prediction of alluvial channel pattern of perennial rivers abstract purely braided meandering and straight channels can be considered as end members of a continuum of alluvial channel patterns several researchers have succeeded in separating channel patterns in fields defined by flow related parameters however the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry in this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains the method is based on two almost channel pattern independent boundary conditions median grain size of the river bed material and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient this can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition p 1 based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with p 1 5 the function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation with a bankfull or mean annual flood discharge above 10 m3 s and a median bed material grain size between 0 1 and 100 mm

large eddy simulation of shallow cumulus over land a composite case based on arm long term observations at its southern great plains site abstractbased on long term observations by the atmospheric radiation measurement program at its southern great plains site a new composite case of continental shallow cumulus shcu convection is constructed for large eddy simulations les and single column models the case represents a typical daytime nonprecipitating shcu whose formation and dissipation are driven by the local atmospheric conditions and land surface forcing and are not influenced by synoptic weather events the case includes early morning initial profiles of temperature and moisture with a residual layer diurnally varying sensible and latent heat fluxes which represent a domain average over different land surface types simplified large scale horizontal advective tendencies and subsidence and horizontal winds with prevailing direction and average speed observed composite cloud statistics are provided for model evaluation the observed diurnal cycle is well reproduced by les however the cloud amount liquid water path and shortw

long term bedload mobility in gravel bed rivers using iron slag as a tracer abstract bedload dispersion is evaluated in gravel bed rivers using slag elements from ironworks established along rivers in the ardenne region between the fourteenth and the nineteenth centuries large quantities of slag were dumped close to these rivers or even directly into the channels for centuries slag elements were dispersed in the bedload and transported by floods of varying importance consequently slag may be considered as a reliable tracer to analyze bedload dispersion over several centuries the size of slag elements was studied along 16 ardenne rivers the longitudinal size trend of the largest slag particles allows the effective competence of these rivers to be determined between 19 and 129 mm for rivers where specific stream power for the bankfull discharge ranges between 20 and 134 w m a direct relationship doesn t exist between these two parameters as the size of slag elements must be considered with regard to the d 50 of the bed selective transport was analyzed directly downstream of the input sites the sorting distance varies from river to river and depends on the velocity of the coarse elements introduced into the river since the inception of the iron industry downstream of two metallurgic sites the slag propagation fronts were located as the periods of activity at these sites are known from historical studies the virtual velocity of bedload movement in these rivers was estimated to be 2 4 km century

assessment of the debris flow susceptibility in tropical mountains using clast distribution patterns abstract channel morphometric parameters and clast distribution patterns in selected basins of the ferriferous quadrangle tropical mountains brazil were analyzed in order to assess susceptibility to debris flows median bed surface clast size d 50 in the main stream channel of these basins shows a coarsening downstream trend with drainage areas of up to 6 km 2 which is attributed to debris flow dominated channels by some authors the composition and roundness of the bed load clast sand and the presence of allochthonous large boulders throughout the channels also suggest the occurrence of past debris flow in the region luminescence optically stimulated loe dating points out that debris flow could have occurred as a consequence of climate changes in the late pleistocene and holocene and it can now be triggered by deforestation or extreme rainfall events there has not been any record of past debris flow in the study area or in other mountainous regions of brazil where debris flows have recently occurred thus the adopted approach can be useful to assess debris flow susceptibility in this and other similar areas

plateau reduction by drainage divide migration in the eastern cordillera of colombia defined by morphometry and 10be terrestrial cosmogenic nuclides catchment wide erosion rates were defined using 10be terrestrial cosmogenic nuclides for the eastern cordillera of the colombian andes to help determine the nature of drainage development and landscape evolution the eastern cordillera characterized by a smooth axial plateau bordered by steep flanks has a mean erosion rate of 11 1 mm ka across the plateau and 70 10 mm ka on its flanks with local high rates of 400 mm ka the erosional contrast between the plateau and its flanks was produced by the increase in the orogen regional slope derived from the progressive shortening and thickening of the eastern cordillera the erosion rates together with digital topographic analysis show that the drainage network is dynamic and confirms the view that drainage divides in the eastern cordillera are migrating towards the interior of the mountain belt resulting in progressive drainage reorganization from longitudinal to transverse dominated rivers and areal reduction of the sabana de bogota plateau this article is protected by copyright all rights reserved

