conceptual framework for assessing the response of delta channel networks to holocene sea level rise abstract recent research has identified two fundamental unit processes that build delta distributary channels the first is mouth bar deposition at the shoreline and subsequent channel bifurcation which is driven by progradation of the shoreline the second is avulsion to a new channel a result of aggradation of the delta topset the former creates relatively small branching networks such as wax lake delta the latter generates relatively few long distributaries such as the mississippi and atchafalaya channels on the mississippi delta the relative rate of progradation to aggradation and hence the creation of accommodation space emerges as a controlling parameter on channel network form field and experimental research has identified sea level as the dominant control on holocene delta growth worldwide and has empirically linked channel network changes to changes in the rate of sea level rise here i outline a simple modeling framework for distributary network evolution and use this to explore large scale changes in holocene channel pattern that have been observed in deltas such as the rhine meuse and mississippi rapid early to mid holocene sea level rise forced many deltas into an aggradational mode where i hypothesize that avulsion and the generation of large scale branches should dominate slowing of sea level rise in the last 6000 yr allowed partitioning of sediment into progradation facilitating the growth of smaller scale distributary trees at the shorelines of some deltas and a reduction in the number of large scale branches significant antecedent topography modulates delta response the filling of large incised valleys for example caused many deltas to bypass the aggradational phase human effects on deltas can be cast in terms of geologic controls affecting accommodation constriction of channels forces rapid local progradation and mouth bar bifurcation while accelerated sea level rise increases aggradation and induces more frequent channel avulsion

interpreting avulsion process from ancient alluvial sequences guadalope matarranya system northern spain and wasatch formation western colorado alluvial deposits of the guadalope matarranya system oligocene ebro basin spain and the wasatch formation eocene western colorado provide time integrated records of the process of river channel avulsion these sequences consist of isolated channel belt sandstones incised into and abruptly overlain by flood plain siltstones indicating deposition by avulsive river systems the geometry and distribution of channel incisions suggest that avulsion was not controlled by tectonics climate or base level changes but formed by autocyclic processes measurements from 221 channel fills in the guadalope matarranya system and 38 from the wasatch formation allow us to statistically characterize channel geometries we infer to be associated with establishment and abandonment of individual river avulsions paleoflow depths in both systems average 1 4 to 1 6 m aggradation height superelevation of channel margin levees are on average 0 6 and 1 1 times paleoflow depth in the guadalope matarranya and wasatch systems respectively these results are consistent with values from recently avulsed modern rivers and suggest that 1 flow depth is the appropriate parameter against which to scale the critical superelevation necessary for channel avulsion and 2 the increase in potential energy due to channel perching drives the lateral instability that is needed for avulsion to be successful numerous stacked channel fills indicate repeated reoccupation of the same site by avulsing channels these reoccupation channels indicate that inherited flood plain topography here abandoned channel forms was an important control on the arrival site of newly avulsed channels comparison of our results to others suggests two end member types of avulsion can take place incisional avulsion seen here is characterized by an early incision phase followed by infilling by migrating bar forms aggradational avulsion begins with aggradation followed in time by stream integration into a single downcutting channel we suggest that the type of avulsion is strongly influenced by whether or not the adjacent flood plain is well or poorly drained in both cases subsequent aggradation and channel perching increase the chances that some triggering event will lead to avulsion

pacific north american teleconnection controls on precipitation isotope ratios across the contiguous united states large scale climate teleconnections such as the pacific north american pna pattern strongly influence atmospheric processes and continental climate here we show that precipitation 18o values in the contiguous united states are correlated with an index of the pna pattern the 18o pna relationship varies across the study region and exhibits two prominent modes with positive correlation in the western usa and negative correlation in the east this spatial pattern appears not to reflect variation in local climate variables but rather primarily reflects differences in atmospheric circulation and moisture sources associated with pna our results suggest that strong antiphase variation in paired paleo water 18o proxy records from regions characterized by the two modes of 18o pna correlation especially in the midwest and southwestern usa may provide a robust basis for reconstruction of past variation in the pna pattern

sediment transport and topographic evolution of a coupled river and river plume system an experimental and numerical study sediment transfer from rivers to the ocean is the fundamental driver of continental sedimentation with implications for carbon burial land use dynamics and unraveling global climate change and earth history from sedimentary strata coastal rivers are dynamically coupled to their offshore plumes at the river mouth creating regions of nonuniform flow that can dictate patterns of erosion and deposition both onshore and offshore however there are limited experimental and modeling studies on sediment transport and morphodynamics of coupled river and river plume systems and their response to multiple flood events to address this knowledge gap we developed a quasi 2 d morphodynamic numerical model and conducted exploratory flume experiments in a 7 5 m long flume where a 10 cm wide river channel was connected to a 76 cm wide ocean basin both the numerical model and the flume results demonstrate that 1 during low discharge flows backwater hydrodynamics cause spatial flow deceleration and deposition in the river channel and the offshore plume area and 2 during high flows the water surface is drawn down to sea level resulting in spatial flow acceleration and bed scour during high discharge flows we also found that the offshore river plume self channelized owing to both levee formation and bed scour our study suggests that coastal rivers may be in a perpetual state of morphodynamic adjustment and highlights the need to link rivers and river plumes under a suite of flow discharges to accurately predict fluvio deltaic morphodynamics and connectivity between fluvial sediment sources and marine sinks

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

grain size sediment transport regime and channel slope in alluvial rivers the general relationship between channel morphology and the grain size of sediment in the channel bed is an important but poorly known aspect of alluvial rivers an analysis of an equation for total sediment flux in the limits of suspension bedload and mixed modes of transport indicates distinct steady state regimes of channel morphology such regimes are readily seen in published data for modern alluvial rivers by way of a conventional shields plot or a plot of channel slope as a function of relative grain size d h and the ratio ws u where d and ws are respectively mean diameter and fall speed of bed sediments and h and u are respectively mean depth and friction velocity of the flow with slope and mode of transport in an alluvial river constrained by grain size and channel depth alone estimates of discharge and sediment flux follow directly introduction of the sediment flux relationship into conventional diffusion models for the evolution of an alluvial system provides nominal estimates of

morphology and controls on the position of a gravel sand transition fraser river british columbia alluvial river channels often exhibit a relatively abrupt transition from gravel to sand bedded conditions the phenomenon is well documented but few prior studies have analyzed the spatial variability through reaches where transitions occur the downstream fining pattern observed in the fraser river is cited as a classic example of an abrupt gravel sand transition in a large alluvial channel however important questions regarding the exact location of the transition its sedimentology and morphology and what controls its location remain unanswered here we present observations of the downstream change in bed material grain size river bed topography and channel hydraulics through the reach within which the transition occurs these observations indicate that the gravel sand transition is characterized by a terminating gravel wedge but there are patches of gravel downstream of the wedge forming a diffuse extension we show that there is a dramatic decrease in shear stress at the downstream end of the wedge and a consequent cessation of general gravel mobility we argue that the patches of gravel observed beyond the wedge are the result of enhanced mobility of fine gravel over a sand bed we also find that sand in suspension declines rapidly at the downstream end of the wedge suggesting that sand is delivered to the bed completing the sedimentary conditions for a gravel sand transition we propose that the break in river slope associated with the transition is a consequential feature of the transition

