ALBERT

Description: This paper reports on a first attempt of using the virtual velocity approach to assess sediment mobility and transport in two wide and complex gravel-bed rivers of northern Italy. Displacement length and virtual velocity of spray-painted tracers were measured in the field. Also, the thickness of the sediment active layer during floods was measured using scour chains and post-flood morphological changes as documented by repeated survey of channel cross-sections. The effects of 8 and 7 floods were studied on the Tagliamento and Brenta rivers, where 259 and 277 spray-painted areas were surveyed, respectively. In the Tagliamento Rivers 36 % of the spray-painted areas experienced partial transport, whereas in the Brenta this accounted for 20%. Full removal/gravel deposition was whereas observed on 37 % and 26 % of these areas on the Tagliamento and Brenta rivers, respectively. The mean displacement length of particles, the thickness of the active layer and the extent of partial transport are well correlated with the dimensionless shear stress. The virtual velocity approach allowed calculation of bed material transport over a wide range of flood magnitudes. Annual coarse sediment transport was calculated up to 150 for the Tagliamento, and 30 × 10 3  m 3  yr -1 for the Brenta. The outcomes of this work highlight the relevance of partial transport condition, as it could represent more than 70% of the total bed material transported during low-magnitude floods, and up to 40% for near-bankfull events. Results confirm that bed material load tends to be overestimated by traditional formulas. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Abstract: The level of storminess in Ireland during the winter of 2013/2014 was exceptional, the effects of which cost the Irish state in excess of €260 Million in infrastructure repair and insurance claims. In Ireland, a lack of coastal process data from monitoring programmes means that the response of protective barrier coasts to such events remains largely un-investigated. This study addresses this issue through an examination of the geomorphic impacts of recent storms, including those that occurred during the winter 2013/2014, on a breached barrier on the southwest coast of Ireland. Data from a two-year terrestrial laser scanning (TLS) monitoring campaign shows that the W2013/2014 events caused a major (〉50 m) dune recession at Rossbehy, Co. Kerry. Results from a simple linear regression analysis indicate storm duration plays an important role in the removal of foredunes at the study site. Given the fact that the frequency of intense storms in the vicinity of Ireland is forecast increase within the next century, a scientific understanding of barrier response to such events is critical to inform sound management practices. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Spheroidal weathering, one of the important rock weathering styles, has been attributed to chemical weathering by the water from joint surfaces, and mechanical aspects of the weathering have not been well addressed. We made an investigation on spheroidal weathering of Miocene granite porphyry with well-developed columnar joints and found that this spheroidal weathering proceeds through chemical processes and accompanying mechanical processes. The investigation of the textures, physical properties, mineralogy, and chemistry of the porphyry revealed the presence of a brown band on the surface margins of corestones, representing the oxidation of pyrite and chlorite, and the precipitation of iron hydroxides, and the consequent generation of micro-cracks within the band. During weathering, oxidation progresses inwards from joints that surround the rindlets, including both high-angle columnar and low-angle planar joints, and causes rounding of the unweathered interior portion of the rock. Microscopic observations of the brown band embedded with fluorescent resin show that pores are first filled with iron hydroxides, and that micro-cracks then form parallel to the oxidation front in the outer portion of the brown band. Iron hydroxide precipitation increases the P-wave velocity in the brown band, while micro-crack formation decreases the tensile strength of the rock. Where the brown band has thickened to ~6 cm, the micro-cracks are connected to one another to create continuous cracks, which separate the rindlets from the corestone. Micro-crack formation parallel to the corestone surface may be attributed to compressive stresses generated by small amounts of volumetric expansion due to the precipitation of iron hydroxides in the brown band. Earth surface is under oxidizing environments so that precipitation of iron hydroxides commonly occurs; the spheroidal weathering in this paper is a typical example of the combination of chemical and mechanical processes under such environments. This article is protected by copyright. All rights reserved.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: ABSTRACT Cultivated fields have been shown to be the dominant sources of sediment in almost all investigated UK catchments, typically contributing 85 to 95% of sediment inputs. As a result, most catchment management strategies are directed towards mitigating these sediment inputs. However, in many regions of the UK such as the Nene basin there is a paucity of sediment provenance data. This study used the 137 Cs inventories of lake and floodplain cores as well as the 137 Cs activities of present day sediment to determine sediment provenance. Sediment yields were also reconstructed in a small lake catchment. This article is protected by copyright. All rights reserved. Low 137 Cs inventories were present in the lake and floodplain cores in comparison to the reference inventory and inventories in cores from other UK catchments. 137 Cs activities in the present day sediments were low; falling close to those found in the channel bank catchment samples. It was estimated that 60 to 100% of the sediment in the Nene originated from channel banks. This article is protected by copyright. All rights reserved. Pre 1963 sediment yields were approximately 11.2 t km −2 yr −1 and post 1963 was approximately 11.9 t km −2 yr −1 . The lack of increased sediment yield post 1963 and low sediment yield is unusual for a UK catchment (where a yield of 28 to 51 t km −2 yr −1 is typical for a lowland agricultural catchment), but is explained by the low predicted contribution of sediment from agricultural topsoils. The high channel bank contribution is likely caused by the river being starved of sediment from topsoils, increasing its capacity to entrain bank material. This article is protected by copyright. All rights reserved. The good agreement between the results derived using cores and recently transported sediments, highlight the reliability of 137 Cs when tracing sediment sources. However, care should be taken to assess the potential impacts of sediment particle size, sediment focusing in lakes and the possible remobilisation of 137 Cs from sedimentary deposits. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Reporting uncertainty in environmental measurements and estimates is important for cross comparison and inter-comparison of sites and other spatial units. One such measure is the load of large in-stream wood in river systems. In this paper we propose the use of the Weibull distribution to describe the central tendency and variability of wood loads along a river reach. We illustrate the link between the average wood load and the central tendency or scale parameter of the Weibull distribution. The shape of the Weibull distribution is strongly related to the ability of rivers to transport and rearrange the wood in a reach. We use six Victorian rivers to test the fit of the Weibull distribution, showing that the Weibull is a useful and flexible distribution that provides common reporting metrics useful for future studies. Using a common reporting metrics provides a stronger tool for comparisons of wood loads between rivers and with reaches. This article is protected by copyright. All rights reserved.

Description: Riverbank stabilization using rock riprap is commonly used for protecting road and bridge structures from fluvial erosion. However, little is known about how streams adjust to such perturbation or how this can affect fish habitat in different fluvial environments, particularly for non-salmonid species in small streams. The objective of this study is to assess impacts of riprap on fish habitat quantity and quality through a pairwise comparison of 27 stabilized and non-stabilized stream reaches in two physiographic regions, the St. Lawrence Lowlands and the Appalachian highlands of Montérégie-Est (Quebec, Canada). Both quantitative (hydro-morphological index of diversity, HMID) and qualitative (Qualitative Habitat Evaluation Index , QHEI) fish habitat assessment techniques are applied in order to compare results between methods. For each stream reach depth and velocity were measured to calculate HMID. In-stream cover (woody debris, overhanging vegetation, undercut banks, aquatic macrophytes) and habitat units (pools, riffles, runs, glides) were also documented and used to determine QHEI. Results show that overall bank stabilization using riprap at bridge and stream crossings alters fish habitat characteristics. Loss of in-stream covers and riparian vegetation lower QHEI scores at stabilized reaches, especially in more pristine Appalachian streams, but has less impact on already altered straightened Lowlands streams. In this latter context, some positive alterations of fish habitat were observed in riprapped reaches due to the coarsening of the substrate and an induced increase of slope. The two metrics (HMID and QHEI) revealed similar differences between stabilized and non-stabilized sites for Lowlands sites, but their level of agreement was much less in the Appalachian streams, suggesting caution when interpreting habitat quality results based on a single metric. This article is protected by copyright. All rights reserved.

Description: Field based palaeoflood event reconstruction has the potential to contribute to the development of our understanding of longterm landscape evolution. However the reconstruction of past flow event histories (magnitude and frequency) over long-term (Quaternary) timescales is fraught with difficulties. Here we make a preliminary exploration of some of the practicalities of flood reconstruction from fluvial terrace archives using commonly available sedimentological and geomorphological observations from a field perspective. We utilize Manning and palaeostage indicators to reconstruct historic events that can be used as benchmarks for a lesser used competence based approach (Clarke 1996), which is applied to coarse-grained strath terrace deposits. We evaluate the results against gauged records for extreme and catastrophic events that affected the same region in 1973 and 2012. The findings suggest that the competence approach is most effectively applied to terrace deposits if the channel geometry is taken into account when sampling both in cross section and in longitudinal section and calibrated against the sedimentology for palaeo-flow depth. Problems can arise where constrictive channel geometries allow boulder jams to develop, acting as sediment traps for the coarsest material and leading to downstream ‘boulder starvation’. Useful sites to target for palaeoflood reconstruction, therefore, would be upstream of such constrictive reaches where the coarsest transportable bedload has been effectively trapped. Sites to avoid would be downflow, where the deposited material would poorly represent palaeoflood competence. Underestimation from maximum boulder preservation and limited section exposure issues would appear to outweigh possible overestimation concerns related to fluid density and unsteady flow characteristics such as instantaneous acceleration forces. Flood data derived from river terrace deposits suggests that basal terrace geometries and coarse boulder lags common to many terrace sequences are likely the result of extreme flow events which are subsequently filled by lesser magnitude flood events, in this environmental setting. This article is protected by copyright. All rights reserved.

Description: Bedrock erosion rates in natural landscapes are usually slow, of the order of millimeters per year or less, and sophisticated techniques have been developed to measure them. Different techniques have proved to be valuable depending on the spatial and temporal scale on which information is needed, on the environment and on the scientific question that is asked. Here, we give an overview of the various methods that have been developed. We introduce their working principles and outline their advantages and disadvantages. Further, we provide comprehensive references to relevant literature, both on the methods and on scientific examples of their application. This article is protected by copyright. All rights reserved.

Description: This study aims to understand (mainly qualitatively) the long-term role of human impact on avulsion processes and the development of fluvial (mega-) fans in semi-arid environments. In this paper we refer to human impact as the direct influences of actions on the river's hydraulics (i.e. flow regulation, flow diversion and channel engineering). In five case-studies drawn from the Khuzestan plains in SW Iran we have analysed the setup and triggering conditions of specific avulsions that occurred in the past (timescale of millennia) and identified the role of human interference in their causation. Our analysis is based on the integration of historical, archaeological, geomorphological and geological data. Through this study we demonstrate that avulsions in the Khuzestan plains are the result of long-term and complex interplay between multiple human-induced and natural causes. In similar ways human-induced actions may play important roles during different phases of avulsion development. The “success” of an avulsion in the post-triggering phase may be defined by human-induced setup causes as well as morphodynamic processes. We suggest that present-day flood events may be partly inherited from long-term human alterations of the natural processes. These finding could have implications for any fluvial system (e.g. distributive fluvial systems, deltas) where avulsion plays a major role in their development and research tends to emphasise on natural mechanisms. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In arid and semi-arid rangeland environments, an accurate understanding of runoff generation and sediment transport processes is key to developing effective management actions and addressing ecosystem response to changes. Yet, many primary processes (namely sheet and splash and concentrated flow erosion, as well as deposition) are still poorly understood due to a historic lack of measurement techniques capable of parsing total soil loss into these primary processes. Current knowledge gaps can be addressed by combining traditional erosion and runoff measurement techniques with image-based 3D soil surface reconstructions. In this study, data (hydrology, erosion and high-resolution surface microtopography changes) from rainfall simulation experiments on twenty-four plots in saline rangelands communities of the Upper Colorado River Basin were used to improve understanding on various sediment transport processes. A series of surface change metrics were developed to quantify and characterize various erosion and transport processes (e.g., plot-wide vs. concentrated flow detachment and deposition) and were related to hydrology and biotic and abiotic land surface characteristics. In general, erosivity controlled detachment and transport processes while factors modulating surface roughness such as vegetation controlled deposition. The extent of the channel network was a positive function of slope, discharge and vegetation. Vegetation may deflect runoff in many flow paths but promoted deposition. From a management perspective, this study suggests that effective runoff soil and salt load reduction strategies should aim to promote deposition of transported sediments rather than reducing detachment which might not be feasible in these resource-limited environments. This article is protected by copyright. All rights reserved.