successful predictions of river characteristics across england and wales based on ordination predictions of river channel form under current conditions or in response to environmental or management changes and the rapid comparison of different channel reaches are important tasks in river management river classification is a common and valuable framework to address these aims but may suffer from the necessity to force a continuum of channel morphology into discrete groups more generally the scope to test the ability of predictive tools has been limited because of a shortage of field data in this study we used principal component analysis pca to identify the main sources of variation among river reaches in england and wales based on a set of 20 variables expected to correlate with channel morphology the pca scores were then used to predict the distributions of a wide range of hydromorphic features based on 4000 reaches surveyed in the river habitat survey baseline for comparison the predictive ability of three pairs of variables channel slope discharge slope catchment area and specific power catchment area was also tested the pca identified specific stream power channel size and groundwater input as the main sources of variation among reaches regression models using pca scores or paired variables were effective predictors of a range of channel characteristics including predominant substrate flow biotopes and channel vegetation channel cross sections and anthropogenic modifications were less predictable all of the approaches permitted simple plots of river reaches and quantitative comparisons of the dis similarity among individual reaches whilst the paired variables also minimised the data requirements our work reiterates the value of simple paired variables as a basis for rapidly comparing river reaches and for the first time quantifies the predictive ability of these approaches across a wide range of channel characteristics at a national scale principal component analysis provides a valuable exploratory tool for identifying the main sources of variation in complex multivariate data from which a simplified version e g specific power and area could be adopted

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

a predictive typology for characterising hydromorphology abstract whilst traditionally poorly quantified the link between physical habitat and ecological response in rivers is widely recognised and is currently rising up legislative and policy agendas in europe this is reflected in the water framework directive which dictates that hydromorphological condition of water bodies should be capable of supporting good ecological status methods are developed that integrate river system hydrology geomorphology and ecology and the complex interplay between these three variables whilst hydrological and biological methods for characterisation are relatively well established geomorphological methods are not effective characterisation of geomorphology physical habitat with full spatial coverage at a range of scales can be used to explore spatial interactions between habitat and biological data and potentially further our understanding of ecological response managers need to know what aspects of physical habitat and at which critical locations intervention will lead to greatest improvements in ecological condition this requires information on hydromorphological character and condition existing applied approaches for capturing geomorphological data are highly dependent on intensive fieldwork which is unlikely to be resourced at sufficiently extensive scales to meet management needs this paper outlines a typology approach for characterising the physical template of rivers it draws on a range of hydromorphological data to develop a framework for a channel typology with data collation from secondary sources followed by targeted fieldwork to i assess to what extent individual channel types are characteristic of field conditions and ii to collect information on reach scale variability within each type results suggest that characterisation of channel types based on stream power floodplain width and stream order does result in a distinct set of channel types field survey subsequently found that these types had a characteristic suite of patch scale habitat features flow types the approach was applied to a catchment where geomorphological processes exert a dominant control over physical habitat

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

understanding erosion rates in the himalayan orogen a case study from the arun valley understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution denudation rates derived from terrestrial cosmogenic nuclides tcns are commonly used to quantify erosion and bridge tectonic myr and climatic up to several kiloyears time scales however how the processes of erosion in active orogens are ultimately reflected in 10be tcn samples remains a topic of discussion we investigate this problem in the arun valley of eastern nepal with 34 new 10be derived catchment mean denudation rates the arun valley is characterized by steep north south gradients in topography and climate locally denudation rates increase northward from 0 2 mm yr 1 to 1 5 mm yr 1 in tributary samples while main stem samples appear to increase downstream from 0 2 mm yr 1 at the border with tibet to 0 91 mm yr 1 in the foreland denudation rates most strongly correlate with normalized channel steepness r2 0 67 which has been commonly interpreted to indicate tectonic activity significant downstream decrease of 10be concentration in the main stem arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample this results in 10be concentrations and denudation rates that do not uniformly represent the upstream catchment area we observe strong impacts on 10be concentrations from local nonfluvial geomorphic processes such as glaciation and landsliding coinciding with areas of peak rainfall rates pointing toward climatic modulation of predominantly tectonically driven denudation rates

geomorphic effectiveness of a long profile shape and the role of inherent geological controls in the himalayan hinterland area of the ganga river basin india abstract long profiles of rivers provide a platform to analyse interaction between geological and geomorphic processes operating at different time scales identification of an appropriate model for river long profile becomes important in order to establish a quantitative relationship between the profile shape its geomorphic effectiveness and inherent geological characteristics this work highlights the variability in the long profile shape of the ganga river and its major tributaries its impact on stream power distribution pattern and role of the geological controls on it long profile shapes are represented by the sum of two exponential functions through the curve fitting method we have shown that coefficients of river long profile equations are governed by the geological characteristics of subbasins these equations further define the spatial distribution pattern of stream power and help to understand stream power variability in different geological terrains spatial distribution of stream power in different geological terrains successfully explains spatial variability in geomorphic processes within the himalayan hinterland area in general the stream power peaks of larger rivers lie in the higher himalaya and rivers in the eastern hinterland area are characterised by the highest magnitude of stream power

