ALBERT

Description: Abstract The development of glacier karst at the margins of melting ice sheets produces complex glaciofluvial sediment‐landform assemblages that provide information on ice sheet downwasting processes. We present the first combined geomorphological, sedimentological and geophysical investigation of the Brampton Kame Belt, an important glaciofluvial depositional zone at the centre of the last British‐Irish Ice Sheet. Ground‐penetrating radar (GPR) data allow the broad scale internal architecture of ridges (eskers) and flat‐topped hills (ice‐walled lake plains) to be determined at four sites. In combination with sediment exposures, these provide information on lateral and vertical variations in accretion styles, depositional boundaries, and grain size changes. Building on existing work on the subject, we propose a refined model for the formation of ice‐walled lake plains resulting from the evolution and collapse of major drainage axes into lakes as stable glacier karst develops during deglaciation. The internal structure of esker ridges demonstrates variations in sedimentation that can be linked to differences in ridge morphologies across the kame belt. This includes low energy flow conditions and multiple accretion phases identified within large S‐N oriented esker ridges; and fluctuating water pressures, hyperconcentrated flows, and significant deformation within a fragmented SW‐NE oriented esker ridge. In combination with updated geomorphological mapping, this work allows us to identify two main styles of drainage within the kame belt: (1) major drainage axes aligned broadly S‐N that extend through the entire kame belt and collapsed into a chain of ice‐walled lakes; and (2) a series of smaller, fragmented SW‐NE aligned esker ridges that represent ice‐marginal drainage as the ice sheet receded south‐eastwards up the Vale of Eden. Our study demonstrates the importance of integrated geomorphological, sedimentological and geophysical investigations in order to understand complex and polyphase glaciofluvial sediment‐landform assemblages.

Description: Abstract The stable longitudinal dunes in the northern Simpson Desert, Australia, were observed in satellite imagery to become more active after vegetation cover was reduced by fire and drought. Subsequent rainfall events also resulted in significant vegetation regrowth and dune stabilisation. These switches between more active and stable conditions have not been previously described in the largely vegetated dune fields of central Australia. The observations, made on 12 dune sites, relied on high spatial resolution satellite imagery to observe dune crest activity, and seasonal Landsat fractional cover imagery to observe vegetation cover changes. The non‐photosynthetic vegetation (NPV) component of the fractional vegetation cover images revealed significant changes in hummock grass cover on the dunes between 1988‐2018, with a positive relationship with the 3‐year cumulative rainfall, disrupted by two periods of patchy burning. Only those sites that had burnt became active, and only after vegetation cover had remained low (NPV 〈 16%) during the ‘Millennium Drought’. There is no threshold in vegetation cover, below which dune crests become active, but active dune features require 4‐years of low NPV cover (〈16%) to develop. The large rainfall event that ended the drought increased NPV cover, stabilising the dunes. Similar hummock grass covered dunes are present across large areas of the arid zone, and are likely to respond in similar ways, given that fire and drought are common occurrences in Australia.

Description: Abstract The role of wave forcing on the main hydro‐morphological dynamics evolving in the shallow waters of the nearshore and at river mouths is analyzed. Focus is mainly on the cross‐shore dynamics that evolve over mildly sloping barred, dissipative sandy beaches from the storm up to the yearly time scale, at most. Local and nonlocal mechanisms as well as connections across three main inter‐related subsystems of the nearshore ‐ the region of generation and evolution of nearshore bars, river mouths and the swash zone ‐ are analyzed. The beach slope is a major controlling parameter for all nearshore dynamics. A local mechanism that must be properly described for a suitable representation of wave‐forced dynamics of all such three subsystems is the proper correlation between orbital velocity and sediment concentration in the bottom boundary layer; while specific dynamics are the wave‐current interaction and bar generation at river mouths and the sediment presuspension at the swash zone. Fundamental nonlocal mechanisms are both Infragravity (IG) waves and large‐scale horizontal vortices (i.e. with vertical axes), both influencing the hydrodynamics, the sediment transport and the seabed morphology across the whole nearshore. Major connections across the three subsystems are the upriver propagation of IG waves generated by breaking sea waves and swash‐swash interactions, the interplay between the swash zone and along‐river‐flank sediment transport and the evolution of nearshore sand bars.

Description: Abstract Erosion of volcanic islands ultimately creates shallow banks and guyots, but the ways erosion proceeds to create them over time and how coastline retreat rate relates to wave conditions, rock mass strength and other factors are unclear. The Capelinhos volcano was formed in 1957/58 during a Surtseyan and partly effusive eruption that added a ~2.5 km2 tephra and lava promontory to the western end of Faial Island (Azores, central North Atlantic). Subsequent coastal and submarine erosion has reduced the subaerial area of the promontory and created a submarine platform. This study uses historical information, photos and marine geophysical data collected around the promontory to characterize how the submarine platform developed following the eruption. Historical coastline positions are supplemented with coastlines interpreted from 2004 and 2014 Google Earth images in order to work out the progression of coastline retreat rate and retreat distance for lava‐ and tephra‐dominated cliffs. Data from swath mapping sonars are used to characterise the submarine geometry of the resulting platform (position of the platform edge, gradient and morphology of the platform surface). Photographs collected during SCUBA and ROV dives on the submarine platform reveal a rugged surface now covered with boulders. The results show that coastal retreat rates decreased rapidly with time after the eruption and approximately follow an inverse power law relationship with coastal retreat distance. We develop a finite‐difference model for wave attenuation over dipping surfaces to predict how increasing wave attenuation contributed to this trend. The model is verified by reproducing the wave height variation over dipping rock platforms in the UK (platform gradient 1.2° to 1.8°) and Ireland (1.8°). Applying the model to the dipping platform around Capelinhos, using a diversity of cliffs resistance predicted from known lithologies, we are able to predict erosion rate trends for some sectors of the edifice. We also explore wider implications of these results, such as how erosion creates shallow banks and guyots in reef‐less mid‐oceanic archipelagos like the Azores.

Description: Abstract Exceptional flood events with a return period of about 50 years can be destructive to step‐pool channel segments. However, field investigations and flume experiments have not examined the hydraulic and morphological feedbacks of step‐pool morphology during unsteady hydrographs of exceptional flood events. We performed a series of flume experiments with a manually constructed step model, perturbed with three hydrographs that varied in the rate of water supply change. The bed texture, topography, flow regimes, surface flow field and water depth were characterized and measured as the flow rate was increased during the experiments. A distinct pool feature emerged downstream of the manually constructed step when the flow rate exceeded the threshold scaled to the peaks of ordinary flood events in well‐graded mountain streams. The pool feature was modified in several different ways with flow rate increase. The bed surface steadily coarsened, micro‐bedforms developed and became more pronounced, the bed topography became more spatially complex based on analysis using the Hurst exponent, and last, pool depth steadily increased. Pool modification was also linked to the flow regime: the impinging jet regime led to grain size segmentation in the pool while the jump regime contributed to decelerating flow velocity. The steeper rising limb of hydrograph led to a less developed pool feature, with smaller sized micro‐bedforms in the pool bottom to outlet, and higher discharge threshold for distinct coarsening and scouring in the pool. The estimated energy dissipation within the step‐pool unit decreased as a power function from low to high flow, quantified as the ratio hc/HS, where hc is the critical water depth and HS is scour depth. Our results highlight the interaction between morphology, hydraulics, and energy dissipation of step‐pool unit and the crucial role of hydrograph shape on the interaction during flow increase.

Description: Earth Surface Processes and Landforms, Volume 44, Issue 9, Page 1876-1878, July 2019.

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

Description: Abstract Stream channel morphology forms the template upon which hydraulic aspects of aquatic habitat are created, yet spatial and temporal variability in habitat imposed by changing morphology is not well understood. This paper presents a conceptual model linking sediment supply patterns to spatial and temporal variability in channel form and aquatic habitat. To evaluate this model, change over time in three habitat variables is quantified using a 2D hydrodynamic modeling approach. A 45‐year record of topographic data from Carnation Creek, a catchment in coastal British Columbia, is used for the flow modeling. Using the Nays2DH modeling platform, water depths and velocities are simulated in eight channel segments located at different positions relative to locations of historical colluvial input using seven flow levels ranging from 3% to 400% of mean annual discharge (0.02 to 3.31 m3s‐1). Results indicate that habitat availability changes through time as a result of sediment supply‐driven changes to channel morphology and wood loads, but patterns in habitat vary as a function of dominant channel segment morphology. Spatial and temporal variability in morphology also influences the relationship between habitat availability and river discharge, leading to non‐stationary habitat‐discharge rating curves. When habitat areas are predicted by applying these curves to daily flow series spanning annual dry seasons, over 50% of the variance in cumulative seasonal habitat area can be explained by year‐to‐year changes in channel morphology and wood loading, indicating that changing morphology is an important factor for driving temporal habitat variability. This variance is related to the morphological variability of a channel segment, which in turn is associated with the segment position relative to zones of colluvial input. Collectively, these results suggest that variability in habitat is impacted by channel morphology, and can be evaluated partly on the basis of a channel's sediment supply regime.

Description: Abstract Secondary circulation in river confluences results in a spatial and temporal variation of fluid motion and a relatively high level of morphodynamic change. Acoustic Doppler current profiler (aDcp) vessel‐mounted flow measurements are now commonly used to quantify such circulation in shallow water fluvial environments. It is well established that such quantification using vessel‐mounted aDcps requires repeated survey of the same cross‐section. However, less attention has been given to how to process these data. Most aDcp data processing techniques make the assumption of homogeneity between the measured radial components of velocity. As acoustic beams diverge with distance from the aDcp probe, the volume of the flow that must be assumed to be homogeneous between the beams increases. In the presence of secondary circulation cells, and where there are strong rates of shear in the flow, the homogeneity assumption may not apply, especially deeper in the water column and close to the bed. To reduce dependence on this assumption, we apply a newly‐established method to aDcp data obtained for two medium‐sized (~60‐80 m wide) gravel‐bed river confluences and compare the results with those from more conventional data processing approaches. The comparsion confirms that in the presence of strong shear our method produces different results to more conventional approaches. In the absence of a third set of fully independent data, we cannot demonstrate conclusively which method is best, but our method involves less averaging and so in the presence of strong shear is likely to be more reliable. We conclude that it is wise to apply both our method and more conventional methods to identify where data analysis might be impacted upon by strong shear and where inferences of secondary circulation may need to be made more cautiously.

Description: Abstract Human activities have increasingly strong impacts on the sediment dynamics of watersheds, directly, for example through water abstraction and sediment extraction, but also indirectly through climate change. This study aims at disentangling these impacts on natural sediment fluxes for the Borgne river, located in the Alps of South‐West Switzerland, using two approaches: First, an assessment of contemporary sediment sources and their relative contribution to the sediment delivered to the catchment outlet is undertaken by geochemical fingerprinting and a mixing model. Second, a spatially distributed conceptual model of suspended sediment production and transfer is used to quantify the contribution of different portions of the catchment to the total sediment yield. The model describes the influence of hydroclimatic variables (rainfall, snowmelt, and ice melt), water diversions and reservoir trapping on the sediment yield accounting for the erodibility of the different land covers present in the catchment. The analysis of different scenarios based on this conceptual model aids the interpretation of the fingerprinting results and the identification of the most important factors controlling sediment fluxes. Although the conceptual model overestimates the contribution of the downstream source area and underestimates the contribution of the upstream source area, the results allow us to qualitatively assess the impacts of different drivers influencing the sediment yield at the catchment scale. The results suggest: (1) high sediment yield from the uppermost part of the catchment due to sediment delivery by glacial ice melt; (2) delayed sediment transfer from areas impacted by water abstraction; and (3) reduced sediment contribution from areas upstream of a major hydropower reservoir that intercepts and traps sediment. Although process (1) and processes (2) and (3) serve to counter one another, our study emphasizes that the relative impacts of Anthropocene climate change and human impacts on sediment delivery may be disentangled through multi‐proxy approaches.

Description: We examine coastal cliff ground motion due to individual wave impacts using a seismometer and video data to directly link the wave forcing and cliff response. The maximum peak ground shaking did not necessarily coincide with periods of maximum significant wave height. Instead, the type of wave impact controlled peak shaking magnitude, with breaking wave impacts generating the highest shaking velocities. Abstract Coastal cliff erosion is caused by a combination of marine forcing and sub‐aerial processes, but linking cliff erosion to the environmental drivers remains challenging. One key component of these drivers is energy transfer from wave–cliff interaction. The aim of this study is to directly observe cliff ground motion in response to wave impacts at an individual wave scale. Measurements are described from two coastal cliff sites: a 45‐minute pilot study in southern California, USA and a 30‐day deployment in Taranaki, New Zealand. Seismometers, pressure sensors and video are used to compare cliff‐top ground motions with water depth, significant wave height (Hs) and wave impact types to examine cliff ground motion response. Analyses of the dataset demonstrate that individual impact events can be discriminated as discrete events in the seismic signal. Hourly mean ground motion increases with incident Hs, but the largest hourly peak ground motions occurred across a broad range of incident Hs (0.9–3.7 m), including during relatively calm conditions. Mean hourly metrics therefore smooth the short‐term dynamics of wave–cliff interaction; hence, to fully assess wave impact energy transfer to cliffs, it is important also to consider peak ground motion. Video analyses showed that the dominant control on peak ground motion magnitude was wave impact type rather than incident Hs. Wave–cliff impacts where breaking occurs directly onto the cliff face consistently produced greater ground motion compared to broken or unbroken wave impacts: breaking, broken and unbroken impacts averaged peak ground motion of 287, 59 and 38 μm s−1, respectively. The results illustrate a novel link between wave impact forcing and cliff ground motion response using individual wave field measurements, and highlight the influence of wave impact type on peak energy transfer to coastal cliffs. © 2019 John Wiley & Sons, Ltd.

Description: Seasonal variations in u*t and PM10 fluxes for different landform types in northern China. Abstract Representation of dust sources remains a key challenge in quantifying the dust cycle and its environmental and climatic impacts. Direct measurements of dust fluxes from different landform types are useful in understanding the nature of dust emission and characterizing the dynamics of soil erodibility. In this study we used the PI‐SWERL® instrument over a seasonal cycle to quantify the potential for PM10 (particles with diameter ≤10 μm) emission from several typical landform types across the Tengger Desert and Mu Us Sandy Land, northern China. Our results indicate that sparse grasslands and coppice dunes showed relatively high emission potentials, with emitted fluxes ranging from 10−1 to 101 mg m−2 s−1. These values were up to five times those emitted from sand dunes, and one to two orders of magnitude greater than the emissions from dry lake beds, stone pavements and dense grasslands. Generally, PM10 emission fluxes were seen to peak in the spring months, with significant reductions in summer and autumn (by up to 95%), and in winter (by up to 98%). Variations in soil moisture were likely a primary controlling factor responsible for this seasonality in PM10 emission. Our data provide a relative quantification of differences in dust emission potential from several key landform types. Such data allow for the evaluation of current dust source schemes proposed by prior researchers. Moreover, our data will allow improvements in properly characterizing the erodibility of dust source regions and hence refine the parameterization of dust emission in climate models. © 2019 John Wiley & Sons, Ltd.

Description: Abstract Among the numerous environmental factors affecting plant communities in alpine ecosystems, the influence of geomorphic processes and landforms has been minimally investigated. Subjected to persistent climate warming, it is vital to understand how these factors affect vegetation properties. Here, we studied 72 vegetation plots across three sites located in the Western Swiss Alps, characterized by high geomorphological variability and plant diversity. For each plot, vascular plant species were inventoried and ground surface temperature, soil moisture, topographic variables, earth surface processes (ESPs) and landform morphodynamics were assessed. The relationships between plant communities and environmental variables were analysed using non‐metric multi‐dimensional scaling (NMDS) and multivariate regression techniques (generalized linear model, GLM, and generalized additive model, GAM). Landform morphodynamics, growing degree days (sum of degree days above 5 °C) and mean ground surface temperature were the most important explanatory variables of plant community composition. Furthermore, the regression models for species cover and species richness were significantly improved by adding a morphodynamics variable. This study provides complementary support that landform morphodynamics is a key factor, combined with growing degree days, to explain alpine plant distribution and community composition.

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

Description: Abstract The study of the coastal landscapes of hotspot oceanic islands through comprehensive structural metrics and ecological estimators represents an opportunity to explore geomorphological transformations and broad spatiotemporal scale features of coastal evolution. As part of this approach, a new metrical comparative analysis is presented in this study, comprising four islands in different evolutionary stages. They belong to the Cape Verde archipelago, which forms a double insular chain in which an east‐west gradient in age and evolution is particularly evident across the southern chain. A space‐for‐time (SFT) substitution approach is applied to the coasts of (1) Fogo, in the shield stage; (2) Santiago, in the early post‐erosional stage; (3) São Vicente, in the advanced post‐erosional stage; and (4) Boa Vista, in the last erosional stage. From the obtained spatial distributions and frequencies of landforms, the coastal landscapes of these islands are compared in relation to their (i) geomorphic composition, using similarity indices (Whittaker, βw, Sorensen, Cs) and nestedness estimators (NOFD, WNODF), (ii) geomorphic abundance, using morpho‐assembling densities (Dgm), and (iii) geomorphic diversity, using six alpha‐diversity indices (Richness, S, Menhinick, DMN, Simpson, D, Shannon, H', Berger‐Parker, d, and Brillouin, HB). An advanced geomorphological taxonomy is implemented for areas with limited open‐access data, including a set of planform features captured through scale‐frequency decomposition. Photographic, cartographic and field work data are used for landform identification at 1,200 random sampling points, empirically determined by a bootstrap method. The results show a chronological ordering of the compared variables and a possible co‐evolution towards an increase in organizational geomorphic complexity of coastal systems at broad space‐time scales. The method proposed in this study can contribute, from a metrical perspective, to finding new long‐term evolutionary features and constitutes an advance in the development of an integrated model of coastal evolution in oceanic islands.

