Search

Submarine canyons are primary conduits for turbidity currents transporting terrestrial sediments, nutrients, pollutants and organic carbon to the deep sea. The concavity in the longitudinal profile of these canyons (i.e. the downstream flattening rate along the profiles) influences the transport processes and results in variations in turbidite thickness, impacting the transfer and burial of particles. To better understand the controlling mechanisms of canyon concavity on the distribution of turbidite deposits, here we investigate the variation in sediment accumulation as a function of canyon concavity of 20 different modern submarine canyons, distributed on global continental margins. In order to effectively assess the isolated impact of the concavity of 20 different canyons, a series of two-dimensional, depth-resolved numerical simulations are conducted. Simulation results show that the highly concave profile (e.g. Surveyor and Horizon) tends to concentrate the turbidite deposits mainly at the slope break, while nearly straight profiles (e.g. Amazon and Congo) result in deposition focused at the canyon head. Moderately concave profiles with a smoother canyon floor (e.g. Norfolk-Washington and Mukluk) effectively facilitate the downstream transport of suspended sediments in turbidity currents. Furthermore, smooth and steep upper reaches of canyons commonly contribute to sediment bypass (i.e. Mukluk and Chirikof), while low slope angles lead to deposition at upper reaches (i.e. Bounty and Valencia). At lower reaches, the distribution of turbidite deposits is consistent with the occurrence of hydraulic jumps. Under the influence of different canyon concavities, three types of deposition patterns are inferred in this study, and verified by comparison with observed turbidite deposits on the modern or paleo-canyon floor. This study demonstrates a potential difference in sediment transport efficiency of submarine canyons with different concavities, which has potential consequences for sediment and organic carbon transport through submarine canyons. • The impact of submarine canyon concavity on turbidite deposition was assessed. • Distribution of turbidite deposits varies with changes in canyon concavity. • Three distinct deposition patterns were identified. • The recognized deposition patterns align well with the observed turbidite deposits. [ABSTRACT FROM AUTHOR]

Submarine channels are the most extensive sediment transport systems on Earth. They transport sediment over hundreds of kilometers and form sediment deposits in the deep-sea, which can act as hydrocarbon reservoirs. During the Late Miocene, a sinuous submarine channel with sediment processes was discovered in the Yinggehai Basin, northwestern South China Sea. However, process interpretations of the factors that influence the stacking patterns, distribution, and morphology of these sinuous channel deposits in this region are not well understood. Based on the interpretation of high-resolution 3D seismic data and exploration well data, and insights from flow dynamics, we analyzed the factors influencing channel morphology, the architecture of the channel, and its associated geomorphic evolution. The channel can be divided into three sections (Sections Ⅰ, Ⅱ, and Ⅲ) in terms of its planform, and into two seismic units (Unit 1 and Unit 2) in terms of its vertical structure. The sinuous submarine channel originated from a combination of inherent structural features from secondary faults and strong erosion from turbidity currents, which occurred due to a sharp decline in sea level during the Late Miocene. Changes in the channel's orientation led to erosion and channel-margin failures, causing an increase in channel width and a decrease in margin gradient. The distribution and stacking patterns of the deposits are greatly influenced by the provenance, sea level changes, and the morphology of the channel. In Sections Ⅰ and Ⅲ, a river-like secondary flow with a limited lateral density gradient leads to vertical deposits. In Section Ⅱ, changes in the channel's orientation altered its morphology and induced topographic forcing, producing a strong river-like secondary flow. This flow consistently caused sediment to accumulate on the inner bank and erode on the outer bank, leading to lateral stacking of deposits in Unit 2. During the filling of Unit 2, diapiric activity uplifted the strata, resulting in thinner deposition in Section Ⅲ, while deposition thickness increased in Section Ⅱ with sufficient provenance. Unit 1 of Section Ⅲ displays desirable properties for a hydrocarbon reservoir, including thick sandstone with good sorting and roundness. This study provides valuable insights into the diverse architectures of spatially and temporally linked submarine channels, and establishes a correlation between the evolutionary process of the channel and the stacking patterns of its constituent elements. • Five depositional elements and three stacking patterns of the channel are identified from a 3D seismic perspective. • The geomorphology of the channel is affected by faults, provenance, sea level changes, and diapir. • Channel morphology controls the evolutionary process of the channel and the stacking patterns of its constituent elements. [ABSTRACT FROM AUTHOR]

[Display omitted] • The sediment provenance of North Manila Trench is mainly from Taiwan Island. • Turbidity currents carry biogenic debris and fresh organic carbon into deep ocean. • Turbidity currents bury organic carbon as much as millennium sedimentation. Turbidity currents play a significant role in sediment transport in deep ocean, profoundly impacting sedimentation in the abyssal sea. This study focused on a 375 cm long sediment core collected from the Manila Trench, revealing a distinctive 15 cm turbidite layer characterized by coarse sediment, an upward fining pattern, and a basal erosion surface. Analysis of rare earth elements and Nd isotope indicates that this turbidite layer originated from Taiwan Island. Initiated in the estuarine shelf region of southwestern Taiwan Island, the turbidity current transported substantial biogenic debris and marine fresh organic carbon into the Manila Trench. Consequently, the turbidite layer exhibited an elevated CaO content and more positive δ13C values. Despite lower TOC content in the turbidite layer due to coarse particle size, the mixture of marine fresh organic matter significantly lowered the carbon age of this layer compared to the strata both below and above it. The rapid sedimentation of the turbidite deposit led to an organic carbon burial flux comparable to the rate at which normal deep-sea sediment buries organic carbon over seven hundred years. Notably, finer sediment overlaying the turbidite layer acted as a cap, enhancing carbon sequestration within the trench. In contrast to nearby core GEO6, which documented over 11 turbidity currents, core S02 recorded only one event. Detailed bathymetric analysis highlights the crucial role of local topography in detecting and preserving turbidity currents. The insights gained from this study would advance our understanding of how turbidity currents shape and influence the deep ocean sedimentation. [ABSTRACT FROM AUTHOR]

The upper third member of Eocene Dongying Formation (Ed 3 u) is considered to be one of the most important hydrocarbon-rich intervals in Nanpu Sag, Bohai Bay Basin, China. Through integrated analysis of the drilling cores, wire-line logs, and high-quality three-dimensional (3-D) seismic data, the sedimentary characteristics of Ed 3 u were analyzed by utilizing the seismic geomorphology approach in the double slope systems of Laoyemiao transverse anticline, Nanpu Sag. The Ed 3 u, a third-order sequence, can be subdivided into three fourth-order sequences (from base to top as SS1, SS2, and SS3). The fan delta front and sublacustrine fan have been identified from well-based analysis of the sedimentary facies and core examinations reveal that the sublacustrine fan deposits were dominated by six types of resedimented lithofacies, namely, slides, slumps, sandy debris flows, muddy debris flows, turbidity currents, and hyperpycnal flows. Stratal slices were obtained from 3-D single-frequency seismic volumes to map the sediment dispersal characteristics and document the evolution of the depositional systems constrained by the double slope break zones of Laoyemiao transverse anticline. The unique structures of the double slope break zones and the variation in the lake level associated with the system tracts of the third-order sequence jointly control the dispersal patterns of the sand bodies and the spatial-temporal evolution of the depositional systems. Based on the above analysis, the depositional evolution model of Ed 3 u was established. The proposed facies-controlled model and sediment transport model can be used to accurately predict the favorable reservoir sandstones. • Analysis lithofacies and origin of sublacustrine fan. • Investigate the controls of double slope break zones over the distribution of sedimentary systems and sand bodies. • Exhibit the spatial-temporal evolution of fan delta front and sublacustrine fan in the systems tract. • Establish the depositional model from source to sink under the control of the transfer zones and slope systems. [ABSTRACT FROM AUTHOR]

• Based on Taylor series expansion to compute spatial derivatives, the consistent particle method (CPM) is expanded to simulate turbidity current involving sediment convection and turbulence-induced diffusion of water-sediment flow. • The proposed second-order CPM-upwind scheme to compute sediment convection is relatively easy to implement as it does not use kernel function which has the requirements of symmetry and unity. • In computing sediment diffusion, CPM shows very good accuracy for both isotropic diffusivity and anisotropic diffusivity. • In simulating turbidity current due to sudden release of water-sediment mixture into ambient water, the method captures the vortices and Kelvin-Helmholtz instability as well as achieves quantitatively good agreement with experimental results in the frontal motion and deposit density of water-sediment mixture. This paper expands the Consistent Particle Method (CPM) to simulation of turbidity currents with focus on turbulent water-sediment flow. A mixture model is adopted in solving the sediment transport equation to simulate the sediment mass transfer due to settling convection and turbulent diffusion. To compute the gravity-driven convection term, the proposed CPM-upwind scheme is relatively easy to implement as it avoids the use of a kernel function which has the requirements of symmetry and unity. Two sand settling problems demonstrate the good accuracy of the CPM-upwind scheme. For suspended sediment diffusion caused by turbulence, CPM is able to model anisotropic diffusion without the averaging effect caused by the isotropy requirement if a kernel function is used. The validated CPM methodology is then applied to simulate a sudden flow of water-sediment mixture into ambient water. The results of the mixture front motion and sediment deposit density agree well with published experimental results. [ABSTRACT FROM AUTHOR]

