ALBERT

Description: ABSTRACT In a review of the role of plants in river systems, Gurnell (2014) explains how living riparian vegetation can exert physical controls that enable it to modify and manipulate many fluvial processes. Those traits, in combination with their tendency to speed up the recovery of river systems between extreme flow events through their stabilising influence, imply that plants may act as ‘river system engineers’. In this sense, vegetation may be important in attenuating erosion during high flow and stabilising river features both during and after extreme flow conditions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This paper is a response to commentary on the review by Gurnell (2014). It covers three themes. First, it explains how the review focused on physical ecosystem engineering by plants, particularly in the northern humid temperate zone. Second, it explains how the review was structured to address that theme and why annual species were not highlighted. Within the humid temperate zone, mature plants of annual species are not present during the seasons of the year when fluvial processes are most active: they survive as seeds or young seedlings, and so their ability to act as river ecosystem engineers is limited. Third, some comments are made regarding the annual species, Himalayan balsam ( Impatiens glandulifera ), including the traits that enable it to be successful in riparian environments, its competitive ability, its potential role in influencing fluvial sediment dynamics, and the need for controlled experiments to characterise and quantify the latter over one or more complete years. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Reef islands on the Great Barrier Reef are influenced by a range of environmental factors. for a meta-analysis of 103 islands expresses variation in island size (area and volume) as a function of latitudinal and cross shelf gradients in regional oceanographic factors (exposure to incident waves, tidal range and tropical cyclone frequency) and local physical factors (position on the shelf, area, length and depth of supporting reef platform, vegetative cover). Models performed well for unvegetated sandcays (R 2  = 0.89), vegetated sandcays (R 2  = 0.72) and low wooded islands (R 2  = 0.78), with a moderate level of variation explained when all islands were simultaneously regressed (R 2  = 0.58). Future island dynamics were simulated for anticipated changes in cyclone regime, wave activity and sea level. For 38 islands mapped on the 1973 Royal Society and Universities of Queensland Expedition to the Northern Great Barrier Reef , change over the same 22 year period (1973 to 1995) was determined andthe relative magnitude of observed and modelled changes was compared and found to be consistent through rank correlation analysis (Γ = 0.84 for unvegetated sandcays, Γ = 0.81 for vegetated sandcays). Simulations of island area or volume change from 2000 to 2100 indicated that under a 30% decrease in tropical cyclone activity, unvegetated sandcays continue to accrete at a lower rate, whereas all island types erode under a 38% increase in tropical cyclone activity. Vegetated sandcays initially accrete at higher levels of cyclone activity, entering an erosive state with a 60% increase in activity. Low wooded islands are unresponsive to environmental change. A sensitivity analysis of vegetated and unvegetated sandcays indicated that the presence of vegetation increases the tropical cyclone activity threshold at which islands begin to erode. Greatest sedimentary losses occur within the central band of high cyclone activity between Cooktown and Mackay. This article is protected by copyright. All rights reserved.

Description: ABSTRACT We present a new numerical surface process model allowing us to take into account submarine erosion processes due either to submarine landslides or to hyperpycnal currents. A first set of models show that the frequency of hyperpycnal flows influences the development of submarine canyons at the mouth of continental rivers. Further experiments show that an increase in submarine slope leads to faster regressive canyon erosion and a more dentritic canyon network, whereas increasing the height of the unstable sediment pile located on the shelf break leads to wider and less dendritic canyons. The models are then applied to the western segment of the north Ligurian margin (northwestern Mediterranean), which displays numerous submarine canyons with various sizes and morphologies. From west to east, canyon longitudinal profiles as well as margin-perpendicular profiles progressively change from moderately steep, concave-up shapes to steeper linear to convex-up shapes suggesting increasing eastward margin uplift. Moreover, the foot of the margin is affected by a marked slope increase with evidences of mass transport due to landslides. Numerical models which reproduce well the North Ligurian margin morphologic features indicate that the western part of the margin is submitted to rather low (i.e. 0.4 mm yr −1 ) uplift and intense submarine erosion due to frequent hyperpycnal currents, whereas the eastern part bears more rapid (i.e. 0.7 mm yr −1 ) uplift and has little or no hyperpycnal currents. Copyright © 2014 John Wiley & Sons, Ltd.

Description: ABSTRACT Lavaka represent a typical erosional landform in Madagascar. The chronology of their formation remains, however, under discussion. Our research focuses on the Ankarokaroka lavaka, a spectacular landform located in NW Madagascar (Ankarafantsika natural reserve), which is characterized by the presence of sandy units of regional extension at its top. The two main units correspond to white and red sands, and are closely associated with specific vegetations (dry dense forest for the white sands, savannah grasslands for the red sands). We applied a geochronological approach based on Optically Stimulated Luminescence (for the coversands) associated to radiocarbon dating performed on archaeological remains found at the contact between the sands and the lavaka. The combination of this approach with field work and sedimentological analyses makes it possible to show that the sands experienced a complex history, both in terms of sedimentation and post-sedimentary pedogenesis (podzolisation of the white sands, rubefaction of the red sands). The numerical ages furthermore indicate that the Ankarokaroka lavaka formed between 18.5 ± 2.3 ka ago and the 14th century AD. The present study demonstrates that this lavaka has a climatic origin, and highlights the potential of OSL to date sediments associated with Madagascar lavaka. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Identifying the influence of neotectonics on the morphology of elevated passive margins is complicated in that major morpho-structural patterns might plausibly be explained by processes related to late Mesozoic to early Cenozoic rifting and/or differential erosion induced by Cenozoic epeirogenic uplift. The proportional contribution of each process can vary from continent to continent, and potentially even within the same passive margin. In the passive margin setting of the south-east Australian highlands the documented occurrence of neotectonic deformation is rare, and accordingly its role in landscape evolution is difficult to establish. The results of investigations within the Lapstone Structural Complex, which forms the eastern range front of the Blue Mountains Plateau, provide evidence for two periods of Cenozoic neotectonic uplift in this part of the highlands. The first, demonstrated by seismic and structural evidence, is suggested to have occurred in the Paleogene, and is thus unrelated to Cretaceous rifting. The second period, demonstrated by evidence from the Kurrajong Fault (presented herein) suggests that uplift occurred in both the Mio-Pliocene and the Middle Pleistocene. The cumulative Neogene and younger uplift of ~15 m determined for the Kurrajong Fault is less than 10% of the 130 m of total measured throw across the fault. The apparently minor contribution of neotectonism to the current elevation of the Blue Mountains Plateau supports a predominantly erosional exhumation origin for the topographic relief at the plateau's eastern edge. This finding contrasts with evidence from fault complexes associated with similar topographic relief elsewhere in the south-eastern highlands, indicating that present-day topography cannot be directly related to relief generated by Neogene and younger uplift, even from relatively closely-spaced (〈150 km) structures within the same passive margin. These findings have implications for understanding the spatio-temporal variability of post-rift faulting in continental passive margin settings and the evolution of landscapes therein. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The paper presents the result of an application of the GeoWEPP model in a heterogeneous semi-agricultural catchment located in the northern Italian Apennines mountain range. The objectives were: (a) to evaluate the GeoWEPP model in a heterogeneous catchment in a Mediterranean climate and (b) to examine the effect of digital elevation model grid size on hydrological and sediment yield simulations. The catchment is characterized by large heterogeneity in geology, soil type, vegetation cover and topography. In addition, 10% of its area is occupied by calanchi (badlands), characterized by steep, bare soil and accentuated erosion. Experimental stream flow data were compared with those simulated by GeoWEPP for a period of 8 years and the results were evaluated by means of statistical indices, with the analysis of the flow duration curve. Simulated sediment yields were compared with experimental data for one year. The stream flow cumulative annual results were satisfactory with NSE oscillating between 0.40 and 0.83 and RMSE between 1.1 and 2.9 mm. Also, the performance of the model with daily stream flow data was positive (NSE = 0.68 and RMSE = 1.9 mm). The flow duration curve indicated that GeoWEPP could represent the experimental stream flow for fluxes over 1 mm d -1 . The model performance for simulation of sediment yield was satisfactory with both digital elevation models of different grid sizes (NSE 0.84 and 0.87). Indeed, the sensitivity analysis tests of the model showed that there was no statistically significant improvement in the accuracy of the digital elevation model between 10 and 2 meter resolution. These results were confirmed for both stream flow as well as sediment yield. Additional sensitivity analysis of other model parameters performed on the entire catchment and badlands hillslopes showed that bedrock hydraulic conductivity primarily affected the model in both settings. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Forecasts of water level during river floods require accurate predictions of the evolution of river dune dimensions, because the hydraulic roughness of the main channel is largely determined by the bed morphology. River dune dimensions are controlled by processes like merging and splitting of dunes. Particularly the process of dune splitting is still poorly understood and – as a result - not yet included in operational dune evolution models. In the current paper, the process of dune splitting is investigated by carrying out laboratory experiments and by means of a sensitivity analysis using a numerical dune evolution model. In the numerical dune evolution model, we introduced superimposed TRIAS ripples (i.e. TRIangular Asymmetric Stoss side-ripples) on the stoss sides of underlying dunes as soon as these stoss sides exceed a certain critical length. Simulations with the model including dune splitting showed that predictions of equilibrium dune characteristics were significantly improved compared to the model without dune splitting. As dune splitting is implemented in a parameterized way, the computational cost remains low which means that dune evolution can be calculated on the time scale of a flood wave. Subsequently, we used this model to study the mechanism of dune splitting. Literature showed that the initiation of a strong flow separation zone behind a superimposed bed forms is one of the main mechanisms behind dune splitting. The flume experiments indicated that besides its height also the lee side slope of the superimposed bed form is an important factor to determine the strength of the flow separation zone and therefore is an important aspect in dune splitting. The sensitivity analysis of the dune evolution model showed that a minimum stoss side length was required to develop a strong flow separation zone. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In the last few centuries humans have modified rivers, and rivers have responded with noticeable changes in sedimentary dynamics. The objective of this study is to assess these responses of the sedimentary dynamics. Therefore, we calculated a sediment budget for eroded and deposited sediment volumes in a ~12-km long floodplain section of the largest semi-natural embanked but still dynamic lower Rhine distributary, for ~50-years time slices between 1631 AD and present. This is the period during which embanked floodplains were formed by downstream migration of meander bends between confining dykes. Our sediment budget involves a detailed reconstruction of vertical and lateral accretion rates and erosion rates of floodplain sediment. To do so, we developed a series of historical geomorphological maps, and lithogenetic cross-sections. Based on the maps and cross-sections, we divided the floodplain into building blocks representing channel bed and overbank sediment bodies. Chronostratigraphy within the blocks was estimated by interpretation of heavy metal profiles and from optically stimulated luminescence (OSL) dating results. Sediment budgets were hence calculated as a change of volume of each building block between time steps. The amount of lateral accretion initially increased, as a result of island and sand bar formation following embankment. From the 18 th century onwards, there was a decrease of lateral processes in time, which is a result of straightening of the river by human activities, and a reduction of water and sediment supply due to the construction of a new upstream bifurcation. With straightening of the river, the floodplain area grew. Artificial fixation of the channel banks after 1872 AD prevented lateral activity. From then on, overbank deposition became the main process, leading to a continuous increase of floodplain elevation, and inherent decrease of flooding frequency and sediment accumulation rate. This article is protected by copyright. All rights reserved.

Description: ABSTRACT There has been increasing use of live vegetation in laboratory experiments, in particular in fluvial geomorphology. The results from these studies have provided useful insight into the role that vegetation plays in impacting and modifying geomorphic systems. However there has been little published on the seed preparation techniques and vegetation growing conditions required for use in these experiments. This commentary presents results from a series of experiments investigating these factors using Medicago sativa and Avena Sativa , with the aim of highlighting the optimal growing conditions found to provide a starting point for researchers interested in implementing these techniques. This article is protected by copyright. All rights reserved.