Description: Abstract In biological evolution, creativity occurs in the appearance of new entities by evolutionary dynamics. This is linked to mutations and genetic drift, which cannot occur in geophysical phenomena. Biota can exhibit evolutionary creativity that influences landforms, but how does creativity (defined here as the capacity for emergence of new entities that increase the adjustedness of the landscape to environmental conditions) occur in landforms and landscapes as entities independent of biota? Creativity in geomorphic evolution does not require any sort of goal functions or purposeful innovation‐‐just that geomorphic development is capable of producing novelties that may be better adapted (more efficient or durable) than predecessors. Independently of biota, evidence exists that landforms may develop to become more or less "fit" in terms of efficiency and/or durability. Thus emergence of novel features may lead to their persistence. Emergence of novel forms is illustrated for the case of karst sinkholes (dolines), which indicates increasing geomorphic diversity over Ma and Ga timescales. A case study of fluviokarst chronosequences in Kentucky demonstrates emergence and elimination of landforms as landscapes evolve. Some of these may represent generally (as opposed to locally) novel landforms. While this paper is more suggestive than demonstrative, results strongly suggest evolutionary creativity in geomorphology both tied to, and independent of, biological evolution. This occurs due to emergence of geomorphic entities that are subject to selection that tends to increase efficiency and durability.

Description: Abstract Prior numerical modeling work has suggested that incision into sub‐horizontal layered stratigraphy with variable erodibility induces non‐uniform erosion rates even if base‐level fall is steady and sustained. Erosion rates of cliff bands formed in the stronger rocks in a stratigraphic sequence can greatly exceed the rate of base‐level fall. Where quartz in downstream sediment is sourced primarily from the stronger, cliff‐forming units, erosion rates estimated from concentrations of cosmogenic 10Be in detrital sediment will reflect the locally high erosion rates in retreating cliff bands. We derive theoretical relationships for threshold hillslopes and channels described by the stream‐power incision model as a quantitative guide to the potential magnitude of this amplification of 10Be‐derived erosion rates above the rate of base‐level fall. Our analyses predict that the degree of erosion rate amplification is a function of bedding dip and either the ratio of rock erodibility in alternating strong and weak layers in the channel network, or the ratio of cliff to intervening‐slope gradient on threshold hillslopes. We test our predictions in the cliff‐and‐bench landscape of the Grand Staircase in southern Utah, USA. We show that detrital cosmogenic erosion rates in this landscape are significantly higher (median 300 m/Ma) than the base‐level fall rate (~75 m/Ma) determined from the incision rate of a trunk stream into a ~0.6 Ma basalt flow emplaced along a 16 km reach of the channel. We infer a 3‐6 fold range in rock strength from near‐surface P‐wave velocity measurements. The ~4‐fold difference between the median 10Be‐derived erosion rate and the long‐term rate of base‐level fall is consistent with our model and the observation that the stronger, cliff‐forming lithologies in this landscape are the primary source of quartz in detrital sediments.

Description: ABSTRACT Inducing biological soil crust (biocrust) development is an appealing approach for dust mitigation in drylands due to the resistance biocrusts can provide against erosion. Using a portable device, we evaluated dust emissions from surfaces either inoculated with biocrust, amended with a plant‐based soil stabilizer, or both at varying wind friction velocities. Four months after application, emissions from all treatments were either indistinguishable from or greater than controls, despite evidence of biocrust establishment. All treatments had greater surface roughness and showed more evidence of entrapment of windblown sediment than controls, factors which may have been partially responsible for elevated emissions. There was a synergistic effect of inoculation and stabilizer addition, resulting in a nearly 2‐fold reduction in estimated emissions compared to either treatment alone. Stepwise regression analysis indicated that variables associated with surface crust strength (aggregate stability, penetration resistance) were negatively associated with emissions and variables associated with sediment supply (sand content, loose sediment cover) were positively associated with emissions. With more time to develop, the soil‐trapping activity and surface integrity of biocrust inoculum and soil stabilizer mixtures is expected to increase with the accumulation of surface biomass and enhancement of roughness through freeze‐thaw cycles.

Description: Abstract We present a critical analysis of experimental findings on vegetation‐flow‐sediment interactions obtained through both laboratory and field experiments on tidal and coastal environments. It is well established that aquatic vegetation provides a wide range of ecosystem services (e.g., protecting coastal communities from extreme events, reducing riverbank and coastal erosion, housing diverse ecosystems), and the effort to better understand such services has led to multiple approaches to reproduce the relevant physical processes through detailed laboratory experiments. State‐of‐the‐art measurement techniques allow researchers to measure velocity fields and sediment transport with high spatial and temporal resolution under well‐controlled flow conditions, yielding predictions for hydrodynamic and sediment transport scenarios that depend on simplified or bulk vegetation parameters. However, recent field studies have shown that some simplifications on the experimental setup (e.g., the use of rigid elements, a single diameter, a single element height, regular or staggered layout) can bias the outcome of the study, by either hiding or amplifying some of the relevant physical processes found in natural conditions. We discuss some observed cases of bias, including general practices that can lead to compromises associated with simplified assumptions. The analysis presented will identify potential pathways to move forward with laboratory and field measurements, that could better inform predictors to produce more robust, universal, and accurate predictions on flow‐vegetation‐sediment interactions.

Description: Abstract The investigation of form and processes in geomorphology and ecology is highly dependent on topographic data: a reliable digital terrain representation is in fact a key issue across environmental and earth sciences. In many cases, the processing of high‐resolution topographic data (e.g., LiDAR, SfM) has to face issues like void filling, vegetation/feature removal and interpolation accuracy that are usually related to (i) intrinsic limitations of the adopted technology, (ii) local conditions affecting the survey, or (iii) specific design scenario. In this paper, we develop a methodology to test the accuracy of an image inpainting algorithm to fill data voids in complex mountain areas. The devised experiment exploits the availability of a high resolution, LiDAR‐derived Digital Terrain Model and the inpainting approach accuracy is checked against some widely used interpolation techniques (Natural neighbor, Spline, IDW, Kriging). In order to better mimic the actual surface texture, a methodology to introduce local topographic variability to the interpolated surface is also presented. The results show a better performance of the inpainting algorithm especially in case of complex and rugged topography. Two examples showing an effective usage and accuracy of the proposed technique are reported, highlighting the drawbacks that a poor surface representation can introduce. The whole procedure is made freely available within a Matlab® script with the addition of sample files.

Description: Schematic of the SediNet architecture. An input image is passed to the feature extractor consisting of a series of convolutional blocks. The last set of feature maps is fed into one of three multi‐layer perceptrons; one each for the task of estimating grain size percentiles, sediment population, and grain shape. Abstract I describe a configurable machine‐learning framework to estimate a suite of continuous and categorical sedimentological properties from photographic imagery of sediment, and to exemplify how machine learning can be a powerful and flexible tool for automated quantitative and qualitative measurements from remotely sensed imagery. The model is tested on a dataset consisting of 409 images and associated detailed label data. The data are from a much wider sedimentological spectrum than previous optical granulometry studies, consisting of both well‐ and poorly sorted sediment, terrigenous, carbonate, and volcaniclastic sands and gravels and their mixtures, and grain sizes spanning over two orders of magnitude. I demonstrate the model framework by configuring it in several ways, to estimate two categories (describing grain shape and population, respectively) and nine numeric grain size percentiles in pixels from a single input image. Grain size is then recovered using the physical size of a pixel. Finally, I demonstrate that the model can be configured and trained to estimate equivalent sieve diameters directly from image features, without the need for area‐to‐mass conversion formulas and without even knowing the scale of one pixel. Thus it is the only optical granulometry method proposed to date that does not necessarily require image scaling. The flexibility of the model framework should facilitate numerous application in the spatiotemporal monitoring of the grain size distribution, shape, mineralogy and other quantities of interest of sedimentary deposits as they evolve, as well as other texture‐based proxies extracted from remotely sensed imagery. © 2019 John Wiley & Sons, Ltd.

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

Description: Abstract Soil‐covered upland landscapes comprise a critical part of the habitable world and our understanding of their evolution as a function of different climatic, tectonic, and geologic regimes is important across a wide range of disciplines. Soil production and transport play essential roles in controlling the spatial variation of soil depth and therefore hillslope hydrological processes, distribution of vegetation, and soil biological activity. Field‐based confirmation of the hypothesized relationship between soil thickness and soil production is relatively recent, however, and here we quantify a direct, material strength‐based influence on variable soil production across landscapes. We report clear empirical linkages between the shear strength of the parent material (its erodibility) and the overlying soil thickness. Specifically, we use a cone penetrometer and a shear vane to determine saprolite resistance to shear. We find that saprolite shear strength increases systematically with overlying soil thickness across three very different field sites where we previously quantified soil production rates. At these sites, soil production rates, determined from in situ produced 10Be and 26Al, decrease with overlying soil thickness and we therefore infer that the efficiency of soil production must decrease with increasing parent material shear strength. We use our field‐based data to help explain the linkages between biogenic processes, chemical weathering, hillslope hydrology, and the evolution of the Earth's surface.

Description: Abstract Coastal foredunes provide the first line of defense against rising sea levels and storm surge and for this reason there is increasing interest in understanding and modeling foredune formation and post‐storm recovery. However, there is limited observational data available to provide empirical guidance for the development of model parameterizations. To provide guidance for improved representation of dune grass growth in models, we conducted a two‐year multi‐species transplant experiment on Hog Island, VA, U.S.A. and measured the dependence of plant growth on elevation and distance from the shoreline, as well as the relationship between plant growth and sand accumulation. We tracked total leaf growth (length) and aboveground leaf length and found that Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats) grew more than Spartina patens (saltmeadow cordgrass) by a factor of 15% (though not statistically significant) and 45%, respectively. Our results also suggest a range of basal/frontal area ratios (an important model parameter) from 0.5‐1 and a strong correlation between transplant growth and total sand deposition for all species at the scale of two years, but not over shorter temporal scales. Distance from the shoreline and elevation had no effect on transplant growth rate but did have an effect on survival. Based on transplant survival, the seaward limit of vegetation at the end of the experiment was approximately 30 m from the MHWL and at an elevation of 1.43 m, corresponding to inundation less than 7.5% of the time according to total water level calculations. Results from this experiment provide evidence for the dune‐building capacity of all three species, suggesting S. patens is not a maintainer species, as previously thought, but rather a moderate dune builder even though its growth is less stimulated by sand deposition than A. breviligulata and U. paniculata.

Description: Abstract Glacial cirques are widely used palaeoenvironmental indicators, and are key to understanding the role of glaciers in shaping mountain topography. However, notable uncertainty persists regarding the rate and timing of cirque erosion. In order to address this uncertainty, we analyse the dimensions of 2208 cirques in Britain and Ireland and model ice accumulation to investigate the degree of coupling between glacier occupation times and cirque growth. Results indicate that during the last ~120 ka, cirques were glacier‐free for an average of 52.0 ± 21.2 ka (43 ± 18%); occupied by small (largely cirque‐confined) glaciers for 16.2 ± 9.9 ka (14 ± 8%); and occupied by large glaciers, including ice sheets, for 51.8 ± 18.6 ka (43 ± 16%). Over the entire Quaternary (i.e., 2.6 Ma), we estimate that cirques were glacier‐free for 1.1 ± 0.5 Ma; occupied by small glaciers for 0.3 ± 0.2 Ma; and occupied by large glaciers for 1.1 ± 0.4 Ma. Comparing occupation times to cirque depths, and calculating required erosion rates reveals that continuous cirque growth during glacier occupation is unlikely. Instead, we propose that cirques attained much of their size during the first occupation of a non‐glacially sculpted landscape (perhaps during the timeframe of a single glacial cycle). During subsequent glacier occupations, cirque growth may have slowed considerably, with the highest rates of subglacial erosion focused during periods of marginal (small glacier) glaciation. We propose comparatively slow rates of growth following initial cirque development because a ‘least resistance’ shape is formed, and as cirques deepen, sediment becomes trapped subglacially, partly protecting the bedrock from subsequent erosion. In support of the idea of rapid cirque growth, we present evidence from northern British Columbia, where cirques of comparable size to those in Britain and Ireland developed in less than 140 ka.

Description: Abstract The Three Gorges Dam (TGD) has altered downstream flow‐sediment regimes and led to significant changes in the morphodynamic processes in the Middle Yangtze River (MYR). However, due to the complexity of this large river, the driving forces and implication of the morphodynamic processes remain insufficiently understood. This study selected two typical meandering and bar‐braided reaches, the Zhicheng (ZC) and Shashi (SS) reach, to examine their responses to the TGD operation. The results showed that in the post‐dam period significant channel erosion occurred with a higher erosion rate in the ZC reach (closer to the TGD) compared with the SS reach. The area of the Guanzhou mid‐channel bar (ZC reach) and the Sanba mid‐channel bar (SS reach) shrank by 30% and 90% from 2003 to 2015, respectively. The increased fluvial erosion intensity due to the reduction in suspended sediment concentration (SSC) drove the shrinkage of the mid‐channel bars as demonstrated by empirical relationships between bar geometry and fluvial erosion intensity. An increase of 22 days per year in the frequency of post‐dam medium‐high discharges (10,000‐25,000 m3/s), and associated with the reduction in SSC, jointly led to the greater erosion at the convex (inner) banks than the concave (outer) banks, which has negatively affected the designed navigation channels at the concave banks by decreasing their discharge partitioning ratios. Post‐dam water level at a given high discharge (〉 25,000 m3/s) showed no evident change, but the water level at a given low discharge (〈 10,000 m3/s) decreased. The reduction in water levels at low flows can affect water supply and riverine ecosystems in the MYR.

Description: Summary Landscape experiments of fluvial environments such as rivers and deltas are often conducted with live seedlings to investigate effects of biogeomorphological interactions on morphology and stratigraphy. However, such experiments were limited to a single species, usually Alfalfa (Medicago sativa), while important environments in nature have many different vegetation types and eco‐engineering effects. Landscape experimentation would therefore benefit from a larger choice of tested plant species. For the purpose of experimental design our objective was to identify fast‐germinating and fast‐growing species and determine their sensitivity to flow conditions during and after settling, their maximum growth, hydraulic resistance and added bank strength. We tested germination time and seedling growth rate of eighteen candidate species with readily available seeds that are fast‐growing and occur at waterlines, plus Medicago sativa as a control. We selected five species that germinate and develop within days and measured properties and eco‐engineering effects depending on plant age and density, targeting typical experimental conditions of 0‐0.3 m/s flow velocity and 0‐30 mm water depth. Tested eco‐engineering effects include bank strength and flow resistance. We found that Rumex hydrolapathum can represent riparian trees. The much smaller Veronica beccabunga and Lotus pedunculatus can represent grass and saltmarsh species as they grow in dense patches with high flow resistance but are readily erodible. Sorghum bicolor grows into tall, straight shoots, which add significantly to bank strength, but adds little flow resistance and may represent sparse hardwood trees. Medicago sativa also grows densely under water, suggesting a use for mangroves and perhaps peat. In stronger and deeper flows the application of all species changes accordingly. These species can now be used in a range of landscape experiments to investigate combined effects on living landscape patterns and possible facilitation between species. The testing and treatment methodology can be applied to new species and other laboratory conditions. This article is protected by copyright. All rights reserved.

Description: Abstract Rockwall slope erosion is defined for the upper Bhagirathi catchment using cosmogenic 10Be concentrations in sediment from medial moraines on Gangotri glacier. Beryllium‐10 concentrations range from 1.1±0.2 to 2.7±0.3x104 at/g SiO2, yielding rockwall slope erosion rates from 2.4±0.4 to 6.9±1.9 mm/a. Slope erosion rates are likely to have varied over space and time and responded to shifts in climate, geomorphic and/or tectonic regime throughout the late Quaternary. Geomorphic and sedimentological analyses confirm that the moraines are predominately composed of rockfall and avalanche debris mobilized from steep relief rockwall slopes via periglacial weathering processes. Slope erosion affects sediment flux and storage of snow and ice at the catchment head on diurnal to millennial timescales, and more broadly influences catchment configuration and relief, glacier dynamics and microclimates. The slope erosion rates exceed the averaged catchment‐wide and exhumation rates of Bhagirathi and the Garhwal region on geomorphic timescales (103−105 years), supporting the view that erosion at the headwaters can outpace the wider catchment. The 10Be concentrations of medial moraine sediment for the upper Bhagirathi catchment and the catchments of Chhota Shigri in Lahul, northern India and Baltoro glacier in Central Karakoram, Pakistan show a tentative relationship between 10Be concentration and rainfall. As such there is more rapid slope erosion in the monsoon‐influenced Lesser and Greater Himalaya compared to the semi‐arid interior of the orogen. Rockwall slope erosion in the three study areas, and more broadly across the NW Himalaya is likely governed by individual catchment dynamics that vary across space and time.

Description: Abstract River confluences are characterized by a complex mixing zone with three‐dimensional (3D) turbulent structures which have been described as both streamwise‐oriented structures and Kelvin‐Helmholtz (KH) vertical‐oriented structures. The latter are visible where there is a turbidity difference between the two tributaries, whereas the former are usually derived from mean velocity measurements or numerical simulations. Few field studies recorded turbulent velocity fluctuations at high frequency to investigate these structures, particularly at medium‐sized confluences where logistical constraints make it difficult to use devices such as Acoustic Doppler Velocimeter (ADV). This study uses the ice cover present at the confluence of the Mitis and Neigette Rivers in Quebec (Canada) to obtain long‐duration, fixed measurements along the mixing zone. The confluence is also characterized by a marked turbidity difference which allows to investigate the mixing zone dynamics from drone imagery during ice‐free conditions. The aim of the study is to characterize and compare the flow structure in the mixing zone at a medium‐sized (~ 40 m) river confluence with and without an ice cover. Detailed 3D turbulent velocity measurements were taken under the ice along the mixing plane with an ADV through eight holes at around 20 positions on the vertical. For ice‐free conditions, drone imagery results indicate that large (KH) coherent structures are present, occupying up to 50% of the width of the parent channel. During winter, the ice cover affects velocity profiles by moving the highest velocities towards the centre of the profiles. Large turbulent structures are visible in both the streamwise and lateral velocity components. The strong correlation between these velocity components indicates that KH vortices are the dominating coherent structures in the mixing zone. A spatio‐temporal conceptual model is presented to illustrate the main differences on the 3D flow structure at the river confluence with and without the ice cover.

