ALBERT

Description: Abstract A deeper understanding of the sediment characteristics associated with the rock fragment content can improve our knowledge of the erosional processes and transport mechanisms of sediments on steep rocky slopes. This research used simulated rainfall experiments lasting for 1 h at a rate of 90 mm h‐1 and employed 5× 1 × 0.4 m parallel troughs filled with purple soils with different rock fragment volumetric contents (0, 5, 10, 20, 30 and 40%) on a 15° slope gradient. For each simulated event, runoff and sediment were sampled at 1‐ and 3‐min intervals, respectively, to study, in detail, the temporal changes in the size distributions of the eroded sediments. The results show that sediment concentrations, soil erosion rates and soil loss ratios significantly decreased as rock fragment content increased for rock fragment contents from 0 to 40% in purple soils. During the transportation process, clay particles often formed aggregates and were then transported as larger particles. Silt particles were more likely to be transported as primary particles with a low degree of sediment aggregation. Sand‐sized particles, which constituted a greater proportion of the original soil than the eroded sediments, were formed from other fine particles and transported as aggregates rather than as primary particles. Suspension–saltation, which mainly transports fine particles of 0.02‐0.05 mm and coarse particles larger than 0.5 mm in size, was the most important transport mechanism on steep rocky slopes. The results of this study can help to explain the inherent laws of erosional processes on steep rocky slopes and can provide a foundation for improving physical models of soil erosion.

Description: Abstract This paper aims to evaluate sources of uncertainty and variability associated with rock glacier inventories compiled from remotely sensed imagery. To this end, we ran three mapping exercises in Kaiserbergtal, Austria. To evaluate interactions between mapping style and imagery resolution, we asked six operators to map and assess the degree of activity of all rock glaciers they could identify: first, on Google Earth (GE) imagery, and then on a set of higher resolution orthophotos and LiDAR‐derived images (LO) (exercise 1). To compare mapping attributes on a common set of rock glaciers, we asked fourteen operators to delineate the outline of four designated rock glaciers (exercise 2) and to classify the activity of fifteen designated rock glaciers (exercise 3) on LO. Results show strikingly high inter‐operator variability. Specifically, we show that the number of mapped rock glaciers on GE can vary up to a factor of 3, and that using LO lowers this figure to a factor of 2, while producing an increase in the number of mapped landforms, which become systematically smaller (exercise 1). Examination of polygon outlines identifies highest inter‐operator variability at the transition with the rooting zone and, in polymorphic rock glaciers, on adjacent creeping lobes. Variability is higher for relict landforms (exercise 2). Operators’ activity assessments, evaluated against an independent quantitative activity index (RGI), display reasonable agreement for active and relict landforms, whereas inactive counterparts meet least consensus and therefore are problematic (exercise 3). We further show that this variability in mapping outcomes propagates across compound variables, and must considered when assessing uncertainties and confidence levels of environmental evaluations that rely on rock glacier inventories, such as the lower altitudinal limit of discontinuous permafrost, or water storage potential. We call for an international effort to establish guidelines for rock glacier classification and mapping, towards more homogeneous inventories.

Description: We record a real‐time, natural, field‐scale response of fluvial systems to lake level fall in the Dead Sea – analogues to continental shelf and slope emergence, including the evolution of the fluvial processes and the onset and intensification of sediment bypass. We demonstrate that hydroclimatology and shelf geometry potentially produce high spatio‐temporal variability in patterns of sediment routing of adjacent streams during low levels. We also discuss implications for fluvial responses to global sea level fall. Abstract Global eustatic lowstands can expose vast areas of continental shelves, and occasionally the shelf edge and the continental slope. The degree of fluvial connectivity to receding shores influences the redistribution of sediments across these emerging landscapes. Shelf and slope emergence in the Dead Sea since the middle of the 20th century, offers a rare opportunity to examine evolution of stream connectivity in response to continuous base‐level decline. We characterize the connectivity evolution of two streams, using high‐resolution time series of aerial imagery and elevation models, field mapping, and grain‐size analyses. Our rich spatiotemporal dataset of evolving channel geomorphology, sediment transport conditions, and sediment redistribution, allows calculating potential coarse sediment mobility in response to base level decline. Following shelf emergence, alluvial fans first prograded onto the low‐gradient shelf under unfavourable conditions for transporting coarse sediment to the regressing shoreline. Then, with shelf and slope emergence, the two adjacent streams evolved differently. The smaller, more arid watershed still maintains its highstand delta progradation on the shelf and is practically disconnected from the receding lake. The larger catchment, heading in wetter environments and having a narrower shelf, has incised the shelf and renewed and gradually intensified the sediment transport from the highstand to the lowstand delta. Sediment mobilization to lowstand shorelines is controlled by the evolution of the channel profile and by the average speed of gravel transport (10s‐100s m yr‐1). These findings from the Dead Sea are relevant to fluvial processes operating on continental shelves during glacial maxima. Streams would have commonly stored high proportions of their coarse sediment on the continental shelves rather than efficiently connecting with the lowstand level. Additionally, differences in sediment routing patterns should exist among nearby streams, primarily due to continental margin geometry and watershed hydrology. © 2019 John Wiley & Sons, Ltd.

Description: Abstract The morphodynamics of topographic expansion has been recently investigated both experimentally (Sittoni et al., 2014, Shaw et al., 2018) and numerically (Sittoni et al., 2014). Here, we study the basic mechanism that governs the evolution of topographic expansions and explore the instability of the bottom topography under conditions of steady but spatially expanding flow. We model the expanding flow via a configuration where water and sediments are supplied from a central hole and flow on a cone shaped surface confined by lateral walls. The governing equations are the shallow‐water equations coupled with the Exner equation, written in cylindrical coordinates. We initially approach the problem analytically by considering the conditions required for the basic state, consisting of a pure radial flow and bottom profile, to lose stability to small amplitude perturbations. This analysis suggests that more than one mode may be unstable, encouraging us to extend the analysis to the nonlinear regime. We do this through numerical modeling of the full governing equations, which allows us to predict the establishment of a bar pattern whose features are similar to those experimentally observed. Two prominent features of the finite‐amplitude bar pattern are (1) bar apices are distributed at radial distance from the inflow, consistent with work of Shaw et al. 2018; and (2) that the flow aspect ratio of the interbar areas remain high without provoking further instability. Both features imply that in general expansion acts to reduce bar development relative to an equivalent rectilinear flow. This article is protected by copyright. All rights reserved.

Description: Abstract Geomorphological controls and catchment sediment characteristics control the formation of floodplains and affect their capacity to sequester carbon. Organic carbon stored in floodplains is typically a product of pedogenic development between periods of mineral sediment deposition. However, in organically‐dominated upland catchments with a high sediment load, eroded particulate organics may also be fluvially deposited with potential for storage and/or oxidation. Understanding the redistribution of terrestrial carbon laterally, beyond the bounds of river channels is important, especially in eroding peatland systems where fluvial particulate organic carbon exports are often assumed to be oxidised. Floodplains have the potential to be both carbon cycling hotspots and areas of sequestration. Understanding of the interaction of carbon cycling and the sediment cascade through floodplain systems is limited. This paper examines the formation of highly organic floodplains downstream of heavily eroded peatlands in the Peak District, UK. Reconstruction of the history of the floodplains suggests that they have formed in response to periods of erosion of organic soils upstream. We present a novel approach to calculating a carbon stock within a floodplain, using XRF and radiograph data recorded during Itrax core scanning of sediment cores. This carbon stock is extrapolated to the catchment scale, to assess the importance of these floodplains in the storage and cycling of organic carbon in this area. The carbon stock estimate for the floodplains across the contributing catchments is between 3482‐13460 tonnes, equating on an annualised basis to 0.8‐4.5% of the modern‐day POC flux. Radiocarbon analyses of bulk organic matter in floodplain sediments revealed that a substantial proportion of organic carbon was associated with re‐deposited peat and has been used as a tool for organic matter source determination. The average age of these samples (3010 years BP) is substantially older than Infrared Stimulated Luminesence dating which demonstrated that the floodplains formed between 430‐1060 years ago. Our data suggest that floodplains are an integral part of eroding peatland systems, acting as both significant stores of aged and eroded organic carbon and as hotspots of carbon turnover.

Description: Abstract Beaches of tropical island coasts exhibit high levels of diversity in composition and form in comparison with their continental counterparts. To investigate the nature and origin of this diversity, individual beach morphology and sedimentology was investigated in the British Virgin Islands (BVI), a Caribbean archipelago of 〉 60 high volcanic and low reef islands. The islands exhibit a diversity of orientations (some facing the Atlantic and some the Caribbean), elevation and gradient, rock type and wave energy. An examination of 100 beaches in the archipelago revealed a first order division into sand (70 beaches) and coral rubble (30 beaches). These beaches occur in seven planform types (determined by the antecedent geological framework) and are further subdivided according to shoreface type (seagrass, sandy shoreface, or reef). Mainland‐attached headland‐embayment beaches are the most common form of sand beach while coral rubble beaches usually occur as barriers that enclose salt ponds and wetlands. Among sand beaches, carbonate content is greatest on Atlantic‐facing beaches, and coral rubble beaches are more common on Caribbean‐facing beaches. Grain size characteristics on sandy beaches are highly variable and range from fine to very coarse sands while coral rubble beaches range up to boulder‐sized clasts. The local source material is a primary determinant of sediment composition. The local factors such as the underlying geology, source and availability of sediments are the primary determinants of beach form, composition and texture in the BVI. Oceanographic and climatic conditions such as the prevailing easterly trade winds and waves which seasonally range in direction from east‐northeast to southeast as well as beach orientation to Atlantic or Caribbean facing waves also contribute to the variability, but in a secondary role.

Description: Abstract Landsliding usually occurs on specific hillslope aspect, which may reflect the control of specific geo‐environmental factors, triggering factors, or their interaction. To explore this notion, this study used island–wide landslide inventories of the Chi–Chi earthquake in 1999 (Mw = 7.6) and Typhoon Morakot in 2009 in Taiwan to investigate the preferential orientation of landslides and the controls of landslide triggers and geological settings. The results showed two patterns. The orientations of earthquake‐triggered landslides were toward the aspect facing away from the epicenter in areas with PGA ≥ 0.6 g and landslide ratio ≥ 1%, suggesting that the orientations were controlled by seismic wave propagation. Rainfall‐triggered landslides tended to occur on dip slopes, instead of the windward slopes, suggesting that geological settings were a more effective control of the mass wasting processes on hillslope scale than the rainfall condition. This study highlights the importance of the endogenic processes, namely seismic wave and geological settings, on the predesigned orientation of landslides triggered by either earthquake or rainfall, which can in turn improve our knowledge of landscape evolution and landslide prediction.

Description: Abstract For being able to understand year‐round river channel evolution both at present and in the future, the spatial variation of the flow characteristics and their sediment transport capabilities under ice cover need to be detected. As the measurements done through cross‐sectional drill holes cover only a small portion of the river channel area, the numerical simulations give insight into the wider spatial horizontal variation of the flow characteristics. Therefore, we simulate the ice‐covered flow with a hydrodynamic 2D model in a meandering subarctic river (Pulmanki River, Finland) in mid‐winter conditions and compare them to the pre‐winter open‐channel low flow situation. Based on the simulations, which are calibrated with reference measurements, we aim to detect 1) how ice‐covered mid‐winter flow characteristics vary spatially and 2) the erosion and sedimentation potential of the ice‐covered flow compared to open‐channel conditions. The 2D hydrodynamic model replicated the observed flow characteristics in both open‐channel and ice‐covered conditions. During both seasons, the greatest erosional forces locate in the shallow sections. The narrow, freely flowing channel area found in mid‐winter cause the main differences in the spatial flow variation between seasons. Despite the causes of the horizontal recirculating flow structures being similar in both seasons, the structures formed in different locations depending on whether the river was open or ice covered. The critical thresholds for particle entrainment are exceeded more often in open‐channel conditions than during ice‐covered flow. The results indicate spatially extensive sediment transport in open‐channel conditions, but that the spatial variability and differences in depositional and erosional locations increase in ice‐covered conditions. Asymmetrical bends and straight reaches erode throughout the year, whereas symmetrical, smaller bends mainly erode in open‐channel conditions and are prone to deposition in winter. The long ice‐covered season can greatly affect the annual morphology of the submerged channel.

Description: Abstract Accurately measuring river meander migration over time is critical for understanding how rivers function and respond to changes in hydrology or sediment supply. Current approaches often compare estimates of channel planform adjustment measured at different times and over dissimilar intervals. Empirical data and results from a probabilistic reduced complexity river migration model both confirm a temporal measurement‐scale dependence. The dependence is illustrated in systematic underestimations of migration rates measured over longer timescales that can confound comparisons of rates over time. For example, due to increased frequency of aerial image acquisition, comparing historical rates measured over decades to contemporary rates measured annually will necessarily favor the conclusion that contemporary migration rates have increased. We find that frequency of channel migration reversals exert the primary control on measurement bias for longer time intervals by erasing the record of migration. Furthermore, we conclude that without a sufficient number of short‐term migration measurements, extrapolations will distort long‐term sediment remobilization projections, sediment budgets, sediment flux estimates, and perceptions of fluvial change. In contrast, rates measured over timescales longer than 20‐25 years are more consistent, but tend to be underestimated due to channel reversals. We evaluate the role of timescale dependence for the Root River, a single threaded meandering sand‐ and gravel‐bedded river in southeastern Minnesota, USA, with 76 years of aerial photographs spanning an era of landscape changes that have drastically altered flows.

Description: Conceptual model of the daily subglacial sediment transport dynamics with flow cycle induced by melting ice integrating the glacial surface uplift. Phase c: before the critical transport capacity of coarse sediments is achieved (schematic cross‐section East–West of glacial tongue of the Haut Glacier d'Arolla with median supgraglacial moraine). Abstract Sediment export from glaciated basins involves complex interactions between ice flow, basal erosion and sediment transfer in subglacial and proglacial streams. In particular, we know very little about the processes associated with sediment transfer by subglacial streams. The Haut Glacier d'Arolla (VS, Switzerland) was investigated during the summer melt season of 2015. LiDAR survey revealed positive surface changes in the ablation zone, indicating glacier uplift, at the end of the morning during the period of peak ablation. Instream measures of sediment transport showed that suspended load and bedload responded differently to diurnal flow variability. Suspended load depended on the availability of fine material whereas bedload depended mainly on the competence of the flow. Interpretation of these results allowed development of a conceptual model of subglacial sediment transport dynamics. It is based upon the mechanisms of clogging (deposition) and flushing (transport/erosion) in sub‐glacial channels as forced by diurnal flow variability. Through the melt season, the glacier hydrological response evolves from being buffered by glacier snow cover with a poorly developed subglacial drainage system to being dominated by more rapid ice melt with a more hydraulically efficient subglacial channel system. The resultant changes in the shape of diurnal discharge hydrographs, and notably higher peak flows and lower base flows, causes sediment transport to become discontinuous, with overnight clogging and late morning flushing of subglacial channels. Overnight clogging may be sufficient to reduce subglacial channel size, creating temporarily pressurized flow and lateral transfer of water away from the subglacial channels, leading to the late morning glacier surface uplift. However, without further data, we cannot exclude other hypotheses for the uplift. © 2018 John Wiley & Sons, Ltd.

Description: Sedimentary architecture and a new concept for the development of polar gravel spits and the interplay of glacier retreat, glacio‐isostatic adjustment and coastal progradation is presented, allowing for the prediction of future developments. Abstract Sedimentary architecture and morphogenetic evolution of a polar bay‐mouth gravel‐spit system are revealed based on topographic mapping, sedimentological data, radiocarbon dating and ground‐penetrating radar investigations. Data document variable rates of spit progradation in reaction to atmospheric warming synchronous to the termination of the last glacial re‐advance (LGR, 0.45–0.25 ka BP), the southern hemisphere equivalent of the Little Ice Age cooling period. Results show an interruption of spit progradation that coincides with the proposed onset of accelerated isostatic rebound in reaction to glacier retreat. Spit growth resumed in the late 19th century after the rate of isostatic rebound decreased, and continues until today. The direction of modern spit progradation, however, is rotated northwards compared with the growth axis of the early post‐LGR spit. This is interpreted to reflect the shift and strengthening in the regional wind field during the last century. A new concept for the interplay of polar gravel‐spit progradation and glacio‐isostatic adjustment is presented, allowing for the prediction of future coastal evolution in comparable polar settings. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: We investigate the effect of water depth and turbidity on the water and sediment temperature and on the microphytobenthos growth in shallow water environments. The results show that the water temperature dynamics is poorly affected by turbidity variations, while the sediment temperature increases significantly in clear water conditions. Clear waters favor the microphytobenthos growth, suggesting the existence of a positive feedback between microphytobenthos' proliferation and water turbidity, given the bio‐stabilization provided by the microphytobenthos to the surface sediments. Abstract Shallow tidal environments (e.g. bays, estuaries, lagoons) represent one of the most productive ecosystems in the world, and they are threatened by current climate change and increasing human pressure. Monitoring the bio‐morphodynamic evolution of these environments is therefore a crucial task that requires a detailed and holistic scrutiny. The present study aims to investigate the temperature of the water–sediment continuum, its effect on the related microphytobenthos (MPB) growth and the related bio‐stabilization of the bed sediment surface under different water depth and water turbidity conditions. We investigated the vertical energy transfer and the temperature dynamics by applying a 1‐D model to a shallow coastal lagoon. Our results show that the water temperature does not substantially change under different turbidity conditions, whereas the sediment temperature exhibits important changes. Two major factors driving the MPB photosynthetic growth are the sediment surface temperature and the light availability at the sediment bed, which can both be computed using the vertical energy transfer model. We observed that, in general, clear water conditions better promote MPB growth over the entire year. The limiting factor for the photosynthetic process is usually the light availability at the bottom, which increases under clear water conditions. As MPB provides a bio‐stabilizing effect on the bed sediments by producing a biofilm on the sediment surface that reduces sediment resuspension, our results suggest a positive feedback between MPB growth and water column turbidity. Furthermore, MPB growth and the related sediment bio‐stabilization are clearly affected by the seasonal variation of surface sediment temperature and light availability. This seasonal variation of MPB growth rate and surface sediment bio‐stabilization must be considered when studying the long‐term morphodynamic evolution of tidal environments. ©  2018 John Wiley & Sons Ltd.

Description: The Equotip surface hardness tester has important applications in studies of rock and building stone weathering, but questions remain over the factors controlling the measurements and the impacts on vulnerable surfaces. Here, we demonstrate, for a range of porous sandstones, that moisture content has an important influence while surface roughness up to 800 microns does not. We use 3D optical microscopy to quantify the impact marks created using C and D probes under SIM and RIM methods. Abstract The Equotip rebound tester is a simple, non‐destructive technique to measure the surface hardness of materials. Having a low impact energy gives the Equotip advantages over the commonly used Schmidt Hammer on weathered rock and stone. In this study we have investigated the influence of different parameters (sample size, moisture content and surface roughness) on the surface hardness values obtained from freshly cut blocks of four types of sandstone. In a series of laboratory experiments both Single Impacts (SIM) and Repeat Impacts (RIM) methods have been used with C and D probes (which have different impact energies). Our results show that whilst sample size is of great importance we find that smaller samples can be reliably evaluated than previously reported. Moisture contents are also found to exert a more important influence on both SIM and RIM results than previously thought, with up to 26% lower hardness values recorded on saturated vs dry sandstone. Conversely, we find that surface roughness (over Sz values of 100 to 800 microns) does not have a significant impact on SIM measurements collected using the D probe. Both SIM and RIM data are found to be good proxies for compressive strength and open porosity, with SIM data collected with the C probe showing the best fits. Data collected using 3D microscopy helps visualize and quantify the small impact marks created by the Equotip and confirms that these are much reduced when using the C vs D probe. The results highlight the benefits of the Equotip to studies of the nature and deterioration of sandstone, the need for careful evaluation of any confounding factors which might influence the values obtained, and illustrate the different advantages of C and D probes. © 2019 John Wiley & Sons, Ltd.

