Search

Following the eruption of the Taal Volcano in January 2020 and its continuous signs of unrest in the preceding years, this study delves into the investigation of sediment transport in the Pasig River, Philippines. The historical data of total suspended solids (TSS) and arsenic indicated a notable increase starting from the year 2020. The field measurements were conducted in February and March of 2022, two years after the eruption. Due to the observed homogeneity in the river's mixing, a refined 1D sediment transport model was developed. In this study, HEC-RAS modeling software was employed. The calibration process using the Laursen transport function yielded an impressive R2 value of 0.9989 for the post-eruption model. This predictive accuracy underscores the robustness of the developed model. The study's scope was further expanded by creating a model for February 2020, incorporating water quality data gathered by the Pasig River Coordinating and Management Office. The model simulation results showed peak TSS values of 120.63 mg/L and 225.15 mg/L in February 2022 and February 2020, respectively. The results of the study highlight the probable impact of geological events on sediment dynamics within the Pasig River, which could help manage and sustain ongoing river improvements. [ABSTRACT FROM AUTHOR]

The characterisation of particle shape is an important analysis in the field of sedimentary geology. At finer scales, it is key for understanding sediment transport while at coarser scales, such as boulders, it is vital for coastal protection. However, the accurate characterisation of particle shape is restricted by the application of 2D imaging for 3D objects or expensive and time-consuming 3D imaging methods such as X-ray tomography or laser scanning. This research outlines a low-cost, easy-to-use 3D particle imaging and shape characterisation methodology employing structure-from-motion (SfM) photogrammetry. A smartphone device was used to capture 2D images of pebble/cobble-sized samples, which were converted to 3D image models using SfM. The 3D image models were then analysed using a comprehensive set of 16 size and shape parameters. Furthermore, a minimum resolution, independent of particle size, is proposed here for the 3D image models for reliable and reproducible size and shape analysis. Thus, the methodology presented here for 3D particle imaging and size and shape analysis can be translated for a range of particle sizes. This work thus opens a pathway for the use of readily accessible imaging devices, such as smartphones, to flexibly obtain image data both in situ as well as in laboratories, thus providing an immensely powerful tool for research and teaching. [ABSTRACT FROM AUTHOR]

As sea-level rise (SLR) and human-made interventions affect coastal currents and sediment transport, coastal barriers have become more vulnerable to the effect of storms, hurricanes, and climate variability. The response of each barrier is unique and depends on wave regime, coastline orientation, weather conditions, bathymetry, and type of human-made interventions, among other factors. In the Magdalena River deltaic barrier, located on the Colombian Caribbean coast, coastal erosion has caused the loss of hundreds of square kilometers of critical ecosystems, such as wetlands and lagoons, since the 1960s. This work aims to analyze the short-term drivers behind the observed loss of lagoons, particularly the drivers of lagoon breaching events and subsequent healing along the deltaic barrier. Lagoon breaching events and healings were detected using satellite imagery, and the timing of these events was related to prior local atmospheric, oceanographic, and fluvial conditions. The findings reveal that the dynamics of the lagoons are driven by extreme river discharges and energetic wave conditions associated with storms or hurricanes. Healing is driven by the sediment supplied by littoral currents and average waves punctuated by energetic events. The cumulative effect of breaching and healing has resulted in a deltaic barrier that has rolled over the lagoons, reducing their size over time. These findings provide a better understanding of the forces of coastal retreat and will help inform future management decisions of the coastal zone. [ABSTRACT FROM AUTHOR]

The importance of topography generated by Eocene Eurekan deformation as a sediment source for sandstones deposited on the western Barents Shelf margin is evaluated through a sediment provenance study conducted on wellbore materials retrieved from Spitsbergen and from the Vestbakken Volcanic Province and the Sørvestsnaget Basin in the southwest Barents Sea. A variety of complementary techniques record a provenance change across the Paleocene-Eocene boundary in wellbore BH 10-2008, which samples Paleogene strata of the Central Tertiary Basin in Spitsbergen. Sandstones containing K-feldspar with radiogenic Pb isotopic compositions, chrome spinel in the heavy mineral assemblage, and detrital zircons and rutiles with prominent Palaeoproterozoic and Late Palaeozoic—Early Mesozoic U-Pb age populations are up-section replaced by sandstone containing albitic plagioclase feldspar, metasedimentary schist rock fragments, a heavy mineral assemblage with abundant chloritoid, metamorphic apatite with low REE contents, metapelitic rutile with Silurian U-Pb ages and zircons with predominantly Archaean and Palaeoproterozoic U-Pb age populations. Our results clearly demonstrate the well-known regional change in source area from an exposed Barents Shelf terrain east of the Central Tertiary Basin during the Paleocene to the emerging Eurekan mountains west and north of the Central Tertiary Basin during the Eocene. Eocene sandstones deposited in the marginal basins of the southwestern Barents Shelf, which were sampled in wellbores 7316/5-1 and 7216/11-1S, contain elements of both the Eurekan and the eastern Barents Shelf provenance signatures. The mixing of the two sand types and delivery to the southwest margin of the Barents Shelf is consistent with a fill and spill model for the Central Teritary Basin, with transport of Eurekan-derived sediment east then south hundreds of kilometres across the Shelf. [ABSTRACT FROM AUTHOR]

