The role of channel morphology on the mobility and dispersion of bed sediment in a small gravel‐bed stream

This study uses a unique 10‐year tracer dataset from a small gravel‐bed stream to examine bed mobility and sediment dispersion over long timescales and at a range of spatial scales. Seasonal tracer data that captured multiple mobilizing events was examined, while the effects of morphology on bed mobility and sediment dispersion were captured at three spatial scales: within morphological units (unit scale), between morphological units (reach scale) and between reaches with different channel morphologies (channel scale). This was achieved by analyzing both reach‐average mobility and travel distance data, as well as the development of ‘mobility maps’ that capture the spatial variability in tracer mobility within the channel. The tracer data suggest that sediment transport in East Creek remains near critical the majority of the time, with only rare large events resulting in high mobility rates and grain travel distances large enough to move sediment past dominant bedforms. While a variable capturing both the magnitude and frequency of flow events within a season yielded a better predictor to sediment mobility and dispersion than peak discharge alone, the distribution of events of different magnitude within the season played a large role in determining tracer mobility rates and travel distances. The effects of morphology differed depending on the analysis scale, demonstrating the importance of scale, and therefore study design, when examining the effect of morphology on sediment transport. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluating fine sediment mobilization and storage in a gravel‐bed river using controlled reservoir releases

Two controlled flow events were generated by releasing water from a reservoir into the Olewiger Bach, located near Trier, Germany. This controlled release of near bank‐full flows allowed an investigation of the fine sediment (<63 µm) mobilized from channel storage. Both a winter (November) and a summer (June) release event were generated, each having very different antecedent flow conditions. The characteristics of the release hydrographs and the associated sediment transport indicated a reverse hysteresis with more mass, but smaller grain sizes, moving on the falling limb. Fine sediment stored to a depth of 10 cm in the gravels decreased following the release events, indicating the dynamic nature and importance of channel‐stored sediments as source materials during high flow events. Sediment traps, filled with clean natural gravel, were buried in riffles before the release of the reservoir water and the total mass of fine sediment collected by the traps was measured following the events. Twice the mass of fine sediment was retained by the gravel traps compared with the natural gravels, which may be due to their altered porosity. Although the amount of fine sediment collected by the traps was not significantly related to measures of gravel structure, it was found to be significantly correlated to measures of local flow velocity and Froude number. A portion of the traps were fitted with lids to restrict surface exchange of water and sediment. These collected the highest amounts of event‐mobilized sediments, indicating that inter‐gravel lateral flows, not just surface infiltration of sediments, are important in replenishing and redistributing the channel‐stored fines. These findings regarding the magnitude and direction of fine sediment movement in gravel beds are significant in both a geomorphic and a biological context. Copyright © 2006 John Wiley & Sons, Ltd.     

Regionalizing mean annual flow and daily flow variability for basin‐scale sediment and nutrient modelling

River discharges vary strongly through time and space, and quantifying this variability is fundamental to understanding and modelling river processes. The river basin is increasingly being used as the unit for natural resource planning and management; to facilitate this, basin‐scale models of material supply and transport are being developed. For many basin‐scale planning activities, detailed rainfall‐runoff modelling is neither necessary nor tractable, and models that capture spatial patterns of material supply and transport averaged over decades are sufficient. Nevertheless, the data to describe the spatial variability of river discharge across large basins for use in such models are often limited, and hence models to predict river discharge at the basin scale are required. We describe models for predicting mean annual flow and a non‐dimensional measure of daily flow variability for every river reach within a drainage network. The models use sparse river gauging data, modelled grid surfaces of mean annual rainfall and mean annual potential evapotranspiration, and a network accumulation algorithm. We demonstrate the parameterization and application of the models using data for the Murrumbidgee basin, in southeast Australia, and describe the use of these predictions in modelling sediment transport through the river network. The regionalizations described contain less uncertainty, and are more sensitive to observed spatial variations in runoff, than regionalizations based on catchment area and rainfall alone. Copyright © 2006 John Wiley & Sons, Ltd.     

