post oligocene river incision southern sierra madre occidental mexico the sierra madre occidental of western mexico consists of a granitic basement covered by oligocene ignimbrites that define a reference surface from which to estimate late cenozoic river incision a 90 m grid digital elevation model was used to characterize contemporary topography and interpolate the late oligocene surface of the ignimbrite plateau from a surface fit to the highest points in the relatively undissected uplands between major river valleys long term river incision rates calculated from the difference between this reference surface and longitudinal profiles of 11 rivers that flow toward the tepic zacoalco rift zone range from about 0 01 to 0 2 mm year 1 river profiles of this region also show evidence of river capture driven by flexural uplift along the flank of the rift zone river profile concavity values in the sierra madre occidental range from 0 22 to 0 63 a range similar to that reported previously for a wide range of environments in contrast the empirically constrained ratio of exponents in the stream power model of river incision m n ranges from 0 44 to 0 52 close to the expected theoretical value of 0 5 the wider range of observed values may illustrate how can differ from the driving values of m n in non steady state bedrock river systems

effects of hydraulic roughness on surface textures of gravel bed rivers field studies of forest gravel bed rivers in northwestern washington and southeastern alaska demonstrate that bed surface grain size is responsive to hydraulic roughness caused by bank irregularities bars and wood debris we evaluate textural response by comparing reach average median grain size d50 to that predicted from the total bank full boundary shear stress t0 bf representing a hypothetical reference condition of low hydraulic roughness for a given t0 bf channels with progressively greater hydraulic roughness have systematically finer bed surfaces presumably due to reduced bed shear stress resulting in lower channel competence and diminished bed load transport capacity both of which promote textural fining in channels with significant hydraulic roughness observed values of d50 can be up to 90 smaller than those predicted from t 0 bf we find that wood debris plays an important role at our study sites not only providing hydraulic roughness but also influencing pool spacing frequency of textural patches and the amplitude and wavelength of bank and bar topography and their consequent roughness our observations also have biological implications we find that textural fining due to hydraulic roughness can create usable salmonid spawning gravels in channels that otherwise would be too coarse

climate exposed source rock lithologies crustal uplift and surface erosion a theoretical analysis calibrated with data from the alps north alpine foreland basin system paleofloristic data imply that paleoclimate changed in the swiss alps at the oligocene miocene boundary from humid and hot conditions toward a climate with high temperature and low humidity the aridization is associated with a change in depositional pattern from alluvial fans to lakes and floodplains suggesting decreasing sediment discharge a further 25 40 decrease of sediment discharge occurred at ca 20 ma when the orogenic core of the alps became exposed to the surface we applied a surface processes model to explore potential controls on the pattern of sediment discharge and on the evolution of the alpine drainage basin the model is based on the presumption that the rates of fluvial incision into bedrock are proportional to shear stress exerted by the flowing water the model results imply that the paleoclimate change resulted in an instantaneous decrease of sediment discharge and a vertical topographic growth until steady state conditions between erosional and crustal mass flux are established however exposure of the crystalline core of the alps at ca 20 ma is likely to have resulted in the 25 40 decrease of sediment discharge and the reorganization of the drainage pattern from an orogen normal to an orogen parallel orientation of dispersion

drainage basin sensitivity to tectonic and climatic forcing implications of a stochastic model for the role of entrainment and erosion thresholds long term average rates of channel erosion and sediment transport depend on the frequency magnitude characteristics of ood ows that exceed an erosion threshold using a poisson model for rainfall and runoff analytical solutions are developed for average rates of stream incision and sediment transport in the presence of such a threshold solutions are derived and numerically tested for three erosion transport formulas the howard kerby shear stress incision model the bridge dominic sediment transport model and a generic shear stress sediment transport model results imply that non linearity resulting from threshold effects can have a rst order impact on topography and patterns of dynamic response to tectonic and climate forcing this non linearity becomes signi cant when fewer than about half of ood events are capable of detaching rock or sediment predicted morphology and uplift gradient scaling is more closely consistent with observations and laboratory experiments than conventional slope linear or shear linear erosion laws these results imply that particle detachment thresholds are not details that can be conveniently ignored in long term landscape evolution models copyright 2004 john wiley sons ltd

struggles with stream power connecting theory across scales abstract two empirically consistent explanations exist for the morphology and dynamics of bedrock rivers the stream power law appears to explain rates of rock incision at large scale large drainage basins or landscape scale but appears to be of limited value in predicting reach scale morphology and dynamics the underlying reason why stream power is such an effective tool for understanding landscape evolution is because it is an explicit representation of the inverse power relation between slope and area in rivers incising bedrock this morphometric relation is nearly universal subject to exogenous contingencies independent testing and validation of the stream power incision model is challenging because of the contingencies that exist in almost all landscapes mechanistic models of erosion have been tested and validated at small scales generally below the reach scale and opportunities exist for independent testing and validation by using them to predict reach scale morphologies predicting larger scale bedrock river morphology requires the assumption that flow sediment fluxes and bedrock erosion processes that occur at smaller scale are adequately averaged at larger scales which is not well supported reconciling these two scales of explanation is one of the grand challenges of fluvial geomorphology unless we accept that theory and explanations will be scale delimited