Description: ABSTRACT We measured longitudinal spacing and wood volume of channel-spanning logjams along 30 1-km reaches of forest streams in the Colorado Front Range, USA. Study streams flow through old-growth (〉 200 year stand age) or younger subalpine conifer forest. Evaluating correlations between the volume and longitudinal spacing of logjams in relation to channel and forest characteristics, we find that old-growth forest streams have greater instream wood loads and more jams per kilometer than streams in younger forest. Old-growth forests have a larger basal area close to the stream and correlate with larger piece diameters of instream wood. Jam volume correlates inversely with the downstream spacing for ramp and bridge pieces that can act as key pieces in jams. Most importantly, old-growth streams have shorter downstream spacing for ramp and bridge pieces (〈 20 m). Our results suggest that management of instream wood and associated stream characteristics can be focused most effectively at the reach scale, with an emphasis on preserving old-growth riparian stands along lower gradient stream reaches or mimicking the effects of old growth by manipulating the spacing of ramp and bridge pieces. Our finding that average downstream spacing between jams declines as wood load increases suggests that the most effective way to create and retain jams is to ensure abundant sources of wood recruitment, with a particular emphasis on larger pieces that are less mobile because they have at least one anchor point outside the active channel. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Glacial bedforms’ heights, H , and volumes, V , likely preserve important information about the behaviour of former ice sheets. However, large systematic errors exist in the measurement of H and V . Three semi-automated methods to isolate drumlins from other components of the landscape (e.g., trees, hills) as portrayed by NEXTMap have recently been devised, however it is unclear which is most accurate. This paper undertakes the first quantitative comparison of such readily implementable methods, illustrating the use of statistically representative ‘synthetic landscapes’ as a diagnostic tool. From this analysis, guidelines for quantifying the 3D attributes of drumlins are proposed. Specifically, to avoid obtaining incorrect estimates caused by substantial systematic biases, interpreters should currently take three steps; declutter the DEM for estimating H but not for V , remove height data within the drumlin, then interpolate across the resultant hole to estimate a basal surface using Delaunay triangulation. Results are demonstrated through analysis of drumlins in an area in western Central Scotland. The guidance arguably represents the best current advice for subglacial bedforms in general, highlighting the need for more studies into the quality of mapped data using synthetic landscapes. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In poorly mobile static armour, sorting is usually considered the result of hiding/exposure effects. We called this effect ‘static sorting’ in opposition to a very efficient grain-to-grain mechanisms produced by a mobile mixture, called ‘kinetic sorting’. We hypothesized that kinetic sorting can be an important contributor to the morphodynamics of mountain streams and attempted to demonstrate this with new flume experiments. Two long runs were produced with natural poorly sorted sediments, and with transport stages of the coarse fraction (defined by the ratio between the shear stress and the critical shear stress for transport), smaller and higher than 1, respectively. Both runs produced an efficient transfer downstream of the injected material, but with a major difference: the first run (no kinetic sorting) produced permanent armour figuring clusters, akin to what has already been observed in similar experiments; the second run (with kinetic sorting) also produced bed armouring, but this armour was periodically totally destroyed, leading to substantial bed erosion. This phenomenon was explained by kinetic sorting, the effects of which are to produce an efficient downward migration of fine materials and bed surface armouring. The consequence is that fine materials are hidden to the flow during aggradation, allowing the slope to attain values much steeper than what would have been expected at equilibrium for the mixture. However, whereas the surface armouring tends to stabilize the bed, construction of a layer of fine sediments at the subsurface also contributes to making it very unstable. These two contradictory effects explain the complex bed behaviours and the existence of very large bedload and slope fluctuations. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Predicting spatial and temporal variations in bank erosion due to extreme floods presents a long-standing challenge in geomorphology. We develop two methodologies for rapid, regional-scale assessments of stream reaches susceptible to channel widening. The first proposes that channel widening occurs when unit stream power exceeds a critical threshold (300 W/m 2 ). The second is motivated by the observation that widening often occurs at channel bends. We introduce a new metric, the bend stress parameter, which is proportional to the centripetal force exerted on a concave bank. We propose that high centripetal forces generate locally high bank shear forces and enhance channel bank erosion. We test both metrics using the geomorphic signature of Tropical Storm Irene (2011) on the White and the Saxtons Rivers, Vermont. Specifically, we test if reaches where significant channel widening occurred during Irene required one or both metrics to exceed threshold values. We observe two distinct styles of channel widening. Where unit stream power and bend stress parameter are high, widening is usually due to bank retreat. Elsewhere widening is usually due to the stripping of the upstream end of mid-channel islands. Excluding widening associated with the stripping of the heads of mid-channel islands, almost all the widening (〉 98 percent) occurred along reaches identified as susceptible to widening. The combined metrics identify up to one-quarter of the reaches lacking susceptibility to channel widening. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Patterned landscapes are often evidence of biotic control on geomorphic processes, emerging in response to coupled ecosystem processes acting at different spatial scales. Self-reinforcing processes at local scales expand patches, while self-inhibiting processes, operating at a distance, impose limits to expansion. In Big Cypress National Preserve (BICY) in southwest Florida, isolated forested wetland depressions (cypress domes) appear to be evenly distributed within a mosaic of short-hydroperiod marshes and pine uplands. To test the hypothesis that the apparent patterning is regular, we characterized frequency distributions and spatial patterns of vegetation communities, surface and bedrock elevation, and soil properties (thickness and phosphorus content). Nearest neighbor distances indicate strongly significant wetland spatial overdispersion, and bedrock elevations exhibited periodic spatial autocorrelation; both observations are consistent with regular patterning. Bedrock elevations and soil P were clearly bimodal, suggesting strong positive feedbacks on wetland patch development. Soil-surface elevations exhibited weaker bimodality, indicating smoothing of surface morphology by some combination of sediment transport, mineral reprecipitation, and organic matter production. Significant negative autocorrelation of bedrock elevations at scales similar to wetland spacing suggest the presence of distal negative feedbacks on patch expansion. These findings support the inference of regular patterning, and are consistent with the presence of local positive feedbacks among hydroperiod, vegetation productivity and bedrock dissolution. These processes are ultimately constrained by distal negative feedbacks, potentially induced by landscape scale limitations on the water volume required to enable this biogeomorphic mechanism. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Blowouts are depressions that occur on coastal dunes, deserts and grasslands. The absence of vegetation in blowouts permits high speed winds to entrain and remove sediment. Whereas much research has examined patterns of wind flow and sediment transport on the stoss slopes and lee of sand dunes, no study has yet investigated the connections between secondary air-flow structures and sediment transport in a blowout where zones of streamline compression, expansion and steering are less clearly delineated. In this study we investigated the variability of sediment flux and its relation to near-surface wind speed and turbulence within a trough blowout during wind flow that was oblique to the axis of the blowout. Wind flow was measured using six, 3-D ultrasonic anemometers while sediment flux by eight sand traps, all operating at 25 Hz. Results demonstrated that sediment flux rates were highly variable throughout the blowout deflation basin, even over short distances (〈 0.5 m). Where flow was steadiest, flux was greatest. Consequently the highest rates of sediment transport were recorded on the erosional wall crest where flow was compressed and accelerated. The strength of correlation between sediment flux and wind parameter improved with an increase in averaging interval, from 10 seconds to 1 minute. At an interval of 10 seconds, however, wind speed correlated best with flux at seven of eight traps, whereas at an interval of 1 minute Turbulent Kinetic Energy (TKE) provided the best correlation with flux at six of the eight traps. Correlation between sediment flux and wind parameters was best in the centre of the blowout and poorest on the erosional wall crest. The evidence from this paper suggests, for the first time, that TKE may be a better predictor of sediment transport at minute scale averaging intervals, particularly over landforms where wind flow is highly turbulent. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Most models of cave formation in limestone that remains near its depositional environment and has not been deeply buried (i.e. eogenetic limestone) invoke dissolution from mixing of waters that have different ionic strengths or have equilibrated with calcite at different p CO 2 values. In eogenetic karst aquifers lacking saline water, mixing of vadose and phreatic waters is thought to form caves. We show here calcite dissolution in a cave in eogenetic limestone occurred due to increases in vadose CO 2 gas concentrations and subsequent dissolution of CO 2 into groundwater, not by mixing dissolution. We collected high-resolution time series measurements (one year) of specific conductivity (SpC), temperature, meteorological data, and synoptic water chemical composition from a water table cave in central Florida (Briar Cave). We found SpC, p CO 2 and calcite undersaturation increased through late summer, when Briar Cave experienced little ventilation by outside air, and decreased through winter, when increased ventilation lowered cave CO 2(g) concentrations. We hypothesize dissolution occurred when water flowed from aquifer regions with low p CO 2 into the cave, which had elevated p CO 2 . Elevated p CO 2 would be promoted by fractures connecting the soil to the water table. Simple geochemical models demonstrate changes in p CO 2 of less than 1% along flow paths are an order of magnitude more efficient at dissolving limestone than mixing of vadose and phreatic water. We conclude that spatially or temporally variable vadose CO 2(g) concentrations are responsible for cave formation because mixing is too slow to generate observed cave sizes in the time available for formation. While this study emphasized dissolution, gas exchange between the atmosphere and karst aquifer vadose zones that is facilitated by conduits likely exerts important controls on other geochemical processes in limestone critical zones by transporting oxygen deep into vadose zones, creating redox boundaries that would not exist in the absence of caves. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Sediment distribution is investigated applying grain size analysis to 279 surface samples from the transitional zone between high mountains (Qilian Shan) and their arid forelands (Hexi Corridor) in northwestern China. Six main sediment types were classified. Medium scale (10 3  m) geomorphological setting is carefully considered as it may play an important role concerning sediment supply and availability. A tripartite distribution of sedimentological landscape units along the mountain to foreland transition is evident. Aeolian sediments, (e.g., loess and dune sands) are widespread. They are used to identify aeolian transport pathways. The mU/fS-ratio (5 – 11 µm / 48 – 70 µm) among primary loess opposes the two grain size fractions being most sensitive to varying accumulation conditions. The first fraction is attributed to long-distance transport in high suspension clouds whereas the latter represents local transport in saltation mode. The ratio shows strong correlation with elevation (R 2  = 0.77). Thus, it indicates a relatively higher far-travelled dust supply in mountainous areas (〉3000 m asl) compared to the foreland. Westerlies' contribution to high mountain loess deposits is considered likely. Hereby, the influence of the geomorphological setting on grain size composition of aeolian sediments becomes apparent: The contribution from distant dust sources is ubiquitous in the study area. However, the far-distance contribution may be reduced by the availability of fine sand provided in low topography settings. Plain foreland areas support fine sand deflation from supplying river beds, allowing the formation of sandy loess in foreland areas and intramontane basins. In contrast, high mountain topography inhibits strong sand deflation into loess deposits. Eastern parts of the Hexi Corridor show higher aeolian sand occurrence. In contrast, the western parts are dominated by gravel gobi surfaces. This is attributed to higher sand supply in eastern parts provided by the Badain Jaran Desert and fluvial storages as sand sources. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The rate of erosion of hillside gullies depends both on gully flow characteristics and the resistance offered by the gully soil profile to erosion. This paper describes a method for quantifying a physically-based resistance measure, illustrated by application to a gully feeding sediment into the Bremer River, SE Queensland, Australia. The dynamics of discharge down the gully during runoff events is the driver of erosion, but this was unknown. A new method is described whereby this unmeasured flow can be estimated using data on rainfall rate and river gauge monitoring. The data collected on the gully was the increase in dimensions and volume (and so soil loss) over a two year period. This information was obtained from a digital elevation model (DEM) of the catchment, derived from Light Detection and Ranging (LiDAR) observations made at either end of the two year period. The soil profile resistance characteristic evaluated is the energy required to erode a unit mass of soil from the gully walls, a physically-defined parameter, J, present in flow-driven erosion theory, which was adapted and applied to predict soil loss from the Bremer River gully. The value of J was evaluated by equating predicted to measured gully soil loss over the two year period using two alternative descriptions of gully cross-section. Firstly a realistic gully shape description was used, made possible by LiDAR data, yielding J  = 405.5 J/kg. Secondly, in order to allow use of more widely-available aerial photography for such studies, the simplifying assumption of a semi-circular gully shape was made, yielding J  = 455 J/kg. Allowing a +/-30% error in estimated effective runoff rate for this ungauged gully, the estimated J value would have an uncertainty of +1%/-7% using the actual gully geometry. The assumptions made in estimating J are discussed, and possible applications of this information listed. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Gully delineation is a critical aspect of accurately determining soil losses but associated methodologies are rarely detailed. Here, we describe a new gully mapping method, the normalized topographic method (NorToM), based on processing digital elevation model data, and we assess associated errors when it is applied over a range of geomorphological scales. The NorToM is underpinned by two gully detection variables (normalized slope and elevation) calculated over local windows of prescribed size, and a group of filtering variables. For four study sites, DEMs of gullies were obtained using field and airborne photo-reconstruction and evaluated using total station and differential-GPS survey. NorToM provided accurate areal and volume estimates at the individual gully scale but differences increased at the larger gully system and gully network scales. We were able to identify optimal parameters for using the NorToM approach and so confirm that is represents a useful scale-independent means of gully mapping that is likely to be valid in other environments. Its main limitations are that the normalization process might be time-consuming at regional scales and the need for a fixed window size when applied to landforms with extreme variations in dimensions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Barbara Kennedy has left only a small body of work, consisting principally of eight research papers, 9 commentaries and two books. Its extent belies its importance. Read systematically, the work represents a sustained and important critique of the direction taken by mainstream geomorphology since the process-focused reorientation of the mid-twentieth century. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Numerous morphological changes can occur where two channels of distinct sediment and flow regimes meet, including abrupt shifts in channel slope, cross-sectional area, planform style, and bed sediment size along the receiving channel. Along the Rio Chama between El Vado and Abiquiu Dams, northern New Mexico, arroyo tributaries intermittently deliver sediment from erodible sandstone and shale canyon walls to the mainstem channel. Much of the tributary activity occurs in flash floods and debris flows during summer thunderstorms, which often load the channel with sand and deposit coarser material at the mainstem confluence. In contrast, mainstem channel flow is dominated by snowmelt runoff. To examine tributary controls, we systematically collected cross-section elevation and bed sediment data up and downstream of 26 tributary confluences along a 17 km reach. Data from 203 cross-sections were used to build a one-dimensional hydraulic model for comparing estimated channel parameters at bankfull and low-flow conditions at these sites As compared to intermediate reaches, confluences primarily impact gradient and bed sediment size, reducing both parameters upstream of confluences and increasing them downstream. Cross-section area is also slightly elevated above tributary confluences and reduced below. Major shifts in slope and bed sediment size at confluences appear to drive variations in sediment entrainment and transport capacity and the relative storage of sand along the channel bed. The data were analyzed and compared to models of channel organization based on lateral inputs, such as the Network Variance Model (Benda et al., 2004) and the Sediment Link Concept (Rice and Church, 1998). At a larger scale, hillslope-channel coupling increases in the downstream third of the study reach, where the canyon narrows, resulting in steeper slopes and more continuous coarse bed material along the mainstem, and thus, limiting the contrast with tributary confluences. However, channel form and sediment characteristics are highly variable along the study reach, reflecting variations in the size and volume of sediment inputs related to the surface geology in tributary watersheds, morphology of the Rio Chama at the junction (i.e., bends, confinement), and the relative magnitude and location of past depositional events. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Pacific salmon are biogeomorphic agents shown to induce positive feedbacks on their natal watersheds. However, the literature documenting their ecological effects on in-stream natal environments is more divisive. The disturbance salmon create during redd construction has the potential to reduce stream productivity. The pulse of salmon organic matter (SOM) and marine derived nutrients (MDN) released during carcass decay has been reported as either stimulating in-stream productivity or having no local effect. To evaluate the ecological costs and benefits of salmon spawning events, MDN delivery and storage processes need to be identified and quantified. A simulation was conducted in three flow-through flumes (2 m*2 m*30 m) over a 33-day period (consisting of 15 baseline, four MDN exposure, and 14 post-exposure days) to assess near-field sediment and organic matter dynamics during active and post-spawn simulations. The objective of the study was to measure changes in the amounts and particle sizes of suspended and gravel-stored fine sediment, in order to elucidate the process and significance of SOM recruitment to the gravel bed via sedimentation. Gravel beds in all flumes were enriched with SOM following treatments but the response was highest in the active spawn simulation. The more effective delivery in the active spawn simulation was attributed to its higher inorganic sediment concentration, which is known to enhance floc formation. Although the active spawn simulation delivered more SOM to the gravel bed, the post-spawn phase may be equally important to natural streams because its decay phase is longer than the active spawn and may consequently provide SOM to the streambed as long as carcasses remain in-stream. The delivery, and potential retention, of SOM to spawning streambeds and the intergravel environment may be particularly important for interior streams, which experience low flow conditions during the spawning phase and accordingly have the potential for hyporheic nutrient recruitment and storage. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This work investigates wood dynamics in braided streams through physical modelling in a mobile bed laboratory flume, with the specific objective to characterise wood storage and turnover as a function of wood input rate and of wood element type. Three parallel channels (1.7 m wide, 10 m long) filled with uniform sand were used to reproduce braided networks with constant water discharge and sediment feeding. Wood dowels with and without simplified root wads were regularly added at the upstream end of each flume at different input rates, with a 1:2:3 ratio between the three flumes. Temporal evolution of wood deposition patterns and remobilisation rates were monitored by series of vertical images that permitted the recognition of individual logs. Results show that wood tends to disperse in generally small accumulations (〈5 logs), with higher spatial density on top of sediment bars, and is frequently remobilised due to the intense morphological changes. The amount of wood stored in the channel depends on log input rate through a non-linear relationship, and input rates exceeding approximately 100 logs/hr determine a sharp change in wood dynamics, with higher storage volume and augmented formation of large jams (〉10 elements) that are less prone to remobilisation. Presence of root wads seems to play a minor role on wood deposition, but it reduces the average travel distance of logs. Turnover rates of logs were similar in the three flumes, independently of wood input rate and largely resembling the turnover rate of exposed bars. For the simulated conditions, significant effects of wood on bed morphology were not observed, suggesting that interactions with fine sediments and living vegetation are crucial to form large, stable wood jams able to bring about relevant morphological changes. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The sediment flux from a catchment is driven by tectonics and climate but is moderated by the geomorphic response of the landscape system to changes in these two boundary conditions. Consequently, catchment response time and the non-linear behavior of landscapes in response to boundary condition change control the downstream propagation of climatic or tectonic perturbations from catchments to neighboring basins. In order to investigate the impact of catchment response time on sediment flux, we integrated a spatially-lumped numerical model PaCMod (Forzoni et al., 2013), with new routines simulating the evolution of landscape morphology and erosion rates under tectonic and climatic forcing. We subsequently applied the model to reconstruct the sediment flux from a tectonically perturbed catchment in Central Italy. Finally, we coupled our model to DeltaSim, a process-response model simulating fluvio-deltaic stratigraphy, and investigated the impact of catchment response time on stratigraphy, using both synthetic scenarios and a real world system (Fucino Basin, Central Italy). Our results demonstrate that the differential response of geomorphic elements to tectonic and climatic changes induces a complex sediment flux signal, and produces characteristic stratigraphic architectures and shoreline trajectories. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Monitoring large wood (LW: width 〈10 cm, length 〈1 m) in transport within rivers is a necessary next step in the development and refinement of wood budgets and is essential to a better understanding of basin-wide controls and patterns of LW flux and loads. Monitoring LW transport with coarse interval (〉1 min) timelapse photography enables the deployment of monitoring cameras at large spatial and long temporal scales. Although less precise than continuous sampling with video, it allows investigators to answer broad questions about basin connectivity, compare drainages and years, and identify transport relationships and thresholds. This paper describes methods to: (i) construct fluvial wood flux curves, (ii) analyze the effects of sample interval lengths on transport estimates, and (iii) estimate total wood loads within a specified time period using coarse interval timelapse photography. Applying these methods to the Slave River, a large volume (10 3 cms), low gradient (10 −2  m/km) river in the subarctic (60° N), yielded the following results. A threshold relationship for wood mobility was located around 4500 cms. More wood is transported on the rising limb of the hydrograph because wood flux rapidly declines on the falling limb. Five- and 10-minute sampling intervals provided unbiased equal variance estimates of 1-minute sampling, whereas 15-minute intervals were biased towards underestimation by 5-6%, possibly due to periodicity in wood flux. Total LW loads estimated from the 1-minute dataset and adjusted for a 15% mis-detection rate from July 13th through Aug 13th are: 1600 ± 200 # pieces, 600 ± 200 m 3 and on the order of 1.3 × 10 5  kg carbon. The total wood load for the entire summer season is probably at least double this estimate because only the second half of the summer flows were monitored and a large early summer peak freshet was missed. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Accurate mapping of water surface boundaries in rivers is an important step for monitoring of water stages, estimating discharge, flood extent, and geomorphic response to changing hydrologic conditions, and assessing riverine habitat. Nonetheless, it is a challenging task in spatially and spectrally heterogeneous river environments, commonly characterized by high spatiotemporal variations in morphology, bed material, and bank cover. In this study, we investigate the influence of channel morphology and bank-cover type on the delineation of water surface boundaries in rivers using high-spatial resolution passive remote sensing and a template-matching (an object-based) algorithm, and compare its efficacy with that of Support Vector Machine (SVM) (a pixel-based) algorithm. We perform a detailed quantitative evaluation of boundary-delineation accuracy, using spatially explicit error maps, in tandem with the spatial maps of geomorphic and bank-cover classes. Results show that template matching is more successful than SVM in delineating water surface boundaries in river sections with spatially challenging geomorphic landforms (e.g., sediment bar structures, partially submerged sediment deposits) and shallow water conditions. However, overall delineation accuracy by SVM is higher than that of template matching (without iterative hierarchical learning). Vegetation and water indices, especially when combined with texture information, improve the accuracy for template matching, for example, in river sections with overhanging trees and shadows—the two most problematic conditions in water surface-boundary delineation. By identifying the influence of channel morphology and bank-cover type on water surface-boundary mapping, this study helps determine river sections with higher uncertainty in delineation. In turn, the most suitable methods and data sets can be selectively utilized to improve geomorphic/hydraulic characterization. The methodology developed here can also be applied to similar studies on other geomorphic landforms including floodplains, wetlands, lakes, and coastlines. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The NE margin of the Tibetan Plateau, as a particularly important area to understand the mechanism of plateau formation, is characterized by large transpressional arcuate faults. There is debate on the amount of Quaternary sinistral displacement on the major Haiyuan Fault. Previously unrecognized systemic asymmetrical valleys have developed between the Haiyuan and Xiangshan faults. Southeast tilting and sinistral displacement on the NE side of the Haiyuan Fault resulted in SE migration of large rivers and asymmetrical widening of their valleys, leaving a systematic distribution of tilted strath terraces along the their NW sides. Where asymmetrical widening created by tilting kept pace with sinistral displacement, rivers have not been deflected, and the increase in valley width downstream from the fault should equate to total lateral displacement since river formation (e.g. Yuan River, a 7 km asymmetrical valley with a c. 2.2 Ma paleomagnetic age). Where river deflection and asymmetrical valley growth are coeval, valley width is less than total horizontal displacement (e.g. Hebao River, a c. 2.1 km asymmetrical valley with c. 2 km deflection). All rivers north of the Haiyuan Fault converge to cut across the Xiangshan Mountains as a gorge. Northeast thrusting of the upthrown side of the Xiangshan Fault has resulted in degradation and related strath terrace formation as the valleys asymmetrically widened. A probable earthquake-induced landslide caused by movement on the Xiangshan Fault in latest Pleistocene blocked the gorge causing aggradation along all rivers and their tributaries. Deposition terraces were formed after the landslide dam was breached. Together with previous research on the Xiangshan Fault, it is concluded that there has been c.7 km of Quaternary sinistral displacement on the Haiyuan and Xiangshan faults along the NE margin of the Tibetan Plateau since the formation of rivers that intersect them. This article is protected by copyright. All rights reserved.