Submarine sediment flows is one of the main means for transporting sediment to the deep sea, often traveling long-distance and transporting significant volumes of sediment for tens or even hundreds of kilometers. Its strong destructive force often causes serious damage to submarine utilities on its course of movement. The sediment concentration of the sediment flow determines its density difference with the ambient seawater, and this density difference determines the flow ability of the sediment flow, and thus affects the final deposition locations of the transported sediment. In this paper, sediment flows of different sediment concentration with various silt and clay weight ratios (referred to as silt/clay ratio) are studied using flume tests. Our test results indicate that there is a critical sediment concentration at which sediment flows travel the fastest for a specific sediment composition. The critical sediment concentrations and their corresponding maximum velocities for each of the four silt/clay ratios are obtained. The results further indicate that the clay content is linearly negatively correlated with the critical sediment concentration. As the sediment concentration increases, the flow behaviors of sediment flows transform from the flow state to the collapsed state, and the fluid properties of the two turbid suspensions with changing flow behaviors are both Bingham fluids. Additionally, this paper also provides a microscopic explanation of the above-mentioned results by analyzing the arrangement of particles within the sediment flow. • The concept of critical sediment concentration is proposed, under which the turbidity current have the fastest flow velocity. • Sediment component of turbidity current influenced critical sediment concentration. • Model of particle arrangement was constructed to explain the fastest velocity. [ABSTRACT FROM AUTHOR]

Patterns of sediment yield have been widely investigated across a variety of scales, but few of these studies have been carried out in urban watersheds. The design of this study represented a unique opportunity to use high-frequency sensor data to compare sediment yields across spatial and temporal scales in an urbanized watershed. Near real-time turbidity and discharge data were collected continuously for four years at five stream gages over three nested spatial scales in the highly impervious 14.2-km2 Dead Run watershed, located in Baltimore County, Maryland, USA. Monthly suspended sediment yields varied by over two orders of magnitude across all stations. Two mid-watershed stations on tributaries to the mainstem of Dead Run are located only about 500 m apart and about 500 m upstream of their confluence, yet displayed observable differences in the timing of their highest sediment yields. Average annual suspended sediment yield was higher at the headwater station with older development (78.2 t/km2/yr) than at the headwater station with more recent development (47.0 t/km2/yr). Average annual yields increased with watershed size from the headwater stations to the mid-watershed stations (87.0 t/km2/yr and 60.4 t/km2/yr). Additionally, yields at the station farthest downstream (81.7 t/km2/yr) were slightly larger than the yield calculated from the sum of both mid-watershed stations (74.6 t/km2/yr), which together represented about 80% of the upstream drainage area. Several additional patterns highlighting spatial heterogeneity of the system were observed. The ratio of sediment yields between the headwater stations increased steadily over time while the runoff ratio remained almost constant. Yields at one mid-watershed station were consistently higher than yields at the other mid-watershed station, despite similarity in runoff totals. Upstream watersheds show year-to-year variation in sediment yield. In contrast, yields at the farthest downstream station show minimal variation. This observation is consistent with the possibility that internal storage and remobilization tend to modulate downstream yields even with spatial and temporal variation in upstream sources. Observable inconsistencies in sediment yields between subwatersheds at monthly time scales suggest that there is a substantial degree of heterogeneity in terms of sediment response to large storm events. Despite significant internal variability, the overall range of sediment yield values at each site was consistent with values reported for multiple urban mid-Atlantic Piedmont watersheds. Comparison with global values indicates that sediment yields from Dead Run are in the same general range as the 25% quartile of urban sediment yields. • Urban sediment data collected from 5 gages at 3 nested scales for 4 years • Temporal patterns of sediment yield differ from temporal patterns of runoff. • Dominant sources of sediment vary spatially in a 14 km2 highly impervious catchment. • Downstream site exhibits lower variation in annual sediment yield than tributaries. • Storage has a substantial role in the sediment dynamics of a small, urban watershed. [ABSTRACT FROM AUTHOR]

Abstract An instrumented seabed lander was deployed in the head of Logan Canyon in ~280 m water depth in 2005 to obtain the first observations of near-bed hydrodynamics and sediment transport processes in a shelf incising canyon on the glaciated Scotian Slope under strong influence of storms and ocean currents. The seafloor at the head of Logan Canyon is quite dynamic. Hourly mean current speeds can reach 35 cm/s while the maximum instantaneous currents are up to 70 cm/s. Under the forcing of semi-diurnal tides, the bottom currents are dominated by high frequency alternating up- and down-canyon current pulses of internal tides that cause periodic bedload and suspended load sediment transport. The current and sediment transport processes of the internal tides likely extend down to 800–1000 m depths along the canyon to contribute to the observed distribution of Holocene fine sand in the head and talweg of Logon Canyon. The high-frequency current and sediment concentration data show that the temporal changes of the current pulses are well correlated with the changes of temperature and sediment resuspension to demonstrate strong asymmetric patterns. The amplified currents of the internal tides cause the fine sands at the head of Logan Canyon to be transported as bedload in 2.1% of the time and in suspended-load in 1.2% of the time. Suspended-load transport is dominant over bedload transport. The maximum suspended sediment concentrations may reach ~100 mg/l in strong current events. As down-canyon transport is generally stronger and more frequent and the residual current is down-canyon, the net transport of sediment is in the down-canyon direction. Summer storms do not seem to directly impact the bottom currents at the head of Logan Canyon. However, sediments resuspended on the shelf during storms can be advected down slope into the canyon to cause events of substantially high sediment concentration enhancing sediment supply and transport at the head of Logan Canyon. Highlights • First observations of bottom currents and sediment transport process in Logan Canyon. • Seafloor dominated by high-frequency up- and down-canyon currents of internal tides. • Currents and sediment resuspension show correlated, asymmetric patterns. • Amplified bottom currents cause periodic bedload and suspended-load transport. • Down-canyon transport stronger and more frequent to result down-canyon net transport. [ABSTRACT FROM AUTHOR]

Submarine canyons are the principal conduits for turbidity currents transporting sediments to the deep sea. Thus, turbidites, as sedimentary products of turbidity currents, can be used to trace sediment sources and transport processes and to reconstruct mechanisms of turbidity currents in submarine canyons during the geological past. Herein, clay mineral assemblage of late Holocene turbidites at Core MD18–3565 in the Gaoping Submarine Canyon is investigated to reveal the triggering mechanisms of turbidity currents. High-resolution grain-size analysis of typical coarse-grained layers characterized by basal erosion surface and fining-upward sequence in the core verifies their turbidity current origin. A total number of 318 such turbidite layers, covering ∼30% of the total thickness (19.68 m) of the core, are recognized in the late Holocene sediments (33–3954 cal yr BP). Clay mineral assemblage of the turbidites is composed mainly of illite (52–60%) and chlorite (35–45%), with small quantities of smectite (0–5%) and kaolinite (0–4%), while clay mineral assemblage of the non-turbidite sediments (hemipelagites) is composed of approximately the same contents of illite (51–62%) and chlorite (34–43%), but with slightly higher smectite (0–10%) and kaolinite (1–6%). Despite the small differences in smectite and kaolinite contents, the provenance analysis identifies the Gaoping river as the predominant source of sediments in the turbidite layers, while the hemipelagite layers receive small amounts of sediments from the neighboring Erhjen, Tsengwen, and Pachang rivers besides the Gaoping river in southwest Taiwan. In combination with clay mineral compositions of surface sediments in the adjacent continental shelf and slope, as well as in-situ observational results by subaqueous moorings, we believe that the turbidity currents, in which the Gaoping river directly supplied clay minerals to the submarine canyon to form the turbidites, have been triggered mainly by typhoons passing through Taiwan. The frequency of turbidites generally keeps pace with long-term variations of El Niño-Southern Oscillation (ENSO) events, implying the potential modulation of ENSO on occurrences of late Holocene typhoon activities in the Western Pacific. • Turbidites in Gaoping Submarine Canyon mainly come from Gaoping river in SW Taiwan. • Turbidity currents triggered by typhoons are responsible for turbidite occurrence. • ENSO regulates the occurrence of late Holocene submarine canyon turbidity currents. [ABSTRACT FROM AUTHOR]

New biostratigraphic investigations based on palynomorphs (mainly dinoflagellate cysts), foraminifera and calcareous nannoplankton recovered from eight geological sections indicate that the Hangu Formation near the Pluton-Pipirig area (Tarcău Nappe, Eastern Carpathians, Romania), previously assigned to the Senonian–Paleocene interval, includes only uppermost Cretaceous deposits. The palynological assemblages are moderately rich, with a total of 167 well-preserved taxa. The marine palynomorphs – essentially consisting of dinoflagellate cysts (dinocysts) – are dominated by peridinioid taxa, mainly recorded in upper Upper Campanian–lower Maastrichtian deposits, and by a high-diversity assemblage of gonyaulacoid taxa during the late Maastrichtian. Marine algae and dinogymnioid dinocysts were less common. The terrestrial palynoflora is dominated by fern spores and angiosperm pollen, with subordinate gymnosperm pollen. The foraminiferal assemblages include an assortment of well-preserved agglutinated forms, present mainly in the upper Maastrichtian deposits, whereas calcareous benthics and planktonic foraminifera are rare and poorly preserved. Calcareous nannoplankton assemblages are also rare, often represented by two taxa (Micula staurophora and Watznaueria barnesiae); certain important biostratigraphic markers were found to be reworked in the analyzed deposits. Age assignments for the studied sections were mainly provided by dinocysts, through the identification of significant marker taxa and comparisons with well-calibrated Campanian–Maastrichtian dinocyst assemblages from well-dated sections and stratotypes, located mostly in the Northern Hemisphere. Indices such as particulate organic matter (POM) composition, the relative abundance of dinocyst eco-groups, as well as agglutinated foraminiferal morphogroups, were used to reconstruct the depositional environments of the Hangu Formation from the studied area. The upper Upper Campanian–lower Maastrichtian deposits from the Pluton-Pipirig sections were mainly deposited in neritic marine conditions, although occasional redeposition of the sediments transported by turbidity currents towards deeper water settings is not excluded, either. The depositional environments evolve towards outer neritic to distal (bathyal) during the late Maastrichtian, as indicated by palynofacies constituents and by high frequencies of gonyaulacoid dinocysts and deep-water benthic foraminifera. • Upper Campanian–Maastrichtian microfossils, Eastern Carpathians, Romania, are studied. • Palaeoenvironmental and palaeoecological conditions are discussed. • A new detailed geological map for the studied area was proposed. [ABSTRACT FROM AUTHOR]