Description: In desert regions, spatiotemporal variations in erosion and deposition are influenced by the behavior of individual plants as well as by larger plant communities. Here we present a realistic model of desert shrub dynamics that also possesses the granularity appropriate for geomorphic simulations. Developing more rigorous models of pertinent biotic processes and coupling them with existing sediment transport models can improve our understanding of complex shrub–sediment interactions across a broad range of scenarios (e.g. droughts, climate change, fires). Abstract Across arid landscapes, desert shrubs affect where and how sediment is transported by various physical processes such as overland flow, wind, and rain splash. Simplistic biological models such as logistic growth curves offer important first steps towards representing and linking life to landscape dynamics. More sophisticated descriptions of desert shrub dynamics on scales commensurate with downslope sediment transport, however, are essential for more rigorously understanding how complex shrub‐sediment interactions may be affecting hillslope geomorphology. Here we present such a model that features a strong biophysical foundation by including, for example, basic aspects of desert soil‐water hydrology and population ecology such as recruitment, growth, and mortality. Model input parameters can also be modified to account for the influence of different environmental conditions and stressors (e.g. precipitation, soil types, droughts, grazing, fires, and climate change). Model behaviors mimic well documented aspects of how desert shrub populations respond to changes in precipitation, for example, productivity decreases with increasingly arid conditions and density declines during prolonged periods of drought. Model output (position and size of shrubs occupying a hillslope in a given year) represents the basic biological input variables necessary for calculating, for example, how rain‐splash induced mound building by individual shrubs may be affecting downslope sediment fluxes. Future research aimed at coupling this biological model with existing sediment transport models can therefore help advance our understanding for how desert shrub populations affect hillslope erosion across a broad range of scenarios. © 2018 John Wiley & Sons, Ltd.

Description: The dynamics of wind flow over a small, 0.6 m high foredune scarp is investigated. For an incident oblique wind, an alongshore helicoidal flow is formed within a separation region along the scarp basal region. The flow at the scarp crest is compressed, streamlined and accelerated, turbulence is suppressed, and local jets may occur. Abstract The nature of wind flow over a small, 0.6 m high foredune scarp is investigated on the Sir Richard Peninsula, South Australia during a variety of incident wind directions and speeds. The study provides additional supporting evidence that the presence of the scarp and the dune exerts a strong influence on a landwards trending reduction in wind velocity and an increase in turbulence, with the greatest area of turbulence occurring near and at the foredune scarp base. For an incident oblique wind, an alongshore helicoidal flow is formed within a separation region along the scarp basal region. In this region, the coefficient of variation (CV) of wind speed is high and displays significant fluctuations. The flow at the scarp crest is compressed, streamlined and accelerated, turbulence is suppressed, and local jets may occur depending on the incident wind approach angle. Jets are more likely where the incident flow is perpendicular or nearly so. A flow separation region does not develop downwind of the scarp crest where the morphology of the foredune stoss slope downwind of the scarp is more convex (as in this case) rather than relatively flat, and possibly due to the presence of vegetation at the scarp crest. A tentative model of the flow regions developed across a backshore–scarp–foredune region during oblique incident flow is provided. © 2018 John Wiley & Sons, Ltd.

Description: The implementation of annual leaf area variations, as well as forest expansion and growth enhance the explanatory power and the prediction accuracy of the dynamic, physically based slope stability model STARWARS/PROBSTAB. The multi‐annual simulation of inherent properties and spatial development of land cover yields better predictive performance of the model and more conservative prediction of unstable areas compared with static land cover without inherent variations. Abstract Despite the importance of land cover on landscape hydrology and slope stability, the representation of land cover dynamics in physically based models and their associated ecohydrological effects on slope stability is rather scarce. In this study, we assess the impact of different levels of complexity in land cover parameterisation on the explanatory power of a dynamic and process‐based spatial slope stability model. Firstly, we present available and collected data sets and account for the stepwise parameterisation of the model. Secondly, we present approaches to simulate land cover: 1) a grassland landscape without forest coverage; 2) spatially static forest conditions, in which we assume limited knowledge about forest composition; 3) more detailed information of forested areas based on the computation of leaf area development and the implementation of vegetation‐related processes; 4) similar to the third approach but with the additional consideration of the spatial expansion and vertical growth of vegetation. Lastly, the model is calibrated based on meteorological data sets and groundwater measurements. The model results are quantitatively validated for two landslide‐triggering events that occurred in Western Austria. Predictive performances are estimated using the Area Under the receiver operating characteristic Curve (AUC). Our findings indicate that the performance of the slope stability model was strongly determined by model complexity and land cover parameterisation. The implementation of leaf area development and land cover dynamics further yield an acceptable predictive performance (AUC ~0.71‐0.75) and a better conservativeness of the predicted unstable areas (FoC ~0.71). The consideration of dynamic land cover expansion provided better performances than the solely consideration of leaf area development. The results of this study highlight that an increase of effort in the land cover parameterisation of a dynamic slope stability model can increase the explanatory power of the model. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: Unit bar and dune dynamics are quantified for the sandy braided South Saskatchewan River, Canada, using images captured from aeroplane, unmanned aerial vehicle (UAV) and satellite platforms. Dune and unit bar migration rates are spatially variable in response to local planform morphology. Sediment transport rates can be estimated for dunes and unit bars using plane and UAV images and Digital Surface Models (DSMs) but just 2D imagery, including from satellite platforms, may provide reasonable first‐order estimates of bed sediment flux. Abstract Images from specially‐commissioned aeroplane sorties (manned aerial vehicle, MAV), repeat unmanned aerial vehicle (UAV) surveys, and Planet CubeSat satellites are used to quantify dune and bar dynamics in the sandy braided South Saskatchewan River, Canada. Structure‐from‐Motion (SfM) techniques and application of a depth‐brightness model are used to produce a series of Digital Surface Models (DSMs) at low and near‐bankfull flows. A number of technical and image processing challenges are described that arise from the application of SfM in dry and submerged environments. A model for best practice is presented and analysis suggests a depth‐brightness model approach can represent the different scales of bedforms present in sandy braided rivers with low‐turbidity and shallow (〈 2 m deep) water. The aerial imagery is used to quantify the spatial distribution of unit bar and dune migration rate in an 18 km reach and three ~1 km long reaches respectively. Dune and unit bar migration rates are highly variable in response to local variations in planform morphology. Sediment transport rates for dunes and unit bars, obtained by integrating migration rates (from UAV) with the volume of sediment moved (from DSMs using MAV imagery) show near‐equivalence in sediment flux. Hence, reach‐based sediment transport rate estimates can be derived from unit bar data alone. Moreover, it is shown that reasonable estimates of sediment transport rate can be made using just unit bar migration rates as measured from 2D imagery, including from satellite images, so long as informed assumptions are made regarding average bar shape and height. With recent availability of frequent, repeat satellite imagery, and the ease of undertaking repeat MAV and UAV surveys, for the first time, it may be possible to provide global estimates of bedload sediment flux for large or inaccessible low‐turbidity rivers that currently have sparse information on bedload sediment transport rates. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: Historical aerial images show that vegetation cover has increased significantly in one of Australia's largest dune systems, the Younghusband Peninsula dunefield (SA). In the last seven decades, vegetation cover has changed from less than 7% to almost 40% (1949‐2017), increasing dune stabilization and forming parabolic dunes. The reduction of grazing by exotic rabbits was found to be the primary factor linked to the rapid modification of the vegetation cover and indirectly the geomorphology of the dunefield. Abstract Studies have shown that the impact of climate change, human and animal actions on coastal vegetation can turn stabilized dunes into active mobile dunes and vice versa. Yet, the driving factors that trigger vegetation changes in coastal dunes are still not fully understood. In the transgressive dunefields of the Younghusband Peninsula (south‐east coast of South Australia) historical aerial photographs show an increase in vegetation cover over the last ~70 years. This study attempts to identify the causes of the changes in vegetation cover (1949 to 2017) observed in a typical section of the coastal dune systems of the Peninsula. Vegetation cover was first estimated for various years using the available historical aerial photography (long‐term changes – 1949 to 2017) and recent satellite imagery (short‐term annual changes – 2010 to 2017) for the area, and then results were discussed against the observed changes in climatic variables and rabbit density, factors that could have played a role in this transformation. Results of long‐term changes show that the vegetation cover has increased significantly from 1949 to 2017, from less than 7% vegetation cover to almost 40%, increasing dune stabilization and forming parabolic dune systems. Periods with the largest growth in vegetation cover (1952‐1956 and 2009‐2013) coincide with a significant decline in rabbit numbers. Rabbit density was found to be the primary factor linked to the rapid vegetation growth and stabilization of the dunefield, for both decadal long‐term (last 68 years) and annual short‐term changes (last 8 years). Other factors such as changes in rainfall, aeolian sediment transport, land use practices, and the introduction of invasive plants have apparently played a limited to negligible role in this stabilization process. © 2018 John Wiley & Sons, Ltd.

Description: Topobathymetric airborne LiDAR, ‘Green LiDAR’, allows mapping of the riverscape at valley scale with meter‐scale resolution and errors, quantified as root mean square errors, against ground surveys of 0.11 m. Figure shows a three‐dimensional map (water flows from lower right corner to upper left corner, vertical length is 4 times exaggerated with respect to horizontal lengths) of Reach 2 from the LiDAR survey, which shows streambed topographical features from pools to riffles. Abstract Advances in topobathymetric LiDARs could enable rapid surveys at sub‐meter resolution over entire stream networks. This is the first step to improving our knowledge of riverine systems, both their morphology and role in ecosystems. The Experimental Advanced Airborne Research LiDAR B (EAARL‐B) system is one such topobathymetric sensor, capable of mapping both terrestrial and aquatic systems. Whereas the original EAARL was developed to survey littoral areas, the new version, EAARL‐B, was also designed for riverine systems but has yet to be tested. Thus, we evaluated the ability of EAARL‐B to map bathymetry and floodplain topography at sub‐meter resolution in a mid‐size gravel‐bed river. We coupled the EAARL‐B survey with highly accurate field surveys (0.03 m vertical accuracy and approximately 0.6 by 0.6 m resolution) of three morphologically distinct reaches, approximately 200 m long 15 m wide, of the Lemhi River (Idaho, USA). Both point‐to‐point and raster‐to‐raster comparisons between ground and EAARL‐B surveyed elevations show that differences (ground minus EAARL‐B surveyed elevations) over the entire submerged topography are small (root mean square error, RMSE, and median absolute error, M, of 0.11 m), and large differences (RMSE, between 0.15 and 0.38 m and similar M) are mainly present in areas with abrupt elevation changes and covered by dense overhanging vegetation. RMSEs are as low as 0.03 m over paved smooth surfaces, 0.07 m in submerged, gradually varying topography, and as large as 0.24 m along banks with and without dense, tall vegetation. EAARL‐B performance is chiefly limited by point density in areas with strong elevation gradients and by LiDAR footprint size (0.2 m) in areas with topographic features of similar size as the LiDAR footprint. © 2018 John Wiley & Sons, Ltd.

Description: Abstract Biogeomorphic ecosystems (e.g. rivers, salt marshes, mangroves and coastal dunes) are shaped by feedbacks between geomorphology and engineer plants that occur at various spatiotemporal scales. The classical bivariate and multivariate statistical methods currently used in biogeomorphology do not permit clear identification of reciprocal causality between geomorphic and biological variables. The aim of this article is to present the potential of the cross‐lagged panel model (CLPM) to estimate reciprocal associations (causality) between one geomorphic and one biological variable over time. This tool, which originates from behavioural, social, medical and educational sciences, has clear potential as a novel approach to causal analysis in the context of biogeomorphic ecosystems. We provide a case study of the application of CLPM for analysing biogeomorphic feedbacks between topography and Populus nigra L. physiognomy on a wooded point bar of the Garonne River, France. © 2018 John Wiley & Sons, Ltd.

Description: Spatial and temporal variations in simulated wind erosion were found to occur across Xinjiang Province of northwest China. Variations in wind erosion were in part caused by differences in soil type and wind speed. Wind erosion was most intense during May and was lower for cropland than bare soil. Maintaining vegetative cover on the soil surface during a portion of the year is critical to protecting the soil from wind erosion. Abstract The prediction of wind erosion and dust emissions is important for controlling erosion and identifying dust sources in arid and semiarid regions of the world. This study predicts quantitatively wind erosion and dust emissions in Xinjiang Province, central Asia. The wind erosion prediction system (WEPS) was used to simulate annual soil and PM10 (particulate matter ≤10 μm in aerodynamic diameter) loss at 64 meteorological stations across the province. Soil and PM10 loss were simulated from bare surfaces at all 64 stations and from cotton and wheat fields at 11 stations. Simulated annual bare soil and PM10 loss were lowest in the Junggar (soil and PM10 loss were, respectively, 121.7 and 7.6 kg m‐2) and Tarim basins (soil loss was 78.2 kg ha‐1 and PM10 loss was 6.5 kg m‐2) and highest in the Tu‐ha Basin (soil and PM10 loss were, respectively, 638.2 and 37.7 kg m‐2). Stations with the highest annual soil loss in the Tarim and Tu‐ha basins also had the highest number of days with wind speeds 〉8 m s‐1. This indicated wind influenced erosion, but other factors such as soil type also affect wind erosion. The maximum monthly bare soil and PM10 loss occurred in May in the three basins, substantiating that dust storms occur most frequently during spring in the region. Simulated soil and PM10 loss were lower for cotton and wheat than bare soil, thus suggesting that maintaining vegetative cover during a portion of the year provided some protection to the soil surface from wind erosion. © 2018 John Wiley & Sons, Ltd.

Description: Simulations suggest that the propensity for landslide occurrence at the Luquillo Critical Zone Observatory is expected to be significant in the 21st century. Relatively large landslides are expected to persist at the granitic Icacos watershed, while the occurrence of smaller rainfall‐triggered landslides at the adjacent volcaniclastic Mameyes watershed remains high. While projections of precipitation decrease at the study site may lead to moderate decline in hillslope erosion rates, the simulated erosional potential of the two diverse landscapes likely remains significant. Abstract The potentially important influence of climate change on landscape evolution and on critical zone processes is not sufficiently understood. The relative contribution of hydro‐climatic factors on hillslope erosion rates may significantly vary with topography at the watershed scale. The objective of this study is to quantify the hydro‐geomorphic behavior of two contrasting landscapes in response to different climate change scenarios in the Luquillo Critical Zone Observatory, a site of particular geomorphological interest, in terms of hillslope erosion and rainfall‐triggered landslides. We investigate the extent to which hillslope erosion and landslide occurrence remain relatively invariant with future hydro‐climatic perturbations. The adjacent Mameyes and Icacos watersheds are studied, which are underlain by contrasting lithologies. A high resolution coupled hydro‐geomorphic model based on tRIBS (Triangulated Irregular Network‐based Real‐time Integrated Basin Simulator) is used. Observations of landslide activity and hillslope erosion are used to evaluate the model performance. The process‐based model quantifies feedbacks among different hydrologic processes, landslide occurrence, and topsoil erosion and deposition. Simulations suggest that the propensity for landslide occurrence in the Luquillo Mountains is controlled by tropical storms, subsurface water flow, and by non‐climatic factors, and is expected to remain significant through 2099. The Icacos watershed, which is underlain by quartz diorite, is dominated by relatively large landslides. The relative frequency of smaller landslides is higher at the Mameyes watershed, which is underlain by volcaniclastic rock. While projections of precipitation decrease at the study site may lead to moderate decline in hillslope erosion rates, the simulated erosional potential of the two diverse landscapes likely remains significant. © 2018 John Wiley & Sons, Ltd.

Description: Abstract The complex morphodynamic interactions between nearshore, shoreface and dune systems are usually simplified by studying these zones and their associated processes in isolation. However, the established relationships between each of them suggests that an integrated approach is required to examine the genesis, evolution and adaptation of the entire morphodynamic system. The Cabopino dune system in southern Spanish Mediterranean Sea provides a clear example of a linked morphodynamic system in which a relatively large dune system has been generated and grown through the supply of sediments from an adjacent littoral supply environment. Here, we present a conceptual model of how the nearshore has provided suitable conditions for beach and dune development. We purport that synchronisation of sediment activation in the marine and aeolian sections of the system have played a major role in this microtidal setting in which temporal aspects are not only tied to storm action, but to large sedimentary features moving alongshore.

Description: 1. In agricultural lands with a smooth surface relief, the soil's nature and conditions play a key role in the erosion process, giving rise to the appearance of ephemeral gullies. 2. Soil susceptibility to ephemeral gully development has been reflected in a set of 13 soil variables, representing a wide range of soil physico‐chemical properties. 3. A coefficient of erodibility, determined by means of the Jet Test technique, stands out. Abstract The soil factor is crucial in controlling and properly modeling the initiation and development of ephemeral gullies (EGs). Usually, EG initiation has been related to various soil properties (i.e. sealing, critical shear stress, moisture, texture, etc.); meanwhile, the total growth of each EG (erosion rate) has been linked with proper soil erodibility. But, despite the studies to determine the influence of soil erodibility on (ephemeral) gully erosion, a universal approach is still lacking. This is due to the complex relationship and interactions between soil properties and the erosive process. A feasible soil characterization of EG erosion prediction on a large scale should be based on simple, quick and inexpensive tests to perform. The objective of this study was to identify and assess the soil properties – easily and quickly to determine – which best reflect soil erodibility on EG erosion. Forty‐nine different physical–chemical soil properties that may participate in establishing soil erodibility were determined on agricultural soils affected by the formation of EGs in Spain and Italy. Experiments were conducted in the laboratory and in the field (in the vicinity of the erosion paths). Because of its importance in controlling EG erosion, five variables related to antecedent moisture prior to the event that generated the gullies and two properties related to landscape topography were obtained for each situation. The most relevant variables were detected using multivariate analysis. The results defined 13 key variables: water content before the initiation of EGs, organic matter content, cation exchange capacity, relative sealing index, two granulometric and organic matter indices, seal permeability, aggregates stability (three index), crust penetration resistance, shear strength and an erodibility index obtained from the Jet Test erosion apparatus. The latter is proposed as a useful technique to evaluate and predict soil loss caused by EG erosion. Copyright © 2018 John Wiley & Sons, Ltd.

Description: Aiming to bridge the gap between field and laboratory results, we established a direct link of the virtual velocity of bedload tracers to the actual variables of flow events. For increased comparability, the formulations of bedload relations served as templates for the introduced ‘unsteady’ virtual velocity. The developed regression program ‘graVel’, which is provided as supplementary material to this paper, was applied to own and to published data followed by a non‐dimensional generalisation of the results. Abstract In a flume experiment with steady flow conditions, H. A. Einstein recognised the transport of bedload particles as consisting of steps of rolling, sliding, or saltation with intermittent rest periods, and introduced the concept of an average, ‘virtual’ transport velocity. This virtual velocity then has also been derived from tracer studies in the field by dividing the travelled distance of a tracer by the duration of competent flow. As a consequence, the virtual velocity in the field is represented by one single value only, despite the unsteady flow variables. Tracer measurements in a river have not been yet used to express transport velocity as a direct function of these actual variables, and insights from tracer measurements into the processes of sediment transport remain limited. In particular, the unsteady conditions for bedload in the field have impeded the derivation of sediment transport characteristics as determined from laboratory experiments, as well as the transfer of laboratory insights to a field setting. We introduce a method of data regression for the derivation of an ‘unsteady’ virtual velocity from repeated surveys of tracer positions. The regression program called graVel (provided as supplementary material) relates the integral of an excess flow variable term to measured travel distances, yielding the most probable threshold value for entrainment and the coefficient of linear and non‐linear formulas. An extended regression allows additional fitting of the exponent in non‐linear formulas. Application to published tracer data from the Mameyes River, Puerto Rico, shows that the unsteady virtual velocity is more likely governed by non‐linear relations to excess Shields stress, similar to bedload transport, than by relations linking the particle velocity linearly to excess shear velocity. Partial agreements with non‐dimensional results derived from the larger, non‐wadeable Mur River encourage the establishment of a generalised formula for the unsteady virtual velocity. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract Beach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms, as well as evidence of earthquake induced sediment pulses. This study is a stratigraphic investigation of the late Holocene mixed sand gravel (MSG) beach ridge plain on the Canterbury coast, New Zealand. The subsurface was imaged along a 370 m shore‐normal transect using 100 and 200 MHz ground penetrating radar (GPR) antennae, and cored to sample sediment textures. Results show that, seaward of a back‐barrier lagoon, the Pegasus Bay beach ridge plain prograded almost uniformly, under conditions of relatively stable sea level. Nearshore sediment supply appears to have created a sustained sediment surplus, perhaps as a result of post‐seismic sediment pulses, resulting in a flat, morphologically featureless beach ridge plain. Evidence of a high magnitude storm provides an exception, with an estimated event return period in excess of 100 years. Evidence from the GPR sequence combined with modern process observations from MSG beaches indicates that a paleo storm initially created a washover fan into the back‐barrier lagoon, with a large amount of sediment simultaneously moved off the beach face into the nearshore. This erosion event resulted in a topographic depression still evident today. In the subsequent recovery period, sediment was reworked by swash onto the beach as a sequence of berm deposit laminations, creating an elevated beach ridge that also has a modern‐day topographic signature. As sediment supply returned to normal, and under conditions of falling sea level, a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern‐day beach as a large flat, uniform progradation plain. This study highlights the importance of extreme storm events and earthquake pulses on MSG coastlines in triggering high volume beach ridge formation during the subsequent recovery period.