Description: High and moderate severity wildfires should increase sediment production from unpaved roads due to the increased surface runoff from upslope, and increase road-stream connectivity due to the decrease in downslope surface roughness as well as the increase in surface runoff and erosion. Because no study has documented these effects, we surveyed road surface erosion features and quantified road-stream connectivity as a function of fire severity and road segment characteristics. The data were collected one year after the High Park wildfire from 141 hydrologically distinct road segments along 6.8 km of an unpaved road west of Fort Collins, Colorado. Road segments below areas burned at high and moderate severity had significantly more rills than road segments below areas that burned at low severity. Road segment slope was an important control on the proportion of segment length with rills, and the strength of the relationship between road segment slope and the amount of rilling increased with burn severity. Flatter road segments tended to capture the sediment eroded from upslope burned areas. In areas burned at high and moderate severity all of the road segments had drainage features extending to a stream, and 78% of the segments in areas burned at low severity also were connected. These exceptionally high rates of road-stream connectivity are attributed to the increased runoff from upslope, the segment-scale collection and funneling of hillslope and road surface runoff to a single drainage point, and the reduced infiltration and trapping capacity of the burned area below the road. The results show the need to either outslope the roads or increase the frequency of constructed drainage features after wildfires, particularly for steeper road segments in areas burned at high or moderate severity. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Flood risk management is an essential responsibility of state governments and local councils to ensure the protection of people residing on floodplains. Globally, floodplains are under increasing pressure from growing populations. Typically, the engineering-type solutions that are used to predict local flood magnitude and frequency based on limited gauging data are inadequate, especially in settings which experience high hydrological variability. This study highlights the importance of incorporating geomorphological understanding into flood risk management in south-east Queensland (SEQ), an area badly affected by extreme flood events in 2011 and 2013. The major aim of this study is to outline the hydrological and sedimentological characteristics of various ‘inundation surfaces’ that are typical of catchments in the sub-tropics. It identifies four major inundation surfaces; within-channel bench ( Q  ~ 2.33y ARI); genetic floodplain ( Q  = 20y ARI); hydraulic floodplain (20y 〈  Q  ≤ 200y ARI) and terrace ( Q  〉 1000y ARI). These surfaces are considered typical of inundation areas within, and adjacent to, the large macrochannels common to this region and others of similar hydrological variability. An additional area within genetic floodplains was identified where flood surfaces coalesce and produce an abrupt reduction in channel capacity. This is referred to here as a Spill-out zone (SOZ). The associated vulnerability and risk of these surfaces is reviewed and recommendations made based on incorporating this geomorphological understanding into flood risk assessments. These recommendations recognise the importance to manage for risks associated with flow inundation and sediment erosion, delivery and deposition. The increasing availability of high resolution topographic data opens up the possibility of more rapid and spatially extensive assessments of key geomorphic processes which can readily be used to predict flood risk. This article is protected by copyright. All rights reserved.

Description: Submerged aquatic vegetation affects flow, sediment and ecological processes within rivers. Quantifying these effects is key to effective river management. Despite a wealth of research into vegetated flows, the detailed flow characteristics around real plants in natural channels are still poorly understood. Here we present a new methodology for representing vegetation patches within computational fluid dynamics (CFD) models of vegetated channels. Vegetation is represented using a Mass Flux Scaling Algorithm (MFSA) and drag term within the Reynolds-Averaged Navier-Stokes Equations, which account for the mass and momentum effects of the vegetation respectively. The model is applied using three different grid resolutions (0.2, 0.1 & 0.05 m) using time-averaged solution methods and compared to field data. The results show that the model reproduces the complex spatial flow heterogeneity within the channel and that increasing the resolution leads to enhanced model accuracy. Future applications of the model to the prediction of channel roughness, sedimentation and key eco-hydraulic variables are presented, likely to be valuable for informing effective river management. This article is protected by copyright. All rights reserved.

Description: The declining costs of small Unmanned Aerial systems (sUAS), in combination with Structure from Motion (SfM) photogrammetry have triggered renewed interest in image-based topography reconstruction. However, the potential uptake of sUAS-based topography is limited by the need for ground control acquired with expensive survey equipment. Direct georeferencing (DG) is a workflow that obviates ground control and uses only the camera positions to georeference the SfM results. However, the absence of ground control poses significant challenges in terms of the data quality of the final geospatial outputs. Notably, it is generally accepted that ground control is required to georeference, refine the camera calibration parameters, and remove any artefacts of optical distortion from the topographic model. Here, we present an examination of DG carried out with low-cost consumer-grade sUAS. We begin with a study of surface deformations resulting from systematic perturbations of the radial lens distortion parameters. We then test a number of flight patterns and develop an novel error quantification method to assess the outcomes. Our perturbation analysis shows that there exists families of predictable equifinal solutions of K 1 -K 2 which minimise doming in the output model. The equifinal solutions can be expressed as K 2  =  f (K 1 ) and they have been observed for both the DJI Inspire 1 and Phantom 3 sUAS platforms. This equifinality relationship can be used as an external reliability check of the self-calibration and allow a DG workflow to produce topography exempt of non-affine deformations and with random errors of 0.1% of the flying height, linear offsets below 10 m and off-vertical tilts below 1°. Whilst not yet of survey-grade quality, these results demonstrate that low-cost sUAS are capable of producing reliable topography products without recourse to expensive survey equipment and we argue that direct georeferencing and low-cost sUAS could transform survey practices in both academic and commercial disciplines. This article is protected by copyright. All rights reserved.

Description: Plants influence river channel topography, but our understanding of the interaction among plants, flow, and sediment is limited, especially when sediment supply is variable. Using laboratory experiments in a recirculating flume with live seedlings in a mobile sand bed, we demonstrate how varying the balance between sediment supply and transport capacity shifts the relationship between plants and bar-surface topography. Each experimental trial contrasted two sediment conditions, in which initially supply was maintained in equilibrium with transport via sediment recirculation, followed by sediment deficit, in which transport capacity exceeded supply, which was set to zero. For both sediment balances, the topographic response was sensitive to plant size, with larger plants inducing greater aggradation relative to a baseline condition. During sediment equilibrium, the positive relationship between plant size and topographic change also depended on species morphology (multi-stemmed shrubs versus single-stemmed plants). Plant morphology effects disappeared when the sediment balance shifted to a deficit, but the presence of plants had a greater impact on the magnitude of change compared to the topographic response under sediment equilibrium. Our results suggest that the interactions among sediment supply, plants, and topography may be strongest on rivers with a balance in sediment supply and transport capacity. Because of the large variability in fluvial sediment supply resulting from natural and anthropogenic influences, these interactions will differ spatially (e.g. longitudinally through a watershed) and at different temporal scales, from single flood events to longer time periods. This article is protected by copyright. All rights reserved.

Description: Vegetation can have an important role in controlling channel planform, through its effects on channel roughness, and root-reinforcement of bank and bar materials. Along the Platte River in central Nebraska, USA, The Platte River Recovery Implementation Program (PRRIP) has been tasked with managing the planform of the river to benefit endangered species. To investigate the potential use of planned Short Duration High Flow events (SDHFs) to manage bar vegetation, this study combined several approaches to determine whether flows of up to 227 m 3 s -1 through the central Platte River, could remove cottonwood, Phragmites and reed canarygrass stands of various ages and densities from in-channel bars. First, fieldwork was carried out to measure the uprooting resistance, and resistance to bending for each species. Second, a set of flume experiments was carried out to measure the forces exerted on the three species of interest under different flow conditions. Finally, a numerical study compared drag forces (driving) measured in the flume study, with uprooting forces (resisting) measured in the field, was carried out for each species to determine the likelihood of plant removal by SDHFs. Results showed that plants with more than a year of root growth, likely cannot be removed through drag and local scour alone, even at the 100-year recurrence interval discharge. At most, a few cottonwood seedlings could be removed from bars through drag, scour and undercutting, where rooting depths are still small. The results presented here help us further understand the positive feedbacks that lead to the creation of permanent, vegetated bars rather than mobile braided channels. As such, the findings could help inform management decisions for other braided rivers, and the combined field, flume and modelling techniques used in this study could be applied to other fluvial systems where vegetation and planform dynamics are of interest. This article is protected by copyright. All rights reserved.

Description: This study aims at evaluating the performance of the Maximum Entropy method in assessing landslide susceptibility, exploiting topographic and multispectral remote sensing predictors. We selected the catchment of the Giampilieri stream, which is located in the north-eastern sector of Sicily (southern Italy), as test site. On 1/10/2009, a storm rainfall triggered in this area hundreds of debris flow/avalanche phenomena causing extensive economical damage and loss of life. Within this area a presence-only-based statistical method was applied to obtain susceptibility models capable of distinguish future activation sites of debris flow and debris slide, which where the main source failure mechanisms for flow or avalanche type propagation. The set of predictors used in this experiment comprised primary and secondary topographic attributes, derived by processing a high resolution digital elevation model, CORINE land cover data and a set of vegetation and mineral indices obtained by processing multispectral ASTER images. All the selected data sources are dated before the disaster. A spatially random partition technique was adopted for validation, generating fifty replicates for each of the two considered movement typologies in order to assess accuracy, precision and reliability of the models. The debris slide and debris flow susceptibility models produced high performances with the first type being the best fitted. The evaluation of the probability estimates around the mean value for each mapped pixel shows an inverted relation, with the most robust models corresponding to the debris flows. With respect to the role of each predictor within the modelling phase, debris flows appeared to be primarily controlled by topographic attributes whilst the debris slides were better explained by remotely sensed derived indices, particularly by the occurrence of previous wildfires across the slope. The overall excellent performances of the two models suggest promising perspectives for the application of presence-only methods and remote sensing derived predictors. This article is protected by copyright. All rights reserved.

Description: In the spawning environment of salmonids, the quality of the intergravel flow is an essential abiotic requirement for the survival success of incubated embryos. As one of the most frequently investigated anthropogenic environmental impacts, the enhanced mobilization of fine sediments (〈1 mm) and their entry into riverine ecosystems is considered as a major cause for the degradation of a variety of biological processes and habitats, including the spawning habitats of salmonids. In catchments draining crystalline bedrock, however, like the Bohemian Massif in the northern part of Austria, the excessive loading of river channels with coarse sand and fine gravel sediments (D = 1-10 mm) and less cohesive than fines is common as a consequence of altered catchment landuse. Here, far less understanding exists for the mechanism and the possible implications of coarse sand infiltration on the functioning of the intergravel flow in salmonid redds. To investigate the intergravel flow hydraulics in response to coarse sand infiltration (D 50  = 2 mm) in brown trout spawning redds (Salmo trutta fario) under controlled conditions, a laboratory flume experiment with three infiltration scenarios was conducted: (1) no infiltration, (2) segmental infiltration and (3) full section infiltration. A more than two times drop in the average intergravel flow velocity was documented from scenario 1 (5.85 cms -1 ) to scenario 2 (2.53 cms -1 ) and another clear reduction was seen from scenario 2 (2.53 cms -1 ) to scenario 3 (1.61 cms -1 ). Moreover, in scenario 3, a clear reduction of the intergravel flow traveling distance was observed. Based on the findings we conclude that future considerations regarding the sustainable catchment management of salmonid fisheries should include programs to reduce not only the excessive entry of fines, but, in the relevant catchments, also the entry of excessive coarse sand into the riverine ecosystem. This article is protected by copyright. All rights reserved.

Description: Those factors controlling the weathering and erosion of sandstone on the field scale are still not well understood. In this study, a specific sandstone overhang (and its surroundings) with artificially induced and extremely high erosion rates was subjected to a complex investigation. Contrast between the erosion rate of the wet and dry portions of the same cliff enabled isolation of the factors responsible for rapid sandstone retreat. Erosion rates, moisture, and salt content, as well as suction were monitored in the field. Mineral phases and water chemistry were analyzed. The measurement of tensile strength, laboratory frost weathering tests, and numerical modeling of stress were performed. The acquired data show that an increase of moisture content in pores in the area of the studied overhang decreased tensile strength of the sandstone to 14 % of its dry value, and increases the sandstone weathering and erosion rate, by nearly 4 orders of magnitude, compared to the same sandstone under natural moisture condition outside on the cliff area. Consequently, frost weathering, in combination with wetting weakening was found to play a major role in weathering/erosion of the sandstone cliff and overhang. Frost weathering rate in both the laboratory and field increases up to 15 times with decreasing gravity-induced stress. The results also indicate that sandstone landforms in temperate climates may potentially develop very rapidly if the pore space is nearly saturated with water, and will later remain relatively stable when the moisture content decreases. As a general implication, it is suggested that overhangs in Central Europe (and elsewhere) might be the result of rapid frost weathering of nearly saturated sandstone during the Last Glacial. This article is protected by copyright. All rights reserved.