quantifying differential rock uplift rates via stream profile analysis despite intensive research into the coupling between tectonics and surface processes our ability to obtain quantitative information on the rates of tectonic processes from topography remains limited due primarily to a dearth of data with which to test and calibrate process rate laws here we develop a simple theory for the impact of spatially variable rock uplift rate on the concavity of bedrock river profiles application of the analysis to the siwalik hills of central nepal demonstrates that systematic differences in the concavity of channels in this region match the predictions of a stream power incision model and depend on the position and direction of the channel relative to gradients in the vertical component of deformation rate across an active fault bend fold furthermore calibration of model parameters from channel profiles argued to be in steady state with the current climatic and tectonic regime indicates that 1 the ratio of exponents on channel drainage area and slope m n is 0 46 consistent with theoretical predictions 2 the slope exponent is consistent with incision either linearly proportional to shear stress or unit stream power n 0 66 or n 1 respectively and 3 the coefficient of erosion is within the range of previously published estimates mean k 4 3 10 4 m 0 2 yr application of these model parameters to other channels in the siwalik hills yields estimates of spatially variable erosion rates that mimic expected variations in rock uplift rate across a fault bend fold thus the sensitivity of channel gradient to rock uplift rate in this landscape allows us to derive quantitative estimates of spatial variations in erosion rate directly from topographic data

fluvial landscape response time how plausible is steady state denudation whether or not steady state topography and denudation are probable states depends on the timescale of system response to tectonic and climatic perturba tions relative to the frequency of those perturbations this paper presents analytical derivations of algebraic relations for the response time of detachment limited fluvial bedrock channel systems both to tectonic and climatic perturbations detachment limited fluvial erosion is described by the stream power incision model and the derivations are limited to the applicability of that model all factors likely to influence system response time that are not adequately captured by the stream power incision model will tend to increase the response time the calculations presented thus provide minimum estimates of landscape response time and therefore over predict the prob ability of attaining and sustaining steady state topography and denudation the central range of taiwan is used as a case study to estimate response times in a landscape often argued to be in steady state model parameters are fit to modern stream profiles by assuming that the topography represents a quasi steady state form estimated response times generally range from 0 25 to 2 5 ma depending on the non linearity of the incision rule and the magnitude and type of perturbation thus it may be reasonably argued that steady state topography and denudation are likely to prevail during periods of climatic stability response time is sufficiently short compared with plate tectonic timescales however rapid climatic fluctuation in the quaternary appears to preclude the attainment of steady state conditions in modern orogens motivation

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

dynamic equilibrium between an active uplift and the sevier river utah in a zone of active tectonic uplift one expects a river to change morphology simply because valley slope deforms but by cutting through a transverse uplift the sevier river in southern utah also adapts to the tectonics by eroding and depositing these localized changes of transport are caused by varying channel geometry pattern sedimentology and slope in the uplift the river is narrow efficiently shaped coarser grained and expends a greater proportion of energy on bed particles it deposits sediments downstream in exaggerated meandering reaches with wider less efficient channels localized erosion and deposition create a dynamic equilibrium with the structural growth but this equilibrium includes nonlinear responses like knickpoints and depositional lobes in response to the required erosion and deposition the river so dramatically alters channel grain size and channel geometry that the increase of sinuosity expected in the tectonically steepened valley does not occur

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

effects of orographic precipitation variations on the concavity of steady state river profiles the concavity or curvature of river profiles has long been taken to be a fundamental indicator of the underlying processes governing fluvial erosion and thereby of landscape evolution however erosion laws have generally been derived without accounting for the strong orographically driven gradients in precipitation typically found in mountainous regions in addition field measurements have found discrepancies between the form of measured stream profiles and theoretically derived values introducing a simple physically based feedback we find that orographically induced variations in precipitation strongly affect the curvature of steady state river profiles this feedback complicates efforts to infer the form of erosion laws from observed profile concavities but could help explain discrepancies between observations and theory our results demonstrate a strong feedback through which climate influences the form of river profiles and show how such climatic effects act to limit the relief of unglaciated mountain ranges

experimental channel response to tectonic uplift 1 we have performed a series of experiments to investigate the relationship between channel geometry and tectonic forcing in steady state landscapes at various uplift rates the experimental setup consists of uniformly uplifted silica paste eroded by artificial rainfall in this setup erosional landscapes evolve by growth and amalgamation of incisions which organize into a drainage network whose dynamics are a function of the interaction between vertical channel cutting hillslope erosion and sediment transport high precision 0 5 mm pixel size digital elevation models were constructed using a stereogrammetric camera system from this data channel bed slope was found to be independent of discharge and position on the experimental surface and to increase linearly with uplift rate geometric parameters of the flow such as channel width or depth could not be observed directly during the experiments using laminar flow equations for the mean flow velocity these parameters were back calculated and relationships to the imposed substrate uplift rate were derived channel width cross sectional area and wetted perimeter decrease with increasing uplift rate to a limit value hydraulic radius and flow depth increase slightly and flow velocity increases approximately linearly with increasing uplift rate these results are qualitatively consistent with recent field surveys and highlight the importance of channel width and slope variations in accommodating channel response to variable rock uplift rates

