly several dams trapped the major part of the sediment load remobilized by lahars

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

extraordinary sediment delivery and rapid geomorphic response following the 2008 2009 eruption of chaiten volcano chile u s geological survey volcano science center sernageomin s programa de riesgos volcanicos conicyt fondecyt grants 1110609 1141064 11130671 conicyt fondap 15090013 vamos research centre

sediment yield following severe volcanic disturbance a two decade perspective from mount st helens explosive volcanic eruptions perturb water and sediment fluxes in watersheds consequently posteruption sediment yields can exceed preeruption yields by several orders of magnitude annual suspended sediment yields following the catastrophic 1980 mount st helens eruption were as much as 500 times greater than typical background level and they generally declined nonlinearly for more than a decade although sediment yields responded primarily to type and degree of disturbance streamflow fluctuations significantly affected sediment yield trends consecutive years 1995 1999 of above average discharge reversed the nonlinear decline and rejuvenated yields to average values measured within a few years of the eruption after 20 yr the average annual suspended sediment yield from the 1980 debris avalanche deposit remains 100 times 10 4 mg megagrams km 2 above typical background level 10 2 mg km 2 within five years of the eruption annual yields from valleys coated by lahar deposits roughly plateaued and average yields remain about 10 times 10 3 mg km 2 above background level yield from a basin devastated solely by a blast pyroclastic current diminished to background level within five years these data demonstrate longterm instability of eruption generated detritus and show that effective mitigation measures must remain functional for decades

case study of variation of sedimentation in the yellow and wei rivers abstractthe sanmenxia dam built in 1960 in the middle reach of the yellow river has experienced severe sedimentation problems not only in the reservoir area itself but also extending hundreds of kilometers in the backwater region morphological responses in the middle yellow river and its tributary the wei river upstream of the dam have generally lagged behind the causal changes in upstream and downstream controls based on the geometrical characteristics of a wedge shaped sedimentation body a method was derived for calculating equilibrium values of the accumulated sedimentation volume ve in the channel reaches combining the method for calculating ve with rate law models for channel morphological adjustment a method for calculating the accumulated deposition volumes was derived the results showed that the proposed method can accurately simulate sedimentation processes in the study reaches during 1960 and 2011 in the response to the integrated impacts of base level fluctuations and changes in incom

the meandering braided river threshold a reappraisal abstract the concept of a threshold discharge slope q s combination that separates braided from meandering streams is critically re examined partly by review of previous data and partly by analysis of new data from south island new zealand it is argue d that discriminant functions that use mean annual discharge provide a poor physical basis for interpretations based on natural processes while bankfull discharge is also deficient because it is not a fully independent variable the common use of channel rather than valley slope adds a further misleading component because channel slope is partly dependent on channel pattern sinuosity most previous studies have inadequately treated the role of bed particle size in pattern discrimination failing to recognize that active gravel streams must plot higher on a q s chart than sand bed channels irrespective of pattern because of the greater power requirements for bed material movement within any one size class of bed material there is no evidence to indicate a clear discrimination between braiding and meandering only a weak statistical association between pattern and slope discharge values while this association may be explicable in terms of the high shear stress and stream power that accompany high qs values promoting braiding the real prerequisite for braiding appears to be high loads of bed calibre material producing wide shallow channels a factor that is only partly controlled by stream power accordingly the search for a pattern threshold based on discharge and slope seems to be a futile exercise an interpretation of existing pattern discriminant functions from the perspective of the threshold shear stress for particle movement is made it is concluded that in effect these functions merely state that gravel bed streams are more likely to be braided than channels in finer sediment statistically this appears to be valid and reasons for that difference are offered based on the balance between imposed bed material load and channel capacity

minimum froude number and the equilibrium of alluvial sand rivers rivers adjust towards an equilibrium condition the stability of which depends upon a set of controlling factors expressed by the froude number as alluvial river channels approach stable conditions the froude number of the channel flow will tend to attain a minimum value which reflects minimum bed material motion and maximum channel stability under the constraints imposed by water discharge sediment load and particle size computer simulations for sand bed rivers show that the froude number of the flow tends to a minimum value when the equilibrium river tends to a certain hydraulic geometry evidence from 57 alluvial sand material rivers and stable canals shows that this simulated hydraulic geometry with minimum froude number corresponds to the natural equilibrium state

massive biomass flushing despite modest channel response in the rayas river following the 2008 eruption of chaiten volcano chile abstract the 2008 eruption of chaiten volcano in southern chile severely impacted several densely forested river catchments by supplying excess pyroclastic sediment to the channel networks our aim is to substantiate whether and how channel geometry and forest stands changed in the rayas river following the sudden input of pyroclastic sediment we measured the resulting changes to channel geometry and riparian forest stands along 17 6 km of the impacted gravel bed rayas river 294 km 2 from multiple high resolution satellite images aerial photographs and fieldwork to quantify yield volume characteristics of the forest stands limited channel changes during the last 60 years before the eruption reflect a dynamic equilibrium condition of the river corridor despite the high annual precipitation and the sediment supply from chaiten and michinmahuida volcanoes in the headwaters images taken in 1945 2004 and 2005 show that total size of the vegetated channel islands nearly doubled between 1945 and 2004 and remained unchanged between 2004 and 2005 pyroclastic sediment entering the rayas river after the 2008 eruption caused only minor average channel widening 7 but killed all island vegetation in the study reach substantial shifts in the size distribution of in channel vegetation patches reflect losses in total island area of 46 from 2005 to 2009 and an additional 34 from 2009 to 2012 the estimated pulsed release of organic carbon into the channel mainly in the form of large wood from obliterated island and floodplain forests was 78 400 tc km y and surpasses most documented yields from small mountainous catchments with similar rainfall forest cover and disturbance history while making up between 20 and 60 of the annual carbon burial rate of fluvial sediments in the northern patagonian fjords we conclude that the carbon footprint of the 2008 chaiten eruption on the rayas river was more significant than the measured geomorphic impacts on channel geometry for the first five years following disturbance the modest post eruptive geomorphic response in this river is a poor indicator of its biogeochemical response

unit stream power equation for gravel the basic assumptions used in the derivation of bedload or gravel transport equations are reviewed and examined to determine their validities laboratory data indicate that unit stream power is mor