Understanding estuarine hydrodynamics and sediment dynamics is of key importance to provide the foundation for sound management of these coastal systems. Turbidity maxima, which are zones of elevated suspended sediment concentration (SSC), are of particular interest as they control biogeochemical cycling and affect the overall environmental quality of the estuary. These turbidity maxima, however, are complex dynamic features that respond to changes in forcing conditions. In this study we use a 3D numerical model to investigate the response of hydrosedimentary dynamics to variations in river inflow and sea level rise in the Gironde estuary, which is one of the largest estuarine systems in Europe. Yearly simulations and comparisons with satellite data and measurements of salinity and SSC show that the model reproduces variations in salinity intrusion and the migration of the turbidity maximum driven by seasonal fluctuations in river inflow. Numerical experiments indicate that the formation of this dynamic turbidity maximum is mainly driven by tidal asymmetry. Density gradients play a secondary role by maintaining the stability of the suspended sediment mass. The model also simulates the presence of a secondary turbidity maximum which is more stable, consistent with observations. Evaluation of the sediment budget shows that sediment export mainly occurs during spring tides and when river discharge is high. Simulations including sea level rise suggest that salinity levels in the middle estuary will increase and rising water levels cause tidal amplification, strengthening of tidal currents and enhanced SSC levels in the upper estuary. On the other hand, the locations of the salinity front and the turbidity maximum remain relatively stable under rising water levels. Overall, our simulations suggest that decadal changes in river inflow can potentially have a larger effect on turbidity maximum dynamics than sea level rise. [ABSTRACT FROM AUTHOR]

Earthquakes, tsunamis and gravity flows are common processes offshore Eastern Sicily and pose a significant hazard to coastal communities and infrastructure. The 1908 Messina earthquake and tsunami resulted in >60,000 casualties. It caused a large turbidity current, which broke the Malta-Zante telegraph cable. Yet, this gravity flow remains poorly characterised in terms of its route and flow behaviour. A comprehensive analysis of multibeam echosounder data, sub-bottom profiles, and sediment cores has been carried out to improve our understanding about gravity flow activity within conduit systems of the western Ionian Basin to reconstruct the characteristics of the 1908 sediment flow (e.g., erosion, velocity, source region). Three main canyon-channel systems can be distinguished within the study area. The easternmost system (C3) appears to be the most active in terms of sediment transport. There are numerous erosional and depositional bedforms, including large-scale scours (>100 m-long), turbidite sediment waves and channel wall collapses that are not overprinted by younger events. The other two canyon-channel systems (C1, C2) do not show many bedforms indicative of repeated and recent gravity flow activity. Indeed, the transport of the majority of sediment discharged into the western system (C1) is limited to <25 km downslope from the continental slope, while the central system (C2) facilitates sediment deposition from gravity flows. C3 is, thus, suggested to have been the main passageway of the 1908 sediment flow. It also leads directly to two of three cable break locations. The most likely source areas for the gravity flow are north-eastern Sicily and southern Calabria. Bedforms indicate a flow thickness of >170 m along the upper channel portion of C3 and > 140 m along its lower portion close to the cable breaks. An average flow velocity of 5.6 to 6.3 ms−1 is reconstructed, given the timing of the breaks and length of the canyon-channel system. The flow may have locally decelerated and accelerated while bypassing morphologic highs and knickpoints. These new findings significantly improve our understanding of the 1908 gravity flow (e.g., passageways, depositional/erosional behaviour, thickness, velocity) and provide important insights into gravity flow events in general, especially those with a large run-out. This knowledge is needed to assess potential hazards associated with these events. • the western Ionian Basin shows three distinct canyon-channel systems. • >140 m-thick gravity flow along main passageway in the east; velocity 5–6 m s−2. • numerous erosional and depositional bedforms (e.g., scours, sediment waves). • north-eastern Sicily and southern Calabria are potential source areas. • main failure likely offshore between San Leo and Bocale (southern Calabria). [ABSTRACT FROM AUTHOR]

This study describes and characterises the spatial distribution and evolution of Carboniferous deep-water sediment gravity flows and their associated deposits in the West Junggar region of north-western China. It uses a combination of outcrop sections, cores and seismic profiles to define nine lithofacies associated with a different sediment gravity flow types, including turbidity currents, debris flows, hyperpycnal flows and supercritical flows. The subduction and closure of the remnant West Junggar Ocean basin demonstrated variable palaeogeographical characteristics and configurations during different periods of the Carboniferous. Fossil assemblages and zircon dating data indicate that the target strata have completely recorded the evolution of the Western Junggar remnant ocean in the Carboniferous. The basin evolution is divided into the stable ocean basin stage, the slow subduction and filling stage and the fast subduction and filling stage. Active faulting and varying slope gradients affected the occurrence and types of sediment gravity flows during each stage. Tectonic and seismic activities associated with subduction caused continental slope instabilities and basinward transport of sediment by gravity flows with active faults on the continental slope triggering sediment gravity flows. At the beginning of subduction, the ability of gravity flows to transport coarse debris was limited owing to the shallow gradient of the continental slope. Sediment transport via gravity flows was dominated by sandy debris flows, muddy debris flows, turbidity currents and less frequent flood-controll3ed hyperpycnal flows. As the basin entered the fast subduction and filling stage, the slope gradient steepened and the frequency of active thrust faulting increased, which triggered high-density turbidity currents and supercritical flows. Additionally, the warm and humid paleoclimate led to the development of hyperpycnal flows during the fast-filling stage. This study demonstrates the importance of understanding the character and distribution of sediment gravity flows and associated deposits, especially, the implications for the hydrocarbon industry. • The evolution of West Junggar remnant ocean basin is divided into three stages. • Sediment gravity flow deposits formed during the subduction and closure of the remnant ocean basin. • Slope gradient and thrust faults were key controls on types of gravity flow type and resultant deposit character. • In china, the ancient deep water gravity flow reservoirs are discovered in Junggar Basin. [ABSTRACT FROM AUTHOR]

This research examines whether or not mixes of clay and silt in a turbulent suspension act and settle independent of each other. More specifically, we examine the following three questions: (1) does the presence of silt in suspension alter the size of mud flocs relative to those from a pure clay suspension of equivalent concentration? (2) can silt particles become bound inside clay flocs?; and (3) if silt is bound within flocs, how does this change the settling properties of the clay and silt mixture? These questions are explored through a series of laboratory experiments in which: (a) images of flocs and silt particles within the turbulent suspension are used to measure their size distribution as a function of time; and (b) the settling velocity of the individual aggregates from each of the suspensions are measured in a settling column. The experiments use pure clay, pure silt, and two different mixture ratios of silt and clay. The results show three primary conclusions. First, the presence of silt has no significant impact on floc size. Second, most of the silt in suspension became bound up within the floc aggregates. And third, the bound silt within the flocs increased the floc settling velocity by at least 50%. These results have potential implications for the modeling of suspended mud mixtures in rivers, estuaries, and turbidity currents. [ABSTRACT FROM AUTHOR]

Bottom trawling leads to recurrent sediment resuspension events over fishing grounds. Recent studies have shown how bottom trawling can drive seascape reshaping at large spatial scales and enhance sediment transport in submarine canyons, which subsequently impacts deep-sea ecosystems. Present knowledge on the transfer and accumulation of sediment flows triggered by bottom trawling is based on localized and infrequent measurements whilst a more complete picture of the process is needed. The present work focuses on the modeling of sediment transport and accumulation resulting from trawling activities in La Fonera submarine canyon, northwestern Mediterranean Sea, thus contributing to an improved assessment of trawling impacts. Based on mooring data within a canyon gully, we use an inverse model to retrieve the unknown time series of resuspension due to trawling over the fishing grounds. This resuspension is later used as forcing for the direct problem: we simulate trawling-induced flows through the canyon and provide a 3D visualization of potential trawling impacts on sediment dynamics, including the identification of the propagation patterns of sediments resuspended by trawling. Flows coming from shallower fishing grounds are funneled through canyon flank gullies towards the canyon axis, with part of the resuspended sediment reaching the continental rise out of the canyon across the open continental slope. Trawling-induced sediment flows promote sediment accumulation beyond the canyon mouth. Given the wide geographical distribution of bottom trawling, our results have far-reaching implications that go much beyond La Fonera submarine canyon. Our study represents a starting point for the assessment of the sedimentary impact of bottom trawling in deep continental margins. [ABSTRACT FROM AUTHOR]