Description: Abstract Alluvial fans at tributary junctions modulate sediment flux through river networks, by buffering the mainstem channel from disturbance in the tributaries. Buffering occurs through the storage (and release) of sediment in fans. Here, we use an extensive historic dataset to characterise the ways in which fan buffering can change as sediment supply varies. In New Zealand's East Coast region, sediment supply and fluvial transport are prolific by global standards. We reconstruct how tributary‐junction fans in this region have responded to sediment generated by deforestation and extreme storms. The dynamics of five fans along the Tapuaeroa River are examined for the period 1939‐2015. In response to major sediment loading, fans aggraded by up to 12 m and prograded by up to 170 m. Net sediment accumulation ranged from near zero to 1.5 ×106 m3. Fan size, gradient, sediment storage and buffering were influenced by both upstream and downstream controls. Key upstream (tributary) influences were sediment supply and stream power; downstream (mainstem) influences included distal confinement and, importantly, the nature of fan interaction with the mainstem, which aggraded by up to 6 m. The fans' ability to buffer the Tapuaeroa River from change in the tributaries was largely governed by this downstream interaction: red as the mainstem aggraded, it increasingly curtailed fan progradation, thus limiting buffering. Previous studies of tributary‐junction fans have related fan morphometry to basin characteristics. However, we find that fan slope and area can vary considerably at decadal, annual or even monthly timescales. Consequently, we suggest that such studies could benefit by examining regional histories of disturbance.

Description: The impact of sub‐threshold flow duration on three sediment beds has been quantified. Results show that increasing antecedent duration increases the average threshold shear stress of the D50 by up to 18% and decreases bedload flux by up to 90%. The rate of response of both variables is non‐linear and inversely proportional to antecedent duration and there is a grade dependent response where the uniform bed is up to twice as responsive to the graded beds. Abstract Limited field and flume data suggests that both uniform and graded beds appear to progressively stabilize when subjected to inter‐flood flows as characterized by the absence of active bedload transport. Previous work has shown that the degree of bed stabilization scales with duration of inter‐flood flow, however, the sensitivity of this response to bed surface grain size distribution has not been explored. This article presents the first detailed comparison of the dependence of graded bed stability on inter‐flood flow duration. Sixty discrete experiments, including repetitions, were undertaken using three grain size distributions of identical D50 (4.8 mm); near‐uniform (σg = 1.13), unimodal (σg = 1.63) and bimodal (σg = 2.08). Each bed was conditioned for between 0 (benchmark) and 960 minutes by an antecedent shear stress below the entrainment threshold of the bed (τ*c50). The degree of bed stabilization was determined by measuring changes to critical entrainment thresholds and bedload flux characteristics. Results show that (i) increasing inter‐flood duration from 0 to 960 minutes increases the average threshold shear stress of the D50 by up to 18%; (ii) bedload transport rates were reduced by up to 90% as inter‐flood duration increased from 0 to 960 minutes; (iii) the rate of response to changes in inter‐flood duration in both critical shear stress and bedload transport rate is non‐linear and is inversely proportional to antecedent duration; (iv) there is a grade dependent response to changes in critical shear stress where the magnitude of response in uniform beds is up to twice that of the graded beds; and (v) there is a grade dependent response to changes in bedload transport rate where the bimodal bed is most responsive in terms of the magnitude of change. These advances underpin the development of more accurate predictions of both entrainment thresholds and bedload flux timing and magnitude, as well as having implications for the management of environmental flow design. © 2019 John Wiley & Sons, Ltd.

Description: Abstract Groundwater dolocretes may exert an important geomorphic control on landscape evolution within sub‐humid to arid regions. However, the geomorphic and hydrogeological settings of dolocrete remain poorly described. The hydrochemical conditions of dolomite precipitation in groundwater environments are also not well known. Classic models of dolocrete formation explain dolomite precipitation from highly evolved groundwaters at the terminus of major drainage but do not explain dolocrete distributed in regionally elevated landscapes, upgradient of major drainage. This study investigated the mineralogy, micromorphology and stable carbon and oxygen isotope compositions of three dolocrete profiles within a regionally elevated sub‐basin of the Hamersley Ranges in the Pilbara region of northwest Australia. We sought to establish the environmental and hydrochemical conditions and present a model for dolocrete formation. We found that dolocrete formed within zones of emerging groundwater under saline‐evaporitic conditions within internally draining sub‐basins, most likely during the Late Miocene and Pliocene. Saline‐evaporitic conditions were indicated by: i) the mineralogy, dominated by dolomite, palygorskite and smectite; ii) desiccation features and the presence of phreatic and vadose cements, indicative of a shallow fluctuating water table, and; iii) dolomite δ18O values (median = ‐5.88‰). Dolomite precipitation was promoted by evaporation and CO2 degassing from shallow Mg‐rich groundwater. These factors appear to have been the major drivers of dolocrete development without a requirement for significant down‐dip hydrochemical modification. Primary dolomite precipitation was possible due to the presence of microbial extracellular polymeric substances (EPS). EPS provided negatively charged nucleation sites, which bound Mg2+, overcoming kinetic effects. High microbial activity within groundwater systems suggest these processes may be important for dolocrete formation worldwide and that groundwater dolocretes may be more pervasive in landscapes than currently recognised.

Description: Earth Surface Processes and Landforms, Volume 0, Issue ja, -Not available-.

Description: Abstract In Mediterranean mountain agroecosystems, soil erosion associated with the development of ephemeral gullies is a common environmental problem that contributes to a loss of nutrient‐rich topsoil. Little is known about the influence of ephemeral gully erosion on particle size distribution and its effect on soil organic (SOC) and inorganic (SIC) carbon among different sized soil particles in agricultural soils. In this study, laboratory tests were conducted using velocity settling tube experiments to examine the effects of erosion on sediment particle size distributions from an incised ephemeral gully, associated with an extreme event (265 mm). We also consider subsequent deposition on an alluvial fan in order to assess the distribution of SOC and SIC concentrations and dissolved carbon before and after the extreme event. Soil fractionation was carried out on topsoil samples (5 cm) collected along an ephemeral gully in a cultivated field, located in the lower part of a Mediterranean mountain catchment. The results of this study showed that the sediment transported downstream by runoff plays a key role in the particle size distribution and transportability of soil particles and associated carbon distribution in carbonate rich soils. The eroding sediment is enriched in clay and silt‐sized particles at upslope positions with higher SOC contents and gradually becomes coarser and enriched in SIC at the end of the ephemeral gully because the finest particles are washed‐out of the study field. The extreme event was associated with an accumulation of dissolved organic carbon at the distal part of the depositional fan. Assessment of soil particle distribution using settling velocity experiments provides basic information for a better understanding of soil carbon dynamics in carbonate rich soils. Processes of soil and carbon transport and relationships between soil properties, erodibility and aggregate stability can be helpful in the development of more accurate soil erosion models.

Description: Abstract Rills are generated on homogeneous hillslopes by the action of different discharges and evolve morphologically over short timescales due to a strong interaction between the flow and bed morphology. Such an interaction generates a reconfiguration of the bed geometry. Previous works suggest that bed geometry is often characterized by alternation between pools and flat reaches (steps). Each step‐pool unit may contribute to hydraulic resistance and affects flow behaviour. The objectives of this work are (i) to assess different (innovative) techniques for the in situ assessment of rill bed geometry, (ii) to use these techniques to assess the geometry of eroded rills in situ in order to determine the spatial arrangement in the bed macro‐scale roughness and (iii) finally to analyse the role of slope and discharge as driving factors associated with the development of these macroforms. Roughly rectilinear, long rills were formed in the field as a result of combining different slope and discharges. Photogrammetry provided detailed digital elevation models (DEMs) before and after the experiments. The rills were morphologically characterized from the DEMs. In each rill, the presence of step‐pools was identified from long profiles according mainly to morphological criteria published elsewhere, but with ad hoc critical threshold values more appropriate for small eroded channels. The minimum slope required for the development of step‐pool units seem to be somewhere in between 5% and 15%. Discharge seems to affect pool size or roughness amplitude. There does not seem to be a clear step‐pool periodicity. However, external factors could have affected the normal growth and alternation of these structures. Identification of steps and pools from longitudinal elevation profiles can be objectively accomplished using a series of geometric rules originally proposed for rivers and large channels, and adapted to rills.

Description: Abstract Many models of incision by bedrock rivers predict water depth and shear stress from discharge; conversely, palaeoflood discharge is sometimes reconstructed from flow depth markers in rock gorges. In both cases assumptions are made about flow resistance. The depth‐discharge relation in a bedrock river must depend on at least two roughness length scales (exposed rock and sediment cover) and possibly a third (sidewalls). A conceptually attractive way to model the depth‐discharge relation in such situations is to partition the total shear stress and friction factor, but it is not obvious how to quantify the friction factor for rough walls in a way that can be used in incision process models. We show that a single flow resistance calculation using a spatially‐averaged roughness length scale closely approximates the partitioning of stress between sediment and rock, and between bed and walls, in idealised scenarios. Both approaches give closer fits to the measured depth‐discharge relations in two small bedrock reaches than can be achieved using a fixed value of Manning's n or the Chézy friction factor. Sidewalls that are substantially rougher or smoother than the bed have a significant effect on the partitioning of shear stress between bed and sidewalls. More research is needed on how best to estimate roughness length scales from observable or measurable channel characteristics.

Description: Abstract Dissolved inorganic carbon (DIC) is the most important carbon component in karst aquatic system where fluid is highly transmissive, but has rarely been examined in subtropical karst critical zone (K‐CZ). In this study, concentrations of dissolved solutes and isotopic compositions of DIC (δ13CDIC) at 11 sites of a 73.4 km2 karstic catchment in Southwestern China were analyzed monthly in order to uncover the spatiotemporal variations of both DIC and its dominant sources, and to identify relevant controlling factors. Both DIC concentrations and δ13CDIC were highly variable, ranging from 2.52 to 5.85 mmol/L and from ‐15.7‰ to ‐4.5‰, respectively. DIC in underground water (UGW) was higher in concentration and more depleted in 13C compared to surface water (SFS). DIC concentrations showed an inconsistent seasonal trend with other solutes, with higher values in the wet season at some sites. δ13CDIC values were lower in the wet season than in the dry season. The results of mixing model IsoSource revealed spatiotemporal patterns of DIC sources. During the dry season, carbonate weathering was the primary contributor to DIC in UGW (excluding in the middle reaches). However, during the wet season, soil CO2 was the dominant source of DIC in both UGW and SFS, and it was higher than in the dry season. Overall, there are significant spatiotemporal disparities and highly transmissive characteristics of both DIC and its sources in the K‐CZ, which are controlled by multiple factors. This study also highlights that rainfall may plays a crucial role in accelerating carbon dynamics in the K‐CZ. High‐frequency sampling campaigns in high‐flow periods and deep‐going analyses are needed in future work to elucidate the related processes and mechanisms.

Description: Deforestation, cultivation and stocking density increases influenced the incessant growth of erosion rates since the second half of the nineteenth century. Stocking density, bare soil and stream power index are factors that affect the spatial variation of the soil erosion rates along hillsides. Abstract Changes in land use are common in Mediterranean areas and are reported as having produced changes in the intensity of soil erosion. Dehesas are rangelands with a disperse tree cover, widespread in the south‐western part of the Iberian Peninsula and similar ecosystems are also common in other areas with a Mediterranean climate. The aim of the present study is to analyse temporal and spatial variations of soil erosion rates estimated along three hillsides, located in two farms (Buitrera and Parapuños) in southwest Spain. To understand the temporal variation, soil erosion rates were studied in light of land use‐management changes that took place during the last few centuries. Results indicate very low erosion rates prior to the 18th century in both farms. In Buitrera, a first increase of soil loss rates was identified during the period 1831‐1897, amounting to 7.4 t ha‐1 y‐1. A further increase took place during the 20th century, reaching a mean erosion rate of 29.1 t ha‐1 y‐1. In Parapuños, data points to a significant increase from 1881 onwards, with an estimated mean erosion rate of 18.5 t ha‐1 y‐1. Those increases were presumably connected with an intensification of land use, such as cultivation and excessive livestock populations. Regarding spatial variation, the bare surface and the erosive power of run‐off along the hillsides accounts for 76% of the soil erosion rates dispersion. At a local scale, the variability of erosion rates could not be explained, because of (i) uncertainty related to the micromorphology of the past soil surface and (ii) the role of tillage erosion in the past. However, the results obtained offer valuable data on the temporal and spatial variation of erosion rates in dehesas at the hillslope scale and a similar approach could be used for other rangelands with a disperse tree cover. © 2019 John Wiley & Sons, Ltd.

Description: 1. Erosion and deposition occur in distinct regions with a circular blowout. Deposition in the upwind third and erosion in the downwind third. 2. Comparison of numerically modelled wind flow and surface elevation change showed strong negative relationships for overall topographic surface change and wind speed, and for erosion and vertical wind velocity. 3. Wind flow and topographic change analysis suggests that a ‘bowl’ morphology is the net evolutionary response of blowouts in a bi‐ to multi‐ directional wind environment. Abstract A number of studies have measured and numerically modelled near surface wind velocity over a range of aeolian landforms and made suppositions about topographic change and landform evolution. However, the precise measurement and correlation of flow dynamics and resulting topographic change have not yet been fully realized. Here, using repeated high‐resolution terrestrial laser scanning and numerical flow modelling within a bowl blowout, we statistically analyse the relationship between wind speed, vertical wind velocity, turbulent kinetic energy and topographic change over a 33‐day period. Topographic results showed that erosion and deposition occurred in distinct regions within the blowout. Deposition occurred in the upwind third of the deflation basin, where wind flow became separated and velocity and turbulent kinetic energy decreased, and erosion occurred in the downwind third of the deflation basin, where wind flow reattached and aligned with incident wind direction. Statistical analysis of wind flow and topographic change indicated that wind speed had a strong correlation with overall topographic change and that vertical wind velocity (including both positive and negative) displayed a strong correlation with negative topographic change (erosion). Only weak or very weak correlations exist for wind flow parameters and positive topographic change (accretion). This study demonstrates that wind flow modelling using average incident wind conditions can be utilized successfully to identify regions of overall change and erosion for a complex aeolian landform, but not to identify and predict regions where solely accretion will occur. © 2019 John Wiley & Sons, Ltd.

Description: We use the unique Glacsweb wireless in situ probe (embedded in the ice and till) to record seasonal water pressure changes and till deformation from Skálafellsjökull, Iceland. Water pressures are high during summer and experience melt‐driven cyclical behaviour during winter, with till deformation occurring all year. Due to the soft bed the subglacial hydrology is dominated by a distributed system that may become more channelized in winter, and these systems are very responsive to melt water inputs. Abstract We investigate the spatial and temporal englacial and subglacial processes associated with a temperate glacier resting on a deformable bed using the unique Glacsweb wireless in situ probes (embedded in the ice and the till) combined with other techniques [including ground penetrating radar (GPR) and borehole analysis]. During the melt season (spring, summer and autumn), high surface melt leads to high water pressures in the englacial and subglacial environment. Winter is characterized by no surface melting on most days (‘base’) apart from a series of positive degree days. Once winter begins, a diurnal water pressure cycle is established in the ice and at the ice/sediment interface, with direct meltwater inputs from the positive degree days and a secondary slower englacial pathway with a five day lag. This direct surface melt also drives water pressure changes in the till. Till deformation occurred throughout the year, with the winter rate approximately 60% that of the melt season. We were able to show the bed comprised patches of till with different strengths, and were able to estimate their size, relative percentage and temporal stability. We show that the melt season is characterized by a high pressure distributed system, and winter by a low pressure channelized system. We contrast this with studies from Greenland (overlying rigid bedrock), where the opposite was found. We argue our results are typical of soft bedded glaciers with low englacial water content, and suggest this type of glacier can rapidly respond to surface‐driven melt. Based on theoretical and field results we suggest that the subglacial hydrology comprises a melt season distributed system dominated by wide anastomosing broad flat channels and thin water sheets, which may become more channelized in winter, and more responsive to changes in meltwater inputs. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Description: Key findings: Organic carbon (OC) was evenly enriched in each sediment particles by aggregate breakdown. The more severe aggregate breakdown enriched OC in smaller aggregates. Low stream power and runoff depth were necessary factors for aggregate breakdown. Abstract Organic carbon (OC) is easily enriched in sediment particles of different sizes due to aggregate breakdown and selective transport for sheet erosion. However, the transport of aggregate‐associated OC has not been thoroughly investigated. To address this issue, 27 simulated rainfall experiments were conducted in a 1 m × 0.35 m box on slope gradients of 15°, 10°, and 15°and under three rainfall intensities of 45 mm h−1, 90 mm h−1 and 120 mm h−1. The results showed that OC was obviously enriched in sediment particles of different sizes under sheet erosion. The soil organic carbon (SOC) concentrations of each aggregate size class in sediments were different from those in the original soil, especially when the rainfall intensity or slope was sufficiently low, such as 45 mm h–1 or 5°, respectively. Under a slope of 5°, the SOC enrichment ratios (ERocs) of small macroaggregates and microaggregates were high but decreased over time. As rainfall intensity increased, OC became enriched in increasingly fine sediment particles. Under a rainfall intensity of 45 mm h–1, the ERocs of the different aggregate size classes were always high throughout the entire erosion process. Under a rainfall intensity of 〉 45 mm h–1 and slope of 〉 5°, the ERocs of the different aggregate size classes were close to 1.0, especially those of clay and silt. Therefore, the high ERocs in sediments resulted from the first transport of effective clay. Among total SOC loss, the proportion of OC loss caused by the transport of microaggregates and silt plus clay‐sized particles was greater than 50%. We also found that low stream power and low water depth were two requirements for the high ERocs in aggregates. Stream power was closely related to sediment particle distribution. Flow velocity was significantly and positively related to the percentage of OC‐enriched macroaggregates in the sediments (P 〉 0.01). Our study will provide important information for understanding the fate of SOC and building physical‐based SOC transport models. © 2019 John Wiley & Sons, Ltd.