Modelling of sediment dynamics in a laboratory‐scale experimental catchment

The variability of hillslope form and function is examined experimentally using a simple model catchment in which most landscape development parameters are either known or controlled. It is demonstrated that there is considerable variability in sediment output from similar catchments, subjected to the same hydrological processes, and for which the initial hillslope profiles are the same. The results demonstrate that, in the case of catchments with a linear initial hillslope profile, the sediment output is initially high but reduces through time, whereas for a concave initial profile the sediment output was smaller and relatively constant. Concave hillslope profiles also displayed reduced sediment output when compared with linear slopes with the same overall slope. Using this experimental model catchment data, the SIBERIA landscape evolution model was tested for its ability to predict temporal sediment transport. When calibrated for the rainfall and erodible material, SIBERIA is able to simulate mean temporal sediment output for the experimental catchment over a range of hillslope profiles and rainfall intensities. SIBERIA is also able to match the hillslope profile of the experimental catchments. The results of the study provide confidence in the ability of SIBERIA to predict temporal sediment output. The experimental and modelling data also demonstrate that, even with all geomorphic and hydrological variables being known and/or controlled, there is still a need for long‐term stream gauging to obtain reliable assessments of field catchment hydrology and sediment transport. Copyright © 2005 John Wiley & Sons, Ltd.     

Dynamics of suspended sediment transport at field‐scale drain channels of irrigation‐dominated watersheds in the Sonoran Desert,southeastern California

Suspended sediment is a major source of pollution in irrigation‐dominated watersheds. However, little is known about the process and mechanisms of suspended sediment transport in drain channels directly connected to agricultural fields. This paper explains sediment dynamics using averaged 5 min flow discharge Q (m³ s^?1) and suspended sediment concentration C (mg l^?1) collected during one crop season in a small catchment containing a first‐order drain channel and its connected six agricultural fields within the Salton Sea watershed. The statistical properties and average trends of Q and C were investigated for both early (i.e. November) and late (i.e. January) stages of a crop season. Further in‐depth analysis on sediment dynamics was performed by selecting two typical single‐field irrigation events and two multiple‐field irrigation events. For each set of irrigation events, the process of suspended sediment transport was revealed by examining hydrograph and sediment graph responses. The mechanisms underlying suspended sediment transport were investigated by analysing the types of corresponding hysteresis loop. Finally, sediment rating curves for both hourly and daily data at early and late stages and for the entire crop season were established to seek possible sediment‐transport predictive model(s). The study suggests that the complicated processes of suspended sediment transport in irrigation‐dominated watersheds require stochastic rather than deterministic forecasting. Copyright © 2007 John Wiley & Sons, Ltd.     

Bedload tracing in a high‐sediment‐load mountain stream

This paper reports a radiofrequency identification (RFID) tracing experiment implemented in a high‐sediment‐load mountain stream typical of alpine gravel‐bed torrents. The study site is the Bouinenc Torrent, a tributary to the Bléone River in southeast France that drains a 38·9‐km² degraded catchment. In spring 2008, we deployed 451 tracers with b‐axis ranging from 23 to 520 mm. Tracers were seeded along eight cross‐sections located in the upstream part of the lowest 2·3 km of the stream. Three tracer inventories were implemented in July 2008, 2009 and 2010. Recovery rates calculated for mobile tracers declined from 78% in 2008 to 45% in 2009 and 25% in 2010. Observations of tracer displacement revealed very high sediment dispersion, with frontrunners having travelled more than 2 km only three months after their deployment. The declining recovery rate over time was interpreted as resulting from rapid dispersion rather than deep burial. We evaluated that 64% of the tracers deployed in the active channel were exported from the 2·3‐km study reach three years after the onset of the tracing experiment. Travel distances were characterized by right‐skewed and heavy‐tailed distributions, correctly fitted by a power‐law function. This supports the idea that in gravel‐bed rivers with abundant sediment supply relative to transport capacity, bedload transport can be viewed as a superdiffusive sediment dispersion process. It is also shown that tracers initially deployed in the low‐flow channel were characterized by a 15‐ to 30‐fold increase of mobility compared to tracers deployed in gravel bars. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydro‐morphodynamic evolution in a 90° movable bed discordant confluence with low discharge ratio