Description: Abstract Inorganic sediment is not the only solid‐fraction component of river flows; flows may also carry significant amounts of large organic material (i.e., large wood), but the characteristics of these wood‐laden flows (WLF) are not well understood yet. With the aim to shed light on these relatively unexamined phenomena, we collected home videos showing natural flows with wood as the main solid component. Analyses of these videos as well as the watersheds and streams where the videos were recorded allowed us to define for the first time WLF, describe the main characteristics of these flows and broaden the definition of wood transport regimes (adding a new regime called here hypercongested wood transport). According to our results, WLF may occur repeatedly, in a large range of catchment sizes, generally in steep, highly confined single thread channels in mountain areas. WLF are typically highly unsteady and the log motion is non‐uniform, as described for other inorganic sediment‐laden flows (e.g., debris flows). The conceptual integration of wood into our understanding of flow phenomena is illustrated by a novel classification defining the transition from clear water to hypercongested, wood and sediment‐laden flows, according to the composition of the mixture (sediment, wood, and water). We define the relevant metrics for the quantification and modelling of WLF, including an exhaustive discussion of different modelling approaches (i.e., Voellmy, Bingham and Manning) and provide a first attempt to simulate WLF. We draw attention to WLF phenomena to encourage further field, theoretical, and experimental investigations that may contribute to a better understanding of flows river basins, leading to more accurate predictions, and better hazard mitigation and management strategies.

Description: Magnetic susceptibility of metal tracers can be used for effective and inexpensive sediment fingerprinting in aeolian transport and redistribution studies. The novel magnetic susceptibility‐based method showed the microsite‐scale post‐fire changes in aeolian sediment sources and sinks in the landscape and sediment homogenization in the shrub‐grass ecotone. Abstract Aeolian processes – the erosion, transport, and deposition of sediment by wind – play important geomorphological and ecological roles in drylands. These processes are known to impact the spatial patterns of soil, nutrients, plant‐available water, and vegetation in many dryland ecosystems. Tracers, such as rare earth elements and stable isotopes have been successfully used to quantify the transport and redistribution of sediment by aeolian processes in these ecosystems. However, many of the existing tracer techniques are labor‐intensive and cost‐prohibitive, and hence simpler alternative approaches are needed to track aeolian redistribution of sediments. To address this methodological gap, we test the applicability of a novel metal tracer‐based methodology for estimating post‐fire aeolian sediment redistribution, using spatio‐temporal measurements of low‐field magnetic susceptibility (MS). We applied magnetic metal tracers on soil microsites beneath shrub vegetation in recently burned and in control treatments in a heterogeneous landscape in the Chihuahuan desert (New Mexico, USA). Our results indicate a spatially homogeneous distribution of the magnetic tracers on the landscape after post‐burn wind erosion events. MS decreased after wind erosion events on the burned shrub microsites, indicating that these areas functioned as sediment sources following the wildfire, whereas they are known to be sediment sinks in the undisturbed (e.g. not recently burned) ecosystem. This experiment represents the first step toward the development of a cost‐effective and non‐destructive tracer‐based approach to estimate the transport and redistribution of sediment by aeolian processes. © 2018 John Wiley & Sons, Ltd.

Description: This methodology provides robust, novel and quantitative information regarding decadal to secular channel changes that have occurred on a regional scale. The case study was conducted for the Po basin in the Piedmont region, northwest of Italy. From our analysis, it emerges that regionally 74% of the river network has riverbed incisions exceeding one meter, while 66% of channels have halved their historical widths with a total of 617 ha of land subtracted from the active channel. Abstract Remote Sensing (RS) technology has recently offered new and promising opportunities to analyze river systems. In this paper, we present a calibration of characteristic Hydraulic Scaling Law (HSL) using a regional database of river geomorphic features. We consistently linked discharge with channel geometry features for estimated Bankfull Channel Depth (eBCD), Active Channel Width (ACW), and Low Flow water Channel Width (LFCW), which are continuously available from RS data along the river course. We then used historical information and external sources of information on channel reaches that were relatively unaffected by human pressure over periods ranging from a few decades to a century (measured in comparable geographical areas) to infer relatively Unaltered HSLs (rUHSLs). Adopting rUHSL validated with available local historical evidence on channel geometry, we were able to assess historical changes in channel geometry consistently over the entire region and within the studied temporal window. The case study was conducted for the Po basin in the Piedmont Region, north‐west Italy. From our analysis, it emerges that regionally 74% of the river network has riverbed incisions exceeding 1 m, while 66% of channels have halved their historical widths with a total of 617 ha of land subtracted from the active channel. LFCW is, on average, wider in Alpine rivers compared with those located in the North Apennines. Although it is currently not possible to measure the accuracy of these estimates, the evidence generated is coherent with available historical information, characteristic hydraulic scaling laws, evidence from relatively unaltered reaches and the available literature on local fluvial systems. This methodology provides robust, novel and quantitative information regarding decadal to secular channel changes that have occurred on a regional scale. This new layer of information enriches our ability to rationally address assessments of large‐scale past and future channel trajectories. © 2018 John Wiley & Sons, Ltd.

Description: Abstract 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 km^2 catchment on Vancouver Island, British Columbia. Sediment is supplied episodically to the channel, including additions from debris flows in the early 1980's 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. This article is protected by copyright. All rights reserved.

Description: Abstract Intertidal bars are common in meso‐macrotidal low‐to‐moderate energy coastal environments and an understanding of their morphodynamics is important from the perspective of both coastal scientists and managers. However, previous studies have typically been limited by considering bar systems two‐dimensionally, or with very limited alongshore resolution. This paper presents the first multi‐annual study of intertidal alongshore bars and troughs in a macro‐tidal environment using airborne LiDAR data to extract three‐dimensional bar morphology at high resolution. Bar and trough positions are mapped along a 17.5 km stretch of coastline in the northwest of England on the eastern Irish Sea, using eight complete, and one partial, LiDAR surveys spanning 17 years. Typically, 3 – 4 bars are present, with significant obliquity identified in their orientation. This orientation mirrors the alignment of waves from the dominant south‐westerly direction of wave approach, undergoing refraction as they approach the shoreline. Bars also become narrower and steeper as they migrate onshore, in a pattern reminiscent of wave shoaling. This suggests that the configuration of the bars is being influenced by overlying wave activity. Net onshore migration is present for the entire coastline, though rates vary alongshore, and periods of offshore migration may occur locally, with greatest variability between northern and southern regions of the coastline. This work highlights the need to consider intertidal bar systems as three‐dimensional, particularly on coastlines with complex configurations and bathymetry, as localised studies of bar migration can overlook three‐dimensional behaviour. Furthermore, the wider potential of LiDAR data in enabling high‐resolution morphodynamic studies is clear, both within the coastal domain and beyond.

Description: Drainage integration of Aravaipa Creek basin drove a rapid, transient response carving Aravaipa Canyon and excavating at atleast 50 km3 of basin fill. Rates of transient incision associated with drainage reorganization can be equal to those driven by active tectonics. Abstract Drainage reorganization events have the potential to drive incision and erosion at high rates normally attributed to tectonic or climatic forcing. It can be difficult, however, to isolate the signal of transient events driven by drainage integration from longer term tectonic or climatic forcing. We exploit an ideal field setting in Aravaipa Creek Basin of southeastern Arizona, USA, to isolate just such a signal. Aravaipa Creek Basin underwent a period of transient incision that formed Aravaipa Canyon, evacuating a significant volume of sedimentary basin fill and Tertiary bedrock from the previously internally drained basin. We use digital terrain analyses to reconstruct the pre‐incision landscapes of both Aravaipa Creek Basin and the adjacent Lower San Pedro Basin, which we use to quantify the magnitude of incision and erosion since the drainage basins integrated. Terrestrial cosmogenic nuclide burial dates from 10Be and 26Al concentrations in latest stage basin fill in Aravaipa Creek enable us to calculate long‐term incision and erosion rates from 3 Myr to the present. A 10Be concentration–depth profile from the Lower San Pedro Basin confirms that the San Pedro River incised into its high stand deposits prior to 350 000–400 000 years ago. Combining our landscape reconstructions with these age constraints, we determine that the transient rates of incision that created Aravaipa Canyon were 150 m/Myr or more, but that the background rate of erosion since integration is an order of magnitude lower, between 10 and 20 m/Myr. These results support our growing understanding that tectonic and climatic forcings need not apply for all episodes of rapid, transient incision and erosion during landscape evolution. © 2018 John Wiley & Sons, Ltd.

Description: During the last glacial cycle the retreat and advance of the North Sea Lobe left a ‘mixed‐bed’ glacial landsystem imprint on the floor of the western North Sea. The production of this unusual landform assemblage represents a dynamic switch from a terrestrial piedmont‐lobe margin with a net surplus of sediment to the south, to a partially erosive/excavational, quasi‐stable, ice margin as ice withdrew northwards under glaciomarine conditions. Abstract During the last glacial cycle an intriguing feature of the British‐Irish Ice Sheet was the North Sea Lobe (NSL); fed from the Firth of Forth and which flowed south and parallel to the English east coast. The controls on the formation and behaviour of the NSL have long been debated, but in the southern North Sea recent work suggests the NSL formed a dynamic, oscillating terrestrial margin operating over a deforming bed. Further north, however, little is known of the behaviour of the NSL or under what conditions it operated. This paper analyses new acoustic, sedimentary and geomorphic data in order to evaluate the glacial landsystem imprint and deglacial history of the NSL offshore from NE England. Subglacial tills (AF2/3) form a discontinuous mosaic interspersed with bedrock outcrops across the seafloor, with the partial excavation and advection of subglacial sediment during both advance and retreat producing mega‐scale glacial lineations and grounding zone wedges. The resultant ‘mixed‐bed’ glacial landsystem is the product of a dynamic switch from a terrestrial piedmont‐lobe margin with a net surplus of sediment to a partially erosive, quasi‐stable, marine‐terminating, ice stream lobe as the NSL withdrew northwards. Glaciomarine sediments (AF4) drape the underlying subglacial mixed‐bed imprint and point to a switch to tidewater conditions between 19.9 and 16.5 ka cal BP as the North Sea became inundated. The dominant controls on NSL recession during this period were changing ice flux through the Firth of Forth ice stream onset zone and water depths at the grounding line; the development of the mixed‐bed landsystem being a response to grounding line instability. © 2018 John Wiley & Sons, Ltd.

Description: Abstract Large scale geomorphic drivers that operate at continental scale are often climate driven. Changes in land use can accelerate wind erosion. The range of land management practises within one land use can have dramatic effect on ground cover and wind erosion. This study uses meteorological observations, land use, land management and dust concentration measurements of 129 dust events recorded between 1990 and 2007 to describe a dust chronology of Mildura, in South Eastern Australia. Frontal and frontal trough weather systems account for 74% of dust events. Eighty eight percent of dust events come from rangelands in the north west and the cropping lands to the south west. the cropping areas to the south west are the most common source of dust, accounting for 66% of events There is no relationship between rainfall and dust activity in this study, suggesting that land management practices, especially on cropping lands, over‐ride the controlling effect of rainfall. When cropping lands received above average rainfall in spring and summer during the 1990s, cultivation for weed control lead to rapid decline in ground cover that predisposed the land to wind erosion in following summer and autumn. In drought years, dust blows into Mildura from all directions suggesting that dust is climate driven rather than controlled by land use.

Description: Global map of regional coastal cliff percentage. Abstract Previous studies have estimated that coastal cliffs exist on about 80% of the global shoreline, but have not been validated on a global scale. This study uses two approaches to capture information on the worldwide existence and erosion of coastal cliffs: a detailed literature survey and imagery search, and a GIS‐based global mapping analysis. The literature and imagery review show coastal cliffs exist in 93% of the combined recognized independent coastal states and non‐independent coastal regions worldwide (total of 213 geographic units). Additionally, cliff retreat rates have been quantified in at least one location within 33% of independent coastal states and 15% of non‐independent regions. The GIS‐based mapping used the near‐global Shuttle Radar Topography Mission 3 arc second digital elevation model and Arctic Coastal Dynamics Database to obtain near‐global backshore coastal elevations at 1 km alongshore intervals comprising about 1,340,000 locations (81% of the world vector shoreline). Backshore coastal elevations were compared with the mapped distribution of European coastal cliffs to produce a model training set, and this relationship was extended globally to map the likelihood of coastal cliff locations. About 21% of the transects (17% of the world vector shoreline) were identified as mangroves and eliminated as potential cliff locations. The results were combined with estimates of cliff percentages for Greenland and Antarctica from the literature, extending the global coverage to estimate cliff occurrence across 89% of the world vector shoreline. The results suggest coastal cliffs likely exist on about 52% of the global shoreline. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: Step‐pool systems are ubiquitous in mountain regions, but their formation is debated. A field test of competing step formation models reveals that steps form by jamming in narrow channel reaches and around keystones in wide channel reaches. Abstract Steep streams often feature a step‐pool morphology where the steps determine channel stability and dissipate the stream's energy, and thus are important for local flow hydraulics and bedload transport. Steps also play a key‐role for the coupling of channels and adjacent hillslopes by controlling hillslope stability. Although step‐pool systems have been investigated in various modelling and experimental efforts, the processes of step formation and destruction remain under debate. Theories of step formation consider a wide range of dominant drivers and fall into three groups favouring hydraulic controls (HC), granular interactions during flow (GI) or random drivers (RD) as relevant factors for step location. A direct evaluation of these models with field observations is challenging, as step formation cannot be directly observed. Based on the physical mechanisms of the various formation models we derive diagnostic morphometric parameters and test them with a field data set from a steep stream in Switzerland. Our results suggest that one class of alluvial steps form due to jamming in narrow and narrowing sections of the channel, while steps in wide and widening sections form around rarely mobile keystones. These two models of step formation apply in our study reach at the same time in different locations of the channel. A third class of steps is forced by logs. Such steps are typically located close to the original growth position of the tree and therefore reflect strong channel‐hillslope coupling. Wood‐forced steps make up a minor fraction of the step population, but contribute significantly to the cumulative step height and are therefore relevant to reach‐scale flow resistance of the channel. © 2019 John Wiley & Sons, Ltd.

Description: We explore the multiple ecohydrologic feedbacks that shape evenly‐spaced isolated depressional wetlands in a low‐relief South Florida landscape. Incipient depressions deepen as biogenic acid accelerates bedrock weathering. Soil thickness and vegetation inundation are the most important constraints on depression growth, but do not stabilize wetland size for 0.2–0.4 Myr. However, basin expansion rapidly inhibits weathering in adjacent uplands, which may explain the regular patterning of depressions. Local and distal feedbacks decouple landscape‐scale self‐organization from self‐organization of its constituent agents. Abstract Many landforms on Earth are profoundly influenced by biota. In particular, biota play a significant role in creating karst biogeomorphology, through biogenic CO2 accelerating calcite weathering. In this study, we explore the ecohydrologic feedback mechanisms that have created isolated depressional wetlands on exposed limestone bedrock in South Florida – Big Cypress National Preserve –as a case study for karst biogeomorphic processes giving rise to regularly patterned landscapes. Specifically, we are interested in: (1) whether cypress depressions on the landscape have reached (or will reach) equilibrium size; (2) if so, what feedback mechanisms stabilize the size of depressions; and (3) what distal interactions among depressions give rise to the even distribution of depressions in the landscape. We hypothesize three feedback mechanisms controlling the evolution of depressions and build a numerical model to evaluate the relative importance of each mechanism. We show that a soil cover feedback (i.e. a smaller fraction of CO2 reaches the bedrock surface for weathering as soil cover thickens) is the major feedback stabilizing depressions, followed by a biomass feedback (i.e. inhibited biomass growth with deepening standing water and extended inundation period as depressions expand in volume). Strong local positive feedback between the volume of depressions and rate of volume expansion and distal negative feedback between depressions competing for water likely lead to the regular patterning at the landscape scale. The individual depressions, however, are not yet in steady state but would be in ~0.2–0.4 million years. This represents the first study to demonstrate the decoupling of landscape‐scale self‐organization and the self‐organization of its constituent agents. © 2018 John Wiley & Sons, Ltd.

Description: We reconstructed 1800‐year precipitation (Pm) and net primary productivity (NPP) of vegetation over the Yellow River basin. The temporal variations in Pm, NPP and the frequency of artificial levee breachings (Fb) exhibited anti‐phase relation (Type I) and in‐phase relation (Type II) alternately with time. Type I occurred when the vegetation remained in quasi‐natural condition and Type II occurred when the vegetation had been changed by man, reflecting complex river behaviors in response to climate change and human activity. Abstract Rivers are closely related to climate, and the hydrogeomorphic features and stability of river channels respond sensitively to climatic change. However, the history of instrumental observations of climatic, hydrological and channel changes is short, notably limiting our ability to understand the complex river responses to long‐term climate change and human activity. In this study, we show that cave stalagmite records reflected the variations in precipitation and temperature in the Yellow River basin, and the net primary productivity (NPP) of vegetation over the past 1800 years can therefore be reconstructed. We found that the reconstructed annual mean precipitation (Pm) and NPP closely related to the 1800‐year variation of the lower Yellow River (LYR) channel instability indexed by the frequency of the LYR levee breaching events (LBEs) (Fb) derived from historical documents. The temporal variations in Pm, NPP and Fb exhibited an anti‐phase relationship (negative correlation) and in‐phase relationship (positive correlation), referred to as Type I and Type II relationships, respectively. The two types alternately appeared, dividing the studied period into several sub‐periods. Type I occurred when the vegetation remained in a quasi‐natural condition, and Type II occurred when the vegetation had been altered by humans to some degree. These features reflect complex river behaviours in response to climate change and human activity and may be explained by the interaction between climate, vegetation and human activity on the millennial timescale. © 2018 John Wiley & Sons, Ltd.