changes in braided river morphology resulting from aggradation and degradation forty three experiments were completed in a large flume 1 8 x 18 3 m to examine the effects of sediment load sediment size and channel gradient on braided river morphology the laboratory results were supported by field research and analogs from the published literature subaerially exposed braid bars were formed by the dissection and further accretion of stalled linguoid dunes which are actively migrating bedforms bar forming processes and channel dynamics were the same in both sand and gravel bed channels however linguoid dunes stalled and were transformed into braid bars more frequently in gravel bed channels and therefore gravel bed channels were more intensely braided aggradation resulted in the development of more bars rather than in an increase in the size of preexisting braid bars the number of actively migrating linguoid dunes also increased with sediment load in the highly mobile sand bed channels conversely in degrading channels the number of braid bars decreased and average bar

least action principle equilibrium states iterative adjustment and the stability of alluvial channels the energy based least action principle lap has proven to be very successful for explaining natural phenomena in both classical and modern physics this paper briefly reviews its historical development and details how in three ways it governs the behaviour and stability of alluvial rivers first the lap embodies the special stationary equilibrium state of motion and so its incorporation with the principle of energy conservation explains why so many optimizing hypotheses have been proposed in fluvial geomorphology second the variational approach underlying the lap provides a more straightforward and simpler fuzzy object orientated method for solving river regime problems than do the various complex newtonian formulations third it is shown that in fluvial systems with surplus energy the surplus can be expended with slope and or channel geometry adjustments with the degree of channel geometry adjustment quantified by the dimensionless numbers f for depth dominated adjustment and h for width depth dominated adjustment different planforms are preferred at different energy levels with h providing a quantitative measure of the flow s efficiency for moving sediment in rivers with insufficient energy the interactions of endogenous and exogenous factors are shown to be capable in certain circumstances of achieving a stationary equilibrium condition which acts as the attractor state importantly this study describes how iterative changes enable systems to achieve such a stable equilibrium copyright 2007 john wiley sons ltd

morphological evolution of the north fork toutle river following the eruption of mount st helens washington abstract the north fork toutle river nftr has undergone extensive morphological changes following the catastrophic eruption of mount st helens washington in 1980 especially the upper reaches affected by a 2 5 km3 debris avalanche deposit caused by the eruption this paper reports analysis and interpretation of vertical adjustments to the thalweg long profile at some 33 km river reaches redeveloped on the debris avalanche deposit during the 30 year period since the eruption the results confirm that adjustments in the upper part of the study reaches have generally been led by degradation while that in the lower reaches have been led by aggradation with the middle reaches acting as a hinge zone trends of change in the thalweg long profile and bedslope reveal that channel gradients have decreased nonlinearly through time and with distance downstream from the volcano values of stream power have decreased with time commensurately owing to reductions in slope and channel widening while the bed has coarsened so that rates of erosion of the debris avalanche deposit in the upper nftr have slowed to the point that the long profile now perched and slightly steeper is relaxing toward a new equilibrium or graded condition thirty year relaxation paths for thalweg elevation were simulated at seven key cross sections using newly developed comprehensive rate law models based on nonlinear decay in rates of morphological response to perturbation the results indicate that both single and multistep rate law models can simulate the observed records consequently the rate law approach provides an effective method for studying and simulating morphological response of the fluvial system to a major instantaneous disturbance such as a volcanic eruption

energy time and channel evolution in catastrophically disturbed fluvial systems abstract two diverse fluvial systems show that with time channels adjust such that the rate of energy dissipation is minimized one fluvial system characterized by high relief and coarse grained sediment was subjected to an explosive volcanic eruption the other system characterized by low relief and fine grained sediment was subjected to dredging and straightening study of the expenditure of kinetic and potential energy components of total mechanical energy provide an energy based rationale of the interdependency between processes and forms during channel evolution spatial and temporal trends of aggradation and degradation are similar although relative amounts of aggradation in the high energy system are greatly enhanced by the deposition of large amounts of eroded bank material from upstream reaches degradation accompanied by widening is the most efficient means of energy dissipation because all components of total mechanical energy decrease with time widening dominates energy dissipation in the coarse grained system to offset increases in hydraulic depth caused by incision in the low energy fine grained system channel adjustment and energy dissipation are dominated by vertical processes because of low relative values of kinetic energy and because eroded bank sediment is transported out of the drainage basin and does not aid in downstream aggradation energy dissipation or channel recovery specific energy is shown to decrease nonlinearly with time during channel evolution and provides a measure of reductions in available energy at the channel bed data from two sites show convergence towards a minimum specific energy with time time dependent reductions in specific energy at a point act in concert with minimization of the rate of energy dissipation over a reach during channel evolution as the fluvial systems adjust to a new equilibrium

stratigraphic expression of basement fault zones in northern west virginia stratigraphic relationships of upper devonian lower mississippian subsurface and outcrop strata in northern west virginia indicate that two basement structures influenced the deposition of the catskill and price rockwell delta complexes these structures are herein named the harrison fault zone and the barbour fault zone the harrison fault zone trends north south through north central west virginia and is recognized by the stacking arrangement of shoreline and marine sandstones and by trends of rapid interval thickening of shelf deposits the trend and sense of movement indicated by these features is consistent with that expected for cambrian age basement normal faults along the eastern margin of the rome trough the barbour fault zone is a cross strike feature recognized by the vertical stacking of hampshire group fluvial sandstones facies relationships within the price formation and the configuration of the sub greenbrier lime stone unconformity the barbour fault zone marks the northern edge of the west virginia dome

discharge and sediment supply controls on erosion and deposition in a dynamic alluvial channel research on dynamic alluvial channels has recognised the influence on river channel change of both discharge and sediment supply although it has proved difficult to measure the latter this paper presents the first accurate data from a dynamic alluvial channel that describe the interrelated effect on channel morphological change of both discharge and sediment supply variations over different timescales reliable information on the spatial patterns of erosion and deposition were obtained using combined photogrammetry and tacheometric survey of the meltwater stream of a glacierised catchment over a 5 week period over the full time period the morphological evidence suggested the passage of a wave of sediment counter intuitively the period of aggradation was associated with increasing diurnal peak and base flow discharge magnitude while degradation occurred during a period of steady peak diurnal discharge this suggests that the channel change was controlled by variation in upstream sediment supply over a shorter timescale information on diurnal changes in morphology reveals that although discharge was responsible for some aspects of channel change this was modified by the effects of upstream sediment supply consideration of the spatial patterns of erosion and deposition at the within reach scale reinforces this point with spatial aspects of morphological change being driven by discharge and sediment supply fluctuations but modified by spatial feedbacks associated with internal channel morphology the implications of these findings for fluvial geomorphology in general are considered