Confluences with low discharge and momentum ratios, where narrow steep tributaries with high sediment load join a wide low‐gradient main channel that provides the main discharge, are often observed in high mountain regions such as in the upper‐Rhone river catchment in Switzerland. Few existing studies have examined the hydro‐morphodynamics of this type of river confluence while considering sediment discharge in both confluent channels. This paper presents the evolution of the bed morphology and hydrodynamics as observed in an experimental facility with a movable bed. For that purpose, one experiment was carried out in a laboratory confluence with low discharge and momentum ratios, where constant sediment rates were supplied to both flumes. During the experiment, bed topography and water surface elevations were systematically recorded. When the bed topography reached a steady state (so‐called equilibrium) and the outgoing sediment rate approximated the incoming rate, flow velocity was measured at 12 different points distributed throughout the confluence, and the grain size distribution of the bed surface was analyzed. Typical morphodynamic features of discordant confluences such as a bank‐attached bar and a flow deflection zone are identified in this study. Nevertheless, the presence of a marked scour hole in the discordant confluence and distinct flow regimes for the tributary and main channel, differ from results obtained in previous studies. Strong acceleration of the flow along the outer bank of the main channel is responsible for the scour hole. This erosion is facilitated by the sediment discharge into the confluence from the main channel which inhibits bed armoring in this region. The supercritical flow regime observed in the tributary is the hydrodynamic response to the imposed sediment rate in the tributary. Copyright © 2015 John Wiley & Sons, Ltd.     

Channel response to an extreme flood and sediment pulse in a mixed bedrock and gravel‐bed river

We exploit a natural experiment caused by an extreme flood (~500 year recurrence interval) and sediment pulse derived from more than 2500 concurrent landslides to explore the influence of valley‐scale geomorphic controls on sediment slug evolution and the impact of sediment pulse passage and slug deposition and dispersion on channel stability and channel form. Sediment slug movement is a crucial process that shapes gravel‐bed rivers and alluvial valleys and is an important mechanism of downstream bed material transport. Further, increased bed material transport rates during slug deposition can trigger channel responses including increases in lateral mobility, channel width, and alluvial bar dominance. Pre‐ and post‐flood LiDAR and aerial photographs bracketing the 2007 flood on the Chehalis River in south‐western Washington State, USA, document the channel response with high spatial and temporal definition. The sediment slug behaved as a Gilbert Wave, with both channel aggradation and sequestration of large volumes of material in floodplains of headwaters' reaches and reaches where confined valleys enter into broad alluvial valleys. Differences between the valley form of two separate sub‐basins impacted by the pulse highlight the important role channel and channel‐floodplain connectivity play in governing downstream movement of sediment slug material. Finally, channel response to the extreme flood and sediment pulse illustrate the connection between bed material transport and channel form. Specifically, the channel widened, lateral channel mobility increased, and the proportion of the active channel covered by bars increased in all reaches in the study area. The response scaled tightly with the relative amount of bed material sediment transport through individual reaches, indicating that the amount of morphological change caused by the flood was conditioned by the simultaneous introduction of a sediment pulse to the channel network. Copyright © 2015 John Wiley & Sons, Ltd.     

Application of the SHETRAN basin‐scale,landslide sediment yield model to the Llobregat basin,Spanish Pyrenees

The first application of the SHETRAN basin‐scale, landslide erosion and sediment yield model is carried out for a major landsliding event in the upper 505 km² of the Llobregat basin, in the eastern Spanish Pyrenees, in November 1982. The model simulates the spatial distribution of shallow landslides and their sediment yield. Acknowledging uncertainty in the model parameter evaluation, the aim of the application was not to reproduce the observed occurrence of landslides as accurately as possible with one simulation, but to bracket the observed pattern with several simulations representing uncertainty in the key input conditions. Bounds on the landslide simulations were thus determined as a function of uncertainty in the vegetation root cohesion (used in the model factor of safety calculations). The resulting upper bound considerably overestimates the observed pattern (17 000 landslides compared with an observation of around 700), but it reproduces several of the principal clusters in the observed pattern. The lower bound contains around 500 landslides. The sediment yield estimates (2670–14 630 t km^?2) are comparable to measurements elsewhere in the Pyrenees for extreme events. The results demonstrate an ability to simulate the basin‐scale landslide response to a rainfall event and the resulting sediment yield. They also highlight the need for further research in setting the uncertainty bounds and in avoiding large overestimates of landslide occurrence arising in part from a current inability to model small‐scale controls for a basin of the given size. Copyright © 2006 John Wiley & Sons, Ltd.     