Description: First, we show how two complementary, but independent, methods for quantifying the concentration of tracer from images can produce highly resolved estimates of particle concentrations in the laboratory. Second, we demonstrate the power of the method for collecting spatial information on soil redistribution, with mm precision, over an approximately 50 m hillslope and vertically down the soil profile. Our work demonstrates the potential to collect quantitative time‐resolved data about soil movement without disturbing the soil surface that is being studied. Abstract Generating high resolution spatial information on the movement of sediment in response to soil erosion remains a major research challenge. In this paper we present a new tracing method that utilises LED (light emitting diode) light to induce fluorescence in a sand‐sized tracer, which is then detected, using a complementary metal oxide semiconductor (CMOS) sensor in a commercial digital camera, at mm‐resolution without the need for removal of soil material. First, we detail two complementary, but independent, methods for quantifying the concentration of tracer from images: particle counting and an intensity based method. We show that both methods can produce highly resolved estimates of particle concentrations under laboratory conditions. Secondly, we demonstrate the power of the method for collecting spatial information on soil redistribution by tillage, with mm precision, over an approximately 50 m hillslope and vertically down the soil profile. Our work demonstrates the potential to collect quantitative time‐resolved data about soil movement without disturbing the soil surface which is being studied, and with it the possibility to parameterise or evaluate dynamic distributed soil erosion models or to undertake fundamental research focused on particle movement that has been impossible to conduct previously. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: Grounding zone wedges (GZWs) preserved in outcrops on Whidbey Island,WA, USA are documented and interpreted. Results provide insight into the formative processes of GZWs and support a punctuated style of retreat of the Cordilleran Ice Sheet through the Puget Lowlands. GZWs form primarily through sediment gravity flows yet evidence for basal melt‐out of entrained debris, channelized meltwater flows and tidal activity was observed. Abstract Grounding‐zone wedges (GZWs) mark the grounding terminus of flowing marine‐based ice streams and, in the presence of an ice shelf, the transition from grounded ice to floating ice. The morphology and stratigraphy of GZWs is predominantly constrained by seafloor bathymetry, seismic data, and sediment cores from deglaciated continental shelves; however, due to minimal constraints on GZW sedimentation processes, there remains a general lack of knowledge concerning the production of these landforms. Herein, outcrop observations are provided of GZWs from Whidbey Island in the Puget Lowlands (Washington State, USA). These features are characterized by prograded diamictons bounded by glacial unconformities, whereby the lower unconformity indicates glacial advance of the southern Cordilleran Ice Sheet and the upper unconformity indicates locally restricted ice advance during GZW growth; the consistent presence of an upper unconformity supports the hypothesis that GZWs facilitate ice advance during landform construction. Based on outcrop stratigraphy, GZW construction is dominated by sediment transport of deformation till and melt‐out of entrained basal debris at the grounding line. This material may be subsequently remobilized by debris flows. Additionally, there is evidence for subglacial meltwater discharge at the grounding line, as well as rhythmically bedded silt and sand, indicating possible tidal pumping at the grounding line. A series of GZWs on Whidbey Island provides evidence of punctuated ice sheet movement during retreat, rather than a rapid ice sheet lift‐off. The distance between adjacent GZWs of 102–103 m and the consistency in their size relative to modern ice stream grounding lines suggests that individual wedges formed over decades to centuries. © 2018 John Wiley & Sons, Ltd.

Description: Erosion at Mount St. Helens continues to supply excessive sediment to the Toutle‐Cowlitz River system, making this one of the most protracted gravel‐bed river disasters to date. The Portland District, US Army Corps of Engineers has revised its long‐term sediment management plan, drawing on applied geomorphological principles and using engineering science that makes best use of the existing Sediment Retention Structure. These geomorphic principles and the engineering science that underpins them are transferrable to other gravel‐bed river disasters. Abstract Thirty‐seven years post‐eruption, erosion of the debris avalanche at Mount St Helens continues to supply sediment to the Toutle–Cowlitz River system in quantities that have the potential to lower the Level of Protection (LoP) against flooding unacceptably, making this one of the most protracted gravel‐bed river disasters to date. The Portland District, US Army Corps of Engineers (USACE) recently revised its long‐term plan for sediment management (originally published in 1985), in order to maintain the LoP above the Congressionally‐authorized level, while reducing impacts on fish currently listed under the Endangered Species Act, and minimizing the overall cost of managing sediment derived from erosion at Mount St Helens. In revising the plan, the USACE drew on evidence gained from sediment monitoring, modelling and uncertainty analysis, coupled with assessment of future LoP trends under a baseline scenario (continuation of the 1985 sediment management strategy) and feasible alternatives. They applied geomorphological principles and used engineering science to develop a phased Sediment Management Plan that allows for uncertainty concerning future sediment yields by implementing sediment management actions only as, and when, necessary. The phased plan makes best use of the potential to enhance the sediment trap efficiency and storage capacity of the existing Sediment Retention Structure (SRS) by incrementally raising its spillway and using novel hydraulic structures to build islands in the North Fork Toutle River (NFTR) and steepen the gradient of the sediment plain upstream of the structure. Dredging is held in reserve, to be performed only when necessary to react to unexpectedly high sedimentation events or when the utility of other measures has been expended. The engineering‐geomorphic principles and many of the measures in the phased Sediment Management Plan are transferrable to other gravel‐bed river disasters. The overriding message is that monitoring and adaptive management are crucial components of long‐term sediment‐disaster management, especially in volcanic landscapes where future sediment yields are characterized by uncertainty and natural variability. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: Abstract Tree roots provide surface erosion protection and improve slope stability through highly complex interactions with the soil due to the nature of root systems. Root reinforcement estimation is usually performed by in‐situ pullout tests, in which roots are pulled out of the soil to reliably estimate the root strength of compact soils. However, this test is not suitable for the scenario where a soil progressively fails in a series of slump blocks, for example, in unsupported soils near streambanks and road cuts where the soil has no compressive resistance at the base of the hillslope. The scenario where a soil is unsupported on its downslope extent and progressively deforms at a slow strain rate has received little attention, and we are unaware of any study on root reinforcement that estimates the additional strength provided by roots in this situation. Thus, we designed two complementary laboratory experiments to compare the force required to pull the root out. The results indicate that the force required to pullout roots is reduced by up to 50% when the soil fails as slump blocks compared to pullout tests. We also found that, for slump block failure, roots had a higher tendency to slip than to break, showing the importance of active earth pressure on root reinforcement behaviour, which contributes to reduced friction between soil and roots. These results were then scaled up to a full tree and tree stand using the root bundle and field‐measured spatial distributions of root density. Although effects on the force mobilized in small roots can be relevant, small roots have virtually no effect on root reinforcement at the tree or stand scale on hillslopes. When root distribution has a wide range of diameters, the root reinforcement results are controlled by large roots that hold much more force than small roots. This article is protected by copyright. All rights reserved.

Description: 3D laser scanning technique was applied to create high resolution DEMs. Gully morphology was described quantitatively according to its characteristic parameters and a method of differentiation between gully head and gully sidewalls was proposed. V–L and V–Ag empirical equations were established. Abstract Gully morphology characteristics can be used effectively to describe the status of gully development. The Chabagou watershed, located in the hilly‐gully region of the Loess Plateau in China, was selected to investigate gully morphological characteristics using a 3D laser scanning technique (LIDAR). Thirty‐one representative gullies located at different watershed locations and gully orders were chosen to quantitatively describe gully morphology and establish empirical equations for estimating gully volume based on gully length and gully surface area. Images and point cloud data for the 31 gullies were collected, and digital elevation models (DEMs) with 10‐cm resolution were generated. ArcGIS 10.1 was then used to extract fundamental gully morphological parameters covering gully length (L), gully width (WT) and gully depth (D), and some derivative morphological parameters, including gully head curvature (C), gully width–depth ratio (w/d), gully bottom‐to‐top width ratio (WB/WT), gully surface area (Ag) and gully volume (Vg). The results indicated that gullies in the upper watershed and the second order were more developed based on their high values of gully head curvature. The potential for gully development increased from the second order to the fourth order. Within the same gully orders, gullies in the lower watershed were more active with more development potential. A method for differentiating between gully head and gully sidewalls based on the gully head curvature value was proposed with a mean relative error of 8.77%. U‐shaped cross‐sections were widely distributed in the upper watershed and upper positions of a gully, while V‐shaped cross‐sections were widely distributed in the lower watershed and lower positions of a gully. V–L and V–Ag empirical equations with acceptable accuracy were established and can be used to estimate gully erosion in the Loess hilly‐gully region. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Headcut height had a significant impact on flow energy consumption, and thus influenced the changes in sediment yield and surface landform during the process of gully headcut erosion. As headcut height increased from 25 to 125 cm, flow energy consumption, soil loss volume and retreat distance at gully heads all increased significantly. Abstract To quantify the changes in flow energy, sediment yield and surface landform impacted by headcut height during bank gully erosion, five experimental platforms were constructed with different headcut heights ranging from 25 to 125 cm within an in situ active bank gully head. A series of scouring experiments were conducted under concentrated flow and the changes in flow energy, sediment yield and surface landform were observed. The results showed that great energy consumption occurred at gully head compared to the upstream area and gully bed. The flow energy consumption at gully heads and their contribution rates increased significantly with headcut height. Gully headcuts also contributed more sediment yield than the upstream area. The mean sediment concentrations at the outlet of plots were 2.3 to 7.3 times greater than those at the end of upstream area. Soil loss volume at gully heads and their contribution rates also increased with headcut height significantly. Furthermore, as headcut height increased, the retreat distance of gully heads increased, which was 1.7 to 8.9 times and 1.1 to 3.2 times greater than the incision depth of upstream area and gully beds. Positive correlations were found between energy consumption and soil loss, indicating that energy consumption could be used to estimate soil loss of headcut erosion. Headcut height had a significant impact on flow energy consumption, and thus influenced the changes in sediment yield and landform during the process of gully headcut erosion. Headcut height was one of the important factors for gully erosion control in this region. Further studies are needed to identify the role of headcut height under a wide condition. Copyright © 2018 John Wiley & Sons, Ltd.

Description: This study selected the Liangshan town watershed to quantify variation in the vertical zonality of rill erodibility (kr) in China's ecologically fragile Hengduan Mountains. As elevation increased, the kr values decreased. The highest kr values were observed during the seepage treatment, followed by the saturation treatment then drainage treatment, indicating that variation in vertical hydraulic gradients could significantly alter kr values. This study also found that land‐use types could also alter kr and Ʈc values. Abstract Soil erodibility is an essential parameter used in soil erosion prediction. This study selected the Liangshan town watershed to quantify variation in the vertical zonality of rill erodibility (kr) in China's ecologically fragile Hengduan Mountains. Soil types comprised of yellow–brown (soil A), purple (soil B), and dry‐red (soil C) in a descending order of occurrence from the summit to the valley, which roughly corresponds to the vertical climate zone (i.e. cool‐high mountain, warm‐low mountain, and dry‐hot valley sections) of the study area. With elevation, vertical soil zonality varied in both soil organic matter (SOM) content and soil particle‐size fractions. A series of rill erosion‐based scour experiments were conducted, using water discharge rates of 100, 200, 300, 400, 500, and 600 mL min‐1. Additionally, detachment rates (Dr) were measured under three hydrological conditions (the drainage, saturation, and seepage treatments). Results show that both Dr and flow shear stress (Ʈ) values increased as discharge increased. As elevation increased, the kr values decreased, while the vertical zonality of critical shear stress (Ʈc) values showed no obvious variation. The highest kr values were observed during the seepage treatment, followed by the saturation treatment then drainage treatment, indicating that variation in vertical hydraulic gradients could significantly alter kr values. This study also found that land‐use types could also alter kr and Ʈc values. Further research, however, is necessary to better quantify the effects of subsurface hydrological conditions and land‐use types on kr under different soil zonalities in China's Hengduan Mountains. © 2018 John Wiley & Sons, Ltd.

Description: Gully erosion is a global driver of soil and landscape degradation. Since 2000, international symposia have been organized to address gully erosion processes, and this paper and special issue provide additional context for the 7th International Symposium on Gully Erosion held at Purdue University in 2016. Several important themes emerged that include the importance and impact of technology transfer, disciplinary fragmentation as an impediment for research advancement, the difficulty in defining the erodibility of sediment within gullies, and the opportunities afforded by remote sensing technology. Abstract The development and evolution of gullies on soil‐mantled hillslopes can devastate agricultural regions and cause widespread soil and landscape degradation. Since 2000, international symposia have been organized to address gully erosion processes, and this paper and special issue provide additional context for the 7th International Symposium on Gully Erosion held at Purdue University in 2016. Several important themes of gully erosion emerged during this symposium that warranted additional discussion here. These topics include the importance and impact of technology transfer, disciplinary fragmentation as an impediment for research advancement, the difficulty in defining the erodibility of sediment within gullies, and the opportunities afforded by remote sensing technology. It is envisioned that such symposia will continue to enhance the capabilities of researchers and practitioners to monitor, model, and manage these important geomorphic processes and to mitigate landscape degradation. © 2018 John Wiley & Sons, Ltd.

Description: The microtopography of two sandstone blocks with and without colonization of biofilms were measured with a traversing micro‐erosoin meter (TMEM) under different simulated environmental conditions. Two‐hourly microtopographic fluctuations of supratidal sandstone were mainly induced by the colonized biofilms and influenced by environmental factors. By increasing the magnitude and number of cycles of expansion and contraction, lithobiontic biofilms were proposed to play an erosive role in rock decay at hourly scale. Abstract In this study laboratory experiments were used to explore the role of biofilms, formed by lithobiontic microorganism communities, in causing hourly surface changes of supratidal sandstone and the potential linkage to long‐term rock decay. To isolate the influence of individual environmental factors (temperature and humidity) on rock surface changes (expansion and contraction), a colonized (biofilm‐covered) and a non‐colonized sandstone block (biofilm‐free) underwent the same univariate microclimatic simulations closely controlled by an environmental chamber. Simulations were run under three different light conditions, with a natural light lamp on, on and off at 20‐min intervals and off, to investigate the impact of light on rock surface dynamics. Measured with a traversing micro‐erosion meter (TMEM), two‐hourly microtopographic fluctuations of these two sandstone blocks were compared in the same environment. Induced by microclimatic variations, surface movements of significantly higher magnitude (12–120% under varying tempeature and 121–154% under varying humidity) and different change patterns were observed on the colonized block, indicating the primary role of biofilm in driving microtopographic fluctuations of supratidal sandstone. However, thermally driven changes of similar magnitude and pattern were observed on both surfaces, suggesting other mechanisms also operating on the non‐colonized rock surface in this process. Due to the sensitivity of biofilm microorganism communities to light, the magnitude and pattern of surface changes was impacted by light condition. Because biofilms increased the magnitude and number of cycles of expansion and contraction of the experimental rock surface, we propose that lithobiontic biofilms facilitate the detachment of grains and granular disintegration on the rock surface, consequently contributing to rock decay and accelerating the rate of breakdown of supratidal rock. This short‐term episode therefore needs to be superimposed on longer term studies to fully understand the role of biofilms in rock surface change. © 2019 John Wiley & Sons, Ltd.

Description: The slope of the mean wind profile, the turbulent kinetic energy and Reynolds stress increase with the surface roughness. The roughness seems to suppress the ejection events. Surface roughness will not only weaken the energy of the very large‐scale motions (VLSMs), but also reduce the scale values of VLSMs near the wall. These influences may cause some changes about the dust transportation in streamwise and vertical direction during the sand and dust storm. Abstract Accurate knowledge of the contacts between surface roughness and the resultant wind speed are important for climatic models, wind power meteorology, agriculture and erosion hazards especially on sand saltation in arid and semi‐arid environments, where vegetation cover is scarce. In this study, synchronous measurements of three‐dimensional wind speed below 5 m are carried out in three different surface roughness conditions in Minqin, China, and the difference in the turbulence statistics and the structure of the very large‐scale motions (VLSMs) were revealed. The results show that the slope of the mean wind profile (MVP), the turbulent kinetic energy (TKE) and Reynolds stress increase with the surface roughness. The roughness seems to suppress the ejection events and the surface roughness will not only weaken the energy of the VLSMs, but also reduce the scale values of VLSMs near the wall. These influences may cause some changes regarding the dust transportation in streamwise and vertical directions during the sand and dust storm (SDS). That is, the decrease of the mean velocity near the ground will reduce the dust transportation in the streamwise direction and influence of the roughness on the ejection and sweep events will change the dust transportation in the vertical direction. Furthermore, the increase of roughness will weaken the scale and energy of VLSMs, which will lead to the decrease of the capacity of dust transportation. © 2019 John Wiley & Sons, Ltd.

Description: Here we show that bias correction methods significantly affect projected changes in extreme precipitation, which may increase or decrease. Subsequently, an increase or decrease of soil loss is projected, while individual climate models may project the opposite change with respect to the ensemble mean. We conclude that the impact of climate change on soil erosion can only accurately be assessed with a bias correction method that best reproduces the projected climate change signal, in combination with a representative ensemble of climate models. Abstract Climate change will most likely cause an increase in extreme precipitation and consequently an increase in soil erosion in many locations worldwide. In most cases, climate model output is used to assess the impact of climate change on soil erosion; however, there is little knowledge of the implications of bias correction methods and climate model ensembles on projected soil erosion rates. Using a soil erosion model, we evaluated the implications of three bias correction methods (delta change, quantile mapping and scaled distribution mapping) and climate model selection on regional soil erosion projections in two contrasting Mediterranean catchments. Depending on the bias correction method, soil erosion is projected to decrease or increase. Scaled distribution mapping best projects the changes in extreme precipitation. While an increase in extreme precipitation does not always result in increased soil loss, it is an important soil erosion indicator. We suggest first establishing the deviation of the bias‐corrected climate signal with respect to the raw climate signal, in particular for extreme precipitation. Furthermore, individual climate models may project opposite changes with respect to the ensemble average; hence climate model ensembles are essential in soil erosion impact assessments to account for climate model uncertainty. We conclude that the impact of climate change on soil erosion can only accurately be assessed with a bias correction method that best reproduces the projected climate change signal, in combination with a representative ensemble of climate models. ©  2018 John Wiley & Sons, Ltd.

Description: Our research shows that a strategic approach to sampling allows the scope for a more complex chronology to be identified subsequently enhancing our understanding of dune development. In contrast to previous studies, we demonstrate that dune accumulation in the Thar was persistent throughout much of the Holocene, with a strong record of dune activity and disturbance in recent millennia and centuries. Abstract The Thar Desert dune system in north‐west India and eastern Pakistan provides a rich archive of past environmental, geomorphological and climatic change. Much of the knowledge about the timing of dune accumulation in the Thar stems from scattered and sporadic records, based on older luminescence dating protocols. If the Thar dune record is to be incorporated within a growing multiproxy framework of past climate and environmental dynamics, it is necessary to generate a systematic record of the timing of dunefield accumulation. From this, relationships to climate and other drivers of dune activity may then be better established. To this end, an intensive programme of field sampling and optically stimulated luminescence (OSL) dating was carried out from a dunefield in the east‐central Thar Desert. This study presents the first detailed Holocene dune accumulation history from the region, and sheds light on the development of the multi‐generational parabolic dune systems. In contrast to previously published work, we identify the importance of the Holocene and the last millennium as periods with a number of preserved accumulation phases. OSL ages suggest that accumulation was persistent during the early and mid‐Holocene (within 11.7‐5.5 ka), late Holocene (2‐1 ka), as well as two major phases in the last millennium (600 – 200 a and within the last 70 a). Potential drivers of dune mobility in the last century include a strong anthropogenic dimension. Rapid net accumulation is recorded in the last 70 years, with rates varying between 2 and 5 m/year, in an environment where agricultural pressures have increased dramatically with the advent of irrigation schemes expanding into dunefield areas. © 2019 John Wiley & Sons, Ltd.

Description: The long‐term evolution of coastal geomorphic structure is examined by analyzing and comparing the geomorphological composition, abundance and diversity of the coasts of three hot‐spot islands in different stages of development. A pattern of change in the geomorphological composition was observed, associated with an increasing coastal geomorphic abundance and diversity from the youngest to the oldest island. This may provide a new interpretation of the coastal evolution on hot‐spot oceanic islands. Abstract The Canary Islands form a volcanic archipelago in which a west–east (W–E) chain of progressively older and less active islands can be observed. In the Canary Islands, unlike most hot‐spot archipelagos, certain geodynamic peculiarities have promoted longer periods of island survival, exceeding 20 Myr. This factor makes these islands a suitable context for this work, which aims to analyze extensively the coastal geomorphic structure on islands with different development states. For this, three islands in different volcanic phases were selected: La Palma (1.8 Myr), Gran Canaria (14.5 Myr) and Fuerteventura (22.6 Myr). An ad hoc landform‐based hierarchical taxonomy was designed to analyze the coastal geomorphic structure of the three islands. Based on a multi‐sourced analysis in geographic information system (GIS) and field recognition, a comprehensive cartographic database was collected using the coastline data‐storing (CDS) method as a feature abundance proxy. Three different aspects of the geomorphological structure were compared and related between the islands: (i) composition, (ii) abundance and (iii) diversity. Through their comparison, we attempt to explore geomorphological aspects of coastal evolution over geological spatiotemporal scales. Composition was explored analyzing the distribution of the feature's longshore frequencies (p). Abundance, by metrics of local abundance (N∩) and whole density (NU). Diversity, through four indices: normalized richness (S) and Margalef index (M) to estimate richness; Simpson index (D) and Shannon index (H’) to estimate evenness. We identified a systematic transformation in the dominant landform composition and a systematic trend in increasing geomorphological abundance and diversity from younger to older islands. The results show a long‐term structural pattern defined by the increase in coastal geomorphic complexity (abundance and diversity) over geological time, as the coasts evolve from predominantly rocky‐erosive to increasingly clastic‐depositional environments. This long‐term geomorphological pattern may be a general aspect of hot‐spot island archipelagos, which can bring a new perspective to the knowledge of their coastal evolution. © 2018 John Wiley & Sons, Ltd.

