ALBERT

Description: ABSTRACT Datasets containing large numbers (〉10,000) of glacial lineaments are increasingly being mapped from remotely sensed data in order to develop a palaeo-glacial reconstruction or “inversion”. The palimpsest landscape presents a complex record of past ice flow and deconstructing this information into a logical history is an involved task. One stage in this process requires the identification of sets of genetically linked lineaments that can form the basis of a reconstruction. This paper presents a semi-automated algorithm, CLustre, for lineament clustering that uses a locally adaptive, region growing, methodology. After outlining the algorithm, it is tested on synthetic datasets that simulate parallel and orthogonal cross-cutting lineaments, encompassing 1,500 separate classifications. Results show robust classification in most scenarios, although parallel overlap of lineaments can cause false positive classification unless there are differences in lineament length. Case studies for Dubawnt Lake and Victoria Island, Canada, are presented and compared to existing datasets. For Dubawnt Lake 9 out of 14 classifications directly match incorporating 89% of lineaments. For Victoria Island 57 out of 58 classifications directly match incorporating 95% of lineaments. Differences are related to small numbers of unclassified lineaments and parallel cross-cutting lineaments that are of a similar length. CLustre enables the automated, repeatable, assignment of lineaments to flow sets using defined user criteria. This is important as qualitative visual interpretation may introduce bias, potentially weakening the testability of palaeo-glacial reconstructions. In addition, once classified, summary statistics of lineament clusters can be calculated and subsequently used during the reconstruction process. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Large wood tends to be deposited in specific geomorphic units within rivers. Nevertheless, predicting the spatial distribution of wood deposits once wood enters a river is still difficult because of the inherent complexity of its dynamics. In addition, the lack of long-term observations or monitored sites has usually resulted in a rather incomplete understanding of the main factors controlling wood deposition under natural conditions. In this study, the deposition of large wood was investigated in the Czarny Dunajec River, Polish Carpathians, by linking numerical modelling and field observations so as to identify the main factors influencing wood retention in rivers. Results show that wood retention capacity is higher in unmanaged multi-thread channels than in channelized, single-thread reaches. We also identify preferential sites for wood deposition based on the probability of deposition under different flood scenarios, and observe different deposition patterns depending on the geomorphic configuration of the study reach. In addition, results indicate that wood is not always deposited in the geomorphic units with the highest roughness, except for low-magnitude floods. We conclude that wood deposition is controlled by flood magnitude and the elevation of flooded surfaces in relation to the low-flow water surface. In that sense, the elevation at which wood is deposited in rivers will differ between floods of different magnitude. Therefore, together with the morphology, flood magnitude represents the most significant control on wood deposition in mountain rivers wider than the height of riparian trees. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This paper presents a comparison between two methods for estimating shear stress in an atmospheric internal boundary layer over a beach surface under optimum conditions, using wind velocities measured synchronously at 13 heights over a 1.7 m vertical array using ultrasonic anemometry. The Reynolds decomposition technique determines at-a-point shear stresses at each measurement height, while the Law-of-the-Wall yields a single boundary layer estimate based on fitting a logarithmic velocity profile through the array data. Analysis reveals significant inconsistencies between estimates derived from the two methods, on both a whole-event basis and as time-series. Despite a near-perfect fit of the Law-of-the-Wall, the point estimates of Reynolds shear stress vary greatly between heights, calling into question the assumed presence of a constant stress layer. A comparison with simultaneously measured sediment transport finds no relationship between transport activity and the discrepancies in shear stress estimates. Results do show, however, that Reynolds shear stress measured nearer the bed exhibits slightly better correlation with sand transport rate. The findings serve as a major cautionary message to the interpretation and application of single-height measurements of Reynolds shear stress and their equivalence to Law-of-the-Wall derived estimates, and these concerns apply widely to boundary layer flows in general. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Following perturbation, an ecosystem (flora, fauna, soil) should evolve as a function of time at a rate conditioned by external variables (relief, climate, geology). More recently, biogeomorphologists have focused upon the notion of co-development of geomorphic processes with ecosystems over very short through to very long (evolutionary) time-scales. Alpine environments have been a particular focus of this co-development. However, work in this field has tended to adopt a simplified view of the relationship between perturbation and succession, including: how the landform and ecosystem itself conditions the impact of a perturbation to create a complex spatial response impact; and how perturbations are not simply ecosystem destroyers but can be a significant source of ecosystem resources. What this means is that at the within landform scale, there may well be a complex and dynamic topographic and sedimentological template that co-develops with soil, flora and fauna. Here, we present and test a conceptual model of this template for a subalpine alluvial fan. We combine detailed floristic inventory with soil inventory, determination of edaphic variables and analysis of historical aerial imagery. Spatial variation in the probability of perturbation of sites on the fan surface was associated with down fan variability in the across-fan distribution of fan ages, fan surface channel characteristics and fan surface sedimentology. Floristic survey confirmed that these edaphic factors distinguished site floristic richness and plant communities up until the point that the soil-vegetation system was sufficiently developed to sustain plant communities regardless of edaphic conditions. Thus, the primary explanatory variable was the estimated age of each site, which could be tied back into perturbation history and its spatial expression due to the geometry of the fan: distinct plant communities were emergent both across fan and down fan, a distribution maintained by the way in which the fan dissipates potentially perturbing events. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Dam construction in the 1960's to 1980's significantly modified sediment supply from the Kenyan uplands to the lower Tana River. To assess the effect on suspended sediment fluxes of the Tana River, we monitored the sediment load at high temporal resolution for one year and complemented our data with historical information. The relationship between sediment concentration and water discharge was complex: at the onset of the wet season, discharge peaks resulted in high sediment concentrations and counterclockwise hysteresis, while towards the end of the wet season, a sediment exhaustion effect led to low concentrations despite the high discharge. The total sediment flux at Garissa (ca. 250 km downstream of the lowermost dam) between June 2012 and June 2013 was 8.8 Mt yr −1 . Comparison of current with historical fluxes indicated that dam construction had not greatly affected the annual sediment flux. We suggest that autogenic processes, namely river bed dynamics and bank erosion, mobilized large quantities of sediments stored in the alluvial plain downstream of the dams. Observations supporting the importance of autogenic processes included the absence of measurable activities of the fall-out radionuclides 7 Be and 137 Cs in the suspended sediment, the rapid lateral migration of the river course, and the seasonal changes in river cross-section. Given the large stock of sediment in the alluvial valley of the Tana River, it may take centuries before the effect of damming shows up as a quantitative reduction in the sediment flux at Garissa. Many models relate the sediment load of rivers to catchment characteristics, thereby implicitly assuming that alterations in the catchment induce changes in the sediment load. Our research confirms that the response of an alluvial river to external disturbances such as land use or climate change is often indirect or non-existent as autogenic processes overwhelm the changes in the input signal.