Description: ABSTRACT We present new data about the morphological and stratigraphic evolution and the rates of fluvial denudation of the Tavoliere di Puglia plain, a low-relief landscape representing the northernmost sector of the Pliocene-Pleistocene foredeep of the southern Apennines. The study area is located between the easternmost part of the southern Apennine chain and the Gargano promontory and it is characterized by several orders of terraced fluvial deposits, disconformably overlying lower Pleistocene marine clay and organized in a staircase geometry, which recorded the emersion and the long-term incision history of this sector since mid-Pleistocene times. We used the spatial and altimetric distribution of several orders of middle to late Pleistocene fluvial terraces in order to perform paleotopographic reconstruction and GIS-aided eroded volumes estimates. Then, we estimated denudation rates on the basis of the terraces chronostratigraphy, supported by published OSL and AAR dating. Middle to upper Pleistocene denudation rates estimated by means of such an approach are slightly lower than 0.1 mm*yr -1 , in good agreement with short-term data coming from direct and indirect evaluation of suspended sediment yield. The analysis of longitudinal river profiles using the stream power erosion model provided additional information on the incision rates of the studied area. Middle to late Quaternary uplift rates (about 0.15 mm*yr -1 ), calculated on the basis of the elevation above sea level of marine deposits outcropping in the easternmost sector of the study area, are quite similar to the erosion rates average value, thus suggesting a steady-state fluvial incision. The approach adopted in this work has demonstrated that erosion rates traditionally obtained by quantitative geomorphic analysis and k sn estimations can be successfully integrated to quantify rates of tectonic or geomorphological processes of a landscape approaching steady-state equilibrium. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Glacier retreat leads to changes in channel pattern during deglaciation, in response to changing water, sediment and base level controls. Recent ongoing retreat at Skaftafellsjökull, Iceland (c. 50 m per year since 1998) has resulted in the formation of a sequence of river terraces, and several changes in river channel pattern. This paper compares widely used models of river channel pattern against the changes observed at Skaftafellsjökull. Doing this reveals the role of topographic forcing in determining proglacial channel pattern, whilst examining the predictive power and limitations of the various approaches to classifying river channels. Topography was found to play a large role in determining channel pattern in proglacial environments for two reasons: firstly, glacier retreat forces rivers to flow through confined moraine reaches. In these reaches, channels which theory predicts should be braided are forced to adopt a single channel. Secondly, proximal incision of proglacial rivers, accompanied by downstream aggradation, leads to changes in slope which force the river to cross channel pattern thresholds. The findings of this work indicate that in the short term, the majority of channel pattern change in proglacial rivers is due to topographic forcing, and that changes due to changing hydrology and sediment supply are initially relatively minor, although likely to increase in significance as deglaciation progresses. These findings have implications for palaeohydraulic studies, where changes in proglacial channel pattern are frequently interpreted as being due to changes in water or sediment supply. This paper shows that channel pattern can change at timescales faster than hydrological or sediment budget changes usually occur, in association with relatively minor changes in glacier mass balance.This article is protected by copyright. All rights reserved.

Description: ABSTRACT The paper focusses on connectivity in the context of infiltration-excess overland flow and its integrated response as slope-base overland flow hydrographs. Overland flow is simulated on a sloping surface with some minor topographic expression and spatially differing infiltration rates. In each cell of a 128 × 28 grid, water from upslope is combined with incident rainfall to generate local overland flow, which is stochastically routed downslope, partitioning the flow between downslope neighbours. Simulations show the evolution of connectivity during simple storms. As a first approximation, total storm runoff is similar everywhere, discharge increasing proportionally with drainage area. Moderate differences in plan topography appear to have only a second order impact on hydrograph form and runoff amount. Total storm response is expressed as total runoff, runoff coefficient or total volume infiltrated; each plotted against total storm rainfall, and allowing variations in average gradient, overland flow roughness, infiltration rate and storm duration. A one-parameter algebraic expression is proposed that fits simulation results for total runoff, has appropriate asymptotic behaviour and responds rationally to the variables tested. Slope length is seen to influence connectivity, expressed as a scale distance that increases with storm magnitude and can be explicitly incorporated into the expression to indicate runoff response to simple events as a function of storm size, storm duration, slope length and gradient. The model has also been applied to a 10-year rainfall record, using both hourly and daily time steps, and the implications explored for coarser scale models. Initial trails incorporating erosion, continuously update topography and suggest that successive storms produce an initial increase in erosion as rilling develops, while runoff totals are only slightly modified. Other factors not yet considered include the dynamics of soil crusting and vegetation growth. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Earth surface processes (ESPs) drive landscape development and ecosystem processes in high–latitude regions by creating spatially heterogeneous abiotic and biotic conditions. Ongoing global change may potentially alter the activity of ESPs through feedback on ground conditions, vegetation and the carbon cycle. Consequently, accurate modelling of ESPs is important for improving understanding of the current and future distributions of these processes. The aims of this study were to: 1) integrate climate and multiple local predictors to develop realistic ensemble models for the four key ESPs occurring at high latitudes (slope processes, cryoturbation, nivation and palsa mires) based on the outputs of ten modern statistical techniques; 2) test whether models of ESPs are improved by incorporating topography, soil and vegetation predictors to climate–only models; and 3) examine the relative importance of these variables in a multivariate setting. Overall, the models showed high transferability with the mean area under curve of a receiver operating characteristics (AUC) ranging from 0.83 to 0.96 and true skill statistics (TSS) from 0.52 to 0.87 for the most complex models. Even though the analyses highlighted the importance of the climate variables as the most influential predictors, three out of four models benefitted from the inclusion of local predictors. We conclude that disregarding local topography and soil conditions in spatial models of ESPs may cause a significant source of error in geomorphological distribution models. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Anthropogenic disturbance often increases surface erosion and this may have potential detrimental effects on downstream aquatic resources. Foot trails are often overlooked as they represent only a small fragment of the landscape, yet they can be important sources of sediment, particularly in pristine areas. The trail network above East End Bay on the island of St. Croix in the U.S. Virgin Islands is the sole anthropogenic source of terrestrial sediment in the area. Concern over the potential for trail erosion to stress nearshore coral reefs of the East End Marine Park led to trail reconstruction and restoration efforts. The objectives of this study were to: (1) quantify trail erosion rates; (2) identify key factors controlling erosion rates; and (3) develop an empirical trail erosion model. Sediment production was measured from twelve trail segments with sediment traps from November 2009 to October 2011. Annual trail erosion rates ranged from 0.6 to 81 Mg ha -1  yr -1 . The lower values were from abandoned trails with a dense vegetation cover, while the highest rates were associated with devegetated trails immediately following construction or restoration. Trail erosion was a function of rainfall, slope, and vegetation cover density raised to the negative 1.7 th power. Annual trail erosion rates were one- to three-orders of magnitude higher than measured surface erosion rates on undisturbed hillslopes. The absence of rills or gullies suggests that traditional parametric or repeated transect monitoring commonly used to assess trail erosion may greatly underestimate actual sediment production rates. The new empirical trail erosion model serves as a tool to assess the effects of trail construction and restoration activities in the generation of sediment from small catchments in East End Bay and in other similar settings. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This study explores factors that affect road surface erosion in a small watershed on the Loess Plateau. GPS-assisted field surveys and geographical information system methods were applied. The results show that road surface rills in the watershed are more easily formed on main roads, which are disturbed by intensive human activities. Secondary unpaved road networks occupied the largest road surface area and contributed 49% of the total road surface rill volumes. Spatial analysis reveals that roads near residential areas or leading to other human-disturbed land use types are at high risk of soil loss. In each road segment, slope gradient, road segment length and drainage area have impacts on surface rill formation and development. Among these factors, slope gradients have been verified as a controlling factor of rill erosion intensification. Both road segment length (R = 0.83, N = 82) and drainage area (R = 0.72 for road segment and 0.76 for upslope drainage areas, N = 82) significantly influence total road surface rill volumes. The interaction variable of road segment length multiplied by slope is more closely correlated with road segment soil loss than that of the independent variables alone. Linear equations composed of slope gradient, road segment length and upslope drainage area are proposed. The new equation performs much better at predicting surface soil loss from secondary road segments compared with the previous models, which have not considered upslope drainage areas. The relationships and equations from this study will be helpful for road erosion evaluation in a small watershed of the study area. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The Mekong Basin in Southeast Asia is facing rapid development, impacting its hydrology and sediment dynamics. Although the understanding of the sediment transport rates in the Mekong is gradually growing, the sediment dynamics in the lower Mekong floodplains (downstream from Kratie) are poorly understood. The aim of this study is to conduct an analysis to increase the understanding of the sediment dynamics at the Chaktomuk confluence of the Mekong River, and the Tonle Sap River in the Lower Mekong River in Cambodia. This study is based on the data from a detailed field survey over the three hydrological years (May 2008 - April 2011) at the two sites (the Mekong mainstream and the Tonle Sap River) at the Chaktomuk confluence. We further compared the sediment fluxes at Chaktomuk to an upstream station (i.e. Mukdahan) with longer time series. Inflow sediment load towards the lake was lower than that of the outflow, with a ratio on average of 84%. Although annually only a small amount of sediment load from the Tonle Sap contributes to the delta (less than 15%), its share is substantial during the February-April period. The annual sediment load transport from the confluence to the delta in 2009 and 2010 accounted for 54 and 50 Mt, respectively. This was on average only 55% of the sediment fluxes measured at Mukdahan, more upstream station. And when compared to sediment loads further downstream at Cambodia-Vietnam border, we found that the suspended sediment flux continued to decline towards the South China Sea. Our findings thus indicate that the sediment load to the South China Sea is much lower than the previous estimate 150-160 Mt/yr. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Rock slopes in a range of environments are among the landscape elements most sensitive to climate change, the latter affecting rock mass properties, altering slope boundary conditions, and changing geosystem configurations. Major climate-dependent influences promoting destabilisation include stress redistribution with changing glacial ice extents, degradation of mountain permafrost, altered slope hydrology and weathering environments, loading and unloading due to deposition and erosion, and changes in the spectrum of magnitude and frequency of driving forces. In steep bedrock terrain, erosional processes control slope morphology by modulating rates of: (i) weathering in response to climate and pre-disposition, (ii) rock slope retreat in response to magnitude and frequency of detachment, and (iii) channel incision or valley infilling in response to variable sediment supply. Modelling landscape evolution and anticipating natural hazards in these environments thus requires deeper insights into the processes driving rock slope instability and erosion. This special issue emphasizes new understanding of rock slope processes through a collection of manuscripts at the forefront of research in the field. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Restoration projects in the United States typically have among the stated goals those of increasing channel stability and sediment storage within the reach. Increased interest in ecologically based restoration techniques has led to the consideration of introducing beavers to degraded channels with the hope that the construction of beaver dams will aggrade the channel. Most research on beaver dam modification to channels has focused on the long term effects of beavers on the landscape with data primarily from rivers in the western United States. This study illustrated that a role exists for beavers in the restoration of fine-grained, low gradient channels. A channel on the Atlantic Coastal Plain was analyzed before, during, and after beaver dams were constructed to evaluate the lasting impact of the beaver on channel morphology. The channel was actively evolving in a former reservoir area upstream a dam break. Colonization by the beaver focused the flow into the channel, allowed for deposition along the channel banks, and reduced the channel width such that when the beaver dams were destroyed in a flood, there was no channel migration and net sediment storage in the reach had increased. However, the majority of the deposition occurred at the channel banks, narrowing the channel width, while the channel incised between sequential beaver dams. The study indicated that where channels are unstable laterally and bank erosion is a concern, the introduction of beavers can be a useful restoration tool. However, because of the likelihood of increased channel bed erosion in a reach with multiple beaver dams, they may not be the best solution where aggradation of an incised channel bed is the desired result. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Many urban rivers receive significant inputs of metal-contaminated sediments from their catchments. Restoration of urban rivers often creates increased slack water areas and in-channel vegetation growth where these metal-contaminated sediments may accumulate. Quantifying the accumulation and retention of these sediments by in-channel vegetation in urban rivers is of importance in terms of the planning and management of urban river restoration schemes and compliance with the Water Framework Directive. This paper investigates sediment properties at four sites across three rivers within Greater London to assess the degree to which contaminated sediments are being retained. Within paired restored and unrestored reaches at each site, four different bed sediment patch types (exposed unvegetated gravel, sand, and silt-clay (termed ‘fine’) sediments, and in-channel vegetated sediments) were sampled and analysed for a range of metals and sediment characteristics. Many samples were found to exceed Environment Agency guidelines for Cu, Pb and Zn and Dutch Intervention Values for Cu and Zn. At all sites, sediments accumulating around in-channel vegetation were similar in calibre and composition to exposed unvegetated fine sediments. Both bed sediment types contained high concentrations of pseudo-total and acetic acid extractable metal concentrations, potentially due to elevated organic matter and silt/clay content, as these are important sorbtion phases for metals. This implies that the changed sediment supply and hydraulic conditions associated with river restoration may lead to enhanced retention of contaminated fine sediments, particularly around emergent plants, frequently leading to the development of submerged and emergent landforms and potential river channel adjustments. High pseudo-total metal concentrations were also found in gravel bed sediments, probably associated with Fe and Mn oxyhydroxides and discrete anthropogenic metal-rich particles. These results highlight the importance of understanding the potential effects of urban river restoration upon sediment availability and channel hydraulics and consequent impacts upon sediment contaminant dynamics and storage. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The important role of vegetation in adding cohesion and stabilizing streambanks has been widely recognized in several aspects of fluvial geomorphology, including stream restoration and studies of long-term channel change. Changes in planform between braided, meandering, and anabranching forms have been attributed to the impacts of vegetation on hydraulic roughness and bank stability. However, these studies focus either on flume studies where analog vegetation is used, or case studies featuring one species, which is commonly invasive. We present functional differences of bank-stabilizing root characteristics and added cohesion, with vegetation categorized as woody and non-woody and by the vegetation groups of trees, shrubs, graminoids, and forbs. We analyzed root morphology and tensile strength of 14 species common to riparian areas in the southern Rocky Mountains, in field sites along streambanks in the montane and subalpine zones of the Colorado Front Range. Using the vegetation root component (RipRoot) of a physically-based bank stability model (BSTEM), we estimated the added cohesion for various sediment textures with the addition of each of the 14 species. Significant differences exist between woody and non-woody vegetation and between the four vegetation categories with respect to the coefficient of the root tensile strength curve, lateral root extent, and maximum root diameter. Woody vegetation (trees and shrubs) have higher values of all three parameters than non-woody species. Tree roots add significantly more cohesion to streambanks than forb roots. Additionally, rhizomes may play an important role in determining the reach-scale effects of roots on bank stabilization. Differences in root characteristics and added cohesion among vegetation categories have several important implications, including determining the likelihood of planform change, developing guidelines for the use of bank-stabilizing vegetation, and linking the effect of vegetation to geomorphic structure that can benefit ecosystem functioning. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The continuous feedbacks among tectonics, surface processes, and climate are reflected in the distribution of catchments on active mountain ranges. Previous studies have shown a regularity of valley spacing across mountain ranges worldwide, but the origin of this geomorphological feature is currently not well known. In this work, we use a landscape evolution model to investigate the process of fluvial network organization and the evolution of regular ridge-and-valley patterns on simulated mountain ranges. In particular, we investigate the behavior of such patterns when subjected to a perturbation in landscape processes from a previous steady state, resulting from a sudden variation in the pattern of bedrock erodibility, from homogeneous to a gradient. We analyze the time evolution of the mean ratio λ' between the linear spacing of adjacent valleys and the half width of the mountain range. We show how a valley spacing ratio of ~0.5 is first achieved at steady state under uniform bedrock erodibility. After applying the gradient of bedrock erodibility across the landscape, we observe that λ' first increases and then decreases to a new steady-state value that is smaller than the original value. A detailed analysis of the simulations, through observations of surface “snapshots” at repeated time intervals, allows to gain some insight into the mechanisms governing this fluvial network reorganization process, driven by the migration of the main divide toward the side characterized by lower bedrock erodibility. On both sides of the range the new steady-state valley spacing is obtained through mechanisms of catchment reorganization and competition between adjacent fluvial networks. In particular, catchment reorganization is characterized by 1) the growth of smaller catchments between shrinking larger catchments on the side with lower erodibility and 2) the growth of larger catchments on the side with higher erodibility. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The assessment of the dominant flow type on alluvial fans usually refers to two categories: debris-flow fans (i.e., sediment gravity flows) and fluvial fans (i.e., fluid gravity flows). Here we report the results of combined morphometric, stratigraphic and sedimentological approaches which suggest that hyperconcentrated flows, a transitional process rheologically distinct from debris flows and floods and sometimes referred to as debris floods, mud floods, or transitional debris flows, are the dominant fan building process in Eastern Canada. These flows produce transitional facies between those of debris flows which consist of a cohesive matrix-supported diamicton, and those of river flows which display more distinct stratification. The size of the blocks in the channels and the abrasion scars at the base of several trees attest to the high transport capacity of these flows. The fan channels are routed according to various obstacles comprised primarily of woody debris that impede sediment transit. However, these conditions of sediment storage are combined with readily available sediment due to the friable nature of the local lithology. Tree-ring analysis allowed the reconstruction of eight hydrogeomorphic events which are characterised by a return period of 9.25 years for the period 1934–2008, although most of the analyzed events occurred after 1970. Historical weather data analysis indicates that they were related to rare hydrometeorological events at regional and local scales. This evidence led to the elaboration of weather scenarios likely responsible for triggering flows on the fan. According to these scenarios, two distinct hydrologic regimes emerge: the torrential rainfall regime and the nival regime related to snowmelt processes. Hydrogeomorphic processes occurring in a cold-temperate climate, and particularly on small forested alluvial fans of northeastern North America, should receive more attention from land managers given the hazard they represent, as well as because of their sensitivity to various meteorological parameters. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Sound knowledge of the spatial and temporal patterns of rockfalls is fundamental for the management of this very common hazard in mountain environments. Process-based, three-dimensional simulation models are nowadays capable to reproduce the spatial distribution of rockfall occurrences with reasonable accuracy through the simulation of numerous individual trajectories on highly-resolved digital terrain models. At the same time, however, simulation models typically fail to quantify the “real” frequency of rockfalls (in terms of return intervals). The analysis of impact scars on trees, in contrast, yields real rockfall frequencies, but trees may not be present at the location of interest and rare trajectories may not necessarily be captured due to the limited age of forest stands. In this article, we demonstrate that the coupling of modeling with tree-ring techniques may overcome the limitations inherent to both approaches. Based on the analysis of 64 cells (40 × 40 m) of a rockfall slope located above a 1631-m long road section in the Swiss Alps, we illustrate results from 488 rockfalls detected in 1260 trees. We illustrate that tree impact data cannot only be used (i) to reconstruct the real frequency of rockfalls for individual cells, but that they also serve (ii) the calibration of the rockfall model Rockyfor3D, as well as (iii) the transformation of simulated trajectories into real frequencies. Calibrated simulation results are in good agreement with real rockfall frequencies and exhibit significant differences in rockfall activity between the cells (zones) along the road section. Real frequencies, expressed as rock passages per meter road section, also enable quantification and direct comparison of the hazard potential between the zones. The contribution provides an approach for hazard zoning procedures that complements traditional methods with a quantification of rockfall frequencies in terms of return intervals through a systematic inclusion of impact records in trees. This article is protected by copyright. All rights reserved.