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

coarse sediment transport in a bedrock channel with complex bed topography 1 independent lithologic and structural controls in fluvial bedrock systems interact with coarse sediment transport processes to play a key role in bedrock incision processes such as abrasion during a 3 year study on the ocoee river in the blue ridge province of the southern appalachians usa we used painted tracer clasts to measure coarse sediment transport dynamics and address whether different scales of morphologic variability in bedrock channels lead to coarse sediment transport processes that differ from alluvial channels at the reach scale folded metasedimentary units are exposed in the channel bed and appear as linear bedrock ribs that vary in amplitude and orientation to flow under similar flow conditions for which size dependent transport has been observed in alluvial channels dimensionless shields stress within 1 5 2 0 times the dimensionless critical shear stress transport distance was a significant function of grain size where bedrock ribs were longitudinal to flow reach 1 and reach 2 however transport distance was not size dependent where bedrock ribs were oblique to flow reach 3 at different intrareach scales the variables characterizing the local bedrock topography and sediment architecture were the best predictors of transport distance in all three reaches therefore bed load transport processes may be influenced by bed forms in bedrock streams bedrock ribs but at potentially smaller scales than bed forms in alluvial channels the strong influence of bedrock ribs on coarse sediment transport suggested that coarse sediment transport processes are controlled by different factors in bedrock channels only when bedrock ribs cross the channel at a high angle to the flow

reconceptualising the role of organisms in the erosion of rock coasts a new model attempts to understand the morphodynamics of rock coasts focus on the nature and rate of erosion and how this influences the evolution of coastal profiles over century to millennial timescales biological contributions to this process are often ignored or treated in a rather simplistic way as merely producing microscale decreases in rock strength using a combination of field observations and literature review we address two key issues hampering a more rounded assessment of biological impacts erosion of coastal rocks firstly we reconceptualise the biological contributions to erosion of rock coasts into direct and facilitative types and secondly we discuss the need for more appropriate reporting of rates of bioerosion for direct bioerosion this means clearly documenting the percentage of platform surfaces affected by bioerosive agents and quantifying the volume of material eroded and the amount of fine sediment produced for facilitative bioerosion we must quantify the roles of biota in changing the material properties of rocks creating or altering surface morphologies and or weakening joint boundaries in this way facilitative bioerosion is one of several processes mediating geomorphic alteration of rock surfaces contributing to the production of landforms and or reducing the resisting force of rock subsequently we build on these ideas to produce a new conceptual model which more accurately portrays the multiple and cross scalar ways that biological processes notably bioerosion influence the resistance of coastal rocks to erosive forces such a model provides a stronger basis for numerical modelling and understanding the morphodynamics of rock coasts in the future and allows a quantitative assessment of the role of biota

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

the role of sediment in controlling steady state bedrock channel slope implications of the saltation abrasion incision model abstract the saltation abrasion model is a mechanistic model for river incision into bedrock by saltating bedload which we have previously derived and used experimental data to constrain all parameter values here we develop a method for applying the saltation abrasion model at a landscape scale and use the model as a reference for evaluating the behavior of a wide range of alternative incision models in order to consider the implications of the saltation abrasion model as well as other models for predicting topographic steady state channel slope to determine the single valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock we assume all runoff can be partitioned between a low flow and a high flow discharge in which all bedload sediment transport occurs during high flow we then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for using the predictions of the saltation abrasion model as a reference we find that the threshold of motion is the most important effect that should be represented explicitly followed in order of decreasing importance by the cover effect the tools effect and the threshold of suspension effect models that lack the threshold of motion over predict incision rate for low shear stresses and under predict the steady state channel slope for low to moderate rock uplift rates and rock strengths models that lack the cover effect over predict incision rate for high sediment supply rates and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage models that lack the tools effect over predict incision rate for low sediment supply rates and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value overall the saltation abrasion model predicts that steady state channel slope is most sensitive to changes in grain size such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible but as yet poorly understood influence on the size distribution of sediments delivered to channel networks by hillslopes

implications of the saltation abrasion bedrock incision model for steady state river longitudinal profile relief and concavity the saltation abrasion model predicts rates of river incision into bedrock as an explicit function of sediment supply grain size boundary shear stress and rock strength here we use this experimentally calibrated model to explore the controls on river longitudinal profile concavity and relief for the simple but illustrative case of steady state topography over a wide range of rock uplift rates we find a characteristic downstream trend in which upstream reaches are close to the threshold of sediment motion with large extents of bedrock exposure in the channel bed while downstream reaches have higher excess shear stresses and lesser extents of bedrock exposure profile concavity is most sensitive to spatial gradients in runoff and the rate of downstream sediment fining concavity is also sensitive to the supply rate of coarse sediment which varies with rock uplift rate and with the fraction of the total sediment load in the bedload size class variations in rock strength have little influence on profile concavity profile relief is most sensitive to grain size and amount of runoff rock uplift rate and rock strength influence relief most strongly for high rates of rock uplift analysis of potential covariation of grain size with rock uplift rate and rock strength suggests that the influence of these variables on profile form could occur in large part through their influence on grain size similarly covariation between grain size and the fraction of sediment load in the bedload size class provides another indirect avenue for rock uplift and strength to influence profile form copyright 2008 john wiley sons ltd