Description: Results show the QTP mega‐blowouts are some of the largest in the world. Regional patterns of blowout shape and size were observed reflecting extent of aeolian sediments and wind regimes, the relationship between the different morphological parameters showed consistency. Blowouts appear to have been initiated 100 to 500 years ago, coinciding with the Little Ice Age (LIA) climate event. Abstract Blowouts are wind‐eroded landforms that are widely distributed in the north‐eastern part in Qinghai–Tibet Plateau (QTP), China. These blowouts are thought to form in response to climate change and/or human activity but little is known about their morphodynamics. Using field surveys, remote sensing and geographic information system (GIS) spatial analysis, the distribution and morphology of blowouts are analysed and their initiation considered. Results show the QTP mega‐blowouts are some of the largest in the world. The orientations of the trough shaped blowouts are parallel with the prevailing wind, but the saucer and bowl‐shaped blowouts are influenced by bi‐directional transport. Whilst regional patterns of blowout shape and size were observed to reflect the extent of aeolian sediments and wind regimes, the relationship between the different morphological parameters showed consistency. During initial stages of development, the length to width ratios of blowouts increase rapidly with area but after they reach a mega size this relationship stabilizes as blowouts widen. Initial luminescence dating shows that blowouts appear to have initiated ~100 to 500 years ago, coinciding with the Little Ice Age (LIA) climate event when northwest winds are known to have intensified. Further work is required to confirm this initiation period and establish the significance of mega blowouts for landscape degradation and human activities. © 2018 John Wiley & Sons, Ltd.

Description: No abstract is available for this article. © 2019 John Wiley & Sons, Ltd.

Description: The present article focuses on the spatial variation of sediment bed induced by the wave‐blocking phenomenon. Three distinct bed form features along the flume are observed due to the wave‐blocking. Mean flow and turbulence key parameters are examined over the bedforms. Abstract Experiments are conducted in a laboratory flume on the propagation of a surface wave against unidirectional flow with a sediment bed. This article presents the spatial variation of bedforms induced by the wave‐blocking phenomenon by a suitably tuned uniform fluid flow and a counter‐propagating wave. The occurrence of wave‐blocking is confirmed by finding a critical wave frequency in a particular flow discharge in which the waves are effectively blocked and is established using the linear dispersion relation. The purpose of this work is to identify wave‐blocking and its influence on the development of bedforms over the sediment bed. Interestingly bedform signatures are observed at a transition of bedforms in three zones, with asymmetric ripples having a steeper slope downstream face induced by the incoming current, followed by flat sand bars beneath the wave‐blocking zone and more symmetric ripples below the wave‐dominated region at the downstream. This phenomenon suggests that the sediment bed is segmented into three different regions of bed geometry along the flow. The deviations of mean flows, Reynolds stresses, turbulent kinetic energy, and power spectral density due to the wave‐blocking phenomenon are presented along the non‐uniform flow over sediment bed. The bottom shear stress, bed roughness and stochastic nature of the bedform features are also discussed. The results are of relevance to engineers and geoscientists concerned with contemporary process as well as those interested in the interpretation of palaeoenvironmental conditions from fossil bedforms. © 2019 John Wiley & Sons, Ltd.

Description: Rapid shoreline progradation followed by shoreline stability and foredune building at Pedro Beach, southeastern Australia demonstrates the importance of geological inheritance as a morphodynamic factor controlling sandy shoreline evolution. In this case, embayment filling with beach, nearshore and dune sediments, has effectively halted any further shoreline progradation potential as the inherited accommodation space for Holocene sediments is full. Abstract At Pedro Beach on the southeastern coast of Australia a series of foredune ridges provides an opportunity to explore the morphodynamic paradigm as it applies to coastal barrier systems using optically stimulated luminescence (OSL) dating, ground penetrating radar (GPR) and airborne LiDAR topography. A series of sandy dune‐capped ridges, increasing in height seawards, formed from c. 7000 years ago to c. 3900 years ago. During this time the shoreline straightened as the embayment filled and accommodation space for Holocene sediments diminished. Calculation of Holocene sediment accumulation above mean sea level utilising airborne LiDAR topography shows a decline in average sediment supply over this time period coupled with a decrease in shoreline progradation rate from 1.2 m/yr to 0.38 m/yr. The average ridge ‘exposure lifetime’ during this period increases resulting in higher ridges as dune‐forming processes have longer to operate. Increasing exposure to wave and wind energy also appears to have resulted in higher ridges as the sheltering effect of marginal headlands was diminished. An inherited disequilibrium shoreface profile will drive onshore accumulation of sandy sediments forming a prograded barrier; however, if there is no longer ‘accommodation space’ for sediment, this will be an overriding factor causing the cessation of progradation, as occurred c. 3900 years ago at Pedro Beach. Excess sediment in the nearshore zone after 3900 years ago may have been moved northward to nourish downdrift beaches in the compartment. A high outer foredune has formed through vertical accretion after 500 years ago, evidenced by GPR subsurface structures and OSL ages, with a distinct period of vertical and lee slope accretion and dated to the period 1890–1930 AD. The increased dune sediment transport resulting in foredune building is attributed to recent human disturbance. © 2018 John Wiley & Sons, Ltd.

Description: Semi‐automatic LiDAR mapping and landform classification applied to the Verdun battlefield enabled the identification of eight types of features including 600 000 bomb craters and 18 000 shelters. On the basis of these results, landform maps were generated over the 100 km2 of the studied site showing intensely disturbed areas and particular spatial patterns in the feature location. Density analysis permits the quantification of geomorphic disturbance and revealed that at least 1.64 million m3 of earth materials were displaced by shell explosions and defense constructions. Abstract Acting as efficient earth‐movers, soldiers can be viewed as significant geomorphological drivers of landscape change when replaced in the recent debates on Anthropocene Geomorphology. ‘Polemoforms’, generated by military activities, correspond with a set of human‐made landforms of various sizes and geometries. They are particularly common on the World War One battlefield of Verdun (France) which ranks among the largest battles of attrition along the Western Front. The artillery bombardments and building of defensive positions in that battle significantly altered the landscape, resulting in thousands of shell craters, dugouts, and gun positions that have altered both the meso and microtopography. This paper proposes an innovative methodology to make an exhaustive inventory of these small‐scale conflict‐induced landforms (excluding linear features such as trenches) using a digital terrain model (DTM) acquired by airborne LiDAR on the whole battlefield. Morphometric analysis was conducted using Kohonen's self‐organizing maps (SOMs) and hierarchical agglomerative clustering (HAC) in order to quantify and classify the high number of war landforms. This combined approach allowed for mapping more than one million landforms which can be classified into eight different shapes including shell craters and various soldier‐made landforms (i.e. shelters, gun positions, etc.). Detection quality evaluation using field observations revealed the algorithm successfully classified 93% of shell craters and 74% of anthropologically constructed landforms. Finally, the iconographic database and map series produced will help archaeologists and foresters to better manage the historic site of Verdun, today covered by a large forest of ~10 000 ha. © 2019 John Wiley & Sons, Ltd.

Description: Ecological, sedimentological, and sediment transport data were analysed to understand the interconnections between coastal morphology and reef ecology within a fringing reef system. The sediment reservoir is predominantly derived from ‘old’ source material (≥ 1400 years old) but this material is supplied to the shoreline on modern timescales. These results suggest that sediment budgets of similar reef systems may be more resilient to climate change as contemporary reef health and community composition have limited influence on sediment supply. Abstract Reef‐associated landforms are coupled to the health of the reef ecosystem which produces the sediment that forms and maintains these landforms. However, this connection can make reef‐fronted coastlines sensitive to the impacts of climate change, given that any decline in ecosystem health (e.g. decreasing sediment supply) or changes to physical processes (e.g. sea level rise, increasing wave energy) could drive the sediment budgets of these systems into a net erosive state. Therefore, knowledge of both the sediment sources and transport mechanisms is required to predict the sensitivity of reef‐associated landforms to future climate change. Here, we examine the benthic habitat composition, sediment characteristics (composition, texture, and age), and transport mechanisms and pathways to understand the interconnections between coastal morphology and the reef system at Tantabiddi, Ningaloo Reef, Western Australia. Benthic surveys and sediment composition analysis revealed that although live coral accounts for less than 5% of the benthic cover, coral is the dominant sediment constituent (34% on average). Sediment ages (238U/230Th) were mostly found to be thousands of years old, suggesting that the primary sediment source is relic reef material (e.g. Holocene reef framework). Sediment transport across the lagoon was quantified through measurements of ripple migration rates, which were found to be shoreward migrating and responsible for feeding the large shoreline salient in the lee of the reef. The derived sediment fluxes were comparable with previously measured rates of sediment production by bioerosion. These results suggest that sediment budgets of systems dependent on old (〉103 years) source materials may be more resilient to climate change as present‐day reef health and community composition (i.e. sources of ‘new’ carbonate production) have limited influence on sediment supply. Therefore, the vulnerability of reef‐associated landforms in these systems will be dictated by future changes to mechanisms of sediment generation (e.g. bioerosion) and/or physical processes. © 2018 John Wiley & Sons, Ltd.

Description: Quantifying organic carbon (OC) fluxes on a shrinking Arctic glacier surface resulted in net accumulation. The main inputs of this OC are atmospheric deposition and ice melt. Both the particulate and dissolved OC are removed from glacier surfaces with a delay, facilitating surface darkening and a late‐summer release of labile OC. Abstract Arctic glaciers are rapidly responding to global warming by releasing organic carbon (OC) to downstream ecosystems. The glacier surface is arguably the most biologically active and biodiverse glacial habitat and therefore the site of important OC transformation and storage, although rates and magnitudes are poorly constrained. In this paper, we present measurements of OC fluxes associated with atmospheric deposition, ice melt, biological growth, fluvial transport and storage (in superimposed ice and cryoconite debris) for a supraglacial catchment on Foxfonna glacier, Svalbard (Norway), across two consecutive years. We found that in general atmospheric OC input (averaging 0.63 ± 0.25 Mg a‐1 total organic carbon, i.e. TOC, and 0.40 ± 0.22 Mg a‐1 dissolved organic carbon, i.e. DOC) exceeded fluvial OC export (0.46 ± 0.04 Mg a‐1 TOC and 0.36 ± 0.03 Mg a‐1 DOC). Early in the summer, OC was mobilised in snowmelt but its release was delayed by temporary storage in superimposed ice on the glacier surface. This delayed the export of 28.5% of the TOC in runoff. Biological production in cryoconite deposits was a negligible potential source of OC to runoff, while englacial ice melt was far more important on account of the glacier's negative ice mass balance (–0.89 and –0.42 m a‐1 in 2011 and 2012, respectively). However, construction of a detailed OC budget using these fluxes shows an excess of inputs over outputs, resulting in a net retention of OC on the glacier surface at a rate that would require c. 3 years to account for the OC stored as cryoconite debris. © 2018 John Wiley & Sons, Ltd.

Description: We examine the capability of a landscape evolution model (LEM) to predict both soil erosion rate and pattern of erosion and deposition. The outputs from this numerical model (SIBERIA) was compared to field measured soil redistribution rates and patterns determined using the environmental tracer 137Cs. SIBERIA can approximate these independently quantified erosion and deposition patterns and rates suggesting that LEMs can be a reliable alternative to complex and time consuming methods such as that using environmental tracers for the determination of erosion rates. Abstract Excessive soil erosion and deposition is recognised as a significant land degradation issue. Quantifying soil erosion and deposition is a non‐trivial task. One of these methods has been the mathematical modelling of soil erosion and deposition patterns and the processes that drive them. Here we examine the capability of a landscape evolution model to predict both soil erosion rate and pattern of erosion and deposition. This numerical model (SIBERIA) uses a Digital Elevation Model (DEM) to represent the landscape and calculates erosion and deposition at each grid point in the DEM. To assess field soil redistribution rates (SRR) and patterns the distribution of the environmental tracer 137Cs has been analysed. Net hill slope SRR predicted by SIBERIA (a soil loss rate of 1.7 to 4.3 t ha‐1 yr‐1) were found to be in good agreement with 137Cs based estimates (2.1 – 3.4 t ha‐1 yr‐1) providing confidence in the predictive ability of the model at the hillslope scale. However some differences in predicted erosion/deposition patterns were noted due to historical changes in landscape form (i.e. the addition of a contour bank) and possible causes discussed, as is the finding that soil erosion rates are an order of magnitude higher than likely soil production rates. The finding that SIBERIA can approximate independently quantified erosion and deposition patterns and rates is encouraging, providing confidence in the employment of DEM based models to quantify hillslope erosion rates and demonstrating the potential to upscale for the prediction of whole catchment erosion and deposition. The findings of this study suggest that LEMs can be a reliable alternative to complex and time consuming methods such as that using environmental tracers for the determination of erosion rates. The model and approach demonstrates a new approach to assessing soil erosion that can be employed elsewhere. © 2018 John Wiley & Sons, Ltd.

Description: Biostabilization of bio‐sedimentary beds with and without cyclic stress is compared. Results showed that the erosional behaviour of the underlying sand was affected and transition of bed structures were observed. Conceptual erosion framework is proposed for bio‐sedimentary systems recognizing the variation of different growth stages and cyclic effects. Abstract Biofilm mediated intertidal sediments exhibit more complex erosional behaviour than abiotic systems. A major feature of intertidal systems is the exposure to repeated cycles of high and low shear created by tidal conditions and also less predictable episodic events, such as storms. There is very little information on how biofilm‐forming communities respond to these conditions. In this study, the effects of both single and repeated‐cycles of shear on the stability of newly developed bio‐sedimentary beds was examined. Cleaned sand, without any potential biostabilization, was used as the control. For the single‐cycle scenario, biofilms were incubated on a non‐cohesive sandy bed under prolonged low shear periods varying between 5 and 22 days, after which erosional stress was applied. No significant biostabilization was observed for the youngest bio‐sedimentary bed (after five days of low shear incubation). After 22 days, microbial communities were characterized by a firmly attached surface biofilm. To cause erosion, greater hydrodynamic stress (0.28 Pa) was required. The erosional behaviour of the underlying sand was also affected in that bedform ripples noted in the control system were no longer observed. Instead, a sudden ‘mass erosion’ took place (0.33 Pa). The one‐cycle scenario indicated that significant biostabilization of sand only occurred after a relative long calm period. Under repeated cycles of stress (five days of low stress followed by high stress event and re‐incubation, repeated for four cycles = 20 days), frequent cyclic disturbance did not degrade the system stability but enhanced biostabilization. The properties of the sub‐surface sediments were also affected where erosion rates were further inhibited. We hypothesize that organic material eroded from the bed acted as a ‘biofilm precursor’ supporting the development of new biofilm growth. A conceptual framework is presented to highlight the dynamics of bio‐sedimentary beds and the effects of growth history under repeated‐cycles. © 2019 John Wiley & Sons, Ltd.

Description: a) Evaluation of acoustic inversion techniques using down‐looking acoustic Doppler current profilers (ADCP) in quantifying suspended sediment in a large sand bed river with varying bi‐modal particle size distributions and wash‐load and suspended‐sand ratios. b) Calibrations were successfully developed between corrected backscatter and suspended‐sand concentrations for all sites and ADCP frequencies. c) Noise values, calculated using the sonar equation and sediment sample characteristics, were fairly constant, suggesting the applicability of the proposed methodology to other sand bed rivers. Abstract Quantifying sediment flux within rivers is a challenge for many disciplines due, mainly, to difficulties inherent to traditional sediment sampling methods. These methods are operationally complex, high cost, and high risk. Additionally, the resulting data provide a low spatial and temporal resolution estimate of the total sediment flux, which has impeded advances in the understanding of the hydro‐geomorphic characteristics of rivers. Acoustic technologies have been recognized as a leading tool for increasing the resolution of sediment data by relating their echo intensity level measurements to suspended sediment. Further effort is required to robustly test and develop these techniques across a wide range of conditions found in natural river systems. This article aims to evaluate the application of acoustic inversion techniques using commercially available, down‐looking acoustic Doppler current profilers (ADCPs) in quantifying suspended sediment in a large sand bed river with varying bi‐modal particle size distributions, wash load and suspended‐sand ratios, and water stages. To achieve this objective, suspended sediment was physically sampled along the Paraná River, Argentina, under various hydro‐sedimentological regimes. Two ADCPs emitting different sound frequencies were used to simultaneously profile echo intensity level within the water column. Using the sonar equation, calibrations were determined between suspended‐sand concentrations and acoustic backscatter to solve the inverse problem. The study also analyzed the roles played by each term of the sonar equation, such as ADCP frequency, power supply, instrument constants, and particle size distributions typically found in sand bed rivers, on sediment attenuation and backscatter. Calibrations were successfully developed between corrected backscatter and suspended‐sand concentrations for all sites and ADCP frequencies, resulting in mean suspended‐sand concentration estimates within about 40% of the mean sampled concentrations. Noise values, calculated using the sonar equation and sediment sample characteristics, were fairly constant across evaluations, suggesting that they could be applied to other sand bed rivers. © 2018 John Wiley & Sons, Ltd.

Description: Abstract Shore platforms control wave energy transformation which, in turn, controls energy delivery to the cliff toe and nearshore sediment transport. Insight into shore platform erosion rates has conventionally been constrained at mm‐scales using micro‐erosion metres, and at m‐scales using cartographic data. On apparently slowly eroding coasts, such approaches are fundamentally reliant upon long‐term observation to capture emergent erosion patterns. Where in practise timescales are short, and where change is either below the resolution or saturates the mode of measurement, the collection of data that enables the identification of the actual mechanisms of erosion is hindered. We developed a method to monitor shore platform erosion at millimetre resolution within metre‐scale monitoring plots using Structure‐from‐Motion photogrammetry. We conducted monthly surveys at 15 0.25 m2 sites distributed across the Hartle Loup platform in North Yorkshire, UK, over one year. We derived topographic data at 0.001 m resolution, retaining a vertical precision of change detection of 0.001 m. We captured a mean erosion rate of 0.528 mm yr‐1, but this varied considerably both across the platform and through the year. We characterised the volume and shape of eroded material. The detachment volume‐frequency and shape distributions suggest that erosion happens primarily via removal of shale platelets. We identify that the at‐a‐point erosion rate can be predicted by the distance from the cliff and the tidal level, whereby erosion rates are higher closer to the cliff and at locations of higher tidal duration. The size of individual detachments is controlled by local micro‐topography and rock structure, whereby larger detachments are observed on more rough sections of the platform. Faster erosion rates and larger detachments occur in summer months, rather than in more energetic winter conditions. These results have the potential to form the basis of improved models of how platforms erode over both short‐ and long‐timescales.

Description: The loess disintegration process can be divided into three stages—wetting, softening and subsidence—the first two of which are short and show very weak disintegration, thus disintegration is mainly concentrated in the third stage. The main factors influencing the disintegration of loess samples are shape, size and clay mineral content. Abstract Loess structures with large joints and fissures often undergo natural disintegration when subjected to contact with water. The slaking of loess results in the formation of loess gullies, caves, and landslides. To study the disintegration properties and the factors influencing them, we carried out field and laboratory tests. First, we carried out an in situ disintegration test using different sample shapes obtained from Heifangtai and analysed the effect of soil sample shape on loess disintegration. We then developed an improved disintegrator and tested the effect of different factors on the disintegration of loess. The effects of water content, salinity, and composition on disintegration are discussed. The results show that the loess disintegration process can be divided into three broad stages – wetting, softening, and subsidence – the disintegration is mainly concentrated in the third stage, while the first two stages are short and show very weak disintegration. The main factors influencing the disintegration of loess samples are shape, size, and clay mineral content. During the in situ disintegration test, the edge angles of soil samples are disintegrated, to soften all their edges. Disintegration duration increases with increasing sample size, but the extent of disintegration was found to decrease. Disintegration duration is inversely proportional to the loess disintegration rate. The loess disintegration rate is positively correlated with water temperature within a certain range; however, the reverse is observed with soil sample size and initial water content, and salinity was found to have little effect on the disintegration rate. Higher clay content of cohesive soil and weaker permeability leads to a slower disintegration rate. Additionally, lower cementation may easily cause loess disintegration. © 2019 John Wiley & Sons, Ltd.