Description: ABSTRACT A mathematical model was used to examine the effect of Pliocene and Quaternary changes in sea level on the development of tectonically active and inactive rock coasts. The model calculated rates of mechanical wave erosion according to such factors as the deep water wave regime, bottom topography and surface roughness, and the resistance of the rocks. Subaerial terraces were truncated or eliminated by subsequent terrace formation at lower elevations, especially on steeply sloping landmasses experiencing slow rates of uplift. Submarine terraces formed during glacial stillstands were best preserved when rapid subsidence quickly carried them below the level of wave action. On slowly subsiding landmasses, submarine terraces formed during interglacials and glacial periods experienced repeated erosional modification during subsequent periods of rising and falling sea level and were generally less distinctive. On rapidly rising or subsiding (〉5 mm yr -1 ) landmasses, terraces that formed during interglacial stages alternated, above and below present sea level, with terraces formed during glacial stages. Despite some differences in terrace occurrence and elevational distribution, it may be difficult to distinguish profiles cut during accelerating or decelerating uplift. The amount of erosion during sea level oscillations increases with oscillation amplitude and the larger oscillations in the middle to late Quaternary were therefore more conducive to erosion than the smaller oscillations of the Pliocene and early Quaternary. The effect of oscillation amplitude may have been countered during the earlier stages of profile development, however, by steeper submarine gradients and reduced rates of wave attenuation. This article is protected by copyright. All rights reserved.

Description: The action of organisms in shaping landforms is increasingly recognized; the field of biogeomorphology and the conceptual framework of ecosystem engineering have arisen in response to the need for integrated studies of the interactions between biotic and abiotic components of landscapes. Pathways by which organisms influence landscape development may be complex. For example, primary change initiated by one biotic element may initiate a cascade of other changes that eventually produce a significant landscape change. Mound-like landforms in North America and southern Africa are widely cited examples of biogenic structures, yet there is considerable controversy regarding the processes responsible for their formation. Heuweltjies (Afrikaans for little hills ) are circular mounds ranging from 10-30 m diameter and 0.5-2 m height and are widespread in western South Africa. Colonies of the termite ( Microhodotermes viator ) are typically associated with heuweltjies and some investigators have attributed heuweltjie formation to the direct action of termites in redistributing earthen materials. However, rather than being directly responsible in this way, termites simply creates nutrient-rich islands, which support denser vegetation, thereby inducing the localized accretion of aeolian sediments and upward growth of mounds. Contrasting soil features in heuweltjies in one locale indicate these processes have occurred throughout the late Quaternary. Geographic variation in sizes of mounds is explained in part by the local availability of sediments that can be mobilized and redistributed by the wind. Recognition of the operation of aeolian processes in the formation of heuweltjies has important implications for conservation. Any land use that diminishes the sediment-trapping effect of vegetation on heuweltjies truncates the very process by which new aeolian materials can accrue and may promote irreversible erosion and landscape degradation. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Because cuspate coastlines are especially sensitive to changes in wave climate, they serve as potential indicators of initial responses to changing wave conditions. Previous work demonstrates that Cape Hatteras and Cape Lookout, NC, which are largely unaffected by shoreline stabilization efforts, have become increasingly asymmetric over the past 30 years, consistent with model predictions for coastline response to increases in Atlantic Ocean summer wave heights and resulting changes in the distribution of wave-approach angles. Historic and recent shoreline change observations for Cape Fear, North Carolina, and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment, produce comparable differences in shoreline change rates in response to changes in wave climate. Results suggest that the effect of beach nourishment is to compensate for—and therefore to mask—natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone. Therefore, this case study suggests that the effects of wave climate change on human-modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities. Similar analyses of cuspate features in areas where the change in wave climate is less pronounced (i.e., Fishing Point, Maryland/Virginia) and where local geology appears to exert control on coastline shape (i.e., Cape Canaveral, Florida), suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave-dominated coastlines where the change in wave climate has been most pronounced. However, if hurricane-generated wave heights continue to increase, large-scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger-scale coastline shape comes into equilibrium with changing wave conditions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Low altitude flights by a micro-drone were made in 2012 and 2013 over two boulder beaches in northwestern Spain. Geographical information system software was used to map the data. Boulder outlines from the first flight were recorded on 4796 clasts at Laxe Brava and 2508 clasts at Oia. Changes in location were identified by overlaying these outlines on the 2013 images. About 17.5 % of the boulders (mean surface area 0.32 m 2 ) moved at Laxe Brava and about 53 % (mean surface area 0.23 m 2 ) at Oia. Most movement on both beaches was between the mid-tide to about 2 m above the high tidal level. The location and elevation of the highest points were also recorded on the 2012 images on 4093 boulders at Laxe Brava and 3324 boulders at Oia. These elevations were compared with the elevations at the same locations in 2013. The occurrence and scale of the elevational changes were generally consistent with changes in the boulder outlines. The study confirmed that boulder beaches can be cheaply and effectively monitored using high resolution, micro-drone technology. This article is protected by copyright. All rights reserved.

Description: ABSTRACT A wide range of sedimentological and geomorphological field research depends on the availability of accurate and detailed depositional age models. Although exposure dating techniques such as cosmogenic nuclide and luminescence dating are now widely available, they remain expensive and time-consuming, and this frequently limits the density of age constraints and the resolutions of age models for many study areas. We present a simple and effective, field-based approach for extending and correlating existing age models to un-dated surfaces. In Owens Valley, California, we make use of detailed beryllium-10 ( 10 Be) chronologies reported for four different alluvial fan systems, to precisely calibrate the rate at which weathering fractures are enlarged in granitic surface boulders. We show that these fractures have widened at a time-integrated rate of 1.05 ± 0.03 mm ka −1 for at least 140 ka at this location, and this relationship can be represented by a linear regression that makes them ideal chronometers for surface dating. Our analysis offers a new approach to refining the uncertainties of both surface erosion rate and cosmogenic age estimates at this location. Ultimately, we integrate our observations to devise a robust age calibration for clast fracture widths in Owens Valley, and we demonstrate its application by estimating the ages of 27 additional local fan surfaces. We present an updated and extended stratigraphy for eight Sierra Nevada fan systems in total, with exceptional age control. This novel approach to dating sedimentary surfaces is inexpensive and easily applied in the field, and has the potential to significantly increase the temporal and spatial density of age constraints available for a particular study area. Copyright © 2014 John Wiley & Sons, Ltd.

Description: ABSTRACT Glacier recessions caused by climate change may uncover proglacial lakes that form important sedimentation basins regulating the downstream sediment delivery. The impact of modern proglacial lakes on fluvial sediment transport from three different Norwegian glaciers: Nigardsbreen, Engabreen and Tunsbergdalsbreen, and their long term development has been studied. All of these lakes developed in modern times in overdeepened bedrock basins. The recession of Nigardsbreen uncovered a 1.8 km long and on average 15 m deep proglacial lake basin during 1937 to 1968. Since then the glacier front has been situated entirely on land, and the sediment input and output of the lake was measured. The suspended sediment transport into and out of the lake averaged 11 730 t yr -1 and 2 340 t yr -1 , respectively. Thus, 20% remained in suspension at the outlet. The measured mean annual bedload supplied to the lake was 11 800 t yr -1 , giving a total transport of 23 530 t yr -1 which corresponds to a specific sediment yield of 561 t km -2  yr -1 . A 1.9 km long and up to 90 m deep proglacial lake basin downstream from Engabreen glacier was uncovered during 1890 to 1944. The average suspended sediment load delivered from the glacier during the years 1970-1981 amounted to 12 375 t yr -1 and the transport out of the lake was 2 021 t yr -1 , giving an average of 16% remaining in suspension. The mean annual bedload was 8 000 t yr -1 , thus the total transport was 20 375 t yr -1 , giving a specific sediment yield of 566 t km -2  yr -1 . For Tunsbergdalsbreen glacier, measurements in the early 1970s indicated that the suspended sediment transport was on average 44 000 t yr -1 . From 1987 to 1993 the recession of the glacier uncovered a small proglacial lake, 0.3 km long and around 9 m deep. Downstream from this, the suspended sediment load measured in 2009 was 28 000 t yr -1 , indicating that as much as 64% remained in suspension. Flow velocity, grain size of sediment, and morphology of the lake are important factors controlling the sedimentation rate in the proglacial lakes. A survey of the subglacial morphology of Tunsbergdalsbreen revealed that there are several overdeepened basins beneath the glacier. The largest is 4 km long and 100 m deep. When the glacier melts back they will become lakes and act as sedimentation basins. Despite an expected increase in sediment yield from the glacier, little sediment will pass these lakes and downstream sediment delivery will be reduced markedly. Beneath Nigardsbreen there was only a small depression that may form a lake and the sediment delivery will not be significantly affected. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This study examines the spatial distribution of wind speed across a coastal dune system located at Jockey's Ridge State Park, North Carolina. The study area consists of a trough blowout through a foredune ridge, and the landforms that have developed behind the foredune. Wind speed and direction were measured simultaneously with single sensors placed at a fixed height in thirteen locations across the blowout/dune complex. Fractional wind speed-up is computed for sampling stations using data from a mast located on the beach as the reference. Results show that wind speeds were generally accelerated across the study site. The highest speeds were recorded on the foredune ridges adjacent to the blowout. Wind was accelerated through the center of the blowout throat and along the downwind lateral wall. Further into the blowout, at the base of the ramp to the depositional lobe, higher wind speeds shifted to the upwind lateral wall and continued to accelerate up the ramp as air exited to the rear. Significant variations in the wind speed-up pattern were associated with different wind approach angles, with greater speed-up occurring when the winds were aligned normal to the dune system. The speed-up decreased as the angle of approach became increasingly oblique to the ridge. The patterns of wind speed-up across the site point to the influence of topography on airflow. To quantify the relationship, measures of several topographic variables were obtained along sample transects running upwind from each sample station along flow lines representing different wind approach angles. Examination of correlation coefficients between wind speed-up and topographic variables suggests that for groups of stations with similar topographic characteristics, 30-50% of the variations in speed-up may be explained by the upwind topographic variability. This article is protected by copyright. All rights reserved.