Description: This study offers a new combination of InSAR techniques and structural field observations, along with morphometric and seismologic correlations to identify and quantify slope‐instability phenomena along a tectonically active mountain front. We identified deep‐seated gravitational slope deformation (DSGSD) and slow mass movements with continuous downslope speed of approximately 71 mm year−1 in the southern Tien Shan Mountains front using interferometric synthetic aperture radar (InSAR) time‐series from ALOS/PALSAR satellite data. Abstract We investigated deep‐seated gravitational slope deformation (DSGSD) and slow mass movements in the southern Tien Shan Mountains front using synthetic aperture radar (SAR) time‐series data obtained by the ALOS/PALSAR satellite. DSGSD evolves with a variety of geomorphological changes (e.g. valley erosion, incision of slope drainage networks) over time that affect earth surfaces and, therefore, often remain unexplored. We analysed 118 interferograms generated from 20 SAR images that covered about 900 km2. To understand the spatial pattern of the slope movements and to identify triggering parameters, we correlated surface dynamics with the tectono‐geomorphic processes and lithologic conditions of the active front of the Alai Range. We observed spatially continuous, constant hillslope movements with a downslope speed of approximately 71 mm year−1 velocity. Our findings suggest that the lithological and structural framework defined by protracted deformation was the main controlling factor for sustained relief and, consequently, downslope mass movements. The analysed structures revealed integration of a geological/structural setting with the superposition of Cretaceous–Paleogene alternating carbonatic and clastic sedimentary structures as the substratum for younger, less consolidated sediments. This type of structural setting causes the development of large‐scale, gravity‐driven DSGSD and slow mass movement. Surface deformations with clear scarps and multiple crest lines triggered planes for large‐scale deep mass creeps, and these were related directly to active faults and folds in the geologic structures. Our study offers a new combination of InSAR techniques and structural field observations, along with morphometric and seismologic correlations, to identify and quantify slope instability phenomena along a tectonically active mountain front. These results contribute to an improved natural risk assessment in these structures. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd

Description: Abstract Tidal marshes form at the confluence between estuarine and marine environments where tidal movement regulates their developmental processes. Here, we investigate how the interplay between tides, channel morphology, and vegetation affect sediment dynamics in a low energy tidal marsh at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island. Poplar Island is an active restoration site where fine‐grained material dredged from navigation channels in the upper Chesapeake Bay are being used to restore remote tidal marsh habitat toward the middle bay (Maryland, USA). Tidal currents were measured over multiple tidal cycles in the inlets and tidal creeks of one marsh at Poplar Island, Cell 1B, using Acoustic Doppler Current Profilers (ADCP) to estimate water fluxes throughout the marsh complex. Sediment fluxes were estimated using acoustic backscatter recorded by ADCPs and validated against total suspended solid measurements taken on site. A high‐resolution geomorphic survey was conducted to capture channel cross sections and tidal marsh morphology. We integrated simple numerical models built in Delft3d with empirical observations to identify which eco‐geomorphological factors influence sediment distribution in various channel configurations with differing vegetative characteristics. Channel morphology influences flood‐ebb dominance in marshes, where deep, narrow channels promote high tidal velocities and incision, increasing sediment suspension and reducing resilience in marshes at Poplar Island. Our numerical models suggest that accurately modelling plant phenology is vital for estimating sediment accretion rates. In‐situ observations indicate that Poplar Island marshes are experiencing erosion typical for many Chesapeake Bay islands. Peak periods of sediment suspension frequently coincide with the largest outflows of water during ebb tides resulting in large sediment deficits. Ebb dominance (net sediment export) in tidal marshes is likely amplified by sea‐level rise and may lower marsh resilience. We couple field observations with numerical models to understand how tidal marsh morphodynamics contribute to marsh resilience.

Description: Abstract Anthropogenic global warming might cause expansion of the drylands and trigger socio‐economic challenges in the water deficit subtropical regions. Changes in hydroclimate during the intervals of variable global temperature over the recent geological past, however, could provide useful information about the possible responses of these arid ecosystems to the near future warmer conditions. We evaluated hydroclimates of two different parts of the subtropical North America by generating new records of surface processes and regional vegetation from the drought‐prone northeast Mexico and subsequently compared them with paleoclimate of the central‐southern USA. Our study suggests congruent changes occurred in both the parts during ~13.5‐9.5 cal ka BP, an interval with no warm pool in the northern Gulf of Mexico. The precipitation and erosion responded to temperature‐modulated variations in positions of the Inter‐Tropical Convergence Zone (ITCZ). Conditions were wetter than today in the subsequent warmer interval (~9.5‐8.2 cal ka BP) with generally stable ITCZ and the highest summer insolation. Hydroclimate changes of both the parts lacked congruency during ~8.2‐6.8 cal ka BP as the northern Gulf of Mexico began hosting a warm pool. Similar to the modern conditions, this warm pool might have modified trajectories of the tropical storms. Erosion and abundance of C3 plants decreased in the northeast Mexico. Higher wetness in the Mississippi River Basin and the southern Great Plains during this interval suggested that the storms made landfall more frequently in the central‐southern USA.

Description: Two shoals in the mouth zone of the Yangtze Estuary accreted progressively prior to 2010, but reverted to erosion thereafter. Human activities such as dredging and dumping activities contribute to the erosion, masking the impacts of sediment source reduction. The morphodynamic response time of the mouth zone to riverine sediment decrease is further suggested to be 〉30 years (starting from the mid‐1980s). Abstract The morphology of the Yangtze Estuary has changed substantially at decadal time scales in response to natural processes, local human interference and reduced sediment supply. Due to its high sediment load, the morphodynamic response time of the estuary is short, providing a valuable semi‐natural system to evaluate large‐scale estuarine morphodynamic responses to interference. Previous studies primarily addressed local morphologic changes within the estuary, but since an overall sediment balance is missing, it remains unclear whether the estuary as a whole has shifted from sedimentation to erosion in response to reduced riverine sediment supply (e.g. resulting from construction of the Three Gorges Dam). In this paper we examine the morphological changes of two large shoals in the mouth zone (i.e. the Hengsha flat and the Jiuduan shoal) using bathymetric data collected between 1953 and 2016 and a series of satellite images. We observe that the two shoals accreted at different rates before 2010 but reverted to erosion thereafter. Human activities such as dredging and dumping contribute to erosion, masking the impacts of sediment source reduction. The effects of local human intervention (such as the construction of a navigation channel) are instantaneous and are likely to have already resulted in new dynamic equilibrium conditions. The morphodynamic response time of the mouth zone to riverine sediment decrease is further suggested to be 〉30 years (starting from the mid‐1980s). Accounting for the different adaptation time scales of various human activities is essential when interpreting morphodynamic changes in large‐scale estuaries and deltas. © 2019 John Wiley & Sons, Ltd.

Description: ABSTRACT Results from computational morphodynamics modeling of coupled flow‐bed‐sediment systems are described for ten applications as a review of recent advances in the field. Each of these applications is drawn from solvers included in the public‐domain International River Interface Cooperative (iRIC) software package. For mesoscale river features such as bars, predictions of alternate and higher mode river bars are shown for flows with equilibrium sediment supply and for a single case of oversupplied sediment. For microscale bed features such as bedforms, computational results are shown for the development and evolution of two‐dimensional bedforms using a simple closure‐based two‐dimensional model, for two‐ and three‐dimensional ripples and dunes using a three‐dimensional large‐eddy simulation flow model coupled to a physics‐based particle transport model, and for the development of bed streaks using a three‐dimensional unsteady Reynolds‐averaged Navier‐Stokes solver with a simple sediment‐transport treatment. Finally, macroscale or channel evolution treatments are used to examine the temporal development of meandering channels, a failure model for cantilevered banks, the effect of bank vegetation on channel width, the development of channel networks in tidal systems, and the evolution of bedrock channels. In all examples, computational morphodynamics results from iRIC solvers compare well to observations of natural bed morphology. For each of the three scales investigated here, brief suggestions for future work and potential research directions are offered.

Description: Within a multidisciplinary approach, we mapped with unprecedented detail the seafloor morphology, sediment distribution and benthic habitats of a tidal inlet which has been highly impacted by human activity. We identified an unusual habitat for lagoon environment connected to rip‐rap used for jetties and hard structures and we estimated that the new pattern of flow around these hard structures caused the erosion of 430 000 m3 of sediment in eight years. Abstract Adopting a multidisciplinary approach, we mapped with unprecedented detail the seafloor morphology, sediment distribution and benthic habitats of a tidal inlet in the Venice Lagoon, Italy, which has been greatly impacted by human activity. Thanks to very high‐resolution multibeam data, we identified ebb and flood‐tidal deltas, a tidal point bar, active dune fields, pools and scour holes. The seafloor substrate of the inlet was investigated by integrating automatically classified multibeam backscatter data with sediment samples and underwater seafloor images. The sediment composition comprises four textural classes with 75% overall thematic accuracy. The particle size distribution of each morphological feature was assessed distinguishing, in particular, sediments over crests and troughs of small‐dune fields with wavelengths and heights of less than 4 m and 0.2 m, respectively. Adopting state‐of‐the‐art benthic habitat mapping procedures, we found seven distinctive benthic habitats that reflect spatial variability in hydrodynamics and sediment transport pathways. The dominant classes were Sand with sparse shell detritus (46%) and Bare sand (32%). The rip‐rap revetment used for the inlet jetties and for the hard structures, built in the inlet channel to protect Venice from flooding, created a new habitat that covers 5.5% of the study area. This study shows how combining geomorphological and ecological analyses is crucial for the monitoring and management of tidal inlets and coastal infrastructures. © 2019 John Wiley & Sons, Ltd.

Description: ABSTRACT This paper presents novel methods for robust statistical testing of particle shape data. Shape (the relative lengths of three orthogonal axes) is a key property of sedimentary particles, providing information on provenance, transport history and depositional environment. However, the usefulness of shape data, including the ability to make robust comparisons between samples, has been constrained by the absence of a satisfactory definition of the mean shape for a sample of particles. Such a definition is proposed and used to develop confidence regions for the population mean shape using both parametric (theoretical) and computational (bootstrap) methods. These techniques are based on a transform that permits multivariate statistical methods for the analysis of compositional data to be extended to shape. These techniques are validated with reference to a dataset of 169 clast samples and found to perform well. A statistical test on the mean – using the multivariate extension of Student's t‐test, Hotelling's T2 – is presented. The benefits of the methods presented are demonstrated with reference to a case study.

Description: Successive wildfires alter burned area hydrologic response in ways that may lead to greater debris flow potential. Abstract Climate and land use changes have led to recent increases in fire size, severity, and/or frequency in many different geographic regions and ecozones. Most post‐wildfire geomorphology studies focus on the impact of a single wildfire but changing wildfire regimes underscore the need to quantify the effects of repeated disturbance by wildfire and the subsequent impacts on system resilience. Here, we examine the impact of two successive wildfires on soil hydraulic properties and debris flow hazards. The 2004 Nuttall‐Gibson Complex and the 2017 Frye Fire affected large portions of the Pinaleño Mountains in southern Arizona, creating a mosaic of burn severity patterns that allowed us to quantify differences in wildfire‐induced hydrologic changes as a function of burn severity and recent fire history (i.e. burned in only the Frye Fire or burned in both fires). Field observations after the 2017 Frye Fire indicated debris flow activity in areas burned predominantly at low severity. Many of these areas, however, were also affected by the 2004 Nuttall‐Gibson Complex, suggesting that the relatively short recovery time between the two wildfires may have played a role in the geomorphic response to the most recent wildfire. Field measurements of soil hydraulic properties suggest that soils burned at moderate severity in 2004 and low severity in 2017 have a lower infiltration capacity relative to those that remained unburned in 2004 and burned at low severity in 2017. Simulations of runoff demonstrate that measured differences in infiltration capacity between once‐ and twice‐burned soils are sufficient in some cases to influence the rainfall intensities needed to initiate runoff generated debris flows. Results quantify the impact of wildfire history and burn severity on runoff and debris flow activity in a landscape affected by successive wildfires and provide insight into how the resilience of geomorphic systems may be affected by successive wildfires. © 2019 John Wiley & Sons, Ltd.

Description: Given the ease with which we can now measure river morphology, morphological estimation of the bedload transport rate is appealing. Here, we show how this can be done in 2D to estimate the spatial distribution of transport rates over large areas of a braided river, and discuss both the limits of the method and its potential to study fluvial processes. Abstract Research in the 1990s showed that bed‐material transport rates could be estimated at the reach scale in both one‐dimension and, over small spatial scales (10s of m), in two‐dimensions. The limit on the latter was the spatial scale over which it was possible to obtain distributed data on morphological change. Here, we revisit the morphological method given progress in both topographical data acquisition and hydraulic modelling. The bed‐material transport needed to conserve mass is calculated in both one and two dimensions for a 1600 m × 300 m Alpine braided river “laboratory”. High‐resolution topographical data were acquired by laser scanning to quantify Digital Elevation Models (DEMs), and morphological changes caused by the flushing of the water intake were derived from repeated surveys. Based on DEMs of differences, 1D bed‐material transport rates were calculated using the morphological method. Then, a 2D hydraulic model was combined with a topographic correction to route sediment through the network of braided channels and to obtain a spatially variable estimate of transport in both downstream and cross‐stream directions. Monte Carlo simulation was applied to the routing model parameters, allowing identification of the most probable parameter values needed to minimize negative transport. The results show that within‐section spatial compensation of erosion and deposition using the 1D treatment leads to substantial local errors in transport rate estimates, to a degree related to braiding intensity. Even though the 2D application showed that a large proportion of the total transport was actually concentrated into one main channel during the studied low flow event, the proportion of transport in secondary anabranches is substantial when the river starts braiding. Investigations of the effects of DEM resolution, competent flow duration and survey frequency related to ‘travelling bedload’ and sequential erosion‐deposition emphasized the critical importance of careful data collection in the application of the morphological method. © 2019 John Wiley & Sons, Ltd.

Description: Simulating network‐scale, post‐wildfire sediment cascades for the spatially explicit prediction of downstream sediment impacts. A new framework linking new and existing models of post‐wildfire debris flows generation, storage of debris flow sediment within valleys, delivery of debris flow sediment to active channels, and the routing of sediment through large river networks. Abstract Wildfires represent one of the largest disturbances in watersheds of the Intermountain West. Yet, we lack models capable of predicting post‐wildfire impacts on downstream ecosystems and infrastructure. Here we present a novel modeling framework that links new and existing models to simulate the post‐wildfire sediment cascade, including spatially explicit predictions of debris flows, storage of debris flow sediment within valleys, delivery of debris flow sediment to active channels, and the downstream routing of sediment through river networks. We apply the model to sediment dynamics in Clear Creek watershed following the 2010 Twitchell Canyon Fire in the Tushar Mountains of southern Utah. The debris flow generation model performed well, correctly predicting 19 out of 20 debris flows from the largest catchments, with only four false positives and two false negatives at observed rainfall intensities. In total, the model predicts the occurrence of 160 post‐wildfire debris flows across the Clear Creek watershed, generating more than 650 000 m3 of sediment. Our new storage and delivery model predicts the vast majority of this sediment is stored within valleys, and only 13% is delivered to the river network. The sediment routing model identifies numerous sediment bottlenecks within the network, which alter transport dynamics and may be hotspots for aggradation and aquatic habitat alteration. The volume of sediment exported from the watershed after seven years of simulation totals 17% of that delivered, or 2% of the total generated debris flow sediment. In the case of the Twitchell Canyon Fire, this highlights that significant post‐wildfire sediment volumes can be stored in valleys (87%) and within the stream network (11%). Finally, we discuss useful insights that can be gleaned from the model framework, as well as the limitations and need for more monitoring and theory development in order to better constrain essential inputs, process rates, and morphodynamics. © 2019 John Wiley & Sons, Ltd.

Description: We successfully reconstruct soil reworking using feldspar single‐grain luminescence. A new conceptual model explains the observed luminescence trends along a hillslope catena. We are able to disentangle bioturbation, soil production and erosion/ deposition based on two luminescence proxies. Luminescence data provides more robust measures of soil thickness than field observations. Abstract The interplay of bioturbation, soil production and long‐term erosion–deposition in soil and landscape co‐evolution is poorly understood. Single‐grain post‐infrared infrared stimulated luminescence (post‐IR IRSL) measurements on sand‐sized grains of feldspar from the soil matrix can provide direct information on all three processes. To explore the potential of this novel method, we propose a conceptual model of how post‐IR IRSL‐derived burial age and fraction of surface‐visiting grains change with soil depth and along a hillslope catena. We then tested this conceptual model by comparison with post‐IR IRSL results for 15 samples taken at different depths within four soil profiles along a hillslope catena in the Santa Clotilde Critical Zone Observatory (southern Spain). In our work, we observed clear differences in apparent post‐IR IRSL burial age distributions with depth along the catena, with younger ages and more linear age–depth structure for the hill‐base profile, indicating the influence of lateral deposition processes. We noted shallower soils and truncated burial age–depth functions for the two erosional mid‐slope profiles, and an exponential decline of burial age with depth for the hill‐top profile. We suggest that the downslope increase in the fraction of surface‐visiting grains at intermediate depths (20 cm) indicates creep to be the dominant erosion process. Our study demonstrates that single‐grain feldspar luminescence signature‐depth profiles provide a new way of tracing vertical and lateral soil mixing and transport processes. In addition, we propose a new objective luminescence‐based criterion for mapping the soil‐bedrock boundary, thus producing soil depths in better agreement with geomorphological process considerations. Our work highlights the possibilities of feldspar single grain techniques to provide quantitative insights into soil production, bioturbation and erosion–deposition. © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd

Description: This study uses the depth‐age information derived from feldspar‐based single grain post Infrared Stimulated Luminescence (post‐IR IRSL) to quantify erosion and bioturbation processes along a hillslope We propose, for the first time, an analytical solution for the diffusion–advection equation to calculate diffusivity constant and erosion‐deposition rates. A sensitivity and uncertainty analysis were applied to the model Abstract Particles on soil‐mantled hillslopes are subject to downslope transport by erosion processes and vertical mixing by bioturbation. Both are key processes for understanding landscape evolution and soil formation, and affect the functioning of the critical zone. We show here how the depth–age information, derived from feldspar‐based single grain post‐infrared infrared stimulated luminescence (pIRIR), can be used to simultaneously quantify erosion and bioturbation processes along a hillslope. In this study, we propose, for the first time, an analytical solution for the diffusion–advection equation to calculate the diffusivity constant and erosion–deposition rates. We have fitted this model to age–depth data derived from 15 soil samples from four soil profiles along a catena located under natural grassland in the Santa Clotilde Critical Zone Observatory, in the south of Spain. A global sensitivity analysis was used to assess the relative importance of each model parameter in the output. Finally, the posterior probability density functions were calculated to evaluate the uncertainty in the model parameter estimates. The results show that the diffusivity constant at the surface varies from 11.4 to 81.9 mm2 a‐1 for the hilltop and hill‐base profile, respectively, and between 7.4 and 64.8 mm2 a‐1 at 50 cm depth. The uncertainty in the estimation of the erosion–deposition rates was found to be too high to make a reliable estimate, probably because erosion–deposition processes are much slower than bioturbation processes in this environment. This is confirmed by a global sensitivity analysis that shows how the most important parameters controlling the age–depth structure in this environment are the diffusivity constant and regolith depth. Finally, we have found a good agreement between the soil reworking rates proposed by earlier studies, considering only particle age and depth, and the estimated diffusivity constants. The soil reworking rates are effective rates, corrected for the proportion of particles actually participating in the process. © 2019 John Wiley & Sons, Ltd.