assessment of downstream trends in channel gradient total and specific stream power a gis approach geographic information systems gis analyses of digital elevation models dems coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient total stream power and in riverscapes conducive to regime analysis also specific stream power for a small high relief coastal catchment in se australia good agreement was obtained between channel gradients derived from a 25 m cell size dem and field survey equivalents over distances of several kilometres indicating that channel gradients derived from dems can have a reasonable degree of absolute as well as relative accuracy over multi kilometre reach scales assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream modelling of downstream trends in channel gradient total and specific stream power from catchment wide dems has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient stream power and the form and dynamics of river systems

lithologic and hydrologic controls of mixed alluvial bedrock channels in flood prone fluvial systems bankfull and macrochannels in the llano river watershed central texas usa abstract the rural and unregulated llano river watershed located in central texas usa has a highly variable flow regime and a wide range of instantaneous peak flows abrupt transitions in surface lithology exist along the main stem channel course both of these characteristics afford an opportunity to examine hydrologic lithologic and sedimentary controls on downstream changes in channel morphology field surveys of channel topography and boundary composition are coupled with sediment analyses hydraulic computations flood frequency analyses and geographic information system mapping to discern controls on channel geometry profile pattern and shape and dimensions along the mixed alluvial bedrock llano river and key tributaries four categories of channel classification in a downstream direction include i uppermost ephemeral reaches ii straight or sinuous gravel bed channels in cretaceous carbonate sedimentary zones iii straight or sinuous gravel bed or bedrock channels in paleozoic sedimentary zones and iv straight braided or multithread mixed alluvial bedrock channels with sandy beds in precambrian igneous and metamorphic zones principal findings include i a nearly linear channel profile attributed to resistant bedrock incision checkpoints ii statistically significant correlations of both alluvial sinuosity and valley confinement to relatively high f mean depth hydraulic geometry values iii relatively high b width hydraulic geometry values in partly confined settings with sinuous channels upstream from a prominent incision checkpoint iv different functional flow categories including frequently occurring events

hack s relation and optimal channel networks the elongation of river basins as a consequence of energy minimization as pointed by hack 1957 river basins tend to become longer and narrower as their size increases this work shows that this property may be partially regarded as the consequence of competition and minimization of energy expenditure in river basins

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

a morpho statistical classification of mountain stream reach types in southeastern australia abstract the concepts of sediment transport capacity q c and sediment supply q s have shown promise in broadly differentiating mountain streams the important role of lithology in determining reach characteristics is also noted but as yet not fully included in existing process domain frameworks this study uses topographic and grain size surveys undertaken over 42 channel reaches with slopes between 0 01 and 0 20 m m to describe mountain stream morphology in southeastern australia reaches with two different lithologies are surveyed to specifically address the role of lithology in resultant channel morphology spatial autocorrelation analysis based on moran s i is used to detect the frequency and occurrence of in stream features such as bars and pools these data are combined with the grain size data to describe eight dominant reach morphologies most channel morphologies display broad characteristics similar to previous accounts of mountain streams although a number of intermediate morphologies affecting subtle variations in form and process where evident there was no significant longitudinal arrangement of the observed morphologies particularly with respect to catchment area and slope this is related to the strongly segmented longitudinal profiles characteristic of these streams where increasing catchment area does not result in a commensurate decrease in slope five of the eight channel morphologies identified are lithology dependent with respect to grain size and shape regime diagrams applied to quantify the physical controls on the different reach morphologies identified different q c q s domains for most morphologies however some lithology dependent morphologies could not be differentiated supporting the need to incorporate the effects of dominant grain shape or sphericity in assigning dimensionless critical shear stress values in determining q s overall the differences in mountain stream reach morphologies described in this study reflect the characteristic segmentation of the longitudinal profiles of these streams and contrasts in the supply and breakdown of parent material