At least 17 subsea telecommunications cables cross the Gaoping Canyon and Manila Trench system in the Strait of Luzon between Taiwan and the Philippines. There, cable breaks record rapid (5–16 ms − 1 ), long run-out (> 300 km) sediment density flows triggered by earthquakes and typhoons. Four major cable-breaking events have occurred in the last decade. In 2006, the Pingtung M L = 7.0 earthquakes formed up to 3 individual flows, some of which ran-out for up to 460 km. In 2009, Typhoon Morakot generated two sediment flows; the first was triggered by hyperpycnal river discharge, whereas a second flow formed 3 days later, possibly due to failure of recently deposited flood sediment in upper Gaoping Canyon. A flow in 2010 formed during a swarm of M L = 3–5 earthquakes that followed the M L = 6.4 Jiashian earthquake. Finally, Typhoon Soudelor of 2015 caused the Gaoping River to form a hyperpycnal plume that failed to break cables at < 2600 m depth, but broke at least 6 cables in deeper water. The 2006 Pingtung earthquakes produced the largest sediment flow(s) that produced 22 cable breaks. The other events were less destructive with each causing 6–9 breaks. Sources of the sediment flows varied with the triggering mechanism: those associated with hyperpycnal discharges probably began near the mouth of the Gaoping River. In contrast, earthquake-triggered landslides and subsequent sediment density flows formed anywhere on the adjacent continental margin. Flow speeds generally declined with increased run-out, lower seabed slope and increased channel width. Most variability (7–20 ms − 1 ) was observed over the 0.4°–1.0° slopes of Gaoping Canyon but speeds were mainly restricted to 5–8 ms − 1 in the 0.3° sloping Manila Trench. The 2006–2015 period of frequent cable-damaging flows is the first for the past two decades or longer. In the absence of evidence for increased seismic or anthropogenic activity, this disruptive period may reflect increased typhoon intensity and fluvial sediment discharge. Such typhoon-related flows may complicate interpretation of palaeo-seismic records derived from turbidites in such settings. [ABSTRACT FROM AUTHOR]

Up to date, most in-situ studies and observations of turbidity currents were conducted in submarine canyons that are either, large, shelf incising or adjacent to big perennial rivers, or a combination of these features. Little if any observations have been made in the numerous, small submarine canyons (<20 km) that are confined to the continental slope and located far offshore smaller and often ephemeral streams, which are far more common globally. In this study, measurements were collected from October 2019 until June 2020 in Bat-Galim Canyon, a small (5 km long) submarine canyon located offshore Haifa, Israel, in the Eastern Levantine Basin (southeastern Mediterranean) where only minor, ephemeral streams reach the sea. This was performed using two similar mooring stations, positioned at depths of 350 and 710-meter along the canyon, which carried an array of measuring instruments, set between 2 and 50 meters above the canyon thalweg. Our data shows that the small Bat-Galim canyon is an active conduit for significant sediment transport to the deep-sea, much of it via turbidity currents that flow down the canyon during winter storms. The characteristic values of the turbidity currents in the Bat-Galim canyon were similar to those reported in much bigger submarine canyons. In addition, we observed temperature inversions during these events, wherein the sediment-laden warm surface water plunged and flowed underneath the colder, and otherwise denser, canyon water. This temperature inversion may lead to sediment lofting and upward convection through the water column for hundreds of meters, once sediment settling relieves the warm water of some of its ballast. These unique findings highlight the need to investigate the importance of small submarine canyons on continental slopes worldwide as water and sediment conduits to the deep-sea, even in dryer regions, and the impact of temperature inversions by turbidity currents on various water column processes. • First time-series measurements within a submarine canyon in the Levantine Basin. • Turbidity currents observed in the small (5km long) and confined to the slope canyon. • Similar traits of turbidity currents and sediment transport in this and much larger, shelf-incising canyons. • These winter events caused temperature inversions in the water column. [ABSTRACT FROM AUTHOR]

The ever growing importance of sustainable management of reservoir sedimentation has promoted the development and applications of turbidity current models. However, there are few effective and practical models in literature for turbidity currents in a reservoir where the impounded area involves both the main river and its many tributaries. An integrated numerical model coupling open-channel flow, turbidity current and flow exchanges between main river and tributaries is proposed, which can simulate the complex flow and sediment transport in a reservoir where these three physical processes coexist. The model consists of two sets of governing equations for the open-channel flow and turbidity current, which are based on the modified St. Venant equations by taking into account the effect of lateral flow exchanges. These two sets of equations are solved in the finite volume method framework and the solutions are executed in an alternating calculation mode. Different methods are respectively proposed to calculate the discharge of flow exchange caused by free surface gradient and turbidity current intrusion. For the surface-gradient driven flow exchange, a storage cell method, which re-defines the relationship between water level and representative cross-sectional area, is used to update the water level at confluence. For the turbidity current intrusion, a discharge formula is proposed based on the analysis of the energy and momentum transformation in the intruding turbid water body. This formula differs from previous ones in that the effect of tributary bed slope is considered. Two events of water-sediment regulation conducted in the Xiaolangdi Reservoir in 2004 and 2006 were simulated to test the ability of this model. The predicted reservoir drawdown process, the turbidity current evolution and the sediment venting efficiency were in close agreement with the measurements. The necessity to couple the flow exchanges was demonstrated by comparing the performance of the proposed model with different intrusion discharge formulas and the common one-dimensional model neglecting the main river and tributary interaction. [ABSTRACT FROM AUTHOR]

Rivers and turbidity currents are the two most important sediment transport processes by volume on Earth. Various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths, including direct plunging of river discharge, delta mouth bar flushing or slope failure caused by low tides and gas expansion, earthquakes and rapid sedimentation. During 2011, 106 turbidity currents were monitored at Squamish Delta, British Columbia. This enables statistical analysis of timing, frequency and triggers. The largest peaks in river discharge did not create hyperpycnal flows. Instead, delayed delta-lip failures occurred 8–11 h after flood peaks, due to cumulative delta top sedimentation and tidally-induced pore pressure changes. Elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water. Elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta-lip, which is the most significant of all controls on flow timing in this setting. [ABSTRACT FROM AUTHOR]

• The maximum possible intrusion length is derived for turbidity current intrusion. • A method is developed for predicting flow and sediment transport rates. • Correlation between relative intrusion length and intensity is discovered. • Predictions agree well with laboratory and field measurements. Turbidity current intrusion often occurs in canals, approach channels and tributary areas of large reservoirs, causing sedimentation problems in these environments. Many models and semi-empirical equations have been proposed to calculate flow and sediment transport rates for turbidity current intrusion, under an assumption that the current front can keep propagating freely in the channel before dying out, but the effect of the finite length of closed-end channels has rarely been considered. A self-similar solution to the vertical two-dimensional model for turbidity currents is used to obtain the equation of the maximum possible length for the intrusion of turbidity currents. The maximum possible length is then used to modify an existing discharge equation for turbidity current intrusion in long channels and establish a more general calculation method that can be applied for intrusion in closed end channels. Data from two existing flume experiments are used to calibrate the derived equation of sediment transport rate for turbidity current intrusion. Field measurements obtained from several tributary mouths in the Xiaolangdi Reservoir are also used to calibrate the derived intrusion discharge equation. The agreement between predictions and observations, as well as the comparison between the proposed calculation method and the one before modification, demonstrate that the intrusion discharge is not only determined by the depth of turbid water and sediment concentration at the inlet of the tributary channel, but also influenced by the ratio of the real intrusion length to the maximum possible intrusion length. [ABSTRACT FROM AUTHOR]

• The maximum possible intrusion length is derived for turbidity current intrusion. • A method is developed for predicting flow and sediment transport rates. • Correlation between relative intrusion length and intensity is discovered. • Predictions agree well with laboratory and field measurements. Turbidity current intrusion often occurs in canals, approach channels and tributary areas of large reservoirs, causing sedimentation problems in these environments. Many models and semi-empirical equations have been proposed to calculate flow and sediment transport rates for turbidity current intrusion, under an assumption that the current front can keep propagating freely in the channel before dying out, but the effect of the finite length of closed-end channels has rarely been considered. A self-similar solution to the vertical two-dimensional model for turbidity currents is used to obtain the equation of the maximum possible length for the intrusion of turbidity currents. The maximum possible length is then used to modify an existing discharge equation for turbidity current intrusion in long channels and establish a more general calculation method that can be applied for intrusion in closed end channels. Data from two existing flume experiments are used to calibrate the derived equation of sediment transport rate for turbidity current intrusion. Field measurements obtained from several tributary mouths in the Xiaolangdi Reservoir are also used to calibrate the derived intrusion discharge equation. The agreement between predictions and observations, as well as the comparison between the proposed calculation method and the one before modification, demonstrate that the intrusion discharge is not only determined by the depth of turbid water and sediment concentration at the inlet of the tributary channel, but also influenced by the ratio of the real intrusion length to the maximum possible intrusion length. [ABSTRACT FROM AUTHOR]

A two-phase numerical model using Smoothed Particle Hydrodynamics (SPH) is applied to two-phase liquid-sediments flows. The absence of a mesh in SPH is ideal for interfacial and highly non-linear flows with changing fragmentation of the interface, mixing and resuspension. The rheology of sediment induced under rapid flows undergoes several states which are only partially described by previous research in SPH. This paper attempts to bridge the gap between the geotechnics, non-Newtonian and Newtonian flows by proposing a model that combines the yielding, shear and suspension layer which are needed to predict accurately the global erosion phenomena, from a hydrodynamics prospective. The numerical SPH scheme is based on the explicit treatment of both phases using Newtonian and the non-Newtonian Bingham-type Herschel-Bulkley-Papanastasiou constitutive model. This is supplemented by the Drucker-Prager yield criterion to predict the onset of yielding of the sediment surface and a concentration suspension model. The multi-phase model has been compared with experimental and 2-D reference numerical models for scour following a dry-bed dam break yielding satisfactory results and improvements over well-known SPH multi-phase models. With 3-D simulations requiring a large number of particles, the code is accelerated with a graphics processing unit (GPU) in the open-source DualSPHysics code. The implementation and optimisation of the code achieved a speed up of x58 over an optimised single thread serial code. A 3-D dam break over a non-cohesive erodible bed simulation with over 4 million particles yields close agreement with experimental scour and water surface profiles. [ABSTRACT FROM AUTHOR]