Description: ABSTRACT The Tangra Yum Co graben is one of the active structures that accommodate the east-west extension of the southern Tibetan Plateau and hosts one of the largest Tibetan lakes, which experienced lake-level changes of ~200 m during the Holocene. In this study, cosmogenic 10 Be is employed to (1) quantify catchment-wide denudation rates in fault-bounded mountain ranges adjacent to the Tangra Yum Co graben, (2) date palaeo-shorelines related to the Holocene lake-level decline, and (3) determine the age of glacial advances in this region. The fault-bounded, non-glaciated mountain range north of Tangra Yum Co – and presumably most other areas around the lake – erode at low rates of 10–70 mm/ka. Owing to the slow erosion of the landscape, the sediments delivered to Tangra Yum Co have high 10 Be concentrations. As a consequence, accurate exposure dating of sediment-covered terraces and beach ridges is difficult, because the pre-depositional 10 Be concentration may exceed the post-depositional 10 Be concentration from which exposure ages are calculated. This difficulty is illustrated by a rather inaccurate 10 Be exposure age of 2.3 ± 1.4 ka (i.e. an error of 60%) for a terrace that is located 67 m above the lake. Nevertheless, the age is consistent with luminescence ages for a series of beach ridges and provides further evidence for the decline of the lake level in the late Holocene. At Tangra Yum Co exposure dating of beach ridges via 10 Be depth profiles is not feasible, because the pre-depositional 10 Be component in these landforms varies with depth, which violates a basic assumption of this approach. 10 Be ages for boulders from two moraines are much older than the early Holocene lake-level highstand, indicating that melting of glaciers in the mountain ranges adjacent to Tangra Yum Co has not contributed significantly to the lake-level highstand in the early Holocene.

Description: ABSTRACT Extreme events such as storm surges and tsunamis in combination with subsidence of densely populated coastal areas pose an increasing threat to millions of people in the tropics. Intertidal mangrove forests may form a natural protection against some extreme events, but have also widely been destroyed by coastal development. The establishment of mangroves and the maintenance of their stability over the short- to long-term requires an understanding of sedimentary processes and landforms in the coastal zone, making geomorphology a crucial, but sometimes neglected discipline when attempting restoration for disaster risk reduction. Mangrove geomorphic setting varies markedly across the tropics, depending on abiotic parameters such as suspended sediment supply and tidal range, with different restoration strategies suitable for each. In this study we provide a global categorization of mangrove geomorphic settings, based on the literature and global remote sensing data. The world's mangroves can be broadly defined as 1) minerogenic and high tidal range; 2) minerogenic and low tidal range; and 3) organogenic and low tidal range. We further discuss restoration and management approaches most suitable for each geomorphic setting. Overall, this study can be used to inform managers about the relevance of geomorphic knowledge for successful mangrove restoration, how an understanding of geomorphology can influence site selection and restoration success, and how to match specific restoration methods to the prevailing geomorphic context. The stronger incorporation of geomorphic knowledge into site planning and design will improve the success rates of restoration for this important and globally threatened ecosystem. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Dissolved silica (DSi) plays an important biogeochemical role in the fjords of northern Chilean Patagonia (44–48°S), where it drives high biogenic productivity and promotes carbon burial. It is generally believed that the DSi riverine input to lakes and coastal environments is controlled by a combination of factors including lithology, climate, topography, vegetation, and meltwater input. In northern Chilean Patagonia several authors have proposed that the postglacial volcanic ash soils (andosols) may play a significant role in the high supply of DSi to the regional fjords. To assess the influence of andosols on DSi concentrations in north Patagonian rivers, we mapped andosol thickness and compared our results to river chemistry. The mineralogical and geochemical composition of three representative andosol profiles was also examined to evaluate the efficiency of weathering processes. The andosol thickness map clearly demonstrates that volcanic ash was predominantly deposited on the eastern side of the regional volcanoes, reflecting the influence of the prevailing westerly winds on the distribution of pyroclastic material. Mineralogical and geochemical results show that the andosol parent material has the typical andesitic basaltic signature of the regional volcanoes, i.e., high amounts of amorphous material, plagioclase, K-feldspar, and pyroxene. Down-profile variations in soil mineralogy and geochemistry indicate increased leaching of silica with depth, resulting from weathering of the volcanic parent material. For the five studied watersheds, a highly positive correlation (R 2  = 0.98) was found between average andosol thickness and DSi concentrations, suggesting that andosol thickness is the main parameter affecting DSi concentrations in north Patagonian river systems. On seasonal timescales, increased precipitation (winter) and glacial meltwater (summer) input can significantly reduce DSi concentrations. We argue that the weathering of andosols constitutes the most important source of DSi to the lakes and fjords of northern Chilean Patagonia, explaining the particularly high regional rates of biogenic silica production. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Soil surface roughness contains two elementary forms, depressions and mounds, which affect water flow on the surface differently. While depressions serve as temporary water storage, mounds divert water away from their local summits. Although roughness impacts on runoff and sediment production have been studied, almost no studies have been designed explicitly to quantify the evolution of depressions and mounds and how this impacts runoff generation and sediment delivery. The objectives of this study were to analyze how different surface forms affect runoff and sediment delivery and to measure the changes in surface depressions and mounds during rainfall events. A smooth surface was used as the control. Both mounds and depressions delayed the runoff initiating time, but to differing degrees; and slightly reduced surface runoff when compared to the runoff process from the smooth surface. Surface mounds significantly increased sediment delivery, whilst depressions provided surface storage and hence reduced sediment delivery. However, as rainfall continued and rainfall intensity increased, the depression effect on runoff and erosion gradually decreased and produced even higher sediment delivery than the smooth surface. Depressions and mounds also impacted the particle size distribution of the discharged sediments. Many more sand-sized particles were transported from the surface with mounds than with depressions. The morphology of mounds and depressions changed significantly due to rainfall, but to different extents. The difference in change had a spatial scale effect, i.e., erosion from each mound contributed to its own morphological change while sediments deposited in a depression came from a runoff contributing area above the depression, hence a much greater source area than a single mound. The results provide a mechanistic understanding of how soil roughness affects runoff and sediment production. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Biological soil crusts (BSCs) cover up to 60%-70% of the soil surface in grasslands after the “Grain for Green” project was implemented in 1999 to rehabilitate the Loess Plateau. However, few studies exist that quantify BSC's effects on the soil detachment process by overland flow in the Loess Plateau. This study investigated the potential effects of BSCs on the soil detachment capacity ( D c ), and soil resistance to flowing water erosion reflected by rill erodibility and critical shear stress. Two dominant BSC types that developed in the Loess Plateau (the later successional moss and the early successional cyanobacteria mixed with moss) were tested against natural soil samples collected from two abandoned farmland areas. The samples were subjected to flow scouring under six different shear stresses ranging from 7.15 to 24.08 Pa. The results showed that D c decreased significantly with crust coverage under both moss and mixed crusts. The mean D c of bare soil (0.823 kg m -2 s -1 ) was 2.9 to 48.4 times greater than those of moss covered soil (0.017-0.284 kg m -2 s -1 ), while it (3.142 kg m -2 s -1 ) was 4.9 to 149.6 times greater than those of mixed covered soil (0.021-0.641 kg m -2 s -1 ). The relative detachment rate of BSCs compared with bare soils decreased exponentially with increasing BSC coverage for both types of BSCs. D c can be simulated by flow shear stress, cohesion, and BSC coverage using a power function (NSE ≥ 0.59). Rill erodibility also decreased with coverage of both crust types. Rill erodibility of bare soil was 3 to 74 times greater than those of moss covered soil and was 2 to 165 times greater than those of mixed covered soil. Rill erodibility could also be estimated by BSC coverage in the Loess Plateau (NSE ≥ 0.91). The effect of crust coverage on critical shear stress was not significant. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This paper reports a novel method for the incorporation of complex plant morphologies into a computational fluid dynamics (CFD) model, allowing the numerical prediction of flows around individual plants. The morphological complexity, which comprises the vertical and lateral distribution of individual branches and leaves is captured through terrestrial laser scanning (TLS) and is maintained in the numerical prediction of flow fields. This is achieved where the post-processed, voxelised plant representation is incorporated into a CFD scheme through a mass flux scaling algorithm (MFSA). Flow around Prunus laurocerasus has been modelled under foliated and defoliated states following the removal of leaves. The complex plant morphologies are shown to produce spatially heterogeneous downstream velocity fields, with velocity profiles that deviate significantly from the idealised inflected shape. Rapid transition between the high velocity free stream zone and the zone of reduced velocity in the plant wake indicate shearing of flow, with the point of reattachment extending up to seven plant lengths downstream. The presence of leaves significantly modifies the flow field response, with development of a second, more pronounced wake structure around the dense foliage. This approach provides a full flow numerical description of the pressure field, enabling the vegetative drag force to be quantified. For the example given here, drag force is an order of magnitude greater for the foliated state. The methodology outlined here demonstrates the importance of accurately representing complex plant morphology in hydraulic models, and allows drag forces and coefficients to be calculated for specific plant species. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Rapidly rising populations of low-lying megacities in Asia mean that understanding the potential risk of coastal flooding by storm surge is of paramount concern. The city of Bangkok and the wider Chao Phraya River delta at the head of the Gulf of Thailand is a region topographically vulnerable to coastal flooding, but without the record of a high-energy marine inundation (HEMI) event in historical time owing to the atypical path that a typhoon must take to be able to produce such an event. This work builds upon previous findings that identified coastal depositional evidence for HEMI events in the form of coastal carbonate boulders (CCBs) located on Ko Larn island in the eastern Bay of Bangkok. The HEMI events were most likely driven by typhoons and the CCBs are therefore interpreted as typhoon deposits. Through uranium/thorium dating, it is revealed that from AD1400–1600 the Bay of Bangkok possibly experienced a phase of relatively heightened storm impact. During this period, the frequency of typhoon-driven HEMI events was approximately four events in 200 years. Waves generated onshore minimum flow velocities (MFVs) in excess of 5 m/s. Such exceptional MFVs are unlikely to be produced during the annual northeast monsoon, but are consistent with typhoon-impacted coastlines elsewhere in the tropical Asia–Pacific region where similar CCB evidence exists. Since AD1600, the Bay of Bangkok has enjoyed a relatively quiescent phase, recording less frequent HEMI events and of lower magnitude. However, the reoccurrence of a typhoon-driven HEMI event on the scale of the prehistorical events that emplaced carbonate boulders at elevation on Ko Larn island would threaten low-lying coasts in the Bay of Bangkok, including the Chao Phraya delta, with potentially damaging inundation. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In 2008-2009, a severe cold snap affected the otherwise temperate mid-latitude coasts of the English Channel of France. In March 2009, we gathered rock spalling observations at Mesnil Val, NW France, to document the effect of frost on platform lowering in macro-tidal environments. Six epochs of frost were recorded in two months, the two longest lasted 16 and 8 days, with minimum air temperature dropping to -9.5°C. Semi-diurnal tides flood the entire platform, imposing up to 25 freeze-thaw cycles below -2.5°C, the freezing temperature of seawater. 19 cycles occurred at neap tidal elevation lasting at most 3.5 hrs. Our integrated observations indicate that these frost cycles were responsible for a platform lowering of about 0.8±0.5 mm during a single winter. No clear spatial trend appears, nor do macroscopic chalk types clearly stand out as being more susceptible to erosion. Assuming that the long-term platform retreat model preserves a constant slope, frost shattering would then account for 10 to 20% of the expected annual platform erosion rate. Under more contrasted climates, frost is thus likely to be a prominent shaping process for rocky coastal platforms. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Different high-resolution techniques can be employed to obtain information about the 3D surface of glaciers. This is typically carried out using efficient, but also expensive and logistically demanding, light detection and ranging (LiDAR) technologies, such as airborne scanners and terrestrial laser scanners (TLSs). Recent technological improvements in the field of image analysis and computer vision have prompted the development of a low-cost photogrammetric approach, which is referred to as ‘structure from motion’. Combined with dense image-matching algorithms, this method has become competitive for the production of high-quality 3D models. However, several issues typical of this approach should be considered for application in glacial environments. In particular, the surface morphology, the different substrata, the occurrence of sharp contrast from solar shadows and the variable distance from the camera positions can negatively affect the image texture, and reduce the possibility of obtaining a reliable point cloud from the images. The objective of this study is to test the Structure from Motion-Multi View Stereo (SfM-MVS) approach in a small debris-covered glacier located in the Eastern Italian Alps, using a consumer-grade reflex camera and the computer vision-based software PhotoScan. The quality of the 3D models produced by the SfM-MVS process was assessed via the comparison with digital terrain models obtained from TLS surveys that were performed at the same epochs. The effect of different terrain gradients and different substrata (debris, snow and firn) was also evaluated in terms of the accuracy of the reconstruction by SfM-MVS vs. TLS. Our results show that the quality of this new photogrammetric approach is similar to the quality of TLS and that point cloud densities are comparable or even higher compared with TLS. However, special care should be taken while planning the SfM survey geometry, to optimize the 3D model quality and spatial coverage. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Despite soil erosion through water being a ubiquitous process and its environmental consequences being well-understood, its effects upon the Global Carbon Cycle still remain largely uncertain. How much soil organic carbon (SOC) is removed each year from soils by sheet wash, an important if not the most efficient mechanism of detachment and transport of surficial soil material? What are the main environnemental controls worldwide? These are important questions which largely remain unanswered. Empirical data from 240 runoff plots studied over entire rainy seasons from different regions of the world were analysed to estimate particulate organic carbon (POC) losses (POC L ), and POC enrichment in the sediments compared to the bulk soil (ER), which can be used as a proxy of the fate of the eroded POC. The median POC L was 9.9 g C m -2 y -1 with highest values observed for semi-arid soils (POC L  = 10.8 g C m -2 y -1 ), followed by tropical soils (POC L  = 6.4 g C m -2 y -1 ) and temperate ones (POC L  = 1.7 g C m -2 y -1 ). Considering the mean POC L of 27.2 g C m -2 y -1 , the total amount of SOC displaced annually by sheet erosion from its source would be 1.32 ± 0.20 Gt C, i.e. 14.6% of the net annual fossil fuel induced C emissions of 9 Gt C. Because of low sediment enrichment in POC, erosion-induced CO 2 emissions are likely to be limited in clayey environments while POC burial within hillslopes is likely to constitute an important carbon sink. In contrast, most of the POC displaced from sandy soils is likely to be emitted to the atmosphere. These results underpin the major role sheet wash plays in the displacement of SOC from its source and in the fate of the eroded SOC, with large variations across the different pedo-climatic regions of the world. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Glaciers are a major erosive force that increase sediment load to the downstream fluvial system. The Castle Creek Glacier, British Columbia, Canada, has retreated ~1.0 km in the past 70 years. Suspended sediment concentration (SSC) and streamflow (Q) were monitored independently at five sites within its proglacial zone over a 60 day period from July to September, 2011, representing part of the ablation season. Meteorological data were collected from two automatic weather stations proximal to the glacier. The time-series were divided into hydrologic days and the shape and magnitude of the SSC response to hydro-meteorological conditions (‘cold and wet’, ‘hot and dry’, ‘warm and damp’, and ‘storm’) were categorized using principal component analysis (PCA) and cluster analysis (CA). Suspended sediment load (SSL) was computed and summarized for the categories. The distribution of monitoring sites and results of the multivariate statistical analyses describe the temporal and spatial variability of suspended sediment flux and the relative importance of glacial and paraglacial sediment sources in the proglacial zone. During the 2011 study period, ~ 60% of the total SSL was derived from the glacial stream and sediment deposits proximal to the terminus of the glacier; during ‘storm’ events, that contribution dropped to ~40% as the contribution from diffuse and point sources of sediment throughout the proglacial zone and within the meltwater channels increased. While ‘storm’ events accounted for just 3% of the study period, SSL was ~600% higher than the average over the monitoring period, and ~20% of the total SSL was generated in that time. Determining how hydro-meteorological conditions and sediment sources control sediment fluxes will assist attempts to predict how proglacial zones respond to future climate changes. This article is protected by copyright. All rights reserved.

Description: ABSTRACT An important and highly active research agenda has developed at the interface of fluvial geomorphology and ecology that addresses the capacity for vegetation and animals to act as ecosystem engineers within fluvial systems. This paper briefly introduces this research domain and describes the fifteen papers that contribute to the special issue on ‘Dynamic riverine landscapes: the role of ecosystem engineers’. The papers illustrate the breadth of research activity at this interface, investigating the influence of a range of ecosystem engineering organisms through a combination of field study, laboratory experiments, numerical simulation and analysis of remotely sensed data. Together, the papers address a series of key themes: conceptual frameworks for feedbacks between aquatic biota, hydraulics, sediment dynamics and nutrient dynamics and their quantification through experimental and field research; the potential contribution of ecosystem engineering species to assist river recovery and restoration; and the contribution of riparian vegetation to bank stability and morphodynamics across a range of spatio-temporal scales. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Reservoir siltation is one of the most important off-site effects of soil erosion. In Burkina Faso a large number of small dams have been built to store rainfall and runoff water in the rainy season, which is much needed for domestic use, irrigation and stock watering in the dry season. This study quantifies the siltation rates of two small reservoirs in southwestern Burkina Faso by comparing the initial and current reservoir bed morphology and by analyzing variations in accumulated sediment in terms of stratigraphical changes and 137 Cs concentrations. Results of a bathymetric survey show that both reservoirs have already lost approximately 10 % to 15 % of their original storage capacity at normal pool level and more than 60 % of their initial inactive storage volume at spillway level in the last 15 to 20 years. During this period, inflow sediment had accumulated on the bottom of the reservoir to a thickness of 0.3 m to 0.5 m. Sediment core measurements confirmed this thickness by showing a clear stratigraphical change in core properties with significant variations in the 137 Cs concentrations at these specific depths. The thickness of accumulated sediment on top of the relict soil indicates that the reservoirs have a “half-life” of about 40 to 45 years before siltation might affect its water supply and flood control. Compared to other reservoir studies in West Africa these siltation rates can be seen as reasonable but not alarmingly high. Nevertheless, many of the small dams built during the 1980s are likely to reach their “half-life” in about 10 to 20 years causing hydrological and geomorphological changes upstream and downstream of the dams. Therefore, further research studies should focus on prevention measures to reduce the off-site effects of erosion and thus to slow down the process of siltation. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Miocene continental saltpans are scattered in the Central Valley of the Atacama Desert, one of the driest regions on Earth. These evaporitic deposits are hydrologically inactive, and are detached from groundwater brines or aquifers. The surface of the saltpans, also known as salars, comprises desiccation polygons, commonly with nodular salt structures along their sides. The morphology and bulk mineralogy of salt polygons differs between and within salars, and the shape and internal structure of salt nodules varies between different polygon types. Based on field observation, and mineralogy and crystallography data, we generated a conceptual model for the genesis and evolution of these surface features, whereby rare rainfall events are responsible for the transformation of desiccation salt polygons and the initial formation of salt nodules along polygon borders. In addition, frequent, but less intense, deliquescence events further drive the evolution of salt nodules, resulting in a characteristic internal structure that includes laminations, and changes in porosity and crystal morphologies. As a result, and despite the extreme dryness, the surfaces of fossil salars are dynamic on timescales of several years to decades, in response to daily cycles in atmospheric moisture, and also to rare and meager rainfall events. We propose that fossil salars in the Atacama Desert represent an end stage in the evolution of evaporitic deposits under extreme and prolonged dryness. This article is protected by copyright. All rights reserved.