Offshore sand banks are an important resource for coastal protection, marine aggregates, and benthic habitats and are the site of many offshore wind farms. Consequently, a comprehensive understanding of the baseline processes controlling sand bank morphodynamics is imperative. This knowledge will aid the development of a long-term robust marine spatial plan and help address the environmental instability arising from anthropogenic activities. This study uses a validated, dynamically coupled, two-dimensional hydrodynamic and sediment transport model to investigate the hydrodynamic processes controlling the highly mobile upper layer of Arklow Bank, while maintaining overall long-term bank base stability. The results reveal a flood and ebb tidal current dominance on the west and east side of the bank, respectively, ultimately generating a large anticlockwise residual current eddy encompassing the entire bank. This residual current flow distributes sediment along the full length of the sand bank. The positioning of multiple off-bank anticlockwise residual current eddies on the edge of this cell is shown to influence east–west fluctuations of the upper slopes of the sand bank and act as a control on long-term stability. These off-bank eddies facilitate this type of movement when the outer flows of adjacent eddies, located on both sides of the bank, flow in a general uniform direction. Whereas they inhibit this east–west movement when the outer flows of adjacent eddies, on either side of the bank, flow in converging directions towards the bank itself. These residual eddies also facilitate sediment transport in and out of the local sediment transport system. Within Arklow Bank's morphological cell, eight morphodynamically and hydrodynamically unique bank sections or 'sub-cells' are identified, whereby a complex morphodynamic–hydrodynamic feedback loop is present. The local east–west fluctuation of the upper slopes of the bank is driven by migratory on-bank stationary and transient clockwise residual eddies and the development of 'narrow' residual current cross-flow zones. Together, these processes drive upper slope mobility but maintain long-term bank base stability. This novel understanding of sand bank morphodynamics is applicable to bedforms in tidally dominated continental shelf seas outside the Irish Sea. [ABSTRACT FROM AUTHOR]

With the recent push for a transition towards a climate-resilient economy, the demand on marine resources is accelerating. For many economic exploits, a comprehensive understanding of environmental parameters underpinning seabed morphodynamics in tidally-dominated shelf seas, and the relationship between local and regional scale sediment transport regimes as an entire system, is imperative. In this paper, high-resolution, time-lapse bathymetry datasets, hydrodynamic numerical modelling outputs and various theoretical parameters are used to describe the morphological characteristics of sediment waves and their spatio-temporal evolution in a hydrodynamically and morphodynamically complex region of the Irish Sea. Analysis reveals sediment waves in a range of sizes (height = 0.1 to 25.7 m, and wavelength = 17 to 983 m), occurring in water depths of 8.2 to 83 mLAT, and migrating at a rate of 1.1 to 79 m/yr. Combined with numerical modelling outputs, a strong divergence of sediment transport pathways from the previously understood predominantly southward flow in the south Irish Sea is revealed, both at offshore sand banks and independent sediment wave assemblages. This evidence supports the presence of a semi-closed circulatory hydrodynamic and sediment transport system at Arklow Bank (an open-shelf linear sand bank). Contrastingly, the Lucifer–Blackwater Bank complex and associated sediment waves are heavily influenced by the interaction between a dominant southward flow and a residual headland eddy, which also exerts a strong influence on the adjacent banner bank. Furthermore, a new sediment transfer system is defined for offshore independent sediment wave assemblages, whereby each sediment wave field is supported by circulatory residual current cells originating from offshore sand banks. These new data and results improve knowledge of seabed morphodynamics in tidally-dominated shelf seas, which has direct implications for offshore renewable developments and long-term marine spatial planning. [ABSTRACT FROM AUTHOR]