Submarine canyons are one of the most important pathways for sediment transport into ocean basins. For this reason, understanding canyon architecture and sedimentary processes has importance for sediment budgets, carbon cycling, and geohazard assessment. Despite increasing knowledge of turbidity current triggers, the down-canyon variability in turbidity current frequency within most canyon systems is not well constrained. New AMS radiocarbon chronologies from canyon sediment cores illustrate significant variability in turbidity current frequency within Nazaré Canyon through time. Generalised linear models and Cox proportional hazards models indicate a strong influence of global sea level on the frequency of turbidity currents that fill the canyon. Radiocarbon ages from basin sediment cores indicate that larger, canyon-flushing turbidity currents reaching the Iberian Abyssal Plain have a significantly longer average recurrence interval than turbidity currents that fill the canyon. The recurrence intervals of these canyon-flushing turbidity currents also appear to be unaffected by long-term changes in global sea level. Furthermore, canyon-flushing and canyon-filling have very different statistical distributions of recurrence intervals. This indicates that the factors triggering, and thus controlling the frequency of canyon-flushing and canyon-filling events are very different. Canyon-filling appears to be predominantly triggered by sediment instability during sea level lowstand, and by storm and nepheloid transport during the present day highstand. Canyon-flushing exhibits time-independent behaviour. This indicates that a temporally random process, signal shredding, or summation of non-random processes that cannot be discerned from a random signal, are triggering canyon flushing events. [ABSTRACT FROM AUTHOR]

• First monitoring of sediment transfer in submarine channel from source to sink. • River input and lobe aggradation approximately balances over decadal timescales. • Most turbidity currents deposit within the proximal part of the channel. • Infrequent large flows flush the channel; transporting sediment onto the lobe. • Flushing events can occur without obvious triggers, and can be internally generated. Submarine channels are the primary conduits for land-derived material, including organic carbon, pollutants, and nutrients, into the deep-sea. The flows (turbidity currents) that traverse these systems can pose hazards to seafloor infrastructure such as cables and pipelines. Here we use a novel combination of repeat seafloor surveys and turbidity current monitoring along a 50 km-long submarine channel in Bute Inlet, British Columbia, and discharge measurements from the main feeding river. These source-to-sink observations provide the most detailed information yet on magnitude-frequency-distance relationships for turbidity currents, and the spatial-temporal patterns of sediment transport within a submarine channel-lobe system. This analysis provides new insights into mass redistribution, and particle residence times in submarine channels, as well as where particles are eventually buried and how that is recorded in the deposits. We observe stepwise sediment transport down the channel, with turbidity currents becoming progressively less frequent with distance. Most flows dissipate and deposit within the proximal (< 11 km) part of the system, whilst longer run-out flows then pick up this sediment, 'shuffling' it further downstream along the channel. This shuffling occurs mainly through upstream migration of knickpoints, which can generate sediment bypass along the channel over timescales of 10–100 yrs. Infrequent large events flush the channel and ultimately transport sediment onto the lobe. These flushing events can occur without obvious triggers, and thus might be internally generated. We then present the first ever sediment budget analysis of an entire submarine channel system, which shows that the river input and lobe aggradation can approximately balance over decadal timescales. We conclude by discussing the implication of this sediment shuffling for seafloor geohazards and particle burial. [ABSTRACT FROM AUTHOR]

Understanding how subaqueous sediment gravity flows (SSGF) evolve in time and space, and how their deposits vary spatially, is a key research focus for gravity flow sedimentology. This study investigates depositional facies, depositional elements, and sediment transport processes of supercritical flows and hybrid event beds (HEBs) of the Lingshandao Formation in Lingshan Island, Eastern China. Three kinds of depositional elements were recognized: mass transport deposits (MTDs), channel-lobe transition zone (CLTZs), and lobe complexes. MTDs can be sub-divided into proximal and distal deposits. CLTZs are characterized by facies changes from massive coarse-grained pebbly sandstone to backset bedding sandstone in a down-slope direction, which are the deposits of supercritical turbidity currents. HEBs are common in both proximal and distal lobe settings. Tripartite structure in HEBs, which may be caused by up-slope substrate erosion, implies a relatively proximal origin compared with bipartite HEBs, perhaps caused by fluid fractionation in the research area. The succession is formed by a prograding lobe unit, followed by MTDs which are themselves overlain by deposits from a CLTZ. This vertical stacking pattern implies the potential longitudinal facies tract from CLTZ; to lobe complex deposits, is accompanied by emplacement of MTDs at the slope break. The flow types accompanied by sediment transport processes imply that erosion by supercritical turbidity currents associated with a hydraulic jump in the channel-lobe transition zone may be the main reason for mud-clasts and matrix addition to the flow. The large-scale addition of mud-clasts and suspended mud may dampen turbulence in proximal to medial lobe settings, and result in medium-to thick-bedded HEBs with common erosional features and tripartite structures. The remaining suspension flow (with abundant mud) may further transport down-dip and form medium-to thin-bedded HEBs with bipartite structures and rare mud-clasts. These findings may be applicable to other SSGF systems with supercritical flow deposits and hybrid event beds, emphasizing the downdip and lateral variation in depositional elements associated with gravity flow evolution. • CLTZs are characterised by bypass lags, backset bedding, cut-and-fill deposits, soft sediment deformation structures. • The erosion by supercritical turbidity currents caused mud matrix and clasts being added to the flow, and result in HEBs. • Vertical distribution represents the longitudinal sediment transport processes from CLTZ to lobe complex deposits. [ABSTRACT FROM AUTHOR]

Abstract: The capacity of turbidity currents to carry sand and coarser sediment from shallow to deep regions in the submarine environment has attracted the attention of researchers from different disciplines. Yet not only are field measurements of oceanic turbidity currents a rare achievement, but also the data that have been collected consist mostly of velocity records with very limited or no suspended sediment concentration or grain size distribution data. This work focuses on two turbidity currents measured in Monterey Canyon in 2002 with emphasis on suspended sediment from unique samples collected within the body of these currents. It is shown that concentration and grain size of the suspended material, primarily controlled by the source of the gravity flows and their interaction with bed material, play a significant role in shaping the characteristics of the turbidity currents as they travel down the canyon. Before the flows reach their normal or quasi-steady state, which is defined by bed slope, bed roughness, and suspended grain size, they might pass through a preliminary adjustment stage where they are subject to capacity-driven deposition, and release heavy material in excess. Flows composed of fine (silt/clay) sediments tend to be thicker than those with sands. The measured velocity and concentration data confirm that flow patterns differ between the front and body of turbidity currents and that, even after reaching normal state, the flow regime can be radically disrupted by abrupt changes in canyon morphology. [Copyright &y& Elsevier]

Sublacustrine fans developed in structurally active settings are commonly characterized by complicated depositional characteristics, which create great challenges to hydrocarbon exploration. To advance understanding their sedimentary architecture and depositional processes, a large-scale sublacustrine fan system in the Eocene Weixinan Depression, northern South China Sea has been identified and investigated through the comprehensive analysis of 3-D seismic, well-logging, and core data. This fan was deposited during a lake-level falling stage, covering an area of 55 Km2. It can be divided into two sections in the vertical direction by the sedimentary characteristics. The lower section mainly consists of thin layers of well-sorted fine sandstones with parallel bedding, which are interpreted as deposits of turbidity currents. By contrast, the upper section comprises thick layers of gravelly coarse sandstones with various deformation structures and widespread floating clasts, which should be the deposits of cohesive debris flows. Provenance analysis suggests that the development of complicated sedimentary characteristics has a close relationship with the occurrence of multiple sediment supply directions. The lower section was sourced by the western delta with long-distance transported well-sorted sediments, while the northern fan delta sourced the upper section with short-distance transported coarse-grained sediments. Its depositional process was mainly controlled by paleo-geomorphology, sediment supply, and relative lake level changes. The lower section, controlled by the flexure slope belt, is a typical sand-rich sublacustrine fan characterized by the low gradient (<1°–1.5°), while the upper section, controlled by the steep slope fault belt, is a gravel-rich sublacustrine fan dominated by intense faulting and high gradient (3.2°–4.5°). In addition, during the depositional period of the upper section, the relay ramps between en-echelon faults provided major entry points for coarse-grained sedimentary flows into the depression. Therefore, a deep-lacustrine model is proposed for the sublacustrine fan system, showing the detailed "triggering-transportation-deposition" process. This study outlines the complexity of the sedimentary architecture of sublacustrine fans in structurally active settings, and the proposed model may be applicable in other lacustrine basins. • The sublacustrine fan is characterized by complicated sedimentary characteristics. • It consists of two types of gravity flows: cohesive debris flows and turbidity currents. • The development of complicated sedimentary characteristics is related to multi-source supply. • Its deposition process was controlled by small infections in gradient of paleo-slopes. • A deep-lacustrine model is proposed for sublacustrine fans in structurally active settings. [ABSTRACT FROM AUTHOR]

Abstract: Turbidity currents are the most common flows of water, and suspended and bed load sediment occurring in the relatively deep sea and lakes, and act as large systems of sediment distribution. Due to the turbid nature of the flow, they may impact subaqueous infrastructures, as well as ecosystems, during motion, so quantifying the turbidity degree is important to predict the current impact. A particular type of these currents is the so-called volcaniclastic turbidity currents or subaqueous ash flows, which are mostly composed of fine-grained volcanic particles, and are used here as synonymous (sensu hydraulic) with the meaning of secondary current. In this paper, a method to estimate the water entrainment (column condition model), as well as the sedimentation and deposition rates (conveyer model), in volcaniclastic turbidity currents is proposed, by starting from the physical features of the deposits or inverse procedure. Some criteria of sediment mechanics are used to approximate the flow hydraulic parameters needed to quantify the water entrainment, as well as the shear velocity in volcaniclastic turbidity currents. The deposits used as case study are the impressive, meters thick, well-sorted rhyolitic ash turbidites of Late Pliocene cropping out in Southern Italy, particularly in the Craco area, Matera. The water entrainment coefficient of the currents is calculated in a range of particle concentration and slope angle, whereas the slope angle giving the sedimentation rate is calculated in a range of flow shear velocity, which in turns gives the deposition rate. The results have a general validity for depositional turbidity currents laden with well-sorted sediment, and they show that the water entrainment is low for relatively dense, slow-moving, subcritical flows, but it increases as the Richardson number decreases for relatively dilute, fast, supercritical flows. Moreover, the sedimentation and deposition rates are high for relatively intense flows moving over gentle slopes, but they decrease for relatively weak flows moving over steep slopes. The deposit sedimentary structures thus infer sedimentation, and particularly depositional processes. Finally, the conveyer model is extended conceptually to pyroclastic density currents, when approximating, but not exclusively, the column condition model in the flow above the flow boundary zone. [Copyright &y& Elsevier]