Description: 3D landscape schematization of wild boar damages (red circles) and their potential connections (arrows) to different landscape features. The purpose of this research is to analyse the role of wild boars as a geomorphologic agent, presenting a general diagnostic framework regarding the geomorphic impact of this species, classifying and mapping potential sediment hotspots and their likely connection to rivers and road networks. Abstract Among the main invasive species, the wild boar (Sus scrofa) is the most responsible for soil degradation in Europe and many Italian regions. At the same time, the stable presence of this species in agricultural areas has induced a conflict with humans, causing economic losses, environmental degradation and also social issues. A clear quantification of the potential damages (in terms of soil bioturbation) of this species at large scale is, however, still obscure. The purpose of this research is to analyse the role of wild boars as a geomorphologic agent, presenting a general diagnostic framework regarding the geomorphic impact of this species, classifying and mapping potential sediment hotspots and their likely connection to rivers and road networks. Accordingly, a record of wild boar damage types is first presented, and their possible interaction with hydrological and geomorphological processes is described. Then, a pilot case study is discussed on mapping and quantifying wild boar damages in a hilly agricultural landscape located in northeast Italy. The wild boar damages were geolocalized using a geographical positioning system (GPS) in two years of intensive field campaigns among agricultural fields involved in wild boar damaging activities. For each damaged area (total 406), several measures of soil erosion depth were taken and the degradation surface of interest mapped for a total of 10 150 measures. The volume of removed soil was then estimated, considering the average depth of damages previously recorded. Finally, the Index of Connectivity was applied to provide a classification of the considered damages based on their connection to both river and road networks. The results indicate that the ongoing uncontrolled wild boar expansion may not affect crops only or be a risk for people, but can also increase soil erosion, with a potential connection to hydrographic networks and human infrastructures. © 2019 John Wiley & Sons, Ltd.

Description: Abstract Sediment in urban stormwater systems creates a significant maintenance burden, while a lack of coarse‐grained bed sediment in streams limits their ecological value and geomorphic resilience. Gravel substrates, for example, provide benthic habitat yet are often scoured from the channel bed only to end up in a detention basin or treatment wetland. This dual problem of both ‘too much’ and ‘too little’ coarse‐grained sediment reflects a watershed sediment budget that is profoundly altered. We developed a conceptual urban coarse‐grained (〉 0.5 mm) sediment budget across three domains: hillslopes (urban land surfaces), the built stormwater network and stream channels. We then quantified key sources, sinks and storages for a suburban case study, using a combination of hillslope and in‐channel monitoring, and interrogation of local government records. Around 36% of the sediment supplied to the stormwater network reached the catchment outlet, a level of sediment delivery much higher than observed in similar‐sized natural catchments. The remainder was deposited in the sediment cascade and either stored, or extracted and removed from the catchment (e.g. material deposited in sediment ponds and gross pollutant traps). Conventional urban drainage networks are characterised by high hillslope sediment supply and low storage, resulting in efficient sediment delivery. Channel erosion, deposition in (and extraction from) pipes and channels, and floodplain deposition are small compared to sediment transport through the cascade. An understanding of the sediment budget of urban headwater catchments can provide stormwater and waterway managers with the information they need to address specific sediment problems such as sedimentation in stormwater assets and geomorphic recovery of urban streams.

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

Description: Abstract Knowledge of soil microtopography and its changes in space and over time is important to the understanding of how tillage in uences infiltration, runoff generation and erosion. In this study, the use of a Terrestrial Laser Scanner (TLS) is assessed for its ability to quantify small changes in the soil surface at high spatial resolutions for a relatively large surface area (100 m2). Changes in soil surface morphology during snow cover and melt are driven by frost heave, slaking, pressure exertion by the snow pack and overland ow (erosion and deposition). An attempt is undertaken to link these processes to observed changes at the soil surface. A new algorithm for soil surface roughness is introduced to make optimal use of the raw point cloud. This algorithm is less scale‐dependent than several commonly used roughness calculations. The results of this study show that TLS can be used for multitemporal scanning of large surfaces and that small changes in surface elevation and roughness can be detected. Statistical analysis of the observed changes against terrain indices did not yield significant evidence for process differentiation. This article is protected by copyright. All rights reserved.

Description: Abstract Current techniques assessing longshore sediment transport rates have large uncertainties, pleading for the development of alternative and complementary approaches. The present study proposes a method to estimate the decadal average rate of longshore transport at modern ebb‐tidal deltas based on a sediment budget analysis of the outer shoal growth. This transport is obtained as the balance of the other contributions to the shoal with the total sediment input rate obtained from an inverse application of the inlet reservoir model. The method is applied to the Guadiana ebb‐tidal delta, yielding an average longshore sediment transport rate (~85,000 m3/yr) in good agreement with expectations for the region. It is exemplified that this decadal averaged rate can be used to improve longshore sediment transport expressions in order to study its variability over shorter time scales. At the Guadiana, the yearly longshore sediment transport from the improved formula ranges from ~25,000 m3 (westward) to ~245,000 m3 (eastward) and is related to the North Atlantic Oscillation index. Overall, the proposed method constitutes an alternative tool to constrain the average longshore sediment transport rate over decades in the vicinity of tidal inlets. It is applicable to ebb‐tidal deltas where the outer shoal growth (from an early to a mature stage) is well‐documented by bathymetric maps, and where the main transport pathways towards the outer shoal can be specified.

Description: Tidal channels along the Amazon River convey water and sediment between the mainstem and tidal floodplain. This paper explores tidal‐channel processes along the length of the tidal river that may lead to the sequestering of riverine sediment on the tidal floodplain, preventing its discharge to the ocean. Although the amount of water and sediment transported through these tidal channels is small compared to the total Amazon discharge, it is large compared to rivers globally. Abstract Mainstem–floodplain material exchange in the tidal freshwater reach of major rivers may lead to significant sequestration of riverine sediment, but this zone remains understudied compared to adjacent fluvial and marine environments. This knowledge gap prompts investigation of floodplain‐incising tidal channels found along the banks of tidal rivers and their role in facilitating water and suspended‐sediment fluxes between mainstem and floodplain. To evaluate this role, and how it evolves along the tidal river and with time, we measured water level, flow velocity, temperature, and suspended‐sediment concentration (SSC) in four tidal channels along the tidal Amazon River, Brazil. Eleven deployments were made during low, rising, high, and falling seasonal Amazon discharge. Generally, channels export high‐SSC water from the mainstem to the tidal floodplain on flood tides and transfer low‐SSC water back to the mainstem on ebbs. Along the length of the tidal river, the interaction between tidal and seasonal water‐level variations and channel–floodplain morphology is a primary control on tidal‐channel sediment dynamics. Close to the river mouth, where tides are large, this interaction produces transient flow features and current‐induced sediment resuspension, but the importance of these processes decreases with distance upstream. Although the magnitude of the exchange of water and sediment between mainstem and floodplain via tidal channels is a small percentage of the total mainstem discharge in this large tidal‐river system, tidal channels are important conduits for material flux between these two environments. This flux is critical to resisting floodplain submergence during times of rising sea level. © 2019 John Wiley & Sons, Ltd.

Description: Abstract Suspended sediment concentrations (SSC) in rivers are variable in time due to interacting soil erosion and sediment transport processes. While many hydro‐meteorological variables are correlated to suspended sediment concentrations, interpretation of these correlations in terms of driving processes requires in‐depth knowledge of the catchment. Detailed sediment source information is needed to establish the causal linkages between driving processes and variations in SSC. This study innovatively combined sediment fingerprinting with multivariate statistical analyses of hydro‐meteorological data to investigate how differential contributions of sediment sources control SSC in response to hydro‐meteorological variables during high‐flow events in rivers. Applied to the River Aire (UK), five sediment sources were classified: grassland topsoil in three lithological areas (limestone, millstone grit and coal measures), eroding riverbanks, and street dust. A total of 159 suspended sediment samples were collected during 14 high‐flow events (2015‐2017). Results show substantial variation in sediment sources during high‐flow events. Limestone grassland and street dust, the dominant contributors to the suspended sediment, show temporal variations consistent with variations in total SSC, and are correlated with precipitation and discharge shortly prior and during high‐flow events (i.e. fast mobilisation to and within river). Contrarily, contributions from millstone and coals grassland appear to be driven by antecedent hydro‐meteorological conditions (i.e. lag‐time between soil erosion and sediment delivery). Riverbank material is poorly correlated to hydro‐meteorological variables, possibly due to weak source discrimination or the infrequent nature of its delivery to the channel. Differences in source‐specific drivers and process interactions for sediment transport demonstrate the difficulty in generalising sediment transport patterns and developing targeted suspended sediment management strategies. While more research is essential to address different uncertainties emerging from the approach, the study demonstrates how empirical data on sediment monitoring, fingerprinting, and hydro‐meteorology can be combined and analysed to better understand sediment connectivity and the factors controlling SSC.

Description: The Stargard drumlin field consists of over 1300 drumlins and related streamlined subglacial bedforms generated by a major palaeo‐ice stream of the Scandinavian Ice Sheet. The drumlins are composed of various glacial deposits that do not correlate with drumlin shapes and likely pre‐date the drumlinizing process. It is suggested that the drumlin field was formed by a combination of glacial erosion and subglacial meltwater erosion by removing antecedent material from the inter‐drumlin areas and streamlining the resultant bumps. Abstract Drumlins are landforms essential to understanding of ice sheet movement over soft beds, sediment transport along the ice/bed interface, and the formation of a wide range of glacial deposits. Although investigated more than any other glacial landform, the origin of drumlins remains contentious. Using high‐resolution LiDAR imagery and field data, we investigate the geomorphology and internal composition of one of the biggest drumlin fields in the North European Lowland. The Stargard drumlin field consists of over 1300 drumlins and related streamlined subglacial bedforms in a terminal part of a major Weichselian palaeo‐ice stream of the southern Scandinavian Ice Sheet. The drumlins are typically 600‐800 m long, 200‐250 m wide, 3‐6 m high and have axial elongation ratios ~2 but in some cases exceeding 15. Several subzones inferred from drumlin morphometry exist reflecting different ice flow dynamics. The most elongated drumlins occur in areas where ice moved down‐slope and where thick fine‐grained deposits of low hydraulic conductivity occur in the substratum. The largest portion of land occupied by drumlins and the greatest frequency density of drumlins occur where the ice moved up‐slope. Stargard drumlins are composed of a wide variety of glacial deposits including various types of tills and meltwater sediments, which range from undisturbed to heavily deformed. There is no correlation between the deposits in the drumlins and the drumlin forms indicating that the deposits pre‐date the drumlinizing process. It is suggested that the drumlin field was generated by a combination of direct glacial erosion and subglacial meltwater erosion by removing antecedent material from the inter‐drumlin areas and streamlining the resultant bumps. Our data support the search for a unifying theory of drumlin formation and suggest erosion as the most plausible single mechanism generating drumlin landscapes. © 2019 John Wiley & Sons, Ltd.

Description: Abstract We draw on published studies of floodplain organic carbon storage, wildfire‐related effects on floodplains in temperate and high latitudes, and case studies to propose a conceptual model of the effects of wildfire on floodplain organic carbon storage in relation to climate and valley geometry. Soil organic carbon typically constitutes the largest carbon stock in floodplains in fire‐prone regions, although downed wood can contain significant organic carbon. We focus on the influence of wildfire on soil organic carbon and downed wood as opposed to standing vegetation to emphasize the geomorphic influences resulting from wildfire on floodplain organic carbon stocks. The net effect of wildfire varies depending on site‐specific characteristics including climate and valley geometry. Wildfire is likely to reduce carbon stock in steep, confined valley segments because increased water and sediment yields following fire create net floodplain erosion. The net effect of fire in partly confined valleys depends on site‐specific interactions among floodplain aggradation and erosion, and, in high‐latitude regions, permafrost degradation. In unconfined valleys in temperate latitudes, wildfire is likely to slightly increase floodplain organic carbon stock as a result of floodplain aggradation and wood deposition. In unconfined valleys in high latitudes underlain by permafrost, wildfire is likely in the short‐term to significantly decrease floodplain organic carbon via permafrost degradation and reduced organic‐layer thickness. Permafrost degradation reduces floodplain erosional resistance, leading to enhanced stream bank erosion and greater carbon fluxes into channels. The implications of warming climate and increased wildfires for floodplain organic carbon stock thus vary. Increasing wildfire extent, frequency, and severity may result in significant redistribution of organic carbon from floodplains to the atmosphere via combustion in all environments examined here, as well as redistribution from upper to lower portions of watersheds in the temperate zone and from floodplains to the oceans via riverine transport in the high‐latitudes.

Description: Abstract How soil erosion rates evolved over the last about 100 kyr and how they relate to environmental and climate variability is largely unknown. This is due to a lack of suitable archives that help to trace this evolution. We determined in‐situ cosmogenic 10Be along vertical landforms (tors, boulders and scarps) on the Sila Massif to unravel their local exhumation patterns to develop a surface denudation model over millennia. Due to the physical resistance of tors, their rate of exhumation may be used to derive surface and, thus, soil denudation rates over time. We derived soil denudation rates that varied in the range of 0–0.40 mm year‐1. The investigated boulders, however, appear to have experienced repositioning processes about ~20–25 ka BP and were therefore a less reliable archive. The scarps of the Sila upland showed a rapid bedrock exposure within the last 8–15 ka. Overall, the denudation rates increased steadily after 75 ka BP but remained low until about 17 ka BP. The exhumation rates indicate a denudation pulse that occurred about 17–5 ka BP. Since then the rates have continuously decreased. We identify three key factors for these developments – climate, topography and vegetation. Between 75 and 17 ka BP, climate was colder and drier than today. The rapid changes towards warmer and humid conditions at the Pleistocene‐Holocene transition apparently increased denudation rates. A denser vegetation cover with time counteracted denudation. Topography also determined the extent of denudation rates in the upland regime. On slopes, denudation rates were generally higher than on planar surfaces. By determining the exhumation rates of tors and scarps, soil erosion rates could be determined over long timescales and be related to topography and particularly to climate. This is key for understanding geomorphic dynamics under current environmental settings and future climate change.

Description: Abstract We propose a physical model for the high‐frequency (〉 1 Hz) spectral distribution of seismic power generated by debris flows. The modeled debris flow is assumed to have four regions where the impact rate and impulses are controlled by different mechanisms: the flow body, a coarser‐grained snout, a snout lip where particles fall from the snout on the bed, and a dilute front composed of saltating particles. We calculate the seismic power produced by this impact model in two end‐member scenarios, a thin‐flow and thick‐flow limit, which assume that the ratio of grain sizes to flow thicknesses are either near unity or much less than unity. The thin‐flow limit is more appropriate for boulder‐rich flows that are most likely to generate large seismic signals. As a flow passes a seismic station, the rise phase of the seismic amplitude is generated primarily by the snout while the decay phase is generated first by the snout and then the main flow body. The lip and saltating front generate a negligible seismic signal. When ground properties are known, seismic power depends most strongly on both particle diameter and average flow speed cubed, and also depends on length and width of the flow. The effective particle diameter for producing seismic power is substantially higher than the median grain size and close to the 73rd percentile for a realistic grain size distribution. We discuss how the model can be used to estimate effective particle diameter and average flow speed from an integrated measure of seismic power. This article is protected by copyright. All rights reserved.

Description: Millimeter to centimeter‐scale structure‐from‐motion (SfM) surveys of bed topography and computational fluid dynamics (CFD) simulations were used in combination to better evaluate surface roughness and rapidly quantify flow resistance in mountain streams. Three scaling regimes were identified that correspond to important roughness length scales and surface complexity contributing to flow resistance. The standard deviation of detrended streambed elevation, as a proxy for the vertical roughness length scale, emerges as the primary control on flow resistance, when scaled by flow depth. Abstract Flow resistance in mountain streams is important for assessing flooding hazard and quantifying sediment transport and bedrock incision in upland landscapes. In such settings, flow resistance is sensitive to grain‐scale roughness, which has traditionally been characterized by particle size distributions derived from laborious point counts of streambed sediment. Developing a general framework for rapid quantification of resistance in mountain streams is still a challenge. Here we present a semi‐automated workflow that combines millimeter‐ to centimeter‐scale structure‐from‐motion (SfM) photogrammetry surveys of bed topography and computational fluid dynamics (CFD) simulations to better evaluate surface roughness and rapidly quantify flow resistance in mountain streams. The workflow was applied to three field sites of gravel, cobble, and boulder‐bedded channels with a wide range of grain size, sorting, and shape. Large‐eddy simulations with body‐fitted meshes generated from SfM photogrammetry‐derived surfaces were performed to quantify flow resistance. The analysis of bed microtopography using a second‐order structure function identified three scaling regimes that corresponded to important roughness length scales and surface complexity contributing to flow resistance. The standard deviation σz of detrended streambed elevation normalized by water depth, as a proxy for the vertical roughness length scale, emerges as the primary control on flow resistance and is furthermore tied to the characteristic length scale of rough surface‐generated vortices. Horizontal length scales and surface complexity are secondary controls on flow resistance. A new resistance predictor linking water depth and vertical roughness scale, i.e.  H/σz, is proposed based on the comparison between σz and the characteristic length scale of vortex shedding. In addition, representing streambeds using digital elevation models (DEM) is appropriate for well‐sorted streambeds, but not for poorly sorted ones under shallow and medium flow depth conditions due to the missing local overhanging features captured by fully 3D meshes which modulate local pressure gradient and thus bulk flow separation and pressure distribution. An appraisal of the mesh resolution effect on flow resistance shows that the SfM photogrammetry data resolution and the optimal CFD mesh size should be about 1/7 to 1/14 of the standard deviation of bed elevation. © 2019 John Wiley & Sons, Ltd.