Description: Surface infiltration and internal drainage properties of five soil types from arid drylands of South Africa were studied under double ring infiltrometer, rainfall simulation plots (1 m 2 ) and instantaneous drainage plots (9 m 2 ). Changes in soil water content during 40 min rainfall simulation for a rainstorm with average intensity of 1.61 mm min -1 and 30 day drainage period were measured at various depths by 1.5 m long capacitance soil water measuring (DFM) probe. Different (P 〈 0.05) mean surface steady infiltration rate ranged from 0.05 to 4.47 mm min -1 and had a negative power relationship (R 2  = 0.65) with horizon clay plus fine silt content. Power regression (R 2  ≥ 86%) described rainstorm infiltration and obtained steady rates within an average time of 15 min. Mean total infiltrated soil water content was lowest (P 〈 0.05) from surface horizons with either 47.7% clay plus fine silt content or bulk density of 1.91 gcm -3 and exchangeable sodium of not less than 44 mgkg -1 . Surface horizons with lower surface bulk density and total sand fraction of more than 72% had infiltrated depth and mean total infiltrated soil water content up to 40 cm deeper and 0.55 mm mm -1 greater, respectively. Drainage rate at drained upper limit calculated from the Wilcox drainage model (R 2  ≤ 0.97%) was 0.2 mm day -1 or less were from underlying horizons with either clay plus fine silt of 45% or soft calcium carbonate. Higher drainage rate with accumulative drainage amount greater than 60 mm were from soil profile horizons with clay plus fine silt content of less than 20% and above unity steady infiltration rates. Rainstorm infiltration and drainage rates was shown to depend on permeability and coarseness of the respective soil surface and subsurface horizons; a phenomenon critical for harnessing rain and flood water to recharge groundwater. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Description: The relative efficiency of various hillslope processes through Quaternary glacial-interglacial cycles in the mid-latitudes is not yet well constrained. Based on a unique set of topographic and soil thickness data in the Ardennes (Belgium), we combine the new CLICHE model of climate-dependent hillslope evolution with an inversion algorithm in order to get deeper insight into the ways and timing of hillslope dynamics under one such climatic cycle. We simulate the evolution of a synthetic hill reproducing the slope, curvature, and contributing area distributions of the hillslopes of a ~2500 km 2 real area under a simple two-stage 120-kyr-long climatic scenario with linear transitions between cold and warm stages. The inversion method samples a misfit function in the model parameter space, based on estimates of the fit of topographic derivative distributions in classes of soil thickness and of the relative frequencies of the predicted soil thickness classes. Though the inversion results show remarkable convergence patterns for most parameters, no unique solution emerges. We obtain five clusters of good fits, whose centroids are taken as acceptable model solutions. Based on the predicted time series of average denudation rate and soil thickness, plus snapshots of the soil distribution at characteristic times, we discuss these solutions and, comparing them with independent data not involved in the misfit function, we identify the most realistic scenario. Beyond providing first-order estimates of several parameters that compare well with published data, our results show that denudation rates increase dramatically for a short time at both warm-cold and cold-warm transitions, when the mean annual temperature passes through the [0, -5 °C] range. We also point to the overwhelming importance of solifluction in shaping hillslopes and transporting soil, and the role of depth-dependent creep (including frost creep) throughout the climatic cycle, whereas the contributions of simple creep and overland flow are minor. This article is protected by copyright. All rights reserved.

Description: Active deposition across the floodplains of large rivers arises through a variety of processes; collectively these are here termed ‘spillage sedimentation’. Three groups of eleven spillage sedimentation styles are identified and their formative processes described. Form presences on large river floodplains show different combinations of active spillage styles. Only some large floodplains have prominent levees; some have coarse splays; many have accessory channel dispersion and reworking, whilst still-water sedimentation in lacustrine environments dominates some lower reaches. Infills are also commonly funnelled into prior, and often linear, negative relief forms relating to former migration within the mainstream channel belt. This article is protected by copyright. All rights reserved. Shuttle Radar Topography Mission (SRTM) and Landsat 8 data are used to map spillage form types and coverage along a 1700 km reach of the Amazon that has an active floodplain width of up to 110 km with a systematic character transformation down-valley. Spillage forms associated directly with mainstream processes rarely account for more than 5% of the floodplain deposits. There is a marked decrease in floodplain point bar complexes (PBC) over 1700 km downstream (from 34% to 5%), and an increase in the prevalence of large water bodies (2% to 37%) and accompanying internal crevasses and deltas (0% to 5%). Spillage sedimentation is likely within the negative relief associated with these forms, depending on mainstream sediment-laden floodwater inputs. This article is protected by copyright. All rights reserved. Spillage style dominance depends on the balance between sediment loadings, hydrological sequencing, and morphological opportunity. Down-river form sequences are likely to follow gradient change, prior up-river sediment sequestration and the altered nature of spilled loads, but also crucially, local floodplain relief and incident water levels and velocities at spillage times. Considering style distribution quantitatively, as a spatially distributed set of identifiable forms, emphasises the global variety to spillage phenomena along and between large rivers. This article is protected by copyright. All rights reserved.

Description: In February 2014, a rock pillar with a volume of around 150'000 m 3 collapsed at Piz Kesch in the Eastern Swiss Alps. A reconstruction of the conditions prior to the event and of the event itself is presented on the basis of different sources of data. The methods applied include photogrammetry, terrestrial laser scanning, structural geological analysis, examination of meteorological data, 14 C dating of organic material in permafrost ice from a tension crack and numerical modelling of likely modes of failure. Despite a complete lack of in-situ measurements in the rock wall prior to the event and of direct observations during the event, the available data allow the determination of the approximate timing of the event as well as the structural predisposition, the probable mode of failure and the time scale of several millennia involved in the triggering of the failure of the rock pillar. The interdisciplinary analysis of this event contributes towards understanding the complex interaction of processes involved in large rock slope failures currently occurring in warming mountain permafrost regions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Mangrove forests dominate many tropical coastlines and are one of the most bio-diverse and productive environments on Earth. However, little is known of the large-scale dynamics of mangrove canopies and how they colonize intertidal areas. Here we focus on a fringe mangrove forest located in the Mekong river delta, Vietnam, a fast prograding shoreline where mangroves are encroaching tidal flats. The spatial and temporal evolution of the mangrove canopy is studied using a time series of Landsat images spanning two decades as well as Shuttle Radar Topography Mission (SRTM) elevation data. Our results show that fast mangrove expansion is followed by an increase in Normalized Difference Vegetation Index (NDVI) in the newly established canopy. We observe three different dynamics of the mangrove fringe: in the southwest part of the fringe, near a deltaic distributary where the fringe boundary is linear, the canopy expands uniformly on the tidal flats with a high colonization rate and high NDVI values. In the northeast part of the fringe, near another distributary, the canopy expands at a much lower rate with low NDVI values. In the fringe center far from the river mouths the fringe boundary is highly irregular and mangroves expansion in characterized by sparse vegetated patches displaying low NDVI values. We ascribe these different dynamics to wave action and southwest longshore transport triggered by energetic northeasterly monsoons during winter. We further link the large-scale dynamics of the fringe to small-scale physical disturbances (waves, erosion and deposition) that might prevent the establishment of mangrove seedlings. Based on these results, we include mangrove encroachment in an already published conceptual model of progradation of the Mekong river delta. We conclude that high NDVI values and a constantly linear vegetation-water interface are indicative of stable mangrove canopies undergoing fast expansion, probably triggered by sediment availability at the shore. Our results can be applied more generally to mangrove forests growing in minerogenic and high tidal range environments with high sediment inputs. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Predicted climate change and the associated sea level rise poses an increased threat of flooding due to wave overtopping events at sea and river dikes. To safeguard the land from flooding it is important to keep the soil erosion resistance at the dikes high. As plant roots can be very effective in reducing soil erosion rates by concentrated flow, the main goal of this study is to explore the variability in root system characteristics of five dike vegetation communities along the Scheldt River (Belgium) and to assess their effectiveness in controlling soil erosion rates during concentrated flow. This study is the first one to investigate systematically the erosion-reducing potential of the root properties of representative dike vegetation communities in a temperate humid climate. Results show that the presence of U. dioica resulted in large differences in root length density (RLD) among dike vegetation communities. Observed RLD values in the topsoil ranged from 129 to 235 km m -3 for dike vegetation communities without U. dioica, while smaller values ranging from 22 to 58 km m -3 were found for vegetation communities with U. dioica. The erosion-reducing effect of the dike vegetation communities was estimated based on a global Hill curve model, linking the root length density to the soil detachment ratio (SDR; i.e. the ratio of the soil detachment rate for root-permeated topsoils to the soil detachment rate for root-free topsoils). Concentrated flow erosion rates are likely to be reduced to 13 – 16% of the erosion rates for root-free topsoils if U. dioica is present compared to 22 – 30% for vegetation communities without U. dioica. Hence, to maintain a high resistance of the soil against concentrated flow erosion it is important to avoid the overgrowth of grassland by U. dioica through an effective vegetation management.

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

Description: ABSTRACT Mountain hillslopes are generally shaped by a combination of various types of sediment transport processes (e.g., surface erosion, soil creep, and dry ravel), which can occur simultaneously in the same area. Since sediment transport is generally affected by multiple microclimatic factors, such as heavy rainfall and changes in ground temperature, the types of predominant sediment transport processes vary by season. We conducted field observations in the southern Japanese Alps in the period from 2009 to 2013, using sediment traps and time lapse cameras, to investigate the seasonal changes in the type and flux of hillslope sediment transport on steep mountains in which both rainfall and diurnal freeze-thaw triggered sediment transport. In winter and early spring, sediment transport via diurnal freeze-thaw (soil creep and dry ravel) was highly active, whereas rainfall-induced soil creep and selective transport by overland flow were active in summer and autumn when precipitation is abundant (average sediment flux of 0.033 and 0.074 kg m -1 day -1 , respectively). Sediment flux was spatially variable and was affected by the form of the slope; sediment flux on the concave slope was higher than on the ridge-shaped slope during both freeze-thaw and rainfall periods. Sediment flux on an old landslide exceeded that in second-growth forest regardless of the slope shape. Temporal changes in the sediment flux were not completely synchronized among monitoring plots and were affected by slope shape, grain size, and episodic sediment supply events such as release of sediment from woody debris.

Description: ABSTRACT Least action principle (LAP) in rivers is demonstrated by maximum flow efficiency (MFE) and is the foundation of variational mechanics based on energy and work rather than Newtonian force and momentum. Empirical evidence shows it to be the primary control for the adjustment of alluvial channels. Because most rivers flow with imposed water and sediment loads down valley gradients they have largely inherited, they self-regulate energy expenditure to match the work they are required to do to remain stable. Overpowered systems develop a variety of channel patterns to expend excess energy and remain stable. Australia offers an opportunity to study low-energy rivers closely adjusted to very low continental gradients. The anabranching Marshall and single-thread Plenty Rivers flow down nearly straight channels with average H numbers (ratio between excess bed shear and width/depth ratio) close to the optimum of 0.3 for stationary equilibrium. Ridge-form divisions of the original channel width create anabranches that radically alter W/D ratios relative to bed shear, the same being true for short-wide islands on the large low-gradient Yangtze River in China. In contrast, Mount Chambers Creek in Australia's tectonically more active Flinders Ranges is accreting an alluvial fan with unstable distributary channels exhibiting H numbers well below the optimum. LAP also explains profound biases in Earth's stratigraphic record. Because meandering is an energy-shedding mechanism, sinuous rivers sequester relatively little sediment resulting in all sequences being just a few tens of metres thick. In contrast, low-energy braided disequilibrium systems can sequester sediment piles over a kilometre in thickness and tens of kilometres wide. LAP provides a new paradigm for river research by identifying the attractor state controlling river channel evolution. It links advances in theoretical physics to fluvial geomorphology, stratigraphy and hydraulic engineering and opens opportunities for diverse investigations in Earth system science. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Abstract: The process of channelization on river floodplains plays an essential role in regulating river sinuosity and creating river avulsions. Most channelization occurs within the channel belt (e.g., chute channels), but growing evidence suggests some channels originate outside of the channel-belt in the floodplain. To understand the occurrence and prevalence of these floodplain channels we mapped 3,064 km 2 of floodplain in Indiana, USA using 1.5 m resolution digital elevation models (DEMs) derived from airborne light detection and ranging (LiDAR) data. We find the following range of channelization types on floodplains in Indiana: 6.8% of floodplain area has no evidence of channelization, 55.9% of floodplains show evidence (e.g., oxbow lakes) of chute-channel activity in the channel belt, and 37.3% of floodplains contain floodplain channels that form long, coherent down-valley pathways with bifurcations and confluences active only during overbank discharge. Whereas the first two types of floodplains are relatively well studied, only a few studies have recognized the existence of floodplain channels. To understand why floodplain channels occur, we measured floodplain width, floodplain slope, river width, river meander rate, sinuosity, flooding frequency, soil composition, and land cover. Results show floodplain channels occur when the fluvial systems is characterized by large floodplain-to-river widths, relatively higher meandering rates, and are dominantly used for agriculture. More detailed reach-scale mapping reveals that up to 75% of channel reaches within floodplain channels are likely paleo-meander cutoffs. The meander cutoffs are connected by secondary channels to form floodplain channels. We suggest that secondary channels within floodplains form by differential erosion across the floodplain, linking together pre-existing topographic lows, such as meander cutoffs. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Eutrophication of aquatic ecosystems is one of the most pressing water quality concerns in the U.S. and around the world. Bank erosion has been largely overlooked as a source of nutrient loading, despite field studies demonstrating that this source can account for the majority of the total phosphorus load in a watershed. Substantial effort has been made to develop mechanistic models to predict bank erosion and instability in stream systems; however, these models do not account for inherent natural variability in input values. To quantify the impacts of this omission, uncertainty and sensitivity analyses were performed on the Bank Stability and Toe Erosion Model (BSTEM), a mechanistic model developed by the USDA-ARS that simulates both mass wasting and fluvial erosion of streambanks. Generally, bank height, soil cohesion, and plant species were found to be most influential in determining stability of clay (cohesive) banks. In addition to these three inputs, groundwater elevation, stream stage, and bank angle were also identified as important in sand (non-cohesive) banks. Slope and bank height are the dominant variables in fluvial erosion modeling, while erodibility and critical shear stress had low sensitivity indices; however, these indices do not reflect the importance of critical shear stress in determining the timing of erosion events. These results identify important variables that should be the focus of data collection efforts while also indicating which less influential variables may be set to assumed values. In addition, a probabilistic Monte Carlo modeling approach was applied to data from a watershed-scale sediment and phosphorus loading study on the Missisquoi River, Vermont to quantify uncertainty associated with these published results. While our estimates aligned well with previous deterministic modeling results, the uncertainty associated with these predictions suggests that they should be considered order of magnitude estimates only. This article is protected by copyright. All rights reserved.