Abstract: A computational investigation is presented of mono-, bi-, and polydisperse lock-exchange turbidity currents interacting with complex bottom topography. Simulation results obtained with the software TURBINS are compared with laboratory experiments of other authors. Several features of the flow, such as deposit profiles, front location, suspended mass, and runout length, are discussed. For a monodisperse lock-exchange current propagating over a flat surface, we investigate the influence of the boundary conditions at the streamwise and top boundaries, and we generally find good agreement with corresponding laboratory experiments. However, we note some differences with a second set of experimental data for polydisperse turbidity currents over flat surfaces. A comparison with experimental data for bidisperse currents with varying mass fractions of coarse and fine particles yields good agreement for all cases except those where the current consists almost exclusively of fine particles. For polydisperse currents over a two-dimensional bottom topography, significant discrepancies are observed. Possible reasons are discussed, including erosion and bed load transport. Finally, we investigate the influence of a three-dimensional Gaussian bump on the deposit pattern of a bidisperse current. [Copyright &y& Elsevier]

Summary: Turbidity currents play a critical role in effective sediment and reservoir management in alluvial rivers. Yet previous estimations of reservoir turbidity currents are mostly based on simple empirical relations and it remains unclear how and to what extent physically based numerical models can resolve current evolution as compared against field observations. This paper presents a physically-based,process-resolved computational study of turbidity currents in the Xiaolangdi reservoir in the lower Yellow River, China. A coupled layer-averaged 2Dnumerical model is applied, which explicitly incorporates the interactions between the current, sediment transport and morphological evolution, and features a new well-balanced numerical scheme dealing with irregular topography. Two turbidity current events in July 2004 are numerically simulated to calibrate and validate the model. The current advance and the sediment transport rate computed by the model compare favourably with field measurements. These suggest the present model is a viable tool for determining the timing for operating the bottom outlets, which is critical for effective reservoir sediment management. The sediment entrainment flux and bed resistance are key factors dictating the evolution of turbidity current and warrant further investigations. [ABSTRACT FROM AUTHOR]

Abstract: In the last five years, horizontal acoustic Doppler current profilers have come onto the market as an instrument designed to measure real-time horizontal current profiles from a permanent fixed mount. The focus of this paper is on the feasibility of using these commercial instruments to measure suspended sediment fluxes in rivers. Measurements are presented from a study site that was equipped with an optical turbidity meter and three horizontal ADCPs operating at 300kHz, 600kHz and 1200kHz between November 2009 and June 2010. Laser grain size measurements showed the primary particles of the suspended sediment to be predominantly silts with some clay and occasionally some fine sand. Measurements of sediment attenuation by the three horizontal ADCPs are presented for two high concentration events during which concentrations reached 2.5 and 8kg/m3, respectively. Very clear linear relationships are seen between sediment attenuation and particle concentration and the sediment attenuation is consistent with the theory for viscous absorption by fine sediments. Using the relationship between attenuation and concentration, we are able to reconstruct the concentration time series for events during which the turbidity data are unavailable. Our findings show that, when properly positioned, horizontal ADCPs can provide suitable measurements of sediment transport during extreme river flow conditions such as floods, at least for predominantly silt-sized particles. This ability is of primary interest for river survey applications since the long term sediment transfer is believed to be driven by these intense events. [Copyright &y& Elsevier]

Abstract: The internal stress distribution within weakly depositional turbidity currents has often been assumed to be similar to saline gravity currents. This assumption is investigated by analyzing a series of experiments to quantify and compare the shear stress distribution in the bottom boundary layer (BBL) of saline and particle-laden gravity currents. Vertical profiles of Reynolds stresses, viscous stresses and turbulent kinetic energy (TKE) were obtained from the mean downstream velocity profiles and turbulent velocity fluctuations, and were broadly similar in both flow types, suggesting that saline gravity currents are a good analogue to turbidity currents. Maximum positive Reynolds stresses occur where the velocity gradient is largest in the BBL but below this maximum, the Reynolds stresses decrease significantly and are balanced by an increase of viscous stresses. The bulk drag coefficients is defined for both flows using three methods, (i) a log-fit method based on the law of the wall, (ii) the observed maximum total stress and (iii) direct measurements of turbulent velocities. The values of both flow types were broadly similar but each method led to values of different orders of magnitude. The log-fit method yielded the largest drag coefficients of whereas measurements of turbulent velocities gave relatively small values of . The best correlation with drag coefficients observed in field measurements of was obtained by using the maximum total stresses next to the wall. The variation of is discussed in relation to parameterization methods in experimental and numerical modeling. [Copyright &y& Elsevier]

Abstract: Submarine canyons can efficiently drain sediments from continental margins just as river systems do in subaerial catchments. Like in river systems, submarine canyons are often arranged as complex drainage networks that evolve from patterns of erosion and deposition. In the present paper we use a morphometric analysis of submarine canyon-channel long-profiles to study the recent sedimentary history of the Valencia Trough turbidite system (VTTS) in the NW Mediterranean Sea. The VTTS is unique in that it drains sediment from margins with contrasting morphologies through a single “trunk” conduit, the Valencia Channel. The Valencia Channel has been active since the late Miocene, evolving in response to Plio-Quaternary episodes of erosion and deposition. The integrated analysis of long-profiles obtained from high-resolution bathymetric data across the entire turbidite system shows evidence for transient canyon incision in the form of knickpoints and hanging tributaries. Multiple factors appear to have triggered these periods of incision. These include a large debris flow at 11,500yrBP that disrupted the upper reaches of the VTTS and glacio-eustatic lowstands that forced shifting of sediment input to the VTTS. Based on these inferences, long-term time-averaged incision rates for the Valencia Channel have been estimated. The evidence we present strongly suggests that Foix Canyon has played a key role in the drainage dynamics of the VTTS in the past. This study builds conceptually on a recent modeling study that provides a morphodynamic explanation for the long-term evolution of submarine canyon thalweg profiles. The procedure and results from this work are of potential application to other submarine sediment drainage systems, past and present, including those containing mid-ocean type valleys like the Valencia Channel. [Copyright &y& Elsevier]

Abstract: The aim of this study is to assess the global occurrence of large submarine canyons to provide context and guidance for discussions regarding canyon occurrence, distribution, geological and oceanographic significance and conservation. Based on an analysis of the ETOPO1 data set, this study has compiled the first inventory of 5849 separate large submarine canyons in the world ocean. Active continental margins contain 15% more canyons (2586, equal to 44.2% of all canyons) than passive margins (2244, equal to 38.4%) and the canyons are steeper, shorter, more dendritic and more closely spaced on active than on passive continental margins. This study confirms observations of earlier workers that a relationship exists between canyon slope and canyon spacing (increased canyon slope correlates with closer canyon spacing). The greatest canyon spacing occurs in the Arctic and the Antarctic whereas canyons are more closely spaced in the Mediterranean than in other areas. River-associated, shelf-incising canyons are more numerous on active continental margins (n=119) than on passive margins (n=34). They are most common on the western margins of South and North America where they comprise 11.7% and 8.6% of canyons respectively, but are absent from the margins of Australia and Antarctica. Geographic areas having relatively high rates of sediment export to continental margins, from either glacial or fluvial sources operating over geologic timescales, have greater numbers of shelf-incising canyons than geographic areas having relatively low rates of sediment export to continental margins. This observation is consistent with the origins of some canyons being related to erosive turbidity flows derived from fluvial and shelf sediment sources. Other workers have shown that benthic ecosystems in shelf-incising canyons contain greater diversity and biomass than non-incising canyons, and that ecosystems located above 1500m water depth are more vulnerable to destructive fishing practices (bottom trawling) and ocean acidification caused by anthropogenic climate change. The present study provides the means to assess the relative significance of canyons located in different geographic regions. On this basis, the importance of conservation for submarine canyon ecosystems is greater for Australia, islands and northeast Asia than for other regions. [Copyright &y& Elsevier]

Abstract: Sandy deposits from the 29 September 2009 tsunami on the east coast of Upolu, Samoa were investigated to document their characteristics and used to apply an inverse sediment transport model to estimate tsunami flow speed. Sandy deposits 6 to 15cm thick formed from ~25 to ~250m inland. Sedimentary layers in the deposits, that are defined by vertical grain size variation and contacts, are interpreted to have formed during onshore runup of two waves. Deposits at 3 locations (100, 170, and 240m inland) contained two layers that are predominately normally graded (~80%), but contained massive sections (~15%) and inversely graded sections (~5%) at their bases. About 75% of the total thickness of normally graded intervals exhibits a signature of sediment falling out of suspension at their top. This type of grading, termed suspension grading here, was first recognized in turbidity current deposits and is characterized by the entire distribution shifting finer upwards in a layer as high-settling velocity, coarser material deposits first and low-settling velocity finer material deposits last. The Jaffe and Gelfenbaum (2007) inverse sediment transport model was applied to intervals within layers that exhibited suspension grading to estimate tsunami flow speed and was able to reproduce the general trends of the observed suspension grading. A key unknown input in the modeling is the bottom roughness. For a bottom roughness parameterization using a Manning''s n of 0.03 (equivalent to a z0 ~0.006m for the observed flow depths of 2–3m) flow speeds calculated for the 2 layers at the 3 locations were 3.8, 3.6, and 3.7m/s (bottom layer/earlier wave) and 4.4, 4.4, and 4.1m/s (top layer/later wave) at 100, 170, and 240m inland, respectively. These estimates are consistent with the ~3–8m/s tsunami flow speed from boulder transport calculations and result in Froude numbers of ~0.7–1.0 when maximum measured flow depths are used. Because the inverse model assumes the deposit was formed by sediment falling out of suspension care must be taken to model only intervals of the deposit exhibiting suspension grading. Including intervals deposited by either bedload or suspended load transport convergences result in higher, and sometimes unrealistic, tsunami flow speed estimates. [Copyright &y& Elsevier]

