Search

La estimación de la carga máxima de sedimentos sobre el lecho de río permite determinar las zonas de acumulación y posterior formación de bancos de arena, en este artículo se presentan los resultados de la estimación de la carga máxima de sedimentos sobre el lecho del Río Cauca. La zona de estudio se caracteriza por presentar un gradiente bajo y de forma sinusoidal, además de una climatología tropical de solo dos estaciones, donde se tienen temporadas de lluvia en la que se da el transporte, seguidas de calurosas épocas de verano donde se acumula el material de arrastre sobre el lecho del río, características suficientes para la formación de bancos de arena. Se partió de estudios realizados en ríos con características fluviales y topográficas muy parecidas a las de la zona de estudio, los cuales, a partir de la aplicación de modelos matemáticos a los valores de pixel de las fotografías aéreas del río, permitieron el reconocimiento de cauce y formación de bancos de arena sobre el lecho. Para el cálculo de transporte de sedimentos o carga de fondo se utilizó la relación de Meyer- Peter & Muller (Ferguson, 2008) y la función de Shields, Church (2006), modelos que dependen de las características topográficas del lecho del río. Se utilizó el modelo digital de elevación obtenido del procesamiento fotogramétrico, así mismo, se estableció un tamaño de grano de 4mm y una velocidad virtual de 1.3 m/s, para el reconocimiento definitivo del lecho se optó por las funciones de potencia y tensión de corte o erosión Lorang et al. (2005). Los resultados obtenidos mostraron que el Río Cauca tiene gran capacidad de acumulación, al igual que de transporte de sedimentos, se destacaron zonas de acumulación, que para el año de estudio presentaban un potencial para la formación de bancos de arena, los que a la fecha continúan siendo explotados, los resultados de carga de fondo, formación de bancos de arena y reconocimiento del lecho de río, mostraron coherencia entre sí, permitiendo tener validez en los resultados, para un río de las características estudiado.

Climatologic and anthropogenic pressures in coastal areas affect the coastal zone at different scales. With the development of new missions in open-access, satellites now represent an attractive solution for a broad public to capture local-scale coastal impacts at large scales. Here, the capability of the Sentinel 2 constellation to cover coastal areas and measure coastal processes –physical and biological. We show that Sentinel 2 enables high-frequency measurements across the globe. Cloud coverage at higher latitudes is overcome by decrease revisit time-intervals. Only around the equator, the longest revisit intervals and high cloud cover probability limits coastal measurements there. Sentinel 2 based methods are capable of estimating Digital Elevation Models for mid- to high-latitude coastal zones and sporadic spots for lower latitudes where 2 orbit swaths overlap. For the majority of the world’s coastal bathymetries can be obtained with the Sentinel 2 imagery surpassing the depth of closure (beyond this offshore limit sediment transport is limited). Only in sheltered areas, wave-based bathymetry inversion is limited but at these areas inversion through colouring (light penetration) prevails. This works shows that Sentinel 2 enables coastal monitoring as never before, large spatial scale with revisits of a few days at most of the world.

Journal of marine science and engineering 9(8), 850 (2021). doi:10.3390/jmse9080850 special issue: "Special Issue "Morphodynamic Evolution and Sustainable Development of Coastal Systems" / Special Issue Editors: Dr. Pushpa Dissanayake, Guest Editor ; Dr. Jennifer Brown, Guest Editor ; Dr. Marissa Yates, Guest Editor", Published by MDPI, Basel

Based on an analysis of a series of digital elevation models obtained using a terrestrial laser scanning (TLS) technique, assessment of mean sand transport rate was performed in seasonal scale. Analytical procedures based on the method of finite differences were performed to quantify the volume of moved material. Coastal hydrodynamic processes, as well as the meteorological regime were taken into account as forcing or limiting factors of aeolian processes. The TLS method is successfully used to assess variability and embryo dunes formation in different areas by other researchers. Two characteristic coastal areas on the territory of the Сuronian Spit National Park in Southeastern Baltic Sea were selected as key sites for morphodynamic processes studying. The results of the analysis of coastal hydrodynamic and related morphodynamic processes show that only one site is suitable for estimating the average rate of sand transport on a seasonal scale. The received relationship between cross-shore mean sand transport rate and the cross-shore directions average wind speed are in a good agreement with the Bagnold formula and with field measurements using sand traps. Extreme hydrodynamic situations leading to beach inundation, as well as precipitation, limit the development of aeolian processes on a seasonal scale.

Understanding the evolutionary trends of tidal flat development is crucial for local ecological protection, tidal flat development and utilization. However, obtaining such knowledge is often challenging due to the lack of frequently updated topography. This is particularly true for the middle section of Jiangsu Coast, which has complex sedimentary features and is the largest and the most rapidly changing tidal flat area in China. In this study, long-term remote sensing images (1973–2016) and a recently developed method for generating a Digital Elevation Model (DEM) were combined to construct a historical topological dataset with 24 phases of DEM, which was used to track changes of the Jiangsu Coast during the past four decades. The results demonstrate that: (1) the slope of the Jiangsu Coast from north to south exhibits a prominent increasing trend during the past 40 years, with the high tidal flat moving seawards and the low tidal flat moving landwards. (2) Large offshore sandbanks (Dongsha Sandbank, especially) are generally undergoing erosion in both the high tidal flat and low tidal flat, with the exception of Gaoni Sandbank where the high tidal flat is still in accretion. (3) Although there are discernible differences in rate, almost all the small offshore sandbanks have moved in the principal direction of the tidal channels, in good agreement with an independent sediment transport model study. Our findings provide useful baseline information for both future researchers and local authorities, in support of future environmental management, coastal protection, and storm forecasting.