Fine‐grained bed sediment storage within the main channel systems of the Frome and Piddle catchments,Dorset, UK

Lowland permeable catchments in the UK are particularly prone to sedimentation problems, on account of the increased fine sediment loadings generated by recent land‐use change and their stable seasonal hydrological regimes, which are frequently depleted by groundwater abstraction. Fine‐grained sediment storage on the bed of the main channel systems of the Frome (437 km²) and Piddle (183 km²) catchments, Dorset, UK, has been examined at 29 sites using a sediment remobilization technique. Measurements encompassed the period February 2003–July 2004. At individual sites in the Frome, average values ranged between 410 and 2630 g m^?2, with an overall mean of 918 g m^?2. In the Piddle, the average values for individual sites varied between 260 and 4340 g m^?2, with an overall mean of 1580 g m^?2. Temporal variations in fine bed sediment storage at each site were appreciable, with the coefficients of variation ranging between 43 and 155% in the Frome and between 33 and 160% in the Piddle. Average reach‐scale specific bed sediment storage increased markedly downstream along each main stem from 2 to 29 t km^?1 (Frome) and from 4 to 19 t km^?1 (Piddle). Total fine sediment storage on the channel bed of the Frome varied between 479 t (5 t km^?1) and 1694 t (17 t km^?1), with a mean of 795 t (7 t km^?1), compared with between 371 t (5 t km^?1) and 1238 t (14 t km^?1) with a mean of 730 t (9 t km^?1) in the Piddle. During the study period, fine bed sediment storage was typically equivalent to 18% (Frome) and 57% (Piddle) of the mean annual suspended sediment flux at the study catchment outlets. Copyright © 2006 John Wiley & Sons, Ltd.     

Suspended sediment dynamics in a steep,glacier‐fed mountain stream,Place Creek,Canada

This study examined suspended sediment concentration (SSC) during the ablation seasons of 2000 and 2001 in Place Creek, Canada, a steep, glacier‐fed mountain stream. Comparison of stream flow in Place Creek with that in an adjacent, almost unglacierized catchment provided a rational basis for separating the ablation seasons into nival, nival–glacial, glacial and autumn recession subseasons. Distinct groupings of points in plots of electrical conductivity against discharge supported the validity of the subseasonal divisions in terms of varying hydrological conditions. Relationships between SSC and discharge (Q) varied between the two study seasons, and between subseasons. Hysteresis in the SSC–Q relationship was evident at both event and weekly time‐scales. Some suspended sediment released from pro‐glacial Place Lake (the source of Place Creek) appeared to be lost to channel storage at low flows, especially early in the ablation season, with re‐entrainment at higher flows. Multiple regression models were derived for the subseasons using predictor variables including Q, Q², the change in Q over the previous 3 h, cumulative discharge over the ablation season, total precipitation over the previous 24 h and SSC measured at 1500 hours as an index value for each day. The models produced adjusted R² values ranging from 0·71 to 0·91, and provided tentative insights into the differences in SSC dynamics amongst subseasons. Introduction of the index value of SSC significantly improved the model fit during the nival–glacial and glacial subseasons for both years, as it adjusts the model to the current condition of sediment supply. Copyright © 2003 John Wiley & Sons, Ltd.     