experimental measurement of the relative importance of controls on shoreline migration abstract shoreline position in sedimentary rocks is a sensitive recorder of the interplay of several controlling factors the most important of these are thought to be the stratigraphic trinity eustatic sea level subsidence and sediment supply in ancient rock sequences it is generally difficult to disentangle the effects of these variables here we analyze the relative influence of sea level subsidence sediment supply and other controlling variables on shoreline migration in an experimental basin equipped with a subsiding floor the experiment used a linear hinge type subsidence profile for which the rate was kept constant in time constant overall sediment supply and base level variation on two time scales that were first applied separately and then superimposed although base level was the only controlling variable that was externally varied in time the base level changes induced changes in other variables indirectly e g by changing the partitioning of sediment between the fluvial and offshore segments of the system we examine the relative importance of measured direct and indirect changes in all the governing variables through the use of a moving boundary equation for shoreline migration when measured values are used for all the variables in the equation shoreline migration rate throughout the run can be predicted with a maximum r2 of 0 92 starting with this optimal prediction of the observed shoreline behavior we successively replace variables in the equation with their run averaged values degrading the prediction the relative loss of prediction accuracy as each variable is replaced is a measure of the importance of that variable in accounting for the observed shoreline migration by this measure base level is the most important variable followed in turn by sediment supply to the foreset geometry of the foreset and the average subsidence rate over the foreset from the shoreline migration equation we also derive a quantitative version of the a s ratio often applied in sequence stratigraphy the new formulation reduces to a form comparable to the traditional descriptive a s ratio if changes in foreset slope gain or loss of sediment to the fluvial system and spatial variation in subsidence rate are all negligible

testing morphodynamic controls on the location and frequency of river avulsions on fans versus deltas huanghe yellow river china a mechanistic understanding of river avulsion location and frequency is needed to predict the growth of alluvial fans and deltas the huanghe china provides a rare opportunity to test emerging theories because its high sediment load produces regular avulsions at two distinct nodes where the river debouches from the loess plateau avulsions occur at an abrupt decrease in bed slope and reoccur at a time interval 607 yrs consistent with a channel filling timescale set by the superelevation height of the levees downstream natural deltaic avulsions reoccur at a timescale that is fast 7 yrs compared to channel filling timescale due to large stage height variability during floods unlike the upstream node deltaic avulsions cluster at a location influenced by backwater hydrodynamics and show evidence for episodic downstream migration in concert with progradation of the shoreline providing new expectations for the interplay between avulsion location frequency shoreline rugosity and delta morphology

morphodynamic modeling of fluvial channel fill and avulsion time scales during early holocene transgression as substantiated by the incised valley stratigraphy of the trinity river texas the trinity river system provides a natural laboratory for linking fluvial morphodynamics to stratigraphy produced by sea level rise because the sediments occupying the trinity incised valley are well constrained in terms of timing of deposition and facies distribution herein the trinity river is modeled for a range of base level rise rates avulsion thresholds and water discharges to explore the effects of backwater induced in channel sedimentation on channel avulsion the findings are compared to observed sediment facies to evaluate the capability of a morphodynamic model to reproduce sediment deposition patterns base level rise produces mobile locations of in channel sedimentation and deltaic channel avulsions for scenarios characteristic of early holocene sea level rise 4 3 mm yr 1 the trinity fluvial deltaic system progrades 13 m yr 1 followed by backstepping of 27 m yr 1 avulsion is reached at the position of maximum sediment deposition located 108 km upstream of the outlet after 3 548 model years based on sedimentation filling 30 of the channel under scenarios of greater base level rise avulsion is impeded because the channel fill threshold is never achieved accounting for partitioning of bed material sediment between the channel and floodplain influences the timing and location of avulsion over millennial time scales the time to avulsion is greatly increased sedimentation patterns within the valley modeled and measured indicate preference toward sandy bed material and the rates of deposition are substantiated by previous measurements although the results here are specific to the trinity river the analysis provides a framework that is adaptable to other lowland fluvial deltaic systems

connecting the backwater hydraulics of coastal rivers to fluvio deltaic sedimentology and stratigraphy fluvial channels encounter a backwater reach when they approach a standing body of water and recent studies have shown that the transition from normal flow to backwater influenced flow is associated with sediment mass extraction through deposition here we test the hypothesis that systematic changes in the geometry of channel belt deposits and sedimentary architecture occur across this transition using data from the late holocene mississippi southern usa and rhine the netherlands fluvio deltaic systems we use the estimated backwater length and average channel width as characteristic length scales to non dimensionalize the downstream trends in channel belt width for these systems the collapsed data follow similar trends suggesting that the observed variations in channel belt geometry and fluvio deltaic stratigraphy are tied to the location of the backwater transition zone these findings suggest a unifying hydraulic control on fluvio deltaic channel belts and provide a new framework for predicting and understanding the properties of ancient rivers in the coastal zone

beyond kriging dealing with discontinuous spatial data fields using adaptive prior information and bayesian partition modelling the technique of kriging is widely known to be limited by its assumption of stationarity and performs poorly when the data involve localized efiects such as discontinuities or nonlinear trends the bayesian partition model bpm of denison et al 2002 is compared with results from ordinary kriging for various synthetic discontinuous one dimensional functions as well as for 1986 precipitation data from switzerland this latter data set has been analyzed during a comparison of spatial interpolation techniques and has been interpreted as a stationary distribution and one thus suited to kriging the results demonstrate that the bpm outperformed kriging in all of the data sets compared when tested for prediction accuracy at a number of validation points with improvements of up to a factor of 6 for the synthetic functions abbreviated title dealing with discontinuities via the bpm number of words 6340 number of figures 15 number of tables 2 number of references 19

processes controlling river mouth lagoon dynamics on high energy mixed sand and gravel coasts abstract the river mouth lagoons of new zealand s gravel bed braided rivers are highly dynamic responding to changes in waves and river flows at timescales of hours and days to years unlike other freshwater dominated coastal wetlands and lagoons they exist along open coasts that are typically retreating with cliffed hinterlands these lagoons are common on new zealand s high energy coarse sediment coastlines and are known locally as h pua this paper employs field observations from the hurunui h pua to investigate the main processes controlling the dynamics of h pua lagoons based on two years of time lapse imagery plus concurrent wave river flow and sea level data an improved conceptual model of lagoon dynamics was developed the model describes how onshore bar migration of river sourced gravel and sand drives initial constriction offsetting of the river mouth following floods it also explains how gravel deposition in the lagoon reduces the threshold flow required to cause primary breach of the barrier opposite the point the river enters the lagoon three processes are identified which affect lagoon width wave overwashing of the gravel barrier narrows the lagoon migration of the highly dynamic lagoon outlet channel resets the barrier position to seaward and river floods occurring while the outlet channel is offset from the river flush sediment from the lagoon system eroding its bed and banks both processes affecting lagoon widening rely on lagoon outlet channel migration indicating that outlet channel dynamics are an important control on lagoon size

accelerated river avulsion frequency on lowland deltas due to sea level rise sea level rise subsidence and reduced fluvial sediment supply are causing river deltas to drown worldwide affecting ecosystems and billions of people abrupt changes in river course called avulsions naturally nourish sinking land with sediment however they also create catastrophic flood hazards existing observations and models conflict on whether the occurrence of avulsions will change due to relative sea level rise hampering the ability to forecast delta response to global climate change here we combined theory numerical modeling and field observations to develop a mechanistic framework to predict avulsion frequency on deltas with multiple self formed lobes that scale with backwater hydrodynamics results show that avulsion frequency is controlled by the competition between relative sea level rise and sediment supply that drives lobe progradation we find that most large deltas are experiencing sufficiently low progradation rates such that relative sea level rise enhances aggradation rates accelerating avulsion frequency and associated hazards compared to preindustrial conditions some deltas may face even greater risk if relative sea level rise significantly outpaces sediment supply then avulsion frequency is maximized delta plains drown and avulsion locations shift inland posing new hazards to upstream communities results indicate that managed deltas can support more frequent engineered avulsions to recover sinking land however there is a threshold beyond which coastal land will be lost and mitigation efforts should shift upstream