In desert dune environments, vegetation may be an indicator of dune stability and rates of sediment transport. As topography and underlying controls of vegetation vary over large spatial areas, variations in dune form make scaling up of field research difficult. To mitigate this, and to identify spatial variations in vegetation distributions in a Saudi Arabian sand sea, spectral information from high resolution satellite images was classified to map polygons of shrub vegetation over 360 km2 of well-defined linear dunes, broken linear dunes and dome dune forms. When compared to topographic characteristics of the landscape, extracted from a digital elevation model, vegetation densities were often highest on 10–20° slopes elevated above interdune salt deposits on dune flanks. Spatially this was confined to small areas, and density was not always related to dune form, more to access of groundwater which encouraged colonisation on the tops of some dunes. Field observations identified shrubs of mainly Calligonum genus whose size is related to the amounts of salts, moving sediment, and access to the water table that varies within and between dune forms. Shrub density is likened to surface roughness (z0) to better understand sediment movement and modelling in dunes.

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

Estimation of sedimentation in reservoirs helps in the management and design of the reservoir׳s useful capacity. This research was done on the Awash River basin at the Koka Dam Reservoir in Ethiopia. The method applied was the loose integration of the Soil and Water Assessment Tool (SWAT) model and Hydrologic Engineering Center-River Analysis System (HEC-RAS) model for the estimation of the sediment load reaching the reservoir. The SWAT model was used for the estimation of erosion at the catchment level, and the HEC-RAS model was applied to estimate the sediment transport in the river channel. The implemented method allows sedimentation in the floodplains and bed shear stress to be considered in the sediment modeling, which cannot be considered in the SWAT model. In addition, the river cross sectional properties and the hydrodynamic processes in the rivers were considered in the modeling process. The data used in this study are a combination of i) observed data collected by government agencies, ii) data available online in data repositories, and iii) data extracted from remote sensing in the Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model (DEM). The calibration and validation of the SWAT model was done by using Sequential Uncertainty Fitting (SUIF-2) calibration and validation tools. The HEC-RAS model was calibrated by adjusting the roughness factor. The output from the integrated approaches gives better estimates of flow and sediment near the inlet to the reservoir, with coefficients of determination of 0.85 and 0.67, respectively, and Nash Sutcliffe coefficients of model fit efficiency of 0.90 and 0.62, respectively, for daily simulations.

The production of coarse sediment in mountain landscapes depends mainly on the type and activity of geomorphic processes and topographic and natural conditions (e.g. vegetation cover) of these catchments. The supply of sediment from these slopes to mountain streams and its subsequent transport lead to sediment connectivity, which describes the integrated coupled state of these systems. Studies from the Northern Calcareous Alps show that the size of the sediment contributing area (SCA), a subset of the drainage area that effectively delivers sediment to the channel network, can be used as a predictor of sediment delivery to mountain streams. The SCA concept is delineated on a digital elevation model (DEM) using a set of rules related to the steepness and length of slopes directly adjacent to the channel network, the gradient of the latter and the vegetation cover. The present study investigates the applicability of this concept to the Western Alps to identify geomorphologically active areas and to estimate mean annual sediment yield (SY) in mainly debris‐flow‐prone catchments. We use a statistical approach that shows a parameter optimisation and a linear regression of SY on SCA extent. We use a dataset of ~25 years of assessed coarse sediment accumulation in 35 sediment retention basins. In the investigated catchments, sediment transport is governed by several factors, mainly by the extent of vegetation‐free areas with a minimum slope of 23° that is coupled to the channel network with a very low gradient of the latter. With our improved framework, we can show that the SCA approach can be applied to catchments that are widely distributed, in a large spatial scale (hectare area) and very heterogeneous in their properties. In general, the investigated catchments show high connectivity, resulting in significant correlations between long‐term average yield and the size of the SCA., Based on the delineation of the sediment contributing area (SCA), a subset of the hydrological catchment area where sediments are assumed to reach the channel and are transferred further, we investigated the coefficient of determination of several regression models to identify the geomorphically active areas in torrent catchments. For this analysis, we used long‐term measurements of sediment yield (SY) of 35 sediment retention basins. This approach is a simple set of DEM‐based rules including topographic parameters and landcover information.