Description: Profiles of concentration, velocity and granular temperature are measured in tilting flume and analyzed using kinetic theory of granular flow. Distributions of granular stresses across collisional transport layer are determined and linked to flow transport and friction conditions. Conditions under which the kinetic theory is applicable to intense bedload are evaluated. Abstract Intense bed load refers to a regime which is responsible of most of sediment transport in torrents and rivers during floods. Even if restricted to uniform steady conditions and well sorted particles, the liquid and solid phases interact in a rather complex way over the plane mobile bed. We focus on flow conditions where the sediment grains in the flow are supported by mutual contacts, primarily collisions, and not by the fluid turbulence. Nonetheless, the turbulent liquid stresses are important everywhere, but the top of the bed, and may not be neglected. Being particles and fluid reciprocally affecting at various scale, mechanical interpretations are challenging and not consolidated, yet. In this picture, it is clear that experimental evidences provide a fundamental, still lacking, piece of information. We contribute with new experiments in a tilting flume to face this need. Compared to previous laboratory tests, we apply various measuring techniques, getting to a robust validation of the acquired dataset. We exploited stereoscopic imaging techniques to capture the solid concentration and the three components of grain velocity, and extract the velocity fluctuations from the local mean values. Measured velocity distributions are independently checked by using an Ultrasonic Doppler Velocimetry technique. With all the needed quantities available, we exploited the constitutive relations based on the kinetic theory for granular flow, to highlight how the comparison between predictions and measurements works, deploying some accuracy deficiencies in the measurement and/or interpretation limits. Our results also address the attention to interfaces that separate layers affected by different rheological mechanisms. Along with pure experimental and theoretical aspects, we grasp the chance to use the data to check how the relations involving global quantities (discharges, friction factor, bed slope, flow depth), so common in hydraulic practice, work when the sediment transport is intense. © 2019 John Wiley & Sons, Ltd.

Description: We report a case of extreme barrier breaching in the absence of an extreme storm that engendered some of the highest recorded rates of shoreline retreat and shoreface erosion. Abstract We document a case of exceptionally large natural breaching of a sandy spit (Sacalin spit, Danube Delta) using multiannual to seasonal surveys of topography and bathymetry on successive cross‐barrier and shoreface profiles, LiDAR data, satellite imagery, and wind and wave data. The large breach, which quickly reached 3.4 km in May 2014, is attributed to morphological preconditioning of the narrow (50–150 m) barrier, which was susceptible to breaching even during moderate storm conditions. The event switched the barrier's decadal evolution from low cross‐shore transport to high cross‐shore transport over the barrier, which is an order of magnitude larger than during the non‐breach period. Upper shoreface erosion, as indicated by the extensive erosion down to −4 m, indicates that this zone is a significant source for the rebuilding of the barrier. Barrier recovery and widening trigger a negative feedback which limits the back‐barrier sediment transfer. As a result, back‐barrier deposition decreases whilst the barrier aggradation through overwash becomes more frequent. The Big Breach (TBB) closed naturally in three years. The very high deposition rate of sediment in the breach is a testimony of the high sediment volumes supplied by the longshore transport and the high sediment released through shoreface retreat, and resulted in widening the barrier to a maximum of 1 km. Since the newly‐formed barrier shoreline retreated 500 m, this reveals that barrier breaching is an important mechanism which significantly accelerates the landward migration of the barrier system and is a proof of the highly non‐linear morphodynamics involved in the barrier island translation. © 2019 John Wiley & Sons, Ltd.

Description: Abstract Constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins. The geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem, because the viability of methods can be highly influenced by geomorphic attributes. For example, sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating. Similarly, the rate of sediment transport from source‐to‐sink may determine the maturity and/or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating. Here, we explore the viability and quirks of dating and instrumental methods that have been applied in the Bengal Basin, and review the records that they have yielded. This immense, dynamic, and spatially variable system hosts the world's most inhabited delta. Outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans, here and in other populated deltas worldwide. Our review covers radiocarbon dating, luminescence dating, archaeological records and historical maps, short‐lived radioisotopes, horizon markers and rod surface elevation tables, geodetic observations, and surface instrumentation. Combined, these tools can be used to reconstruct the history of the Bengal Basin from Late Pleistocene to present‐day. The growing variety and scope of Bengal Basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales.

Description: Abstract Solar radiation controlled microclimatic variation has been considered a major force on hillslope evolution via feedback among geomorphology, vegetation, soil, and hydrology. In this study, we investigate the influence of solar radiation on hillslope dynamics on Santa Catalina Island of California by comparing hillslope morphology, and frequency‐magnitude relationships of shallow landslides, rills and gullies on slopes receiving low annual solar radiation (LSR) and high annual solar radiation (HSR), which were found equivalent to north‐ and south‐facing slopes, respectively. LSR slopes on Santa Catalina Island were found more vegetated compared to HSR slopes. LiDAR elevation derived hillslope morphology showed LSR slopes steeper, rougher, and more concave than HSR slopes. Similarly, frequency‐magnitude plots showed larger relative frequency of high magnitude shallow landslides, rills, and gullies on LSR slopes, and low magnitude shallow landslides, rills, and gullies on HSR slopes. We argue that the morphology, mass movement, and erosion characteristics of LSR and HSR slopes reflect the process‐response of microclimate‐controlled variation in type and density of vegetation cover, soil physical properties including moisture, texture, structure, infiltration and erodibility, and surface and sub‐surface hydrology.

Description: Abstract Lateral movements of alluvial river channels control the extent and reworking rates of alluvial fans, floodplains, deltas, and alluvial sections of bedrock rivers. These lateral movements can occur by gradual channel migration or by sudden changes in channel position (avulsions). Whereas models exist for rates of river avulsion, we lack a detailed understanding of the rates of lateral channel migration on the scale of a channel belt. In a two‐step process, we develop here an expression for the lateral migration rate of braided channel systems in coarse, non‐cohesive sediment. On the basis of photographic and topographic data from laboratory experiments of braided channels performed under constant external boundary conditions, we first explore the impact of autogenic variations of the channel‐system geometry (i.e., channel‐bank heights, water depths, channel‐system width, and channel slope) on channel‐migration rates. In agreement with theoretical expectations, we find that, under such constant boundary conditions, the laterally reworked volume of sediment is constant and lateral channel‐migration rates scale inversely with the channel‐bank height. Furthermore, when channel‐bank heights are accounted for, lateral migration rates are independent of the remaining channel geometry parameters. These constraints allow us, in a second step, to derive two alternative expressions for lateral channel‐migration rates under different boundary conditions using dimensional analysis. Fits of a compilation of laboratory experiments to these expressions suggest that, for a given channel bank‐height, migration rates are strongly sensitive to water discharges and more weakly sensitive to sediment discharges. In addition, external perturbations, such as changes in sediment and water discharges or base level fall, can indirectly affect lateral channel‐migration rates by modulating channel‐bank heights.

Description: Abstract Understanding the historical activity of desert dune systems is important for identifying both the palaeoenvironmental drivers of change and the likelihood of future reactivation. Dating dune sediments in the Nebraska Sandhills has identified regional‐scale dune activity over centennial and millennial timescales during the Holocene, occurring at 9.6‐6.5 ka, 3.8 ka, 2.5 ka and most recently spanning the Medieval Climatic Anomaly 1050‐650 years BP. These periods have been interpreted as palaeoclimatic evidence of intense aridity lasting decadal and centennial timescales. A detailed record of dune activity in the historical period, since EuroAmerican arrival, is however lacking, yet important for interpreting the role of human agency amongst the factors influencing disturbance. Without a high‐resolution record of short term, historical, local sediment mobilisation, it is not possible to distinguish the environmental factor(s) responsible for local reactivation. In this paper, the individual drivers of vegetation disturbance are reviewed and presented alongside a luminescence‐dated reconstruction of dune sediment deposition ages. This allows an integrated assessment of the relationship between drivers and environmental response over a recorded period. We focused our investigation on the aeolian reactivations of surface dune sediments and blowout features around the Niobrara Valley Preserve in the northern limits of the Nebraska Sandhills. Results show a near‐continuous (within uncertainties) timeline of local reactivation across the sites studied, with variation between the individual features indicating that both regional (i.e. climatic) and local (i.e. land use) forcings contribute to surface disturbance.

Description: Abstract Repeated measurement of tephra erosion near Mount St. Helens over a 30‐year period at steel stakes, installed on 10 hillslopes in the months following the 1980 eruption, provides a unique long‐term record of changing processes, controls, and rates of erosion. Intensive monitoring in the first three post‐eruption years showed erosion declined rapidly as processes shifted from sheetwash and rilling to rainsplash. To test predictions about changes to long‐term rates and processes made based on the three‐year record, we remeasured sites in 1992, 2000, and 2010. Average annual erosion from 1983 – 1992 averaged 3.1 mm yr‐1 and ranged from 1.4 to 5.9 mm yr‐1, with the highest rate on moderately steep slopes. Stakes in rills in 1983 generally recorded deposition as the rills became rounded, filled, and indistinct by 1992, indicating a continued shift in process dominance to rainsplash, frost action, and bioturbation. Recovering plants, where present, also slowed erosion. However, in the second and third decades even unvegetated hillslopes ceased recording net measurable erosion; physical processes had stabilized surfaces from sheetwash and rill erosion in the first few years, and they appear to have later stabilized surfaces against rainsplash erosion in the following few decades. Comparison of erosion rates with suspended sediment flux indicates that within about 6 years post‐eruption, suspended sediment yield from tephra‐covered slopes was indistinguishable from that in forested basins. Thirty years after its deposition, on moderate and gentle hillslopes, most tephra remained; in well‐vegetated areas, plant litter accumulated and soil developed, and where the surface remained barren, bioturbation and rainsplash redistributed and mixed tephra. These findings extend understanding from shorter‐term studies of the evolution of erosion processes on freshly created substrate, confirm earlier predictions about temporal changes to tephra erosion following eruptions, and provide insight into the conditions under which tephra layers are preserved.

Description: Abstract Beach erosion poses significant threat to small island economies which are generally highly dependent on coastal tourism. This work investigates the evolution of the low‐lying sandy coast of Boa Vista through an integrated characterization of coastline and shoreline indicators (over the past four decades) based on aerial imagery. It was found that tandem use of the two indicators was important to obtain a reliable perspective of the Boa Vista low‐lying coastal evolution across a wide range of coastal environments. Results indicate that between 1968 and 2010 the coast was relatively stable, although some spatial variability was recognized. The largest changes were observed at the tips of embayed beaches and a clear coastal progradation was found at the southern (downwind) coastal sectors. Coastal evolution has been dominated by sediment budget and the results put in evidence the sedimentary connections between the beaches across the island, either through bypass and overpass processes. Findings show that understanding coastal evolution at low‐lying islands should be supported on island‐scale observations, being the only scale capable to capture the sedimentary connections between beach systems, that often control coastal evolution.

Description: Abstract Biological soil crust, or biocrust communities, are the dominating lifeform in many extreme habitats, such as arid and semiarid badlands, where water scarcity and highly erodible substrates limit vegetation cover. While climate, soil and biotic factors have been described as environmental filters influencing biocrust distribution in such biomes, little is known about the effect of terrain attributes on creating specific microhabitats that promote or restrict biocrust colonization. This study aimed to identify the main terrain attributes controlling biocrust distribution in the driest badland system in Europe, the Tabernas Badlands (SE Spain). To do this, we analyzed the influence of different terrain attributes related to landscape stability and microclimate formation on the spatial distribution of lichen and cyanobacteria, using field measurements and topographical information from a LIDAR survey. Our results showed that the spatial distribution of cyanobacteria‐dominated biocrusts, which are physiologically and morphologically adapted to extreme drought and high UVA radiation, was mostly associated with areas with high‐potential incoming solar radiation. The exception was bare south‐aspect hillslopes with very high sediment transport potential, where bare physically crusted soils were the dominant ground cover. Lichen‐dominated biocrusts, on the other hand, colonized near the top of north‐aspect hillslopes, characterized by low‐potential incoming solar radiation and potential evapotranspiration, and their cover decreased downstream, as conditions became good enough for vascular plants.

Description: Abstract Humans triggered or accelerated erosion processes since prehistoric times through agricultural practices. Optically Stimulated Luminescence (OSL) is widely used to quantify phases and rates of the corresponding landscape change, by measuring the last moment of daylight exposure of sediments. However, natural and anthropogenic mixing processes, such as bioturbation and tillage, complicate the use of OSL as grains of different depositional ages become mixed, and grains become exposed to light even long after the depositional event of interest. Instead, OSL determines the stabilization age, indicating when sediments were buried below the active mixing zone. These stabilization ages can cause systematic underestimation when calculating deposition rates. Our focus is on colluvial deposition in a kettle hole in the Uckermark region, northeastern Germany. We took 32 samples from five locations in the colluvium filling the kettle hole to study both spatial and temporal patterns in colluviation. We combined OSL dating with advanced age modeling to determine the stabilization age of colluvial sediments. These ages were combined with an archeological reconstruction of historical ploughing depths to derive the levels of the soil surface at moment of stabilization; the deposition depths, which were then used to calculate unbiased deposition rates. We identified two phases of colluvial deposition. The oldest deposits (~5 ka) were located at the fringe of the kettle hole and accumulated relatively slowly, whereas the youngest deposits (〈0.3 ka) rapidly filled the central kettle hole with rates of two orders of magnitude higher. We suggest that the latter phase is related to artificial drainage, facilitating accessibility in the central depression for agricultural practices. Our results show the need for numerical dating techniques that take archeological and soil‐geomorphological information into account to identify spatiotemporal patterns of landscape change, and to correctly interpret landscape dynamics in anthropogenically influenced hilly landscapes.

Description: The dune migration rate depended on wind regime, dune morphology, dune density, and vegetation cover; the rate was negatively related to dune height, density, and vegetation cover, but positively related to the length/width ratio and to the decrease in this ratio. Dune evolution and migration in the Quruq Desert are complex processes controlled by interactions among many factors, and that this complexity led to obvious regional variation in dune characteristics. Abstract Barchan dunes are common on Earth, Mars and Titan. Previous studies have shown that their formation, migration and evolution are influenced by the wind regime and other factors, but details vary among regions. Understanding barchan morphology and migration will both improve our understanding of dune geomorphology and provide a basis for describing the environmental conditions that affect the formation and development of these dunes on Earth and other planets. Here, we provide detailed measurements of barchan dune migration in China's Quruq Desert, in the lower reaches of the Tarim River. We monitored their migration direction and rate, and their morphological changes during migration, by comparing Google Earth images acquired in 2003 and 2014. The dunes migrated west‐southwest, close to the local resultant drift direction. The migration rate averaged 8.9 to 32.1 m year−1, with obvious spatial variation. In addition to the wind regime, the migration rate depended on dune morphology, density and vegetation cover; the rate was negatively related to dune height, density and vegetation cover, but positively linearly related to the length/width ratio (LU/W) and to the decrease in this ratio from 2003 to 2014. We found correlations among the dune morphometric parameters, but the relationships were weaker than in previous research. Due to the complexity of the factors that affect the processes that underlie sand dune development and migration, the morphological changes during dune migration were also complex. Our measurements suggest that the aeolian environment played a dominant role in dune migration and its spatial variation in the Quruq Desert. These results will support efforts to control dune migration in the western Quruq Desert and improve our understanding of dune morphodynamics. © 2019 John Wiley & Sons, Ltd.

Description: Laboratory experiments of tide‐influenced deltas are able to produce composite deltas wherein different processes create varying morphologies across the delta. All other parameters equal, experimental tide‐influenced deltas show transgressive shorelines as compared to fluvial deltas under relative sea‐level rise. Net deposition data reveal that the major effect of tides is the removal of fluvial sediment that would otherwise be deposited in the delta topset. Abstract Tide‐influenced deltas are among the largest depositional features on Earth and are ecologically and economically important as they support large populations. However, the continued rise in relative sea level threatens the sustainability of these landscapes and calls for new insights on their morphological response. While field studies of ancient deposits allow for insight into delta evolution during times of eustatic adjustment, tide‐influenced deltas are notoriously hard to identify in the rock record. We present a suite of physical experiments aimed at investigating the morphological response of tide‐influenced deltas subject to relative sea‐level rise. We show that increasing relative tidal energy changes the response of the delta because tides effectively act to remove fluvially deposited sediment from the delta topset. This leads to enhanced transgression, which we quantify via a new methodology for comparing shoreline transgression rates based on the concept of a ‘transgression anomaly’ relative to a simple reference case. We also show that stronger tidal forcing can create composite deltas where distinct land‐forming processes dominate different areas of the delta plain, shaping characteristic morphological features. The net effect of tidal action is to enhance seaward transfer of bedload sediment, resulting in greater shoreline transgression compared to identical, yet purely fluvial, deltaic systems that exhibit static or even regressive shorelines. © 2019 John Wiley & Sons, Ltd.

Description: Our lake sediment reconstruction for a large catchment in NW England shows that the cluster of extreme floods in the last two decades is without precedent in a 558 year palaeoflood record. Applying flood magnitude and frequency (FMF) analyses to the palaeoflood record shows that the largest flood in 〉558 years (November 2009) had a recurrence interval larger (1:2200 year) than that revealed by conventional flood estimation using gauged records. Abstract We present the first quantitative reconstruction of palaeofloods using lake sediments for the UK and show that for a large catchment in NW England the cluster of devastating floods from 1990 to present is without precedent in this 558‐year palaeo‐record. Our approach augments conventional flood magnitude and frequency (FMF) analyses with continuous lake sedimentary data to provide a longer‐term perspective on flood magnitude recurrence probabilities. The 2009 flood, the largest in 〉558 years, had a recurrence interval larger (1:2,200 year) than revealed by conventional flood estimation using shorter duration gauged single station records (1:1,700 year). Flood‐rich periods are non‐stationary in their correlation with climate indices, but the 1990‐2018 cluster is associated with warmer Northern Hemisphere Temperatures and positive Atlantic Multidecadal Oscillation. Monitored records rarely capture the largest floods and our palaeoflood series shows, for this catchment, such omissions undermine evaluations of future risk. Our approach provides an exemplar of how to derive centennial palaeoflood reconstructions from lakes coupled well with their catchments around the world. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.