hanging valleys in fluvial systems controls on occurrence and implications for landscape evolution 1 we document and characterize hanging valleys in a fluvially eroded landscape in eastern taiwan our conceptual model for the initiation of hanging valleys builds on a recently proposed model of bedrock incision in which erosion actually becomes less efficient on very steep channel gradients if a pulse of incision in the main stem outpaces the tributary response the gradients at tributary mouths may therefore pass a threshold value beyond which erosional efficiency declines giving rise to a mismatch between trunk and tributary erosion rates this mismatch is expected at junctions with small tributaries where a step function decrease in drainage area also leads to sharp contrasts in water and sediment flux between trunk and tributary channels the occurrence of hanging valleys in actively uplifting fluvial landscapes such as the central range of taiwan suggests that the most common parameterizations of bedrock erosion which typically assume a monotonic positive correlation between channel gradient and incision rate may be violated in very steep channels in addition hanging valleys could greatly increase the response time of landscapes to tectonic perturbations since catchments above these tributary mouths will be insulated from these perturbations until a new suite of processes e g weathering and rock mass failure wear through the hanging valley lip the results of this study underscore the need for a more complete understanding of bedrock erosion processes and the incorporation of process transitions and threshold conditions into landscape evolution models

the signature of an unbalanced earthquake cycle in himalayan topography fifty percent of the relative motion between the indian and asian plates is accommodated by active convergence at the himalayan range front hrf earthquake cycle processes on shallowly dipping hrf thrust faults generate large earthquakes mw 7 and contribute to the growth of hrf topography interseismic rock uplift rates reach a maximum north of the active main frontal thrust and have been suggested to significantly influence the collocated convex bulge in hrf topography using geodetically constrained models of interseismic rock uplift rates and simple channel erosion rate laws we show that convex channel profiles are predicted when interseismic deformation outpaces coseismic deformation applying this model to the observed elevation profiles of 20 hrf spanning channels in nepal yields a minimum mean residual elevation 72 m if interseismic deformation has outpaced coseismic deformation by a factor of four the long term earthquake deficit required for the application of this model is consistent with some estimates of historical moment imbalance but requires temporally variable fault system activity the spatial correlation between nominally interseismic rock uplift and the hrf topographic bulge may be explained by 1 a noncausal geometric coincidence 2 geodetic observations of significant deformation not directly related to earthquake cycle processes or 3 an unbalanced earthquake cycle at the hrf

sediment supply controls equilibrium channel geometry in gravel rivers in many gravel bedded rivers floods that fill the channel banks create just enough shear stress to move the median sized gravel particles on the bed surface d50 because this observation is common and is supported by theory the coincidence of bankfull flow and the incipient motion of d50 has become a commonly used assumption however not all natural gravel channels actually conform to this simple relationship some channels maintain bankfull stresses far in excess of the critical stress required to initiate sediment transport we use a database of 300 gravel bedded rivers and 600 10be derived erosion rates from across north america to explore the hypothesis that sediment supply drives the magnitude of bankfull shear stress relative to the critical stress required to mobilize the median bed surface grain size formula see text we find that formula see text is significantly higher in west coast river reaches 2 35 n 96 than in river reaches elsewhere on the continent 1 03 n 245 this pattern parallels patterns in erosion rates and hence sediment supplies supporting our hypothesis we find a significant correlation between upstream erosion rate and local formula see text at sites where this comparison is possible our analysis reveals a decrease in bed surface armoring with increasing formula see text suggesting channels accommodate changes in sediment supply through adjustments in bed surface grain size as also shown through numerical modeling our findings demonstrate that sediment supply is encoded in the bankfull hydraulic geometry of gravel bedded channels through its control on bed surface grain size

long river profiles tectonism and eustasy a guide to interpreting fluvial terraces along three rivers at the mendocino triple junction northern california strath cut and fill terraces have formed in response to tectonic and eustatic processes detailed surveying and radiometric dating at multiple sites indicate that lower reaches of the rivers are dominated by the effects of oscillating sea level primarily aggradation and formation of fill terraces during sea level high stands alternating with deep incision during low stands a eustasy driven deposi tional wedge extends tens of kilometers upstream on all rivers tapering to zero thickness this distance is greater than expected from studies of the effects of check dams on much smaller streams elsewhere due in part to the large size of these rivers however the change in gradient is nearly identical to other base level rise studies the depositional gradient is about half that of the original channel middle to upper reaches of each fiver are dominated by the effects of long term uplift primarily lateral and vertical erosion and formation of steep unpaired strath terraces exposed only upstream of the depositional wedge vertical incision at a rate similar to that of uplift has occurred even during the present sea level high stand along rivers with highest uplift rates strath terraces have steeper gradients than the modem channel bed and do not merge with marine terraces at the river mouth consequently they cannot be used to determine altitudes of sea level high stands strath formation is a continuous process of response to long term uplift and its occurrence varies spatially along a river depending on stream power and hence position upstream strath terraces are found only along certain parts of a coastal stream upstream of the aggradational effects of oscillating sea level and far enough downstream that stream power is in excess of that needed to transport the prevailing sediment load for a given size fiver the greater the uplift rate the greater the rate of vertical incision and consequently the less the like lihood of strath terrace formation and preservation