The chronostratigraphy of coastal sedimentary records such as washover fans or beach-ridge sequences may be used to reconstruct storm chronologies on centennial to millennial time scales. However, modern analogues are crucial for interpretations of depositional processes and for reducing uncertainty in evaluating the typically complex chronostratigraphic architecture of these landforms. Such a modern analogue was provided by category 3 tropical cyclone (TC) Olwyn in 2015, which caused a significant storm surge in the Gulf of Exmouth, Western Australia, and which activated large washover fans located in the southwestern part of the Gulf. Pre- and post-TC Olwyn geomorphological surveys and high-resolution drone-derived topographical data of one of these washover fans document a detailed history of erosion and deposition during the event. The modern analogue deposits provided an excellent opportunity to evaluate the use of luminescence-based proxies (luminescence inventories) including quartz single-grain age distributions and associated remnant ages, as well as quartz and feldspar luminescence signal comparisons for tracing event-related sediment source environments and understanding transport processes (May et al., 2020). Sediments deposited during Olwyn show a systematic relationship between luminescence characteristics and washover fan position. Seaward and central washover sections are indicated by well-bleached deposits due to the beach as the dominant source and/or long transport distances across the fan. Lateral washover deposits, in contrast, are characterised by rather local source areas and short transport distances, resulting in higher remnant ages of 70-140 a. This data shows that the combination of sediment source environments and sediment transport length across the fan represents the main control in resetting the luminescence signal and enabling reliable depositional ages to be calculated. It documents the benefit of investigating luminescence inventories when establishing chronologies from complex sedimentary records, thereby demanding a careful consideration of local processes and source areas when interpreting sedimentary TC records.May, S. M., Callow, J. N., Brill, D., Hoffmeister, D., & May, J.-H. (2020). Revealing sediment transport pathways and geomorphic change in washover fans by combining drone-derived digital elevation models and single grain luminescence data. Journal of Geophysical Research: Earth Surface, 125, e2020JF005792. https://doi.org/10.1029/2020JF005792

Check dams act as soil collectors during floods, thus retaining a large amount of sediments. The estimation of the soil volumes stored behind a check dam is a key activity for a proper design of these control works and for evaluation of soil delivery after restoration measures at watershed level. Several topographic techniques have been proposed for this activity, but the sediment wedge mapping tools are complex and time consuming. Conversely, the use of unmanned aerial vehicles (UAVs) has been proposed to support aerophotogrammetric techniques for several survey activities with promising results. However, surveys by UAVs have never applied to calculate the size of the sediment wedge behind check dams that are built in fire-affected watersheds, where soil loss and sediment transport may be high after a wildfire. To fill this gap, this study evaluates the efficiency and efficacy of aerophotogrammetric surveys using UAVs to estimate the volume of the sediments stored behind ten check dams, built as post-fire channel treatment in a forest watershed of Castilla La Mancha (Central Eastern Spain). The results of the aerophotogrammetric technique were compared to traditional topographic surveys using a total station and GNSS/RTK, assumed as reference. The estimation of sediment wedge volume provided by UAVs was more accurate (mean RMSE of 0.432), extensive (density of mapped points of 328 m−2) and quick (two days of fieldwork) compared to surveys using the topographic method (RMSE &lt, 0.04 m, six days of field work and density of mapped points of 0.194 m−2) by the topographic method. The differences in the sediment volume estimated by the two methods were not significant, but the UAV method was more accurate for the larger check dams. Moreover, a significant correlation was observed between the volume estimates provided by the two methods, shown by a coefficient of determination close to 0.98. Overall, these results propose a larger use of the aerial surveys for mapping activities in channels regulated by check dams, such as those built for restoration of fire-affected forest watersheds.

A discrete period of hydraulic gold mining in the northwestern Sierra Nevada, California (1853-1884) and extreme channel aggradation provide an opportunity to examine long-term catchment-scale sediment transport. This study used high-resolution LiDAR topographic data to reconstruct historical surfaces and compute spatially distributed sediment budgets in Greenhorn Creek, a small (42-km2) unregulated mountainous catchment. Digital elevation models (DEMs) were constructed for three periods: pre-mining (ca.1853), maximum aggradation (ca.1884), and modern (2013-14). Differencing DEMs enabled computation of changes in sediment volume between dates, and computation of sediment production, storage, and flux. Hydraulic mines in upper Greenhorn Creek produced 41×106m3 of sediment, of which 16×106m3 (38%) and 4.8×106m3 (12%) were stored by 1884 and 2014, respectively. Mining-sediment fluxes were high compared to global sediment-yield databases averaging 33,042 t km-2yr-1 (1853-1884) and 3,845 t km-2yr-1 (1884-2014). Catchment denudation rates computed from mine-pit volumes ranged from one to four orders of magnitude greater than background. Valley-bottom mining-sediment storage decreased through time but remained substantial 130 years after mining ceased. Storage in 2014 occurred mostly in the lower catchment except for substantial storage in two cut-off valley bends. Many studies compute or model sediment delivery ratios as an inherent property of basin size or physiography that can be used to route sediment, but how do sediment delivery ratios change through time? A hypothesis that post-mining sediment delivery ratios were at least 10% greater during the mining period was not rejected. Results support a dynamic sediment-delivery ratio concept in which the proportion of sediment delivered increases through time following a discrete sediment pulse. Large sediment-production events can leave lasting legacies that should be recognized by river managers.