Description: ABSTRACT We test the acquisition of high-resolution topographic and terrain data using hand-held smartphone technology, where the acquired images can be processed using technology freely available to the research community. This is achieved by evaluating the quality of digital terrain models (DTM) of a river bank and an Alpine alluvial fan generated with a fully automated, free to use, Structure-from-Motion package and a smartphone integrated camera (5 megapixels) with terrestrial laser scanning (TLS) data used to provide a benchmark. To evaluate this approach a 16.2 megapixel digital camera and an established, commercial, close-range and semi-automated software are also employed, and the product of the four combination of the two types of cameras and software are compared. Results for the river bank survey demonstrate that centimeter precision DTMs can be achieved at close range (10 m or less), using a smartphone camera and a fully automated package. Results improve to sub-centimeter precision with either higher resolution images or by applying specific post-processing techniques to the smartphone DTMs. Application to an entire Alpine alluvial fan system shows that the degradation of precision scales linearly with image scale, but that (1) the expected level of precision remains and (2) difficulties in separating vegetation and sediment cover within the results are similar to those typically found when using other photo-based techniques and laser scanning systems. This article is protected by copyright. All rights reserved.

Description: Fluvial sediment delivery is the main form of sediment transfer from the land to the sea, but this process is currently undergoing significant variations due to the alteration of catchment and base level controls related to climate change and human activities, especially the widespread construction of dams. Using the lower Wei River as an example and an integrated approach, this study investigates the variation of fluvial sediment delivery, as well as the connectivity under the effects of both controls. Based on hydrological records and channel cross-section surveys, sediment budgets were constructed for two periods (1960–1970, 1970–1990) after the dam was closed in 1960. In the period 1960–1969, due to the elevated base level (327.2 ± 1.62 m) caused by the dam, the aggradation rate was 0.451 × 10 8  t yr −1 in the channel and 0.716 × 10 8  t yr −1 on the floodplain, indicating that the positive lateral connectivity between these locations was enhanced. As a consequence, serious sediment storage resulted in a sediment delivery ratio (SDR) that was smaller than that occurring before 1960. In the period 1970–1990, sweeping soil and water conservation (SWC) measures were implemented, resulting in a reduction of the connectivity between the trunk and tributaries, and a decrease of ~31% in the mean sediment input. Additionally, together with the base level fluctuation in the range of 327.47 ± 0.49 m, the annual variation in sediment storage was primarily dependent on the water-sediment regime affected by the SWC. The negative lateral connectivity was enhanced between the channel and floodplain via bank erosion. Consequently, the aggradation rate was reduced by 89% on the floodplain and by 96% in the channel. Sediment output continued to decrease primarily due to the SWC practices and climate changes in this period, whereas the SDR increased due to the enhanced longitudinal connectivity between the upstream and downstream. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Peatlands are an important store of soil carbon, and play a vital role in global carbon cycling, and when located in close proximity to urban and industrial areas, can also act as sinks of atmospherically deposited heavy metals. Large areas of the UK's blanket peat are significantly degraded and actively eroding which negatively impacts carbon and pollutant storage. The restoration of eroding UK peatlands is a major conservation concern, and over the last decade measures have been taken to try to control erosion and restore large areas of degraded peat. This study utilises a sediment source fingerprinting approach to assess the effect of restoration practices on sediment production, and carbon and pollutant export in the Peak District National Park, southern Pennines (UK). Suspended sediment was collected using time integrated mass flux samplers (TIMS), deployed across three field areas which represent the surface conditions exhibited through an erosion-restoration cycle: (i) intact (ii) actively eroding, and (iii) recently re-vegetated. Anthropogenic pollutants stored near the peat's surface have allowed material mobilised by sheet erosion to be distinguished from sediment eroded from gully walls. Re-vegetation of eroding gully systems is most effective at stabilising interfluve surfaces, switching the locus of sediment production from contaminated surface peat to relatively ‘clean’ gully walls. The stabilisation of eroding surfaces reduces particulate organic carbon (POC) and lead (Pb) fluxes by two orders of magnitude, to levels comparable with those of an intact peatland, thus maintaining this important carbon and pollutant store. The re-vegetation of gully floors also plays a key role in decoupling eroding surfaces from the fluvial system, and further reducing the flux of material. These findings indicate that the restoration practices have been effective over a relatively short timescale, and will help target and refine future restoration initiatives. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Theoretical calculations indicate that elastic stresses induced by surface topography may be large enough in some landscapes to fracture rocks, which in turn could influence slope stability, erosion rates, and bedrock hydrologic properties. These calculations typically have involved idealized topographic profiles, with few direct comparisons of predicted topographic stresses and observed fractures at specific field sites. We use a numerical model to calculate the stresses induced by measured topographic profiles and compare the calculated stress field with fractures observed in shallow boreholes. The model uses a boundary element method to calculate the stress distribution beneath an arbitrary topographic profile in the presence of ambient tectonic stress. When applied to a topographic profile across the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania, the model predicts where shear fractures would occur based on a Mohr-Coulomb criterion, with considerable differences in profiles of stresses with depth beneath ridgetops and valley floors. We calculate the minimum cohesion required to prevent shear failure, C min , as a proxy for the potential for fracturing or reactivation of existing fractures. We compare depth profiles of C min with structural analyses of image logs from four boreholes located on the valley floor, and find that fracture abundance declines sharply with depth in the uppermost 15 m of the bedrock, consistent with the modeled profile of C min . In contrast, C min increases with depth at comparable depths below ridgetops, suggesting that ridgetop fracture abundance patterns may differ if topographic stresses are indeed important. Thus, the present results are consistent with the hypothesis that topography can influence subsurface rock fracture patterns and provide a basis for further observational tests. This article is protected by copyright. All rights reserved.

Description: ABSTRACT A field study was carried out to investigate the development of alternate bars in a secondary channel of the Loire River (France) as a function of discharge variations. We combined frequent bathymetric surveys, scour chains and stratigraphical analysis of deposits with measurements and modelling of flow dynamics. The channel exhibited migrating bars, non-migrating bars and superimposed dunes. Possible mechanisms of bar initiation were found to be chutes associated with changes of bank direction and instability resulting from interactions between existing bars during the fall in water level after floods. We propose that the reworking of bar sediments during low flows (high width-to-depth ratio β), reinforced by high values of the Shields mobility parameter, can explain the formation or re-generation of new alternate migrating bars during a subsequent flood. The migration pattern of the bars was found to be cyclic and to depend mainly (i) on channel layout and (ii) on the dynamics of superimposed dunes with heights and lengths depending on location and discharge value. For instance, the hysteresis affecting the steepness of dunes influences the flow resistance of the dunes as well as the celerity of migrating bars during flood events. We compare the findings from the field with results from theoretical studies on alternate bars. This gives insight in the phenomena occurring in the complex setting of real rivers, but it also sheds light on the extent to which bar theories based on idealized cases can predict those phenomena. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This paper presents a review of the current state of the art in the use of terrestrial radar interferometry for the detection of surface changes related to mass movement. Different hardware-types and acquisition concepts are described, which use either real or synthetic aperture for radar image formation. We then present approaches for data processing procedures, thereby paying special attention to the separation of high resolution displacement information from atmospheric phase variations. Recent case studies are used to illustrate recent applications in terrestrial radar interferometry for change detection. Applications range from detection and quantification of very slow moving (mm to cm/year) displacements in rock walls from repeat monitoring to rapid processes resulting in fast displacements (~50 m/year) acquired during single measurement campaigns with durations of only a few hours. Fast and episodic acting processes such as rockfall and snow avalanches can be assessed qualitatively in the spatial domain by mapping decorrelation caused by those processes. A concluding guide to best practice outlines the necessary preconditions that have to be fulfilled for successful application of the technique as well in areas characterized by rapid decorrelation. Empirical data from a Ku-Band sensor show the range of temporal decorrelation of different surfaces after more than two years for rock-surfaces and after a few seconds to minutes in vegetated areas during windy conditions. The examples show that the displacement field can be measured for landslides in dense grassland, ice surfaces on flowing glaciers and snowpack creep. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In parallel with research on surface sediment characteristics of evolving island features (patches) along an island-braided reach of the Tagliamento River, Italy, the present research reconstructed the development of sampled sites using historical information coupled with field measurements. Since any field sediment sampling programme inevitably focuses on small areas (of the order of a few metres), the historical sources were assessed bearing in mind their spatial resolution and geographical accuracy in relation to the size of the sampled sites, and the information they could provide regarding the historical evolution of those sites. The analysis combined four sources of information: (i) river flow records revealed flood events that had the potential to reset bar surfaces and float in wood and seeds to initiate vegetation colonisation; (ii) oblique ground photographs identified areas of the river's active corridor where riparian vegetation colonisation appeared to have been initiated by specific flood events; (iii) dendrochronology was used to estimate the age of sampled sites; (iv) field-measured geographical locations of the sampled sites were combined with historical vertical areal imagery to further establish sampling site age and changes in vegetation cover from 1944 to 2012. A chronosequence of sampled sites (0, 2, 8, 12, 40 years) was established. Vegetation colonisation and island development showed a statistically significant development trajectory among sites of each age across the 40 year period following formative floods in 1965-6, 2000, 2004 and a flow pulse in 2010. The trajectory progressed through pioneer and building island stages until vegetated areas became part of established islands. Evidence from the younger sites indicates that the pioneer island phase lasts up to eight years. Evidence from the oldest site indicates a building island phase lasting a maximum of 30 years, but probably a lot less. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The duration of the soil-depth recovery needed for reoccurrence of shallow colluvial landslides at a given site in humid regions is much longer than the return period of rainfall needed to generate sufficient pore water pressure to initiate a landslide. Knowledge of the rate of change in soil depth in landslide scars is therefore necessary to evaluate return intervals of landslides. Spatial variation in sediment transport at the Kumanodaira landslide scar in central Japan was investigated by field observations. Spatial distribution of the rate of change in soil depth was estimated using sediment transport data and GIS analysis. Observations revealed that the timing of sediment transport differed for shallow and deep soil layers. Near-surface sediment transport (mostly dry ravel and some shallow soil creep at depths ≤0.05 m) measured in sediment traps was active in winter and early spring and was affected by freezing-thawing; soil creep of subsoil (i.e., 〉0.05 m), monitored by strain probes, was active in summer and autumn when precipitation was abundant. Near-surface sediment flux was estimated by a power law function of slope gradient. Deeper soil creep was more affected by relative location to the landslide scar, which influences soil depth, than by slope gradient. Our study indicated that the rate of soil depth recovery is high just below the head scarp of the landslide. Abrupt changes in the longitudinal slope topography immediately above, within and just below the head scarp became smoother with time due to degradation proximate to the landslide head scarp and flanks, as well as aggradation just below the head scarp. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This work addresses the temporal dynamics of riparian vegetation in large braided rivers, exploring the relationship between vegetation erosion and flood magnitude. In particular, it investigates the existence of a threshold discharge, or a range of discharges, above which erosion of vegetated patches within the channel occurs. The research was conducted on a 14 km long reach of the Tagliamento River, a braided river in northeastern Italy. Ten sets of aerial photos were used to investigate vegetation dynamics in the period 1954-2011. By using different GIS procedures, three aspects of geomorphic-vegetation dynamics and interactions were addressed: (i) long-term (1954-2011) channel evolution and vegetation dynamics; (ii) the relationship between vegetation erosion/establishment and flow regime and (iii) vegetation turnover, in the period 1986-2011. Results show that vegetation turnover is remarkably rapid in the study reach with 50 % of in-channel vegetation persisting for less than 5-6 years and only 10 % of vegetation persisting for more than 18-19 years. The analysis shows that significant vegetation erosion is determined by relatively frequent floods, i.e. floods with a recurrence interval of ca . 1-2.5 years, although some differences exist between subreaches with different densities of vegetation cover. These findings suggest that the erosion of riparian vegetation in braided rivers may be not controlled solely by very large floods, as is the case for lower energy gravel-bed rivers. Besides flow regime, other factors seem to play a significant role for in-channel vegetation cover over long time spans. In particular, erosion of marginal vegetation, which supplies large wood elements to the channel, increased notably over the study period and was an important factor for in-channel vegetation trends. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The cultivation method used in agricultural catchments can have a great effect on erosion processes; as such, determining this effect's form and degree is crucial. One commonly held hypothesis is that a shift to minimum tillage methods should reduce the rate of erosion. Here, we examine the effect of cultivation methods and environmental conditions on soil erosion risks in field crops and orchards in an agricultural catchment in northern Israel. The examination was conducted using AHP- (Analytic Hierarchy Process) and GIS-based computer simulations. Field validation of the simulations was conducted during the 2009-10 winter season. The spatially explicit data on cultivation method, combined with environmental and climatic data, yielded an explanation of most of the variation in erosion risks in the catchment (kappa = 0.93). Of ten criteria examined, the cultivation method and slope were the two variables with the greatest effect on increased soil erosion. Furthermore, soil loss risks were reduced substantially as a result of substituting conventional tillage with reduced tillage; substituting reduced tillage with conservation tillage; and changing the tillage direction to perpendicular to the slope's direction. These results are reasonable in light of the modifications that mechanical tools cause in the soil structure, as observed in the penetration depth and the aggregate stability measurements used in this study. Despite the difficulty in collecting spatially explicit data on cultivation methods, we believe that it is of utmost importance to use such data to study erosion risks in agricultural catchments. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The archetypal badass is individualistic, non-conformist, and able to produce disproportionate results. The badass concept is applied here to geomorphology. The individualistic concept of landscape evolution (ICLE) is introduced, based on three propositions: excess evolution space, capacity of all landforms to change, and variable selection pressure from environmental factors within and encompassing landscapes. ICLE indicates that geomorphic systems are idiosyncratic to some extent, and that even where two systems are similar, this is a happenstance of similar environmental selection, not an attractor state. As geomorphic systems are all individualistic, those that are also non-conformist with respect to conventional wisdoms and have amplifier effects are considered badass. Development of meander bends on a section of the Kentucky River illustrates these ideas. The divergence of karst and fluvial forms on the inner and outer bends represents unstable amplifying effects. The divergence is also individualistic, as it can be explained only by combining general laws governing surface and subsurface flow partitioning with a specific geographical and environmental setting and the history of Quaternary downcutting of the Kentucky River. Landscape evolution there does not conform to any conventional theories or conceptual frameworks of geomorphology. The badass traits of many geomorphic systems have implications for the systems themselves, attitudes toward geomorphic practice, and appreciation of landforms. Badass geomorphology and the ICLE reflect a view, and approach to the study of, landforms as the outcome of the interplay of general laws, place-specific controls, and history. Badass geomorphology also implies a research style receptive to contraventional wisdoms. Aesthetically, amplifier effects and individualism guarantee an essentially infinite variety of landforms and landscapes that geoscientists can appreciate both artistically and scientifically. Non-conformity makes the interpretation and understanding of this variety more challenging—and while that increases the degree of difficulty, it also makes for more interesting and compelling professional challenges. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Australian meteorological observers started using the World Meteorological Organisation (WMO) weather coding system in the 1950s. This system is still in use around the world today. However, observing and recording the weather in an organised and systematic manner had been ongoing for over 100 years prior to the adoption of this coding system, and much like Australia, most countries will have historical meteorological records. In this paper we compare the wind erosion of two of the greatest droughts in Australian recorded history; the WWII Drought (1937–1945) and the Millennium Drought (2001–2009). To do this we analysed previously unavailable meteorological observer records from the Australian Bureau of Meteorology (ABM). Wind erosion records, mostly in long-hand written form, were translated to the modern WMO coding system for the WWII Drought and compared with the wind erosion of Australia's recently-ended Millennium Drought, one of the longest and harshest on record. We quantify wind erosion using Dust Event Days (DED) and a modified version of a published Dust Storm Index (DSI) to show that wind erosion during the WWII Drought was up to 4.6 times higher than during the Millennium Drought. This study has international significance because it demonstrates a methodology for tracking changes in wind erosion over the past 75 years based on observer records available in every country with a history of organised weather observation. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Sea stacks are common and striking coastal landforms, but few details are known about how, how quickly, and under what conditions they form. We present numerical and analytical models of sea stack formation due to preferential erosion along a pre-existing headland to address these basic questions. On sediment-rich rocky coasts, as sea cliffs erode and retreat, they produce beach sediment that is distributed by alongshore sediment transport and controls future sea cliff retreat rates. Depending on their width, beaches can encourage or discourage sea cliff erosion by acting either as an abrasive tool or a protective cover that dissipates wave energy seaward of the cliff. Along the flanks of rocky headlands where pocket beaches are often curved and narrow due to wave field variability, abrasion can accelerate alongshore-directed sea cliff erosion. Eventually, abrasion-induced preferential erosion can cut a channel through a headland, separating it from the mainland to become a sea stack. Under a symmetrical wave climate (i.e., equal influence of waves approaching the coastline from the right and from the left), numerical and analytical model results suggest that sea stack formation time and plan-view size are proportional to preferential erosion intensity (caused by, for example, abrasion and/or local rock weakness from joints, faults, or fractures) and initial headland aspect ratio, and that sea stack formation is discouraged when the sediment input from sea cliff retreat is too high (i.e., sea cliffs retreat quickly or are sand-rich). When initial headland aspect ratio is too small, and the headland is “rounded” (much wider in the alongshore direction at its base than at its seaward apex), the headland is less conducive to sea stack formation. On top of these geomorphic and morphologic controls, a highly asymmetrical wave climate decreases sea stack size and discourages stack formation through rock-sediment interactions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Holocene glaciers have contributed to an abundance of unstable sediments in mountainous environments. In permafrost environments, these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution under condition of a warming climate. To understand the influence of ground ice distribution on this activity since the Little Ice Age (LIA), we have investigated the Pierre Ronde and Rognes proglacial areas, two cirque glacier systems located in the periglacial belt of the Mont Blanc massif. For the first time, electrical resistivity tomography, temperature data loggers and DGPS are combined with historical documents and glaciological data analysis to produce a complete study of evolution in time and space of these small landsystems since LIA. This approach allows to explain spatial heterogeneity of current internal structure and dynamics. The studied sites are a complex assemblage of debris-covered glacier, ice-rich frozen debris and unfrozen debris. Ground ice distribution is related to former glacier thermal regime, isolating effect of debris cover, water supply to specific zones, and topography. In relation with this internal structure, present dynamics are dominated by rapid ice melt in the debris-covered upper slopes, slow creep processes in marginal glacigenic rock glaciers, and weak, superficial reworking in deglaciated moraines. Since LIA, geomorphic activity is mainly spatially restricted within the proglacial areas. Sediment exportation has occurred in a limited part of the former Rognes Glacier and through water pocket outburst flood and debris flows in Pierre Ronde. Both sites contributed little sediment supply to the downslope geomorphic system, rather by episodic events than by constant supply. In that way, during Holocene and even in a paraglacial context as the recent deglaciation, proglacial areas of cirque glaciers act mostly as sediment sinks, when active geomorphic processes are unable to evacuate sediment downslope, especially because of the slope angle weakness. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Knowledge and understanding of shore platform erosion and tidal notch development in the tropics and subtropics relies mainly on short-term studies conducted on recently deposited carbonate rocks, predominantly Holocene and Quaternary reef limestones and aeolianites. This paper presents erosion rates, measured over a ten year period on notches and platforms developed on the Permian, Ratburi limestone at Phang Nga Bay, Thailand. In so doing it contributes to informing a particular knowledge gap in our understanding of the erosion dynamics of shore platform and tidal notch development in the tropics and subtropics - notch erosion rates on relatively hard, ancient limestones measured directly on the rock surface using a microerosion meter (MEM) over time periods of a decade or more. The average intertidal erosion rate of 0.231 mm/yr is lower than erosion rates measured over 2 – 3 years on recent, weaker carbonate rocks. Average erosion rates at Phang Nga vary according to location and site and are, in rank order from highest to lowest: Mid-platform (0.324 mm/yr) 〉 Notch Floor (0.289 mm/yr) 〉 Rear notch wall (0.228 mm/yr) 〉 Lower platform (0.140 mm/yr) 〉 Notch roof (0.107 mm/yr) and Supratidal (0.095 mm/yr). The micro-relief of the eroding rock surfaces in each of these positions exhibit marked differences that are seemingly associated with differences in dominant physical and bio-erosion processes. The results begin to help inform knowledge of longer term shore platform erosion dynamics, models of marine notch development and have implications for the use of marine notches as indicators of changes in sea level and the duration of past sea levels. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The distribution of trace metals in alluvial sediments depends on their natural background concentrations, and on the dynamics of contemporary depositional and erosional (mainly flood-induced) processes. Geological and geochemical investigations were carried out in the valley of Vistula River near Magnuszew (central Poland). Sediment samples were collected from a depth of 35 cm and comprise sediments of all defined geomorphological features. Identification and geological interpretation of the morphodynamic sediment features was supported by aerial photographs and high-resolution satellite images. These studies revealed that the distribution of trace metals is closely linked to the morphogenesis of the alluvial floodplain. The highest concentrations of Cu, Co, Zn, V, Cr and Ni were observed in crevasse-splays deposits. By contrast, Sr, Pb and As were concentrated in deposits which fill oxbow lakes (partly infilled with organic deposits). The lowest concentrations of trace metals were detected in flood sediments deposited within erosional troughs. The geomorphological and sedimentological history of the fluvial features explains the pattern of heavy metal distribution on the current floodplain surface. This article is protected by copyright. All rights reserved.