Description: Abstract Probably the largest regular shoreline fluctuations on Earth occur along the 1500 km‐long wave‐exposed Guianas coast of South America between the mouths of the Amazon and Orinoco Rivers, the world's longest muddy coast. The Guianas coast is influenced by a succession of mud banks migrating northwestward from the Amazon. Migrating mud banks dissipate waves, partially weld onshore, and lead to coastal progradation, aided by large‐scale colonization by mangroves, whereas mangrove‐colonized areas between banks (inter‐bank areas) are exposed to strong wave action and undergo erosion. On large tracts of this coast, urbanization and farming have led to fragmentation and removal of mangroves, resulting in aggravated shoreline retreat. To highlight this situation, we determined, in a setting where mangroves and backshore freshwater marshes have been converted into rice polders in French Guiana, shoreline change over 38 years (1976‐2014) from satellite images and aerial orthophotographs. We also conducted four field experiments between October 2013 and October 2014, comprising topographic and hydrodynamic measurements, to determine mechanisms of retreat. The polder showed persistent retreat, at peak rates of up to ‐200 m/yr, and no recovery over the 38‐year period of monitored change. Notwithstanding high erosion rates, mangrove shorelines show strong resilience, with recovery characterized by massive accretion. Retreat of the polder results in a steep wave‐reworked shoreface with a lowered capacity for bank welding onshore and mangrove establishment. Persistent polder erosion is accompanied by the formation of a sandy chenier that retreats landwards at rates largely exceeding those in inter‐bank situations. These results show that anthropogenic mangrove removal can durably modify the morphodynamics of muddy shorefaces. This limits the capacity for shoreline recovery and mangrove re‐establishment even when there is no sustained long‐term deficit in mud supply, as in the case of the Amazon‐influenced Guianas coast.

Description: Based on flume experiments with bimodal sand mixtures (D50 ≤ 410 μm) we show that the effect of the fine fraction in a mixture changes from mobilization to stabilization depending on the grain‐size ratio RD = D50,coarse/D50,fine. The comparison with similar experiments with spherical glass beads indicates that bed mobility decreases with grain angularity. The near‐bed flow velocities and inflow into the grain matrix depend on both grain shape and grain‐size ratio and can be related to events of increased bed mobility. Abstract Different studies investigating the stability of mixed sediment have found that the fine fraction can either stabilize or mobilize the bed. This study aims to find where the transition between these two modes occurs for sandy sediment and to identify the underlying (grain‐scale) processes. Flume experiments with bimodal sediment were used to investigate near‐bed processes of a non‐cohesive sediment bed, and in particular how the grain shape and the ratio of different grain sizes influence bed mobility. Medium sand (D50,c ≈ 400 μm) was mixed with 40 % fine material of different diameters (D50,f = 53; 111; 193 μm) and subjected to increasing flow velocities (U = 1.3–22.2 cm s‐1). The bed mobility (i.e. the change of the bed level over time), turbidity and near‐bed hydrodynamics were analysed. Selected results were compared with similar previous experiments with spherical glass beads. The findings indicate that, due to the complex grain shapes of natural sediment, a sand bed is more stable than a bed composed of glass beads. The grain‐size ratio RD = Dc /Df between the coarse and fine grain diameters controls whether the mixed bed is stabilized or mobilized by the presence of fines, with the transition between the modes occurring at RD = 4–5.5. Mixed beds with a very low RD 〈 2 behave like a unimodal bed. The results suggest that RD and grain shape influence bed roughness, near‐bed flow, bed microstructure and the flow into and through the upper bed layers, which subsequently governs bed mobility. The interplay between all these processes can explain the transition between the stabilizing effect (high RD, small pore space) and the mobilizing effect (low RD, large pore space) of a fine fraction in a grain‐size mixture. © 2018 John Wiley & Sons, Ltd.

Description: We present field and laboratory observations of peat erosion using Structure‐from‐Motion (SfM) photogrammetry. Over a 12 month period, 11 repeated SfM surveys were conducted on four geomorphological sites of 18–28 m2 (peat hagg, gully wall, riparian area and gully head) in a blanket peatland in northern England. The spatial and temporal patterns of topographic change and its topographic controls were illustrated from both field and laboratory surveys. Abstract Little is known about the spatial and temporal variability of peat erosion nor some of its topographic and weather‐related drivers. We present field and laboratory observations of peat erosion using Structure‐from‐Motion (SfM) photogrammetry. Over a 12 month period, 11 repeated SfM surveys were conducted on four geomorphological sites of 18–28 m2 (peat hagg, gully wall, riparian area and gully head) in a blanket peatland in northern England. A net topographic change of –14 to +30 mm yr–1 for the four sites was observed during the whole monitoring period. Cold conditions in the winter of 2016 resulted in highly variable volume change (net surface topographic rise first and lowering afterwards) via freeze–thaw processes. Long periods of dry conditions in the summer of 2017 led to desiccation and drying and cracking of the peat surface and a corresponding surface lowering. Topographic changes were mainly observed over short‐term intervals when intense rainfall, flow wash, needle‐ice production or surface desiccation was observed. In the laboratory, we applied rainfall simulations on peat blocks and compared the peat losses quantified by traditional sediment flux measurements with SfM derived topographic data. The magnitude of topographic change determined by SfM (mean value: 0.7 mm, SD: 4.3 mm) was very different to the areal average determined by the sediment yield from the blocks (mean value: –0.1 mm, SD: 0.1 mm). Topographic controls on spatial patterns of topographic change were illustrated from both field and laboratory surveys. Roughness was positively correlated to positive topographic change and was negatively correlated to negative topographic change at field plot scale and laboratory macroscale. Overall, the importance of event‐scale change and the direct relationship between surface roughness and the rate of topographic change are important characteristics which we suggest are generalizable to other environments. © 2018 John Wiley & Sons, Ltd.

Description: New bedload monitoring using concomitant vertical and horizontal pipe microphones is conducted. A ratio (Rhv) between the numbers of pulses detected by these sensors is proposed. Pulses counted by a centrally located pipe microphone are corrected by the ratio, and correlated well with the bedload discharge calculated from the sampler. Abstract The pipe microphone has been shown to be an effective means for monitoring bedload transport in mountain streams. It is commonly installed perpendicular to the flow direction on a stable river bed, such as that of a check dam. Acoustic pulses caused by bedload collisions with the pipe are detected by a microphone. However, bedload particles saltating over the pipe remain undetected. To overcome this disadvantage, we installed a horizontal as well as a vertical pipe microphone in the Ashi‐arai‐dani supercritical channel located in the Hodaka mountain range, Japan. The vertical pipe was installed on the wall of the channel and the horizontal pipe was installed on the channel bed. The acoustic response of the horizontal pipe is expected to be larger than that of the vertical pipe, because the bedload concentration decreases with increasing height above the bed. However, at high amplifications, the peak pulse value from the vertical pipe is higher than that from the horizontal pipe. We explain this observation as follows: under high bedload discharge conditions, the pulses of the horizontal pipe are saturated but those of the vertical pipe are not. We proposed a ratio (Rhv) between the pulses detected by these sensors, and applied this ratio for calibrating the contemporaneous pulses detected by a microphone located immediately upstream of a bedload slot sampler. Indeed the Rhv‐corrected pulses correlated well with the bedload discharge calculated from the sampler, supporting our explanation. We conclude that bedload monitoring using concomitant vertical and horizontal pipe microphones can be used to calibrate centrally located pipe microphones when the bedload concentration is approximately homogeneous laterally across the width of the channel cross‐section, and thereby represent bedload discharges more accurately than with only a single pipe microphone. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Active gullies increase sediment concentrations in streams, rendering upland soil conservation practices less effective. Conservation programs treating the whole watershed including gullies are the most effective. Abstract Soil erosion, with significant contributions from gullies, is a serious problem in the Ethiopian highlands. The objective of this paper is to examine patterns of discharge and sediment transport in the Ethiopian highlands, and to provide an initial assessment of whether soil and water conservation practices (SWCP) can reduce sediment loads in watersheds with actively eroding gullies. The study was conducted in the 414‐ha Ene‐Chilala watershed with a unimodal sub‐humid monsoon climate and actively eroding gullies in the valley bottoms. In 2013 and 2014, the local community was mandated to install upland infiltration furrows and farmers voluntarily rehabilitated six gully heads and protected 16 m of eroding stream banks. Discharge and sediment concentration were measured in two upslope watersheds and at the outlet. Since median infiltration capacity in the uplands was always greater than the rainfall intensity, saturation excess and interflow were main runoff pathways. After 175 mm cumulative rainfall, the groundwater table reached the surface in the valley bottoms, restricting infiltration, and runoff was generated as saturation excess overland flow and flowed through active gullies out of the watershed. Upland rill erosion on ploughed land early in the rain phase, and gully erosion in saturated valley bottoms thereafter, were sources of sediment in the rivers. The mandated infiltration furrows installed on the contour overtopped and damaged cropland. The off‐contour furrows increased streamflow. Gully rehabilitation of an upland gully effectively reduced stream sediment concentration in the upland weir. However, there was little benefit at the watershed outlet since the stream picked up the unconsolidated sediment from the failing banks in the downstream porting of the watershed. Therefore, soil conservation programs that in addition to installing upland practices, rehabilitate the main sediment source (gullies) appear to be the most effective approach to reducing in‐stream suspended sediment concentrations. © 2018 John Wiley & Sons, Ltd.

Description: Water and erosion control structures that are no longer being maintained can induce erosion, gullying, and headcut advance. Knowledge of land‐use history is critical for managing landscapes to limit the extent of locally induced degradation. Abstract Control over water supply and distribution is critical for agriculture in drylands where manipulating surface runoff often serves the dual purpose of erosion control. However, little is known of the geomorphic impacts and legacy effects of rangeland water manipulation infrastructure, especially if not maintained. This study investigated the geomorphic impacts of structures such as earthen berms, water control gates, and stock tanks, in a semiarid rangeland in the southwestern USA that is responding to both regional channel incision that was initiated over a century ago, and a more recent land use change that involved cattle removal and abandonment of structures. The functional condition of remnant structures was inventoried, mapped, and assessed using aerial imagery and lidar data. Headcut initiation, scour, and channel incision associated with compromised lateral channel berms, concrete water control structures, floodplain water spreader berms, and stock tanks were identified as threats to floodplains and associated habitat. Almost half of 27 identified lateral channel berms (48%) have been breached and 15% have experienced lateral scour; 18% of 218 shorter water spreader berms have been breached and 17% have experienced lateral scour. A relatively small number of 117 stock tanks (6%) are identified as structurally compromised based on analysis of aerial imagery, although many currently do not provide consistent water supplies. In some cases, the onset of localized disturbance is recent enough that opportunities for mitigation can be identified to alter the potentially damaging erosion trajectories that are ultimately driven by regional geomorphic instability. Understanding the effects of prior land use and remnant structures on channel and floodplain morphologic condition is critical because both current land management and future land use options are constrained by inherited land use legacy effects. Published 2017. This article is a U.S. Government work and is in the public domain in the USA

Description: Abstract Salt marshes are crucially important ecosystems at the boundary between the land and the sea, that are experiencing significant losses worldwide mainly dictated by the erosion of their margins. Improving our understanding of the mechanisms controlling marsh edge erosion is a key step to address conservation issues and salt‐marsh response to changes in the environmental forcing. Here we have employed a complete, coupled Wind‐Wave Tidal Model (WWTM) to analyse the temporal evolution of the wave field, and in particular of the mean wave power density, in the Venice Lagoon over the past four centuries (from 1611 to 2012). We have then related wave‐field changes to the observed erosion patterns determined by comparing recent aerial photographs (1978‐2010) and historical bathymetric data. The results of our analyses from the Venice Lagoon show that, while wave‐fields did not significantly change from 1611 to 1901, a rapid increase in wave power densities occurred in the last century. This is suggested to depend on the positive feedback between relevant morphological evolutions and changes in the wave field, both influenced by natural forcing and anthropogenic pressures. We also emphasize the existence of a strong positive linear relationship between the volumetric marsh erosion rate and mean wave power density. We thus suggest that relating salt‐marsh lateral erosion rates to properly computed mean wave power densities provides a valuable tool to address long‐term tidal morphodynamics.

Description: A process based water erosion estimation model, WEPP, is supported by inputs sourced via remote sensing technologies and existing soil geographic databases to yield hill slope sheet and rill erosion estimates across large areas of the Central US. This system can be applied to other regions as well depending on input availability, but output resolution and potential accuracy will depend on input quality and resolution. Erosion rates are currently reported daily at the HUC12 watershed (40‐160 square kilometer) spatial resolution. Abstract Water runoff and sediment transport from agricultural uplands are substantial threats to water quality and sustained crop production. To improve soil and water resources, farmers, conservationists, and policy‐makers must understand how landforms, soil types, farming practices, and rainfall interact with water runoff and soil erosion processes. To that end, the Iowa Daily Erosion Project (IDEP) was designed and implemented in 2003 to inventory these factors across Iowa in the United States. IDEP utilized the Water Erosion Prediction Project (WEPP) soil erosion model along with radar‐derived precipitation data and government‐provided slope, soil, and management information to produce daily estimates of soil erosion and runoff at the township scale (93 km2 [36 mi2]). Improved national databases and evolving remote sensing technology now permit the derivation of slope, soil, and field‐level management inputs for WEPP. These remotely sensed parameters, along with more detailed meteorological data, now drive daily WEPP hillslope soil erosion and water runoff estimates at the small watershed scale, approximately 90 km2 (35 mi2), across sections of multiple Midwest states. The revisions constitute a substantial improvement as more realistic field conditions are reflected, more detailed weather data are utilized, hill slope sampling density is an order of magnitude greater, and results are aggregated based on surface hydrology enabling further watershed research and analysis. Considering these improvements and the expansion of the project beyond Iowa it was renamed the Daily Erosion Project (DEP). Statistical and comparative evaluations of soil erosion simulations indicate that the sampling density is adequate and the results are defendable. The modeling framework developed is readily adaptable to other regions given suitable inputs. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: Annual erosion of mature gullies was monitored for 13 years in grazed rangeland draining to the Great Barrier Reef (a), and for 4 years under long‐term grazing exclosure (b). Under grazing, gully sediment yield contributed between 29 and 44% of catchment sediment yield and wall erosion was the largest sediment source. Under long‐term exclosure gullies were shorter, with sediment yield less than half of gullies under grazing. Abstract Drainage network extension in semi‐arid rangelands has contributed to a large increase in the amount of fine sediment delivered to the coastal lagoon of the Great Barrier Reef, but gully erosion rates and dynamics are poorly understood. This study monitored annual erosion, deposition and vegetation cover in six gullies for 13 years, in granite‐derived soils of the tropical Burdekin River basin. We also monitored a further 11 gullies in three nearby catchments for 4 years to investigate the effects of grazing intensity. Under livestock grazing, the long‐term fine sediment yield from the planform area of gullies was 6.1 t ha‐1 yr‐1. This was 7.3 times the catchment sediment yield, indicating that gullies were erosion hotspots within the catchment. It was estimated that gully erosion supplied between 29 and 44% of catchment sediment yield from 4.5% of catchment area, of which 85% was derived from gully wall erosion. Under long‐term livestock exclusion gully sediment yields were 77% lower than those of grazed gullies due to smaller gully extent, and lower erosion rates especially on gully walls. Gully wall erosion will continue to be a major landscape sediment source that is sensitive to grazing pressure, long after gully length and depth have stabilised. Wall erosion was generally lower at higher levels of wall vegetation cover, suggesting that yield could be reduced by increasing cover. Annual variations in gully head erosion and net sediment yield were strongly dependent on annual rainfall and runoff, suggesting that sediment yield would also be reduced if surface runoff could be reduced. Deposition occurred in the downstream valley segments of most gullies. This study concludes that reducing livestock grazing pressure within and around gullies in hillslope drainage lines is a primary method of gully erosion control, which could deliver substantial reductions in sediment yield. Copyright © 2018 John Wiley & Sons, Ltd.

Description: Dynamic of gully density was evaluated for the Middle Volga region of the Russian Plain for the last 60 years based on the interpretation of aerial photographs and satellite images for the three time windows. We found a strong (order of magnitude) reduction in active gully density for the period 2010–2015 as compared to 1986–1991. The main reason for this is likely the increasing winter air temperatures leading to a significant reduction in surface runoff during snowmelt. Abstract A large‐scale mapping of gully density was carried out for the Middle Volga region of the Russian Plain (188 000 km2) based on the interpretation of aerial photographs (scale 1:17 000; surveys undertaken during 1956–1970). In addition, spatial‐temporal dynamic of gully density were assessed for some parts of the study area (the Udmurt Republic and the Mesha and Ulema River basins of Tatarstan), based on the interpretation of aerial photographs (survey 1986–1991) and high resolution satellite images (2012–2015). Information on factors potentially controlling gully formation and development were collected and a geographic information system (GIS) analysis was conducted. Results show the strong development of gullies in the study area over the 1956–1970 period with an average gully density of 0.21 km km−2. For the Udmurt region, we found that gully densities varied little in the period 1956–1986, during which the total active gully length reduced with only 2%. This period was characterized by low variable climatic conditions and a stable fraction of arable land with a relatively continuous crop rotation system. However, gully dynamics seems to have changed more strongly during recent decades. We found a strong (order of magnitude) reduction in active gully density for the period 2010–2015 as compared to 1986–1991. The main reason for this is likely the increasing winter air temperatures. This leads to a significant reduction in surface runoff during spring as a result of snowmelt. Nonetheless, in some regions (i.e. the Udmurt Republic in the taiga zone), the abandonment of arable land after 1991 likely plays a significant role. Likewise, a decline in the frequency of extreme rainfall events (〉 50 mm) may have played a role. All of these factors contribute to a reduction of surface runoff to the gullies and their subsequent stabilization. © 2018 John Wiley & Sons, Ltd.

Description: The presence of submersed aquatic vegetation (SAV) modifies hydrodynamics and sediment transport processes, and therefore also the morphological evolution of river mouth bars. SAV on the bar top decreased the longitudinal velocity over the top of the developing bar and increased the transverse velocity over the bar, resulting in a velocity redistribution around the bar. Increasing the vegetation height and density decreased the bed shear stress over the bar, resulting in a reduction of sediment transport. Abstract This work is inspired by the sudden resurgence of the submersed aquatic vegetation (SAV) bed in the Chesapeake Bay (USA). Because the SAV bed occurs at the mouth of the Bay's main tributary (Susquehanna River), it plays a significant role in modulating sediment and nutrient inputs from the Susquehanna to the Bay. Previous model studies on the impact of submersed aquatic vegetation on the development of river mouth bars lacked a complete mechanistic understanding. This study takes advantage of new advances in 3D computational models that include explicit physical‐sedimentological feedbacks to obtain this understanding. Specifically, we used Delft3D, a state‐of‐the‐art hydrodynamic model that provides fine‐scale computations of three‐dimensional flow velocity and bed shear stress, which can be linked to sediment deposition and erosion. Vegetation is modeled using a parameterization of hydraulic roughness that depends on vegetation height, stem density, diameter, and drag coefficient. We evaluate the hydrodynamics, bed shear stresses, and sediment dynamics for different vegetation scenarios under conditions of low and high river discharge. Model runs vary the vegetation height, density, river discharge, and suspended‐sediment concentration. Numerical results from the idealized model show that dense SAV on river mouth bars substantially diverts river discharge into adjacent channels and promotes sediment deposition at ridge margins, as well as upstream bar migration. Increasing vegetation height and density forms sandier bars closer to the river mouth and alteration of the bar shape. Thus, this study highlights the important role of SAV in shaping estuarine geomorphology, which is especially relevant for coastal management. © 2019 John Wiley & Sons, Ltd.