complexity in a cellular model of river avulsion abstract we propose a new model of river avulsion that emphasizes simplicity self organization and unprogrammed behavior rather than detailed simulation the model runs on a fixed cellular grid and tracks two elevations in each cell a high elevation representing the channel levee top and a low one representing the channel bottom the channel aggrades in place until a superelevation threshold for avulsion is met after an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation flow path depends sensitively on floodplain topography particularly the presence of former abandoned channels several behavioral characteristics emerge consistently from this simple model 1 a tendency of the active flow to switch among a small number of channel paths which we term the active channel set over extended periods leading to clustering and formation of multistory sand bodies in the resulting deposits 2 a tendency for avulsed channels to return to their previous paths so that new channel length tends to be generated in relatively short segments and 3 avulsion related sediment storage and release leading to pulsed sediment output even for constant input each of these behaviors is consistent with observations from depositional river systems a single valued threshold produces a wide variety of avulsion sizes and styles larger nodal avulsions are rarer because pre existing floodplain topography acts to steer flow back to the active channel channel stacking pattern is very sensitive to floodplain deposition this work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution

conditions for branching in depositional rivers it is often taken for granted that rivers organize transport into a single active channel in some net depositional environments however flow of water and sediment is distributed in several stable channels such branching rivers may be confined in valleys anabranching or anastomosed or unconfined on deltas distributaries and their existence confronts us with the very basic question of what governs the spatial organization of channel patterns in sedimentary landscapes current models for equilibrium channel morphology cannot predict the occurrence of branching rivers because they do not consider dynamical processes such as avulsion i e the rapid abandonment of a channel in favor of a new path at lower elevation the requisite conditions for avulsion have been the subject of ongoing debate here we resolve the conditions leading to channel avulsion and show that branching rivers occur when avulsion is the dominant mechanism of lateral channel motion a compilation of field and laboratory data demonstrates that avulsion frequency scales with the time required for sedimentation on channel beds to produce a deposit equal to one channel depth from the relative rates of bank erosion and channel sedimentation we derive a dimensionless mobility number that accurately predicts the conditions under which anabranching and distributary channels occur results may be directly applied to modeling landscape evolution over human and geologic time scales and for inverting formative environmental conditions from channel deposits on earth and other planetary surfaces

predicting delta avulsions implications for coastal wetland restoration river deltas create new wetlands through a continuous cycle of delta lobe extension avulsion and abandonment but the mechanics and timing of this cycle are poorly understood here we use physical experiments to quantitatively define one type of cycle for river dominated deltas the cycle begins as a distributary channel and its river mouth bar prograde basinward eventually the mouth bar reaches a critical size and stops prograding the stagnated mouth bar triggers a wave of bed aggradation that moves upstream and increases overbank flows and bed shear stresses on the levees an avulsion occurs as a time dependent failure of the levee where the largest average bed shear stress has been applied for the longest time r 2 0 93 these results provide a guide for predicting the growth of intradelta lobes which can be used to engineer the creation of new wetlands within the delta channel network and improve stratigraphic models of deltas

principles of regression and transgression the nature of the interplay between accommodation and sediment supply the rate of change of accommodation at the shoreline a and the rate of sediment supply s are the primary factors controlling regression and transgression in the geological record or retreat and advance of a coastal depositional system the generally accepted notion here referred to as the a s ratio concept stating that the migration of a shoreline is controlled principally by the magnitude of the ratio of a to s is insufficient and somewhat misleading partly owing to the problem of dimensional confusion the interplay of a and s inevitably results in autoretreat of the shoreline whereby the seaward advance of any shoreline is halted and is subsequently turned to landward retreat provided there is a continuous rise of relative sea level how effective the autoretreat process is depends for a given period of relative sea level rising upon the length of potential time period for the seaward advance of shoreline and is proportional to a 2 s and a super 1 5 s super 0 5 in two and three dimensional sediment dispersal modes respectively autoretreat becomes more effective as a increases and or s decreases a functions more critically to the effectiveness than s does the a s ratio concept is only approximately applicable when autoretreat is less effective i e with very low a and or very high s in this sense the autoretreat theory and the a s ratio concept are complementary to each other the autoretreat mechanism is expected to be substantially useful not only in fluvial deltas but also in many other depositional systems e g barrier islands whose evolution has been considered in terms of the a s ratio concept

autogenic erosional surfaces in fluvio deltaic stratigraphy from floods avulsions and backwater hydrodynamics erosional surfaces set the architecture of fluvio deltaic stratigraphy and they have classically been interpreted in terms of changes in boundary conditions such as climate tectonics and base level allogenic forces intrinsic dynamics of sedimentary systems autogenic dynamics can also create a rich stratigraphic architecture and a major knowledge gap exists in parsing the relative roles of autogenic versus allogenic processes emerging theoretical and experimental work suggests that backwater hydrodynamics play an important role in driving transient channel incision in river deltas even those experiencing net aggradation here we identify and quantify two autogenic mechanisms that produce broad erosional surfaces in fluvio deltaic stratigraphy namely floods and avulsions using a simple mass balance model for single threaded delta channel systems we show that flood induced scours begin near the shoreline and avulsion induced scours begin at the avulsion site and both propagate upstream over a distance that scales with the backwater length bed slope and bed grain size we also develop scaling relationships for the maximum scour depths arising from these mechanisms which are functions of characteristic flow depth and formative flood variability we test our theoretical predictions using a flume experiment of river delta evolution governed by persistent backwater hydrodynamics under constant relative sea level results indicate that autogenic dynamics of backwater mediated deltas under conditions of constant base level can result in stratigraphic surfaces and shoreline trajectories similar to those often interpreted to represent multiple sea level cycles our work provides a quantitative framework to decouple autogenic and allogenic controls on erosional surfaces preserved in fluvio deltaic stratigraphy

the statistical connection between tropospheric and stratospheric circulation of the northern hemisphere in winter abstract the associated anomaly patterns of the stratospheric geopotential height field and the tropospheric geopetential and temperature height fields of the northern hemisphere are determined applying the canonical correlation analysis with this linear multivariate technique the coupled modes of variability of lime series of two fields are isolated in the space of empirical orthogonal functions the one dataset is the 50 hpa geopotential height field the other set consists of different height fields of the tropospheric pressure levels 200 500 700 and 850 hpa and the temperature of the 850 hpa pressure level for the winter months december january february two natural coupled modes a barotropic and a baroclinic one of linear relationship between stratospheric and tropospheric circulation are found the baroclinic mode describes a connection between the strength of the stratospheric cyclonic winter vortex and the tropospheric circulation over the north atlantic the corresponding temperature