The significance of mineralogical maturity as a provenance indicator has long been debated and we use this study to demonstrate that it can indeed be a powerful tool to track the distribution of sandstone reservoirs. We investigate the cause of the pronounced geographic and stratigraphic differences in mineralogical composition that are found in the Upper Triassic–Lower Jurassic Gassum Formation across the Norwegian–Danish Basin and surrounding areas. Zircon U-Pb dating of 46 sandstone samples including analysis of 4816 detrital grains are combined with quantifications of the detrital mineralogical composition and placed in a sequence stratigraphic framework. The results show that the Gassum Formation can be divided into a southeastern region with high mineralogical maturity and a less mature region to the northwest with more feldspars, rock fragments, micas, and heavy minerals. Both the mineralogical assemblage and the provenance signature have been thoroughly homogenized in the SE region where sediment supplies from the Fennoscandian Shield and the Variscan Orogen are evident. In the NW region, sediment was initially supplied from Fennoscandia only, but the provenance abruptly changed from the Telemarkia Terrane to comprising also the more distant Caledonian Orogen resulting in a different mineralogical assemblage. The change occurred during a basinwide regression and may be caused by tectonic movements in the hinterland that permanently changed the composition of the sediment supplied to the basin. [ABSTRACT FROM AUTHOR]

In recent years, it has become a common understanding among researchers that one of the significant agents for forming a variety of submarine geomorphologies is turbidity currents that travel long distances, so-called long-runout turbidity currents. In this study, we present a mathematical model of the formation of cyclic steps due to long-runout turbidity currents based on the assumption that the highly concentrated layer near the bottom of the turbidity currents achieves an equilibrium state. The model uses the four governing equations: the momentum equation, the continuity equation, the diffusion/dispersion equation of suspended sediment, and the continuity equation of sediment on the bed (the Exner equation). We simplify the governing equations by ignoring the entrainment from ambient water since there is a distinct density interface above the highly concentrated lower layer of long-runout turbidity currents. We determine the dimensions of cyclic steps based on the solution. Agreement between the predictions and field observations turns out to be reasonable. [ABSTRACT FROM AUTHOR]

The stratigraphic development of foreland basins has mainly been related to surface loading in the adjacent orogens, whereas the control of slab loads on these basins has received much less attention. This has also been the case for interpreting the relationships between the Oligocene to Micoene evolution of the European Alps and the North Alpine foreland basin or Molasse basin. In this trough, periods of rapid subsidence have generally been considered as a response to the growth of the Alpine topography, and thus to the construction of larger surface loads. However, such views conflict with observations where the surface growth in the Alps has been partly decoupled from the subsidence history in the basin. In addition, surface loads alone are not capable of explaining the contrasts in the stratigraphic development particularly between its central and eastern portions. Here, we present an alternative view on the evolution of the Molasse basin. We focus on the time interval between c. 30 and 15 Ma and relate the basin-scale development of this trough to the subduction processes, and thus to the development of slab loads beneath the European Alps. At 30 Ma, the western and central portions of this basin experienced a change from deep marine underfilled (Flysch stage) to overfilled terrestrial conditions (Molasse stage). During this time, however, a deep marine Flysch-type environment prevailed in the eastern part of the basin. This was also the final sedimentary sink as sediment was routed along the topographic axis from the western/central to the eastern part of this trough. We interpret the change from basin underfill to overfill in the western and central basin as a response to oceanic lithosphere slab-breakoff beneath the Central and Western Alps. This is considered to have resulted in a growth of the Alpine topography in these portions of the Alps, an increase in surface erosion and an augmentation in sediment supply to the basin, and thus in the observed change from basin underfill to overfill. In the eastern part of the basin, however, underfilled Flysch-type conditions prevailed until 20 Ma, and subsidence rates were higher than in the western and central parts. We interpret that high subsidence rates in the eastern Molasse occurred in response to slab loads beneath the Eastern Alps, where the subducted oceanic slab remained attached to the European plate and downwarped the plate in the East. Accordingly, in the central and western parts, the growth of the Alpine topography, the increase in sediment flux and the change from basin underfill to overfill most likely reflect the response to slab delamination beneath the Central Alps. In contrast, in the eastern part, the possibly subdued topography in the Eastern Alps, the low sediment flux and the maintenance of a deep marine Flysch-type basin records a situation where the oceanic slab was still attached to the European plate. The situation changed at 20 Ma, when the eastern part of the basin chronicled a change from deep marine (underfilled) to shallow marine and then terrestrial (overfilled conditions). During the same time, subsidence rates in the eastern basin decreased, deformation at the Alpine front came to a halt and sediment supply to the basin increased possibly in response to a growth of the topography in the Eastern Alps. This was also the time when the sediment routing in the basin axis changed from an east-directed sediment dispersal prior to 20 Ma, to a west-oriented sediment transport thereafter and thus to the opposite direction. We relate these changes to the occurrence of oceanic slab breakoff beneath the Eastern Alps, which most likely resulted in a rebound of the plate, a growth of the topography in the Eastern Alps and a larger sediment flux to the eastern portion of the basin. Beneath the Central and Western Alps, however, the continental lithosphere slab remained attached to the European plate, thereby resulting in a continued downwarping of the plate in its central and western portions. This plate downwarping beneath the central and western Molasse together with the rebound of the foreland plate in the East possibly explains the inversion of the drainage direction. We thus propose that slab loads beneath the Alps were presumably the most important drivers for the development of the Molasse basin at the basin scale. [ABSTRACT FROM AUTHOR]