Spatial and temporal patterns of sediment storage over 45 years in Carnation Creek,BC, a previously glaciated mountain catchment

The movement of sediment through mountain river networks remains difficult to predict, as processes beyond streamflow and particle size are responsible for the entrainment and transport of bedload sediment. In deglaciated catchments, additional complexity arises from glacial impacts on landscape organization. Research to date indicates that the quantity of sediment stored in the channel is an important component of sediment transport in systems which alternate between supply and transport limited states, but limited long-term field data exist which can capture storage-transfer dynamics over a timescale encompassing episodic supply typical of mountain streams. We use a 45-year dataset with annual and decadal-scale data on sediment storage, channel morphology, and wood loading to investigate the spatial and temporal organization of storage in Carnation Creek, a previously glaciated 11 km² catchment on Vancouver Island, British Columbia. Sediment is supplied episodically to the channel, including additions from debris flows in the early 1980s just upstream of the studied channel region. Analyzing the spatial and temporal organization of sediment storage along 3.0 km of channel mainstem reveals a characteristic storage wavelength similar to the annual bedload particle travel distance. Over time, two scales of variation in storage are observed: small-scale fluctuation of 3–10 years corresponding to local erosional and depositional processes, and larger scale response over 25–35 years related to supply of sediment from hillslopes. Complex relationships between storage and sediment transfer (i.e., annual change in storage) are identified, with decadal-scale hysteresis present in storage-transfer relations in sites influenced by hillslope sediment and logjams. We propose a conceptual model linking landscape organization to temporal variability in storage and to storage–export cycles. Collectively, our results reaffirm the importance of storage to sediment transport and channel morphology, and highlight the complexity of storage–transport interactions. © 2019 John Wiley & Sons, Ltd.     

Morphological responses and sediment processes following a typhoon‐induced dam failure,Dahan River,Taiwan

The rates and styles of channel adjustments following an abrupt and voluminous sediment pulse are investigated in the context of site and valley characteristics and time‐varying sediment transport regimes. Approximately 10.5 x 10⁶ m³ of stored gravel and sand was exposed when Barlin Dam failed during Typhoon WeiPa in 2007. The dam was located on the Dahan River, Taiwan, a system characterized by steep river gradients, typhoon‐ and monsoon‐driven hydrology, high, episodic sediment supply, and highly variable hydraulic conditions. Topography, bulk sediment samples, aerial photos, and simulated hydraulic conditions are analyzed to investigate temporal and spatial patterns in morphology and likely sediment transport regimes. Results document the rapid response of the reservoir and downstream channel, which occurred primarily through incision and adjustment of channel gradient. Hydraulic simulations illustrate how the dominant sediment transport regime likely varies between study periods with sediment yield and caliber and with the frequency and duration of high flows. Collectively, results indicate that information on variability in sediment transport regime, valley configuration, and distance from the dam is needed to explain the rate and pattern of morphological changes across study periods. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of storms during drought on post‐wildfire recovery of channel sediment dynamics and habitat in the southern California chaparral,USA

Current global warming projections suggest a possible increase in wildfire and drought, augmenting the need to understand how drought following wildfire affects the recovery of stream channels in relation to sediment dynamics. We investigated post‐wildfire geomorphic responses caused by storms during a prolonged drought following the 2013 Springs Fire in southern California (USA), using multi‐temporal terrestrial laser scanning and detailed field measurements. After the fire, a dry‐season dry‐ravel sediment pulse contributed sand and small gravel to hillslope‐channel margins in Big Sycamore Creek and its tributaries. A small storm in WY 2014 generated sufficient flow to mobilize a portion of the sediment derived from the dry‐ravel pulse and deposited the fine sediment in the channel, totaling ~0.60 m³/m of volume per unit length of channel. The sediment deposit buried step‐pool habitat structure and reduced roughness by over 90%. These changes altered sediment transport characteristics of the bed material present before and after the storm; the ratio of available to critical shear stress (τ_o/τ_c) increased by five times. Storms during WY 2015 contributed additional fine sediment from tributaries and lower hillslopes and hyperconcentrated flow transported and deposited additional sediment in the channel. Together these sources delivered sediment on the order of six times that in 2014, further increasing τ_o/τ_c. These storms during multi‐year drought following wildfire transformed channel dynamics. The increased sediment transport capacity persisted during the drought period characterized by the longer residence time of relatively fine‐grained post‐fire channel sedimentation. This contrasts with wetter years, when post‐fire sediment is transported from the fluvial system during the same season as the post‐fire sediment pulse. Results of this short‐term study highlight the complex and substantial effects of multi‐year drought on geomorphic responses following wildfire. These responses influence pool habitat that is critical to longer‐term post‐wildfire riparian ecosystem recovery. Copyright © 2017 John Wiley & Sons, Ltd.     