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: ABSTRACT The processes involved in the development of high-altitude, low-relief areas (HLAs) are still poorly understood. Although cosmogenic nuclides have provided insights into the evolution of HLAs interpreted as paleo-surfaces, most studies focus on estimating how slowly they erode and thereby their relative stability. To understand actual development processes of HLAs, we applied several techniques of cosmogenic nuclides in the Daegwanryeong Plateau, a well-known HLA in the Korean Peninsula. Our denudation data from strath terraces, riverine sediments, soils, and tors provide the following conclusions: 1) bedrock incision rate in the plateau (~127 m Myr −1 ) is controlled by the incision rate of the western part of the Korean Peninsula, and is similar to the catchment-wide denudation rate of the plateau (~93 m Myr −1 ); 2) the soil production function we observed shows weak depth dependency that may result from highly weathered bedrock coupled with frequent frost action driven by alpine climate; 3) a discrepancy between the soil production and catchment-wide denudation rates implies morphological disequilibrium in the plateau; 4) the tors once regarded as fossil landforms of the Tertiary do not reflect Tertiary processes, and 5) when compared to those of global paleo-surfaces (〈20 m Myr −1 ), our rapid denudation rates suggest that the plateau cannot have maintained its probable initial paleo landscape, and thus is not a paleo-surface. Our data contribute to understanding the surface processes of actively eroding upland landscapes as well as call into question conventional interpretations of supposed paleo-surfaces around the world. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Large wood (LW) is an important component of forested headwater streams. The character of LW loads reflects a balance between adjacent valley processes that deliver LW to the channel (herein recruitment processes) and stream channel processes that either retain or transport LW through the reach (herein retention processes). In the central Appalachian Mountains, USA LW characteristics in headwater streams located in eastern hemlock forests are expected to change because of infestation of hemlock woolly adelgid (HWA), an exotic, invasive insect. We examine LW characteristics in 24 headwater streams ranging from un-infested to severe infestation, as determined by hemlock canopy health. The objectives of this work were to (i) quantify wood loads, (ii) assess the relative importance of valley recruitment and in-stream retention mechanisms in controlling reach-scale wood loads, and (iii) assess if there was a detectable influence of HWA on LW loads. We hypothesized that LW loads would be similar to other forested streams in eastern USA and dominated by recruitment processes. In addition, higher LW loads would correspond with advanced HWA infestation. Mean wood frequency was 38 pieces/100 m ± 17 (standard deviation); mean wood volume was 3.69 m 3 /100 m ± 2.76. General LW load characteristics were influenced by both recruitment and retention parameters; jam (accumulations ≥ 3 pieces) characteristics were dominated by retention parameters. Results suggest that adjacent stand basal area influences LW loads and once LW is recruited to the channel, streams lack sufficient hydraulic driving forces, despite having lower resistance structures, to transport LW out of the reach. Sites in moderate decline had higher proportions of short (1-2 m and 1-4 m) and very long (〉10 m) LW with higher frequency of jams that were low in volume. We present a hypothesized conceptual model of expected changes to LW loads associated with HWA infestation and hemlock mortality. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The 1999 jökulhlaup at Sólheimajökull was the first major flood to be routed through the proglacial system in over 600 years. This study reconstructed the flood using hydrodynamic, sediment transport and morphodynamic numerical modelling informed by field surveys, aerial photograph and digital elevation model analysis. Total modelled sediment transport was 469,800 m 3 (+/- 20 %). Maximum erosion of 8.2 m occurred along the ice margin. Modelled net landscape change was -86,400 m 3 (+/- 40 %) resulting from -275,400 m 3 (+/- 20 %) proglacial erosion and 194,400 m 3 (+/- 20 %) proglacial deposition. Peak erosion rate and peak deposition rate were 650 m 3 s −1 (+/- 20 %) and 595 m 3 s −1 (+/- 20 %), respectively, and coincided with peak discharge of water at 1.5 hours after flood initiation. The pattern of bed elevation change during the rising limb suggested widespread activation of the bed, whereas more organisation; perhaps primitive bedform development, occurred during the falling limb. Contrary to simplistic conceptual models, deposition occurred on the rising stage and erosion occurred on the falling limb. Comparison of the morphodynamic results to a hydrodynamic simulation illustrated effects of sediment transport and bed elevation change on flow conveyance. The morphodynamic model advanced flood arrival and peak discharge timings by 100 % and 19 %, respectively. However, peak flow depth and peak flow velocity were not significantly affected. We suggest that morphodynamic processes not only increase flow mass and momentum but that they also introduce a feedback process whereby flood conveyance becomes more efficient via erosion of minor bed protrusions and deposition that infills or subdues minor bed hollows. A major implication of this study is that reconstructions of outburst floods that ignore sediment transport, such as those used in interpretation of long term hydrological record and flood risk assessments, may need considerable refinement. This article is protected by copyright. All rights reserved.