Description: Abstract Raised marine terraces and submerged insular shelves are used through an integrated approach as markers of relative sea level changes along the flanks of the Salina volcanic Island (Aeolian Arc, southern Italy) for the purpose of evaluating its crustal vertical deformation pattern through time. Paleo sea level positions are estimated for the terrace inner margins exposed subaerially at different elevations and the erosive shelf edges recognized offshore at different depths. Compared with the eustatic sea levels at the main highstands (for the terraces) and lowstands (for the shelf edges) derived from literature, these paleo sea level markers allowed us to reconstruct the interplay among different processes shaping the flanks of the island and, in particular, to quantify the pattern, magnitudes and rates of vertical movements affecting the different sectors of Salina since the time of their formation. A uniform uplift process at rates of 0.35 m/ka during the Last Interglacial is estimated for Salina (extended to most of the Aeolian Arc) as the evidence of a regional (tectonic) vertical deformation affecting the sub‐volcanic basement in a subduction‐related geodynamic context. Before, a dominant subsidence at rates of 0.39/0.56 m/ka is instead suggested for the time interval between 465 ka (MIS 12) and the onset of the Last Interglacial (MIS 5.5, 124 ka). By matching the insular shelf edges with the main lowstands of the sea level curve, a relative age attribution is provided for the (mostly) submerged volcanic centres on which the deepest (and oldest) insular shelves were carved, with insights on the chronological development of the older stages of Salina and the early emergence of the island. The shift from subsidence to uplift at the Last Interglacial suggests a major geodynamic change and variation of the stress regime acting on the Aeolian sub‐volcanic basement.

Description: Valley confinement is a useful metric for characterizing and discriminating valley settings across broad spatial scales and distinct process regimes. In this article, we present an approach for measuring confinement across entire drainage networks using nationally available layers of intermediate resolution. This method accounts for channel position on the valley floor and lengths of channel that interact with potential confining margins to produce rapid, consistent, assessment of confinement over large areas with a reasonable degree of accuracy. Abstract In this article, we demonstrate the application of a continuous confinement metric across entire river networks. Confinement is a useful metric for characterizing and discriminating valley setting. At the reach scale, valley bottom confinement is measured and quantified as the ratio of the length of channel confined on either bank by a confining margin divided by the reach length. The valley bottom is occupied by the contemporary floodplain and/or its channel(s); confining margins can be any landform or feature that makes up the valley bottom margin, such as bedrock hillslopes, terraces, fans, or anthropogenic features such as stopbanks or constructed levees. To test the reliability of calculating confinement across entire networks, we applied our geoprocessing scripts across four physiographically distinct watersheds of the Pacific Northwest, USA using freely available national datasets. Comparison of manually digitized and mapped with modeled calculations of confinement revealed that roughly one‐third of reaches were equivalent and about two‐thirds of the sites differ by less than ±15%. A sensitivity analysis found that a 500 m reach segmentation length produced reasonable agreement with manual, categorical, expert‐derived analysis of confinement. Confinement accuracy can be improved (c. 4% to 17% gains) using a more accurately mapped valley bottom and channel position (i.e. with higher‐resolution model inputs). This is particularly important when differentiating rivers in the partly confined valley setting. However, at the watershed scale, patterns derived from mapping confinement are not fundamentally different, making this a reasonably accurate and rapid technique for analysis and measurement of confinement across broad spatial extents. © 2019 John Wiley & Sons, Ltd.

Description: Abstract The modern distribution of monsoonal rainforest in the Australian tropics is patchy and is mainly associated with river corridors and groundwater springs, which indicates a strong dependence on hydrologic and geomorphic conditions. While their present distribution is well known, very little data exists on past spatial and temporal dynamics of these ecosystems, or their medium‐ to longer‐term controls. Factors such as (i) fire frequency and type, and/or (ii) hydroclimatic conditions (e.g. droughts) have been proposed to control riverine corridor rainforest extent. Recent observations, however, also suggest an additional (iii) geomorphic control induced by alluvial knickpoint migration. Sediment sequences provide valuable archives for the reconstruction of longer‐term (i) floodplain sedimentary dynamics, (ii) local vegetation history, and (iii) catchment‐wide fire histories. This study investigates such a sediment sequence at Wangi Creek, and shows that a phase of aggradation, lasting ~4000 years, was recently disrupted by channel incision and floodplain erosion. The aggradational phase is characterized by sand deposition with average vertical floodplain accretion rates of 0.8 cm/year and includes phases of soil development. The recent incisional phase has changed hydro‐geomorphic conditions and caused widespread degradation of vegetation, erosion and lowering of the macro‐channel surface. While there is no evidence in our data for an erosional event of similar magnitude since the onset of late Holocene floodplain aggradation, Wangi Creek experienced significant erosion and incision immediately before ~4000 years, providing the first evidence for a tropical cut‐and‐fill river system. We hence argue that phases of aggradation mainly controlled by biotic processes alternate and depend on feedbacks with incision phases controlled mainly by abiotic processes. The results show that eco‐hydro‐geomorphic feedbacks may play a crucial role in the medium to longer‐term history of tropical fluvial systems and need to be considered when interpreting fluvial archives with regards to climate, fire or human induced change.

Description: Hydrostratigraphy and heterogeneity of floodplain sediments are estimated using a multiscale approach. Two meanders of disparate planform and geomorphic context are compared using field and remote techniques to connect subsurface and surficial features and evaluate the use to surficial features to infer subsurface heterogeneity and its effect on hydrological processes. Abstract Stratigraphy is a fundamental component of floodplain heterogeneity and hydraulic conductivity and connectivity of alluvial aquifers, which affect hydrologic processes such as groundwater flow and hyporheic exchange. Watershed‐scale hydrological models commonly simplify the sedimentology and stratigraphy of floodplains, neglecting natural floodplain heterogeneity and anisotropy. This study, conducted in the upper reach of the East River in the East River Basin, Colorado, USA, combines point‐, meander‐, and floodplain‐scale data to determine key features of alluvial aquifers important for estimating hydrologic processes. We compare stratigraphy of two meanders with disparate geometries to explore floodplain heterogeneity and connectivity controls on flow and transport. Meander shape, orientation, and internal stratigraphy affected residence time estimates of laterally exchanged hyporheic water. Although the two meanders share a sediment source, vegetation, and climate, their divergent river migration histories resulted in contrasting meander hydrofacies. In turn, the extent and orientation of these elements controlled the effective hydraulic conductivity and, ultimately, estimates of groundwater transport and hyporheic residence times. Additionally, the meanders’ orientation relative to the valley gradient impacted the hydraulic gradient across the meanders—a key control of groundwater velocity. Lastly, we combine our field data with remotely sensed data and introduce a potential approach to estimate key hydrostratigraphic packages across floodplains. Prospective applications include contaminant transport studies, hyporheic models, and watershed models. © 2019 John Wiley & Sons, Ltd.

Description: The effects of varying entrance geometry on tidal distortion and asymmetry, bed shear stresses and hypsometric profile shapes are examined in six tidal sub‐basins with different orientations and geometries. Results from a hydrodynamic numerical model indicate that differences in tidal energy within two contrasting basin configurations have a substantial impact on spatial shear patterns and local hypsometry. Abstract Geomorphological characteristics of tidal basins control hydrodynamics and sediment transport potential within such basins, for example, by adjusting the balance in tidal asymmetry. In this study we examine the effects of entrance geometry on tidal velocity asymmetry, slack water asymmetry, bed shear stress patterns and hypsometric profile shapes by comparison of six shallow meso‐tidal basins of Tauranga Harbour, New Zealand. Numerical model results show how tidal distortion increases with distance from a basin entrance. A simple ratio between basin width and entrance width defines levels of basin dilation. Sub‐basins with a constricted geometry and deep entrance channels are associated with small bed shear stress values and high rates of flood‐directed tidal velocity asymmetry in the sheltered basin centres, indicating a large potential for sediment deposition of larger particles. Moreover, slack water asymmetry within these basins is weakly ebb‐directed, indicating a small potential for transport of fine sediments out of the basins. The constricted depositional basins are characterized by convex hypsometric profiles with elevated intertidal regions. Unconstricted geometries are associated with larger bed shear stress values and more ebb‐directed tidal velocity asymmetry within basin centres, suggesting limited potential for overall sediment deposition. The slack tide duration asymmetry is weakly flood‐dominant indicating that limited input of fine sediment into the basins is possible. The comparatively high‐energy conditions within these exposed basins are associated with a less convex hypsometric intertidal profile. The ability to estimate tidal asymmetries is advantageous when developing management strategies related to ecosystem functioning, navigability or coastal protection in specific geomorphic settings. © 2019 John Wiley & Sons, Ltd.

Description: Measured soil field‐saturated soil hydraulic conductivity in the first year after wildfire and prescribed fire in forests from 73 sites across the globe is synthesized and analyzed using meta‐analysis. Abstract Wildfires raise risks of floods, debris flows, major geomorphologic and sedimentologic change, and water quality and quantity shifts. A principal control on the magnitude of these changes is field‐saturated hydraulic conductivity (Kfs), which dictates surface runoff generation and is a key input into numerical models. This work synthesizes 73 Kfs datasets from the literature in the first year following fire at the plot scale (≤ 10 m2). A meta‐analysis using a random effects analysis showed significant differences between burned and unburned Kfs. The reductions in Kfs after fire, expressed by the ratio of Kfs Burned/Kfs Unburned, were 0.46 (95% confidence interval of 0.31‐0.70) combining wildfire and prescribed fire and 0.3 (95% confidence interval of 0.13‐0.71) for wildfire. No significant differences for Kfs were observed between wildfire and prescribed fire or moderate and high fire severity. Both Kfs magnitude and variability depended more on measurement method than measurement support area at the plot scale, with methods applying head ≥0.5 cm producing larger estimates of Kfs. It is recommended that post‐fire efforts to characterize Kfs for modeling or process‐based interpretations use methods that reflect the dominant infiltration processes: tension infiltrometers and simulated rainfall methods when soil matrix flow dominates and ponded head methods when macropore flow is critical. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

Description: Washover fan recovery and accretion at a site on the Danish North Sea coast was observed over a period of 25 years. The fan is a supply‐limited system controlled by the onshore delivery of sand from migrating nearshore and intertidal bars. Aeolian deflation of the fan surface has led to the formation of large dunes around the periphery of the fan and the fan accretion rate correlates with the winter North Atlantic Oscillation (NAO) index. Abstract In this study, the decadal evolution of a washover fan on the west coast of Denmark is examined from its initial generation in 1990 until 2015. Since its inception, the bare and flat washover fan surface has recovered and accreted slowly due to re‐activation by overwash during surges and due to aeolian activity and dune formation, stimulated by vegetation growth. The volume of sand on the washover has increased steadily at an average rate of about 23 m3/yr per unit length of shoreline, and a total of 175,000 m3 of sand is now deposited on the fan, while at the same time the shoreline has receded by some 250 m. The evolution can be divided into three stages: 1) An initiation phase when storm surge levels and energetic wave conditions caused a breach in the foredunes and overwash processes formed a washover fan with a relatively low elevation above mean sea level; 2) An initial recovery phase during which waves supplied sand to the fan during frequent overwash activity and winds transported this sand into marginal dunes surrounding the fan; and 3) A later recovery phase when the surface of the fan had accreted to a level where vegetation could survive and trap sediment into new foredune growth across the fan. The rate of accretion has been overall linear but scales with neither annual overwash frequency, nor with aeolian transport potential. Instead, the linear accretion is more closely related to the steady onshore migration of nearshore bars that weld to the beach and provide a sand supply for transfer to the fan. The fan evolution demonstrates the importance of washover fans in preserving barrier resilience during transgressional phases caused by increasing mean sea level. © 2019 John Wiley & Sons, Ltd.

Description: Short‐ and long‐term soil redistribution rates can be disentangled using 239+240Pu and 10Be, respectively Short‐term rates are up to one‐order of magnitude higher than long‐term rates 239+240Pu and 10Be – in situ and meteoric – are both applicable to agricultural soils as erosion tracers Abstract Two principal groups of processes shape mass fluxes from and into a soil: vertical profile development and lateral soil redistribution. Periods having predominantly progressive soil forming processes (soil profile development) alternate with periods having predominantly regressive processes (erosion). As a result, short‐term soil redistribution – years to decades – can differ substantially from long‐term soil redistribution; i.e. centuries to millennia. However, the quantification of these processes is difficult and consequently their rates are poorly understood. To assess the competing roles of erosion and deposition we determined short‐ and long‐term soil redistribution rates in a formerly glaciated area of the Uckermark, northeast Germany. We compared short‐term erosion or accumulation rates using plutonium‐239 and ‐240 (239+240Pu) and long‐term rates using both in situ and meteoric cosmogenic beryllium‐10 (10Be). Three characteristic process domains have been analysed in detail: a flat landscape position having no erosion/deposition, an erosion‐dominated mid‐slope, and a deposition‐dominated lower‐slope site. We show that the short‐term mass erosion and accumulation rates are about one order of magnitude higher than long‐term redistribution rates. Both, in situ and meteoric 10Be provide comparable results. Depth functions, and therefore not only an average value of the topsoil, give the most meaningful rates. The long‐term soil redistribution rates were in the range of −2.1 t ha‐1 yr‐1 (erosion) and +0.26 t ha‐1 yr‐1 (accumulation) whereas the short‐term erosion rates indicated strong erosion of up to 25 t ha‐1 yr‐1 and accumulation of 7.6 t ha‐1 yr‐1. Our multi‐isotope method identifies periods of erosion and deposition, confirming the ‘time‐split approach’ of distinct different phases (progressive/regressive) in soil evolution. With such an approach, temporally‐changing processes can be disentangled, which allows the identification of both the dimensions of and the increase in soil erosion due to human influence. © 2019 John Wiley & Sons, Ltd.

Description: We test and analyse the methods and scaling models for calculating basin average denudation rates. Based on our findings, we develop a new and freely available GIS toolbox named Basinga which calculates, based on the Lal/Stone and LSD models, the scaling factors, production and denudation rates over multiple drainage basins. This tool also provides several options to correct for topographic shielding, ice cover, lithology and an original approach to account for paleomagnetic changes. Abstract The calculation of denudation rates from the measured cosmogenic nuclide concentrations in river sediments requires assumptions and approximations. Several different approaches and numerical tools are available in the literature. A widely used analytical approach represents the muogenic production with one or two exponentials, assumes the attenuation length of muons to be constant and also neglects temporal variations in the Earth's magnetic field. The denudation rates are then calculated directly and analytically from the measured concentrations. A second numerical and iterative approach was more recently proposed and considers a more rigorous muogenic production law based on pre‐calculated variable attenuation length of muons and accounts for temporal changes of the magnetic field. It also assumes a specific distribution of denudation rates throughout the basin and uses an iterative approach to calculate the basin average denudation rates. We tested the two approaches across several natural basins and found that both approaches provide similar denudation results. Hence, assuming exponential muogenic production and constant attenuation length of muons in the rock has little impact on the derived denudation rates. Therefore, unless a priori known distributions of denudation rates are to be tested, there does not appear to be any particular gain from using the second iterative method which is computationally less effective. Based on these findings, we developed and describe here Basinga, a new ArcGIS® and QGIS toolbox which computes the basin average scaling factors, cosmogenic production rates and denudation rates for several tens of drainage basins together. Basinga follows either the Lal/Stone or the Lifton/Sato/Dunai scaling schemes and includes several optional tools for correcting for topographic shielding, ice cover and lithology. We have also developed an original method for correcting the cosmogenic production rates for past variations in the Earth's magnetic field. © 2019 John Wiley & Sons, Ltd.

Description: Automated measurements of local bed load transport at the particle to the bedform scale were obtained, bridging a gap in measurements of sediment transport. Our measurements show that mean particle velocity and activity increases over the dune slope, in alignment with our general knowledge of accelerating flow velocity over a dune. The particle velocity's spatial variability is large, resulting from the onset and cessation of particles, the effect of the reattachment zone, observed sweep‐transport events and superimposed bedforms. Abstract This work presents measurements and analysis of sand particle velocities over a subaqueous dune with median sand diameter of 0.85 mm. Time‐lapse images of the mobile bed and an automated particle image velocimetry (PIV)‐based cross‐correlation method are used to obtain mean velocity of sand particles. This technique is shown to be consistent with measurements obtained with manual tracing. The measurements indicate an increase in mean particle velocity over a dune slope. Three regions are distinguished over the dune slope: (1) region of fluctuating particle velocity, (2) region of increasing particle velocity, and (3) region of maximum particle velocity. The observations are aligned with experimental and numerical modelling studies, indicating fluctuations in flow velocity over a dune stoss slope. We furthermore show that the standard deviation of the mean particle velocity is affected by the slope location and decreases from the lower slope towards the upper slope. The particle velocity variability is discussed in the context of general onset and cessation of sediment transport, the effect of the reattachment zone, sweep‐transport events, and the existence of superimposed bedforms. With this work we bridge the gap between measurements of bedload transport at the particle‐scale and at the bedform‐scale. © 2019 John Wiley & Sons, Ltd.

Description: Abstract As a topographic modelling technique, structure‐from‐motion (SfM) photogrammetry combines the utility of digital photogrammetry with a flexibility and ease of use derived from multi‐view computer vision methods. In conjunction with the rapidly increasing availability of imagery, particularly from unmanned aerial vehicles, SfM photogrammetry represents a powerful tool for geomorphological research. However, to fully realize this potential, its application must be carefully underpinned by photogrammetric considerations, surveys should be reported in sufficient detail to be repeatable (if practical) and results appropriately assessed to understand fully the potential errors involved. To deliver these goals, robust survey and reporting must be supported through (i) using appropriate survey design, (ii) applying suitable statistics to identify systematic error (bias) and to estimate precision within results, and (iii) propagating uncertainty estimates into the final data products. © 2019 John Wiley & Sons, Ltd.