seismicity and tectonics of the bay of bengal evidence for intraplate deformation of the northern indian plate abstract seismicity and fault plane solutions of several earthquakes in the bay of bengal have been studied to focus attention on the nature of intraplate deformation in the northern indian plate a widely dispersed diffuse seismicity provides evidence that the intraplate region of the entire bay of bengal and peninsular india of the indian plate are seismically active of which the gangetic delta and the eastern flank of the ninety east ridge show somewhat higher seismicity in comparison to the thickly populated epicenters at the eastern plate boundary predominance of thrust faulting earthquake mechanisms with consistent north dipping fault planes and more or less n s pressure axes imply that n s compression is more prevalent in the intraplate region of the bay of bengal which is analogous to the himalayan arc this intraplate seismicity and n s compressive deformation is presumed to be the result of collisional resistance to the north moving indian plate with the eurasian plate at the himalayas where subduction of the indian lithosphere in mantle has stopped recently as a result to compensate the horizontal compressive force by ridge push at the carlsberg ridge the intraplate region of the northern indian plate in continuation to the central indian ocean basin no longer remains passive due to a strong repulsive force at the collisonal plate boundary himalaya that causes stress transmission towards south and makes the intraplate region seismically active

evolution of coarse gravel bed forms field measurements at flood stage field measurements to investigate the origin and growth of mesoscale gravel bed forms in deep flows were made in the north fork toutle river washington sonar observations of the gravel streambed at a stationary point were recorded during two storm flows in december 1989 and january 1990 with concurrent bed load sampling and continuous velocity measurements mean diameter of bed load was about 3 cm flow depths were 1 4 2 4 m and bed shear stresses were 2 5 times the critical stress of mean bed load diameter as computed from the depth slope product these records document the hydrodynamic conditions under which dunelike coarse gravel bed forms were observed coarse gravel dunes height 20 cm length 6 15 m evolved more than 24 hours after peak stage primarily by accretion as inferred from bed form changes revealed in dual sonar records dune heights increased to 40 cm as mean trough elevation rose about 50 cm over several hours smaller dunes wavelength 1 3 m transitional from bed load sheets migrated on the backs of the large dunes the superposed dunes finally became indistinguishable from the large dunes which diminished in height by increasing the mean level of troughs gravel deposition occurred at the observation point in conjunction with migration of gravel dunes the direct comparison of known bed form regimes and gravel bar facies provides alternative interpretations of gravelly deposits

1 66 ga old metamorphosed pbcu deposit in sargipali eastern india manifestations of tidal flat environment and sedex type genesis abstract the metasedimentary rocks and the unusual pb cu mineralization of the sargipali mine area are described and discussed to elucidate the processes involved in their deposition important lines of evidences used for the interpretation of an inter to supratidal flat environment are 1 a general pattern of a shallowing upward sequence from coarse clastics arenaceous through finer clastics argillaceous to carbonate 2 the occurrence of metaconglomerate trough cross bedding and wave ripples within the arenaceous lithostratigraphic unit 3 intercalations of quartzite carbonate skarn dolomite and convolution of chert laminae within the argillaceous lithostratigraphic unit and 4 intercalation of quartz mica chlorite schist laminae within the carbonate lithostratigraphic unit the ores seems to belong to the same environment furthermore in the assessment of the origin of the sargipali ores it is recognized that the orebodies not only represent a sedimentary setting but also show a high pb content and an older age of mineralization than that of deformation metamorphism and granite intrusion along with the lack of stockwork zones wall rock alteration subaerial volcanism and the presence of chert and tourmalinite these features are consistent with a sedex type origin the idea of this origin finds support by yet another observation i e the ore sulphur was mainly derived from the inorganic reduction of the seawater sulphate at more than 300 c while the ore metals were leached from the 238u 204pb enriched singhbhum soda granite of 2200 ma the present study may help in conceiving a new possibility that the sediment hosted pb rich deposits of mvt origin can also be evaluated in terms of the sedex model

case study equivalent widths of the middle rio grande new mexico successive reaches of the rio grande have maintained equivalent channel widths of 50 and 250 m respectively over long periods of time it is hypothesized that alluvial channels adjust bed slope to match the long term changes in channel width analytical relationships show that wider river reaches develop steeper slopes a modeling approach using daily water and sediment discharges simulates the transient evolution of bed elevation changes the analytical and numerical models are in very good agreement with the longitudinal profile measurements of the bosque del apache reach of the rio grande nm from 1992 to 1999 the slope of the 50 m wide reach was 50 cm km and the slope of the 250 m wide reach of the same river increased to 80 cm km this unsteady daily transient model compares well with a steady transient solution at a constant discharge close to the mean annual flow the transient slope adjustments can also be approximated with an exponential model accordingly it takes about 20 25 years for the rio grande to achieve about 90 of its slope adjustment

state of stress and its bearing on tectonics under the tibetan plateau abstract using the composite plot of pressure and tension axes of the available focal mechanism solutions of earthquakes this paper investigates the nature and process of stress systems and their impression on tectonics under the tibetan plateau a composite plot shows that the tibetan plateau is now experiencing a nne ssw directed compressive stress with an almost ese wnw tensile stress and it confirms a wrench movement towards the east along a prominent strike slip fault transcurrent tectonics appear to be the principal phase of deformation in tibet in response to the northward push of india this study also suggests that the extensional tectonics of the tibetan plateau primarily involve a combination of compressive and shear stresses as a consequence of continued continental convergence rather than merely a gravitational body force

flow resistance under conditions of intense gravel transport a study of flow resistance was undertaken in a channelized reach of the north fork toutle river downstream of mount st helens washington hydraulic and sediment transport data were collected in flows with velocities up to 3 m s and shear stresses up to 7 times the critical value needed for bed load transport details of the flow structure as revealed in vertical velocity profiles indicate that weak bed load transport over a plane gravel bed has little effect on flow resistance the plane gravel bed persists up to stresses 3 times critical at which point irregular bed forms appear bed forms greatly increase flow resistance and cause velocity profiles to become distorted the latter arises as an effect of flows becoming depth limited as bed form amplitude increases at very high rates of bed load transport an upper stage plane bed appeared velocity profiles measured in these flows match the law of the wall closely with the equivalent roughness being well represented by ks 3d84 of the bed load the effects noted here will be important in very large floods or in rivers that are not free to widen such as those cut into bedrock