Enid Lake is one of the largest reservoirs located in Yazoo River Basin, the largest basin in the state of Mississippi. The lake was impounded by Enid Dam on the Yocona River in Yalobusha County and covers an area of 30 square kilometers. It provides significant natural and recreational resources. The soils in this region are highly erodible, resulting in a large amount of fine-grained cohesive sediment discharged into the lake. In this study, a 3D numerical model was developed to simulate the free surface hydrodynamics and transportation of cohesive sediment with a median diameter of 0.0025 to 0.003 mm in Enid Lake. Flow fields in the lake are generally induced by wind and upstream river inflow, and the sediment is also introduced from the inflow during storm events. The general processes of sediment flocculation and settling were considered in the model, and the erosion rate and deposition rate of cohesive sediment were calculated. In this model, the sediment simulation was coupled with flow simulation. In this research, remote sensing technology was applied to estimate the sediment concentration at the lake surface and provide validation data for numerical model simulation. The model results and remote sensing data help us to understand the transport, deposition and resuspension processes of cohesive sediment in large reservoirs due to wind-induced currents and upstream river flows. [ABSTRACT FROM AUTHOR]

Wave and tide induced sediment transport pathways and rates govern the morphological evolution of estuarine systems. An understanding of the morphodynamics of these systems is required to maintain their commercial, biological and recreational value. The morphodynamics of Port Stephens estuary, a micro-tidal estuary located on a wave dominated southeast coast of Australia were investigated using bathymetric surveys and current velocity data from several locations over the estuary. This provided detailed insight into the rates and direction of movement for the main sedimentary features of the system, and how these features interact with the processes that drive their evolution. We used these findings to develop a conceptual model for estuarine morphodynamics that accounts for fair weather and storm conditions. Our model explains how sediment eroded from the estuarine beaches is trapped by the adjacent flood-tide delta. The model is applicable to fetch-limited estuaries that do not have offshore sources of sediment, where the tidal currents are weak in relation to the incident ocean waves, and that have a wide, stable entrance through which ocean waves can propagate into the estuary. The model is multi-scale in that it encapsulates both short-term and local process, and large scale evolution of an estuary; therefore, it represents a tool that may be used in developing sustainable estuary management strategies. [ABSTRACT FROM AUTHOR]

Here, we propose a conceptual framework of Aeolian sediment transport initiation that includes the role of turbulence. Upon increasing the wind shear stress τ above a threshold value τtʹ, particles resting at the bed surface begin to rock in their pockets because the largest turbulent fluctuations of the instantaneous wind velocity above its mean value ū induce fluid torques that exceed resisting torques. Upon a slight further increase of τ, rocking turns into a rolling regime (i.e., rolling threshold τt ≃ τtʹ) provided that the ratio between the integral time scale Ti ∝ δ/ū (where δ is the boundary layer thickness) and the time Te ∝ √ d/[1-1/s)g] required for entrainment (where d is the particle diameter and s the particle--air--density ratio) is sufficiently large. Rolling then evolves into mean-wind-sustained saltation transport provided that the mean wind is able to compensate energy losses from particle-bed rebounds. However, when Ti/Te is too small, the threshold ratio scales as τt/τtʹ ∝ Te/Ti ∝ sd²/δ², consistent with experiments. Because δ/d controls Ti/Te and the relative amplitude of turbulent wind velocity fluctuations, we qualitatively predict that Aeolian sediment transport in natural atmospheres can be initiated under weaker (potentially much weaker) winds than in wind tunnels, consistent with indirect observational evidence on Earth and Mars. [ABSTRACT FROM AUTHOR]