Description: Dynamic chute‐cutoff‐dominated meandering with self‐formed floodplain requires sustained inflow perturbations. The implication is that all morphological models and landscape experiments for rivers, estuaries and coasts require sustained dynamic perturbations on a boundary to form complex patterns and develop natural dynamics. Abstract A sustained dynamic inflow perturbation and bar–floodplain conversion are considered crucial to dynamic meandering. Past experiments, one‐dimensional modelling and linear theory have demonstrated that the initiation and persistence of dynamic meandering require a periodic transverse motion of the inflow. However, it remains unknown whether the period of the inflow perturbation affects self‐formed meander dynamics. Here, we numerically study the effect of the inflow perturbation period on the development and meander dynamics of a chute‐cutoff‐dominated river, which requires two‐dimensional modelling with vegetation forming floodplain on bars. We extended the morphodynamic model Nays2D with growth and mortality rules of vegetation to allow for meandering. We tested the effect of a transversely migrating inflow boundary by varying the perturbation period between runs over an order of magnitude around typical modelled meander periods. Following the cutoff cascade after initial meander formation from a straight channel, all runs with sufficient vegetation show series of growing meanders terminated by chute cutoffs. This generates an intricate channel belt topography with point bar complexes truncated by chutes, oxbow lakes, and scroll‐bar‐related vegetation age patterns. The sinuosity, braiding index and meander period, which emerge from the inherent biomorphological feedback loops, are unrelated to the inflow perturbation period, although the spin‐up to dynamic equilibrium takes a longer time and distance for weak and absent inflow perturbations. This explains why, in previous experimental studies, dynamic meandering was only accomplished with a sustained upstream perturbation in flumes that were short relative to the meander wavelength. Our modelling of self‐formed meander patterns is evidence that scroll‐bar‐dominated and chute‐cutoff‐dominated meanders develop from downstream convecting instabilities. This insight extends to many more fluvial, estuarine and coastal systems in morphological models and experiments, which require sustained dynamic perturbations to form complex patterns and develop natural dynamics. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.

Description: Abstract Sediment transport equations typically produce transport rates that are biased by orders of magnitude. A causal component of this inaccuracy is the inability to represent complex grain‐scale interactions controlling entrainment. Grain‐scale incipient motion has long been modelled using geometric relationships based on simplified particle geometry and two‐dimensional (2D) force or moment balances. However, this approach neglects many complexities of real grains, including grain shape, cohesion and the angle of entrainment relative to flow direction. To better represent this complexity, we develop the first vector‐based, fully three‐dimensional (3D) grain rotation entrainment model that can be used to resolve any entrainment formulation in 3D, and which also includes the effect of matrix cohesion. To apply this model we use X‐ray computed tomography to quantify the 3D structure of water‐worked river grains. We compare our 3D model results with those derived from application of a 2D entrainment model. We find that the 2D approach produces estimates of dimensionless critical shear stress ( ) that are an order of magnitude lower than our 3D model. We demonstrate that it is more appropriate to use the c‐axis when calculating 2D projections, which increases values of to more closely match our 3D estimates. The 3D model reveals that the main controls on critical shear stress in our samples are projection of grains, cohesive effects from a fine‐grained matrix, and bearing angle for the plane of rotation (the lateral angle of departure from downstream flow that, in part, defines the grain's direction of pivot about an axis formed by two contact points in 3D). The structural precision of our 3D model demonstrates sources of geometric error inherent in 2D models. By improving flow properties to better replicate local hydraulics in our 3D model, entrainment modelling of scanned riverbed grains has the potential for benchmarking 2D model enhancements. This article is protected by copyright. All rights reserved.

Description: We assess the influence of representative ambient stress conditions, stress history and localized stress concentrations on the geotechnical response of sedimentary rocks to weathering. We find that these factors have limited influence on resultant strength and strain behaviour. However, weathering significantly reduces intact rock strength from unweathered, baseline values. Weathering also results in a change of failure style dominated by multi‐stage brittle failures, characterized by multiple discrete fracture events after peak strength has been exceeded. Abstract Weathering reduces the strength of rocks and so is a key control on the stability of rock slopes. Recent research suggests that the geotechnical response of rocks to weathering varies with ambient stress conditions resulting from overburden loading and/or stress concentrations driven by near‐surface topography. In addition, the stress history experienced by the rock can influence the degree to which current weathering processes cause rock breakdown. To address the combined effect of these potential controls, we conducted a set of weathering experiments on two sedimentary lithologies in laboratory and field conditions. We firstly defined the baseline geotechnical behaviour of each lithology, characterising surface hardness and stress–strain behaviour in unconfined compression. Weathering significantly reduced intact rock strength, but this was not evident in measurements of surface hardness. The ambient compressive stress applied to samples throughout the experiments did not cause any observable differences in the geotechnical behaviour of the samples. We created a stress history effect in sub‐sets of samples by generating a population of microcracks that could be exploited by weathering processes. We also geometrically modified groups of samples to cause near‐surface stress concentrations that may allow greater weathering efficacy. However, even these pronounced sample modifications resulted in insignificant changes in geotechnical behaviour when compared to unmodified samples. The observed reduction in rock strength changed the nature of failure of the samples, which developed post‐peak strength and underwent multiple stages of brittle failure. Although weakened, these samples could sustain greater stress and strain following exceedance of peak strength. On this basis, the multi‐stage failure style exhibited by weaker weathered rock may permit smaller‐magnitude, higher‐frequency events to trigger fracture through intact rock bridges as well as influencing the characteristics of pre‐failure deformation. These findings are consistent with patterns of behaviour observed in field monitoring results. © 2019 John Wiley & Sons, Ltd.

Description: The behaviour of the Cap Ferret barrier spit since 1768 is in phase with decadal to pluri‐decadal trends of the North Atlantic Oscillation. The relationship between the spit's adjacent inlet and sea level variations has also played an underlying controlling part. The ongoing adjustment of the back‐barrier lagoon to sea level rise certainly explains response of the spit to NAO‐related changes in wave climate. These results recall the vulnerability of coastal barriers to climate change. Abstract In coastal areas, sea level rise (SLR) and changing wave climates are expected to be the main oceanic drivers of shoreline adjustments. These drivers have been shown to vary on a wide spectrum of spatial and temporal scales. Nonetheless, a general rule about how this variability impacts global shorelines remains to be articulated. Here, we discuss the impacts of wave climate changes and SLR on the evolution of a barrier spit–inlet system over the last 250 years. The distal end of the Cap Ferret barrier spit, SW France, has undergone large‐scale oscillations that were well correlated with variations of the decadal average of the winter North Atlantic Oscillation (NAO) index. The local wave climate hindcast supports that increased alongshore wave energy fluxes associated with the positive phase of the NAO were responsible for the updrift retreat of the spit. By opposition, the spit has elongated downdrift when waves were less energetic and more shore normal, as during the negative phase of the NAO. In addition, lower rates of SLR appeared to be necessary for the spit to develop, as higher rates of SLR very likely forced the adjacent inlet to enlarge, at the expense of the spit. These results should help to predict and detect coastal adjustments driven by climate change and by climate variability. © 2019 John Wiley & Sons, Ltd.

Description: The roles of wind and underlying topography in the formation and persistence of vernal pond complexes in mineral soil were investigated using remote sensing and observations of sediment movement, water depth, surface and underlying topography, and freezing. Abstract Little is known of the processes that create and maintain vernal ponds in mineral soils in alpine environments. On the Central Plateau, Tasmania, we tested the hypotheses that vernal pond complexes on mineral soils formed in response to the underlying topography of a glacio‐fluvial plain; relate to present day topography; resulted from past damming by organic accumulation; are moulded by wind. The underlying topography did not relate to the surface ponds, nor were they on steeper slopes than adjacent areas without ponds. The morphology of the ponds and the morphological and edaphic characteristics of the pond complexes and adjacent areas are consistent with an origin by organic material damming. The strongest winds orientate most ponds, rather than the aspect of the slope. Sediments were preferentially caught on sticky traps to the northeast of the ponds, away from fierce prevailing southwesterly winds. Temperature measurements and fortnightly observation showed non‐concordant patterns of variation in water levels in the ponds. We deduce that the complexes of vernal ponds may have formed in previous moister conditions more favourable to organic matter accumulation, possibly in the early Holocene, and are maintained by a faster rate of accumulation of mineral and organic particles in the tussock grassland adjacent to the ponds than in the ponds themselves. © 2019 John Wiley & Sons, Ltd.

Description: We measured erosion in an upland blanket peatland catchment (0.017 km2) in northern England using Structure‐from‐Motion (SfM) photogrammetry, sediment traps and stream sediment sampling. A net median topographic change of –27 mm yr–1 was observed over a 12 month period by SfM surveys for a small peat catchment. Stream suspended sediment and particulate organic carbon yields were 926.3 t km–2 yr–1 and 340.9 t km–2 yr–1, respectively, with highest losses during autumn. Abstract Erosion and the associated loss of carbon is a major environmental concern in many peatlands and remains difficult to accurately quantify beyond the plot scale. Erosion was measured in an upland blanket peatland catchment (0.017 km2) in northern England using structure‐from‐motion (SfM) photogrammetry, sediment traps and stream sediment sampling at different spatial scales. A net median topographic change of –27 mm yr–1 was recorded by SfM over the 12‐month monitoring period for the entire surveyed area (598 m2). Within the entire surveyed area there were six nested catchments where both SfM and sediment traps were used to measure erosion. Substantial amounts of peat were captured in sediment traps during summer storm events after two months of dry weather where desiccation of the peat surface occurred. The magnitude of topographic change for the six nested catchments determined by SfM (mean value: 5.3 mm, standard deviation: 5.2 mm) was very different to the areal average derived from sediment traps (mean value: –0.3 mm, standard deviation: 0.1 mm). Thus, direct interpolation of peat erosion from local net topographic change into sediment yield at the catchment outlet appears problematic. Peat loss measured at the hillslope scale was not representative of that at the catchment scale. Stream sediment sampling at the outlet of the research catchment (0.017 km2) suggested that the yields of suspended sediment and particulate organic carbon were 926.3 t km–2 yr–1 and 340.9 t km–2 yr–1, respectively, with highest losses occurring during the autumn. Both freeze–thaw during winter and desiccation during long periods of dry weather in spring and summer were identified as important peat weathering processes during the study. Such weathering was a key enabler of subsequent fluvial peat loss from the catchment. © 2019 John Wiley & Sons, Ltd.

Description: The barrier‐inlet systems of the microtidal east coast of South Africa are driven by overwash processes. Inlets form by washover channelling and seal by washover plugging. The low‐lying barriers and waterbody orientation typical of these systems predisposes them to back‐barrier aggradation by overwash. Together with bedrock limitations on accommodation, these systems are especially vulnerable to rising sea level. Their geomorphic end point involves continual roll over, back‐barrier infilling and ultimate destruction by wave erosion. Abstract The morphodynamics and structure of barriers with persistent tidal inlets have been well studied. In contrast the stratigraphy and functioning of barrier systems with ephemeral inlets is poorly understood. This article examines the barrier‐inlet systems of two intermittently closed open lagoons or temporarily open closed estuaries on the east coast of South Africa. Multiple geophysical surveys using ground‐penetrating radar (GPR) were correlated with exposed sections of the barrier where inlet formation revealed the internal stratigraphy. Stratigraphic observations were placed in the context of the contemporary wave dynamics and mesoscale geomorphic evolution. The integrated databases reveal an absence of migrating channel features. Instead the stratigraphy is dominated by landward dipping sheets of alternating high‐ and low‐amplitude reflectors. These correlate with gravel, shell debris and heavy mineral‐lined beds formed by overwash processes. Where ephemeral inlet structures are preserved in the stratigraphy, their fills comprise aggrading, high‐amplitude reflectors, linked to washover infilling of the inlet mouth. Multiple small channels in the more distal portions of the barrier in georadar stratigraphy are related to channelized washover flow. These barriers often breach during high swell and are subsequently sealed during fairweather wave conditions. Time series analysis of waves and satellite imagery shows a link between storms from the south and breach events. This is consistent with the truncations in subsurface images and inferred barrier lowering by overwash channelling. These barriers experience quasi‐stable oscillations in their landward and seaward shore position, punctuated by periods of barrier rollover associated with the most intense storms. As overwash is responsible in part for both the constructive and destructive phases of the barrier, these barriers have low preservation potential. Persistent rollover driven by overwashing will terminate once accommodation space is eliminated and the barriers are eroded by storm activity. © 2019 John Wiley & Sons, Ltd.

Description: Abstract Clifftop coastal boulders transported by storm waves or tsunamis have been reported around the world. Although numerical calculation of boulder transport is a strong tool for the identification of tsunami or storm boulders, and for estimation of the wave size emplacing boulders, models which can reasonably solve boulder transport from below a cliff or from a cliff‐edge onto a cliff‐top do not yet exist. In this study, we developed a new numerical formulation for cliff‐top deposition of boulders from the cliff edge or below the cliff, with validation from laboratory tests. We then applied the model using storm and tsunami wave forcing to simulate the observed boulder deposits at the northwest coast of Hachijo Island, Japan. Using the model, the actual distribution of boulders was explained well using a reasonable storm wave height without assumption of anomalously high‐water level by storm surge. Results show that boulder transport from the cliff edge or under the cliff onto the cliff‐top was possible from a tsunami with periods of 5~10 min or storm waves with no storm surge. However, the actual distribution of boulders on the cliff was explained only by storm waves, but not by tsunami. Therefore, the boulders distributed at this site are likely of storm wave origin. Our developed model for the boulder transport calculation can be useful for identifying a boulder's origin and can reasonably calculate cliff‐top deposition of boulders by tsunami and storm waves.

Description: A morphometric classification of salt marsh marginal landforms is developed, allowing a regional‐scale inventory to be established from LiDAR data. Comparison of margin type with historical morphological changes reveals clear associations between margin configuration and dynamism, providing a quantitative basis for the rapid evaluation of likely system dynamism that may be useful to conservation practitioners or site managers Abstract The three‐dimensional configuration of sedimentary landforms in intertidal environments represents a major control on regional hydrodynamics. It modulates the location and magnitude of forces exerted by tidal currents and waves on the landform itself and on engineered infrastructure such as sea walls or coastal defences. Furthermore, the effect is reflexive, with the landforms representing an integrated, long‐term response to the forces exerted on them. There is a strong reciprocal linkage between form and process (morphodynamics) in the coastal zone which is significantly lagged and poorly understood in the case of cohesive, vegetated sediments in the intertidal zone. A method is presented that links the geometric properties of the tidal flat–salt marsh interface to the history and potential future evolution of that interface. A novel quantitative classification scheme that is capable of separating marsh margins based on their functional form is developed and is applied to demonstrate that relationships exist between landform configuration and morphological evolution across a regional extent. This provides evidence of a spatially variable balance between self‐organized and external controls on morphodynamic evolution and the first quantitative basis for a quick assessment procedure for likely future dynamism. © 2019 John Wiley & Sons, Ltd.

Description: Abstract Caddisfly (Trichoptera) larvae are an abundant and widespread aquatic insect group characterised by the construction of silk structures, including nets and cases. Case‐building caddisfly have the potential to modify the sorting and mobility of sand and fine gravel via; 1) case construction, resulting in altered sediment properties; 2) transporting sediment incorporated into cases over the river bed and; 3) changing the structure of river‐beds via burrowing. To investigate these mechanisms, it is necessary to understand the mass, size distribution and spatial variability of sediment use by case‐building caddisfly larvae. We quantified the mineral sediment used by individuals and communities of case‐building caddisfly in 27 samples, from three sites on a gravel‐bed stream. The mass and size distribution of sediment in individual cases varied between taxa (mass = 0.001 – 0.83 g, D50 = 0.17 – 4 mm). The mean mass of sediment used by the caddisfly community was 38 g m‐2 and varied locally. Sediment use was predominantly coarse sand (D50 = 1 mm). 64% of sediment use was attributable to Agapetus fuscipes (Glossosomatidae). Due to within‐species variability in case mass, the abundance of most taxa, including A. fuscipes, was only weakly associated with the mass of sediment used at the river scale. Whilst the caddisfly community used a small percentage of the total sediment available (average 2.99% of the 1‐1.4 mm size fraction), A. fuscipes used more fine sediment in their cases at sites where it was more available. Despite variability in local habitat, all sites supported diverse case‐building caddisfly communities utilising mineral sediment. Consequently, geomorphological effects of case‐building caddisfly are potentially widespread. The results provide novel insights into the specific grain sizes and quantities of fine sediment particles (g m‐2) used by caddisfly larvae, which represents an important step towards understanding their zoogeomorphic activities.

Description: Cosmogenic nuclide concentration measurements on supraglacial debris are combined with a statistical evaluation of the relationship between the temporal rockfall distributions, the glacier flows and the origin of the debris in the supra‐glacial cover in order to provide an estimation of sidewall erosion rates in a glaciated catchment. Abstract Sidewall erosion because of rockfalls is one of the most efficient erosional processes in the highest parts of mountain ranges; it is therefore important to quantify sidewall erosion to understand the long‐term evolution of mountainous topography. In this study, we analyse how the 10Be concentration of supraglacial debris can be used to quantify sidewall erosion in a glaciated catchment. We first analyse, in a glaciated catchment, the cascade of processes that move a rock from a rockwall to a supraglacial location and propose a quantitative estimate of the number of rockfalls statistically mixed in a supraglacial sand sample. This model incorporates the size of the rockwall, a power law distribution of the size of the rockfalls and the mean glacial transport velocity. In the case of the Bossons glacier catchment (Mont Blanc massif), the 10Be concentrations obtained for supraglacial samples vary from 1.97 ± 0.24 to 23.82 ± 1.68 × 104 atoms g−1. Our analysis suggests that part of the 10Be concentration dispersion is related to an insufficient number of amalgamated rockfalls that does not erase the stochastic nature of the sidewall erosion. In the latter case, the concentration of several collected samples is averaged to increase the number of statistically amalgamated rockfalls. Variable and robust 10Be‐derived rockwall retreat rates are obtained for three distinct rockfall zones in the Bossons catchment and are 0.19 ± 0.08 mm year−1, 0.54 ± 0.1 mm year−1 and 1.08 ± 0.17 mm year−1. The mean 10Be retreat rate for the whole catchment (ca. 0.65 mm year−1) is close to the present‐day erosion rate derived from other methods. © 2019 John Wiley & Sons, Ltd.