backwater controls on the evolution and avulsion of the qingshuigou channel on the yellow river delta abstract as rivers approach base level their water and sediment dynamics are affected by a transitional reach known as the backwater zone at low flows backwater zones cause flow deceleration and in channel sedimentation but at high flows they cause flow acceleration and erosion over many floods the dynamics of deposition and erosion in the backwater zone are thought to control the locations of avulsions on some large deltaic channels however in various studies the role of the backwater is often inferred or modeled and directly observed evidence of how backwater affects channel dynamics at avulsion sites remains scarce in this study we show how the backwater zone impacts the evolution and avulsion of the qingshuigou channel a recent lobe on the yellow river delta using four decades 1976 2015 of data from systematic surveys of water discharge sediment load cross sectional profiles and water surface elevation the results show that the channel was commonly eroded during flood seasons and aggraded during nonflood seasons erosion rates generally decreased in the downstream direction along the lower channel reach during flood seasons primarily due to downstream channel widening and the subsequent decrease in sediment transport capacity the erosion rate reached zero at the cross sections farthest downstream which is contrary to expectations under hydrodynamic backwater effects where drawdown causes erosion to increase downstream during high flows during nonflood seasons maximum sedimentation occurred upstream of the backwater zone possibly due to impacts of local topography of meandering bends or constriction from dikes morphodynamic backwater accompanied by the deposition and gradual progradation of a mouth bar resulted in downstream increasing sedimentation superelevation and lateral migration rates along the lower channel reach from 1985 to 1996 the predicted avulsion location was near cross sections q6 or q7 with an avulsion length of 20 30 km upstream of the shoreline which was consistent with those for historical avulsions we emphasize the close interplay between backwater effects and channel geometry and argue that morphodynamic backwater may play a more important role than hydrodynamic backwater in setting up and triggering avulsions on the yellow river delta

deformation of the ne basin and range province the response of the lithosphere to the yellowstone plume summary tectonic deformation in the ne basin and range province of the western united states is concentrated in two zones the n s trending northern part of the intermountain seismic belt in northern utah se idaho and sw wyoming and the e w trending central idaho seismic zone which converge at yellowstone in nw wyoming accepting the popular view that the yellowstone volcanic field is above an upwelling plume from the deep mantle i explore the possibility that deformation of the brittle upper crust in these two seismic zones may be caused by return flow from this plume this return flow is assumed sheared sw in the direction of motion of the north american plate relative to yellowstone the snake river plain srp a linear outcrop of neogene and quaternary basalt that trends sw from yellowstone for more than 400 km bisecting the angle between the two seismic zones may be a trail formed as the plate moves sw across the upwelling plume beyond 150 km from yellowstone slip vectors on active normal faults in both deforming zones are oriented inwards at 45 towards the sw azimuth along the srp normal slip rates on these faults are typically 1 mm yr 1 implying extensional strain rate 10 15 s 1 proportions of normal slip and strike slip suggest faults in the intermountain seismic belt are rotating anticlockwise at 2 myr 1 around vertical axes and faults in the central idaho seismic zone are rotating clockwise at similar rates within 100 km of yellowstone observed sense of rotation around vertical axes in both zones appears reversed tilt rates of hanging wall beds suggest most faults in both zones are rotating at 2 myr 1 also 10 15 s 1 around horizontal axes oriented nw the relative size of rotation rate around vertical axes and horizontal extensional strain rate is shown to imply that velocity in the underlying deforming fluid is small in the direction perpendicular to the axis of the srp in an initial model this velocity is set to zero enabling the two dimensional pattern of flow at the horizontal upper boundary of this deforming fluid to be solved straightforwardly this approximation enables observed rates and senses of horizontal extension and rotation around a vertical axis to be explained as consequences of the pattern of horizontal gradients of velocity parallel to the axis of the srp in the deforming fluid beneath the brittle layer a refinement suggests that velocity perpendicular to the srp near the upper boundary of the deforming fluid is small but inward towards the srp from both sides and is accompanied by downwelling beneath the srp beyond 100 km sw of yellowstone this pattern of flow will act to move magma in the uppermost mantle beneath the srp from its sides it may thus reconcile petrological observations that srp basalts do not show deep mantle characteristics expected had they been extruded from the yellowstone plume with the existence of this plume nearby conservation of angular momentum around horizontal axes perpendicular to the srp for the combined system of the plume interacting with the north american plate leads to the deduction that the plume radius is 50 km consistent with results of other investigations and its upwelling velocity is 60 mm yr 1

effects of three gorges dam operation on spatial distribution and evolution of channel thalweg in the yichang chenglingji reach of the middle yangtze river china abstract the evolution of the channel thalweg and pool riffle sequences is a critical feature of morphological adjustments in fluvial systems and might have important effects on aquatic habitat quality channel stability and navigation based on the 220 cross sectional profiles from 2002 to 2016 residual depths and spatial statistical analyses were used to quantitatively analyse the vertical variations and longitudinal distribution of the pool riffle sequences and channel thalweg in the yichang chenglingji reach ycr of the middle yangtze river which consists of the yizhi zhijiang shashi gongan and shishou jianli sub reaches the results showed that the dramatic reduction in the sediment loads following the construction of the three gorges dam tgd has caused significant adjustments in the size morphological diversity and spatial distribution of pool riffle structures in the ycr the average depth of the pools in the yizhi zhijiang reach and the shishou jianli reach overall exhibited a nonlinear growth trend with the average residual depth increasing by 1 4 m and 1 9 m respectively however the average residual depth in the shashi gongan reach showed a decreasing trend with a reduction of approximately 1 2 m the longitudinal lengths of the riffles in all three reaches contracted to different degrees and the specific percentage of longitudinal river length occupied by riffles total riffle length total sub reach length decreased by 8 9 6 and 5 9 in the three sub reaches from upstream to the downstream in addition the morphological diversity of the thalweg elevation in the shashi gongan reach and shishou jianli reach weakened after the construction of the tgd while the bed topography in the yizhi zhijiang reach became more complex and diverse moreover the pool riffle structures in the ycr were rearranged and distributed regularly following the initiation of the tgd operation although the variation characteristics of the average pool spacing in the three sub reaches were quite different quantitative relationship between the average residual depth and the previous four year hydrological condition was proposed for the three sub reaches based on the delayed response model drm and verified using the measurements from 2013 to 2016

channel response to sediment wave propagation and movement redwood creek california usa redwood creek north coastal californa usa has experienced dramatic changes in channel confguation since the 1950s a series of large floods in 1955 1964 1972 and 1975 combined with the advent of widespread commercial timber harvest and road building resulted in extensive erosion in the basin and contributed high sediment loads to redwood creek since 1975 no peak flows have exceeded a 5 year recurrence interval twenty years of cross sectional survey data document the downstream movement of a sediment wave in the lower 26 km of this gravel bedded river at a rate of 800 to 1600 m a i durng this period of moderately low flows higher transit rates are associated with reaches of higher unit stream power the wave was initially deposited at a site with an abrupt decrease in channel gradient and increase in channel width the amplitude of the wave has attenuated more than i m as it moved downstream and the duration of the wave increased from eight years upstream to more than 20 years downstream channel aggradation and subsequent degradation have been accommodated across the entire channel bed channel width has not decreased significantly after initial channel widening from large 25 year recurrence interval floods three sets of longitudinal surveys of the streambed showed the highest increase in pool depths and frequency in a degrading reach but even the aggrading reach exhbited some pool development through time the aggraded channel bed switched from functioning as a sediment sink to a significant sediment source as the channel adjusted to high sediment loads from 1980 to 1990 sediment eroded from temporary channel storage represented about 25 per cent ofthe total sediment load and 95 per cent of the bedload exported from the basin