The integrated analysis of high-resolution multibeam bathymetry and single-channel seismic profiles around Salina Island allowed us to characterize the stratigraphic architecture of the insular shelf. The shelf is formed by a gently-sloping erosive surface carved on the volcanic bedrock, mostly covered by sediments organized in a suite of terraced bodies, i.e. submarine depositional terraces. Based on their position on the shelf, depth range of their edge and inner geometry, different orders of terraces can be distinguished. The shallowest terrace (near-shore terrace) is a sedimentary prograding wedge, whose formation can be associated to the downward transport of sediments from the surf zone and shoreface during stormy conditions. According to the range depth of the terrace edge (i.e., 10-25 m, compatible with the estimated present-day, local storm-wave base level in the central and western Mediterranean), the formation of this wedge can be attributed to the present-day highstand. By assuming a similar genesis for the deeper terraces, mid-shelf terraces having the edge at depths of 40-50 m and 70-80 m can be attributed to the late and early stages of the Post-LGM transgression, respectively. Finally, the deepest terrace (shelf-edge terrace) has the edge at depths of 130-160 m, being thus referable to the lowstand occurred at ca. 20 ka. Based on the variability of edge depth in the different sectors, we also show how lowstand terraces can be used to provide insights on the recent vertical movements that affected Salina edifice in the last 20 ka, highlighting more generally their possible use for neo-tectonic studies elsewhere. Moreover, being these terraces associated to different paleo-sea levels, they can be used to constrain the relative age of the different erosive stages affecting shallow-water sectors. [ABSTRACT FROM AUTHOR]

Libyan Desert Glass (LDG) is a natural silica-rich melted rock found as pieces scattered over the sand and bedrock of the Western Desert of Egypt, northeast of the Gilf Kebir. In this work, a population mixture analysis serves to relate the present spatial distribution of LDG mass density with the Late Oligocene-Early Miocene fluvial dynamics in the Western Desert of Egypt. This was verified from a spatial distribution model that was predicted from the log-normal kriging method using the LDG-mass-dependent transformed variable, Y(x). Both low- and high-density normal populations (-9.2 < Y(x) < -3.5 and -3.8 < Y(x) < 2.1, respectively) were identified. The low-density population was the result of an ordinary fluvial LDG transport/deposition sequence that was active from the time of the melting process, and which lasted until the end of activity of the Gilf River. The surface distribution of the high-density population allowed us to restrict the source area of the melting process. We demonstrate the importance of this geostatistical study in unveiling the probable location of the point where the melting of surficial material occurred and the role of the Gilf River in the configuration of the observed strewn field. [ABSTRACT FROM AUTHOR]

The purpose of the study was to measure in situ the background suspended particulate matter concentration (SPMC) in the DISCOL area (SE Pacific) and its increase due to mechanical mobilization of the seabed. The disturbance experiment imitated future manganese nodule exploitations and was designed to measure the sediment plume generated by such activities. In the direct vicinity of the disturbance, landers equipped with acoustic and optical sensors measured the current velocities and the SPMC. The SPMC at the disturbance was easily up to 10 mg/L and thus about 200 times higher than the background concentration. The downstream sediment plume, measured by the lander, had a SPMC of about 1 mg/L. After tide reversal, the sediment plume was recorded a second time. A sediment transport model reproduced the plume dispersion. After rapid settling of the coarser fraction, a plume of hardly settling fine particles remained in suspension (and no deposition–resuspension cycles). The transport was controlled by the tides and by the vertical velocity component that resulted from bathymetrical differences. The plume may continue to disperse up to 100+ days (up to hundreds of km) depending on the particle size and until background concentration is reached. [ABSTRACT FROM AUTHOR]

Hurricane Charley made landfall on the Gulf Coast of Florida on 13 August 2004 as a category 4 hurricane, devastating North Captiva Island. The hurricane caused a breach to occur to the southern end of the island, which naturally healed itself over the course of three years. By 2008, the cut was completely repaired geomorphologically. LiDAR data analysis shows the northern half of the island has been subjected to persistent erosion from 1998–2018, while the southern half experienced accretion since 2004, including the complete closure of the "Charley cut". The maximum volume of sediment erosion in the northern sector of the island (R71–R73) from 2004–2018 was −85,710.1 m3, which was the source of southern accretion. The breached area of the island (R78b–R79a) obtained 500,163.9 m3 of sediments from 2004–2018 to heal the cut made by Hurricane Charley. Along with LiDAR data analysis, Google Earth Pro historical imageries and SANDS volumetric analysis confirmed the longshore transport of sediments from the northern to the southern end of the island. Winter storms are mainly responsible for this southerly longshore transport and are hypothesized to be the main factor driving the coastal dynamics that restored the breach and helps in widening the southern end of North Captiva Island. [ABSTRACT FROM AUTHOR]