Early-stage bedforms develop into mature dunes through complex interactions between wind, sand transport and surface topography. Depending on varying environmental and wind conditions, the mechanism driving dune formation and, ultimately, the shape of nascent dunes may differ markedly. In cases where sand availability is plentiful one mechanism suggested for triggering dune growth is linear stability theory. Until now, this theory has only been tested using field evidence in unidirectional winds. However, in many areas of the world and on other planets where aeolian processes act, wind regimes are often bimodal or multimodal. Here, we investigate field evidence of protodune formation under bimodal winds by applying linear stability analysis to a developing protodune field. Employing recent theoretical and experimental research, combined with in-situ wind, sediment transport, and topographic measurements during a month long field campaign at Great Sand Dunes National Park, Colorado, USA, we use a development of the linear stability theory to predict the spatial characteristics (orientation and wavelength) and temporal evolution (growth rate and migration velocity) of a protodune field. We find that the theoretical predictions compare well with measured dunefield attributes as characterized by high-resolution Digital Elevation Models measured using repeat terres trial laser scanning. Our findings suggest that linear stability theory is a quantitative predictor of protodune development on sandy surfaces with a bimodal wind regime. Our findings are significant as they offer critical validation of the linear stability theory for explaining the initiation and development of dunes towards maturity in a complex natural environment., 19 pages, 6 figures electronic ISSN: 2169-9011 print ISSN: 2169-9003

Landslides are highly erosional processes that dominate sediment mobilization and reshape landscapes in orogenic belts. Therefore, quantifying and characterizing landslide volume is essential to disaster prevention and understanding landscape evolution in mountainous rivers. Progressive development of the structure-from-motion (SfM) and multi-view stereo (MVS) photogrammetric techniques and Unmanned Aerial Vehicles (UAV) provides low-cost and high-resolution digital elevation models (DEMs), compared to traditional aerial photogrammetry at the same resolution. In this study, we quantified landslide volume and change in river channel volume at meter-scale accuracy for the Laishe River catchment of southern Taiwan from 2009 to 2015, which provides reliable data for discussing sediment transport and morphological response. The observations indicate that Typhoon Morakot in August 2009, induced a landslide volume of 31.63 million (M) m3, which is equal to 87% of the six-year sediment production. Typhoon Morakot also caused the deposition of 8.2 M m3 in the Laishe River. Additionally, this study demonstrates the feasibility of using UAVs to quantify the migration of landslide material and changes in channel area and volume, and the detection of landslide dams. In conclusion, two sources of images, especially those by UAVs, were used to decipher the consequence and potential hazard, social impact, and morphological changes in a mountainous river.

The role of three-dimensionality (3D) in modulating both flow and sediment transport remains poorly understood. 3D bed elevation measurements are difficult to obtain due to irregular dune shapes and submergence. Using photogrammetric tools for topographic reconstruction has become popular in surface studies, yet water refraction makes through-water image capturing of submerged dunes still challenging. We show that through-water images and Structure from Motion (SfM) tools can produce accurate Digital Elevation Models (DEMs) of a measured dune field, with a high level of detail. It is a low-cost and non-intrusive alternative for submerged bed elevation measurements. We provide a detailed SfM workflow, introduce and discuss the use of camera coordinates and underwater ground control points, and processing steps needed to obtain high accuracy DEMs. Our method results in DEMs with mm resolution in controlled laboratory conditions. New data for 23 dune field DEMs from 6 experiments were obtained and are presented. The dune field DEM time series provide insights on dune interaction processes. In our experiments, merging and defect creation were most common. Merging decreases the number of bedforms, and defect creation is responsible for more bedforms. Dunes continue to interact and jostle after achieving equilibrium. Simple crests are much more frequently observed than irregular, sinuous or double crests. Two-dimensional (2D) crest shapes were observed, although crest shapes were generally of 3D nature. Observed dune migration rates are not steady and vary in time and space. Bedform splitting speeds up dune migration, whilst neighbouring dunes tend to accelerate or decelerate. We identify a cascade of processes and show that 3D DEMs at high frequency are required to resolve observed rapid deformations and interaction of dunes. The identified dune interaction processes are inherent to sediment flux (variability), whereas the temporal component of the underlying sediment transport processes is still not well understood in relation to average transport.

Integrating connectivity theory within watershed modelling is one solution to overcome spatial and temporal shortcomings of sediment transport prediction, and Part I and II of these companion papers advance this overall goal. In Part I of these companion papers, we present the theoretical development of probability of connectivity formula considering connectivity's magnitude, extent, timing and continuity that can be applied to watershed modelling. Model inputs include a high resolution digital elevation model, hydrologic watershed variability, and field connectivity assessments. We use the model to investigate the dependence of the probability of connected timing and spatial connectivity on sediment transport predictors. Results show the spatial patterns of connectivity depend on both structural and functional characteristics of the catchment, such as hillslope gradient, upstream contributing area, soil texture, and stream network configuration (structural) and soil moisture content and runoff generation (functional). Spatial connectivity changes from catchment-to-catchment as a function of soil type and drainage area; and it varies from event-to-event as a function of runoff depth and soil moisture conditions. The most sensitive connected pathways provide the stencil for the probability of connectivity, and pathways connected from smaller hydrologic events are consistently reconnected and built upon during larger hydrologic events. Surprisingly, we find the probability of connected timing only depends on structural characteristics of catchments, which are considered static over the timescales analyzed herein. The timing of connectivity does not statistically depend on functional characteristics, which relaxes the parameterization across events of different magnitudes. This result occurs because the pathway stencil accumulates sediment from adjacent soils as flow intensity increases, but this does not statistically shift the frequency distribution.