Description: Reef islands are low-lying accumulations of unconsolidated sediment formed from the skeletal remains of carbonate-producing reef organisms, and are therefore perceived as highly vulnerable to environmental change. However, basic elements such island composition are not well described and given their inter- and intra-basinal variability a better understanding of reef and island sedimentary environments (and the connections between them) are needed to predict future morphological responses. Here, we present a detailed analysis of benthic ecology and sedimentology which are used to delineate key sediment production zones and biosedimentary depositional facies on the surface of Vabbinfaru platform, Maldives. Field measurements of platform hydrodynamics are applied to sedimentary deposits to determine the potential mobility of grains and identify transport pathways. Carbonate production was dominated by coral framework (mean: 52%) at a narrow zone on the outer reef rim (22% of platform area), and coral-rich detrital sediments (reef: 51%, island: 64%) closely resembled living assemblages. The net transfer of sediment occurred lagoonward by wave-driven processes resulting in a decrease in grain size towards the island (R 2  = 0.502), and was a major control on depositional facies development within the lagoon. Island sediments were distinct from reefal deposits, comprising a restricted suite of durable sands (mean: 1.34ϕ) throughout development. Our findings suggest that the production, breakdown and redistribution of coral-derived sediment by platform currents is fundamental to future island stability at Vabbinfaru, and although alterations away from current ecological states may reduce sediment supply, the time-scales over which island morphological response will occur depend on phase lags between initial coral mortality and the conversion of this material into island-grade sand.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: ABSTRACT Wind flow has been studied in situations where it encounters porous and solid windbreaks, but there has been a lack of research exploring turbulent wind dynamics around and in the lee of real vegetation elements. In dryland contexts, sparse vegetation plays an important role in modulating both the erosivity of the wind and the erodibility of surfaces. Therefore, understanding the interactions between wind and vegetation is key for improving wind erosion modelling in desert landscapes. In this study, turbulent wind flow around three typical dryland vegetation elements (a grass clump, a shrub, and a tree) was examined in Namibia using high-frequency (10 Hz) sonic anemometry. Spatial variations in mean wind velocity, as well as Reynolds stresses and coherent turbulent structures in the flow, were compared and related to the porosities and configurations of the study elements. A shelter parameter, originally proposed by Gandemer (1979, J . Ind . Aerodyn ., 4 , 371–389), was derived to describe the combined impact of the different elements on the energy and variability of horizontal wind flow. Wind velocity was reduced by 70% in the immediate lee of the grass and 40% in the lee of the shrub, but velocity recovered exponentially to equilibrium over the same relative distance in both cases (~9 element heights downwind). Quadrant analysis of the high-frequency wind flow data revealed that the grass clump induced a small recirculation zone in its lee, whereas the shrub did not. Also, higher Reynolds shear stress ( ) and higher ‘flow positivity magnitude’ (ratio of Q1 (outward interaction) and Q4 (sweep) quadrants to Q2 (ejection) and Q3 (inward interaction) quadrants) was generally observed in the wake of the grass. These differences arose because the porosity of the grass clump (53%) was lower than the porosity of the shrub (69%), and thus bleed flow through the shrub was more significant. The bluff-body behaviour of the grass resulted in a more intense and more extensive sheltering effect than the shrub, which implies that overall sediment transport potential is lower in the wake of the grass. The tree displayed a different wake structure to the grass and shrub, owing to the elevation of its crown. A ‘bottom gap’ effect was observed, whereby wind velocities increased possibly due to streamline compression in the gap between the ground and the underside of the tree crown. Differences in flow momentum between the bottom gap and the low-pressure leeward region of the crown are a probable explanation for the formation of a large recirculation vortex. The bottom gap effect led to decreased sheltering up to 3 tree heights downwind, but the surface became increasingly protected by the frontal impact of the crown over a further 8 tree heights downwind (~30 m). The extraction of momentum from the air by the tree therefore resulted in a far more extensive sheltering effect compared to the grass and shrub. This study represents an important investigation of the impact of different vegetation types on turbulent wind flow, and results can be integrated as parameterisations into spatial sediment transport models that explore landscape-scale change on semi-vegetated desert surfaces. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The horizontal and vertical sand mass fluxes in aeolian sand transport are investigated in a wind tunnel by PTV (particle tracking velocimetry). According to the particle velocity and volume fraction of each individual particle from PTV images, the total horizontal sand mass flux, the horizontal mass fluxes of ascending and descending sand particles, and upward and downward vertical sand fluxes are analyzed. The results show that the horizontal mass fluxes of ascending and descending sand particles generally decrease with the increase of height and can be described by an exponential function above about 0.03 m height. At the same friction velocity, the decay heights of the total horizontal sand mass flux and the horizontal mass fluxes of ascending and descending sand particles are very similar. The proportion of horizontal mass flux of ascending sand particles is generally about 0.3-0.42, this means the horizontal mass flux of descending sand particles makes the important contribution of the total horizontal sand mass flux. Both the upward and downward vertical sand mass fluxes generally decrease with height and they are approximately equal at the same height and friction velocity. The relation between upward (or downward) vertical sand mass flux and horizontal sand mass flux can be described by a power function. The present study is helpful to understand the transport of ascending and descending sand particles. This article is protected by copyright. All rights reserved.

Description: The Anthropocene is proposed as a new interval of geological time in which human influence on Earth and its geological record dominates over natural processes. A major challenge in demarcating the Anthropocene is that the balance between human-influenced and natural processes varies over spatial and temporal scales owing to the inherent variability of both human activities (as associated with culture and modes of development) and natural drivers (e.g. tectonic activity and sea level variation). Against this backdrop, we consider how geomorphology might contribute towards the Anthropocene debate focussing on human impact on aeolian, fluvial, cryospheric and coastal process domains, and how evidence of this impact is preserved in landforms and sedimentary records. We also consider the evidence for an explicitly anthropogenic geomorphology that includes artificial slopes and other human-created landforms. This provides the basis for discussing the theoretical and practical contributions that geomorphology can make to defining an Anthropocene stratigraphy. It is clear that the relevance of the Anthropocene concept varies considerably amongst different branches of geomorphology, depending on the history of human actions in different process domains. For example, evidence of human dominance is more widespread in fluvial and coastal records than in aeolian and cryospheric records, so geomorphologically the Anthropocene would inevitably comprise a highly diachronous lower boundary. Even to identify this lower boundary, research would need to focus on the disambiguation of human effects on geomorphological and sedimentological signatures. This would require robust data, derived from a combination of modelling and new empirical work rather than an arbitrary ‘war of possible boundaries’ associated with convenient, but disputed, `golden spikes’. Rather than being drawn into stratigraphical debates, the primary concern of geomorphology should be with the investigation of processes and landform development, so providing the underpinning science for the study of this time of critical geological transition.

Description: ABSTRACT Human land-use changes leading to widespread erosion and gully incision have been well studied, but the effects that erosion and sediment mixing, which accompany the deposition of post-(European) settlement alluvium (PSA), have in valley bottoms and wetlands receive considerably less attention. PSA overlying pre-disturbance swampy meadow (SM) wetland sediments is commonly exposed along incised stream channel gully walls throughout the southeastern Australian Tablelands, providing an ideal setting in which to assess and understand better how PSA deposition affects valley bottoms and the wetland environments that often occupy them. Portable optically stimulated luminescence (pOSL) reader data were measured on bulk sediment samples from SM-PSA stratigraphies at sixteen locations throughout the southeastern Australian Tablelands to assess the effects of erosion and sediment mixing at the SM-PSA boundary. Trends of pOSL data with depth at each profile were used in conjunction with visual profile descriptions to identify the stratigraphic boundary between SM and PSA sediment and to infer the degree of valley bottom erosion and sediment mixing during PSA deposition. At most sites, SM sediments experienced minimal, if any, disturbance during PSA deposition, and we refer to these as non-eroded sites. Many sites, however, experienced a significant degree of erosion and sediment mixing – eroded sites – often corresponding to visually diffuse sedimentary boundaries between the two stratigraphic units. Our findings demonstrate that SM landscapes in the Tablelands can be preserved with minimal disturbance under PSA at non-eroded sites and are preserved beneath a mixing zone at all eroded sites.

Description: Tropical cyclones expose river basins to heavy rainfall and flooding, and cause substantial soil erosion and sediment transport. There is heightened interest in the effects of typhoon floods on river basins in North-East Japan, as the migration of radiocaesium-bearing soils contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident will affect future radiation levels. The five main catchments surrounding FDNPP are the Odaka, Ukedo, Maeda, Kuma and Tomioka basins, but little quantitative modelling has been undertaken to identify the sediment redistribution patterns and controlling processes across these basins. Here we address this issue and report catchment-scale modelling of the five basins using the GETFLOWS simulation code. The 3D models of the basins incorporated details of the geology, soil type, land cover, and used data from meteorological records as inputs. The simulation results were checked against field monitoring data for water flow rates, suspended sediment concentrations and accumulated sediment erosion and deposition. The results show that the majority of annual sediment migration in the basins occurs over storm periods, thus making typhoons the main vectors for redistribution. The Ukedo and Tomioka basins are the most important basins in the region in terms of overall sediment transport, followed by the other three basins each with similar discharge amounts. Erosion is strongly correlated with the underlying geology and the surface topography in the study area. A low permeability Pliocene Dainenji formation in the coastal area causes high surface water flow rates and soil erosion. Conversely, erosion is lower in an area with high permeability granite basement rocks between the Hatagawa and Futaba faults in the center of the study area. Land cover is also a factor controlling differences in erosion and transport rates between forested areas in the west of the study area and predominantly agricultural areas towards the east. The largest sediment depositions occur in the Ogaki and Takigawa dams, at the confluence of the Takase and Ukedo rivers, and at the Ukedo River mouth. Having clarified the sediment redistribution patterns and controlling processes, these results can assist the ongoing task of monitoring radioactive caesium redistribution within Fukushima Prefecture, and contribute to the design and implementation of measures to protect health and the environment.