Description: We present the first GPR investigation of the internal structure of a newly identified type of barrier island formed on the Lewisian Gneiss strandflat of the Outer Hebrides. Bedrock topography and sediment supply are interpreted as the dominant controls on variability in barrier structure. A distinctive machair facies of sub‐horizontal, undulating reflections, is the dominant component of the barriers at each site. In areas where deep depressions exist in the bedrock, machair is developed on accumulated transgressive dune deposits. Abstract The barrier islands that fringe the western shore of the Outer Hebrides are globally unusual in that they are developed on a planated bedrock (strandflat) surface. They also contain the most extensive area of machair (a distinctive vegetated sandy plain) in the British Isles. This paper presents the first investigation of the internal structure and morphology of these barrier islands and investigates the controls on their structure. The barriers form extensive (300‐1000 metres wide) but thin (1.5‐2 m) surficial deposits typically resting on bedrock. In areas where depressions exist in the bedrock, and where sediment supply permits, transgressive dunes underlie the machair. A distinctive machair facies of sub‐horizontal, undulating reflections, which are laterally continuous over tens of metres is the dominant component of the barriers at each site. This reflects episodic deposition of windblown sand up to the level of the water table. Thereafter any additional sand is transported through the system to accumulate in topographic lows as lake fills, or on topographic highs as ‘high machair’. Eight radar facies were identified, the extent and presence of which vary between the study sites. Bedrock topography and sediment supply are interpreted as the dominant controls on variability in barrier structure. © 2019 John Wiley & Sons, Ltd.

Description: The HVSR method provides a rapid and inexpensive means of estimating the thickness of laterites (soil + saprolite). The method was tested in Oahu and the Big Island of Hawaii in connection with outcrop and lithologic log control and where MASW profiles had also been obtained. Abstract Lateritic weathering profiles (LWPs) are widespread in the tropics and comprise an important component of the Critical Zone (CZ). The Hawaiian Islands make an excellent natural laboratory for examining the tropical CZ, where the bedrock composition (basalt) is nearly uniform and rainfall varies greatly. This natural laboratory is employed to assess the utility of the HVSR (horizontal/vertical spectral ratio) method to characterize the shear‐wave velocity (Vs) structure of LWPs, particularly the depth to the contact between saprolite and basalt bedrock. LWP thicknesses determined from HVSR provide good agreement with multi‐channel analysis of surface waves (MASW) profiles, well logs and outcrop. LWP thicknesses may be estimated from the fundamental mode equation or through forward models. Prior knowledge about the subsurface from well, outcrop, and MASW profiles may greatly aid modeling in some cases. For the 3.2 to 1.8 Ma Koolau Volcano on Oahu, the downward rate of advance of the weathering front varies from 0.004 to 0.041 m/ka. For the 0.44 to 0.10 Ma Kohala Volcano (Big Island of Hawaii) rates vary from 0.013 to 0.047 m/ka. Simple H/V spectra develop in areas where the combined effects of time and elevated rainfall produce thick LWPs with a flat base and a general absence of core stones with an ideal layered geometry. Abundant buried core stones violate the assumption of simple layered geometries and scatter acoustic energy, leading to uninterpretable results. This is common where low rainfall and a young basaltic substrate leave abundant core stones as well as an undulating contact between saprolite and bedrock. Velocity inversions (high Vs intervals within low Vs saprolite) may also be present and originate from relatively intact bedrock horizons or mineralogical changes within saprolite. At Kohala, a gibbsite‐rich horizon produces such a velocity inversion due to enhanced weathering and subsequent collapse of saprolite in a discrete horizon. © 2019 John Wiley & Sons, Ltd.

Description: The analysis of landscape change based on repeat topographic surveys is becoming an increasingly practical and powerful tool across many earth surface disciplines. This paper re‐iterates the importance of accounting for survey error through error propagation, including subtle systematic errors, and presents statistical methods for doing so. The common practice of removing change measurements below some limit of detection (“thresholding”) is shown to provide biased and potentially misleading results when used to assess net volumetric or mean change. Abstract Topographic surveys inevitably contain error, introducing uncertainty into estimates of volumetric or mean change based on the differencing of repeated surveys. In the geomorphic community, uncertainty has often been framed as a problem of separating out real change from apparent change due purely to error, and addressed by removing measured change considered indistinguishable from random noise from analyses (thresholding). Thresholding is important when quantifying gross changes (i.e. total erosion or total deposition), which are systematically biased by random errors in stable parts of a landscape. However, net change estimates are not substantially influenced by those same random errors, and the use of thresholds results in inherently biased, and potentially misleading, estimates of net change and uncertainty. More generally, thresholding is unrelated to the important process of propagating uncertainty in order to place uncertainty bounds around final estimates. Error propagation methods for uncorrelated, correlated, and systematic errors are presented. Those equations demonstrate that uncertainties in modern net change analyses, as well as in gross change analyses using reasonable thresholds, are likely to be dominated by low‐magnitude but highly correlated or systematic errors, even after careful attempts to reduce those errors. In contrast, random errors with little to no correlation largely cancel to negligible levels when averaged or summed. Propagated uncertainty is then typically insensitive to the precision of individual measurements, and is instead defined by the relative mean error (accuracy) over the area of interest. Given that real‐world mean elevation changes in many landscape settings are often similar in magnitude to potential mean errors in repeat topographic analyses, reducing highly correlated or systematic errors will be central to obtaining accurate change estimates, while placing uncertainty bounds around those results provides essential context for their interpretation. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Description: The dynamic changes of various wind erosion factors and the response of soil wind erosion rate to the change of the factors was observed in a wind tunnel. Wind is the cause of sand flow, while the sand flow can affect the wind in turn. Abstract Aeolian sand transport is a complicated process that is affected by many factors (e.g. wind velocity, sand particle size, surface microtopography). Under different experimental conditions, erosion processes will therefore produce different results. In this study, we conducted a series of wind tunnel experiments across a range of wind velocities capable of entraining sand particles (8.0, 10.0, 12.0, and 14.0 m s‐1) to study the dynamic changes of the shear velocity, aerodynamic roughness length, and sand transport. We found that the shear velocity and aerodynamic roughness length are not constant; rather, they change dynamically over time, and the rules that describe their changes depend on the free‐stream air velocity. For wind tunnel experiments without feeding sand into the airflow, the sand bed elevation decreases with increasing erosion time, and this change significantly affected the values of shear velocity and aerodynamic roughness length. A Gaussian distribution function described the relationships between the sand transport rate (qT) and the duration of wind erosion (T). It is therefore necessary for modelers to consider both deflation of the bed and the time scale used when calculating sand transport or erosion rates. © 2018 John Wiley & Sons, Ltd.

Description: Bar colonization by vegetation and subsequent island formation is a key bio‐geomorphological process in fluvial landscape evolution. We investigate morphological and ecological evolution of river islands over single floods to decades, focussing on islands initiated by deposited trees that sprout to form vegetated patches. Abstract Bar colonization by vegetation and subsequent island formation is a key bio‐geomorphological process in fluvial landscape evolution. Here we investigate morphological and ecological evolution of river islands over timescales from single floods to decades, focusing on islands initiated by deposited trees that sprout to form vegetated patches. On a braided reach of the high‐energy Tagliamento River, Italy, we monitored 30 pioneer islands of 1 to 17 years age in comparison with unvegetated bar surfaces, open areas between islands, and established island surfaces. We integrated morphological, surface sediment and vegetation properties of islands initiated by different flood events, combining evidence from remotely‐sensed and ground observations, flow and climate time series. At a decadal timescale, pioneer islands aggrade rapidly to the elevation of the mean annual flood, showing a steady increase in vegetation canopy height, fining of surface sediments from predominantly gravel to silty‐sand with a notable clay and organic fraction. The standing vegetation included over 130 species, with the largest number on island surfaces of intermediate elevation and flood disturbance. As islands age, standing vegetation becomes comprised mainly of competitor species with transient seed banks and typical of woodland, scrub, pasture and wetland habitats, whereas the winter seedbank is dominated on all surfaces by ruderal species with persistent seedbanks, mainly associated with aquatic, wetland, pasture, arable and wasteland habitats. At shorter timescales, the biogeomorphological trajectory of pioneer islands is initiated by large flood events that control the elevation of deposited trees, and subsequent flows that control tree survival and establishment. Island morphological evolution depends on the frequency‐magnitude of sediment and seed delivery and redistribution by flood and possibly wind events, whereas island ability to retain sediments reflects the degree of vegetation establishment, which in the short‐term may vary with seasonal to annual moisture supply, substrate characteristics and climatic growth conditions. © 2018 John Wiley & Sons, Ltd.

Description: Summary Fluvial biomorphodynamics in actively meandering rivers entail interactions between hydromorphodynamics and pioneering tree species that have eco‐engineering effects. Here we study spatiotemporal patterns of vegetation patches smaller than 150 m2 in a 4 km reach of the river Allier in France in order to unravel causes for tree persistence and mortality and identify spatial trends across the river valley. To this end we analysed aerial photographs by Object‐Based Image Analysis over a period of 56 years and tracked individual patches through time. Furthermore the cover and surface age of the study reach were classified. The large‐scale shifts of channels, bars and vegetation are consistent with the meandering process and chute cutoffs. However, the spatiotemporal patterns of the vegetation patches are surprising in that they are ubiquitous and have ages up to decades on the highly dynamic meander belt, but hardly expand into larger vegetation patches. Patches disappear exponentially as a function of their age, and faster so in the last decades. Causes are amalgamation into the riparian forest flanking the meander belt and mortality likely due to desiccation or erosion. Patches have a higher probability of survival when further away from the active channel and closer to high vegetation patches and valley boundary. The window of opportunity of vegetation settlement widens towards the valley boundaries and in floodplain lows of former channels and chutes. These results imply a gradual cross‐valley gradient of riparian vegetation settling, survival and succession. This article is protected by copyright. All rights reserved.

Description: The over presence of fine sediment and fine sediment infiltration (FSI) in the aquatic environment of rivers are of increasing importance due to their limiting effects on habitat quality and use. Abstract The overpresence of fine sediment and fine sediment infiltration (FSI) in the aquatic environment of rivers are of increasing importance due to their limiting effects on habitat quality and use. The habitats of both macroinvertebrates and fish, especially spawning sites, can be negatively affected. More recently, hydropeaking has been mentioned as a driving factor in fine sediment dynamics and FSI in gravel‐bed rivers. The primary aim of the present study was to quantify FSI in the vertical stratigraphy of alpine rivers with hydropeaking flow regimes in order to identify possible differences in FSI between the permanently wetted area (during base and peak flows) and the so‐called dewatering areas, which are only inundated during peak flows. Moreover, we assessed whether the discharge ratio between base and peak flow is able to explain the magnitude of FSI. To address these aims, freeze‐core samples were taken in eight different alpine river catchments. The results showed significant differences in the vertical stratification of FSI between the permanently wetted area during base flow and the dewatering sites. Surface clogging occurred only in the dewatering areas, with decreasing percentages of fine sediments associated with increasing core depths. In contrast, permanently wetted areas contained little or no fine sediment concentrations on the surface of the river bed. Furthermore, no statistical relationship was observed between the magnitude of hydropeaking and the sampled FSI rate. A repeated survey of FSI in the gravel matrix revealed the importance of de‐clogging caused by flooding and the importance of FSI in the aquatic environment, especially in the initial stages of riparian vegetation establishment. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: Highlights: • Rapid cascades of channel‐floodplain changes characterise the ephemeral lower Río Colorado. • Enhanced local slope created by splays and abandoned channels promotes erosion cell development. • Erosion cells may connect up and form straighter channels. Inset: Example of erosion cell development along an abandoned channel. Letters S, T and F represent scour, transport and fill sections in the erosion cells. Pléiades imagery, with general flow direction from lower right to upper left (i.e. oblique to the abandoned channel), and north oriented to the top. Main image: Example of a relatively straight channel that may have resulted from the elongation and connection of erosion cells. The straightness of this channel contrasts with the higher sinuosity evident along older active or abandoned channels. Pléiades imagery, with general flow direction from bottom to top, and north oriented to the top. Abstract The terminus of the ephemeral Río Colorado is located at the margins of Salar de Uyuni, Bolivia, the world's largest salt lake. The low‐gradient (〈0.0006 m m‐1), non‐vegetated reaches approaching the terminus provide an excellent natural laboratory for investigating cascades of channel‐floodplain changes that occur in response to quasi‐regular flows (at least once annually) and fine‐grained sediment supply (dominantly silt and clay). High‐resolution satellite imagery (〈0.65 m, various dates from 2004 onwards) and field data reveal widespread, pronounced and rapid morphodynamics on sub‐decadal timescales, including channel erosion and chute cutoff formation, and development of crevasse channels and splays, floodouts (unchannelled surfaces at channel termini), and erosion cells (floodplain scour‐transport‐fill features). In particular, following high annual precipitation (〉400 mm) in 2004–2005 and two subsequent high magnitude daily precipitation events (~40 mm), all of which led to widespread flooding, numerous crevasse splays formed between 2004 and 2016, avulsions occurred at nearby floodouts, and erosion cells downstream of the splays and floodouts underwent striking morphological changes. High‐precision GPS data reveal two preferential localities for erosion cell development: partially or fully abandoned channels with crevasse splay remnants, and topographic lows between channels. In this overall low‐gradient setting, comparatively high gradients (up to ~0.0006 m m‐1) at the edge of splay deposits and topography created by crevasses and abandoned channels may initiate knickpoint retreat and thereafter erosion cell development. Abandoned channels with splays tend to give rise to narrow, deep erosion cells, while topographic lows promote relatively shallow, wide erosion cells. In both situations, erosion cells may extend upslope and downslope, and eventually connect to form straight channels. The channel‐floodplain morphodynamics near the Río Colorado terminus extend previous analyses of low‐gradient, dryland river systems, particularly because the lack of vegetation and quasi‐regular floods drive cascades of rapid changes on sub‐decadal timescales. © 2018 John Wiley & Sons, Ltd.

Description: Abstract Suspended load transport can strongly impact ecosystems, dam filling and water resources. However, contrary to bedload, the use of physically based predicting equations is very challenging because of the complexity of interactions between suspended load and the river system. Through the analysis of extensive data sets, we investigated extent to which one or several river bed or flow parameters could be used as a proxy for quantifying suspended fluxes in gravel bed rivers. For this purpose, we gathered in the literature nearly 2400 instantaneous field measurements collected in 56 gravel bed rivers. Among all standard dimensionless parameters tested, the strongest correlation was observed between the suspended sediment concentration and the dimensionless bedload rate. An empirical relation between these two parameters was calibrated. Used with a reach average bedload transport formula, the approach allowed to successfully reproduce suspended fluxes measured during major flood events in seven gravel bed alpine rivers, morphodynamically active and distant from hillslope sources. These results are discussed in light of the complexity of the processes potentially influencing suspended load in a mountainous context. The approach proposed in this paper will never replace direct field measurements, which can be considered the only confident method to assess sediment fluxes in alpine streams; however, it can increment existing panel tools that help river managers to estimate even rough but not unrealistic suspended fluxes when measurements are totally absent.

Description: The cover image is based on the Research Article Effects of estuarine mudflat formation on tidal prism and large-scale morphology in experiments by Lisanne Braat et al., https://doi.org/10.1002/esp.4504.

Description: Around 24% of the sediment was deposited in the channel belt and floodplains within levees, 19–30% was trapped in the floodplains outside the levees, and the rest was delivered to the delta area. Human‐accelerated erosion in the Loess Plateau caused a super‐elevated channel bed on the lower river, which favors sediment trapping in the floodplains outside the levees. Abstract The lower Yellow River channel was maintained by artificial levees between 1580 and 1849. During this period, 280 levee breaches occurred. To estimate sediment storage on the floodplains outside the levees, a regression model with a decadal time step was developed to calculate the outflow ratio for the years when levee breaching occurred. Uncertainty analysis was used to identify the likely outflow ratio. Key variables of the model include annual water discharge, a proxy for levee conditions, and potential bankfull discharge of the channel before flood season. Uncertainty analysis reveals an outflow ratio of 0.35–0.56. We estimate that during this period, 18.8–30.1% of the total ~312 Gt of sediment load was deposited on the floodplains outside the levees. Human‐accelerated erosion in the Loess Plateau caused a 4‐fold increase in sediment delivery to the lower Yellow River, which could not be accommodated by channel morphodynamic changes. As a result, 21.2–27.5% of the total sediment load was deposited within the levees, creating a super‐elevated channel bed that facilitated an uncommonly high breach outflow ratio. Hence, the factor of a large super‐elevation relative to the mean main channel depth should be considered when designing diversions to restore floodplains. © 2018 John Wiley & Sons, Ltd.

Description: Time domain reflectometry (TDR) was applied to determine the deposition height and porosity of sediment below the water surface. •A continuous monitoring method of net sediment volume in a pool was validated through a laboratory experiment. •A combination of this monitoring system and other bedload monitoring methods, such as geophones, can potentially serve as useful tools for better understanding bedload transport processes in steep mountain streams. Abstract In this study, we applied time domain reflectometry (TDR) to determine the deposition height and porosity of sediment at a fine spatiotemporal resolution, and developed a continuous bedload monitoring method that can be applied to pools in steep mountain rivers. The TDR monitoring system consisted of sensor probes, a cable tester, multiplexers and coaxial cables. When the embedded probes penetrated both water and sediment, the boundaries of the sediment and water were consistent with the transition points in the observed waveforms of each TDR measurement. A semi‐automatic analysis of the recorded TDR waveforms, which did not require calibration or parameter fitting, was conducted to establish continuous monitoring. In addition, a flume experiment was performed to test the monitoring system in a model retention basin connected to a flume, with sand of uniform grain size (1.4 mm diameter) supplied for 30 min. The sediment volume in the container representing the model basin was monitored using a load cell underlying the container and eight sensor probes, with a length of almost 0.27 m. The sediment thickness determined by the TDR indicated a gradual deposition, and was consistent with manual measurements. Despite a marginal overestimation of 13% for a sand feed of 30 kg, the sediment volume in the model retention basin and the bedload transport rate were successfully estimated. A combination of our monitoring system and other indirect methods, such as geophones, can potentially serve as useful tools for better understanding bedload transport processes in steep mountain streams. Copyright © 2018 John Wiley & Sons, Ltd.

Description: A small, automatically recording bedload sensor with an iron plate and a pair of load cells is developed to evaluate not only large particles but also sand particles as bedload, and the applicability is confirmed using results of flume tests. Bedload mass is calculated by integrating using both the velocity of sediment particles and the particle weight measured by two load cells, and the velocity tries to be estimated by the cross‐correlation function of weights measured by load cells. Abstract It is important to evaluate bedload discharge and temporal changes of the bed surface, and bed deformation can be estimated during floods if the bedload discharge is properly evaluated in an arbitrary cross‐section. With the exception of grain size and its distribution within the bedload, bedload discharge has been measured using both direct and indirect methods. Bedload slot is a direct method but cannot be used to measure bedload during a flood because of volume limitations. Indirect methods require correlation between the signals and sediment volume measured using another method. In the present study, a small, automatically recording bedload sensor with an iron plate and a pair of load cells is developed in order to evaluate not only large particles but also sand particles as bedload. Bedload mass is calculated by integrating with respect to both the velocity of sediment particles and the averaged particle weight as measured by a pair of load cells, and, as an example, the velocity is estimated by the cross‐correlation function of weights measured by load cells. The applicability of the proposed sensor is discussed based on the results of flume tests in the laboratory (2014) and the observation flume of the Hodaka Sedimentation Observatory of Kyoto University in Japan (2015). The system was installed in the observation flume in November of 2012, and flume data were obtained using natural sediment particles. In particular, it was difficult to estimate the velocity of averaged bedload particles, and it was better to apply a cross‐correlation function in the laboratory tests. However, it appears that the previous estimation can estimate these velocities in the observation flume using a connecting tube and submerged load‐cell systems. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Before and after a perturbation on the hydrological flow regime and sediment supply in a watershed, two indicators are used to characterize these geomorphological drivers (FQ; AS) and to obtain a disturbance vector for each river reach. The magnitude and direction of these vectors are associated with the morphological trajectories. The trajectories are describes by eight fluvial morphological variables and this method was tested in an Alpine watershed. Abstract Predicting morphological channel changes using physically‐based models requires extended data for the description of the river channel and for hydrological and sedimentological inputs. At the watershed scale, these data are usually scarce, and such a refined modeling is typically difficult to build. A simpler modeling of the morphological impacts due to the changes in the principal drivers that control channel shape and dynamics is more adaptable. In this study we focused on the morphological responses of gravel‐bed rivers to flow and sediment source perturbation at watershed scale. The aim is to develop and test a tool capable of semi‐quantitatively predicting the morphological river response at the watershed scale due to a set of spatially distributed perturbations. The model considers flow regime (Q) and sediment supply (S) as the two main factors controlling the fluvial morphology in alluvial rivers. Two indicators have been proposed to evaluate the alteration on Q and S, and they are illustrated as vectors on each reach of the river network. The magnitude of the vectors corresponds to the intensity of the perturbation and its direction represents the changing trend that nine selected morphological variables (bed elevation, slope, width, depth, wetted area, width to depth ratio, d50, terrace formation, and colonization of vegetation) are likely to follow from an initial state. The trends or trajectories of changes were assessed based on empirical relations, case studies, and conceptual models. This method was applied to the Isère watershed (5700 km2) at Grenoble (France), a river that hosts large and complex hydropower plant systems constructed during 50s ‐70s. The predictions over 23 river reaches and eight variables were evaluated in the range where the model was capable of predicting the morphological evolution of the river system. Its performance was verified and in the majority of the cases the results were coherent with field surveys and previous observations. The results indicate that this is a complex problem which needs more careful consideration of constraints that are difficult to assess, such as simultaneous and different sources of perturbations, hypotheses of initial dynamic equilibrium, and sediment supply quantification. Copyright © 2017 John Wiley & Sons, Ltd.