The degree of interaction between sediment transport rate and tectonic activity is a major issue that draws the attention of researchers. Because of the complexity in the modeling process of uplift and subsidence rate, it is quite difficult to determine the rate of interaction between erosion and tectonic activity. In this study, the sediment transport rate of Kizilirmak Basin, which is located on the tectonically active North Anatolian Fault Zone (NAFZ), was investigated to determine the effect of tectonic activity on sediment transport rate. The sediment transport rate of the basin was evaluated by using the drainage channel width, the topographic wetness index (TWI), and the revised universal soil equation (RUSLE) model. The Aster Global Digital Elevation Model (GDEM), Landsat 8 Operational Land Imager (OLI) scenes, a 1:800,000 scale soil map, and 30 years of rainfall records at 41 stations were used for the analysis. The drainage channel width, the TWI, and derivation and grid-based integration of the RUSLE parameters were performed by using GIS (terrain analysis, spatial data analysis) and remote sensing image processing techniques. The relationship among the derived parameters and tectonic activity was evaluated by Getis–Ord $$ {G}_i^{\ast } $$ statistics. The results show that at the 99 and 95% confidence intervals, statistically significant cold spot values of the channel widths, hot spot values of the mean annual soil loss values, and cold spots of the TWI values are more intensely clustered around fault lines. These clustering areas not only indicate the areas where the rate of sediment transport is high, but also the areas where the tectonic activity of the NAFZ is more vigorous.

Gravel-bed clusters are the most prevalent microforms that affect local flows and sediment transport. A growing consensus is that the practice of cluster delineation should be based primarily on bed topography rather than grain sizes. Here we present a novel approach for cluster delineation using patch-scale high-resolution digital elevation models (DEMs). We use a geostatistical interpolation method, i.e., factorial kriging, to decompose the short- and long-range (grain- and microform-scale) DEMs. The required parameters are determined directly from the scales of the nested variograms. The short-range DEM exhibits a flat bed topography, yet individual grains are sharply outlined, making the short-range DEM a useful aid for grain segmentation. The long-range DEM exhibits a smoother topography than the original full DEM, yet groupings of particles emerge as small-scale bedforms, making the contour percentile levels of the long-range DEM a useful tool for cluster identification. Individual clusters are delineated using the segmented grains and identified clusters via a range of contour percentile levels. Our results reveal that the density and total area of delineated clusters decrease with increasing contour percentile level, while the mean grain size of clusters and average size of anchor clast (i.e., the largest particle in a cluster) increase with the contour percentile level. These results support the interpretation that larger particles group as clusters and protrude higher above the bed than other smaller grains. A striking feature of the delineated clusters is that anchor clasts are invariably greater than the D90 of the grain sizes even though a threshold anchor size was not adopted herein. The average areal fractal dimensions (Hausdorff-Besicovich dimensions of the projected areas) of individual clusters, however, demonstrate that clusters delineated with different contour percentile levels exhibit similar planform morphologies. Comparisons with a compilation of existing field data show consistency with the cluster properties documented in a wide variety of settings. This study thus points toward a promising, alternative DEM-based approach to characterizing sediment structures in gravel-bed rivers.

Ripple orientations on small sand dunes (dunes lacking substantial slip faces) at widely distributed sites across Mars have been documented using High Resolution Imaging Science Experiment (HiRISE) images, in an effort to determine the last formative aeolian sediment transport direction experienced at these locations. Howard (1977) used field measurements and first principles to derive an expression for determining how much the surface slope on a sand dune deflects the orientation of sand ripples with respect to the formative wind direction. A Digital Terrain Model derived from stereo HiRISE images was used to assess the potential deflection of ripples on sand dunes on the floor of Lopez crater on Mars. Three-quarters of the area covered by sand dunes within the DTM has a surface slope

The ability to quantify the processes driving geomorphic change in river valley margins is vital to geomorphologists seeking to understand the relative role of transport mechanisms (e.g. fluvial, aeolian, and hillslope processes) in landscape dynamics. High-resolution, repeat topographic data are becoming readily available to geomorphologists. By contrasting digital elevation models derived from repeat surveys, the transport processes driving topographic changes can be inferred, a method termed ‘mechanistic segregation.’ Unfortunately, mechanistic segregation largely relies on subjective and time consuming manual classification, which has implications both for its reproducibility and the practical scale of its application. Here we present a novel computational workflow for the mechanistic segregation of geomorphic transport processes in geospatial datasets. We apply the workflow to seven sites along the Colorado River in the Grand Canyon, where geomorphic transport is driven by a diverse suite of mechanisms. The workflow performs well when compared to field observations, with an overall predictive accuracy of 84% across 113 validation points. The approach most accurately predicts changes due to fluvial processes (100% accuracy) and aeolian processes (96%), with reduced accuracy in predictions of alluvial and colluvial processes (64% and 73%, respectively). Our workflow is designed to be applicable to a diversity of river systems and will likely provide a rapid and objective understanding of the processes driving geomorphic change at the reach and network scales. We anticipate that such an understanding will allow insight into the response of geomorphic transport processes to external forcings, such as shifts in climate, land use, or river regulation, with implications for process-based river management and restoration. Copyright © 2017 John Wiley & Sons, Ltd.