downstream trends in discharge slope and stream power in a lower coastal plain river conceptual models of river estuary interaction are typically based on a notion of systematic downstream change in the intensity of fluvial processes low slopes backwater effects and effects of antecedent topography and landforms may complicate downstream tends in water and sediment flux in coastal plain rivers an analysis of the lower trinity river texas shows no consistent downstream pattern of increases or decreases in the discharge stream power or water surface slope flows may decrease downstream due to coastal backwater effects in the lowermost reaches and due to diversion of flow into valley bottom depressions during high flows in both the fluvial and fluvial estuarine transition reaches in general however stream power and slope decrease in the lower reaches consistent with earlier findings of limited fluvial sediment delivery to the coastal zone some tributaries may become distributaries at high but sub bankfull flows as backwater effects reverse flows into depressions associated with paleomeanders the paleomeanders and possibly the locations of these reversible channels are related to antecedent topography associated with aggradation degradation cycles over the past 100 ka low gradient coastal plain rivers may not function as simple conduits from land to sea further the transition from fluvial to coastal dominance may be variable along the river with the variability controlled not just by the relative magnitude of river and tidal or backwater forcing but also by valley topography controlled in part by antecedent landforms

the parameterization of the planetary boundary layer in the ucla general circulation model formulation and results abstract a planetary boundary layer pbl parameterization for general circulation models gcms is presented it uses a mixed layer approach in which the pbl is assumed to be capped by discontinuities in the mean profiles both clear and cloud topped boundary layers are parameterized particular emphasis is placed on the formulation of the coupling between the pbl and both the free atmosphere and cumulus convection for this purpose a modified coordinate is introduced in which the pbl top and the lower boundary are both coordinate surfaces the use of a bulk pbl formulation with this coordinate is extensively discussed results are presented from a july simulation produced by the ucla gcm pbl related variables are shown to illustrate the various regimes the parameterization is capable of simulating

thresholds and the spatial variability of flood power during extreme floods abstract analysis of the effects of extreme events on overall landscape form has shifted geomorphic attention away from a focus on the magnitude and frequency relationship of discharge to a focus on flood power this paper analyzes the variation in flood power both at a station and downstream in a basin of differing lithologies and discusses the geologic and geomorphic controls on flood power design floods ranging from the 2 year discharge tothe 500 year discharge are routed trough a drainage basin and channel boundary shear stress and unit stream power are calculated using hec 2 along 21 cross valley transects because of the strong lithologic control on valley width and channel slope an irregular downstream pattern of flood power emerges which reflects primarily the pattern in valley width narrow valleys correspond to a greater percent of channel conveyance during large magnitude floods and increasing rates of depth increases thus maximizing flood power in these zones the opposite occurs in anomalously wide valleys where flood power is minimized a downstream spatial pattern emerges reflecting both local and general controls for a given probability event flood power varies at least threefold within the basin with a maximum occuring in a specific downstream section holding flood power constant produces an extremely wide range in flow probabilities in order to establish a link between critical flood power magnitude and flow frequency minimum flood powers are developed from an analysis of previous work on catastrophic flooding for humid alluvial channels these minimum thresholds tentatively correspond to 100 n m2 or 300 w m2 for shear stress and unit stream power respectively discharges required to attain these critical flood powers vary from events roughly twice the 100 year flood to a maximum of roughly 18 times the discharge of the 100 year flood

relative changes in sediment supply and sediment transport capacity in a bedrock controlled river rivers can be affected by multiple natural and human induced changes to sediment supply and to sediment transport capacity assessment of the relative importance of these changes enables appropriate river management here assessments are made of the relative changes in sediment supply and sediment transport capacity of an 83 km section of the bedrock controlled coxs river new south wales australia these relative changes are estimated in turn for land degradation historical climate variations and dam closure measurements of gully erosion extent from aerial photographs indicate that since european settlement the average annual sediment supply to the river has increased by a factor of 20 rainfall records and flow gauging records show a climate shift in the mid 1940s on the basis of hydrologic modeling the increased streamflow in the period since the mid 1940s is estimated to have increased sediment transport capacity by a factor of almost 3 closure of lyell dam in 1982 stopped sediment supply from the upper catchment on the basis of hydrologic modeling the flow regulation and abstraction at the dam is estimated to have reduced the long term average sediment transport capacity downstream by 15 the current sediment transport capacity after the climate shift and dam closure is 2 6 times higher that in the first half of this century in spite of this net increase in sediment transport capacity the huge volume of sediment delivered to the channel from gully erosion has led to widespread sand deposition along much of the river much of the river bed that was previously dominated by bedrock is now alluvial in character only the steepest reaches remain bedrock dominated