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

the lowermost mississippi river a mixed bedrock alluvial channel in this study the distribution of channel bed sediment facies in the lowermost mississippi river is analysed using multibeam data complemented by sidescan sonar and compressed high intensity radar pulse seismic data as well as grab and core samples of bed material the channel bed is composed of a discontinuous layer of alluvial sediment and a relict substratum that is exposed on the channel bed and sidewalls the consolidated substratum is made up of latest pleistocene and early holocene fluvio deltaic deposits and is preferentially exposed in the deepest thalweg segments and on channel sidewalls in river bends the exposed substratum commonly displays a suite of erosional features including flutes that are quantitatively similar in form to those produced under known laboratory conditions a total of five bed facies are mapped three of which include modern alluvial deposits and two facies that are associated with the relict substratum a radius of curvature analysis applied to the mississippi river centreline demonstrates that the reach scale distribution of channel bed facies is related to river planform from a broader perspective the distribution of channel bed facies is related to channel sinuosity higher sinuosity promotes greater substratum exposure at the expense of alluvial sediment for example the ratio of alluvial cover to substratum is ca 1 5 1 for a 45 km segment of the river that has a sinuosity of 1 76 and this ratio increases to ca 3 1 for a 120 km segment of the river that has a sinuosity of 1 21 the exposed substratum is interpreted as bedrock and given the relative coverage of alluvial sediment in the channel the lowermost mississippi river can be classified as a mixed bedrock alluvial channel the analyses demonstrate that a mixed bedrock alluvial channel boundary can be associated with low gradient and sand bed rivers near their marine outlet

geological prior information and its applications to geoscientific problems geological information can be used to solve many practical and theoretical problems both within and outside of the discipline of geology these include analysis of ground stability predicting sub surface water or hydrocarbon reserves and assessment of risk due to natural hazards in many cases geological information is provided as an a priori component of the solution that is information that existed before the solution was formed and which is incorporated into the solution such information is termed geological prior information the key to the successful solution of such problems is to use only reliable geological information in turn this requires that a multiple geological experts are consulted and any conflicting views reconciled b all prior information includes measures of confidence or uncertainty without which their reliability and worth is unknown and c as much information as possible is quantitative and qualitative information or assumptions are clearly defined so that uncertainty or risk in the final result can be evaluated this paper discusses each of these components and proposes a probabilistic framework for the use and understanding of prior information we demonstrate the methodology implicit within this framework with an example this shows how prior information about typical sequence stacking patterns allows aspects of 2 d platform architecture to be derived from 1 d geological data alone such as that obtained from an outcrop section or vertical well this example establishes how the extraction of quantitative multi dimensional geological interpretations is possible using lower dimensional data the final probabilistic description of the multi dimensional architecture could then be used as prior information sequentially for a subsequent problem using exactly the same method

channel response to low water levels in the pearl river delta a multi decadal analysis abstract the pearl river delta is a composite delta with one of the densest channel networks in the world to analyze the internal erosion deposition characteristics of the net channel area this paper studies the upstream evolution characteristics using digital elevation model data from local channel sections we attempt to establish the relationship between the changes in low water level and erosion rate by using the accumulated data for the main stream and hydrological stations over the past 50 years including the distributions of flow and sediment at the top of the net channel area and the erosion deposition data of a typical channel section in fact the net channel area has been in a forced erosion state artificial sand excavation for a long time forcing the flow and sediment distributions at makou and sanshui stations to adjust from 1993 to the present although the incoming sedimentation is far less than the net erosion and there are similarities and differences in the sources of the incoming flow and sediment from the main stream the internal characteristics of the upper and lower reaches of the delta have not changed substantially they have always been stable slow deposition channels the forced undercutting is concentrated within width depth ratios of approximately 50 250 which still meets the evolution characteristics of the natural channel artificial sand excavation during the 1980s tended to enhance the characteristics however the sudden increase in the undercutting rate has forced chaotic changes in the low water level since 1990 and the sediment transport rate decreased sharply the phenomena of salt tides retrogression and retrogressive erosion generally happen the water level evolution in the net channel area is chaotic and continuous undercutting is still occurring

abrupt changes in the rate of andean plateau uplift from reversible jump markov chain monte carlo inversion of river profiles abstract knowledge of the rate of surface uplift of the central andean plateau provides important boundary conditions for regional geodynamic models and paleoclimate reconstructions here we present a fully nonlinear inverse method to extract the rock uplift history of the central andean plateau from the cotahuasi river and its tributaries our approach is based on an analytical solution to the stream power model that relates elevation to rock uplift history under the assumptions of constant climatic conditions in space and time and spatially invariant rock uplift we use a bayesian framework that allows us to quantify the full state of knowledge of model parameters i e uncertainties trade offs the erosional efficiency defines the landscape response time and this must be determined using independent data therefore using thermochronometric data from the cotahuasi ocona canyon which record rapid fluvial incision at 13 10 ma we calibrate our results to infer a rock uplift history for the north central andean plateau we infer a pulse of rock uplift between 25 and 10 ma at rates as high as 0 25 km my however the rock uplift rate inferred during this pulse is not as high as is predicted if the central andean plateau grew as a result of loss of unstable lithospheric mantle therefore our results are more consistent with models requiring gradual uplift of the central andean plateau

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

flood variability determines the location of lobe scale avulsions on deltas madagascar river deltas grow through repeated lobe scale avulsions which often occur at a location that correlates with the backwater lengthscale competing hypotheses attribute the avulsion node origin to either the morphodynamic feedbacks caused by natural flood discharge variability backwater hypothesis or to the prograding delta lobe geometry geometric hypothesis here using theory historical flood records and remotely sensed elevation data we analyzed five lobe scale delta avulsions in madagascar captured by landsat imagery avulsion lengths were 5 55 km distances significantly longer than the backwater lengthscale and inconsistent with the geometric hypothesis we show that the steep silt bedded rivers of madagascar have flood induced bed scour driven by backwater hydrodynamics that propagates farther upstream than the backwater lengthscale the avulsion lengths are 3 1 1 5 times the predicted flood scour lengths similar to low gradient deltas and consistent with backwater hypothesis results demonstrate that erosion initiated by nonuniform flows in the backwater zone is a primary control on delta avulsion locations

controls on the apex location of large deltas the majority of sediment transport to the world9s oceans is routed via large deltas we examine controls on delta apex location using a database of 84 of the world9s largest deltas of the dataset 94 of apices are controlled by either bedrock valleys 80 or pleistocene alluvial valleys 14 suggesting that the principal control on modern apex development is valley exit and or bedslope mediated avulsion and not hydrodynamic backwater length valley exit control on large delta apex location may have been as important in the rock record as it is today and should be considered as a key control on delta development supplementary material tabulated data on backwater length and apex type for studied deltas available at https doi org 10 6084 m9 figshare c 3469770

hydrodynamic controls on alluvial ridge construction and avulsion likelihood in meandering river floodplains this work was funded by uk natural environment research council grants ne h009108 1 and ne h007288 1

avulsion cycles and their stratigraphic signature on an experimental backwater controlled delta river deltas grow in large part through repeated cycles of lobe construction and channel avulsion understanding avulsion cycles is important for coastal restoration and ecology land management and flood hazard mitigation emerging theories suggest that river avulsions on lowland deltas are controlled by backwater hydrodynamics however our knowledge of backwater controlled avulsion cycles is limited here we present results from an experimental delta that evolved under persistent backwater hydrodynamics achieved through variable flood discharges shallow bed slopes and subcritical flows the experimental avulsion cycles consisted of an initial phase of avulsion setup an avulsion trigger selection of a new flow path and abandonment of the parent channel avulsions were triggered during the largest floods 78 of avulsions after the channel was filled by a fraction 0 3 0 13 of its characteristic flow depth at the avulsion site which occurred in the upstream part of the backwater zone the new flow path following avulsion was consistently one of the shortest paths to the shoreline and channel abandonment occurred through temporal decline in water flow and sediment delivery to the parent channel experimental synthetic stratigraphy indicates that bed thicknesses were maximum at the avulsion sites consistent with our morphologic measurements of avulsion setup and the idea that there is a record of avulsion locations and thresholds in sedimentary rocks finally we discuss the implications of our findings within the context of sustainable management of deltas their stratigraphic record and predicting avulsions on deltas