Sediment budget of thelower part of theDanube River haschangedduringthelastdecades, mainlyduetotheconstruction of damsanddykes. The objective of thisstudyistoassessthe sediment budget andmorphologicalchangesalongOlteniţa - CalarasiDanube River reach, withtheuse of a one dimensional hydraulicand sediment transport model. The river schematic networkwasextractedfrom a Digital Terrain Model, builtwithtopobathimetric data, using HEC-GeoRAS. The hydrodynamic model wasbuilt, calibratedandvalidatedwiththe 1D HEC-RAS software underunsteadyflowregime, withhydrologicand sediment data fromthe period 2008-2011 at thetwoupstreamanddownstreamgaugingstations. Measured sediment discharge data wereusedtocomputethesuspendedloadwithdifferent transport functions. The functionthatrepresentsthebest fit for theobservedvalues of suspendedload in 2008 wasusedto model thehydromorphologicalbehaviour of theriverreach for the period 2009-2011. Computed sediment dischargevalueswerefoundtofollowthetendency of previousdecades. The model wasalsousedtoassesspossiblechanges of thechannelbedbyaggradation or degradationalongthestudyreach, over theanalysed period.

Fluvial landscapes are dissected by channels, and at their upstream termini are channel heads. Accurate reconstruction of the fluvial domain is fundamental to understanding runoff generation, storm hydrology, sediment transport, biogeochemical cycling, and landscape evolution. Many methods have been proposed for predicting channel head locations using topographic data, yet none have been tested against a robust field data set of mapped channel heads across multiple landscapes. In this study, four methods of channel head prediction were tested against field data from four sites with high‐resolution DEMs: slope‐area scaling relationships; two techniques based on landscape tangential curvature; and a new method presented here, which identifies the change from channel to hillslope topography along a profile using a transformed longitudinal coordinate system. Our method requires only two user‐defined parameters, determined via independent statistical analysis. Slope‐area plots are traditionally used to identify the fluvial‐hillslope transition, but we observe no clear relationship between this transition and field‐mapped channel heads. Of the four methods assessed, one of the tangential curvature methods and our new method most accurately reproduce the measured channel heads in all four field sites (Feather River CA, Mid Bailey Run OH, Indian Creek OH, Piedmont VA), with mean errors of −11, −7, 5, and −24 m and 34, 3, 12, and −58 m, respectively. Negative values indicate channel heads located upslope of those mapped in the field. Importantly, these two independent methods produce mutually consistent estimates, providing two tests of channel head locations based on independent topographic signatures.

Hydrological indices provide excellent input to geographic information systems for the successful mapping of erosion-prone areas. In this research, a digital elevation model was processed and analyzed to obtain the necessary hydrological indices necessary for erosion modeling. The indices (such as sediment transport index, compound topography index, and stream power index) along with other themes (Like Slope gradient, curvature, distance to channels, and channel density) were overlaid using the “Weighted Sum” overlay tool in the geographic information system. The results showed that 33.14 km2 of the test watershed (sub-basin of Abay, Ethiopia) falls in very high/severe erosion zone and needs immediate conservation measures. A total of 98.26 km2, 153.40 km2, and 263.17 km2 fall in high-, moderate-, and low-erosion hazard zones, respectively. Therefore, the primary and secondary derivatives of the digital elevation model along with morphometric parameters coupled with a Spatial Analyst tool proves to be a powerful integrated approach in demarcating erosion vulnerable zones and could be applied at regional and continental scale for proper watershed management.

This paper presents a digital elevation model (DEM) of the dunes found in the Lençóis Maranhenses National Park, an environmental protection area located in the Maranhão state (Brazil). The DEM supports the modeling studies of sand-dune evolution using multi-temporal satellite images and ground truth data, obtained through the post-processed kinematic Global Navigation Satellite System (GNSS) positioning. The study area is located at the border of three major neotropical ecosystems: the Amazonia, Caatinga, and Brazilian savanna. It is located in the northeastern state of Maranhão and encompasses the largest dune fields in the country. Wide shrubby areas (restingas, in Portuguese), lakes, mangroves, and a multitude off reshwater lagoons compose the park’s natural environments. The objective of the present study is to create an DEM that can evidence the complex dynamics of dune formation in the study area with use of GNSS. Geodetic techniques and precision mapping were employed to monitor the short-term coastal dynamics. The use of GNSS receivers is justified by the difficulty of mapping the dune’s features using conventional methods such as theodolite, level, and total station systems, due to their high cost, time restriction sand low data precision. Surface surveys were carried out annually between December 2015 and January 2017 to create a DEM. The study results reveal that the area has a negative volumetric balance of erosion and a preferential direction of sediment transport by wind, which may justify the pattern of advancement and retraction observed in the dunes of the studied area.

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

The jet induced by a rotating ship propeller can cause scouring of the seabed and consequent deposition of the scoured material nearby. Despite these effects are extremely important for the operability of a harbour, there is currently limited work concerning a detailed investigation of the three-dimensional (3D) characteristics of the bed topography changes induced by the ship propeller. Thus, this paper presents laboratory experiments with the aim of analysing the effects induced by a propeller on a mobile bed, in different conditions of submergence depth (h0) and rotational speed (n). The equilibrium bed surface topography was acquired with the photogrammetry technique combined with a 3D Terrestrial Laser Scanner (TLS), in order to analyse, for the first time, bed elevation data obtained from high-resolution Digital Elevation Models (DEMs). As a result, it was demonstrated that the swirling jet produced by a rotating propeller causes the development of a bed topography not symmetrical with respect to the propeller longitudinal axis, with a deeper scour hole on one side and a higher deposition mound on the other side. Therefore, the scour hole induced by a propeller cannot be assimilated to that produced by a water jet and this behaviour can be noted only with a comprehensive and detailed analysis of a 3D model of the bed topography. Furthermore, it was shown that increasing n for the same h0 (or reducing h0 by keeping n constant) causes a longer, deeper and wider scour hole and a higher deposition mound, with a greater volume of sediments eroded from the bed and deposited nearby the scour hole. To be precise, this is the first study aiming at estimating the eroded and deposited sediment volumes by a propeller jet, thanks to the use of the high-resolution DEMs. The relationships between all the involved variables were analysed, providing equations, graphs and an abacus for the prediction of the effects induced by the propeller as a function of h0 and the Froude number.