a fuzzy gis model to determine confluence morphological sensitivity to tributary inputs at the watershed scale abstract confluences are key nodes of river systems that have the potential of disrupting downstream longitudinal trends in the main river through inputs of water sediment wood or ice delivered from tributaries from a geomorphological perspective confluence zones are particularly active and thus susceptible to increased flooding and bed instability which in turn pose serious threats to infrastructure however not all confluences are active despite major advances in our knowledge of confluence dynamics there has been limited progress in the development of low complexity practical tools that use remotely sensed data to predict the spatial distribution of the main river s sensitivity to tributary inputs we have thus developed a novel semi automated gis model that uses a fuzzy approach to integrate key factors unit stream power valley confinement and sediment connectivity potential in order to map the distribution of the confluence morphological sensitivity cms index at the watershed scale the gis model was tested using digital elevation models of high lidar 1 m and coarser 10 m resolution in the coaticook and gaspesie watersheds quebec canada results indicate that the model is useful for detecting geomorphologically active confluences and the resulting sensitivity of the main channel and thus has potential to be used in diverse river management applications e g hazard reduction and freedom space mapping

an approach for measuring confinement and assessing the influence of valley setting on river forms and processes valley setting and confinement or lack thereof are primary controls on river character and behaviour although there are various proxies for valley confinement direct measures that quantify the nature and extent of confinement are generally lacking and or inconsistently described as such they do not lend themselves to consistent analysis over large spatial scales here we clearly define forms of confinement to aid in quantification of degrees of confinement types of margin that can induce confinement are differentiated as a valley margin valley bottom margin and or anthropogenic margin such margins sometimes overlap and share the same location and in other situations are separated giving immediate clues as to the valley setting we apply this framework to examples from australia united states and new zealand showing how this framework can be applied across the spectrum of river diversity this method can help to inform interpretations of reach scale river behaviour highlighting the role of antecedent controls on contemporary forms and processes clear definitions of confinement are shown to support catchment scale analysis of river patterns along longitudinal profiles and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments e g process zone distribution lateral sediment inputs and dis connectivity copyright 2015 john wiley sons ltd

testing for reach scale adjustments of hydraulic variables to soluble and insoluble strata buckeye creek and greenbrier river west virginia abstract an open question exists as to whether channel geometries and hydraulics are adjusted in bedrock streams with stable concave profiles in a manner analogous to alluvial rivers as a test of this problem a comparison was undertaken of channel geometries and hydraulics among reaches with substrates that are of high mechanical resistance but of variable chemical resistance reaches were selected from buckeye creek and greenbrier river west virginia usa because these streams flow over sandstones limestones and shales the limestones have selby rock resistance scores similar to those of the sandstones a total of 13 reaches consisting of between 6 and 26 cross sections were surveyed in the streams hec ras was used to estimate unit stream power and shear stress for each reach the reaches were selected to evaluate the null hypothesis that that and are equal atop soluble versus insoluble bedrock hypothesis tests consisted of paired t tests and simultaneous multiple comparisons geomorphic setting was included for greenbrier river because previous studies have suggested that bedrock streams are intimately coupled with hillslopes holding geomorphic setting constant three separate comparisons of and reveal that these variables are lowest atop soluble substrates in greenbrier river significance 0 05 and that changes in and are mediated by changes in channel geometry similarly headwater reaches of buckeye creek developed atop shale and sandstone boulders are statistically distinguishable from downstream reaches wherein corrosion of limestone is the primary means of incision however comparisons in each stream reveal that channel geometries and are not strictly controlled by bed solubility for constant substrate solubility along the greenbrier river and are consistently higher where a bedrock cutbank is present or coarse insoluble sediment enters the channel the latter is also associated with locally high values of and in buckeye creek assuming that incision by corrosion requires lower values of and because the channel need not be adjusted for block detachment and tool acceleration we posit that the statistically lower values of and are tentative evidence in favor of differential geometric and hydraulic adjustments to substrate resistance we observe that these adjustments are not made independent of geomorphic setting

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

numerical simulation of tropical cumulus clouds and their interaction with the subcloud layer abstract a two dimensional numerical model suitable for simulating an ensemble of cumulus clouds has been developed it differs from similar models in its greater emphasis on turbulent processes in the boundary layer and in clouds in the model cloud scale dynamics are coupled with a third moment turbulence closure a turbulence scale condensation scheme is used to parameterize the cloud water mixing ratio we studied the response of tropical cumulus clouds to imposed large scale vertical advection by doing two simulations one with upward large scale vertical velocity the disturbed case and one without any the undisturbed case but otherwise identical deep cumulus clouds formed in the disturbed case while only shallow clouds formed in the undisturbed case time averaged and horizontally averaged heat and moisture budgets from the simulations show that the subcloud layer scl in the disturbed case was strongly affected by cumulus circulations and rain evaporation both cumulus updrafts and down