cyclic aggradation and downcutting fluvial response to volcanic activity and calibration of soil carbonate stages in the western grand canyon arizona abstract in the western grand canyon fluvial terraces and pediment surfaces both associated with a pleistocene basalt flow document quaternary aggradation and downcutting by the colorado river illuminate the river s response to overload and the end of overload and allow calibration of soil carbonate stages and determination of downcutting rates four downcutting aggradation cycles are present each begins with erosion of older deposits to form a new river channel in which a characteristic suite of deposits is laid down the current cycle i started 700 yr b p the oldest iv includes the 603 000 8000 to 524 000 7000 yr black ledge basalt flow emplaced when the river channel was 30 m higher than it is now the flow is overlain by basalt cobble gravel and basalt sand soils reach the stage v level of carbonate development calibrated ages for soil stages are stage v 525 000 yr stage iv

channel responses to varying sediment input a flume experiment modeled after redwood creek california article i nfo storage flume aggradation degradation at the reach scale a channel adjusts to sediment supply and flow through mutual interactions among channel form bed particle size and flow dynamics that govern river bed mobility sediment can impair the beneficial uses of a river but the timescales for studying recovery following high sediment loading in the field setting make flume experiments appealing we use a flume experiment coupled with field measurements in a gravel bed river to explore sediment transport storage and mobility relations under various sediment supply conditions our flume experiment modeled adjustments of channel morphology slope and armoring in a gravel bed channel under moderate sediment increases channel bed elevation increased and sediment output increased but channel planform remained similar to pre feed conditions during the following degradational cycle most of the excess sediment was evacuated from the flume and the bed became armored under high sediment feed channel bed elevation increased the bed became smoother mid channel bars and bedload sheets formed and water surface slope increased concurrently output increased and became more poorly sorted during the last degradational cycle the channel became armored and channel incision ceased before all excess sediment was removed selective transport of finer material was evident throughout the aggradational cycles and became more pronounced during degradational cycles as the bed became armored our flume results of changes in bed elevation sediment storage channel morphology and bed texture parallel those from field surveys of redwood creek northern california which has exhibited channel bed degradation for 30 years following a large aggradation event in the 1970s the flume experiment suggested that channel recovery in terms of reestablishing a specific morphology may not occur but the channel may return to a state of balancing sediment supply and transport capacity published by elsevier b v

morphological adjustment of the qingshuigou channel on the yellow river delta and factors controlling its avulsion abstract the avulsion time scale of channels on the yellow river delta yrd is about a decade due to the large sediment load and rapid channel aggradation and progradation nevertheless the qingshuigou channel has been maintained for about four decades since 1976 this channel provides an ideal opportunity to study channel evolution following avulsion and to examine different avulsion criteria in this study we analyzed the geomorphic adjustment of the lower qingshuigou channel during 1976 2015 and calculated normalized gradient advantage and superelevation at the channel to estimate how close the channel was to avulsion results showed that channel evolution processes may be divided into four phases i 1976 1980 rapid aggradation ii 1980 1985 channel widening and enlargement iii 1985 1996 main channel aggradation and shrinkage and iv 1996 2015 main channel incision and deepening evolution phases i ii and iii are similar to the avulsion cycle observed in natural and experimental fluvial systems the calculated values of normalized gradient advantage and superelevation in early 1990s exceeded the critical values suggested by previous studies implying that the channel was prone to avulsion nevertheless avulsion was prevented mainly due to limited overbank flows constriction from artificial dikes and slowed channel extension as a result of reduced sediment load the evolution of the qingshuigou channel confirms previous arguments that superelevation and gradient advantage are not sufficient for avulsion and multiple factors should be considered including flood frequency lateral mobility sediment diameter and human interruptions

shear wave splitting across the ailao shan red river fault zone sw china 1 a broad band seismic array was set up across the ailao shan red river asrr fault zone sw china the shear wave splitting parameters on sks and skks phases are calculated using the method of silver and chan 1991 and indicate the polarization direction of 105 6 and the delay time of 1 68 0 44 s beneath the asrr fault zone combined with previous studies the average polarization direction is 110 19 and the delay time is 1 58 0 44 s to the sw side of the fault while the values are 83 30 and 1 29 0 29 s to the ne side this result implies that the upper mantle anisotropy to two sides of the asrr fault zone are different compared with the se polarization direction observed in the p s phase and the n to s surface movement in gps data our results suggest decoupling of the crust and upper mantle beneath the study region

downstream variation in stream power abstract stream power has a significant influence on many form and process attributes of the fluvial system using a similar approach to that suggested by d m lawler in 1992 and 1995 a model is developed to explore how stream power might vary in the downstream direction based on the assumption that the longitudinal profile of the river has an exponential form no particular discharge is necessarily specified but near bankfull flows are regarded as significant morphologically and one such discharge is the focus here total stream power per unit channel length qs is predicted to peak at an intermediate location the position of which depends on the ratio b where b and are the downstream rates of change of discharge and slope respectively if b is a relatively conservative quantity then the form of the longitudinal profile and in particular its degree of concavity will have the major influence on the position of maximum stream power specific stream power w is even more sensitive to and is expected to peak closer to the headwaters about half way between source and the location of the stream power maximum although this will depend on how channel width w varies with distance from source the model is tested along three connected streams of different size in the catchment of the river trent taking advantage of a relationship between mean annual flood and link magnitude which enables this near bankfull discharge to be estimated at any point within the network the model is verified in so far as stream power does attain a mid basin maximum but the observed and predicted locations of the maxima do not always correspond largely because of the distinctive variation in discharge and especially slope along individual pathways for example maximum power lies far downstream along the trent because of the large increase in mid basin discharge associated with a series of large closely spaced tributaries the importance of slope is borne out by the near headwater locations for specific power maxima which tend to be further upstream than predicted along all three rivers as a result of the steepness of upper reaches the variety of geomorphic settings produces deviations from expectation which has implications for the movement and storage of material in the fluvial system