Suspended sediment collected by vegetation in marshes and wetlands contributes to vertical accretion, which can buffer against rising sea levels. Effective capture efficiency (ECE), a parameter quantifying the fraction of incoming suspended particles directly captured by underwater vegetation surfaces, plays a key role in determining the significance of direct interception in morphodynamic models. The ways in which physical characteristics of collectors and transitionally turbulent flows affect ECE are not yet thoroughly understood. We conducted a set of 12 experiments at three flow velocities and three stem densities (plus equivalent zero-collector control experiments), plus four experiments where biofilm was allowed to accumulate. We determined that ECE decreases with increasing collector Reynolds number (study range: 66 to 200; p < 0.05 for two of three treatments) and increasing collector density (solid volume fraction: 0.22% to 1.17%; p < 0.05 for two of three treatments). Adding biofilm increased ECE in all cases, by a multiplicative factor ranging from 1.53 to 7.15 at different collector densities and biofilm growth durations. In some cases, the impact of biofilm on ECE far outweighed that of collector Reynolds number and density. By combining our data with those of one similar study, we present a preliminary model quantitatively assessing the effect of collector density on ECE. [ABSTRACT FROM AUTHOR]

In the northern South China Sea, pockmarks are widely distributed on the seabed offshore on the southwestern Xisha Uplift. The mineralogy and geochemistry of the clay minerals and surface sediments from the pockmark field were identified using X-ray diffraction (XRD) analysis and X-ray fluorescence (XRF) analysis to trace the provenance, weathering, and sediment transportation system in the area. The clay minerals are primarily comprised of illite, smectite, kaolinite, and chlorite, showing a distribution of average weight percentages of 35%, 35%, 18%, and 13%, respectively. Based on the surrounding fluvial drainage basins and various transport mechanisms (current or monsoon), illite and chlorite primarily originate from rivers in Taiwan and the Mekong and Red Rivers. Kaolinite primarily originates from the Pearl River, and smectite derived from the Luzon arc system is primarily transported by surface currents with significant influence from the Kuroshio intrusion. [ABSTRACT FROM AUTHOR]

Morphodynamic processes on Earth are a result of sediment displacements by the flow of water or the action of wind. An essential part of sediment transport takes place with permanent or intermittent contact with the bed. In the past, numerous approaches for bed-load transport rates have been developed, based on various fundamental ideas. For the user, the question arises which transport function to choose and why just that one. Different transport approaches can be compared based on measured transport rates. However, this method has the disadvantage that any measured data contains inaccuracies that correlate in different ways with the transport functions under comparison. Unequal conditions also exist if the factors of transport functions under test are fitted to parts of the test data set during the development of the function, but others are not. Therefore, a structural formula comparison is made by transferring altogether 13 transport functions into a standardized notation. Although these formulas were developed from different perspectives and with different approaches, it is shown that these approaches lead to essentially the same basic formula for the main variables. These are shear stress and critical shear stress. However, despite the basic structure of these 13 formulas being the same, their coefficients vary significantly. The reason for that variation and the possible effect on the bandwidth of results is identified and discussed. A further result is the finding that not only shear stress affects bed-load transport rates as is expressed by many transport formulas. Transport rates are also significantly affected by the internal friction of the moving sediment as well as by the friction fluid-bed. In the case of not fully rough flow conditions, also viscous effects and thus the Reynolds number becomes of importance. [ABSTRACT FROM AUTHOR]

The Djibouti Ville Drift is part of a contourite depositional system located on the southern side of the Djibouti Ville Seamount in the Alboran Sea (Western Mediterranean). The sedimentary record of a core located in the drift deposits has been characterized to achieve the possible sediment sources for the Saharan dust supply and the paleocurrent variability related to Mediterranean intermediate waters for the last 133 kyr. Three end-member grain-size distributions characterize the sediment record transported by the bottom current to address the different aeolian populations, i.e., coarse EM1, silty EM2, and fine EM3. For these particles, the most likely source areas are the Saharan sedimentary basins and deserts, as well as the cratonic basins of the Sahara-Sahel Dust Corridor. The prevalence of these main source areas is shown in the core record, where a noticeable change occurs during the MIS 5 to MIS 4 transition. Some punctual sediment inputs from the seamount have been recognized during sea-level lowstand, but there is no evidence of fluvial supply in the drift deposits. The paleocurrent reconstruction allows the characterizing of the stadial and cold periods by large increases in the mean sortable silt fraction and UP10, which point to an enhanced bottom current strength related to intermediate water masses. Conversely, interglacial periods are characterized by weaker bottom current activity, which is associated with denser deep water masses. These proxies also recorded the intensified Saharan wind transport that occurred during interstadial/stadial transitions. All these results point to the importance of combining sediment source areas with major climatic oscillations and paleocurrent variability in palaeoceanographic sedimentary archives, which may help to develop future climate prediction models. [ABSTRACT FROM AUTHOR]