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

global river slope a new geospatial dataset and global scale analysis abstract a rivers longitudinal gradient i e slope is a key parameter in fluvial hydrology hydraulics and geomorphology it affects a multitude of fluvial variables such as flow velocity and sediment transport limitations in river slope data both its availability and accuracy constrain the fidelity of fluvial modeling particularly at larger or global scales traditional slope calculation algorithms cannot accurately predict river slopes as these are based on cell by cell calculation which is only suitable for hillslopes and small mountainous streams this paper presents a methodology for calculating global river slope and a procedure to upscale it for relatively coarse resolution suitable for global scale modeling the methodology is based on a simple principle of calculating slope from elevation depression over the length of a river segment which is automated to allow global scale calculations version 1 0 of the global river slope glors geospatial dataset is introduced and shown to be a step improvement over a previous product nhdplus for the contiguous united states and compares favorably to observed slope data collected from the literature statistical analysis of earth s continents and large basins highlights interesting spatial trends a semi empirical regression analysis between basin average river slope and other basin scale parameters show that terrain slope accounts for 67 of the variability in basin average river slope with average discharge sediment load and basin temperature contributing additional improvements to global predictions of 3 4 and 3 respectively

the transfer of modern organic carbon by landslide activity in tropical montane ecosystems 1 geomorphic processes play an important role in the transfer and storage of carbon within steep mountainous terrain among these mass wasting stands out because of its impact on above and below ground carbon pools and its potential for releasing or sequestering carbon a combined remote sensing and gis modeling approach was used to quantify the amount and spatial redistribution of modern organic carbon mobilized by mass wasting activity in a tropical mountain setting the study focused on a population of hundreds of shallow translational landslides triggered by hurricane mitch 1998 on seven watersheds draining the southern flank of the sierra de las minas mountain range slm in central eastern guatemala results illustrate that mass wasting contributed to the transfer of 43 104mgc or 3 of the pre event c in above ground vegetation and soils for an equivalent carbon flux rate of 0 08 0 33 mgc ha 1 y 1 depending on whether we consider hurricane mitch to be a landslide triggering event with a 20 year or an 80 year recurrence interval while 30 of this carbon was delivered to hillslopes or first order streams with a presumed high potential for long term sequestration the remaining 70 was delivered to higher order streams with unknown carbon retention capabilities therefore the ultimate fate of the carbon released by landsliding is very uncertain but depending on the proportion sequestered by colluvial deposits the recurrence interval of landslide triggering events and the rate of ecosystem recuperation at the landslide failure sites mass wasting could be either a net source or sink of carbon in a simulated setting based on the slm study results in which all carbon transferred by landslides from all tropical mountains of the globe is released to the atmosphere it would represent an amount equivalent to 1 11 of the global carbon currently being released by the burning of fossil fuels meanwhile in a projected scenario where a significant proportion of the carbon transferred by landslides is retained within sedimentary deposits sequestration rates would equal 2 19 of the residual land sink

alternative methods for specification of observed forcing in single column models and cloud system models we discuss alternative methods for prescribing advective tendencies in single column models scms and cloud system models these include revealed forcing in which the total advective tendency is prescribed from observations horizontal advective forcing in which the horizontal advective tendencies are prescribed together with the observed vertical motion which is combined with the predicted sounding to determine the tendencies due to vertical advection and relaxation forcing in which the horizontal advective tendencies are computed by relaxing the sounding toward the observed upstream sounding with a relaxation timescale determined by the time required for the wind to carry parcels across the grid column when relaxation forcing is used the horizontal advective tendencies can be diagnosed from the model output and compared with the corresponding observed tendencies we present scm results to illustrate these three forcing methods based on data from several field experiments in both the tropics and the midlatitudes each method is shown to have its strengths and weaknesses overall the results presented here do not show unambiguous differences between revealed forcing and horizontal advective forcing the two methods appear to be generally comparable revealed forcing may therefore be preferred for its simplicity relaxation forcing guarantees realistic soundings of the state variables but can produce large errors in parameterized processes which are driven by rates e g fluxes rather than states in particular relaxation forcing gives large errors in the precipitation rate in this model we demonstrate that relaxation forcing leads to unrealistically high low precipitation in versions of the model which tend to produce unrealistically dry humid soundings the observed horizontal advective tendencies in the tropics are so weak especially for temperature that small absolute errors in the diabatic tendencies diagnosed with relaxation forcing can lead to large relative errors in the diagnosed horizontal advective tendencies