Description: ABSTRACT Raindrop impact is an important process in soil erosion. Through its pressure and shear stress, raindrop impact causes a significant detach ment of the soil material, making this material available for transport by sheet flow. Thanks to the accurate Navier-Stokes equations solver Gerris, we simulate the impact of a single raindrop of diameter D , at terminal velocity, on water layers of different thickness h : D order to study pressures and shear stresses involved in raindrop erosion. These complex numerical simulations help to understand precisely the dynamics of the raindrop impact, quantifying in particular the pressure and the shear stress fields. A detailed analysis of these fields is performed and self-similar structures are identified for the pressure and the shear stress on the soil surface. The evolution of these self-similar structures are in vestigated as the aspect ratio h/D varies. We find that the pressure and the shear stress have a specific dependence on the ratio between the drop diameter and the water layer thickness and that the scaling laws recently proposed in fluid mechanics are also applicable to raindrops, paving the road to obtain effective models of soil erosion by raindrops. In particular, we obtain a scaling law formula for the dependance of the maximum shear stress on the soil on the water depth, quantity that is crucial for quantifying erosion materials. For submission to Earth Surface Processes and Landforms. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In the critical zone, surficial bedrock interactions result in the formation of a mantle of chemically- and physically-altered material defined here as regolith. In the watershed of the Río Icacos, an upland river draining the Luquillo Mountains in tropical Puerto Rico, we explored the influence of lithology (quartz diorite versus hornfels-facies volcaniclastic rock) on weathering. Regolith profiles were studied by drilling boreholes and imaging the subsurface using ground penetrating radar (GPR). Overall, the regolith structure is not laterally continuous but rather is punctuated by zones of deep fractures that host in situ weathering, corestones, and colluvial material. GPR images of these vertical zones show reflectors at 15–20 m depth. Thus, the architecture of the critical zone in the upper Luquillo Mountains is highly dependent on lithology and its influence on fracture development. At the highest elevations where hornfels overlies quartz diorite, positive feedbacks occur when the water table drops so that oxidative weathering of biotite in the more felsic rock creates microfractures and allows deeper infiltration of meteoric waters. Such exposure results in some of the fastest weathering rocks in the world and may contribute to formation of the knickpoint in the Río Icacos watershed. This work represents the first study combining GPR and drilling to look at the structure of the deep critical zone and demonstrates: 1) the importance of combining direct methods (such as drilling) with indirect methods (such as GPR) to understand the architecture of the critical zone in tropical systems; and 2) the interplay of the surficial stress regime, lithology and climate in dictating the architecture of weathering. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The growth and decline of salt marshes may be the result of various interacting biogeomorphic processes and external factors. We present a case study of the Mokbaai on the Wadden island of Texel, where we assess the relative importance and the interaction between the biogeomorphic processes and various disturbances. We analysed changes in vegetation composition in the salt marsh and sedimentation-erosion patterns of the adjoining intertidal flat over a 30-year period. Vegetation underwent regression in the lower parts of the marsh, i.e. the low marsh zone changed into pioneer zone. Comparing elevation measurements from 2013 and 1983 showed that the adjoining intertidal flats eroded 15-25 cm. Maintenance dredging of a nearby harbour might negatively impact the sediment balance indicating that the regression of the lower parts of the salt marsh is caused by a lack of sediment. Simultaneously, a change in the local hydrology led to vegetation succession into high and brackish salt marsh, increased organic sediment production and consequently cliff formation. The results from this case study show that, even in a relatively small salt marsh, changes in external factors may set in motion a series of biogeomorphic processes and feedbacks, leading to locally contrasting trends in spatiotemporal development. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Dolines are closed geomorphological depressions which are surface manifestations of karstic systems. Usually developed on limestones, they also typify the morphology of the New Caledonian landscape, particularly on the southern massif of the main island (known as Massif du Sud). The specificity of dolines here lies in their development on ultramafic rocks. They are evidences of subsidence, suffosion and collapse phenomena resulting from dissolution weathering of peridotites. However, extensive underground drainage systems are still not yet recognized. This article is protected by copyright. All rights reserved. Semi-automatic mapping of dolines is carried out on a 148 km 2 area of the Massif du Sud from a high accuracy LIDAR digital elevation model. 8,601 dolines ranging from 1 m 2 to 2 km 2 are identified and morphologically characterized with precision. Most are small, shallow and round-shaped, yet more complex shapes are locally observed. Size distribution analysis allows the setting of a threshold of 20,000 m 2 above which surface processes rather than chemical weathering control doline evolution. Doline density analysis reveals high concentrations on flat areas where ferricrete overlies the complete weathering profile, especially in the case of elevated rainy watersheds. Dolines are aligned and elongated along a N 135 ± 5° major fracture direction, which is inherited from the obduction of the Pacific Plate upper mantle in the Late Eocene. This article is protected by copyright. All rights reserved. Finally, we propose a pioneering morphometric typology of dolines that provides important clues as to pseudokarstic activity. We define collapse, bowl-shaped and flat bottom dolines. Collapse and bowl-shaped dolines are assumed to denote active pseudokarst. They may widen and deepen, or eventually be filled by sediments. They are distinguished from flat bottom dolines that are partially to completely filled, which suggests that they are associated with paleo-pseudokarsts. However the groundwater flow paths associated with the genesis and evolution of dolines must be clarified, thus collapse and bowl-shaped dolines should be hydrologically monitored. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Climate change is expected to significantly affect flooding regimes of river systems in the future. For Western Europe, flood risk assessments generally assume an increase in extreme events and flood risk, and as a result major investments are planned to reduce their impacts. However, flood risk assessments for the present day and the near future suffer from uncertainty, coming from short measurements series, limited precision of input data, arbitrary choices for particular statistical and modelling approaches, and climatic non-stationarities. This study demonstrates how historical and sedimentary information can extend data records, adds important information on extremes, and generally improves flood risk assessments. The collection of specific data on the occurrence and magnitude of extremes and the natural variability of the floods is shown to be of paramount importance to reduce uncertainty in our understanding of flooding regime changes in a changing climate. For the Lower Rhine (Netherlands and Germany) estimated recurrence times and peak discharges associated with the current protection levels correlate poorly with historical and sedimentary information and seem biased towards the recent multi-decadal period of increased flood activity. Multi-decadal and centennial variability in flood activity is recorded in extended series of discharge data, historical information and sedimentary records. Over the last six centuries that variability correlates with components of the Atlantic climate system such as the North Atlantic Oscillation (NAO) and Atlantic Multi-decadal Oscillation (AMO). These climatic non-stationarities importantly influence flood activity and the outcomes of flood risk assessments based on relatively short measurement series. This article is protected by copyright. All rights reserved.

Description: Ditch cleaning in drained peatland forests increases sediment loads and degrades water quality in headwater streams and lakes. A better understanding of the processes controlling ditch erosion and sediment transport in such systems is a prerequisite for proper peatland management. In order to relate hydrological observations to key erosion processes in headwater peatlands drained for forestry, a two-year study was conducted in a nested sub-catchment system (treated with ditch cleaning) and at two reference sites. The treated catchment was instrumented for continuous discharge and turbidity monitoring, erosion pin measurements of changes in ditch bed and banks and time-integrated sampling of suspended sediment (SS) composition. The results showed that ditch cleaning clearly increased transient SS concentrations (SSCs) and yields (SSYs), and resulted in temporary storage of loosely deposited organic sediment in the ditch network. After exhaustion of this sediment storage, subaerial processes and erosion from ditch banks became dominant in producing sediment for transport. Recorded SSCs were higher on the rising limbs of event hydrographs throughout the study period, indicating that SS transport was limited by availability of erosion-prone sediment. A strong positive correlation (R2 = 0.84, p 〈 0.001) between rainfall intensity (above a threshold of 1 mm h-1) and average SSC obtained on the rising limb of hydrographs for the sub-catchment showed that soil detachment from ditch banks by raindrop impact can directly increase SSC in runoff. At the main catchment outlet, variation in SSC was best explained (R2 = 0.67, p 〈 0.05) by the linear combination of initial discharge (-), peak discharge (+) and the lag time from initial to peak discharge (-). Based on these factors, ditch cleaning slightly increased peak discharges and decreased transit times in the study catchment. The implications of the results for water pollution management in peatland forests are discussed. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Description: In this paper, direct and indirect geomorphic consequences of wind-related tree uprooting are examined, using an extensive dataset from the mountain range of the Sudetes, Poland. The role of local conditions in influencing the geomorphic efficacy of tree uprooting is examined, as well as issues of upscaling individual observations from experimental sites. This problem is approached at a range of spatial and observational scales, from monitoring of root plate degradation over time through to examination of wind effects at a slope scale and region-wide analysis. In our study area the mean root plate volume is between 0.4 and 4.2 m 3 for spruce and 2.4 m 3 for beech, and their degradation may last tens of years. The density of relict pit-and-mound microtopography varies from 2.7 up to 40 pairs per hectare and the maximum coverage of terrain is 4.7%. The volume of treethrow mounds varies from 0.5 to 3.1 m 3 and mounds seem to outlive the pits formed in the same episode of disturbance. However, in specific lithological and topographic conditions, pit-and-mound topography does not form. The maximum biogenic transport attributable to a single windstorm event is ca. 80 m 3  ha -1 , while soil turnover times are calculated in the order of 1,000–10,000 years. Rock fragment “mining” is an important biogeomorphic process, both in terms of impact on hillslope surfaces and on soil properties. Gravel armours and small-scale stepped topography may form instead of typical pit-mound associations in specific circumstances. Managed forests appear more prone to wind damage and associated geomorphic consequences. In the Sudetes Mountains, the variable role of tree uprooting in local and regional hillslope denudational is governed by forest stand structure, topography and regolith properties, with the former significantly influenced by human activity. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: Extensive loess covered areas characterize the mildly arid areas of western Israel, where average annual rainfall is 280 mm. Hydrological data point to a peculiar hydrological behavior of the ephemeral streams. The frequency of sporadic flash floods is very high. However, even in extreme rain events peak discharges are extremely low. Hydrographs are usually characterized by very steep rising and falling limbs, representative of saturated areas, extending over a limited part of the watershed. Following this observation we advanced the hypothesis that storm channel runoff originated in the channel itself, with negligible contribution from the adjoining hillslopes. The study was based on two complementary approaches. The hydrological approach was based on the detailed analysis of rainfall-runoff relationships in a small watershed (11 km 2 ) and on the analysis of the hydrological characteristics of the drainage network. The second approach was based on the toposequence concept. Several boreholes were dug along a hillslope 400 m long. Chemical data obtained show no significant difference in the downslope direction. Similar results were also obtained for the particle size distribution and soil moisture content. Data obtained perfectly fit the concept of “Partial Area Contribution” as it presents an extreme case of hydrological discontinuity at the hillslope-channel interface. The lack of pedological trends in the downslope direction is an additional indication of the limited connectivity between the hillslopes and the adjoining channel. The limited connectivity is attributed to the prevalence of low rain intensities in the study area. The present study is also relevant to our understanding of pedological processes in dry-land areas. The high frequency of intermittent low intensity rainstorms limits runoff generation and flow distances, and casts doubt on the general application of the toposequence approach. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Spatially discontinuous permafrost conditions frequently occur in the European Alps. How soils under such conditions have evolved and how they may react to climate warming is largely unknown. This study focuses on the comparison of nearby soils that are characterised by the presence or absence of permafrost (active-layer thickness: 2 – 3 m) in the alpine (tundra) and subalpine (forest) range of the Eastern Swiss Alps using a multi-method (geochemical and mineralogical) approach. Moreover, a new non-steady-state concept was applied to determine rates of chemical weathering, soil erosion, soil formation, soil denudation, and soil production. Long-term chemical weathering rates, soil formation and erosion rates were assessed by using immobile elements, fine-earth stocks and meteoric 10 Be. In addition, the weathering index (K + Ca)/Ti, the amount of Fe- and Al-oxyhydroxides and clay minerals characteristics were considered. All methods indicated that the differences between permafrost-affected and non-permafrost-affected soils were small. Furthermore, the soils did not uniformly differ in their weathering behaviour. A tendency towards less intense weathering in soils that were affected by permafrost was noted: at most sites, weathering rates, the proportion of oxyhydroxides and the weathering stage of clay minerals were lower in permafrost soils. In part, erosion rates were higher at the permafrost sites and accounted for 79 – 97% of the denudation rates. In general, soil formation rates (8.8 – 86.7 t/km 2 /y) were in the expected range for Alpine soils. Independent of permafrost conditions, it seems that the local microenvironment (particularly vegetation and subsequently soil organic matter) has strongly influenced denudation rates. As the climate has varied since the beginning of soil evolution, the conditions for soil formation and weathering were not stable over time. Soil evolution in high Alpine settings is complex owing to, among others, spatio-temporal variations of permafrost conditions and thus climate. This makes predictions of future behaviour very difficult. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In steep soil-mantled landscapes, the initiation of shallow landslides is strongly controlled by the distribution of vegetation, whose roots reinforce the soil. The magnitude of root reinforcement depends on the number, diameter distribution, orientation and the mechanical properties of roots that cross potential failure planes. Understanding how these properties vary in space and time in forests remains a significant challenge. Here we test the hypothesis that spatio-temporal variations in root reinforcement along a hillslope occur as a function of topographic soil moisture gradients. To test this hypothesis we compared root reinforcement measurements from relatively dry, divergent noses to relatively wet, convergent hollows in the southern Appalachian Mountains, North Carolina, USA. Our initial results showed that root reinforcement decreased in areas of higher soil moisture because the tensile strength of roots decreased. A post-hoc laboratory experiment further demonstrated that root tensile strength decreased as root moisture content increased. This effect is consistent with other experiments on stem woods showing that increased water content in the cell wall decreases tensile strength. Our experimental data demonstrated that roots can adjust to changes in the external root moisture conditions within hours, suggesting that root moisture content will change over the timescale of large storm events (hours-days). We assessed the effects of the dynamic changes in root tensile strength to the magnitude of apparent cohesion within the infinite slope stability model. Slopes can be considerably less stable when precipitation-driven increases in saturated soil depth both increase pore pressures and decrease root reinforcement. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Description: Bed load sediment transport is the basic physical ingredient of river evolution. Formulae exist for estimating transport rates, but the diffusive contribution to the sediment flux, and the associated spreading rate of tracer particles, are not clearly understood. The start-and-stop motions of sediment particles transported as bed load on a streambed mimic aspects of the Einstein-Smoluchowski description of the random-walk motions of Brownian particles. Using this touchstone description, recent work suggests the presence of anomalous diffusion, where the particle spreading rate differs from the linear dependence with time of Brownian behavior. We demonstrate that conventional measures of particle spreading reveal different attributes of bed load particle behavior depending on details of the calculation. When we view particle motions over start-and-stop timescales obtained from high-speed (250 Hz) imaging of coarse-sand particles, high-resolution measurements reveal ballistic-like behavior at the shortest (10 −2 s) timescale, followed by apparent anomalous behavior due to correlated random walks in transition to normal diffusion (〉10 −1 s) — similar to Brownian particle behavior but involving distinctly different physics. However, when treated as a ‘virtual plume’ over this timescale range, particles exhibit inhomogeneous diffusive behavior because both the mean and the variance of particle travel distances increase nonlinearly with increasing travel times, a behavior that is unrelated to anomalous diffusion or to Brownian-like behavior. Our results indicate that care is needed in suggesting anomalous behavior when appealing to conventional measures of diffusion formulated for ideal particle systems.

Description: Rapid, field-based assessments of rock hardness are required in a broad range of geomorphological investigations where rock intact strength is important. Several different methods are now available for taking such measurements, in particular the Schmidt hammer, which has seen increasing use in geomorphology in recent decades. This is despite caution from within the engineering literature regarding choice of Schmidt hammer type, normalization of rebound ( R -) values, surface micro-roughness, weathering degree and moisture content, and data reduction/analysis procedures. We present a pilot study of the use of an Acoustic Energy Meter (AEM), originally produced, tested and developed within the field of underground mining engineering as a rapid measure of rock surface hardness, and compare it with results from a mechanical N-Type Schmidt hammer. We assess its capabilities across six lithological study sites in southeast Queensland, Australia, in the Greater Brisbane area. Each rock exposure has been recently exposed in the 20 th /21 st century. Using a “paired” sampling approach, the AEM G -value shows an inverse relationship with Schmidt hammer R -value. While both devices show variability with lithology, the AEM G -values show less scatter than the Schmidt hammer. We conclude that each device can contribute to useful rock hardness testing in geomorphological research, but the AEM requires further field testing in a range of environments, and particular on older and naturally-exposed rock surfaces. Future evaluations can extend this pilot study by focusing on sampling procedures, energy sources, and data reduction protocols, within the framework of a comparison study with other rock hardness testing apparatus. This article is protected by copyright. All rights reserved.