Abstract: The submarine Dakar Canyon incises the continental margin at the transition of the hyperarid Sahara to the semiarid Sahel Zone, and acts as an effective pathway for gravity-driven sediment transport. Four gravity cores recovered directly from the canyon axis were investigated in order to reconstruct the sedimentation processes in the Dakar Canyon during the Late Quaternary. In addition, a hemipelagic record from the northern levee of the canyon was analysed for monitoring background sediment supply, which is dominated by dust input in the area. Coarse terrigenous silt size data and high Ti/Ca ratios reflect overall increased higher dust supply during the last two peak glacials. During these times wide-extensive sand sea covered the exposed shelf almost completely. However, in interglacial periods wind stress diminished considerably and only minor amounts of dust were supplied to the outer shelf and continental slope. Two major periods of turbidite depositions are recorded in intervals from final glacial sea level lowstands to early deglacial sea level rise of the last two glacial/interglacial cycles (i.e. between 141 and 131kyr BP and from 23.2 to 14.2kyr BP). These turbidite deposits consist of sandy to silty sediments. Detailed grain size analyses were used to reconstruct the sedimentary characteristics and flow processes of these turbidity currents. A much higher frequency in turbidite activity occur around 135kyr BP in contrast to the second interval around 18kyr BP, suggesting a higher sediment budget in the source area. Based on the sedimentological investigation of the turbidites we provide a schematic model for the sedimentation processes in the Dakar Canyon. [Copyright &y& Elsevier]

Abstract: Here we present results from a suite of laboratory experiments that highlight the influence of channel sinuosity on the depositional mechanics of channelized turbidity currents. We released turbidity currents into three channels in an experimental basin filled with water and monitored current properties and the evolution of topography via sedimentation. The three channels were similar in cross-sectional geometry but varied in sinuosity. Results from these experiments are used to constrain the run-up of channelized turbidity currents on the outer banks of moderate to high curvature channel bends. We find that a current is unlikely to remain contained within a channel when the kinetic energy of a flow exceeds the potential energy associated with an elevation gain equal to the channel relief; setting an effective upper limit for current velocity. Next we show that flow through bends induces a vertical mixing that redistributes suspended sediment back into the interiors of depositional turbidity currents. This mixing counteracts the natural tendency for suspended sediment concentration and grain size to stratify vertically, thereby reducing the rate at which sediment is lost from a current via deposition. Finally, the laboratory experiments suggest that turbidity currents might commonly separate from channel sidewalls along the inner banks of bends. In some cases, sedimentation rates and patterns within the resulting separation zones are sufficient to construct bar forms that are attached to the channel sidewalls and represent an important mechanism of submarine channel filling. These bar forms have inclined strata that might be mistaken for the deposits of point bars and internal levees, even though the formation mechanism and its implications to channel history are different. [Copyright &y& Elsevier]

Abstract: A geophysical and geological survey (CHAMAK) has been carried out on the Makran accretionary wedge off Pakistan in order to understand the structure of the margin and the recent sedimentary processes in this self-maintaining prism disconnected from the modern Indus inputs (Qayyum et al., 1997; Gaedicke et al., 2002a; Schluter et al., 2002). Morphostructural analysis, based on the interpretation of bathymetric data and backscatter imagery, as well as a 3.5kHz echo-character mapping, allow us to distinguish three structural domains, from north to south, where sedimentary processes differ: (1) the accretionary wedge to the north, (2) the trench and (3) the northern Murray Ridge at the seaward edge of the trench. The accretionary wedge is cut by canyons responsible for an important erosion of the prism especially in the eastern part of the wedge. Within the trench, sediments transported by the canyons generate sediment waves and are transported westward, parallel to the E–W axis of the trench. The eastern part of the abyssal plain is eroded by strong turbidity currents whereas important sediment deposition occurs in the western part of the abyssal plain, as a consequence of a decrease in the current energy. Nearly no mass transport deposits are recognized in the study area except near the ridges forming the accretionary wedge. Small-scale slope failure scars are described. The prevalence of turbiditic processes and the existence of a morphological barrier formed by the Murray Ridge allow the confinement of turbidites within the trench. Migrating sediment waves seem to be common sedimentary structures in this setting. These features might be produced by important velocity decrease of turbidity currents when reaching the trench. [Copyright &y& Elsevier]

Abstract: Vertical sediment fluxes and their dominant controlling processes in Hueneme and Mugu submarine canyons off south-central California were assessed using data from sediment traps and current meters on two moorings that were deployed for 6months during the winter of 2007. The maxima of total particulate flux, which reached as high as 300+g/m2/day in Hueneme Canyon, were recorded during winter storm events when high waves and river floods often coincided. During these winter storms, wave-induced resuspension of shelf sediment was a major source for the elevated sediment fluxes. Canyon rim morphology, rather than physical proximity to an adjacent river mouth, appeared to control the magnitude of sediment fluxes in these two submarine canyon systems. Episodic turbidity currents and internal bores enhanced sediment fluxes, particularly in the lower sediment traps positioned 30m above the canyon floor. Lower excess 210Pb activities measured in the sediment samples collected during periods of peak total particulate flux further substantiate that reworked shelf-, rather than newly introduced river-borne, sediments supply most of the material entering these canyons during storms. [Copyright &y& Elsevier]

Abstract: Various transformation mechanisms can generate turbidity currents from subaqueous debris flows. Different transformation mechanisms have been described and interpreted in the past from laboratory experiments and from deposits, but the two approaches have not generally been linked. This has made the genetic interpretation and comparison of deposits difficult. In this paper a generic classification scheme of debrite–turbidite couplets is proposed based on transformation mechanisms inferred from laboratory experiments. Five different flow types (called A–E herein) and their resulting deposits are detailed, but they are all part of a continuous spectrum, and a mixture of types is likely to be found in the field. Type A flows are strong, dense debris flows that undergo little transformation. Their deposit will be a debrite overlain by a thin turbidite, which is separated from it by a clear grain size break. Type B flows are weaker and can develop waves at the debris flow-turbidity current interface. The deposit will be a debrite with a wavy top overlain by a turbidite that is thicker than for type A flows. For type C flows, the interfacial waves will grow so much that the debris flow disintegrates into separate parts. The deposit will consist of debrite lenses encased in a turbidite. Type D flows will undergo even more mixing than type C flows so that the debrite parts will be mixed. Their deposit will be a turbidite with laterally varying areas of debrite characteristics near the bed. Type E flows will be so transformed that the debris flow character has disappeared and the flow is a turbidity current with high sediment concentration. The deposit will be largely turbiditic. The flow types and deposits will be illustrated with some examples from two field areas: the Polish Carpathians and the French Maritime Alps. [Copyright &y& Elsevier]

Abstract: As part of the multidisciplinary programme BIOZAIRE devoted to studying deep-sea benthic ecosystems in the Gulf of Guinea, particulate input and its relationship with near-bottom hydrodynamics were monitored using long-term moorings from 2000 to early 2005. Particular attention was given to material input through the Congo (ex-Zaïre) submarine channel that extends 760km from the Congo River mouth to the abyssal plain (>5100m) near 6°S. Due to its direct connection to the Congo River, the Congo canyon and channel system are characterised by particularly active recent sediment transport. During this first in situ long-term monitoring along the channel, an energetic turbidity event was observed in January 2004 at three locations along the channel from 3420 to 4790m in depth. This event tilted and displaced the moorings installed at 3420m (site ZR′) and 4070m (site ZD′), and resulted in high sediment deposition at all three mooring sites. The event moved at an average velocity of 3.5ms−1 along the numerous channel meanders between 3420 and 4070m, then at 0.7ms−1 between 4070m and the end of the channel at 4790m. The particle cloud rose above the top of the valley at 4070m (site ZD′), but not at 3420m (site ZR′) where the channel was too deep. Lastly, the mooring line broke at site ZD′ in October 2004 probably due to a strong event like that of 2001 previously described by Khripounoff et al. [Khripounoff, A., Vangriesheim, A., Babonneau, N., Crassous, P., Denniellou, B., Savoye, B., 2003. Direct observation of intense turbidity activity in the Zaire submarine valley at 4000m water depth. Marine Geology (194), 151–158]. Between these strong events, several peaks of high turbidity and particle flux occurred, but without noticeable current increases. These events were probably due to local sliding of sediment accumulated on the walls or terraces on the side of the channel. The area near 4000m depth and the lobe appear to be the main depocentres of particulate input rich in organic matter derived from the Congo River. [Copyright &y& Elsevier]