unravelling the conundrum of river response to rising sea level from laboratory to field part ii the fly strickland river system papua new guinea the most recent deglaciation resulted in a global sea level rise of some 120 m over ca 12 000 years a moving boundary numerical model is developed to predict the response of rivers to this rise the model was motivated by experiments at small scale which have identified two modes describing the transgression of a river mouth i autoretreat without abandonment of the river delta no sediment starvation at the topset foreset break and ii sediment starved autoretreat with abandonment of the delta in the latter case transgression is far more rapid and its effects are felt much further upstream of the river mouth a moving boundary numerical model that captures these features in experimental deltas is adapted to describe the response of the fly strickland river system papua new guinea in the absence of better information the model is applied to the case of sea level rise without local climate change in new guinea the model suggests that i sea level rise has forced the river mouth to transgress over 700 km since the last glacial maximum ii sediment starved autoretreat has forced enough bed aggradation to block a tributary with a low sediment load and create the present day lake murray iii the resulting aggradation was sufficient to move the gravel sand transition on the strickland river upstream iv the present day fly estuary may be in part a relict river valley drowned by sea level rise and partially filled by tidal effects and v the fly river is presently reforming its bankfull geometry and prograding into the fly estuary a parametric study with the model indicates that sediment concentration during floods plays a key role in determining whether or not and to what extent transgression is expressed in terms of sediment starved autoretreat a sufficiently high sediment concentration can prevent sediment starved autoretreat during the entire sea level cycle this observation may explain why some present day river mouths are expressed in terms of deltas protruding into the sea and others are wholly contained within embayments or estuaries in which water has invaded landward

southern hemisphere atmospheric circulation effects of the 1991 mount pinatubo eruption 1 global average cooling and northern hemisphere winter warming are well known climatic responses to the june 15 1991 eruption of the mount pinatubo volcano in the philippines here we investigate the southern hemisphere response using national centers for environmental prediction national center for atmospheric research reanalysis european centre for medium range weather forecasting reanalysis and simulations with the national aeronautics and space administration goddard institute for space studies modele climate model we find that in contrast to the northern hemisphere there were no strong significant anomalies in atmospheric circulation in the southern hemisphere we examined 50 mb and 500 mb circulation patterns as well as the southern hemisphere annular mode index and found no consistent significant anomalies associated with the volcanic eruption or the previous large volcanic eruptions of the past 50 years the 1963 agung and 1982 el chichon eruptions the few anomalies that occurred after pinatubo are consistent with patterns found during an el nino event which took place that same year

scaling relationships and evolution of distributary networks on wave influenced deltas 1 no genetic model can explain the variability in distributary network pattern on modern deltas here we derive scaling relationships for two processes known to create distributary channels and with these laws construct a simple model for distributary network evolution the first process is mouth bar deposition at the shoreline and subsequent channel bifurcation the second is avulsion the wholesale abandonment of a channel in favor of a new path the former creates relatively small networks with power law distributions of channel length the latter generates relatively few backwater scale distributaries frequency magnitude plots of channel length on natural deltas agree with theoretical predictions and show a clear separation in scale that reflects these processes mouth bar distributary lengths scale with the width of the parent channel and avulsive distributary lengths scale with the backwater length intermediate channel lengths are relatively rare wave energy controls network topology by suppressing mouth bar development thereby preferentially eliminating smaller scale distributaries

experimental alluvial fan evolution channel dynamics slope controls and shoreline growth 1 river deltas and alluvial fans have channelization and deposition dynamics that are not entirely understood but which dictate the evolution of landscapes of great social economic and ecologic value our lack of a process based understanding of fan dynamics hampers our ability to construct accurate prediction and hazard models leaving these regions vulnerable here we describe the growth of a series of experimental alluvial fans composed of a noncohesive grain mixture bimodal in size and density we impose conditions that simulate a gravel sand fan prograding into a static basin with constant water and sediment influx and the resulting fans display realistic channelization and avulsion dynamics we find that we can describe the dynamics of our fans in terms of a few processes 1 an avulsion sequence with a timescale dictated by mass conservation between incoming flux and deposit volume 2 a tendency for flow to reoccupy former channel paths and 3 bistable slopes corresponding to separate entrainment and deposition conditions for grains several important observations related to these processes are an avulsion timescale that increases with time and decreases with sediment feed rate fan lobes that grow in a self similar quasi radial pattern and channel geometry that is adjusted to the threshold entrainment stress we propose that the formation of well defined channels in noncohesive fans is a transient phenomenon resulting from incision following avulsion and can be directly described with dual transport thresholds we present a fairly complete process based description of the mechanics of avulsion and its resulting timescale on our fans because the relevant dynamics depend only on threshold transport conditions and conservation of mass we show how results may be directly applied to field scale systems

observational constraints on the tropospheric and near surface winter signature of the northern hemisphere stratospheric polar vortex a composite analysis of northern hemisphere s mid winter tropospheric anomalies under the conditions of strong and weak stratospheric polar vortex was performed on ncep ncar reanalysis data from 1948 to 2013 considering as additional grouping criteria the coincidental states of major seasonally relevant climate phenomena such as el nino southern oscillation enso quasi biennial oscillation and strong volcanic eruptions the analysis reveals that samples of strong polar vortex nearly exclusively occur during cold enso states while a weak polar vortex is observed for both cold and warm enso the strongest tropospheric and near surface anomalies are found for warm enso and weak polar vortex conditions suggesting that internal tropospheric circulation anomalies related to warm enso constructively superpose on dynamical effects from the stratosphere additionally substantial differences are found between the continental winter warming patterns under strong polar vortex conditions in volcanically disturbed and volcanically undisturbed winters however the small size samples obtained from the multi compositing prevent conclusive statements about typical patterns dominating effects and mechanisms of stratosphere troposphere interaction on the seasonal time scale based on observational reanalysis data alone hence our analysis demonstrates that patterns derived from observational reanalysis time series need to be taken with caution as they not always provide sufficiently robust constraints to the inferred mechanisms implicated with stratospheric polar vortex variability and its tropospheric and near surface signature notwithstanding this argument we propose a limited set of mechanisms that together may explain a relevant part of observed climate variability these may serve to define future numerical model experiments minimizing the sample biases and thus improving process understanding

underestimation of volcanic cooling in tree ring based reconstructions of hemispheric temperatures a large volcanic eruption in ad 1258 1259 is expected to have caused substantial climate cooling but evidence for this effect is absent from tree ring based temperature reconstructions numerical modelling of tree growth shows that the lack of cooling is probably an artefact caused by low sensitivity to cooling in trees growing near the treeline