Description: In the absence of eyewitness reports or clear sedimentary structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K-means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub-perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infrastructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: 1) samples deposited from laminar flow, and 2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large-scale investigations can be more easily performed. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This paper reports on a wind tunnel investigation of particle segregation, ripple formation and surface armoring within sand beds of systematically varied particle size distribution, from coarsely skewed to bimodal. By design, the system was closed with no external inputs of mass from an external particle feed. Particles too coarse to travel in saltation for the given range in wind speed were dyed red in order to distinguish them in optical images from finer sand particles, which could be entrained into the unidirectional airflow. A 3D laser scanner measured the changing bed topography at regular time intervals during 18 experiments involving varied combinations of wind speed and bed texture. Image classification techniques were used to investigate the coincident self-organization of the two populations of particles, as distinguished by their colour. As soon as saltation commenced, some of the red particles segregated into thin discontinuous patches. Particle trapping and sheltering on these rough patches was strongly favoured, causing them to grow preferentially. During the earliest stages of formation, bedform growth coincided with: i) rapid coarsening of the surface texture, and ii) the merging of proto-ripple ‘crests’ to generate larger rhythmic bedforms of lower frequency. Consistent with previous work, ripple size was observed to increase under stronger winds when not exceeding the threshold for entrainment of the coarse-mode or red particles from the crest. With declining rates of mass transport and particle segregation as the bed surface armoured, and the consequent deceleration of ripple propagation through to the end of each experiment, all surfaces eventually attained a steady-state morphometry. At saturation, the largest ripples developed upon beds having the lowest initial concentration of red particles. This article is protected by copyright. All rights reserved.

Description: Long-range terrestrial laserscanning (TLS) is an emerging method for the monitoring of alpine slopes in the vicinity of infrastructure. Nevertheless, deformation monitoring of alpine natural terrain is difficult and gets even more challenging with larger scan distances. In this study we present approaches for the handling of spatially variable measurement uncertainties in the context of geomorphological change detection using multi-temporal data sets. A robust distance measurement is developed, which deals with surface roughness and areas of lower point densities. The level of detection (LOD), i.e. the threshold distinguishing between real surface change and data noise, is based on a confidence interval considering the spatial variability of TLS errors caused by large laser footprints, low incidence angles and surface roughness. Spatially variable positional uncertainties are modelled for each point according to its range and the object geometry hit. The local point cloud roughness is estimated in the distance calculation process from the variance of least-squares fitted planes. Distance calculation and LOD assessment are applied in two study areas in the Eastern Alps (Austria) using multi-temporal laserscanning data sets of slopes surrounding reservoir lakes. At Finstertal, two TLS point clouds of high alpine terrain and scanned from ranges between 300 and 1800 m are compared. At Gepatsch, the comparison is done between an airborne laserscanning (ALS) and a TLS point cloud of a vegetated mountain slope scanned from ranges between 600 and 3600 m. Although these data sets feature different conditions regarding the scan setup and the surface conditions, the presented approach makes it possible to reliably analyse the geomorphological activity. This includes the automatic detection of rock glacier movement, rockfall and debris slides, even in areas where a difference in vegetation cover could be observed. This article is protected by copyright. All rights reserved.

Description: Dam removal has been demonstrated as one of the most frequent and effective fluvial restoration actions but at most dam removals, especially of small dams, there has been little geomorphological monitoring. The results of the geomorphological monitoring implemented in two dams in Urumea and Leitzaran Rivers (northern Spain) are presented. The one from Urumea River, originally 3.5 m high, impounded 500 m of river course, was removed instantaneously whereas that in Leitzaran River, was 12.5 m high, impounded 1,500 m of river course, and it is in its second phase of a 4-stage removal process. Changes in channel morphology, sediment size and mobility and river bed morphologies were assessed. The monitoring included different techniques: topographical measurements of the channel, terrestrial laser scanner measurements of river bed and bars, sediment grain size and transport; all of them repeated in four (May, August, November 2011 and May 2012) and five (July and September 2013, April and August 2014 and June 2015 fieldwork campaigns in Urumea and Leitzaran Rivers, respectively. Geomorphic responses of both dam removals are presented, as well as compared between them. Morphological channel adjustments occurred mainly shortly after dam removals, but with differences among the one removed instantaneously, that was immediate, whereas that conducted by stages took longer. Degradational processes were observed upstream of both dams (up to 1.2 m and 4 m in Urumea and Leitzaran Rivers, respectively), but also aggradational processes (pool filling), upstream of Inturia dam (2.85 m at least). Less evident aggradational processes were observed downstream of the dams (up to 0.37 m and 0.50 m in Urumea and Leitzaran Rivers, respectively). Flood events, specially a 100-year one registered during the monitoring period of Mendaraz dam removal, reactivated geomorphological processes as incision and bank erosion, whereas longitudinal profile recovery, grain-size sorting and upstream erosion took longer. This article is protected by copyright. All rights reserved.

Description: Salt marshes represent a fascinating example of an ecosystem whose dynamic response to climate change is chiefly governed by a two-way bio-physical coupling between marsh ecology and geomorphology. Relationships between vegetation biomass and marsh surface elevation, and between vegetation biomass and its physical properties that influence sedimentation rates, have been progressively formulated in the literature in order to provide mechanistic understandings and mathematical model descriptions of these ecogeomorphic feedbacks. In this study, a field survey was conducted in a temperate salt marsh grown by multiple halophyte species in order to quantify and validate these empirical relationships, yet in a location characterized by different climatic and ecological conditions from the locations were these relationships were initially derived. Regression analysis revealed that vegetation biomass can be expressed as a linearly increasing function of marsh elevation, providing therefore a direct empirical validation for such a relationship previously reported in the literature and implemented in some ecogeomorphic models. However, previously documented allometric relationships between total standing biomass and vegetation morphometrics—namely stem diameter, stem density and projected plant area per unit volume—were not confirmed by our results, which only showed an allometric scaling for stem height. These results suggest that previously documented formulations of mineral sediment trapping processes modulated by plants, which are partly derived on the basis of these allometric relationships, are not generally validated for multi-species salt marshes. Therefore, existing models that apply these process-based equations to study marsh evolution in a multi-species context may not capture in detail the vegetation-induced geomorphic work. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Numerical models have not yet systematically been used to predict properties of fluvial terrace records in order to guide fieldwork and sampling. This paper explores the potential of the longitudinal profile model FLUVER2 to predict testable field properties of the relatively well-studied, Late Quaternary Allier system in France. For the Allier terraces an overlapping 14 C and U-series chronology as well as a record of 10 Be erosion rates exist. The FLUVER2 modelling exercise is focused on the last 50 ka of the upper Allier reach because for this location and period the constraints of the available dating techniques are tightest. A systematic calibration based on terrace occurrence and thicknesses was done using three internal parameters related to 1) the sediment erodibility; 2) the sediment transport distance; and 3) the sediment supply derived from the surrounding landscape. As external model inputs, the best available, reconstructed, tectonic, climatic and base-level data were used. Calibrated model outputs demonstrate a plausible match with the existing fluvial record. Validation of model output was done by comparing the modelled and measured timing of aggradation and incision phases for the three locations. The modelled range of landscape erosion rates showed a reasonably good match with existing erosion rate estimates derived from 10 Be measurements of fluvial sands. The quasi-validated model simulation was subsequently used to make new testable predictions about the timing and location of aggradation and erosion phases for three locations along the Allier river. The validated simulations predict that along the Allier, reach-specific dynamics of incision and aggradation, related to the variations in sediment supply by major tributaries, cause relevant differences in the local fluvial terrace stratigraphy. This article is protected by copyright. All rights reserved.

Description: A two-dimensional shallow water hydro-sediment-morphodynamic model is applied to investigate alternate bar formation, development and sediment sorting in straight channels. The model is coupled, explicitly incorporating the flow-sediment- bed interactions by using the full mass and momentum conservation equations, which are numerically solved by a well-balanced version of the finite volume Slope LImiter Centred (SLIC) scheme. The model is first tested against a flume experiment on alternate bars formed over uniform sediment bed, which clearly exhibits processes of bar formation, migrating and finally approaching an equilibrium state. Then it is applied to another flume experiment on alternate bars due to non-uniform sediment transport. The computational results are evaluated, with a focus on the longitudinal and vertical sediment sorting. It is argued for the first time that the inconsistent sediment sorting patterns observed in previous studies are determined by different sediment transport conditions, i.e., full versus partial transport. When a condition of full transport is achieved, under which all size fractions are fully mobilized and transported, the longitudinal surface sediment shows a sorting pattern of coarse-on-head and fine-in-pool, and the vertical substrate sediment exhibits an immobile-fine-coarse structure upwards. In contrast, for a partial transport condition, under which only finer fraction participates in the transport process, an opposite longitudinal pattern (i.e., fine-on-head and coarse-in-pool) and a different vertical structure (i.e., immobile-coarse-fine) are observed. Concurrently, numerical experiments with specified conditions show that the critical aspect ratio for the formation of migrating alternate bars is approximately equal to 12. With the increase of the aspect ratio, the bar length grows gradually, while the bar height increases rapidly for moderate values of the aspect ratio and then keeps nearly stable. The bar celerity, however, is weakly sensitive to the variation of this ratio. This article is protected by copyright. All rights reserved.

Description: RFID transponders, especially low-frequency Passive Integrated Transponders (PIT tags), are now commonly used for assessing bedload mobility in gravel-bed rivers. Early studies reported high PIT tag recovery rates in small streams, but recovery rates in larger systems remain low. Explanatory factors for low recovery rates have been identified, but only antenna detection ranges and clustering effects have been precisely characterized. Burial below detection limit and dispersion beyond the study site have been indirectly estimated, and PIT tag destruction is assumed to be negligible. In this study, we quantified the resistance of natural limestone pebbles equipped with PIT tags as related to tag insertion methods and distance travelled in an annular flume. We then compared the performance of these natural pebbles with synthetic pebbles made of polyurethane resin and corundum. Creation of synthetic pebbles makes it possible to test bigger transponders with a greater detection range and no clustering effects, bypassing the existing constraints of RFID tracking. We found that breakage of limestone particles leading to PIT tag destruction is far too rare to explain low recovery rates in situ . Further breakage is more affected by initial pebble characteristics than by PIT tag insertion method. Synthetic pebbles are more sensitive to attrition, but less likely to break. Natural and synthetic pebbles show slight differences in mobility patterns, transport distances, and abrasion resistances. One of the two synthetic pebbles travelled faster than the others three indicating that mobility is not only related to density but also potentially to shape. To address clustering and detection range issues, we equipped synthetic pebbles with AIT-tags (Active Integrated Transponders). These were tested for integrity and transponder endurance and show great promise for future applications. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Weathering microforms associated with exfoliation were investigated on 40 granitic spheroidal boulders identified on Pricopan Ridge (Măcin Mts.) in order to establish a spatial distribution pattern. Continuous thermal monitoring allowed the frequency and intensity distribution assessment of short-term temperature changes triggered by summer storms, of intense day-night amplitudes and frost cycles across a uniform rounded boulder. Rock strength estimated by Schmidt hammer tests differentiates a significantly weaker resistance on the southern face of the boulders (rebound values of 27 – 33) in comparison with the northern face (43 – 50). The lowest resistance of the North-South cross-boulder profile corresponds to the southern gentle slopes (0° – 45°) thus defining the most susceptible area to exfoliation and other weathering processes. It is argued that this low-resistant sector fits well with the maximum frequency and intensity of thermal processes recorded on the low and mid slopes (0° – 45°) of the boulders south side, with small differences from one process to another, whilst the sector of 20° – 30° South corresponds to the peak activity of all. In accordance, the overlay map of exfoliated surfaces places the high frequency area on a spherical cap developed similarly (between 5° North and 45° South). The smallest exfoliated surfaces normally appear around 30° South and are inferred to extend in time both to the boulder top and downslope. The correlations between the frequency/intensity maps of thermal processes and the frequency map of exfoliated surfaces point to a complementary action in the exfoliated surfaces development of the short-term temperature changes and diurnal cooling and heating due to the directional insolation effect, as inferred in the development of meridional cracks. This article is protected by copyright. All rights reserved.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: For more than 150 years, humans have tried to limit the geomorphic activity of mountain streams, and the related damages, using torrent control works. Check dams are likely the most emblematic civil engineering structures used in soil conservation programs. Modern mountain societies have inherited thousands of these structures built in upland gullies and streams. To help define their effectiveness and decisions concerning their maintenance or new project designs, a clear understanding of potential effects of check dams on river systems, i.e., their functions, is first needed. The next steps concern quantitative assessments of each function on the flood features and combination of all effects. The present understanding of these sometimes old structures’ functions can be complicated because the societal and environmental contexts in which the original structures were built may have changed. To bridge this gap, this paper traces the purposes for which check dams were built, through a detailed analysis of French archives. We first analyze chronologically how each function was theorized and applied in the field. In the nineteenth century, engineers developed a thorough empirical and conceptual knowledge of mountain soil erosion, torrential geomorphology, and sediment transport processes as well as check dam interactions with these natural processes. The second part of this paper synthesizes conceptual descriptions of the check dams' functions, in the light of more than 150 years of experience, with their implication on the features of the structures. The French experience is compared to other countries’ pioneering works. Finally, the next steps and remaining research challenges toward a comprehensive analysis of check dams' efficiency in torrential hazard mitigation are discussed. This analysis is proposed to remind how, conceptually, check dams may influence geomorphic systems, bearing in mind the knowledge represented in pioneer guidelines and recent works on the subject.