Description: ABSTRACT A growing body of field, theoretical and numerical modeling studies suggests that predicting river response to even major changes in input variables is difficult. Rivers are seen to adjust rapidly and variably through time and space as well as changing independently of major driving variables. Concepts such as Self-Organised Criticality (SOC) are considered to better reflect the complex interactions and adjustments occurring in systems than traditional approaches of cause and effect. This study tests the hypothesis that riverbank mass failures which occurred both prior to, and during, an extreme flood event in south east Queensland (SEQ) in 2011 are a manifestation of SOC. Each wet-flow failure is somewhat analogous to the ‘avalanche’ described in the initial sand-pile experiments of Bak et al. (1987) and, due to the use of multitemporal LiDAR, the time period of instability can be effectively constrained to that surrounding the flood event. The data is examined with respect to the key factors thought to be significant in evaluating the existence of SOC including; nonlinear temporal dynamics in the occurrence of disturbance events within the system; an inverse power-law relation between the magnitude and frequency of the events; the existence of a critical state to which the system readjusts after a disturbance; the existence of a cascading processes mechanism by which the same process can initiate both low-magnitude and high magnitude events. While there was a significant change in the frequency of mass failures pre- and post-flood, suggesting nonlinear temporal dynamics in the occurrence of disturbance events, the data did not fit an inverse power-law within acceptable probability and other models were found to fit the data better. Likewise, determining a single ‘critical’ state is problematic when a variety of feedbacks and multiple modes of adjustment are likely to have operated throughout this high magnitude event. Overall, the extent to which the data supports a self-organised critical state is variable and highly dependent upon inferential arguments. Investigating the existence of SOC, however, provided results and insights that are useful to the management and future prediction of these features. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Channelization of the severely polluted Odra and Vistula rivers in Poland induced intensive accumulation of fine-grained deposits rich in organic matter and heavy metals. These sediments have been identified in vertical profiles in a narrow zone along river banks both in groyne-created basins and on the floodplain. Grain size, organic matter, Zn, Pb, Cu content and 137 Cs was used for sediment dating and, stratigraphy and chemistry have been diagnostic features for these deposits, named industrial alluvium. In the most polluted river reaches stabilized by bank reinforcements and groynes, 2 -m -thick slack water groyne deposits are composed of uniform strata of polluted silts with organic matter content over 10%, Zn content over 1000 mg/kg and average Cu and Pb over 100 mg/kg. The average rate of sediment accretion in groynes is higher than on the floodplain and reaches 5 cm/year. Stratification which appears at higher levels in the groyne fields and on the levees reflects a change from in-channel to overbank deposition and is typified by dark layers separated by bright, sandy, and less polluted strata. Stratified, 4 -m -thick, sediment sequences have been found in groyne fields of incised river reaches. The average rate of sediment accretion in these reaches is of the order of 5 cm/year. In stable and relatively less polluted river reaches, vertical-accretion organic deposits are finely laminated and the average rate of deposition amounts to a few millimeters per year. Investigations indicate that groyne construction favours conditions for long term storage of sediments at channel banks. For this reason, groynes should be considered as structures that efficiently limiting sudden release of sediment-associated heavy metals stored in channels and in floodplains of the historically polluted rivers. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In December 2008, 694 trees uprooted within a 108 hectare (1.08 km 2 ) watershed in central Massachusetts due to a severe ice storm, resulting in the displacement of ~1300 m 3 of root material, unconsolidated sediment, and fractured bedrock. Overall, we find that uprooting and tree throw is often grouped in clusters and cascades; conifers displace more material than deciduous trees; areas with abundant mature hemlock and steep slopes are more susceptible to tree throw, with clusters as dense as 125 per hectare; and failure is predominantly downhill, suggesting that ice storms promote efficient downslope hillslope sediment transport in Northern Hardwood forests. Combining the recurrence interval of severe storms in New England (20-75 years) with the forest response presented here, we calculate a sediment transport rate of 2-5x10 -5  m 3  m -1 a -1 averaged over the entire watershed. Forest susceptibility to tree throw differed based on location in the watershed; some areas experienced up to ~30x higher than average sediment transport rates, while others experienced no tree throw. Two severe storms following the 2008 ice storm (hurricane in 2011; snow storm in October 2012) did not result in significant tree throw within the study area, highlighting that the coupling of storm severity and forest susceptibility controls the amount of tree throw during a given forest disturbance. In addition to recent tree throw from the 2008 ice storm, widespread pit and mound microtopography in the study area indicates that tree throw is a recurrent process in this landscape. Two factors emerge that will influence future ice storms related hillslope sediment transport in the steep forested hillslopes of New England: regional climate gradients and changing climate determine the size, intensity and recurrence of ice storms; forest management practices and health control the tree age and type. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Landscapes respond in complex ways to external drivers such as base level change due to damming events. In this study, landscape evolution modelling was used to understand and analyse long-term catchment response to lava damming events. PalaeoDEM reconstruction of a small Turkish catchment (45 km 2 ) which endured multiple lava damming events in the past 300 ka, was used to derive long-term net erosion rates. These erosion rates were used for parameter calibration and led to a best fit parameter set. This optimal parameter set was used to compare net erosion landscape time series of four scenarios: i) no uplift and no damming events, ii) no uplift and 3 damming events, iii) uplift and no damming events and iv) uplift and 3 damming events. Spatial evolution of net erosion and sediment storage of scenario iii) and iv) were compared. Simulation results demonstrate net erosion differences after 250000 yr between scenarios with and without dams. Initially, trunk gullies show less net erosion in the scenario with damming events compared to the scenario without damming events. This effect of dampened erosion migrates upstream to smaller gullies and local slopes. Finally, an intrinsic incision pulse in the dam scenario results in a higher net erosion of trunk gullies while decoupled local slopes are still responding to the pre-incision landscape conditions. Sediment storage differences also occur on a 100 ka scale. These differences behaved in a complex manner due to different timings of the migration of erosion and sediment waves along the gullies for each scenario. Although the specific spatial and temporal sequence of erosion and deposition events is sensitive to local parameters, this model study shows the manner in which past short-lived events like lava dams have long lasting effects on catchment evolution. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Landscapes exposed by glacial retreat provide an ideal natural laboratory to study the processes involved in transforming a highly disturbed, glacially influenced landscape to a stable, diverse ecosystem which supports numerous species and communities. Large-scale vegetation development and changes in sediment availability, used as a proxy for paraglacial adjustment following rapid deglaciation, were assessed using information from remote sensing. Delineation of broad successional vegetation cover types was undertaken using Landsat satellite imagery (covering a 22 year period) to document the rate and trajectory of terrestrial vegetation development. Use of a space-for-time substitution in Glacier Bay National Park, Alaska, allowed ‘back-calculation’ of the age and stage of development of six catchments over 206 years. The high accuracy (89.2%) of the remotely sensed information used in monitoring successional change allowed detection of a high rate of change in vegetation classes in early successional stages (bare sediment and alder). In contrast, later successional stages (spruce and spruce-hemlock dominated forest) had high vegetation class retention, and low turnover. Modelled rates of vegetation change generally confirmed the estimated rates of successional turnover previously reported. These data, when combined with the known influence of terrestrial succession on soil development and sediment availability, suggest how physical and biological processes interact over time to influence paraglacial adjustment following deglaciation. This study highlights the application of remote sensing of successional chronosequence landscapes to assess the temporal dynamics of paraglacial adjustment following rapid deglaciation and shows the importance of incorporating bio-physical interactions within landscape evolution models. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Gully cut-and-fill dynamics are often thought to be driven by climate and/or deforestation related to population pressure. However, in this case-study of nine representative catchments in the North Ethiopian Highlands, we find that neither climate changes nor deforestation can explain gully morphology changes over the 20 th century. Firstly, by using a Monte Carlo simulation to estimate historical catchment-wide curve numbers, we show that the landscape was already heavily degraded in the 19 th and early 20 th century – a period with low population density. The mean catchment-wide curve number (〉80) one century ago was, under the regional climatic conditions, already resulting in considerable simulated historical runoff responses. Secondly, 20 th century land cover and runoff coefficient changes were confronted with 20 th century changing gully morphologies. As the results show, large-scale land cover changes and deforestation cannot explain the observed processes. The study therefore invokes interactions between authigenic factors, small-scale plot boundary changes, cropland management and sociopolitical forces to explain the gully cut processes. Finally, semi-structured interviews and sedistratigraphic analysis of three filled gullies confirm the dominant impact of (crop)land management (tillage, check dams in gullies and channel diversions) on gully cut-and-fill processes. Since agricultural land management – including land tenure and land distribution – has been commonly neglected in earlier related research, we argue therefore that it can be a very strong driver of 20 th century gully morphodynamics. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The multipart Riffeltal rock glacier, located in a tributary valley of the Kaunertal, Tyrol, Austria is investigated to enlarge the knowledge about spatial and temporal development of rock glaciers in and at the margins of proglacial areas and to get a better understanding about glacier-rock glacier interactions. The subject of interest consists of a complex system of two adjacent rock glacier tongues and various superposed lobes with differing ages, origin and root zones, and therefore diverse development. To determine the reasons for their diverging development, the internal structure and permafrost occurrence on and in the surrounding area of the rock glacier were studied by application of geomorphological mapping, geophysical methods and measurement of the basal temperature of the winter snow cover (BTS). Permafrost modelling was performed on the basis of BTS data and land surface parameters derived from a high resolution airborne laserscanning (ALS) DEM. Additionally, the ALS data were used to measure vertical and horizontal changes of the rock glacier surface between 2006 and 2012. Glacier-rock glacier interactions during and since the Little Ice Age (LIA) are evident for the development of the studied rock glacier. A geomorphic map gives important information about the connection between glacial advance or retreat and permafrost or ground ice occurrence. The combination of all information helps in the analysis of diverse kinematic action of neighbouring rock glacier tongues. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Proglacial groundwater-fed features, such as seeps, substantially impact proglacial geomorphology, hydrology, and ecology. However, there is a paucity of research on the impacts of climate change and glacier retreat on the extent of these important features. This paper aims to investigate the impact of glacier retreat on proglacial groundwater levels and on the extent of groundwater-fed seeps. Research has taken place in western Skeiðarársandur, the large proglacial outwash plain of Skeiðarárjökull, a retreating temperate glacier in SE Iceland. Changes in the extent of proglacial groundwater seeps were mapped using historical aerial photographs from 1986, 1997, and 2012. Proglacial groundwater levels were monitored in shallow boreholes between 2000 and 2012. The western margin of Skeiðarárjökull has retreated approximately 1 km beyond its position in 1986. However, this retreat was punctuated by short periods of readvance. The geomorphology and groundwater systems at the site were substantially impacted by the November 1996 jökulhlaup, whose deposits altered approximately 18% of the area of groundwater seeps. The surface areas of groundwater seeps and lakes in the study area have declined by ~97% between 1986 and 2012. Most of the decline took place after 1997, when the mean annual rate of retreat increased threefold. Groundwater levels also declined substantially between 2000 and 2012, although this trend varies spatially. The paper provides a conceptual model of the controls on proglacial shallow hydrological groundwater systems. Direct impacts of glacier retreat are suggested as the main cause for the declines in proglacial groundwater levels and in the extent of groundwater seeps. These declines are expected to adversely impact sandur ecology. This article is protected by copyright. All rights reserved.