stable channels with mobile gravel beds regime type equations for mobile gravel bed rivers are presented based on data obtained from 62 stable gravel bed river reaches in the united kingdom multiple regression techniques are applied to derive equations relating reach average and riffle values of width mean and maximum depth slope velocity sinuosity and riffle spacing to bankfull discharge bed and bank material characteristics valley slope bank vegetation type and an independent estimate of bankfull bed load transport rates although discharge has a dominant control on channel geometry these equations indicate that bed load discharge also has a significant influence particularly with regard to channel slope bank vegetation has a major control on width and velocity while depth velocity and slope are storngly affected by bed material size reasons for these results are considered in terms of the physical processes controlling channel adjustment the application of these regime equations is discussed and particular consideration is given to the design of sinuous channels with a pool riffle bed topograph

drip instabilities of continental lithosphere acceleration and entrainment by damage summary geological evidence indicates large volume lithospheric drip instabilities form under regions of continental lithosphere the size of these drips suggests that either the base of the lithosphere is volumetrically increased or the highly viscous upper lithosphere participates in the drip previous theoretical models using simple rheologies have been unable to produce unforced large volume drip instabilities thus large drip instabilities are typically induced by thickening or destabilizing the mobile base of the lithosphere through tectonic forcing such as convergent thickening or dense magmatic emplacement following extension here we propose a theory of lithospheric drip instabilities that may arise naturally from the thermal and rheological structure of earth independent of specific tectonic forcings using damage physics relevant for earth we find a large portion of the lithosphere may be mobilized and entrained into growing drip instabilities for a critical amount of damage the growth is accelerated sufficiently that large volume drip instabilities may form within geologically feasible time frames we therefore suggest large volume lithospheric drip instabilities may arise independently of tectonic settings through damage assisted mobilization and entrainment of the highly viscous lithosphere

development of longitudinal profiles of alluvial channels in response to base level lowering degradation of alluvial channels in cohesive sediments was studied in 15 m and 20 m long flumes with a slope of 0 01 cm cm degradation was initiated by lowering base level to a fixed position and the development of the longitudinal profile of the channel is analysed through a model formulated as a heat diffusion equation it is based on the equation of sediment continuity combined with an assumption regarding sediment transport namely that sediment discharge is linearly proportional to the channel slope in accordance with the boundary and initial conditions imposed by the experimental setup and procedure the basic equation is amenable to an analytical solution which defines bed elevation at any distance and time as a function of the amount of base level lowering and a diffusion coefficient additional problems arising from bank erosion and channel armouring are also treated successfully within the framework of the same model the results show that in homogeneous alluvial sediments not subject to armouring the ultimate result of base level lowering by a certain amount is degradation all along the channel by the same amount the main impact of erosion is felt in the early stages after initiation of the process and mainly near the mouth the rate of degradation at any station along the channel reaches a peak and then slowly decreases with time and the peak rate is attenuated with distance from the outlet the model permits the prediction of intermediate stages of profile development at any distance from the outlet and at different times

spatial and temporal patterns in fluvial recovery following volcanic eruptions channel response to basin wide sediment loading at mount pinatubo philippines the june 1991 eruption of mount pinatubo philippines was one of the largest volcanic eruptions of the twentieth century emplacing 5 6 km 3 of pyroclastic fl ow material on the fl anks of the volcano the combination of abundant relatively fi ne grained easily erodible material and intense tropical rainfall led to numerous lahars immediately following the eruption even after major lahars ended sediment yields in some basins remained orders of magnitude above pre eruption levels using data collected from 1996 through 2003 we investigated fi ve basins that experienced varying amounts of sediment loading in the 1991 eruption from 1 to 33 of the basin area covered by valley fi lling pyroclasticfl ow deposits from measurements of fl ow and bed characteristics made through time we developed a general conceptual model for channel recovery following basin wide sediment loading initially fi ner grained sediment and pumice are mobilized preferentially through selective transport once the bed is coarse enough for gravel size clasts to interact with one another clast structures develop increasing form roughness and critical shear stress and inhibiting initial clast mobility as sediment inputs continue to decline the channel incises into valley bottom sediments progressively armoring through winnowing at pinatubo incision and armoring occur fi rst as dry season phenomena due to reduced sediment inputs eventually moving to year round low fl ow bed stability observed timing of the onset of in channel biological recovery suggests that reestablishment of channel stability helps catalyze aquatic ecosystem recovery

fluvial responses to volcanism resedimentation of the 1800a taupo ignimbrite eruption in the rangitaiki river catchment north island new zealand abstract the potential for the generation of dangerous and damaging lahars and floods in response to the eruption of voluminous pyroclastic debris has become increasingly appreciated in recent years the style and tempo of this response varies both between eruptions and between individual catchments impacted by a single eruption so that an understanding of the factors controlling this variation is necessary for precise hazard assessment the 1800a taupo eruption from the taupo volcanic centre in the central north island of new zealand devastated an area of 20 000 km 2 during eruption of a climactic ignimbrite impacting the headwaters of all major rivers draining radially from this region the rangitaiki river the subject of this paper differs from other catchments in that the taupo ignimbrite buried an essentially flat land surface inherited from a suite of welded ignimbrite sheets erupted between 320 340 and 230 ka the middle reaches of the catchment are characterised by narrow steep gorges alternating with low gradient basins developed in tectonic half grabens initially remobilisation of pyroclastic material in the headwaters was dominated by hyperconcentrated sheet flows resulting in shallow reworking in higher gradient areas reintegration of drainage networks was achieved by incision of deep channels and gullies assisted by breakouts from ephemeral lakelets developed in ignimbrite dammed depressions braided and later meandering streams superseded this pattern as rill and gully systems stabilised and sediment yields fell leading to a decline in drainage density gorge reaches acted as efficient conduits for remobilised material while the basins acted as local depocentres for the temporary storage of volcaniclastic sediments mediating the transfer of pyroclastic debris to the bay of plenty coast 100 km to the north reworking and resedimentation of pyroclastic debris began immediately after the eruption peaking early and then rapidly declining so that most geomorphic adjustments occurred within one or two decades of the initial disturbance

response of bankfull discharge to discharge and sediment load in the lower yellow river this paper presents a study on the response of bankfull discharge to incoming discharge and sediment load based on long term hydrological and bankfull discharge data measured on the lower reaches of the yellow river the analysis indicated that the bankfull discharge was a function of the preceding 5 to 6 years flow regimes revealing that bankfull channel dimensions were a result of the accumulative effect of several consecutive years flow discharge and sediment load conditions in other words the mean relaxation time was about 5 to 6 years for channel adjustment theoretical methods for the prediction of bankfull discharge were developed in which the response time or the relaxation time was fully considered testing of the methods using data observed at five hydrologic stations in the lower reaches of the yellow river from 1960 to 2003 showed that the proposed methods can predict the variation of bankfull discharge in response to changes in the incoming discharge and sediment load the proposed methods hold promise for predicting the magnitude and trend of channel response to other rivers undergoing aggradation or degradation from changes in hydrologic or sediment regime