Description: ABSTRACT The Mediterranean domain is characterized by a specific climate resulting from the close interplay between atmospheric and marine processes and strongly differentiated regional topographies. Corsica Island, a mountainous area located in the western part of the Mediterranean Sea is particularly suitable to quantify regional denudation rates in the framework of a source-to-sink approach. Indeed, fluvial sedimentation in East-Corsica margin is almost exclusively limited to its alluvial plain and offshore domain and its basement is mainly constituted by quartz-rich crystalline rocks allowing cosmogenic nuclide 10 Be measurements. In this paper, Holocene denudation rates of catchments from the eastern part of the island of Corsica are quantified relying on in-situ produced 10 Be concentrations in stream sediments and interpreted in a approach including quantitative geomorphology, rock strength measurement (with a Schmidt Hammer) and vegetation cover distribution. Calculated denudation rates range from 15 to 95 mm ka -1 . When compared with rates from similar geomorphic domains experiencing a different climate setting, such as the foreland of the northern European Alps, they appear quite low and temporally stable. At the first order, they better correlate with rock strength and vegetation cover than with morphometric indexes. Spatial distribution of the vegetation is controlled by morpho-climatic parameters including sun exposure and the direction of the main wet wind, so-called “Libecciu”. This distribution, as well as the basement rock strength seems to play a significant role in the denudation distribution. We thus suggest that the landscape reached a geomorphic steady-state due to the specific Mediterranean climate and that Holocene denudation rates are mainly sustained by weathering processes, through the amount of regolith formation, rather than being transport-limited. Al/K measurements used as a proxy to infer present-day catchment-wide chemical weathering patterns might support this assumption.

Description: Tides are often considered to be the dominant hydrodynamic process within mesotidal estuaries although waves can also have a large influence on intertidal erosion rates. Here, we use a combination of hydrodynamic measurements and sediment deposition records to determine the conditions under which observed waves are “morphologically significant”, in which case they influence tidal and suspended sediment flux asymmetry and subsequently infilling over geomorphological timescales. Morphological significant conditions were evaluated using data from contrasting arms in a dendritic mesotidal estuary, in which the orientation of the arms relative to the prevailing wind results in a marked difference in wave conditions, deposition rates and morphology. By defining the morphological significance of waves as a product of the magnitude of bed shear stress and frequency of occurrence, even small (but frequently occurring) winds are shown to be capable of generating waves that are morphologically significant given sufficient fetch. In the arm in which fetch length is restricted, only stronger but rare storm events can influence sediment flux and therefore tides are more morphologically significant over longer timescales. Water depth within this mesotidal estuary is shown to be a critical parameter in controlling morphological significance; the rapid attenuation of short period waves with depth results in contrasting patterns of erosion occurring during neaps and accretion during springs. This article is protected by copyright. All rights reserved.

Description: To reveal river channel steepness patterns and variance in settings with significant variation in rock uplift rate, rock erodibility and moving water divides, we present a series of graphical methods to interpret channel profiles. To complement Cartesian χ plots, longitudinal profiles and mapping methods, we introduce a new method based on a radial coordinate system. We map each basin onto polar coordinates in which the radial dimension is χ and the azimuthal coordinate, φ, is calculated with an increment (Δφ) scaled to the distance to neighboring channel heads. The elevation is contoured on this mapping. Average channel steepness is estimated by fitting a conical surface to the elevation. The graph simplifies the comparison of χ and elevation between channels that share a divide, and helps identify spatial changes in drainage area and patterns of erodibility. This article is protected by copyright. All rights reserved. We apply this approach to derive the uplift pattern in the eastern and southern Central Range of Taiwan, where the high tectonic convergence and uplift rates combined with sub-tropical climate and frequent typhoons results in high exhumation rate, and well-developed, detachment-limited river networks. Additionally, the tectonic activity leads to drainage basin reorganization. We identify examples of divide migration, discrete river capture as well as anomalous steepness that we attribute to local variability in rock erodibility. This article is protected by copyright. All rights reserved. Estimated basin-average steepness values show the highest and a near constant value from Hsinwulu basin to Liwu basin in the center of the Island. To the north and south of this region, the values gradually decrease. These estimates show good correlation with the topography of the Central Range and erosion rates derived from in-situ 10 Be concentrations in river-borne quartz. We conclude that the basin steepness reflects systematic differences in rock uplift rate and erosion rate. This article is protected by copyright. All rights reserved.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: The Blue Ridge escarpment, located within the southern Appalachian Mountains of Virginia and North Carolina, forms a distinct, steep boundary between the lower-elevation Piedmont and higher-elevation Blue Ridge physiographic provinces. To understand better the rate at which this landform and the adjacent landscape are changing, we measured cosmogenic 10 Be in quartz separated from sediment samples ( n  = 50) collected in thirty-two streams and from three exposed bedrock outcrops along four transects normal to the escarpment, allowing us to calculate erosion rates integrated over 10 4 –10 5 years. These basin-averaged erosion rates (5.4–49 m My -1 ) are consistent with those measured elsewhere in the southern Appalachians and show a positive relationship between erosion rate and average basin slope. Erosion rates show no relationship with basin size or relative position of the Brevard fault zone, a fundamental structural element of the region. The cosmogenic isotopic data, when considered along with the distribution of average basin slopes in each physiographic province, suggest that the escarpment is eroding on average more rapidly than the Blue Ridge uplands, which are eroding more rapidly than the Piedmont lowlands. This difference in erosion rates by geomorphic setting suggests that the elevation difference between the uplands and lowlands adjacent to the escarpment is being reduced but at extremely slow rates. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The Gediz (Alaşehir) Graben is located in the highly tectonically active and seismogenic region of Western Turkey. The rivers upstream of the normal fault-bounded graben each contain a non-lithologic knickpoint, including those that drain through inferred fault segment boundaries. Knickpoint heights measured vertically from the fault scale with footwall relief and documented fault throw (vertical displacement). Consequently, we deduce these knickpoints were initiated by an increase in slip rate on the basin-bounding fault, driven by linkage of the three main fault segments of the high-angle graben bounding fault array. Fault interaction theory and ratios of channel steepness suggest that the slip rate enhancement factor on linkage was a factor of 3. We combine this information with geomorphic and structural constraints to estimate that linkage took place between 0.6 Ma and 1 Ma. Calculated pre- and post- linkage throw rates are 0.6 and 2 mm/yr respectively. Maximum knickpoint retreat rates upstream of the faults range from 4.5 to 28 mm/yr, faster than for similar catchments upstream of normal faults in the Central Apennines and the Hatay Graben of Turkey, and implying a fluvial landscape response time of 1.6 to 2.7 Myr. We explore the relative controls of drainage area and precipitation on these retreat rates, and conclude that while climate variation and fault throw rate partially explain the variations seen, lithology remains a potentially important but poorly characterised variable. This article is protected by copyright. All rights reserved.

Description: Identifying the relative contributions of physical and ecological processes to channel evolution remains a substantial challenge in fluvial geomorphology. We use a 74-year aerial photographic record of the Hoh, Queets, Quinault, and Elwha Rivers, Olympic National Park, Washington, U.S.A., to investigate whether physical or trophic-cascade-driven ecological factors—excessive elk impacts after wolves were extirpated a century ago—are the dominant drivers of channel planform in these gravel-bed rivers. We find that channel width and braiding show strong relationships with recent flood history. All four rivers widened significantly after having been relatively narrow in the 1970s, consistent with increased flood activity since then. Channel planform also reflects sediment-supply changes, evident from landslide response on the Elwha River. We surmise that the Hoh River, which shows a multi-decadal trend toward greater braiding, is adjusting to increased sediment supply associated with rapid glacial retreat. These rivers demonstrate transmission of climatic signals through relatively short sediment-routing systems that lack substantial buffering by sediment storage. Legacy effects of anthropogenic modification likely also affect the Quinault River planform. This article is protected by copyright. All rights reserved. We infer no correspondence between channel evolution and elk abundance, suggesting that trophic-cascade effects in this setting are subsidiary to physical controls on channel morphology. Our findings differ from previous interpretations of Olympic National Park fluvial dynamics and contrast with the classic example of Yellowstone National Park, where legacy effects of elk overuse are apparent in channel morphology; we attribute these differences to hydrologic regime and large-wood availability. This article is protected by copyright. All rights reserved.

Description: In this paper, a transient rainfall infiltration and grid-based regional slope-stability model (TRIGRS) was implemented in a case study of Yan'an City, Northwest China. In this area, widespread shallow landslides were triggered by the 12 th July 2013 exceptional rainstorm event. A high-resolution DEM, soil parameters from in-situ and laboratory measurements, water table depths, the maximum depth of precipitation infiltration and rain-gauge-corrected precipitation of the event, were used as inputs in the TRIGRS model. Shallow landslides triggered on the same day were used to evaluate the modeling results. The summarized results are as follows: i) The characteristics and distribution of thirty-five shallow landslides triggered by the 12 th July 2013 rainfall event were identified in the study area and all were classified as shallow landslides with the maximum depth, area and volume less than 3 m, 200 m 2 and 1000 m 3 , respectively; ii) Four intermediate factor of safety (F S ) maps were generated using the TRIGRS model to represent the scenarios 6, 12, 18 and 24 hours after the storm event. The area with F S  〈 1 increased with the rainfall duration. The percentage of the area with F S  〈 1 was 0.2%, 3.3%, 3.8% and 5.1% for the four stages, respectively. Twenty-four hours after the rainstorm, TRIGRS predicted that 1255 grid cells failed, which is consistent with the field data; iii) TRIGRS generated more satisfactory results at a given precipitation threshold than SINMAP, which is ideal for landslide hazard zoning for land-use planning at the regional scale. Comparison results showed that TRIGRS is more useful for landslide prediction for a certain precipitation threshold, also in the regional scale; and iv) Analysis of the responses of loess slope prone to slope failure after different precipitation scenarios revealed that loess slopes are particularly sensitive to extended periods of heavy precipitation. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Upstream damming often causes significant downstream geomorphic adjustments. Remarkable channel changes have occurred in the Jingjiang Reach of the Middle Yangtze River, since the onset of the Three Gorges Project (TGP). Therefore, it is important to investigate the variations in different fluvial variables, for better understanding of the channel evolution characteristics as an example of the Jingjiang Reach. Recent geomorphic adjustments in the study reach have been investigated quantitatively, including variations in sediment rating curve, fluvial erosion intensity, channel deformation volume and bankfull channel geometry. These fluvial variables adjusted in varying degrees in response to the altered flow and sediment regime caused by the TGP operation. A focus of this study has been especially paid on the variation in the bankfull channel geometry. Calculated bankfull dimensions at section- and reach-scale indicate that: (i) there were significant bank-erosion processes in local regions without bank-protection engineering, with empirical relations being developed to reproduce the variation in bankfull widths at four typical sections; (ii) the variation in the reach-scale channel geometry occurred mainly in the component of bankfull depth, owing to the construction of large-scale bank-revetment works, with the depth increasing from 13.7 m in 2002 to 15.0 m in 2014, and with an increase in the corresponding bankfull area of about 11%; and (iii) the reach-scale bankfull channel dimensions responded to the previous five-year average fluvial erosion intensity during flood seasons at Zhicheng, with higher correlations for the depth and area being obtained when calibrated by the measurements in 2002–2012. Furthermore, these developed relations for the section- and reach-scale bankfull channel geometry were also verified by the observed data in 2013–2014, with encouraging results being obtained. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small-scale fragile geomorphological features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor–relief landforms as wind, weather, water and vegetation impacts on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close-range aerial photography of the foreland of Isfallsglaciären, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2 cm horizontal resolution were created from this photography using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss-side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore, the size of this boulder was found to strongly correlate with the width and relief of the lee-side flute. This is consistent with the lee-side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study. This article is protected by copyright. All rights reserved.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: In peatlands, fluvial erosion can lead to a dramatic decline in hydrological function, major changes in the net carbon balance and loss of biodiversity. Climate and land management change are thought to be important influences on rates of peat erosion. However, sediment production in peatlands is different to that of other soils and no models of erosion specifically for peatlands currently exist. Hence, forecasting the influence of future climate or spatially-distributed management interventions on peat erosion is difficult. PESERA-GRID was substantially modified in this study to include dominant blanket peat erosion processes. In the resulting fluvial erosion model, PESERA-PEAT, freeze-thaw and desiccation processes were accounted for by a novel sediment supply index as key features of erosion. Land management practices were parameterized for their influence on vegetation cover, biomass and soil moisture condition. PESERA-PEAT was numerically evaluated using available field data from four blanket peat-covered catchments with different erosion conditions and management intensity. PESERA-PEAT was found to be robust in modelling fluvial erosion in blanket peat. A sensitivity analysis of PESERA-PEAT showed that modelled sediment yield was more sensitive to vegetation cover than other tested factors such as precipitation, temperature, drainage density and ditch/gully depth. Two versions of PESERA-PEAT, equilibrium and time-series, produced similar results under the same environmental conditions, facilitating the use of the model at different scales. The equilibrium model is suitable for assessing the high-resolution spatial variability of average monthly peat erosion over the study period across large areas (national or global assessments), while the time-series model is appropriate for investigating continuous monthly peat erosion throughout study periods across smaller areas or large regions using a coarser-spatial resolution. PESERA-PEAT will therefore support future investigations into the impact of climate change and management options on blanket peat erosion at various spatial and temporal scales. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Combining field reconstruction and landscape evolution modelling can be useful to investigate the relative role of different drivers on catchment response. The Geren Catchment (~45 km 2 ) in western Turkey is suitable for such a study, as it has been influenced by uplift, climate change and lava damming. Four Middle Pleistocene lavaflows ( 40 Ar/ 39 Ar- dated from 310 to 175 ka,) filled and dammed the Gediz River at the Gediz - Geren confluence, resulting in base-level fluctuations of the otherwise uplift-driven incising river. Field reconstruction and luminescence dating suggest fluvial terraces in the Geren Catchment are capped by Middle Pleistocene aggradational fills. This showed that incision of the Geren trunk stream has been delayed until the end of MIS 5. Subsequently, the catchment has responded to base-level lowering since MIS 4 by 30 m of stepped net incision. Field reconstruction left us with uncertainty on the main drivers of terrace formation. Therefore, we used landscape evolution modelling to investigate catchment response to three scenarios of base-level change: i) uplift with climate change (rainfall and vegetation based on arboreal pollen), ii) uplift, climate change and short-lived damming events and iii) uplift, climate and long-lived damming events. Outputs were evaluated for erosion-aggradation evolution in trunk streams at two different distances from the catchment outlet. Climate influences erosion – aggradation activity in the catchment, although internal feedbacks influence timing and magnitude. Furthermore, lava damming events partly control if and where these climate-driven aggradations occur. Damming thus leaves a legacy on current landscape evolution. Catchment response to long-duration damming events corresponds best with field reconstruction and dating. The combination of climate and base level explains a significant part of the landscape evolution history of the Geren Catchment. By combining model results with fieldwork, additional conclusions on landscape evolution could be drawn.