Coarse sediment transport in mountain streams in Colorado and Wyoming,USA

Since the early 1990s, US Forest Service researchers have made thousands of bedload measurements in steep, coarse‐grained channels in Colorado and Wyoming, USA. In this paper we use data from 19 of those sites to characterize patterns and rates of coarse sediment transport for a range of channel types and sizes, including step–pool, plane‐bed, pool–riffle, and near‐braided channels. This effort builds upon previous work where we applied a piecewise regression model to (1) relate flow to rates of bedload transport and (2) define phases of transport in coarse‐grained channels. Earlier, the model was tested using bedload data from eight sites on the Fraser Experimental Forest near Fraser, Colorado. The analysis showed good application to those data and to data from four supplementary channels to which the procedure was applied. The earlier results were, however, derived from data collected at sites that, for the most part, have quite similar geology and runoff regimes. In this paper we evaluate further the application of piecewise regression to data from channels with a wider range of geomorphic conditions. The results corroborate with those from the earlier work in that there is a relatively narrow range of discharges at which a substantial change in the nature of bedload transport occurs. The transition from primarily low rates of sand transport (phase I) to higher rates of sand and coarse gravel transport (phase II) occurs, on average, at about 80 per cent of the bankfull (1·5‐year return interval) discharge. A comparison of grain sizes moved during the two phases showed that coarse gravel is rarely trapped in the samplers during phase I transport. Moreover, the movement and capture of the D₁₆ to D₂₅ grain size of the bed surface seems to correspond with the onset of phase II transport, particularly in systems with largely static channel surfaces. However, while there were many similarities in observed patterns of bedload transport at the 19 studied sites, each had its own ‘bedload signal’ in that the rate and size of materials transported largely reflected the nature of flow and sediment particular to that system. Published in 2005 by John Wiley & Sons, Ltd.     

Hydrologic‐response‐driven sediment transport at a regional scale,process‐based simulation

Assessing hydrologically driven erosion at regional scales from a process‐based perspective presents a significant challenge. Most regional‐scale erosion assessments are based upon a simple steady‐state hydrology foundation. For this study, the sediment transport version of the physics‐based Integrated Hydrology Model (InHM), excited by synthetically generated rainfall, was employed to assess long‐term hydrologically driven erosion for a regional‐scale island boundary‐value problem. The spatiotemporal dynamics of runoff generation, erosion, and deposition are illustrated through saturation, water depth, velocity, and sediment concentration results. The simulations demonstrate that process‐based assessment for concept development is both feasible and tractable at regional spatial and human time scales. Copyright © 2011 John Wiley & Sons, Ltd.     

2D stream hydrodynamic,sediment transport and bed morphology model for engineering applications

A 2D depth‐averaged hydrodynamic, sediment transport and bed morphology model named STREMR HySeD is presented. The depth‐averaged sediment transport equations are derived from the 3D dilute, multiphase, flow equations and are incorporated into the hydrodynamic model STREMR. The hydrodynamic model includes a two‐equation turbulence model and a correction for the mean flow due to secondary flows. The suspended sediment load can be subdivided into different size classes using the continuum (two‐fluid) approach; however, only one bed sediment size is used herein. The validation of the model is presented by comparing the suspended sediment transport module against experimental measurements and analytical solutions for the case of equilibrium sediment‐laden in a transition from a rigid bed to a porous bed where re‐suspension of sediment is prevented. On the other hand, the bed‐load sediment transport and bed evolution numerical results are compared against bed equilibrium experimental results for the case of a meander bend. A sensitivity analysis based on the correction for secondary flow on the mean flow including the effect of secondary flow on bed shear stresses direction as well as the downward acceleration effect due to gravity on transverse bed slopes is performed and discussed. In general, acceptable agreement is found when comparing the numerical results obtained with STREMR HySeD against experimental measurements and analytical solutions. Copyright © 2007 John Wiley & Sons, Ltd.     