To understand the geomorphological contrast between the northern and southern parts of the Southeast Greenland margin with its marked differences in sedimentary regime, bathymetric and seismic reflection, data have been compiled and analysed. While previous studies focused on selected parts of this margin, the present study provides an intergraded overview of the entire margin from Cap Farewell to Denmark Strait. The prominent north–south contrast shows a wide northern shelf and a narrow southern shelf. The origin of this width disparity can be traced back to the initial formation stage of the Irminger Sea due to regional differences in uplift versus oceanic subsidence. This regional tectonic discrepancy also created a difference in sediment accommodation space that, in combination with a weak ocean circulation regime, favoured formation of Oligocene–Miocene turbidite fan complexes along the lower southern slope. These fan complexes became the core of sediment drift ridges that strike perpendicular to the slope. Strong bottom currents, which gradually increase in strength towards the south, were mainly prevalent during warmer climate stages. During glacial periods, downslope transport of glacigenic sediments and hyperpycnal meltwater flow further shaped the large drift ridges and formed several relatively narrow, V-shaped turbidite channels extending towards the deep Irminger Sea basin. These V-shaped channels are still active today when cascading dense winter water from the shelf flows downwards along the shelf to the Irminger Sea basin. [ABSTRACT FROM AUTHOR]

The impact of tide-induced morphological changes and water level variations on the sediment transport in a tidally dominated system has been investigated using the numerical model Delft3D and South-East England as a test case. The goal of this manuscript is to explore the long-term changes in morphology due to sea level rise and the large-scale morphodynamic equilibrium of the South-East England. Our results suggest that the long term (century scale) tidally-induced morphological evolution of the seabed slows down in time and promotes a vanishing net transport across the large scale system. Century-scale morphologically updated simulations show that both morphological changes and net transport values tend to decrease in time as the system attains a dynamic equilibrium configuration. Results further suggest that the presence of a gradual increase in mean sea level accelerates the initial morphological evolution of the system whose morphological rate of change gradually attains, however, same plateau values as in the absence of sea level rise. Given the same base morphology, increasing water levels enhance residual currents and the net transport near the coastline; and vice-versa, decreasing sea levels minimize both residuals and net transport near the coastline. The areas that are more affected by, water level and morphological changes, are the ones where the net transport is the highest. This manuscript explores and allows extending the idea of morphodynamic equilibrium at a regional scale, larger than the one for which this concept has been generally explored i.e., estuarine scale. [ABSTRACT FROM AUTHOR]

The 2004 Indian Ocean tsunami caused massive morphological changes around the coast of Sumatra, Indonesia. This research investigates the coastal morphological changes in the Banda Aceh area via coupling a hydrodynamic model with a sediment transport module. The Cornell Multigrid Coupled Tsunami Model (COMCOT) was coupled with the XBeach Model to simultaneously simulate sediment transport and the hydrodynamic process during the tsunami. The coupled model is known as COMCOT-SED. Field bathymetric data measured in 2006 were used to validate the coupled model. This study reveals that the tsunami's impact was more severe on the eastern part of the coast, where it hit directly. Meanwhile, the western part of the coast suffered a lower impact because of the sheltering effects from a series of small islands and a headland to the north. This study has shown that the model results from COMCOT-SED are consistent with field data and show where the tsunami waves caused offshore erosion. [ABSTRACT FROM AUTHOR]