metamorphic segregations associated with garnet and orthopyroxene porphyroblast growth two examples from the larsemann hills east antarctica in the larsemann hills east antarctica there are two important types of zoned segregations that formed during a proterozoic granulite facies metamorphic event 1 segregations with a large garnet porphyroblast in the core potassium feldspar in the mantle and biotite cordierite and plagioclase in the matrix and 2 segregations with a large orthopyroxene porphyroblast in the core potassium feldspar in the mantle and biotite and quartz in the matrix the main difference between these and zoned metamorphic segregations with leucocratic mantles described by previous authors is that the mantle phases are not a depleted subset of the matrix assemblage but part of the product assemblage the concentrical arrangement in the garnet segregations can be explained by the sequence in which a number of garnet and potassium feldspar producing reactions were met during temperature increase with internal buffering of the activity of h2o these reactions are modelled in the system k2o feo mgo al2o3 sio2 h2o kfmash the main reaction responsible for the garnet porphyroblast bearing segregations is a kfmash divariant equilibrium quartz biotite cordierite garnet potassium feldspar melt taking place in a quartz biotite cordierite garnet assemblage potassium feldspar and melt produced by this reaction are associated spatially with garnet as a consequence of the sparse nucleation of garnet and the chemical potential gradients generated prior to the interception of this equilibrium in order to account for the mineral assemblage of the mantles and the preservation of the porphyroblasts during retrogression some melt loss from the segregation is necessary the orthopyroxene segregations can be explained in an analogous manner within this model the pt conditions in which the two types of segregations formed are consistent with the m1 pressures and temperatures suggested by previous work about 4 5 kbar and 750 c

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

kinematic and thermodynamic characteristics of the flow over the western pacific warm pool during toga coare abstract rawinsonde and satellite infrared radiation ir data from the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare are used to investigate mean and transient behavior and horizontal variability of the atmosphere over the western pacific warm pool infrared data for the 4 mo intensive observing period iop and vertical motion fields indicate that the intensity of convection height of maximum upward motion and sst all increased from west 140 e to east across the coare domain iop mean ir data show a double itcz intertropical convergence zone structure north and south of the intensive flux array ifa centered at 2 s 156 e although marked variability in the patterns occurred on a month to month basis three prominent westerly wind bursts occurred over the ifa during the 4 mo iop in association with the intraseasonal oscillations isos strong upward motion usually occurred 1 3 weeks prior to the peak low level westerlies subsidence dominated when

a gcss model intercomparison for a tropical squall line observed during toga coare i cloud resolving models results from eight cloud resolving models are compared for the first time for the case of an oceanic tropical squall line observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment there is broad agreement between all the models in describing the overall structure and propagation of the squall line and some quantitative agreement in the evolution of rainfall there is also a more qualitative agreement between the models in describing the vertical structure of the apparent heat and moisture sources the three dimensional 3d experiments with an active ice phase and open lateral boundary conditions along the direction of the system propagation show good agreement for all parameters the comparison of 3d simulated fields with those obtained from two different analyses of airborne doppler radar data indicates that the 3d models are able to simulate the dynamical structure of the squall line including the observed double peaked updraughts however the second updraught peak at around 10 km in height is obtained only when the ice phase is represented the 2d simulations with an ice phase parametrization also exhibit this structure although with a larger temporal variability in the 3d simulations the evolution of the mean wind profile is in the sense of decreasing the shear but the 2d simulations are unable to reproduce this behaviour

upper limits of flash flood stream power in europe abstract flash floods are characterized by strong spatial gradients of rainfall inputs that hit different parts of a river basin with different intensity stream power values associated with flash floods therefore show spatial variations that depend on geological controls on channel geometry and sediment characteristics as well as on the variations of flood intensity this stresses the need for a field approach that takes into account the variability of the controlling factors post flood assessment of peak discharge after major floods makes it possible to analyse stream power in fluvial systems affected by flash floods this study analyses the stream power of seven intense return period of rainfall 100 years at least in some sectors of the river basin flash floods that occurred in mountainous basins of central and southern europe from 2007 to 2014 in most of the analysed cross sections high values of unit stream power were observed this is consistent with the high severity of the studied floods the highest values of cross sectional stream power and unit stream power usually occur in mediterranean regions this is mainly ascribed to the larger peak discharges that characterize flash floods in these regions the variability of unit stream power with catchment area is clearly nonlinear and has been represented by log quadratic relations the values of catchment area at which maximum values of unit stream power occur show relevant differences among the studied floods and are linked to the spatial scale of the events values of stream power are generally consistent with observed geomorphic changes in the studied cross sections bedrock channels show the highest values of unit stream power but no visible erosion whereas major erosion has been observed in alluvial channels exceptions to this general pattern which mostly occur in semi alluvial cross sections urge the recognition of local or event specific conditions that increase the resistance of channel bed and banks to erosion or like short flow duration reduce the geomorphic effectiveness of the flood