changing pattern of accretion erosion of the modern yellow river huanghe subaerial delta china based on remote sensing images abstract the yellow river shifted from the diaokou course to the qingshuigou course in 1976 and shifted again at the north bank of the qingshuigou course in 1996 as a result the entire modern yellow river delta has experienced complicated patterns of erosion and accretion multitemporal remote sensing data of landsat mss and tm from 1976 to 2000 totaling twenty scenes were used to examine the changing pattern of accretion and erosion of the modern yellow river subaerial delta with gis tools during the period 1976 to 2000 the maximum erosion occurred at the head of the last two abandoned promontories diaokou and shenxiangou promontories where the coastline retreated landward over 7 and 4 5 km respectively with mean net erosion rates of 0 29 and 0 19 km a respectively in contrast the maximum accretion occurred at the head of the qingshuigou promontory where the coastline advanced seaward over 20 km with a mean net accretion rate of 0 83 km a the coastline at the head of the q 8 promontory also advanced seaward 7 km with a mean net accretion rate of 0 29 km a during the period 1996 to 2000 total area of the diaokou and shenxiangou promontories was reduced by 141 3 km 2 with a mean net erosion rate of 6 03 km 2 a total area of the qingshuigou and q 8 promontories increased by 384 16 and 11 88 km 2 respectively with mean net accretion rates of 16 4 and 3 03 km 2 a respectively relative to the diaokou shenxiangou and qingshuigou promontories the west area of the diaokou promontory and south area of the qingshuigou promontory were relatively stable although minor erosion occurred the general pattern of accretion and erosion of the modern yellow river subaerial delta was divided into three stages rapid accretion stage 1976 1984 accretion erosion adjustment stage 1985 1995 and slow erosion stage 1996 present the factors affecting the pattern of erosion and accretion over the yellow river delta such as structural geology the yellow river sediment discharge coastal processes meteorological conditions human activity sea level rise and land subsidence were summarized the cumulative area of increase over the entire subaerial delta is closely correlated with the cumulative yellow river sediment discharge wave induced longshore current is the major driving force to transport sediment from eroded areas along the last two abandoned promontories diaokou and shenxiangou promontories mostly westerly and partially easterly together with these coastal processes is the geographical shift of the yellow river course associated with its discharge regime after 1976 leading to the accretion along the present qingshuigou promontory and then the q 8 promontory

large scale fluvial grade as a nonequilibrium state in linked depositional systems theory and experiment 1 a graded river conveys its sediment load without net aggradation or degradation grade is thought to represent the equilibrium state of a river system subject to steady allogenic forcing we address the concept of grade in linked depositional systems through a combination of mathematical modeling and flume experiments we develop a moving boundary morphodynamic model of fluviodeltaic sedimentation and use it to quantify the conditions necessary for a state of sustained grade in an alluvial deltaic system developing on a uniformly sloping shelf to test our theory we conducted a series of flume experiments in which we constructed laboratory scale fluviodeltaic systems under specific relative sea level histories on large spatiotemporal scales our theoretical and experimental results suggest an alternative view of grade as an intrinsically nonequilibrium state that requires a fall in relative sea level under conditions of stillstand or rise in relative sea level the equilibrium graded profile does not exist and the alluvial river will always aggrade with a steady sediment supply alluvial grade can be sustained if relative sea level falls with a specific square root of time dependence common sequence stratigraphic conceptualizations of alluvial river response to sea level change suggest that rivers aggrade and degrade in response to relative sea level rise and fall respectively we show that rivers can remain aggradational if the rate of sea level fall is sufficiently small the boundary between aggradational and degradational states is the graded state described here that associated with a relative sea level fall that varies with the square root of time

volcanic eruptions large scale modes in the northern hemisphere and the el nino southern oscillation abstract the author analyzes the impact of 13 major stratospheric aerosol producing volcanic eruptions since 1870 on the large scale variability modes of sea level pressure in the northern hemisphere winter the paper focuses on the arctic oscillation ao and the north atlantic oscillation nao to address the question about the physical nature of these modes the hypothesis that the phase of the el nino southern oscillation enso may control the geographical extent of the dominant mode in the northern hemisphere is also investigated as well as the related possibility that the impact of the eruptions may be different according to the phase of enso the author finds that both the ao and the nao are excited in the first winter after the eruptions with statistical significance at the 95 level both the signal and the significance are larger for the nao than for the ao the excitation of the ao and the nao is connected with the excitation of a secondary mode which resembles an augmented pacific north ame

discharge discharge variability and the bedrock channel profile long term bedrock incision is driven by daily discharge events of variable magnitude and frequency with ineffective events below an incision threshold we explore theoretically how this short term stochastic behavior controls long term steady state incision rates and bedrock channel profiles combining a realistic frequency magnitude distribution of discharge with a deterministic detachment limited incision model in which incision rate is a power function of basal shear stress above a critical shear stress our model predicts a power law relationship between steady state slope and drainage area consistent with observations the exponent of this power law is independent of discharge mean and variability while the amplitude factor which controls mountain belt relief is a power law function of mean runoff with an exponent of 0 5 and a complex function of runoff variability in accordance with evidence that incision occurs between 6 and 20 of time in rapidly incising rivers 1 mm yr our model predicts that channel steepness is virtually insensitive to runoff variability runoff variability can only decrease channel steepness for very slow incision rates and or weak lithologies the relationship between channel steepness and incision rate is always a power law whose exponent depends on the channel cross sectional geometry and runoff variability this contradicts models neglecting discharge stochasticity in which the steepness incision scaling is set by the incision law exponent our results suggest that changes in climate variability cannot explain an increase in bedrock incision rates during the late cenozoic within the context of a detachment limited model

backwater controls of avulsion location on deltas river delta complexes are built in part through repeated river channel avulsions which often occur about a persistent spatial node creating delta lobes that form a fan like morphology predicting the location of avulsions is poorly understood but it is essential for wetland restoration hazard mitigation reservoir characterization and delta morphodynamics following previous work we show that the upstream distance from the river mouth where avulsions occur is coincident with the backwater length i e the upstream extent of river flow that is affected by hydrodynamic processes in the receiving basin to explain this observation we formulate a fluvial morphodynamic model that is coupled to an offshore spreading river plume and subject it to a range of river discharges results show that avulsion is less likely in the downstream portion of the backwater zone because during high flow events the water surface is drawn down near the river mouth to match that of the offshore plume resulting in river bed scour and a reduced likelihood of overbank flow furthermore during low discharge events flow deceleration near the upstream extent of backwater causes enhanced deposition locally and a reduced channel fill timescale there both mechanisms favor preferential avulsion in the upstream part of the backwater zone these dynamics are fundamentally due to variable river discharges and a coupled offshore river plume with implications for predicting delta response to climate and sea level change and fluvio deltaic stratigraphy

principles of regression and transgression the nature of the interplay between accommodation and sediment supply perspectives abstract the rate of change of accommodation at the shoreline a and the rate of sediment supply s are the primary factors controlling regression and transgression in the geological record or retreat and advance of a coastal depositional system the generally accepted notion here referred to as the a s ratio concept stating that the migration of a shoreline is controlled principally by the magnitude of the ratio of a to s is insufficient and somewhat misleading partly owing to the problem of dimensional confusion the interplay of a and s inevitably results in autoretreat of the shoreline whereby the seaward advance of any shoreline is halted and is subsequently turned to landward retreat provided there is a continuous rise of relative sea l vel how effective the autoretreat process is depends for a given period of relative sea level rising upon the length of potential time period for the seaward advance of shoreline and is proportional to a2 s and a1 5 s0 5 in two and three dimensional sediment dispersal modes respectively autoretreat becomes more effective as a increases and or s decreases a functions more critically to the effectiveness than s does the a s ratio concept is only approximately applicable when autoretreat is less effective i e with very low a and or very high s in this sense the autoretreat theory and the a s ratio concept are complementary to each other the autoretreat mechanism is expected to be substantially useful not only in fluvial deltas but also in many other depositional systems e g barrier islands whose evolution has been considered in terms of the a s ratio concept