field measurements of incision rates following bedrock exposure implications for process controls on the long profiles of valleys cut by rivers and debris flows until recently published rates of incision of bedrock valleys came from indirect dating of incised surfaces a small but growing literature based on direct measurement reports short term bedrock lowering at geologically unsustainable rates we report observations of bedrock lowering from erosion pins monitored over 1 7 yr in 10 valleys that cut indurated volcanic and sedimentary rocks in washington oregon california and taiwan most of these channels have historically been stripped of sediment their bedrock is exposed to bed load abrasion plucking and seasonal wetting and drying that comminutes hard intact rock into plates or equant fragments that are removed by higher fl ows consequent incision rates are proportional to the square of rock tensile strength in agreement with experimental results of others measured rates up to centimeters per year far exceed regional long term erosionrate estimates even for apparently minor sediment transport rates cultural artifacts on adjoining strath terraces in washington and taiwan indicate at least several decades of lowering at these extreme rates lacking sediment cover lithologies at these sites lower at rates that far exceed long term rock uplift rates this rate disparity makes it unlikely that the long profi les of these rivers are directly adjusted to either bedrock hardness or rock uplift rate in the manner predicted by the stream power law despite the observation that their profi les are well fi t by power law plots of drainage area vs slope we hypothesize that the threshold of motion of a thin sediment mantle rather than bedrock hardness or rock uplift rate controls channel slope in weak bedrock lithologies with tensile strengths below 3 5 mpa to illustrate this hypothesis and to provide an alternative interpretation for power law plots of area vs slope we combine shields threshold transport concept with measured hydraulic relationships and downstream fi ning rates in contrast to fl uvial reaches none of the hundreds of erosion pins we installed in steep valleys recently scoured to bedrock by debris fl ows indicate any postevent fl uvial lowering these results are consistent with episodic debris fl ows as the primary agent of bedrock lowering in the steepest parts of the channel network above 0 03 0 10 slope

equilibrium and time scales in geomorphology application to sand bed alluvial streams equilibrium is defined as a single valued temporally invariant functional relationship between the values of an output variable and the values of the input variable s in a geomorphic system disequilibrium occurs if the output deviates from the functional relationship by more than a consensual degree natural geomorphic variables are characterized by a relaxation time output variables are insensitive to cyclical inputs with frequencies much greater than the relaxation time but can respond completely for sufficiently low frequencies rapid trends recent step changes or pulse inputs and intermediate frequency inputs can cause disequilibrium the gradient of sand bed alluvial channels the output variable is determined by sediment and water delivery from slopes the input variables and changes in this hydraulic regime require regrading by erosion and deposition initial stages of adjustment to changed regime in a long unbranched channel with sediment and water delivery only at the upstream end propagate downstream but later stages of adjustment occur simultaneously throughout the reach in a dendritic channel network the gradient responds rather uniformly throughout the network to changes in regime during all stages of adjustment the time scale of adjustment to changed regime depends upon the size of the channel network or stream length the sediment and water discharges and to a lesser degree upon the magnitude of the change grade as defined by mackin 1948 is synonymous with equilibrium as used in this paper if a period of years is replaced by a time period commensurate with the relaxation time of the gradient the use of the term grade is best restricted to a single valued relationship between channel gradient and the hydraulic regime

the use of a landscape simulator in the validation of the siberia landscape evolution model transient landforms siberia is a physically based model for the geomorphic evolution of landforms it is essential that the siberia model be tested or validated against controlled landform development previous studies have demonstrated that siberia is able to simulate declining equilibrium landforms and in this paper we examine siberia s ability to simulate landforms as they evolve to their declining equilibrium form these landscapes are termed transient landforms landscapes generated by siberia were compared to those produced by a physical model experimental model landforms at stages of evolution comparison of the experimental landscapes with the simulated landscapes using total mass hypsometric curve width function cumulative area distribution and area slope demonstrate that siberia can simulate the experimental model landscape during development i e transient landscapes copyright 2002 john wiley sons ltd

large scale geomorphology classical concepts reconciled and integrated with contemporary ideas via a surface processes model linear systems analysis is used to investigate the response of a surface processes model spm to tectonic forcing the spm calculates subcontinental scale denudational landscape evolution on geological timescales 1 to hundreds of million years as the result of simultaneous hillslope transport modeled by diffusion and fluvial transport modeled by advection and reaction the tectonically forced spm accommodates the large scale behavior envisaged in classical and contemporary conceptual geomorphic models and provides a framework for their integration and unification the following three model scales are considered micro meso and macroscale the concepts of dynamic equilibrium and grade are quantified at the microscale for segments of uniform gradient subject to tectonic uplift at the larger meso and macroscales which represent individual interfluves and landscapes including a number of drainage basins respectively the system response to tectonic forcing is linear for uplift geometries that are symmetric with respect to baselevel and which impose a fully integrated drainage to baselevel for these linear models the response time and the transfer function as a function of scale characterize the model behavior numerical experiments show that the styles of landscape evolution depend critically on the timescales of the tectonic processes in relation to the response time of the landscape when tectonic timescales are much longer than the landscape response time the resulting dynamic equilibrium landscapes correspond to those envisaged by hack 1960 when tectonic timescales are of the same order as the landscape response time and when tectonic variations take the form of pulses much shorter than the response time evolving landscapes conform to the penck type 1972 and to the davis 1889 1899 and king 1953 1962 type frameworks respectively the behavior of the spm highlights the importance of phase shifts or delays of the landform response and sediment yield in relation to the tectonic forcing finally nonlinear behavior resulting from more general uplift geometries is discussed a number of model experiments illustrate the importance of fundamental form which is an expression of the conformity of antecedent topography with the current tectonic regime lack of conformity leads to models that exhibit internal thresholds and a complex response