In this study, sediment transport rate of the Kizilirmak River basin located in the tectonically active North Anatolian Fault Zone (NAFZ) is evaluated in order to determine the effects of the NAFZ on the Kizilirmak basin sediment transport rate. Vegetation covers the basin area is extracted from the LANDSAT ETM data by using Normalized Difference Vegetation Index (NDVI). On the other hand, topographic attributes (elevation, slope, curvature, and water catchment) were obtained from Digital Elevation Model (DEM) to detect areas associated with sediment transport and accumulation. GIS was used to extract topographic profiles along with the Kizilirmak River and attributes as well as for the implementation of the stream power index (SPI), topographic wetness index (TWI), sediment transport index (STI) and channel width. The relation with the derived indices and NAFZ is determined by integrating hot and cold spot clusters of indices values mapped with Getis-Ord Gi* statistics. According to the derived results which highlighted hot and cold spots of the index values helped to identify the relation between sediment transport rate of the basin area and NAFZ.

Grainflows produce temporary geomorphological signatures on the slipfaces of aeolian dunes, and are a fundamental agency by which dunes migrate. The purpose of this study is to present an algorithm to objectively and efficiently delineate grainflow boundaries by processing Digital Elevation Models (DEMs) in Matlab and ArcGIS. Grainflows can be identified by analyzing temporal changes in slipface elevation, and the morphology can be extracted by defining the boundary that encloses the area of movement. The method allows large numbers of grainflows to be quickly and objectively delineated and extracted from LiDAR data. The process avoids the subjective nature of manual measurement, thereby improving the commensurability of different grainflow regimes in both terrestrial and extraterrestrial environments. The algorithm is presented here in the context of analyzing grainflows and related processes on the slipfaces of dunes, but it is applicable over the broader scope of other forms of slope failure and geophysical flows, such as avalanches, snowslides, landslides, and debris flows.

In situ measurement of grain-scale fluvial morphology is important for studies on grain roughness, sediment transport and the interactions between animals and the geomorphology, topics relevant to many river practitioners. Close-range digital photogrammetry (CRDP) and terrestrial laser scanning (TLS) are the two most common techniques to obtain high-resolution digital elevation models (DEMs) from fluvial surfaces. However, field application of topography remote sensing at the grain scale is presently hindered mainly by the tedious workflow challenges that one needs to overcome to obtain high-accuracy elevation data. A recommended approach for CRDP to collect high-resolution and high-accuracy DEMs has been developed for gravel-bed flume studies. The present paper investigates the deployment of the laboratory technique on three exposed gravel bars in a natural river environment. In contrast to other approaches, having the calibration carried out in the laboratory removes the need for independently surveyed ground-control targets, and makes for an efficient and effective data collection in the field. Optimization of the gravel-bed imagery helps DEM collection, without being impacted by variable lighting conditions. The benefit of a light-weight three-dimensional printed gravel-bed model for DEM quality assessment is shown, and confirms the reliability of grain roughness data measured with CRDP. Imagery and DEM analysis evidences sedimentological contrasts between gravel bars within the reach. The analysis of the surface elevations shows the effect variable grain-size and sediment sorting have on the surface roughness. By plotting the two-dimensional structure functions and surface slopes and aspects we identify different grain arrangements and surface structures. The calculation of the inclination index allows determining the surface-forming flow direction(s). We show that progress in topography remote sensing is important to extend our knowledge on fluvial morphology processes at the grain scale, and how a technique customized for use by fluvial geomorphologists in the field benefits this progress. Copyright © 2016 John Wiley & Sons, Ltd.

Hillslope length is a fundamental attribute of landscapes, intrinsically linked to drainage density, landslide hazard, biogeochemical cycling and hillslope sediment transport. Existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope–area scaling, where the hillslope domain transitions into the fluvial domain. Here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model (DEM), based on flow directions calculated using pixel aspect, until reaching the channel network, defined using recently developed channel extraction algorithms. Through comparisons between these measurement techniques, we show that estimating hillslope length from plots of topographic slope versus drainage area, or by inverting measures of drainage density, systematically underestimates hillslope length. In addition, hillslope lengths estimated by slope–area scaling breaks show large variations between catchments of similar morphology and area. We then use hillslope length–relief structure of landscapes to explore nature of sediment flux operating on a landscape. Distinct topographic forms are predicted for end-member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient. Because our method extracts hillslope profiles originating from every ridgetop pixel in a DEM, we show that the resulting population of hillslope length–relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes. We find that across a broad range of sites across the continental United States, topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient

Seafloors of unconsolidated sediment are highly dynamic features; eroding or accumulating under the action of tides, waves and currents. Assessing which areas of the seafloor experienced change and measuring the corresponding volumes involved provide insights into these important active sedimentation processes. Computing the difference between Digital Elevation Models (DEMs) obtained from repeat Multibeam Echosounders (MBES) surveys has become a common technique to identify these areas, but the uncertainty in these datasets considerably affects the estimation of the volumes displaced. The two main techniques used to take into account uncertainty in volume estimations are the limitation of calculations to areas experiencing a change in depth beyond a chosen threshold, and the computation of volumetric confidence intervals. However, these techniques are still in their infancy and, as a result, are often crude, seldom used or poorly understood. In this article, we explored a number of possible methodological advances to address this issue, including: (1) using the uncertainty information provided by the MBES data processing algorithm CUBE, (2) adapting fluvial geomorphology techniques for volume calculations using spatially variable thresholds and (3) volumetric histograms. The nearshore seabed off Warrnambool harbour - located in the highly energetic southwest Victorian coast, Australia - was used as a test site. Four consecutive MBES surveys were carried out over a four-months period. The difference between consecutive DEMs revealed an area near the beach experiencing large sediment transfers - mostly erosion - and an area of reef experiencing increasing deposition from the advance of a nearby sediment sheet. The volumes of sediment displaced in these two areas were calculated using the techniques described above, both traditionally and using the suggested improvements. We compared the results and discussed the applicability of the new methodological improvements. We found that the spatially variable uncertainty derived from the CUBE algorithm provided the best results (i.e. smaller confidence intervals), but that similar results can be obtained using as a fixed uncertainty value derived from a reference area under a number of operational conditions.

For the management of the tidal flat environment and the preservation of several important functions of the tidal flat, the accurate topographic monitoring is indispensable. However, the appropriate measurement of the tidal flat topography is very difficult because water level changes every moment due to tidal oscillation, and the accountable time for the measurement is limited within several hours under low tide condition. In this study, topographic measurement of tidal flat using Unmanned Aerial Vehicle (UAV) was conducted 5 times over a year, and Digital Elevation Model (DEM) obtained by UAV photogrammetry (UAV-DEM) of the tidal flat was constructed in each measurement. The area of 400m in the land-island (L-I) direction and 100m in the west-east (W-E) direction was set on the developed UAV-DEM to analyze the short-term topographical changes (2 weeks including typhoon events, half year and year). By the influence of typhoon passing, sand on the tidal flat was transported from east to west obviously within typhoon event. However, after the topographic change due to the typhoon event, the sand moved opposite direction. By the estimation of the sand volume on the tidal flat using UAV-DEM, it was found that the change of the volume was quite small in one year. These results indicate that the sand volume on this tidal flat is mostly preserved although active sand transport occurs on the tidal flat.

Sedimentological connectivity describes the continuity of sediment transport across a topographically heterogenous landscape. Sedimentological connectivity reflects the changes in the balance between flow sediment load and transport capacity and is mainly influenced by the longitudinal (dis)continuity of channels that is associated with channel depressions and confluences. Past studies have focused on structural and sedimentological connectivity at the basin scale, with only a few examining this phenomenon at the hillslope scale. Important questions have yet to be answered, including “How do within-channel barriers and channel confluences affect the flow/sediment balance?” and “At what spatial extent do these influences take place?” This study investigated the structural and sedimentological connectivity within a rill network on a hillslope in Loudon, Tennessee, USA. We used the difference in a ground lidar generated time-series of seven digital elevation models (DEMs), the DEM of Difference (DoD or ΔDEM), to quantify the spatio-temporal dynamics of erosion and deposition on a hillslope for 6 periods from December 2014 to December 2016. We found that later periods had the greatest amount of erosion and net sediment loss (0.59 ± 17 m3). We compared the observed sediment redistribution patterns to a GIS-based index of connectivity (IC). In order to examine the influence of structural (dis) connectivity on sedimentological connectivity, we compared the time series of patterns to the occurrences of rill channel confluences and depressions. We found a spatially consistent relationship between the IC and the observed erosion/deposition pattern. However, sediment detachment can also be driven by gravitational sidewall failure, which is not well described by the IC. The scouring at rill confluences leads to higher erosion in both upslope and downslope sections of a rill channel; the ponding at rill depressions yields upslope deposition and downslope erosion.

In the Swiss Alps, climatic changes have not only caused glacier retreat, but also likely increased sedimentation downstream of glaciers. This material either originates from below the glacier or from periglacial environments, which are exposed as glaciers retreat, and often consist of easily erodible sediment. Griesgletscher's catchment in the Swiss Alps was examined to quantify erosion in the proglacial area, possible hydrological drivers and contributions of the sub‐ and periglacial sources. Digital elevation models, created from annual aerial photographs, were subtracted to determine annual volume changes in the proglacial area from 1986 to 2014. These data show a strong increase in proglacial erosion in the decade prior to 2012, coincident with increasing proglacial area size. However, examination of the gradient between discharge and sediment evacuation, and modeled sediment transport, could suggest that the proglacial area began to stabilize and sediment supply is limited. The large influx of sediment into the proglacial reservoir, which is roughly 2.5 times greater than the amount of sediment eroded from the proglacial area, demonstrates the importance of subglacial erosion to the catchment's sediment budget. Although far more sediment originates subglacially, erosion rates in the proglacial area are over 50 times greater than the rest of the catchment. In turn, both sub‐ and periglacial processes, in addition to constraining sediment supply, must be considered for assessing future sediment dynamics as glacier area shrinks and proglacial areas grow. ISSN:0197-9337 ISSN:1096-9837