Description: ABSTRACT A reliable characterization of bedload transport is required to gauge the engineering and theoretical issues related to the dynamics of sediments transport in rivers. However, while significant advances have been made in the development of monitoring techniques, robust quantitative predictive relationships have proven difficult to derive. In this article, we develop a dedicated signal processing technique aimed at improving the usage of impact plate measurements for material transport characterization. Our set-up consists of a piezoelectric hydrophone mounted on the bottom side of a stainless steel plate, thus acting as a “sediment vibration sensor”. While the classical analysis with such systems is usually limited to rather simple procedures, such as impact counting, a large amount of useful information is contained in the actual waveform of the impact signal, which conveys the force and the contact time that the bedload imposes on the plate. An advanced signal processing technique called “first arrival atomic decomposition” is used to improve the characterization of bedload transport by analysing the amplitude and frequency attributes of each single impact. This new processing approach proves to be well suited for bedload transport monitoring using plate systems and allows us to establish a relationship between the median grain size ( D 50 ) and the impact signal properties. This link is first observed and validated with controlled flume experiments and then applied to continuous impact records in a small gravel-bed river during a flood event. The estimated D 50 offers a novel possibility to observe the time-varying grain size distribution of bedload transport. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The Holocene evolution of the Canning Coast of Western Australia has largely been overlooked so far mainly due to its remoteness and low population density. We report on new data from a sequence of foredunes inside the macrotidal Admiral Bay, 110 km southwest of Broome. Based on sediment cores, DGPS-based elevation transects, and stratigraphical analyses on outcrops of the relict foredunes, we aim at reconstructing Holocene coastal changes and relative sea levels (RSL), as well as identifying and dating imprints of extreme-wave events. Sedimentary analyses comprise the documentation of bedding structures, foraminiferal content and macrofaunal remains, grain size distribution, and organic matter. The chronological framework is based on 26 14 C-AMS datings. Marine flooding of the pre-Holocene surface landward of the 2.5 km-wide foredune barriers occurred 7400–7200 cal BP, when mangroves colonized the area. After only 200–400 years, a high-energy intertidal environment established and prevailed until c. 4000 cal BP, before turning into the present supralittoral mudflat. During that time, coastal regression led to beach progradation and the formation of aligned foredunes. Drivers of progradation were a stable RSL or gradual RSL fall after the mid-Holocene and a positive sand budget. The foredunes overlie upper beach deposits located up to 〉2 m above the present upper beach level and provide evidence for a higher mid-Holocene RSL. Discontinuous layers of coarse shells and sand are intercalated in the foredunes, indicating massive coastal flooding events. One such layer was traced over three dune ridges and dated to c. 1700–1550 cal BP. However, it seems that most tropical cyclones induce net erosion rather than deposition at aligned foredunes and thus, they are only suitable for reconstructing temporal variability if erosional features or sedimentation reliably tied to these events can be identified and dated accurately. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Stone surfaces are sensitive to their environment. This means that they will often respond to exposure conditions by manifesting a change in surface characteristics. Such changes can be more than simply aesthetic, creating surface/subsurface heterogeneity in stone at the block scale, promoting stress gradients to be set up as surface response to, for example, temperature fluctuations, can diverge from subsurface response. This paper reports preliminary experiments investigating the potential of biofilms and iron precipitation as surface-modifiers on stone, exploring the idea of block-scale surface-to-depth heterogeneity, and investigating how physical alteration in the surface and near-surface zone can have implications for subsurface response and potentially for long-term decay patterns. Salt weathering simulations on fresh and surface-modified stone suggest that even subtle surface modification can have significant implications for moisture uptake and retention, salt concentration and distribution from surface to depth, over the period of the experimental run. The accumulation of salt may increase the retention of moisture, by modifying vapor pressure differentials and the rate of evaporation. Temperature fluctuation experiments suggest that the presence of a biofilm can have an impact on energy transfer processes that occur at the stone surface (for example, buffering against temperature fluctuation), affecting surface-to-depth stress gradients. Ultimately, fresh and surface-modified blocks mask different kinds of system, which respond to inputs differently because of different storage mechanisms, encouraging divergent behaviour between fresh and surface-modified stone over time. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Proglacial landscapes are some of the most active on Earth. Previous studies of proglacial landscape change have often been restricted to considering either sedimentological, geomorphological or topographic parameters in isolation and are often mono-dimensional. This study utilised field surveys and digital elevation model analyses to quantify planform, elevation and volumetric proglacial landscape change at Sólheimajökull in southern Iceland for multiple time periods spanning from 1960 to 2010. As expected, the most intense geomorphological changes persistently occurred in the ice-proximal area. During 1960 to 1996 the proglacial river was relatively stable. However, after 2001 braiding intensity was higher, channel slope shallower and there was a shift from overall incision to aggradation. Attributing these proglacial river channel changes to the 1999 jökulhlaup is ambiguous because it coincided with a switch from a period of glacier advance to that of glacier retreat. Furthermore, glacier retreat (of ~40 m.yr −1 ) coincided with ice-marginal lake development and these two factors have both altered the proglacial river channel head elevation. From 2001 to 2010 progressive increase in channel braiding and progressive downstream incision occurred; these together probably reflecting stream power due to increased glacier ablation and reduced sediment supply due to trapping of sediment by the developing ice-marginal lake. Overall, this study highlights rapid spatiotemporal proglacial landscape reactions to changes in glacial meltwater runoff regimes, glacier terminus position, sediment supply and episodic events such as jökuhlaups. Recognising the interplay of these controlling factors on proglacial landscapes will be important for understanding the geological record and for landscape stability assessments. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Among the studies on runoff connectivity of soils with heterogeneous properties, the need to understand the relationships between soil heterogeneity and the associated runoff organization and amount is frequently mentioned. In this study, we simulate the stationary runoff-runon process on bi-dimensional (2D) flat slopes for five infiltrability distributions, one of them correlated, as a function of rainfall intensity and flow dimension. We call 1 + ε the flow dimension, where ε is the outflow fraction transferred from one pixel to each of the two lateral downslope pixels. Our aim is to assess the effect of ε and soil heterogeneity on the connectivity function (Allard et al., 1993) compared to the mean runoff flow rate, the wet area and the number of runoff patterns. The analysis of connectivity is carried within the percolation framework. The results show that the integral connectivity scale is more sensitive to the flow dimension and soil heterogeneity compared to the other variables. The wet area fraction does not depend on ε. Unlike previous studies, we find that increased runoff production is not necessarily related to increased connectivity. The use of the connectivity function within the percolation framework appears to be a valuable method for assessing the impact of soil heterogeneity and flow dimension on the runoff organization during a rainfall event. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Sediment flux dynamics in fluvial systems have often been related to changes in external drivers of topography, climate or land cover. It is well known that these dynamics are nonlinear. Recently, model simulations of fluvial activity and landscape evolution have suggested that self-organization in landscapes can also cause internal complexity in the sedimentary record. In this contribution one particular case of self-organization is explored in the Sabinal field study area, Spain, where several dynamic zones of sedimentation and incision are observed along the current river bed. Whether these zones can be caused by internal complexity was tested with LEM LAPSUS. During various 500 year simulations, zones of sedimentation appear to move upstream and downstream in eroding river channels (“waves”). These waves are visualized and characterised for a range of model settings under constant external forcing, and the self-organizing process behind their occurrence is analysed. Results indicate that this process is not necessarily related to simplifications in the model and is more generic than the process of bed-armouring that has recently been recognized as a cause for complexity in landscape evolution model simulations. We conclude that autogenic sediment waves are the result of the spatial propagation in time of feedbacks in local transport limited (deposition) and detachment limited (erosion) conditions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Two datasets of turbulence velocities collected over different bedform types under contrasting experimental conditions show similarity in terms of velocity-intermittency characteristics and suggest a universality to the velocity-intermittency structure for flow over bedforms. One dataset was obtained by sampling flow over static bedforms in different locations, and the other was based on a static position but mobile bedforms. A flow classification based on the velocity-intermittency behaviour is shown to reveal some differences to that based on an analysis of Reynolds stresses, boundary layer correlation and turbulent kinetic energy. This may be attributed to the intermittency variable, which captures the local effect of individual turbulent flow structures. Locations in the wake region or the outer layer of the flow are both shown to have a velocity-intermittency behaviour that departs from that for idealised wakes or outer layer flow because of the superposition of localized flow structures generated by bedforms. The combined effect of this yields a velocity-intermittency structure unique to bedform flow. The use of a time series of a single velocity component highlights the potential power of our approach for field, numerical and laboratory studies. The further validation of the velocity-intermittency method for non-idealised flows undertaken here, suggests that this technique can be used for flow classification purposes in geomorphology, hydraulics, meteorology and environmental fluid mechanics. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Soil erosion is one of the most severe land degradation processes in the Mediterranean region. Although badlands occupy a relatively small fraction of the Mediterranean area, their erosion rates are very high. Many studies investigated to what extent vegetation controls soil erosion rates. This study, however, deals with the impact of erosion on vegetation establishment. In semiarid badlands of the Mediterranean, soil water availability constitutes the main limiting factor for vegetation development. As a consequence, south-facing slopes are typically less vegetated due to a very large water stress. However, these findings do not necessarily apply to humid badlands. The main objective of this paper is to determine the topographic thresholds for plant colonization in relation to slope aspect and to assess the spatial patterns of vegetation cover and species richness. We surveyed 179 plots on highly eroded badland slopes in the Central Pyrenees. We defined four aspect classes subdivided into slope angle classes. Colonization success was expressed in terms of vegetation cover and species richness. Slope angle thresholds for plant colonization were identified for each slope aspect class by means of binary logistic regressions. The results show that a critical slope angle exists below which plants colonize the badland slopes. Below this critical slope angle, plant cover and species richness increase with a decreasing slope angle. The largest critical slope angles in humid badlands are observed on south-facing slopes, which contrasts with the results obtained in semiarid badlands. North-facing slopes on the other hand are characterized by a reduced overall vegetation cover and species richness, and lower topographic threshold values. The possible underlying processes responsible for this slope-aspect discrepancy in vegetation characteristics are discussed in terms of environmental variables that control regolith development, weathering and erosion processes. Moreover, possible restoration strategies through the use of vegetation in highly degraded environments are highlighted. Copyright © 2014 John Wiley & Sons, Ltd.

Description: ABSTRACT Soils in proglacial areas are often approached from a chronosequence viewpoint. In the chronosequence approach, the objective is to derive rates of soil formation from differences in properties between soils of different age. For this reason, in chronosequence studies, soils are sampled in locations that are assumed geomorphically stable and that have different age. As a result, these studies do not necessarily yield a complete view of soil variability in proglacial areas, and may miss important relations between geomorphology and soil development. In this contribution, we present new soil observations from three closely related proglacial areas in Switzerland. These observations were intended to get closer to a complete view of soil variability, and to assess impacts from factors other than time on soil development. About 40 soils were visited in each proglacial valley in a combined design-convenience sampling scheme and described in the field. Linear modelling was used to assess effects of time and topographic factors on soil properties. The time since glacial retreat turned out to rarely explain more than half of the variation in soil properties, and a linear model combining effects of time and topographic variables explained typically about half of the variation in each proglacial valley. Models differed and were not transferable between valleys. Apparently, time and the present-day shape of the landscape combined are insufficient information to accurately predict soil properties. Field evidence points to the importance of the geomorphic history and regime of the valleys as a reason for this. Copyright © 2014 John Wiley & Sons, Ltd.

Description: ABSTRACT A depth-averaged linearized meander evolution model was calibrated and tested using the field data collected at the Quinn River in the Black Rock Desert, Nevada. Two approaches used to test the model were: 1) simulating meander evolution and comparing the results to the observed 38 year migration pattern, and 2) fitting the model parameters to present bank asymmetry (the ratio of the maximum bank gradients on opposite sides of the channel). The data required as input were collected in the field during a high flow in May, 2011 and from aerial photographs and LiDAR data. Both approaches yielded similar results for the best fit parameter values. The bank asymmetry analysis showed that the bank asymmetry and the velocity perturbation have a high correlation at close to zero spatial lag while the maximum correlation between the bank asymmetry and maximum bend curvature is offset by about 25 m. The model sufficiently replicated 38 years of channel migration, with a few locations significantly under- or over-predicted. Inadequacies of the flow model and/or variation in bank properties unaccounted for are most likely the causes for these discrepancies. Flow through the Quinn River was also simulated by a more general 3D model. The downstream pattern of near-bank shear stresses simulated by the 3D model is nearly identical to those resulting from the linearized flow model. Topographic profiles across interior bends are essentially invariant over a wide range of migration rates, suggesting that the traditional formulation that cut bank erosion processes govern migration rates is appropriate for the Quinn River. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This article investigates landscape characteristics and sediment composition in the western Greater Caucasus by using multiple methods at different time scales. Our ultimate goal is to compare short-term versus long-term trends in erosional processes and to reconstruct spatio-temporal changes in sediment fluxes as controlled by partitioning of crustal shortening and rock uplift in the orogenic belt. Areas of active recent uplift are assessed by quantitative geomorphological techniques (DEM analysis of stream profiles and their deviation from equilibrium) and compared with regions of rapid exhumation over longer time intervals as previously determined by fission-track and cosmogenic-nuclide analyses. Complementary information from petrographic and heavy-mineral analyses of modern sands and ancient sandstones is used to evaluate erosion integrated throughout the history of the orogen. River catchments displaying the highest relief, as shown by channel-steepness indices, correspond with the areas of most rapid exhumation as outlined by thermochronological data. The region of high stream gradients is spatially associated with the highest topography around Mount Elbrus, where sedimentary cover strata have long been completely eroded and river sediments display the highest metamorphic indices and generally high heavy-mineral concentrations. This study reinforces the suggestion that the bedrock-channel network can reveal much of the evolution of tectonically active landscapes, and implies that the controls on channel gradient ultimately dictate the topography and the relief along the Greater Caucasus. Our integrated datasets, obtained during a decade of continuing research, display a general agreement and regularity of erosion patterns through time, and consistently indicate westward decreasing rates of erosional unroofing from the central part of the range to the Black Sea. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In some of the world's desert and desert-marginal areas (e.g. Simpson/Strzelecki, Australia) dunefields preserve well-developed palaeosols, whereas in other regions with broadly similar climatic regimes and topography (e.g. southwest Kalahari), the dunes are characterized by very poorly developed internal stratigraphy. It has been postulated that dunes such as those in the Kalahari may never have had conditions conducive to soil formation, or that soils once formed but any evidence of palaeosols has been lost due to reworking. This study develops and applies a one-dimensional numerical model to simulate dune development, soil formation and soil preservation. Variables in the model allowed experimentation on the influence of sediment supply, the time taken for soil to form, and the additional resistance to erosion offered by the soil. Reduced sediment supply plays a vital role in landscape development during periods of initial pedogenesis. Although re-exhumed palaeosols influence sediment supply, the effect is minimal. Although under almost all parameterized conditions more than half (and up to 80-90%) of those soils initially formed are lost due to reworking, evidence of their past formation remains in the large majority of profiles, and the dominant factor in controlling the preservation of palaeosols is the frequency of their formation. The implication is that where dunes are found without palaeosols, the most likely (albeit not certain) inference is that they have never formed. Counter-intuitively, the limited sediment supply means their additional resistance to erosion becomes almost inconsequential to their preservation, at least until the unit approaches complete invulnerability. Short chronostratigraphic hiatuses around palaeosols are normal, and although long gaps can occur, they are extremely infrequent. Where such gaps are observed in field studies, external forcing factors (e.g. climatic or environmental changes) are implied, as they are highly unlikely to result from stochastic net preservation. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The digital elevation model (DEM) has become an essential tool for an increasing array of mountain runoff analyses, particularly the derivation and mapping of stream channel networks. This study examines how well commonly applied DEM-based channel derivation methods at different spatial resolutions can represent the channel network for a glaciated Rocky Mountain headwater catchment. The specific objectives are to (1) examine how differences in gridded DEM resolution affect spatially distributed values of local slope, specific contributing area, and topographic wetness index derived from both eight- and infinite-directional flow algorithms, (2) map the actual stream channel network to examine the influence of surface variables on channel initiation, and (3) assess accuracy of DEM-derived networks as compared to the field surveyed network. Results show that for the same contributing area threshold, increasing grid cell size leads to increased channelization of modeled networks. A plot of local slope versus contributing area reveals a negative relationship similar to that of prior studies in un-glaciated areas but with breaks in slope at contributing areas that are too small to represent thresholds for channelization. Field survey results and evaluation of DEM-derived channel networks suggest that channel network formation is not clearly related to surface topographic variables at Loch Vale. Digitally derived channel networks do not accurately predict low order channel locations, but approximations of the channel network with drainage density and headward extent of channelization similar to the observed network can be derived with both a 1 m and 10 m DEM using a contributing area threshold of approximately 4x10 4 m 2 . This article is protected by copyright. All rights reserved.