longitudinal profiles in simple alluvial systems theoretical considerations suggest that exponential or quadratic functions are apt for describing the longitudinal profiles of aggrading alluvial systems that are unaffected by significant lateral inputs of water or sediment a new set of field data confirms this for individual sedimentary links along a wandering gravel bed river in british columbia canada each link is viewed as a simple alluvial system without major water or sediment inputs within which grain size typically fines downstream in a relatively systematic manner such homogeneous reaches are suitable for the investigation of simple profile form it is found that quadratic approximations are the most flexible descriptor for link longitudinal profiles overall the river forms an irregularly cuspate long profile structured by these fundamental length scale units both link gradients and link fining rate reflect size selective aggradation associated with the bounding lateral inputs

calculating bed load transport in steep boulder bed channels 1 steep rough channels occupy a large fraction of the total channel length in mountainous regions most sediment mobilized on hillslopes must pass through these streams before reaching lower gradient channels steep channels have wide grain size distributions that are composed of finer more mobile sediment and large rarely mobile grains the large grains can bear a significant portion of the total shear stress and thereby reduce the stress available to move the finer sediment conventional bed load transport equations often overpredict the sediment flux in steep channels by several orders of magnitude we hypothesize that sediment transport equations overpredict the sediment flux because they do not 1 account for the stress borne by rarely mobile grains 2 differentiate between highly and rarely mobile sediment and 3 account for the limited availability of mobile sediment here we modify a conventional bed load transport equation to include these three effects we use measurements of the flow bed properties and sediment flux in a small steep flume to test this equation we supply gravel at a constant rate through fields of regularly spaced immobile spheres and measure the bed coverage by gravel and sphere protrusion the percent of the sphere that protrudes above the gravel deposit for a given sphere spacing the proportion of the bed covered by gravel increases and the sphere protrusion decreases with greater sediment supply thus bed coverage and immobile grain protrusion may serve as proxies for sediment availability in steep rough streams unlike most transport equations that we tested our modified bed load equation predicts sediment fluxes to within an order of magnitude of the measured values our results demonstrate that accurately predicting bed load transport in steep rough streams may require accounting for the effects of local sediment availability coverage by mobile sediment and drag due to rarely mobile particles

regional analysis of bedrock stream long profiles evaluation of hack s sl form and formulation and assessment of an alternative the ds form the equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones and in continental margin and other intraplate settings as well as other base level changes such as due to sealevel fluctuations the hack sl form of the long profile which describes a straight line on a log normal plot of elevation normal versus distance logarithmic is the equilibrium long profile form that has been most widely used in such studies slope area analysis has also been used in recent years we show that the sl form is a special case of a more general form of the equilibrium long profile here called the ds form that can be derived from the power relationship between stream discharge and downstream distance and the dependence of stream incision on stream power the ds form provides a better fit than the sl form to river long profiles in an intraplate setting in southeastern australia experiencing low rates of denudation and mild surface uplift we conclude that if an a priori form of the long profile is to be used for investigations of regional landscape history the ds form is preferable in particular the ds form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance parallel shift in the ds plot to be distinguished from disequilibrium steepening due to long profile rejuvenation disordered outliers on the ds plot slope area analysis and the slope distance ds approach outlined here are complementary approaches reflecting the close relationship between downstream distance and downstream catchment area copyright 2006 john wiley sons ltd

grain size along two gravel bed rivers statistical variation spatial pattern and sedimentary links a new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel bed rivers in northeastern british columbia canada a preliminary assessment of grain size variability establishes a basis for examination of the spatial pattern of grain size change standard anova techniques are inappropriate because individual samples have unequal variances and are not normally distributed alternative tests for homoscedasticity and comparison of means are therefore utilized within site between sample variability is not significant the grain size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled in both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining textural variations along the two rivers studied here are complex and show negligible overall fining in over 100 km this is the consequence of a large number of tributary inputs and non alluvial sediment sources which are the legacy of late pleistocene glaciation the identification of lateral sources like these is fundamental for understanding textural changes within rivers the sedimentary link a channel reach between significant lateral sediment inputs provides a means of isolating fluvial maturation processes abrasion and sorting from contingent lateral inputs strong fining trends are apparent in most links and classification of grain size measurements according to their location within particular links greatly improves the statistical explanation of textural variation identification of sedimentary links provides a means of applying models of fluvial fining processes so isolation of link networks will aid the development of basin scale models of textural variation 1998 john wiley sons ltd

lifespan of mountain ranges scaled by feedbacks between landsliding and erosion by rivers an important challenge in geomorphology is the reconciliation of the high fluvial incision rates observed in tectonically active mountain ranges with the long term preservation of significant mountain range relief in ancient tectonically inactive orogenic belts river bedrock erosion and sediment transport are widely recognized to be the principal controls on the lifespan of mountain ranges but the factors controlling the rate of erosion and the reasons why they seem to vary significantly as a function of tectonic activity remain controversial here we use computational simulations to show that the key to understanding variations in the rate of erosion between tectonically active and inactive mountain ranges may relate to a bidirectional coupling between bedrock river incision and landslides whereas fluvial incision steepens surrounding hillslopes and increases landslide frequency landsliding affects fluvial erosion rates in two fundamentally distinct ways on the one hand large landslides overwhelm the river transport capacity and cause upstream build up of sediment that protects the river bed from further erosion on the other hand in delivering abrasive agents to the streams landslides help accelerate fluvial erosion our models illustrate how this coupling has fundamentally different implications for rates of fluvial incision in active and inactive mountain ranges the coupling therefore provides a plausible physical explanation for the preservation of significant mountain range relief in old orogenic belts up to several hundred million years after tectonic activity has effectively ceased