a methodological framework for hydromorphological assessment analysis and monitoring idraim aimed at promoting integrated river management a methodological framework for hydromorphological assessment analysis and monitoring named idraim has been developed with the specific aim of supporting the management of river processes by integrating the objectives of ecological quality and flood risk mitigation the framework builds on existing and up to date geomorphological concepts and approaches and has been tested on several italian streams the framework includes the following four phases 1 catchment wide characterization of the fluvial system 2 evolutionary trajectory reconstruction and assessment of current river conditions 3 description of future trends of channel evolution and 4 identification of management options the framework provides specific consideration of the temporal context in terms of reconstructing the trajectory of past channel evolution as a basis for interpreting present river conditions and future trends a series of specific tools has been developed for the assessment of river conditions in terms of morphological quality and channel dynamics these include the morphological quality index mqi the morphological dynamics index mdi the event dynamics classification edc and the river morphodynamic corridors mc and emc the monitoring of morphological parameters and indicators alongside the assessment of future scenarios of channel evolution provides knowledge for the identification planning and prioritization of actions for enhancing morphological quality and risk mitigation

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

creating and coupling a high resolution dtm with a 1 d hydraulic model in a gis for scenario based assessment of avulsion hazard in a gravel bed river abstract in this paper we explore the development and assimilation of a high resolution topographic surface with a one dimensional hydraulic model for investigation of avulsion hazard potential on a gravel bed river a detailed channel and floodplain digital terrain model dtm is created to define the geometry parameter required by the 1d hydraulic model hec ras the ability to extract dense and optimally located cross sections is presented as a means to optimize hec ras performance a number of flood scenarios are then run in hec ras to determine the inundation potential of modeled events the post processed output of which facilitates calculation of spatially explicit shear stress and level of geomorphic work specific stream power per unit bed area for each of these further enhancing this scenario based approach the dtm is modified to simulate a large woody debris lwd jam and active channel sediment aggradation to assess impact on innundation and under previously modeled flow conditions the high resolution dtm facilitates overlay and evaluation of modeled scenario results in a spatially explicit context containing considerable detail of hydrogeomorphic and other features influencing hydraulics bars secondary and scour channels levees this offers advantages for i assessing the avulsion hazard potential and spatial distribution of other hydrologic and fluvial geomorphic processes and ii exploration of the potential impacts of specific management strategies on the channel including river restoration activities

lateral sediment sources and knickzones as controls on spatio temporal variations of sediment transport in an alpine river modern mixed alluvial bedrock channels in mountainous areas provide natural laboratories for understanding the time scales at which coarse grained material has been entrained and transported from their sources to the adjacent sedimentary sink where these deposits are preserved as conglomerates this article assesses the shear stress conditions needed for the entrainment of the coarse bed particles in the glogn river that drains the 400 km2 val lumnezia basin eastern swiss alps in addition quantitative data are presented on sediment transport patterns in this stream the longitudinal stream profile of this river is characterized by three ca 500 m long knickzones where channel gradients range from 0 02 to 0 2 m m 1 and where the valley bottom confined into a 10 m wide gorge downstream of these knickzones the stream is flat with gradients 0 01 m m 1 and widths 30 m measurements of the grain size distribution along the trunk stream yield a mean d84 value of ca 270 mm whereas the mean d50 is ca 100 mm the consequences of the channel morphology and the grain size distribution for the time scales of sediment transport were explored by using a one dimensional step backwater hydraulic model hydrologic engineering centre river analysis system the results reveal that along the entire trunk stream a two to 10 year return period flood event is capable of mobilizing both the d50 and d84 fractions where the shields stress exceeds the critical shields stress for the initiation of particle motion these return periods however varied substantially depending on the channel geometry and the pebble boulder size distribution of the supplied material accordingly the stream exhibits a highly dynamic boulder cover behaviour it is likely that these time scales might also have been at work when coarse grained conglomerates were constructed in the geological past