observations of downstream fining on the north fork toutle river near mount st helens washington we carried out a series of measurements to provide data for testing models of downstream fining in an actively braiding gravel bed river in particular the model developed in the previous paper we sampled a series of nine cross sections for bulk grain size distributions over a downstream distance of 5 4 km on the north fork toutle river near mount st helens washington in addition we sampled two of the nine sections for detailed analysis of surface grain size distributions in the cross stream direction by wolman counting within areas of distinct mean grain size patches our theory predicts that the rate of downstream fining depends on the distribution of deposition and a relative mobility function that depends on the characteristics of the grain size patches application of the theory to the study area shows that most of the observed downstream fining can be explained using patchiness as the dominant mechanism

measuring the seismic properties of tibetan bright spots evidence for free aqueous fluids in the tibetan middle crust seismic bright spots are commonly interpreted to mark fluid concentrations but their nature melt or aqueous is usually inferred only from circumstantial evidence of the geologic setting a band of bright spot reflections has been imaged by project indepth international deep profiling of tibet and the himalayas at about 15 km depth along 150 km of the northern yadong gulu rift southern tibet we use indepth three component wide angle seismic data to measure seismic velocities at the bright spot reflector and theoretical rock physics bounds to constrain the nature of the fluids merging of data from multiple bright spots allows us to use a one dimensional approximation travel time modeling yields average p and s velocities for the upper crust above the bright spots of 5 3 0 2 and 3 2 0 2 km s 1 respectively reflection amplitude variation with offset avo modeling constrains the p and s velocities of the bright spots to 3 0 0 8 and 1 6 0 8 km s 1 respectively multiple modeling procedures suggest these velocities are not model dependent our results imply that of the order of 10 volume of free aqueous fluids in the tibetan middle crust produces the observed bright spot reflections the presence of relatively large quantities of free aqueous fluids presumably mostly saline supercritical h2o does not preclude the presence of melt but does constrain the maximum temperature at the bright spots to the wet granite solidus about 650 c and thus the maximum surface heat flow to 110 mw m 2 the observed bright spots can alternatively be explained as a result of transient flow of aqueous fluids through a lower temperature and lower heat flow southern tibetan crust

magnitude and timing of downstream channel aggradation and degradation in response to a dome building eruption at mount hood oregon a dome building eruption at mount hood oregon starting in a d 1780 and lasting until ca 1793 produced dome collapse lithic pyroclastic flows that triggered lahars and intermittently fed 10 8 m 3 of coarse volcaniclastic sediment to sediment reservoirs in headwater canyons of the sandy river mobilization of dominantly sandy sediment from these reservoirs by lahars and seasonal floods initiated downstream migration of a sediment wave that resulted in a profound cycle of aggradation and degradation in the lowermost reach of the river depositional reach 61 87 km from the source stratigraphic and sedimentologic relations in the alluvial fill together with dendrochronologic dating of degradation terraces demonstrate that 1 channel aggradation in response to sediment loading in the headwater canyons raised the river bed in this reach at least 23 m in a decade or less 2 the transition from aggradation to degradation in the upper part of this reach roughly coincided with the end of the dome building eruption 3 fluvial sediment transport and deposition augmented by one lahar achieved a minimum average aggradation rate of 2 m yr 4 the degradation phase of the cycle was more prolonged than the aggradation phase requiring more than half a century for the river to reach its present bed elevation and 5 the present longitudinal profile of the sandy river in this reach is at least 3 m above the pre eruption profile the pattern and rate of channel response and recovery in the sandy river following heavy sediment loading resemble those of other rivers similarly subjected to very large sediment inputs the magnitude of channel aggradation in the lower sandy river greater than that achieved at other volcanoes following much larger eruptions was likely enhanced by lateral confinement of the channel within a narrow incised valley a combination of at least one lahar and winter floods from frequent moderate magnitude rainstorms and infrequent very large storms was responsible for flushing large volumes of sediment to the depositional reach these conditions permitted a sedimentation response in the sandy river that approached the magnitude of channel aggradation resulting elsewhere from large explosive eruptions and high intensity rainfall regimes despite the fact that the sandy river aggradation was in response to an unremarkable dome building eruption in a climate dominated by low to moderate rainfall intensities

posteruption suspended sediment transport at mount st helens decadal scale relationships with landscape adjustments and river discharges received 11 december 2002 revised 30 september 2003 accepted 18 november 2003 published 17 january 2004 1 widespread landscape disturbance by the cataclysmic 1980 eruption of mount st helens abruptly increased sediment supply in surrounding watersheds the magnitude and duration of the redistribution of sediment deposited by the eruption as well as decades to centuries old sediment remobilized from storage have varied chiefly with the style of disturbance posteruption suspended sediment transport has been greater and more persistent from zones of channel disturbance than from zones of hillslope disturbance despite the severe landscape disturbances caused by the eruption relationships between discharge magnitudes and frequencies and suspended sediment transport have been remarkably consistent discharges smaller than mean annual flows generally have transported 5 but locally 15 of the annual suspended sediment loads and infrequent p 0 01 large floods have transported as much as 50 of the annual suspended sediment loads in a single day however moderate magnitude discharges those greater than mean annual flows but less than 2 year floods have transported the greatest amounts of sediment from all disturbance zones such discharges have transported on average 60 to 95 of the annual suspended sediment loads usually within cumulative periods of 1 3 weeks each year although small magnitude and largemagnitude discharges have locally and episodically transported considerable amounts of suspended sediment there has not been any notable change in the overall nature of the effective discharges moderate magnitude flows have been the predominant discharges responsible for transporting the majority of suspended sediment during 20 years of posteruption landscape adjustment index terms 1824 hydrology geomorphology 1625 1815 hydrology erosion and sedimentation 1860 hydrology runoff and streamflow keywords sediment yield suspended sediment transport mount st helens erosion volcano geomorphology