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

differentiating the roles of lithology and uplift in the steepening of bedrock river long profiles an example from southeastern australia hack determined that the equilibrium river long profile on a single lithology is a straight line when plotted semi logarithmically deviation from this straight line may be an equilibrium response to lithological variation or disequilibrium following base level change the amount of deviation d ast at any point downstream of the point of departure from the semi log straight line can be measured by projection of the upstream equilibrium profile and subtraction of the actual stream elevation from the projected elevation comparisons between the values of d ast for a trunk and a tributary at their junction can be used to differentiate steepening as a result of base level change from lithologically induced steepening in the former case d ast represents the incision induced by the base level change and will be equal for the trunk and the tributary it is very unlikely that values of d ast will be equal in the case of lithologically induced steepening because d ast in an

cenozoic river profile development in the upper lachlan catchment se australia as a test of quantitative fluvial incision models 1 we have used early miocene valley filling basalts to reconstruct fluvial long profiles in the upper lachlan catchment se australia in order to use these as well constrained initial conditions in a forward model of fluvial incision many different fluvial incision algorithms have been proposed and it is not clear at present which one of these best captures the behavior of bedrock rivers we test five different formulations the ability of these models to reproduce the observed present day stream profiles and amounts of incision is assessed using a weighted mean misfit criterion as well as the structure of the misfit function the results show that for all models parameter combinations can be found that reproduce the amounts of incision reasonably well however for some models these best fit parameter combinations do not seem to have a physical significance whereas for some others best fit parameter combinations are such that the models tend to mimic the behavior of other models overall best fit model predictions are obtained for a detachment limited stream power model or an undercapacity model that includes a river width term that varies as a function of drainage area the uncertainty in initial conditions does not have a strong impact on model outcomes the model results suggest however that lithological variation may be responsible for variations in parameter values of a factor of 3 5

lignin depolymerization products as biomarkers of the organic matter sedimentary record in 210pb 137cs dated lake sediments abstract the composition and concentration of lignin phenols used as biomarkers of organic matter quality gradients and granulometric and mineral composition were studied in order to document land cover variations in a dated using the 210 pb method validated with 137 cs distribution sediment core from a small lake pusty staw in the coastal baltic sea area substantial gradients were found in the granulometric composition these were attributed to varying erosion caused by deforestation and afforestation of the catchment area extrapolation of the dating to deep core layers showed that the deforestation layer originated from 1730 ad close to a period of deforestation found in historical records the core dating was validated by matching a peak in the 137 cs profile with the 1986 chernobyl accident changes in the use of the catchment area caused substantial shifts in organic matter composition and quality as suggested by the gradients of syringyl s cinnamyl c and vanillic v phenols derived from cuo alkaline oxidation of lignin the lignin component of the sedimentary organic matter originated primarily from angiosperm woody material s v 0 8 c v 0 4 a new lignin parameter called delta indicating the burden of lignin derived organic matter deposited in sediments with mineral matter shows changes between the uppermost and middle zones of the core an increased ratio of vanillic acid ad to vanillone al in the uppermost sediment layers was noticed and attributed to the inflow of degraded organic matter washed out from the catchment area soil principal component and cluster analysis indicated the lignin load and quality as the main factors distinguishing the organic material in the core sections both the lignin load and quality gradients were in agreement with the lithology of the core showing the steepest gradients at the boundaries of core sections deposited prior to after the deforestation afforestation events

adcp referenced geostrophic circulation in the bering sea basin abstract a month long circumnavigation of the bering sea basin in august 1991 was designed to study the basin scale circulation for the first time in this region vessel mounted acoustic doppler current profiler adcp measurements provided an absolute reference for geostrophic currents transport in the alaskan stream 01 1500 db was 24 sv sv 106 m3 s 1 westward considerably higher than the 10 15 sv usually inferred from geostrophic calculations referred to 1500 db but in good agreement with previous work relative to moored current meters as previously reported the stream separated from the aleutian ridge forming an anticyclonic eddy that restricted inflow to the bering sea flow through the aleutians varied substantially across the passes the kamchatka current was traceable for 800 km until it left the bering sea carrying 14 sv 0 3000 db eddies were detected from the clustering of centers of curvature of sequential adcp vectors incompletely spanned eddies can bias transports counterrotat

a brief review of the process domain concept and its application to quantifying sediment dynamics in bedrock canyons terra nova 00 000 000 2010 abstract bedrock canyons are most likely to be present in the upper and middle portions of river systems process domains which are spatially identifiable areas characterized by distinct suites of geomorphic processes that govern sediment dynamics provide a conceptual framework for understanding the input storage and transport of unconsolidated material along rivers in bedrock canyons this article introduces and briefly illustrates how process domains can be used to develop a first order categorization of spatial variation in sediment dynamics at the catchment scale using topographic maps or digital elevation models process domains distinguished using parameters of valley geometry readily obtainable from topographic data e g gradient ratio of channel width to valley bottom width effectively delineate steep narrow canyon segments closely coupled to adjacent hillslopes and shallower wider canyon segments with greater alluvial storage the poudre river in colorado usa provides an example of the delineation of process domains and of the implications of these delineations for understanding sediment dynamics