Description: The sediment saturation recovery process (i.e., the adaptation of suspended sediment concentration (SSC) to local forcing) is the main feature of the non-equilibrium suspended sediment transport (SST) frequently occurring in fluvial, estuarine and coastal waters. In order to quantitatively describe this phenomenon, a series solution is analytically derived, including the evolution of both vertical SSC profile and near-bed sediment flux (NBSF), and is verified by net erosion and net deposition experiments, respectively. The results suggest the sediment saturation recovery process involves vertically varying fluxes that are not represented correctly by depth-averaging. Consequently, a vertical two-dimensional (2D) combined scheme is established and applied respectively in to a dredged trench and to a sand wave feature to demonstrate this argument. By analyzing the variations of the calculated depth-averaged SSC and NBSF we reveal the equilibrium state presented by the sediment carrying capacity (SCC) form of the NBSF, which is usually applied in depth-integrated SST models, lags behind the actual dynamic bed equilibrium state. Moreover, the key factor α , the so-called saturation recovery coefficient within this form, is not only a function of local Rouse number but also is influenced by the local SSC profile. Finally, a three-dimensional (3D) non-orthogonal curvilinear body-fitted SST model is developed and validated in the Yangtze Estuary, China, combined with the in situ hourly hydrographic data from 14 to 15 August 2007 during spring tide in the wet season. Model results confirm that the vertically varying sediment saturation recovery process, the discrepancies between the actual and SCC form of NBSF and non-constant value of α are significant in actual real geomorphic cases. The quantitative morphological change resulting from variations in environmental conditions may not be correctly represented by uncorrected depth-integrated SST models if they do not treat the effects of vertical motion on the sediment saturation recovery process.

Description: The Damxung-Yangbajain rift is one of the most active north-south trending rifts in the south Tibetan Plateau, and it has been playing an important role in accommodating the east-west extension of the Tibetan Plateau. Both stream profiles on the Nyainqentanglha Range adjacent to the northwest part of the Damxung-Yangbajain rift and tectonic geomorphology in north of the rift are analyzed to assess the spatial pattern and intensity of rock uplift which is related to neotectonic activity. A total of 85 stream profiles across the Nyainqentanglha Range are analyzed, and 111 knickpoints are interpreted. Most of these stream profiles are characterized by prominent convexities with two or more knickpoints, many of which are formed due to the strong rock uplift evidenced by abnormal concavity and extremely high steepness indices during the Quaternary. Neotectonic activity in this region is well replicated in the stream profile indices and offset landforms. Tectono-geomorphic analysis shows that the concavity and steepness indices correlate with the fault movements at many places. The Damxung-Yangbajain rift is characterized by left-lateral strike-slip in the north of Damxung and by normal movement in middle and southern parts. The middle and southern parts have been undergoing higher uplift than has the northern area. It is most likely that the strong uplift is related to the heat flow under the crust. Earthquakes occurring in the Damxung-Yangbajain rift, including a M8 in 1411 and M6.6 in 2008, are thought to be related to heat flow activity. All of the stream profile indices and tectonic geomorphology show that the Damxung-Yangbajain rift is not in stable state.

Description: Streambank erosion is a pathway for sediment and nutrient loading to streams, but insufficient data exist on the magnitude of this source. Riparian protection can significantly decrease streambank erosion in some locations, but estimates of actual sediment load reductions are limited. The objective of this research was to quantify watershed-scale streambank erosion and estimate the benefits of riparian protection. The research focused on Spavinaw Creek within the Eucha-Spavinaw watershed in eastern Oklahoma, where composite streambanks consist of a small cohesive topsoil layer underlain by noncohesive gravel. Fine sediment erosion from 2003–2013 was derived using aerial photography and processed in ArcMap to quantify eroded area. ArcMap was also utilized in determining the bank retreat rate at various locations in relation to the riparian vegetation buffer width. Box and whisker plots clearly showed that sites with riparian vegetation had on average three times less bank retreat than unprotected banks, statistically significant based on nonparametric t-tests. The total soil mass eroded from 2003 to 2013 was estimated at 7.27 x10 7 kg yr −1 , and the average bank retreat was 2.5 m yr −1 . Many current erosion models assume that fluvial erosion is the dominant stream erosion process. Bank retreat was positively correlated with stream discharge and/or stream power, but with considerable variability, suggesting that mass wasting plays an important role in streambank erosion within this watershed. Finally, watershed monitoring programs commonly characterize erosion at only a few sites and may scale results to the entire watershed. Selection of random sites and scaling to the watershed scale greatly underestimated the actual erosion and loading rates.

Description: No abstract is available for this article.

Description: The results from three years of surveying and monitoring a dynamic foredune and dunefield restoration effort on Vancouver Island, Canada is presented. Complete removal of foredune vegetation occurred in three phases spaced a year apart in an effort to control invasive Ammophila spp . The collection of airborne LIDAR, orthophotographs, and bi-monthly topographic surveys provided a means to quantify and examine sediment budgets and geomorphic responses. Three survey swaths, corresponding with each phase of vegetation removal, were established to provide detailed topographic coverage over the impacted beach, foredune, and dunefield landscape units. The swath corresponding with the first phase of removal recorded a positive sediment budget of 1.3 m 3 m −2 after 3 years. A control swath, with data collected for a year prior and two years following removal, exhibited a distinct pulse of sediment delivery into the dunefield unit with a maximum gain of 0.03 m 3 m −2 pre-removal compared to 0.11 m 3 m −2 post-removal. Vegetation analysis zones, associated with each of the three swaths, demonstrate a range of vegetation responses due to variation in the vegetation removal and subsequent re-invasion or removal methods employed. The first site to be cleared of vegetation, received ongoing invasive re-growth control, and three years following removal vegetation cover dropped from 57% in 2009 to 13% in 2012 (-44%). An adjacent site was cleared of vegetation two years later (only 1 year of recovery) but experienced rapid Ammophila re-invasion and percent cover changed from from 61% in 2009 to 26% in 2012 (-35%). The data presented provides insights for improving the application of sediment budget monitoring in dynamic restorations and discusses the potential for detailed spatial-temporal survey data to improve our understanding of meso-scale landscape morphodynamics following foredune disturbance. Overall, the vegetation removal treatments reduced the extent of invasive grass and increased dunefield mobility and dynamic activity.

Description: ABSTRACT Although the impact of sheet erosion on the selective transportation of mineral soil particles has been widely investigated, little is yet known about the specific mechanisms of organic carbon (OC) erosion, which constitutes an important link in the global carbon cycle. The present study was conducted to quantify the impact of sheet erosion on organic carbon losses from soils. Erosion plots with the lengths of 1- and 5-m were installed at different topographic positions along a hillslope in a mountainous South African region. A total of 32 rainfall events from a three years period (November 2010 up to February 2013), were studied and evaluated for runoff (R), particulate and dissolved organic carbon (POC L and DOC L ). In comparison to the 0-0.05 m bulk soil, the sediments from the 1-m plots were enriched in OC by a factor 2.6 and these from the 5-m long plots by a factor of 2.2, respectively. These findings suggest a preferential erosion of OC. In addition, total OC losses (TOC L ) were incurred mainly in particulate form (~94%) and the increase in TOC L from 14.09 ± 0.68 g C m -1 y -1 on 1-m plots to 50.03 ± 2.89 g C m -1 y -1 on 5-m plots illustrated an increase in sheet erosion efficiency with increasing slope length. Both TOC L and sediment enrichment in OC correspondingly increased with a decrease in soil basal grass cover. The characteristics of rainstorms had no significant impact on the selectivity of OC erosion. The results accrued in this study investigating the links between sheet erosion and OC losses, are expected to be of future value in the generation of carbon specific erosion models, which can further help to inform and improve climate change mitigation measures. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The most important geomorphic responses to storms are qualitative changes in system state. Minor storms produce no state change or very rapid recovery to pre-storm state, and extinction events wipe out the system. In other cases disturbance results in a state change, which may be transitional (change to a previously existing state), state space expansion (change to a new state), and clock-resetting events that return the system to its initial state. Recovery pathways are much more varied than the monotonic progressions represented in classic vegetation succession and linear channel evolution models. Those linear sequential pathways are only one of several archetypal recovery pathways, which also include binary, convergent, divergent, and more complex networks. Filter-dominated systems are more likely to follow linear sequential or convergent patterns, whereas amplifier-dominance is characteristic of divergent and more complex mesh or fully-connected patterns. Amplifier domination is also more likely to lead to evolutionary or state space expansion responses. Amplification and filtering in geomorphic response and recovery can be assessed using the “Four R's” framework of response, resistance, relaxation, and recursion. High resistance and resilience, rapid relaxation times, and stable recursive feedback networks reduce or offset effects of disturbances, thus filtering their impacts. Conversely, low resistance and resilience, slow relaxation, and dynamically unstable feedbacks can exaggerate disturbances, creating disproportionately large and long-lived impacts, thereby amplifying disturbances. Unless new filter mechanisms evolve (either autogenically or anthropically), or the number of extinction or clock-resetting events increases, intensified storminess will result in more geomorphic variability. These ideas are applied to a case study of a flood on the Clark Fork River, Montana, USA. This article is protected by copyright. All rights reserved.

Description: The resiliency of coastal communities is imperative because these areas experience risk of damage from coastal storms as well as increasing population pressures and development. The severity of this hazard is compounded by sea level rise and a potential increase in storm intensities due to climate change. The ability of coastal communities to plan for, resist, and quickly and completely recover from severe coastal storm events and flooding is of critical importance. There is a growing interest in applying complementary and redundant approaches to reduce the flood risk of these vulnerable communities, such as incorporating natural and nature-based features into the project planning process. However, accounting for the benefits of these nature-based features in coastal design is still challenging. One of the natural features generally acknowledged to offer coastal protection benefits is wetlands. Using laboratory experiments of artificial vegetation as a foundation, the bounds of wave dissipation by vegetation are explored analytically and the effectiveness of wave dissipation by vegetation over large scales is investigated using the spectral wave model STWAVE. Wave heights modeled using a vegetation dissipation formulation are compared to those modeled with the current practice of representing vegetation using bottom friction, particularly the Manning formulation. The vegetation dissipation formulation reduced more wave energy than the Manning bottom friction formulation for submerged wetlands. Because the Manning formulation does not integrate vegetation properties, to achieve consistent results would require varying the Manning n coefficient to account for the spatial and temporal variation in form drag induced by the plants due to changes in plant density, diameter, and degree of plant submergence. Thus, a re-evaluation of existing methods for assessing wave dissipation by vegetation is recommended for wider application of vegetation dissipation formulations in numerical models. Such models are critical for evaluating coastal resiliency of communities protected by wetland features.