peak flow responses to landscape disturbances caused by the cataclysmic 1980 eruption of mount st helens washington years of discharge measurements that precede and follow the cataclysmic 1980 eruption of mount st helens washington provide an exceptional opportunity to examine the responses of peak fl ows to abrupt widespread devastating landscape disturbance multiple basins surrounding mount st helens 300 1300 km 2 drainage areas were variously disturbed by 1 a debris avalanche that buried 60 km 2 of valley 2 a lateral volcanic blast and associated pyroclastic fl ow that destroyed 550 km 2 of mature forest and blanketed the landscape with silt capped lithic tephra 3 debris fl ows that reamed riparian corridors and deposited tens to hundreds of centimeters of gravelly sand on valley fl oors and 4 a plinian tephra fall that blanketed areas proximal to the volcano with up to tens of centimeters of pumiceous silt sand and gravel the spatially complex disturbances produced a variety of potentially compensating effects that interacted with and infl uenced hydrological responses changes to water transfer on hillslopes and to fl storage and routing along channels both enhanced and retarded runoff rapid posteruption modifi cations of hillslope surface textures adjustments of channel networks and vegetation recovery in conjunction with the complex nature of the eruptive impacts and strong seasonal variability in regional climate hindered a consistent or persistent shift in peak discharges overall we detected a short lived 5 10 yr increase in the magnitudes of autumn and winter peak fl ows in general peak fl ows were larger and moderate to large fl ows q 2 yr were more substantively affected than predicted by early modeling efforts proportional increases in the magnitudes of both small and large fl ows in basins subject to severe channel disturbances but not in basins subject solely to hillslope disturbances suggest that eruptioninduced modifi cations to fleffi ciency along alluvial channels that have very mobile beds differentially affected fl ows of various magnitudes and likely played a prominent and additional role affecting the nature of the hydrological response

morphodynamic adjustments in the yichang chenglingji reach of the middle yangtze river since the operation of the three gorges project abstract to investigate the evolution characteristics of the yichang chenglingji reach ycr of the middle yangtze river and develop simulation methods the temporal and spatial morphodynamic adjustments of the ycr were analysed comprehensively on the basis of runoff sediment load and cross sectional profiles data at 220 cross sections from 2002 to 2016 results showed that significant channel degradation has occurred in the ycr especially in the low flow channels due to a drastic reduction in sediment yield since the operation of the three gorges project tgp the variations of upstream flow and sediment regimes would drive equilibrium channels to become increasingly narrow and deep and the current bankfull width and depth were less than their equilibrium counterparts in the recent period however the recent channel evolution was mainly characterized by the prominent channel deepening via a one way deformation due to the large scale bank revetments within the ycr where the reach scale bankfull depth increased by 1 6 m in the span of 15 years a semi empirical method for determining the equilibrium values of channel degradation and aggradation volume at the ycr was proposed on the basis of a comprehensive analysis of the effects of flow sediment concentration sediment gradation and water depth moreover the equilibrium values of the channel width and depth were estimated with the least action principle method the calculation methods for the equilibrium width depth width depth ratio and aggradation degradation volume were combined with the delayed response model drm then the methods for calculating the variations in channel geometry and aggradation degradation volume were derived results showed that the proposed methods effectively simulated the channel geometry and cumulative erosion volume in the ycr from 2002 to 2016 in addition the response of the channel evolution in the ycr was closely related to the previous four year hydrological conditions implying that channel evolution may lag behind the variations of flow and sediment discharges

applying geomorphological principles and engineering science to develop a phased sediment management plan for mount st helens washington thirty seven years post eruption erosion of the debris avalanche at mount st helens continues to supply sediment to the toutle cowlitz river system in quantities that have the potential to lower the level of protection lop against flooding unacceptably making this one of the most protracted gravel bed river disasters to date the portland district us army corps of engineers usace recently revised its long term plan for sediment management originally published in 1985 in order to maintain the lop above the congressionally authorised level while reducing impacts on fish currently listed under the endangered species act and minimising the overall cost of managing sediment derived from erosion at mount st helens in revising the plan the usace drew on evidence gained from sediment monitoring modelling and uncertainty analysis coupled with assessment of future lop trends under a baseline scenario continuation of the 1985 sediment management strategy and feasible alternatives they applied geomorphological principles and used engineering science to develop a phased sediment management plan that allows for uncertainty concerning future sediment yields by implementing sediment management actions only as and when necessary the phased plan makes best use of the potential to enhance the sediment trap efficiency and storage capacity of the existing sediment retention structure srs by incrementally raising its spillway and using novel hydraulic structures to build islands in the nftr and steepen the gradient of the sediment plain upstream of the structure dredging is held in reserve to be performed only when necessary to react to unexpectedly high sedimentation events or when the utility of other measures has been expended the engineering geomorphic principles and many of the measures in the phased sediment management plan are transferrable to other gravel bed river disasters the overriding message is that monitoring and adaptive management are crucial components of long term sediment disaster management especially in volcanic landscapes where future sediment yields are characterised by uncertainty and natural variability

crustal volume balance during the india eurasia collision and altitude of the tibetan plateau a working hypothesis a working hypothesis is developed for the two stages of evolution of the tibetan plateau during the continental collision between india and eurasia the first phase was dominated by crustal shortening and thickening in what is now tibet while indochina was expelled southeastward away from eurasia at the end of this phase at 17 ma the estimated tibetan crustal thickness was 51 km the second phase has been dominated by thickening of tibet by the influx of crustal material from india with no associated crustal shortening the crustal thickening that is inferred to have occurred by this process is only feasible because leakage of crust from beneath the plateau is restricted by neighboring archean cratons that block lower crustal flow this leakage to the east and south from tibet to beneath yunnan is estimated as 20 30 of the influx at present but was much smaller at the start of this second phase of deformation it is suggested that at 11 ma the force exerted against the tibetan upper crust by this flowing material first exceeded the threshold that this brittle layer could resist and tibet began to extend eastward any satisfactory working hypothesis for the tibetan plateau must explain its dimensions its 17 ma ending of shortening and 11 ma start of extension and volcanism the eastward slip sense on its active normal and strike slip faults and the ratios of their displacements to present day slip rates which imply that their slip rates have gradually increased this working hypothesis accounts for these features and predicts a smooth and continuing increase in altitude

extensional tectonics in central and eastern asia a brief summary although most of the neotectonics of eastern and central asia seems to be due to the collision and continued convergence between india and eurasia extensional tectonics prevails in four portions of this region tibet the baikal rift system the shansi graben and yunnan we think that the convergence between india and eurasia is responsible for crustal extension in all four regions but the physical mechanisms responsible for the extension are not the same in all of these cases fault plane solutions of earthquakes and clearly defined escarpments and adjacent basins seen on the landsat imagery indicate widespread normal faulting in tibet molnar tapponnier 1975 1978 ni york 1978 the direction of extension appears to be east west but the poorly determined fault plane solutions and the lack of field studies allow some variation in the direction of extension the normal faulting seems to be confined to the areas of highest elevation and some of the normal faults cross the indus zangbu suture into the high himalaya