the response of winter pacific north american pattern to strong volcanic eruptions the impact of volcanic eruptions on large scale atmospheric circulation patterns has been well studied but very little effort has been made on relating the response of pacific north american pna pattern to strong volcanic eruptions here we investigate the response of winter pna to the largest volcanic eruptions using three different reanalysis datasets we demonstrate a significant positive pna circulation response to strong volcanic forcing in the first winter following the eruptions this circulation pattern is associated with enhanced southwesterly winds advecting warm air from the tropical subtropical pacific into northwestern north america and leads to a significant warming in the region however no significant pna signal is found for the second post eruption winter the pna responses to volcanic forcing depend partly upon the modulation of the el nino southern oscillation enso events when the enso influence is linearly removed this positive pna signal is still robust during the first post eruption winter albeit with slightly decreased magnitude and significance our findings provide new evidence for volcanic forcing of the pacific and north american climates the results presented here may contribute to deconvolving modern and past continental scale climate changes over north america

seasonal interannual and mesoscale variability of the black sea upper layer circulation derived from altimeter data 1 topex poseidon and ers altimeter data comprising the period from may 1992 to may 1999 are assimilated into a shallow water model for providing a dynamically consistent interpretation of the sea surface height variations and estimation of the temporal and spatial characteristics of the upper layer circulation in the black sea these 7 year long observations offer a new capability for interpretation of major transient and quasi permanent features of the upper layer circulation the instantaneous flow fields involve a complex eddy dominated system with different types of structural organizations in which the eddies and the gyres of the interior cyclonic cell interact continuously among themselves and with meanders and filaments of the rim current the circulation possesses a distinct seasonal cycle whose major characteristic features repeat every year with some year to year variability an organized two gyre winter circulation system disintegrates gradually into a series of interconnecting eddies in the summer and autumn months which are also characterized by more pronounced and complex mesoscale activity in the peripheral flow system our analyses suggest a revised schematic circulation picture of the major quasi permanent and recurrent elements of the black sea

fluvio marine sediment partitioning as a function of basin water depth progradational fluvio deltaic systems tend towards but cannot reach equilibrium a state in which the longitudinal profile does not change shape and all sediment is bypassed beyond the shoreline they cannot reach equilibrium because progradation of the shoreline requires aggradation along the longitudinal profile therefore progradation provides a negative feedback unless relative sea level falls at a sufficient rate to cause non aggradational extension of the longitudinal profile how closely fluvio deltaic systems approach equilibrium is dependent on their progradation rate which is controlled by water depth and downstream allogenic controls and governs sediment partitioning between the fluvial deltaic and marine domains here six analogue models of coastal fluvio deltaic systems and small prograding shelf margins are examined to better understand the effect of water depth subsidence and relative sea level variations upon longitudinal patterns of sediment partitioning and grain size distribution that eventually determine large scale stratigraphic architecture fluvio deltaic systems prograding in relatively deep water environments are characterized by relatively low progradation rates compared to shallow water systems this allows these deeper water systems to approach equilibrium more closely enabling them to construct less concave and steeper longitudinal profiles that provide low accommodation to fluvial systems glacio eustatic sea level variations and subsidence modulate the effects of water depth on the longitudinal profile systems are closest to equilibrium during falling relative sea level and early lowstand resulting in efficient sediment transport towards the shoreline at those times additionally the strength of the response to relative sea level fall differs depending on water depth in systems prograding into deep water relative sea level fall causes higher sediment bypass rates and generates significantly stronger erosion than in shallow water systems which increases the probability of incised valley formation water depth in the receiving basin thus forms a first order control on the sediment partitioning along the longitudinal profile of fluvio deltaic systems and the shelf clinoform style it also forms a control on the availability of sand grade sediment at the shoreline that can potentially be remobilized and redistributed into deeper marine environments key findings are subsequently applied to the literature of selected shelf clinoform successions

modeling deltaic lobe building cycles and channel avulsions for the yellow river delta china river deltas grow by repeating cycles of lobe development punctuated by channel avulsions so that over time lobes amalgamate to produce a composite landform existing models have shown that backwater hydrodynamics are important in avulsion dynamics but the effect of lobe progradation on avulsion frequency and location has yet to be explored herein a quasi 2 d numerical model incorporating channel avulsion and lobe development cycles is developed the model is validated by the well constrained case of a prograding lobe on the yellow river delta china it is determined that with lobe progradation avulsion frequency decreases and avulsion length increases relative to conditions where a delta lobe does not prograde lobe progradation lowers the channel bed gradient which results in channel aggradation over the delta topset that is focused farther upstream shifting the avulsion location upstream furthermore the frequency and location of channel avulsions are sensitive to the threshold in channel bed superelevation that triggers an avulsion for example avulsions occur less frequently with a larger superelevation threshold resulting in greater lobe progradation and avulsions that occur farther upstream when the delta lobe length prior to avulsion is a moderate fraction of the backwater length 0 3 0 5l b the interplay between variable water discharge and lobe progradation together set the avulsion location and a model capturing both processes is necessary to predict avulsion timing and location while this study is validated by data from the yellow river delta the numerical framework is rooted in physical relationships and can therefore be extended to other deltaic systems

backwater and river plume controls on scour upstream of river mouths implications for fluvio deltaic morphodynamics sediment flux from rivers to oceans is the fundamental driver of fluvio deltaic morphodynamics and continental margin sedimentation yet sediment transport across the river to marine boundary is poorly understood coastal rivers typically are affected by backwater a zone of spatially decelerating flow that is transitional between normal flow upstream and the offshore river plume flow deceleration in the backwater zone as well as spreading of the offshore plume should render rivers highly depositional near their mouths leading to sedimentation and eventual elimination of the backwater zone at steady state this reasoning is counter to observations of riverbed scour erosional bed forms and long lived backwater zones near the mouths of some coastal rivers e g mississippi river united states to explain these observations we present a quasi 2 d model of a coupled fluvial backwater and offshore river plume system and apply it to the mississippi river results show that during high discharge events the normal flow depth can become larger than the water depth at the river mouth resulting in drawdown of the water surface spatial acceleration of flow and erosion of the riverbed as proposed by lane 1957 the transition to drawdown and erosion is ultimately forced by spreading of the offshore river plume this points to the need to model coupled river and river plume systems with a dynamic backwater zone under a suite of discharges to accurately capture fluvio deltaic morphodynamics and connectivity between fluvial sediment sources and marine depositional sinks

is river avulsion style controlled by floodplain morphodynamics river relocation or avulsion is a fundamental process that fills alluvial basins however it is difficult to predict avulsion patterns because the landscape conditions associated with different avulsion styles are currently unknown two end member avulsion styles have been documented in modern rivers progradational avulsions during which significant floodplain deposition occurs as a new channel is built and incisional avulsions during which floodplain erosion captures flow from a parent channel here we propose that avulsion style is related to the tendency for overbank flows to erode or deposit sediment i e floodplain morphodynamics we present a scaling comparison of floodplain erosion and deposition rates test it with morphodynamic modeling and show field data from ancient deposits that are consistent with modeling results these results demonstrate that floodplain morphodynamics may determine how rivers relocate and that assessing the relative influence of floodplain erosion and deposition may be useful for predicting sedimentation patterns in avulsive systems

influence of volcanic eruptions on the troposphere through stratospheric dynamical processes in the northern hemisphere winter it has been suggested that the zonal mean stratospheric zonal wind anomalies can propagate downward into the troposphere producing considerable changes on the other hand volcanic aerosols are thought to produce a stronger polar vortex in the winter stratosphere if these suggestions are correct the influence of volcanic eruptions can be expected to produce changes in the northern hemisphere winter troposphere through stratospheric process in the present study this idea is examined by analyzing changes in the january circulation after three recent volcanic eruptions regional features of observed changes in tropospheric temperatures due to volcanic eruptions can be explained by the changes in the propagation of stationary waves associated with dipole type anomalies in the zonal mean zonal winds which are similar to those observed in a previous work on the influence of polar night jet