Abstract: The rotation rate of the Earth controls the deposition scale of turbidity currents when their flow transit-time is comparable to one day. Using laboratory experiments it is shown that the maximum length-scale L of deposition is set by the scale where the Rossby number of the current is equal to one. The dimensionless Rossby number is defined as Ro = U / fL, where U is a depth-averaged velocity of the turbidity current and f is the Coriolis parameter. In these new laboratory experiments the Coriolis parameter is varied by changing the platform rotation rate and there is good agreement between experimental observations and the prediction that the extent of the deposition scales as L ~(4/ π)1/4(g′V / f)1/4, where g′ is the reduced gravity and V the initial volume of the sediment-laden material. This scaling implies that the depositional patterns will vary with latitude, and that at higher latitudes one would expect smaller, thicker deposits. Using this scaling implies that the 200–400 km spatial extent of the turbidite arising during the 1929 Grand Banks earthquake had Ro ~1, and so Coriolis forces controlled the length-scale of the turbidite deposition. [Copyright &y& Elsevier]

Abstract: The Storegga Slide, which occurred ∼8100 years ago, is one of the world''s largest and best studied exposed submarine landslides. In this study we use novel geomorphometric techniques to constrain the submarine mass movements that have shaped the north-eastern Storegga Slide, understand the link between different forms of failure, and propose a revised development model for this region. According to this model, the north-eastern part of the Storegga Slide has developed in four major events. The first event (event 1) was triggered in water depths of 1500–2000m. In this event, the surface sediments were removed by debris flows and turbidity currents, and deposited in the Norwegian Sea Basin. Loading of the seabed by sediments mobilised by the debris flows and turbidity currents resulted in the development of an evacuation structure. Loss of support associated with this evacuation structure, reactivation of old headwalls and seismic loading activated spreading in the failure surface of event 1 up to the main headwall (event 2). In some areas, spreading blocks have undergone high displacement and remoulding. Parts of the spreading morphology and the underlying sediment have been deformed or removed by numerous debris flows and turbidity currents (event 3). We suggest that the higher displacement and remoulding of the spreading blocks, and their removal by debris flows and turbidity currents, was influenced by increased pore pressures, possibly due to gas hydrate dissolution/dissociation or by lateral variability in the deposition of contourite drifts in palaoeslide scars. The fourth event entailed a large, blocky debris flow that caused localised compression and transpressive shearing in the southern part of the spreading area. [Copyright &y& Elsevier]

Abstract: Motivated by field studies of the Ems estuary which show longitudinal gradients in bottom sediment concentration as high as O(0.01kg/m4), we develop an analytical model for estuarine residual circulation based on currents from salinity gradients, turbidity gradients, and freshwater discharge. Salinity is assumed to be vertically well mixed, while the vertical concentration profile is assumed to result from a balance between a constant settling velocity and turbulent diffusive flux. Width and depth of the model estuary are held constant. Model results show that turbidity gradients enhance tidally averaged circulation upstream of the estuarine turbidity maximum (ETM), but significantly reduce residual circulation downstream, where salinity and turbidity gradients oppose each other. We apply the condition of morphodynamic equilibrium (vanishing sediment transport) and develop an analytical solution for the position of the turbidity maximum and the distribution of suspended sediment concentration (SSC) along a longitudinal axis. A sensitivity study shows great variability in the longitudinal distribution of suspended sediment with the applied salinity gradient and six model parameters: settling velocity, vertical mixing, horizontal dispersion, total sediment supply, fresh water flow, and water depth. Increasing depth and settling velocity move the ETM upstream, while increasing freshwater discharge and vertical mixing move the ETM downstream. Moreover, the longitudinal distribution of SSC is inherently asymmetric around the ETM, and depends on spatial variations in the residual current structure and the vertical profile of SSC. [Copyright &y& Elsevier]

Abstract: Turbidity currents may feature active sediment transport and rapid bed deformation, such as those responsible for the erosion of many submarine canyons. Yet previous mathematical models are built upon simplified governing equations and involve steady flow and weak sediment transport assumptions, which are not in complete accordance with rigorous conservation laws. It so far remains unknown if these could have considerable impacts on the evolution of turbidity currents. Here a fully coupled modeling study is presented to gain new insights into the evolution of turbidity currents. The recent analysis of the multiple time scales of subaerial sediment-laden flows over erodible bed [Cao Z, Li Y, Yue Z. Multiple time scales of alluvial rivers carrying suspended sediment and their implications for mathematical modeling. Adv Water Resour 2007;30(4):715–29] is extended to subaqueous turbidity currents to complement the fully coupled modeling. Results from numerical simulations show the ability of the present coupled model to reproduce self-accelerating turbidity currents. Comparison among the fully and partially coupled and decoupled models along with the analysis of the relative time scale of bed deformation explicitly demonstrate that fully coupled modeling is essential for refined resolution of those turbidity currents featuring active sediment transport and rapid bed deformation, and existing models based on simplified conservation laws need to be reformulated. [Copyright &y& Elsevier]

Abstract: A technique is described to observe and quantify wave-by-wave bed-level changes in the swash zone. The ultrasonic instrument system is non-contact with the beach face surface being measured and the sensors remain outside of the fluid flows causing sediment movement. Sensor resolution combined with the electronic noise inherent within a digital network data-logging system results in a (conservative) measurement accuracy of ±1 mm, equating to a couple of sand grain diameters in height. Illustrative field results demonstrate the practical use of the instrumentation, and a simple data pre-processing method to separate swashes and intervening bed-level ‘events’ is discussed. These example data reveal rather complex fluctuations of the bed observed over time periods of minutes to hours. Rather strikingly, gross bed-level changes per wave are revealed to be up to many orders of magnitude larger than the observed net rate of beach face evolution. It is outlined how observations of successive bed-level changes at multiple locations within a dense grid, combined with a consideration of sediment continuity, will now enable the total net sediment transported per uprush–backwash to be quantified. [Copyright &y& Elsevier]

Abstract: Numerical modeling of a beach nourishment project is conducted to enable a detailed evaluation of the processes associated with the effects of nearshore dredge pits on nourishment evolution and formation of erosion hot spots. A process-based numerical model, Delft3D, is used for this purpose. The analysis is based on the modification of existing bathymetry to simulate “what if” scenarios with/without the bathymetric features of interest. Borrow pits dredged about 30 years ago to provide sand for the nourishment project have a significant influence on project performance and formation of erosional hot spots. It was found that the main processes controlling beach response to these offshore bathymetric features were feedbacks between wave forces (roller force or alongshore component of the radiation stress), pressure gradients due to differentials in wave set-up/set-down and bed shear stress. Modeling results also indicated that backfilling of selected borrow sites showed a net positive effect within the beach fill limits and caused a reduction in the magnitude of hot spot erosion. [Copyright &y& Elsevier]

Abstract: To predict sediment transport under oscillatory sheet flow condition, especially for fine sand, is still a challenging research subject in coastal engineering. This paper describes a newly-developed numerical model based on two-phase theory with the use of a one-equation turbulence closure, and its applications in predicting fine sediment suspension in near-prototype oscillatory sheet flow conditions. Model results were compared with comprehensive laboratory measurements of flow velocity and sediment concentration under both symmetrical and asymmetrical oscillatory sheet flows from a large-scale water tunnel. Good agreements between the model results and measurements were achieved and the results demonstrated that the model is capable of reproducing detailed characteristics of sediment entrainment process in the sheet flow regime. The comparisons also revealed the fact that the concentration peaks at flow reversal is associated with the strong vertical sediment transport flux in the pickup layer, which has been widely observed in many laboratory experiments. The effects of flow reversal events on total sediment transport were also discussed. [Copyright &y& Elsevier]

Abstract: A large number of studies have been done dealing with sinusoidal wave boundary layers in the past. However, ocean waves often have a strong asymmetric shape especially in shallow water, and net of sediment movement occurs. It is envisaged that bottom shear stress and sediment transport behaviors influenced by the effect of asymmetry are different from those in sinusoidal waves. Characteristics of the turbulent boundary layer under breaking waves (saw-tooth) are investigated and described through both laboratory and numerical experiments. A new calculation method for bottom shear stress based on velocity and acceleration terms, theoretical phase difference, φ and the acceleration coefficient, a c expressing the wave skew-ness effect for saw-tooth waves is proposed. The acceleration coefficient was determined empirically from both experimental and baseline k–ω model results. The new calculation has shown better agreement with the experimental data along a wave cycle for all saw-tooth wave cases compared by other existing methods. It was further applied into sediment transport rate calculation induced by skew waves. Sediment transport rate was formulated by using the existing sheet flow sediment transport rate data under skew waves by Watanabe and Sato [Watanabe, A. and Sato, S., 2004. A sheet-flow transport rate formula for asymmetric, forward-leaning waves and currents. Proc. of 29th ICCE, ASCE, pp. 1703–1714.]. Moreover, the characteristics of the net sediment transport were also examined and a good agreement between the proposed method and experimental data has been found. [Copyright &y& Elsevier]

Abstract: Sedflux 2.0 is the newest version of the Sedflux basin-filling model. Sedflux 2.0 provides a framework within which individual process-response models of disparate time and space resolutions communicate with one another to deliver multigrain-sized sediment load across a continental margin. Version 2.0 introduces a series of new process models, and the ability to operate in one of two modes to track the evolution of stratigraphy in either two or three dimensions. Additions to the 2D mode include the addition of models that simulate (1) erosion and deposition of sediment along a riverbed, (2) cross-shore transport due to ocean waves, and (3) turbidity currents and hyperpycnal flows. New processes in the 3D mode include (1) river channel avulsion, (2) two-dimensional diffusion due to ocean storms, and (3) two-dimensional flexure due to sediment loading. The spatial resolution of the architecture is typically 1–25cm in the vertical and 10–100m in the horizontal when operating in 2D mode. In 3D mode, the horizontal resolution usually extends to kilometers. In addition to fixed time steps (from days to hundreds of years), Sedflux 2.0 offers event-based time stepping as a way to conduct long-term simulations while still modeling low-frequency but high-energy events. [Copyright &y& Elsevier]