Description: ABSTRACT Two computational methods to measure particle rotations from shadow images of sand particles saltating in a wind tunnel are presented. One method calculates the maximum of the cross correlations through multiple angular rotations of an imaged particle. The second method polar transforms both images and then calculates the correlation coefficient for multiple pixel displacements in the θ axis, corresponding to particle rotations. The results from both methods were analysed as a function of height above sand bed (3.7-33.4 mm) and particle size (0.32-0.93 mm equivalent mean diameter). Our results indicate little evidence that particle rotation speeds depend on either their size or height above the sand bed. Though similar results were obtained from both methods, there existed different advantages and disadvantages between the methods. Erroneous results likely arose from particles that were inadequately described by a 2-D rotation axis, or from poorly imaged particles. At a wind tunnel speed of about 12 m/s, most particles rotated at around 300-400 rev/s. Negative rotations were also found, and their proportion was approximately 15% within the total range of -450 to 850 rev/s. The ratio of displacement kinetic energy to rotation energy was compared across the various groups and had values between 15 and 40. The quotient showed little dependence on height, though decreased with increasing particle size. Wider applicability of the measurement methodology to study snow particle rotation is also discussed. This article is protected by copyright. All rights reserved.

Description: ABSTRACT We use the concentration of in situ 10 Be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to Greenland's sediment budget. We sampled along the western, eastern, and southern margins of the Greenland Ice Sheet, and collected sediment sourced from glacerized ( n  = 19) and non-glacerized terrain ( n  = 10), from channels where sediment from glacerized and non-glacerized terrain is mixed ( n  = 28), from Holocene glacial-fluvial terraces ( n  = 4), and from one sand dune. In situ 10 Be concentrations in sediment range from 1,600 to 34,000 atoms g -1 . The concentration of in situ 10 Be in sediment sourced from non-glacerized terrain is significantly higher than in sediment sourced from glacerized areas, in mixed channel sediment, and in terrace sediment that was deposited during the Holocene. To constrain the timing of landscape exposure for the deglaciated portion of the Narsarsuaq field area in southern Greenland, we measured in situ 10 Be concentration in bedrock ( n  = 5) and boulder ( n  = 6) samples. Paired bedrock and boulder ages are indistinguishable at 1σ uncertainty and indicate rapid exposure of the upland slopes at ~10.5 ka. The isotope concentration in sediment sourced from non-glacerized terrain is higher than in sediment sourced from glacerized terrain because the non-glacerized landscape has been exposed to cosmic radiation since early Holocene deglaciation. Sediment from glacerized areas contains a low, but measurable concentration of 10 Be that likely accumulated at depth during a prolonged period of exposure, probably before the establishment of the Greenland Ice Sheet. The concentration of 10 Be in mixed fluvial sediment and in terrace sediment is low, and similar to the concentration in sediment from glacerized areas, which indicates that the Greenland Ice Sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the sectors we sampled. This article is protected by copyright. All rights reserved.

Description: ABSTRACT We derived a high-resolution, spatially continuous map of erosion and deposition associated with the debris-laden flows triggered by the 2011 Las Conchas wildfire and subsequent rainstorms over a 197 km 2 area in New Mexico, USA. This map was produced using airborne-lidar-derived bare-earth Digital Elevation Models (DEMs) acquired approximately one year before and one year after the wildfire. Differencing of the pre-wildfire and post-wildfire-and-rainstorm bare-earth DEMs yielded a DEM-of-Difference (DoD) map that quantifies the magnitude of ground-surface elevation changes due to erosion/deposition within each 1 m 2  pixel. We applied a 0.3 m threshold filter to our DoD to remove changes that could have been due to artifacts and/or imperfect georeferencing. The 0.3 m value for the threshold filter was chosen based on the stated accuracy of the lidar as well as a comparison of areas of significant topographic change mapped in aerial photographs with those predicted using a range of candidate threshold values for the DoD filter. We developed an automated procedure that accepts the DoD map as input and computes, for every pixel in the DEM, the net sediment volume exported through each pixel by colluvial and/or fluvial processes using a digital routing algorithm. An analysis of the resulting sediment volume map for the Las Conchas fire demonstrates that sediment volume is proportional to upstream contributing area. After normalized by contributing area, the average sediment yield (defined as the sediment volume divided by the contributing area) increases as a power-law functions of the average terrain slope and soil burn severity class (SBSC) with exponents equal to approximately 1.5. Our analysis quantifies the relationships among sediment yield, average terrain slope, and average soil burn severity class at the watershed scale and should prove useful for predicting the geomorphic response of wildfire-affected drainage basins. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Active and semi-active anastomosing Holocene channels upstream of the delta in the lower valley of the meandering Neches River in southeast Texas represent several morphologically distinct and hydrologically independent channel systems. These appear to have a common origin as multi-thread crevasse channels strongly influenced by antecedent morphology. Levee breaching leads to steeper cross-valley flows toward floodplain basins associated with Pleistocene meander scars, creating multi-thread channels that persist due to additional tributary contributions and ground water inputs. Results are consistent with the notion of plural systems where main channels, tributaries, and sub-channels may have different morphologies and hydrogeomorphic functions. The adjacent Trinity and Sabine Rivers have similar environmental controls, yet the Trinity lacks evidence of extensive anastomosing channels on its floodplain, and those of the Sabine appear to be of different origin. The paper highlights the effects of geographical and historical contingency and hydrological idiosyncrasy. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Application of Schmidt hammer exposure-age dating (SHD) to landforms has substantially increased in recent years. The original mechanical Schmidt hammer records R-(Rebound) values. Although the newly introduced electronic Schmidt hammer (SilverSchmidt) facilitates greatly improved data processing, it measures surface hardness differently, recording Q-(Velocity) values that are not a priori interconvertible with R-values. This study is the first to compare the performance of both instruments in the context of field-based exposure-age dating with a particular focus on the interconvertibility of R-values and Q-values. The study was conducted on glacially polished pyroxene-granulite gneiss, Jotunheimen, Southern Norway. Results indicate that mean Q-values are consistently 8–10 units higher than mean R-values over the range of values normally encountered in the application of SHD to glacial and periglacial landforms. A convenient conversion factor of ± 10 units may, therefore, be appropriate for all but the softest rock types close to the technical resolution of the instruments. The electronic Schmidt hammer should therefore be regarded as a useful complement and potential replacement for the mechanical Schmidt hammer. Conversion of published R-values data to Q-values requires, however, careful control and documentation of instrument calibration. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In this study we develop an empirical method to estimate the volume threshold for predicting coseismic landslide dam formation using landscape parameters obtained from DEMs. We hypothesize that the potential runout and volume of landslides, together with river features, determine the likelihood of the formation of a landslide dam. To develop this method, a database was created by randomly selecting 140 damming and 200 non-damming landslides from 501 landslide dams and 〉60 000 landslides induced by the M w 7.9 2008 Wenchuan earthquake in China. We used this database to parameterise empirical runout models by stepwise multivariate regression. We find that factors controlling landslide runout are landslide initiation volume, landslide type, internal relief ( H ) and the H/L ratio (between H and landslide horizontal distance to river, L ). In order to obtain a first volume threshold for a landslide to reach a river, the runout regression equations were converted into inverse volume equations by taking the runout to be the distance to river. A second volume threshold above which a landslide is predicted to block a river was determined by the correlation between river width and landslide volume of the known damming landslides. The larger of these two thresholds was taken as the final damming threshold. This method was applied to several landslide types over a fine geographic grid of assumed initiation points in a selected catchment. The overall prediction accuracy was 97.4% and 86.0% for non-damming and damming landslides, respectively. The model was further tested by predicting the damming landslides over the whole region, with promising results. We conclude that our method is robust and reliable for the Wenchuan event. In combination with pre-event landslide susceptibility and frequency-size assessments, it can be used to predict likely damming locations of future coseismic landslides, thereby helping to plan emergency response. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The success of seedlings and rejuvenated woody debris growing on river bedforms depends on the resistance to uprooting by flow provided by their simple root architecture. Avena sativa and Medicago sativa seedlings were used in flume experiments as prototypes for juvenile riparian plants. Very little is known about the magnitude of root anchoring forces and the role of secondary roots of such simple root systems. We performed 1550 vertical uprooting experiments on Avena sativa and Medicago sativa seedlings grown in quartz sand. Seedlings were pulled up by direct traction using a wheel driven by a computer-controlled motor and the force was recorded. Roots were scanned and architectural parameters (root length and number of roots) determined. Uprooting force and work (the integral of the applied force times the distance over which it is applied) were then related to root architecture and soil variables. Resistance to uprooting increased with decreasing sediment size and sediment moisture content. The initial response of the root-soil system to uprooting showed linear elastic behaviour with modulus increasing with plant age. While the maximum uprooting force was found to increase linearly with total root length and be mainly dependent on the length of the main root, uprooting work followed a power law and has to be related to the whole root system. Thus, for the young plants we considered, secondary roots are responsible for the ability to withstand environmental disturbances in terms of duration rather than magnitude. This distinction between primary and secondary roots can be of crucial importance for seedlings of riparian species germinating on river bars and islands where inundation is a main cause of mortality. Beyond clarifying the biomechanical role of soil and root variables, the uprooting statistics that we obtained are useful in interpreting and designing ecomorphodynamic flume experiments. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Contemporary patterns in river basin sediment dynamics have been widely investigated but the timescales associated with current sediment delivery processes have received much less attention. Furthermore, no studies have quantified the effect of recent land use change on the residence or travel times of sediment transported through river basins. Such information is crucial for understanding contemporary river basin function and responses to natural and anthropogenic disturbances or management interventions. To address this need, we adopt a process-based modelling approach to quantify changes in spatial patterns and residence times of suspended sediment in response to recent agricultural land cover change. The sediment budget model SedNet was coupled with a mass balance model of particle residence times based on atmospheric and fluvial fluxes of three fallout radionuclide tracers ( 7 Be, excess 210 Pb and 137 Cs). Mean annual fluxes of suspended sediment were simulated in seven river basins (38-920 km 2 ) in south-west England for three land cover surveys (1990, 2000 and 2007). Suspended sediment flux increased across the basins from 0.5-15 to 1.4-37 kt y -1 in response to increasing arable land area between consecutive surveys. The residence time model divided basins into slow (upper surface soil) and rapid (river channel and connected hillslope sediment source areas) transport compartments. Estimated theoretical residence times in the slow compartment decreased from 13-48 to 5.6-14 ky with the increase in basin sediment exports. In contrast, the short residence times for the rapid compartment increased from 185-256 to 260-368 d as the modelled connected source area expanded with increasing sediment supply from more arable land. The increase in sediment residence time was considered to correspond to longer sediment travel distances linked to larger connected source areas. This novel coupled modelling approach provides unique insight into river basin responses to recent environmental change not otherwise available from conventional measurement techniques. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The plants and animals that inhabit river channels may act as zoogeomorphic agents affecting the nature and rates of sediment recruitment, transport and deposition. The impact of benthic-feeding fish, which disturb bed material sediments during their search for food, has received very little attention, even though benthic feeding species are widespread in rivers and may collectively expend significant amounts of energy foraging across the bed. An ex-situ experiment was conducted to investigate the impact of a benthic feeding fish (Barbel Barbus barbus ) on particle displacements, bed sediment structures, gravel entrainment and transport fluxes. In a laboratory flume changes in bed surface topography were measured and grain displacements examined when an imbricated, water-worked bed of 5.6-16 mm gravels was exposed to feeding juvenile Barbel (on average, 0.195 m in length). Grain entrainment rates and bedload fluxes were measured under a moderate transport regime for substrates that had been exposed to feeding fish and control substrates which had not. On average, approximately 37% of the substrate, by area, was modified by foraging fish during a four-hour treatment period, resulting in increased microtopographic roughness and reduced particle imbrication. Structural changes by fish corresponded with an average increase in bed load flux of 60% under entrainment flows, whilst on average the total number of grains transported during the entrainment phase was 82% higher from substrates that had been disturbed by Barbel. Together, these results indicate that by increasing surface microtopography and undoing the naturally stable structures produced by water working, foraging can increase the mobility of gravel bed materials. An interesting implication of this result is that by increasing the quantity of available, transportable sediment and lowering entrainment thresholds, benthic feeding might affect bedload fluxes in gravel-bed rivers. The evidence presented here is sufficient to suggest that further investigation of this possibility is warranted. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This paper addresses a series of geomorphic questions relating to large-scale (〉1 km), long-term (100 – 1,000 years) coastal planshape evolution. Previous research on soft-cliff coasts has recognised the role of protective fronting beach volumes on reducing rates of cliff toe retreat. However, it is the maintenance of this critical threshold that ultimately determines two contrasting modes of shoreline behaviour: Mode A, in which there is little beach sediment and shoreline evolution is controlled by material strength; and, Mode B, when ample beach sediment means that shoreline evolution is controlled by longshore sediment transport. Here we use a numerical model (SCAPE) to investigate temporal and spatial changes in beach volume on a broader range of feedbacks than considered in previous models. The transition between Mode A and Mode B coasts is defined by relative sediment inputs to outputs and used to explore how these contrasting modes control the evolution of an initial linear frontage exhibiting longshore changes in cliff lithology (material resistance and the proportion of beach grade material in the eroded bedrock). Under Mode A, relative changes in material resistance result in long term heterogeneous rates of retreat, which result in the development of persistent headland and embayment features. However, under Mode B, feedbacks between coastal planshape, longshore sediment transport, beach volume and wave energy result in steady state retreat rates regardless of longshore variations in resistance. Results are compared and contrasted to previous simulations and site specific examples and a conceptual model of Mode A and Mode B interactions presented. Copyright © 2014 John Wiley & Sons, Ltd.

Description: ABSTRACT River classifications provide useful frameworks to understand complex fluvial landscapes and to manage freshwater ecosystems. Alluvial floodplains for rivers in low-relief glacially conditioned catchments of southern Ontario (Canada) are classified and tested using a sequence of multivariate statistical analyses. An original dataset of 109 floodplain sites is investigated using k-means clustering, principal component analysis, and discriminant analysis statistical approaches. Four primary floodplain types are proposed representing basic morphological, stratigraphical, and sedimentological characteristics. Classifications are successfully discriminated by two principal dimensions: (1) stream power-resistance; and (2) floodplain sedimentology. The latter is most efficiently represented by the availability of alluvial sand, and specifically a new variable defined as floodplain sand equivalent ( FSE ). Floodplain types are generally consistent with previous river classifications, however the glacial legacy requires refined classifications which account for inherited cobble bed materials and patterns of sand supply. Representing the residual variability of stream power-resistance correlations, a third explanatory dimension of sediment transport is suggested, and may explain some within-class variability in channel morphology. Balancing the opposing concepts of fluvial process domains and landform continuums, the potential for transitional floodplain types is also explored. The proposed first-order alluvial floodplain classifications provide a basis from which to further investigate geomorphological diversity within the context of complex glacial legacy effects in low-relief settings. Future research to reveal the spatial arrangement and linkages of distinct morphological groups within a regional landscape mosaic is expected to provide insights into patterns of post-glacial fluvial adjustment. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This short communication describes the development and application of analytical reasoning to quantify instability of an aeolian environment using scale-dependent information coupled with conceptual knowledge of process and feedback mechanisms. Specifically, a simple Fuzzy Cognitive Map (FCM) for aeolian landscape instability was developed that represents conceptual knowledge of key biophysical processes and feedbacks. Model inputs include satellite-derived surface biophysical and geomorphometric parameters. FCMs are a knowledge-based Artificial Intelligence (AI) technique that merges fuzzy logic and neural computing in which knowledge or concepts are structured as a web of relationships that is similar to both human reasoning and the human decision-making process. Given simple process-form relationships, the analytical reasoning model is able to map the influence of land management practices and the geomorphology of the inherited surface on aeolian instability within the South Texas Sandsheet. Results suggest that FCMs can be used to formalize process-form relationships and information integration analogous to human cognition with future iterations accounting for the spatial interactions and temporal lags across the sand sheets. This article is protected by copyright. All rights reserved.