Description: Intertidal habitats provide numerous ecosystem services, including the sequestration and storage of carbon, a topic of great recent interest owing to land-cover transitions and climate change. Mangrove forests and seagrass meadows form a continuum of intertidal habitats, alongside unvegetated mudflats and sandbars, however, studies that consider the carbon stocks across these spatially-linked, threatened ecosystems are limited world-wide. This paper presents the results of a field-based carbon stock assessment of aboveground, belowground and sediment organic carbon stock to a depth of 1 m at Chek Jawa, Singapore. It is the first study of ecosystem carbon stocks of both vegetated and unvegetated intertidal habitats in the tropics. Ecosystem carbon stock was 497 Mg C ha -1 in the mangrove forest and 138 Mg C ha -1 in the seagrass meadow. Sediment organic carbon stock dominated the total storage in both habitats, constituting 62% and 〉99% in the mangrove forest and seagrass meadow respectively. In the adjacent mudflat and sandbars, which had no vegetative components, sediment organic carbon stock ranged from 124-143 Mg C ha -1 , suggesting that unvegetated habitats have a carbon storage role on the same order of importance as seagrass meadows. This study reinforces the importance of sediment in carbon storage within the intertidal ecosystem, and demonstrates the need to consider unvegetated habitats in intertidal ‘blue carbon’ stock assessments. This article is protected by copyright. All rights reserved.

Description: Vegetation evapotranspiration (ET) induced soil water suction reduces permeability and increases shear strength of slopes. Several field studies have been conducted to investigate suction distribution in vegetated slopes. However, these studies were conducted on natural slopes, which are prone to heterogeneity in vegetation and soil conditions. Moreover, studies quantifying effect of different vegetation species, root characteristics (root depth, root area index) and transpiration reduction function (T rf ) on suction in slopes under natural variation are rare. This study investigated the suction distribution and root characteristics in recompacted slopes vegetated with two different species i.e., Cynodon dactylon (Bermuda grass) and Schefflera heptaphylla (Ivy tree). Bare slopes served as a control. Suction distributions under different seasons and rainfall events were monitored. It is found that during the dry season, slopes vegetated with young Schefflera heptaphylla seedlings have substantially higher suction within root zone compared with bare slopes and slopes vegetated with Cynodon dactylon . This is because Schefflera heptaphylla has a higher root biomass, T rf and ET than Cynodon dactylon . It was also found that suctions within root zones of vegetated slopes and bare slope were completely destroyed under rainfall events corresponding to 2 years and 20 years of return period. 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: ABSTRACT Stream burning is a common flow enforcement technique used to correct surface drainage patterns derived from digital elevation models (DEM). The technique involves adjusting the elevations of grid cells that are coincident with the features of a vector hydrography layer. This paper focuses on the problematic issues with common stream-burning practices, particularly the topological errors resulting from the mismatched scales of the hydrography and DEM data sets. A novel alternative stream burning method is described and tested using five DEMs of varying resolutions (1 to 30 arc-seconds) for an extensive area of southwestern Ontario, Canada. This TopologicalBreachBurn method uses total upstream channel length (TUCL) to prune the vector hydrography layer to a level of detail that matches the raster DEM grid resolution. Network pruning reduces the occurrence of erroneous stream piracy caused by the rasterization of multiple stream links to the same DEM grid cell. The algorithm also restricts flow within individual stream reaches, further reducing erroneous stream piracy. In situations where two vector stream features occupy the same grid cell, the new tool ensures that the larger stream, designated by higher TUCL, is given priority. TUCL-based priority minimizes the impact of the topological errors that occur during the stream rasterization process on modeled regional drainage patterns. The test data demonstrated that TopologicalBreachBurn produces highly accurate and scale-insensitive drainage patterns and watershed boundaries. The drainage divides of four large watersheds within the study region that were delineated from the TopologicalBreachBurn -processed DEMs were found to be highly accurate when compared with the official watershed boundaries, even at the coarsest grid resolutions, with Kappa index of agreement values ranging from 0.952 to 0.921. The corresponding Kappa coefficient values for a traditional stream burning method ( FillBurn ) ranged from 0.953 to 0.490, demonstrating a significant decrease in mapping accuracy at coarser DEM grid resolutions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Valley setting and confinement (or lack thereof) are primary controls on river character and behaviour. Although there are various proxies for valley confinement, direct measures that quantify the nature and extent of confinement are generally lacking and/or inconsistently described. As such they do not lend themselves to consistent analysis over large spatial scales. Here we clearly define forms of confinement to aid in quantification of degrees of confinement. Types of margin that can induce confinement are differentiated as a valley margin, valley bottom margin, and/or anthropogenic margin. Such margins sometimes overlap and share the same location, and in other situations are separated, giving immediate clues as to the valley setting. We apply this framework to examples from Australia, USA and New Zealand, showing how this framework can be applied across the spectrum of river diversity. This method can help to inform interpretations of reach-scale river behaviour, highlighting the role of antecedent controls on contemporary forms and processes. Clearer definitions of confinement are shown to support for catchment-scale analysis of river patterns along longitudinal profiles and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments (e.g process zone distribution, lateral sediment inputs and (dis)connectivity). This article is protected by copyright. All rights reserved.