shock fitting of aggradational profiles due to backwater the paper attempts to demonstrate the use of shock fitting to locate and track the evolution and movement of deltas in backwater environments emphasis is placed on the use of bedload transport the modeling approach is described and the development of the shock fitting procedure the experiments are described and compared with the numerical model besides modeling the physical process of deltas correctly shock fitting is also an efective way to reduce computer time when modeling aggradational environments because the computational grid may be made more sparse upstream of the delta lip where bed conditions change only slowly

origin of a preferential avulsion node on lowland river deltas river deltas are built by cycles of lobe growth and abrupt channel shifts or avulsions that occur within the backwater zone of coastal rivers previous numerical models differ on the origin of backwater scaled avulsion nodes and their consistency with experimental data to unify previous work we developed a numerical model of delta growth that includes backwater hydrodynamics river mouth progradation relative sea level rise variable flow regimes and cycles of lobe growth abandonment and reoccupation for parameter space applicable to lowland deltas we found that flow variability is the primary mechanism to cause persistent avulsion nodes by focusing aggradation within the backwater zone backwater scaled avulsion nodes also occur under less likely scenarios of initially uniform bed slopes or during rapid relative sea level rise and marine transgression our findings suggest that flow variability is a fundamental control on long term delta morphodynamics

wave controls on deltaic shoreline channel morphodynamics insights from a coupled model it is widely recognized that waves inhibit river mouth progradation and reduce the avulsion timescale of deltaic channels nevertheless those effects may not apply to downdrift deflected channels in this study we developed a coupled model to explore the effects of wave climate asymmetry and alongshore sediment bypassing on shoreline channel morphodynamics the shoreline position and channel trajectory are simulated using a shoreline module which drives the evolution of the river profile in a channel module by updating the position of river mouth boundary whereas the channel module provides the sediment load to river mouth for the shoreline module the numerical results show that regional alongshore sediment transport driven by an asymmetric wave climate can enhance the progradation of deltaic channels if sediment bypassing of the river mouth is limited which is different from the common assumption that waves inhibit delta progradation as such waves can have a trade off effect on river mouth progradation that can further influence riverbed aggradation and channel avulsion this trade off effect of waves is dictated by the net alongshore sediment transport sediment bypassing at the river mouth and wave diffusivity based on the numerical results we further propose a dimensionless parameter that includes fluvial and alongshore sediment supply relative to wave diffusivity to predict the progradation and aggradation rates and avulsion timescale of deltaic channels the improved understanding of progradation aggradation and avulsion timescale of deltaic channels has important implications for engineering and predicting deltaic wetland creation particularly under changing water and sediment input to deltaic systems

river morphodynamic evolution under dam induced backwater an example from the po river italy abstract river systems evolve in response to the construction of dams and artificial reservoirs offering the possibility to investigate the short term effects of base level oscillations on fluvial architecture a major effort has been dedicated to the understanding of river response downstream of large dams where deep channel incisions occur in response to the removal of sediment that is sequestered in the upstream reservoir integrating field observations and numerical modeling results this work quantifies the sedimentary and morphological changes of the po river italy upstream of the isola serafini dam to investigate the impact of dam induced backwater on river morphodynamics the construction of a reservoir generates a new base level that forces an upstream shift of alluvial lithofacies and a change in the planform geometry of the river the lateral migration rate of the channel is up to 45 m yr upstream of the influence of backwater flow and ca 10 m yr at the transition from normal to backwater flow conditions 30 km from the dam within this reach a reduction of the bed shear stress promotes deposition of coarse grained sediment and the emergence of the gravel sand transition of the river the lateral migration of the channel continuously decreases over time and rates 5 m yr can be observed in the reservoir backwater zone this trend is accompanied by the drowning of channel bars the reduction of river competence and an increase in bedform spacing oscillatory backwater and drawdown surface water profiles can be observed closer to the dam which are associated with varying low discharge and high discharge events respectively while low flow conditions persisting for much of the year allow the deposition of fine grained sediment high discharge events promote not only the resuspension and transport of fine material but also the progressive erosion of channel bars and the overall deepening of the thalweg this study provides a clear picture of the river evolution in response to the construction of a hydropower dam that may be of help in predicting how other fluvial systems will respond to future human interventions moreover the result of how changes in base level and oscillations in water surface profile backwater and drawdown control river hydro morphodynamics and sediment transport may provide new insights when reconstructing ancient fluvial and deltaic sequences

el nino events and their relation to the southern oscillation 1925 1986 relationships among sea surface temperatures ssts at the coast of peru and offshore river discharge in northern peru and sea level pressure at darwin australia during the period 1925 1986 are investigated using time series plots frequency distributions and a simple statistical analysis it is shown that ssts undergo a larger seasonal cycle offshore than at the coast exhibit more interannual variability during the warm than the cool season are positively skewed during much of the year and exhibit greatest month to month persistence during the cool season many but not all episodes of above normal coastal ssts are accompanied by enhanced river discharge in northern peru comparison of the darwin pressure and coastal sst records during the past 60 years shows that el nino events episodes of above normal ssts along the coast of peru have occurred both in advance of and subsequent to major negative swings of the southern oscillation and associated climatic changes in the central equatorial pacific in addition el nino events and negative swings of the southern oscillation have occurred separately hence el nino and the southern oscillation are more loosely coupled than other studies would imply

unravelling the conundrum of river response to rising sea level from laboratory to field part i laboratory experiments the most recent deglaciation resulted in a global sea level rise of some 120 m over approximately 12 000 years in this part i of two parts a moving boundary numerical model is developed to predict the response of rivers to this rise the model was motivated by experiments at small scale which have identified two modes describing the transgression of a river mouth autoretreat without abandonment of the river delta no sediment starvation at the topset foreset break and sediment starved autoretreat with abandonment of the delta in the latter case transgression is far more rapid and its effects are felt much further upstream of the river mouth the moving boundary numerical model is checked against experiments the generally favourable results of the check motivate adaptation of the model to describe the response of the much larger fly strickland river system papua new guinea to holocene sea level rise this is done in the companion paper part ii

bi decadal variability excited in the coupled ocean atmosphere system by strong tropical volcanic eruptions decadal and bi decadal climate responses to tropical strong volcanic eruptions sves are inspected in an ensemble simulation covering the last millennium based on the max planck institute earth system model an unprecedentedly large collection of pre industrial sves up to 45 producing a peak annual average top of atmosphere radiative perturbation larger than 1 5 wm 2 is investigated by composite analysis post eruption oceanic and atmospheric anomalies coherently describe a fluctuation in the coupled ocean atmosphere system with an average length of 20 25 years the study provides a new physically consistent theoretical framework to interpret decadal northern hemisphere nh regional winter climates variability during the last millennium the fluctuation particularly involves interactions between the atlantic meridional overturning circulation and the north atlantic gyre circulation closely linked to the state of the winter north atlantic oscillation it is characterized by major distinctive details among them the most prominent are a a strong signal amplification in the arctic region which allows for a sustained strengthened teleconnection between the north pacific and the north atlantic during the first post eruption decade and which entails important implications from oceanic heat transport and from post eruption sea ice dynamics and b an anomalous surface winter warming emerging over the scandinavian western russian region around 10 12 years after a major eruption the simulated long term climate response to sves depends to some extent on background conditions consequently ensemble simulations spanning different phases of background multidecadal and longer climate variability are necessary to constrain the range of possible post eruption decadal evolution of nh regional winter climates