Three experiments were conducted in the Belgian part of the North Sea to investigate short-term variation in seafloor backscatter strength (BS) obtained with multibeam echosounders (MBES). Measurements were acquired on predominantly gravelly (offshore) and sandy and muddy (nearshore) areas. Kongsberg EM3002 and EM2040 dual MBES were used to carry out repeated 300-kHz backscatter measurements over tidal cycles (~13 h). Measurements were analysed in complement to an array of ground-truth variables on sediment and current nature and dynamics. Seafloor and water-column sampling was used, as well as benthic landers equipped with different oceanographic sensors. Both angular response (AR) and mosaicked BS were derived. Results point at the high stability of the seafloor BS in the gravelly area (<0.5 dB variability at 45° incidence) and significant variability in the sandy and muddy areas with envelopes of variability >2 dB and 4 dB at 45° respectively. The high-frequency backscatter sensitivity and short-term variability are interpreted and discussed in the light of the available ground-truth data for the three experiments. The envelopes of variability differed considerably between areas and were driven either by external sources (not related to the seafloor sediment), or by intrinsic seafloor properties (typically for dynamic nearshore areas) or by a combination of both. More specifically, within the gravelly areas with a clear water mass, seafloor BS measurements where unambiguous and related directly to the water-sediment interface. Within the sandy nearshore area, the BS was shown to be strongly affected by roughness polarization processes, particularly due to along- and cross-shore current dynamics, which were responsible for the geometric reorganization of the morpho-sedimentary features. In the muddy nearshore area, the BS fluctuation was jointly driven by high-concentrated mud suspension dynamics, together with surficial substrate changes, as well as by water turbidity, increasing the transmission losses. Altogether, this shows that end-users and surveyors need to consider the complexity of the environment since its dynamics may have severe repercussions on the interpretation of BS maps and change-detection applications. Furthermore, the experimental observations revealed the sensitivity of high-frequency BS values to an array of specific configurations of the natural water-sediment interface which are of interest for monitoring applications elsewhere. This encourages the routine acquisition of different and concurrent environmental data together with MBES survey data. In view of promising advances in MBES absolute calibration allowing more straightforward data comparison, further investigations of the drivers of BS variability and sensitivity are required. [ABSTRACT FROM AUTHOR]

The results of this study have allowed verification that longshore sediment transport along the coast of Napoli Gulf (southern Italy) takes place from Northwest to Southeast. The current analysis describes the results of an integrated sedimentological and geomorphological study of the Neapolitan coastal area. A sedimentological and morphosedimentary study was carried out by bathymetric survey and sampling of bottom sediments. The analysis of modal isodensity curves shows that all the sediments are moved from NW to SE by longshore currents parallel to the coastline. The morphological evolution of the Castellammare di Stabia Gulf coastal area, based on historical coastline changes, starts from 1865, when the sandy littoral was wide and in its natural state. Since the construction of the Torre Annunziata harbor in 1871, sediments transported by a NW-SE longshore drift have become trapped, inducing the genesis of a new wide triangular-shaped beach on the updrift side (NW) of the harbor breakwall. This process induced a significant shoreline retreat of the south-east sector of the littoral. Widespread beach erosion of the coastal physiographic unit of Castellammare di Stabia Gulf (delimited by two ports) is more developed in the southern portion. This study highlights a slight rotation of the shoreline toward the East and a general trend of regression, with typical overall accentuation of shoreline concavity, and significant widening of the triangular-shaped beaches at the end of the falcate. This reduced sediment input removed from the sedimentary budget a large amount of deposits, which are hardly restorable due to the scarce supply of sediment load by the Sarno river and its tributaries. In addition to this new and important derived morphologic feature, other recent human interventions have contributed to further modifications of morphologic characteristics of emerged and submerged beach. The intense use of the territory caused modifications on both the fluvial course and river mouth with direct and indirect effects on the shoreline and the drainage network of the Sarno River. [ABSTRACT FROM AUTHOR]

Sediment transport is a key evolution process of rivers and water basins. This process can pose flood hazards to nearby areas. The Eulerian and Lagrangian methods are usually employed to describe sediment transport in mountain rivers. The application of different methods was proposed by scientists to analyze specific aspects of solid transport, however a complete understanding still alludes us. After a brief review of the most common methods, the coupling of three different methods is proposed and tested in order to study sediment dynamics, and its spatial and temporal variability, in mountain rivers. Tracers, painted bed patches, and digital elevation model (DEM) comparisons are used to characterize sediment transport at both a micro-scale short-term and a macro-scale long-term level on a test reach on Caldone River, Italy. Information about travel distance, critical diameters, active width, and morphological evolution was sought. We focused on how water discharge is changing the relationships between different measurement techniques. High discharge events force the channel to behave in a unique way, while low discharge events generate more intrinsic variability. Only measurement technique coupling can overcome this issue. Results are encouraging and show the potential of a mixed Eulerian-Lagrangian approach. [ABSTRACT FROM AUTHOR]