Description: ABSTRACT Anthropogenic activities on peatlands, such as drainage, can increase sediment transport and deposition downstream resulting in harmful ecological impacts. The objective of this study was to quantify changes in erosion/deposition quantities and surface roughness in peatland forest ditches by measuring changes in ditch cross-sections and surface microtopography with two alternative methods: manual pin meter and terrestrial laser scanning (TSL).The methods were applied to a peat ditch and a ditch with thin peat layer overlaying erosion sensitive mineral soil within a period of two years following ditch cleaning. The results showed that erosion was greater in the ditch with exposed mineral soil than in the peat ditch. The two methods revealed rather similar estimates of erosion and deposition for the ditch with thin peat layer where cross-sectional changes were large, whereas the results for smaller scale erosion and deposition at the peat ditch differed. The TLS-based erosion and deposition quantities depended on the size of the sampling window used in the estimations. Surface roughness was smaller when calculated from the pin meter data than from the TLS data. Both methods indicated that roughness increased in the banks of the ditch with thin peat layer. TLS data showed increased roughness also in the peat ditch. The increase in surface roughness was attributed to erosion and growth of vegetation. Both methods were suitable for the measurements of surface roughness and microtopography at the ditch cross-section scale, but the applicability, rigour, and ease of acquisition of TLS data were more evident. The main disadvantage of the TLS instrument (Leica ScanStation 2) compared to pin meter was that even a shallow layer of humic (dark brown) water prevented the detection of ditch bed. The geomorphological potential of the methods was shown to be limited to detection of surface elevation changes 〉~0.1 m. 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 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: To assess potential differences in stormwater runoff and sediment yield between plots of blue gum eucalyptus ( Eucalyptus globulus ) and coast live oak ( Quercus agrifolia ), we measured runoff, sediment yield, water repellency and soil moisture at eight paired sites. Eucalyptus has been associated in many studies worldwide with elevated soil water repellency and increased runoff, a likely contributor to soil erosion. To better understand these connections and their relationship to land cover, there is a need for studies employing either rainfall simulators or natural rainfall. Our research employs the latter, and was subject to contrasting hydrologic conditions in the two years of the study. Field work was conducted from October 2006 to February 2008 in the San Francisco Bay Area of central California. During the 2006–07 winter wet season, runoff was significantly higher under eucalypts than at paired oak sites, and in the early phases of the season was connected with elevated water repellency. However, sediment yield at all sites during the 2006–2007 hydrologic year was below the detection limit of the Gerlach sediment collection traps, possibly due to a limited wet season, and only appeared as suspended sediment captured in overflow buckets. Intensive rainfall events in January 2008 however created substantial runoff of sediment and litter with significantly greater yield at oak sites compared to paired eucalyptus sites. Water repellency likely had little effect on runoff during these events, and the primary cause of greater erosion under oaks is the thinner cover of leaf litter in comparison to eucalyptus. Our study is limited to undisturbed sites with intact litter cover that have not experienced recent wildfires; if disturbed, we would expect a different picture given the propensity for crown fires of eucalypts, enhancement of rainsplash erosion, and the likely greater potential for stream-connected sediment yield from post-disturbance soil erosion events. This article is protected by copyright. All rights reserved.

Description: Landslides contribute to dismantle active mountain ranges and faults control the location of landslides. Yet, evidence of the long-term, regional dependency of landslides on active faults is limited. Previous studies focused of the transient effects of earthquakes on slope stability in compressive and transcurrent regimes. Here we show that in the Peloritani range, NE Sicily, Italy, one of the fastest uplifting areas in the Mediterranean, a clear geographical association exists between large bedrock landslides and active normal faults of the Messina Straits graben. By interpreting aerial photographs, we mapped 1590 landslides and sackungs and 626 fault elements and their facets in a 300-km 2 area in the E part of the range. We used the new landslide and fault information, in combination with prior geological and seismic information, to investigate the association between bedrock landslides and faults. We find that the distribution and abundance of landslides is related to the presence of large active normal faults, and matches the pattern of the local historical seismicity. Landslide material is more abundant along the East Peloritani Fault System where the long-term activity of the faults, measured by the average yearly geological moment rate, is larger than in the West Peloritani Fault System where landslides are less abundant. Along the fault systems landslide material concentrates where the cumulated fault throws are largest. We conclude that large landslides and their cumulated volume are sensitive to local rates of tectonic deformation, and discriminate the deformation of the single fault segments that dissect the Peloritani range. Our findings are a direct test of landscape evolution models that predict higher rates of landslide activity near active faults. Our work opens to the possibility of exploiting accurate landslide and fault maps, in combination with geological and seismic information, to characterize the long-term seismic history of poorly instrumented active regions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Lacustrine sediment archives indicate that flooding during Tropical Storm Irene (2011) in the northeastern US caused the most severe erosion of any flood in the historic record, surpassing that of events with greater precipitation and peak discharges. Compared to deposition from historic floods, Irene's event layer was more massive and more enriched in unweathered upland sediments, indicating an anomalously high incidence of mass wasting and sediment entrainment. Precipitation records indicate that neither precipitation intensity nor total accumulation distinguished Irene from less erosive historic floods. However, cumulative precipitation prior to Irene exceeded the 95 th percentile of all days in the record. When allowing for non-stationarity in 20 th century background precipitation, we find a fourfold increase in the probability of Irene-like conditions, where impacts of extreme rainfall are enhanced by high antecedent precipitation. We conclude that irrespective of increases in extreme precipitation, the risk of highly erosive flooding in the region is increasing due to the influence of wetter baseline conditions associated with a changing climate.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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