Gravel‐bed river evolution in earthquake‐prone regions subject to cycled hydrographs and repeated sediment pulses

Sediment often enters rivers in the form of sediment pulses associated with landslides and debris flows. This is particularly so in gravel‐bed rivers in earthquake‐prone mountain regions, such as Southwest China. Under such circumstances, sediment pulses can rapidly change river topography and leave the river in repeated states of gradual recovery. In this paper, we implement a one‐dimensional morphodynamic model of river response to pulsed sediment supply. The model is validated using data from flume experiments, so demonstrating that it can successfully reproduce the overall morphodynamics of experimental pulses. The model is then used to explore the evolution of a gravel‐bed river subject to cycled hydrographs and repeated sediment pulses. These pulses are fed into the channel in a fixed region centered at a point halfway down the calculational domain. The pulsed sediment supply is in addition to a constant sediment supply at the upstream end. Results indicate that the river can reach a mobile‐bed equilibrium in which two regions exist within which bed elevation and surface grain size distribution vary periodically in time. One of these is at the upstream end, where a periodic discharge hydrograph and constant sediment supply are imposed, and the other is in a region about halfway down the channel where periodic sediment pulses are introduced. Outside these two regions, bed elevation and surface grain size distribution reach a mobile‐bed equilibrium that is invariant in time. The zone of fluctuation‐free mobile‐bed equilibrium upstream of the pulse region is not affected by repeated sediment pulses under the scenarios tested, but downstream of the pulse region, the channel reaches different fluctuation‐free mobile‐bed equilibriums under different sediment pulse scenarios. The vertical bed structure predicted by the simulations indicates that the cyclic variation associated with the hydrograph and sediment pulses can affect the substrate stratigraphy to some depth. Copyright © 2017 John Wiley & Sons, Ltd.     

A catchment scale evaluation of the SIBERIA and CAESAR landscape evolution models

Landscape evolution models provide a way to determine erosion rates and landscape stability over times scales from tens to thousands of years. The SIBERIA and CAESAR landscape evolution models both have the capability to simulate catchment–wide erosion and deposition over these time scales. They are both cellular, operate over a digital elevation model of the landscape, and represent fluvial and slope processes. However, they were initially developed to solve research questions at different time and space scales and subsequently the perspective, detail and process representation vary considerably between the models. Notably, CAESAR simulates individual events with a greater emphasis on fluvial processes whereas SIBERIA averages erosion rates across annual time scales. This paper describes how both models are applied to Tin Camp Creek, Northern Territory, Australia, where soil erosion rates have been closely monitored over the last 10 years. Results simulating 10 000 years of erosion are similar, yet also pick up subtle differences that indicate the relative strengths and weaknesses of the two models. The results from both the SIBERIA and CAESAR models compare well with independent field data determined for the site over different time scales. Representative hillslope cross‐sections are very similar between the models. Geomorphologically there was little difference between the modelled catchments after 1000 years but significant differences were revealed at longer simulation times. Importantly, both models show that they are sensitive to input parameters and that hydrology and erosion parameter derivation has long‐term implications for sediment transport prediction. Therefore selection of input parameters is critical. This study also provides a good example of how different models may be better suited to different applications or research questions. Copyright © 2010 John Wiley & Sons, Ltd and Commonwealth of Australia     

A coupled sediment routing and lateral migration model for gravel‐bed rivers

We describe additions made to a multi‐size sediment routing model enabling it to simulate width adjustment simultaneously alongside bed aggradation/incision and fining/coarsening. The model is intended for use in single thread gravel‐bed rivers over annual to decadal timescales and for reach lengths of 1–10 km. It uses a split‐channel approach with separate calculations of flow and sediment transport in the left and right sides of the channel. Bank erosion is treated as a function of excess shear stress with bank accretion occurring when shear stress falls below a second, low, threshold. A curvature function redistributes shear stress to either side of the channel. We illustrate the model through applications to a 5·6‐km reach of the upper River Wharfe in northern England. The sediment routing component with default parameter values gives excellent agreement with field data on downstream fining and down‐reach reduction in bedload flux, and the width‐adjustment components with approximate calibration to match maximum observed rates of bank shifting give plausible patterns of local change. The approach may be useful for exploring interactions between sediment delivery, river management and channel change in upland settings. Copyright © 2011 John Wiley & Sons, Ltd.