Description: We present the FreeXSapp methodology, a new piece of freely‐available software based on existing SfM tools (MicMac and PMVS2) and augmented‐reality targets (ArUco markers) which performs the automated 3‐D reconstruction, scaling, orientation and analysis of gully cross‐sections (XSs) from images taken from the gully margin. This methodology showed excellent performance in terms of accuracy, time and cost requirements when compared with typical 3‐D and 2‐D techniques. The FreeXSapp interface is downloadable for free for Windows OSs at http://www.uco.es/users/ccastillo/freexsapp. Abstract During recent years, 3‐D techniques such as LiDAR and Structure‐from‐Motion (SfM) photogrammetry have been increasingly used for gully erosion assessment. However, innovative image‐based approaches based on these advances may also be used to provide accurate cross‐sectional measurements which are less expensive and time‐demanding. In this work, we present the FreeXSapp methodology, a new piece of freely‐available software based on existing SfM tools (MicMac and PMVS2) and augmented‐reality targets (ArUco markers) which performs the automated 3‐D reconstruction, scaling, orientation and analysis of gully cross‐sections (XSs) from images taken from the gully margin using a smartphone camera. As a field application, the volume of a 60‐m‐long medium‐size gully was evaluated, where a total of 10 XSs were measured and analyzed in approximately 30 min. The relative accuracy in estimating width and depth dimensions was in the order of 0.5%, with a precision ratio (relative to the camera–XS distance) of ~1500. Overall, using this methodology showed excellent performance in terms of time and cost requirements when compared with typical 3‐D and conventional 2‐D techniques. The FreeXSapp interface is downloadable for free for Windows operating systems at http://www.uco.es/users/ccastillo/freexsapp. Copyright © 2018 John Wiley & Sons, Ltd.

Description: We propose a theoretical framework for investigating the interaction between two different mechanisms that can break the symmetry of river bifurcations: (i) the free, autogenic instability; (ii) the forcing effect that may derive from the curvature of the upstream channel and/or from different downstream slopes. Results reveal that the bifurcation response to changing conditions depends on the aspect ratio of the main channel falling above or below the resonant threshold that controls the possibility of upstream morphodynamic influence. Abstract Water and sediment distribution by river bifurcations is often highly unbalanced. This may result from a variety of factors, such as migration of bars, channel curvature and backwater effects, which promote an uneven partition of flow and sediment fluxes in the downstream branches, which we call ‘forcings’. Bifurcations also display an intrinsic instability mechanism that leads to unbalanced configurations, as occurs in the idealized case of a geometrically symmetric bifurcation, which we call ‘free’, provided the width‐to‐depth ratio of the incoming flow is large enough. Most frequently, these free and forced mechanisms coexist; however, their controlling roles in bifurcation dynamics have not been investigated so far. In this paper we address this question by proposing a unified free‐forced modelling framework for bifurcation morphodynamics. Upstream channel curvature and different slopes of downstream branches (slope advantage) are specifically investigated as forcing effects typically occurring in bifurcations of alluvial channels. The modelling strategy is based on the widely used two‐cell model of Bolla Pittaluga et al. (Water Resources Research, 2003, 39(3), 1–13), here extended to account for the spatially non‐uniform fluxes entering the bifurcation node. Results reveal that the relative role of free and forced mechanisms depends on the width‐to‐depth ratio falling above or below the resonant threshold that controls the stability of free bifurcations: when the main channel is relatively wide and shallow (super‐resonant regime) the bifurcation invariably evolves towards unbalanced configurations, whatever the combination of curvature and slope advantage values, which instead control the bifurcation response under sub‐resonant conditions. Detection of the resonant aspect ratio as a key threshold also releases the modelling approach from the need for parameter calibration that characterized previous approaches, and allows for interpreting under a unified framework the opposite behaviours shown by gravel‐bed and sand‐bed bifurcations for increasing Shields parameter values. © 2018 John Wiley & Sons, Ltd.

Description: • A model for turbidity channel systems in fjords and deep‐water settings is proposed. • Bimodal delta morphology is linked to river drainage basin character. • Turbidity channel morphology is linked to river discharge, avulsion and mass‐wasting. Abstract River deltas and associated turbidity current systems produce some of the largest and most rapid sediment accumulations on our planet. These systems bury globally significant volumes of organic carbon and determine the runout distance of potentially hazardous sediment flows and the shape of their deposits. Here we seek to understand the main factors that determine the morphology of turbidity current systems linked to deltas in fjords, and why some locations have well developed submarine channels while others do not. Deltas and associated turbidity current systems are analysed initially in five fjord systems from British Columbia in Canada, and then more widely. This provides the basis for a general classification of delta and turbidity current system types, where rivers enter relatively deep (〉200 m) water. Fjord‐delta area is found to be strongly bimodal. Avalanching of coarse‐grained bedload delivered by steep mountainous rivers produces small Gilbert‐type fan deltas, whose steep gradient (11°–25°) approaches the sediment's angle of repose. Bigger fjord‐head deltas are associated with much larger and finer‐grained rivers. These deltas have much lower gradients (1.5°–10°) that decrease offshore in a near exponential fashion. The lengths of turbidity current channels are highly variable, even in settings fed by rivers with similar discharges. This may be due to resetting of channel systems by delta‐top channel avulsions or major offshore landslides, as well as the amount and rate of sediment supplied to the delta front by rivers. © 2018 John Wiley & Sons, Ltd.

Description: A LiDAR‐recorded geomorphic change induced by an erosive debris‐flow event is compared to modelled properties of a debris‐flow. Momentum and shear stresses explain debris‐flow erosion by 50‐68 %. Abstract Debris flows are among the most destructive and hazardous mass movements on steep mountains. An understanding of debris‐flow erosion, entrainment and resulting volumes is a key requirement for modelling debris‐flow propagation and impact, as well as analysing the associated risks. As quantitative controls of erosion and entrainment are not well understood, total volume, runout and impact energies of debris flows are often significantly underestimated. Here, we present an analysis of geomorphic change induced by an erosive debris‐flow event in the German Alps in June 2015. More than 50 terrestrial laser scans of a 1.2 km long mountain torrent recorded geomorphic change in comparison to an airborne laser scan performed in 2007. Errors were calculated using a spatial variable threshold based on the point density of airborne laser scanning and terrestrial laser scanning and the slope of the digital elevation models. Highest erosion rates approach 5.0 m3/m2 (mean 0.6 m3/m2). During the event 9550 ± 1550 m3 was eroded whereas only 650 ± 150 m3 was deposited in the channel. Velocity, flow pressure, momentum and shear stress were calculated using a carefully calibrated RAMMS Debris Flow model including material entrainment. Here we present a linear regression model relating debris‐flow erosion rates to momentum and shear stress with an R2 up to 68%. Channel transitions from bedrock to loose debris sections cause excessive erosion up to 1 m3/m2 due to previously unreleased random kinetic energy now available for erosion. © 2019 John Wiley & Sons, Ltd.

Description: Mudflats form on the sides of estuaries and on top shoals. The mud accretion elevates high intertidal areas up to supratidal elevations, which decreases tidal prism. This leads to a decrease in channel migration and to a near‐equilibrium planform that is smaller in volume and especially narrower upstream with increased bar heights and no channel deepening. Abstract Human interference in estuaries has led to increasing problems of mud, such as hyper‐turbidity with adverse ecological effects and siltation of navigation channels and harbours. To deal with this mud sustainably, it is important to understand its long‐term effects on the morphology and dynamics of estuaries. The aim of this study is to understand how mud affects the morphological evolution of estuaries. We focus on the effects of fluvial mud supply on the spatial distribution of mudflats and on how this influences estuary width, depth, surface area and dynamics over time. Three physical experiments with self‐forming channels and shoals were conducted in a new flume type suitable for tidal experiments: the Metronome. In two of the experiments, we added nutshell grains as mud simulant, which is transported in suspension. Time‐lapse images of every tidal cycle and digital elevation models for every 500 cycles were analysed for the three experiments. Mud settles in distinct locations, forming mudflats on bars and sides of the estuary, where the bed elevation is higher. Two important effects of mud were observed: the first is the slight cohesiveness of mud that causes stability on bars limiting vertical erosion, although the bank erosion rate by migrating channels is unaffected. Secondly, mud fills inactive areas and deposits at higher elevations up to the high‐water level and therefore decreases the tidal prism. These combined effects cause a decrease in dynamics in the estuary and lead to near‐equilibrium planforms that are smaller in volume and especially narrower upstream, with increased bar heights and no channel deepening. This trend is in contrast to channel deepening in rivers by muddier floodplain formation. These results imply large consequences for long‐term morphodynamics in estuaries that become muddier due to management practices, which deteriorate ecological quality of intertidal habitats but may create potential area for marshes. © 2018 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.

Description: Analysis of historical aerial photography, hyperscale DEMs used to map grain‐size and hydraulic modelling explains channel adjustment at the reach scale. Multiple bar forming discharges exist, whereby frequent flood flows rework tail and back channel areas, while much larger, less frequent floods are required to mobilise the coarser sediment fraction on bar heads. Reach‐scale sensitivity is largely a product of the proportion of the bar made up of active, frequently reworked units and the more static bar head. Abstract Bars are key morphological units in river systems, fashioning the sediment regime and bedload transport processes within a reach. Reworking of these features underpins channel adjustment at larger scales, thereby acting as a key determinant of channel stability. Despite their importance to channel evolution, few investigations have acquired spatially continuous data on bar morphology and sediment‐size to investigate bar reworking. To this end, four bars along a 10 km reach of a wandering gravel‐bed river were surveyed with terrestrial laser scanning (TLS), comparing downstream changes in slope, bed material size and channel planform. Detrended standard deviations (σz) were extracted from TLS point clouds and correlated to underlying physically measured median grain‐size (D50), across a greater range of σz values than have hitherto been reported. The resulting linear regression model was used to create a 1 m resolution median grain‐size map. A fusion of airborne LiDAR and optical‐empirical bathymetric mapping was used to develop reach‐scale digital elevation models (DEMs) for rapid two‐dimensional hydraulic modelling using JFlow® software. The ratio of dimensionless shear stress over critical shear stress was calculated for each raster cell to calculate the effectiveness of a range of flood events (2.33–100 year recurrence intervals) to entrain sediment and rework bar units. Results show that multiple bar forming discharges exist, whereby frequent flood flows rework tail and back channel areas, while much larger, less frequent floods are required to mobilise the coarser sediment fraction on bar heads. Valley confinement is shown to exert a primary influence on patterns of bar reworking. Historical aerial photography, hyperscale DEMs and hydraulic modelling are used to explain channel adjustment at the reach scale. The proportion of the bar comprised of more frequently entrained units (tail, back channel, supra‐platform) relative to more static units (bar head) exerts a direct influence upon geomorphic sensitivity. © 2018 John Wiley & Sons, Ltd.

Description: Abstract The textbook concept of an equilibrium landscape, which posits that soil production and erosion are balanced and equal channel incision, is rarely quantified for natural systems. In contrast to mountainous, rapidly eroding terrain, low relief and slow‐eroding landscapes are poorly studied despite being widespread and densely inhabited. We use three field sites along a climosequence in South Africa to quantify very slow (2‐5 m/My) soil production rates that do not vary across hillslopes or with climate. We show these rates to be indistinguishable from spatially invariant catchment‐average erosion rates while soil depth and chemical weathering increase strongly with rainfall across our sites. Our analyses imply landscape‐scale equilibrium although the dominant means of denudation varies from physical weathering in dry climates to chemical weathering in wet climates. In the two wetter sites, chemical weathering is so significant that clay translocates both vertically in soil columns and horizontally down hillslope catenas, resulting in particle size variation and the accumulation of buried stone lines at the clay‐rich depth. We infer hundred‐thousand‐year residence times of these stone lines and suggest that bioturbation by termites plays a key role in exhuming sediment into the mobile soil layer from significant depths below the clay layer. Our results suggest how tradeoffs in physical and chemical weathering, potentially modulated by biological processes, shape slowly eroding, equilibrium landscapes.

Description: ABSTRACT Six plains cottonwoods along the axis of a meander were excavated to determine if dendrochronology could identify the year and location of germination and date past overbank sedimentation events. Samples from all excavated trees showed clear anatomical changes associated with burial, including increased vessel size, decreased definition of annual ring boundaries, and decreased ring widths. Some of these burial signatures were created by deposition of only a few centimeters of sediment, and most burial events were detected by multiple samples from the same tree. Four of the trees germinated at or near the upper surfaces of bar deposits, while two germinated within thin overbank deposits draped over bar deposits, indicating that germination is closely associated with bars. Dates and inferred thicknesses of overbank sedimentation events are consistent with repeated topographic surveys and data obtained from 137Cs analyses. However, the record of overbank sedimentation extracted from the trees does not entirely reflect the history of past peak discharges documented by stream gaging, largely because individual trees are progressively less likely to be flooded through time as the river migrates farther away. Germination dates and locations closely track past positions of the river channel. Germination elevations and the elevations of the tops of point bars appear to be decreasing with time as the bend migrates, implying vertical incision by Powder River at a rate of 7.1 +/‐ 4.3 mm/yr. The rate of floodplain growth determined by elevation changes decreases progressively through time, ultimately reaching an apparent plateau after 0.8‐1.3 m of vertical accretion. While similar patterns of vertical accretion have previously been interpreted as resulting from decreasing flood probability with increasing floodplain elevation, distance from the channel is also a first‐order control on vertical floodplain growth.

Description: Simulated rill erosion experiments were used to evaluate hillslope erosion with hand scarification on contour, agricultural straw mulch, wood mulch, burned controls and unburned reference plots. Sediment flux rates were significantly greater on control and scarified plots than the straw and wood mulch treatments plots. Ten years after the fire, there were no significant differences in sediment flux rates across treatments although the wood mulch treatment closely approached the unburned condition. Abstract Large wildfires can have profound and lasting impacts not only from direct consumption of vegetation but also longer‐term effects such as persistent soil erosion. The 2002 Hayman Fire burned in one of the watersheds supplying water to the Denver metropolitan area; thus there was concern regarding hillslope erosion and sedimentation in the reservoirs. The efficacy of various treatments for reducing erosion was tested, including hand scarification on contour, agricultural straw mulch, wood mulch, burned controls and unburned reference plots. Simulated rill erosion experiments were used both immediately after the fire and again 10 years post fire. To better understand untreated recovery, the same experiments were applied to control plots in post‐fire years 1, 2, 3 and 4, and in unburned reference plots in years 4 and 10. Results indicate that control and scarified plots produced significantly greater sediment flux rates – 1.9 and 2.8 g s−1 respectively – than the straw and wood mulch treatments – 0.9 and 1.1 g s−1 – immediately after the fire. Mulch treatments reduced runoff rate, runoff velocity, and sediment concentration and flux rate. The straw mulch cover was no longer present, whereas the wood mulch was still there in year 10. Vegetation regrowth was slow and mulch treatments provided effective cover to reduce sediment right after the fire. In post‐fire year 10, there were no significant differences in sediment flux rates across treatments; it is notable, however, that the wood mulch treatment (0.09 g s−1) most closely approached the unburned condition (0.07 g s−1). The burned control plots had high sediment flux rates until post‐fire year 3, when flux rates significantly decreased and were statistically no longer higher than the unburned levels from year 4 and 10. These results will inform managers of the longer‐term post‐fire sediment delivery rates and of the ability of post‐fire emergency hillslope treatments to mitigate erosion rates. Published 2019. This article is a U.S. Government work and is in the public domain in the USA..

Description: Abstract While it is well‐recognized that vegetation can affect erosion, sediment yield, and over longer time scales landform evolution, the nature of this interaction and how it should be modeled is not obvious and may depend on the study site. In order to develop quantitative insight into the magnitude and nature of vegetation's influence on catchment erosion, we build a landscape evolution model to simulate erosion in badlands then calibrate and evaluate it against sediment yield data for two catchments with contrasting vegetation cover. The model couples hillslope gravitational transport and stream alluvium transport. Results indicate that hillslope transport processes depend strongly on the vegetation cover whereas stream transport processes do not seem to be affected by the presence of vegetation. The model performance in prediction is found to be higher for the denuded catchment than for the reforested one. Moreover, we find that vegetation acts on erosion mostly by reducing soil erodibility rather than by reducing surface runoff. Finally, the methodology we propose can be a useful tool to evaluate the efficiency of previous revegetation operations, and provide guidance for future restoration work.

Description: Abstract Silting of reservoirs is a ubiquitous process whenever water is impounded. Despite substantial work on the rates of silting, the spatial pattern of silting in reservoirs is not clearly understood. While it is anticipated that the variability of silting increases with decreasing reservoir size, not much is known about siltation in sub‐tropical humid regions affected by monsoon rainfall. This paper presents the initial results of geomorphic analysis of six earthen check dams in the Shiwalik foot hills of the Himalayas (India) in areas that are inhabited by high proportions of disempowered populations. These check dams include three small‐sized dams (Dhamala‐II, Rel Majra, and Sukhomajri‐II) and three medium‐sized dams (Bunga‐I, Parachh‐II, and Siswan). Field data were collected from each reservoir. The methods used included spatial interpolations of bed depth and silt thickness in each reservoir, Structure from Motion photogrammetry to extract multiple channel cross‐sections from photographic scans along tributary mouths, texture analysis of bed and bank materials, and visual observations of hill slope around the check dams. Based on this study, silt tended to concentrate either in the middle portion of the reservoir or near the dam; however, silt accumulation did not always occur along the dam or in the deepest portion of the reservoirs. Areas located downstream from these check dams are heavily used for various human activities and the channel network has almost been eliminated. While these earthen check dams may be cost‐effective tools for water conservation in economically marginalized areas; however, if abandoned, these structures may pose a physical hazard to downstream communities.

Description: Abstract Despite recent rapid advances in the field of Structure from Motion (SfM) photogrammetry, the use of high‐resolution data to investigate small scale processes is a relatively underdeveloped field. In particular, rock weathering is rarely investigated using this suite of techniques. This research uses a combination of traditional non‐destructive rock weathering measurement techniques (rock surface hardness) and SfM to map deterioration and loss of cohesion of the surface using 3‐dimensional data. The results are used to interpret weathering behaviour across two different lithologies present on the site, namely shale and limestone. This new approach is tested on seven sites in Longyearbyen, Svalbard, where active weathering of a rock surface was measured after 13 years of exposure to extreme temperature regimes and snow cover. The surface loss was quantified with SfM and combined with rock surface hardness measurement distributions extrapolated in GIS. The combined results are used here to quantify the difference in response of both lithologies to these extreme temperatures. This research demonstrates the potential for further integration of SfM in rock weathering research and other small‐scale geomorphological investigations, in particular in difficult field conditions where portability of field equipment is paramount.