flexural models of continental lithosphere based on the long term erosional decay of topography summary the most easily observed geophysical characteristic of continents is their surface topography topographic power in the spectral range 1000 100 km has been computed for north american geological provinces and is found to decrease systematically as the tectonic age of the underlying crust increases these data have been quantitatively modelled in terms of topographic erosion and stress relaxation within the continental lithosphere through geological time spans the lithosphere is treated as a thin maxwell viscoelastic plate which deforms flexurally in response to the vertical surface loads of topography and its erosion effective rheological model parameters are flexural rigidity d a measure of the lithosphere s elastic strength and viscous relaxation time constant a measure of its viscosity erosion is assumed to occur at a rate linearly proportional to the height of topography at any given time the proportionality being determined by the erosion time constant the models are constructed in space and time frequency domains using simple linear systems theory two loading schemes are considered model 1 assumes that a flexurally competent lithosphere is suddenly loaded by topography which subsequently erodes whereas model 2 ignores the emplacement and erosion of topography during orogenesis when the lithosphere is thermally activated and considers only the load effected by erosion beginning some time later when the lithosphere has cooled and strengthened both models predict that the remnant topography of very old regions such as the canadian shield can be maintained in fact is favoured by a viscoelastic lithosphere with as small as 1 10ma the continued existence of such topography does not necessarily imply significant long term lithospheric strength model 1 results indicate low values of the flexural rigidity d 1021 1022nm which are interpreted to characterize not so much presentday d but that which was effective when topography was formed model 2 more successfully reproduces the data and constrains the product d to values 1024 1025nm ma which compare very favourably to those found from studies of individual loads on continental lithosphere the model results show that the erosion time constant is probably wavenumber dependent and falls in the range 200 400ma for the topographic wavelengths under consideration

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

sediment and rock strength controls on river incision into bedrock recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply challenging the common assumption that incision rate is simply proportional to stream power our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits maximum erosion rates occur at a critical level of coarse grained sediment supply where the bedrock is only partially exposed fine grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate furthermore we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief

bed load transport i mechanical characteristics this paper deals with the mechanical characteristics of saltation of bed load transport in flowing water experiments have been carried out by means of high speed photography and advanced data processing techniques taking saltation as the mode of bed load transport systematic analysis has been made with regard to the forces acting on grains and the variation of their magnitudes along the saltation trajectories to obtain the kinematic and dynamic properties of these grains moveover the relations between magnitudes of saltation parameters and flow intensity are attained from the measured data some parameters in bagnold s theory of bed load transport are also discussed

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

colorado river long profile metrics knickzones and their meaning abstract the numerical analysis of river long profiles has a rich history and is experiencing a rejuvenation with the advent of improved terrain models and computational tools the highly variable profile and the unusual hydrology of the green colorado river system crossing the colorado plateau provide an example that is germane to debates about transient versus equilibrium knickzone features about the controls of baselevel change due to drainage integration or differential uplift and the role of adjustments to climate hydrology and changing bedrock in order to explore these controls in more detail we define objective geologic study reaches along the green colorado river calculate unit stream power and develop a discharge adjusted steepness index kqsn that avoids the scaling assumptions in substituting contributing area for discharge which are erroneous in this dryland setting determining the nature of knickzones is key and the colorado plateau is a prime setting for study because of the legacy of previous work and a burst of new research and debate the four canyon knickzones along the green colorado are characterized by energy expenditure an order of magnitude greater than in intervening reaches and our kqsn proxy tracks stream power well the strong coincidence of the grand canyon cataract canyon and eastern uinta knickzones with stronger bedrock and mass movement inputs suggests they are pinned equilibrium adjustments to greater bed resistance with the possible exception of desolation canyon as a transient feature marked by anomalous profile convexity along the trunk drainage the knickzone anomalies become greater downstream this and patterns of kqsn in headwater tributaries correspond to some proposed sources of broad mantle driven uplift but they do not match other proposed uplift patterns thus a poorly understood decoupling of topography and proposed uplift exists in some regions

causes of concavity in longitudinal profiles of rivers a smooth concave configuration represents the most common quasi equilibrium profile of alluvial rivers in the present paper a generalized unified set of models for the longitudinal profile of rivers is presented various independent effects that drive concavity in longitudinal rivers are considered and classified the driving mechanisms considered here are 1 horizontal wavelike progradation of the river profile 2 abrasion of bed particles 3 aggradation of the river profile balancing subsidence at a constant speed and 4 the effect of tributaries adding sediment and water to the main stem of the river for simplicity it is assumed that the long term supply of water and sediment is constant hence a single discharge that is bank full discharge is used as an approximate characterization of the hydrologic regime for each point along the river sediment sorting has been studied elsewhere and is excluded from this analysis the river is assumed to have uniform bed material although the mean size may vary downstream it is concluded that the quasi equilibrium longitudinal profile created by each of the first three driving mechanisms mentioned above is concave the degree of concavity varies however depending on a set of physical conditions that can be identified by a set of dimensionless numbers a comparison of these numbers reveals the relative importance of the driving mechanisms for concavity a condition for concavity driven by the fourth mechanism that is tributary input is delineated