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This work reports a study into the possibility of using the GoogleNet neural network in the optoelectronic channel of the Data Fusion system. The search for the most accurate algorithms for detecting and recognizing unmanned aerial vehicles (UAVs) in Data Fusion systems has been carried out. The data processing scheme was selected (merging SVF state vectors and merging MF measurements), as well as the sensors and recognition models on each channel of the system. The Data Fusion model based on the Kalman Filter was chosen, integrating radar and optoelectronic channels. Mini-radars LPI-FMCW were used as a radar channel. Evaluation of the effectiveness of the selected Data Fusion channel model in UAV detection is based on the recognition accuracy. The main study is aimed at determining the possibility of using the GoogleNet neural network in the optoelectronic channel for UAV recognition under conditions of different range classes. The neural network for the recognition of drones was developed using transfer training technology. For training, validation, and testing of the GoogleNet neural network, a database has been built, and a special application has been developed in the MATLAB environment. The capabilities of the developed neural network were studied for 5 variants of the distance to the object. The detection objects were the Inspire 2, DJI Phantom 4 Pro, DJI F450, DU 1911 UAVs, not included in the training database. The UAV recognition accuracy by the neural network was 98.13 % at a distance of up to 5 m, 94.65 % at a distance of up to 20 m, 92.47 % at a distance of up to 20 m, 90.28 % at a distance of up to 100 m, and 88.76 % at a distance of up to 200 m. The average speed of UAV recognition by this method was 0.81 s., У цій роботі повідомляється про дослідження можливості використання нейронної мережі GoogleNet в оптико-електронному каналі системи Data Fusion. Проведено пошук найбільш точних алгоритмів виявлення та розпізнавання безпілотних літальних апаратів (БПЛА) в системах Data Fusion. Було обрано схему обробки даних (об’єднання векторів стану SVF та об’єднання вимірювань MF), а також датчики та моделі розпізнавання на кожному каналі системи. Була обрана модель Data Fusion на основі фільтра Калмана, яка об’єднує радіолокаційні та оптико-електронні канали. В якості радіолокаційного каналу використовувалися мінірадари LPI-FMCW. Оцінка ефективності обраної моделі каналу Data Fusion у виявленні БПЛА базується на точності розпізнавання. Основне дослідження спрямоване на визначення можливості використання нейронної мережі GoogleNet в оптико-електронному каналі розпізнавання БПЛА в умовах різних класів дальності. Нейронна мережа для розпізнавання дронів була розроблена з використанням технології трансферного навчання. Для навчання, перевірки та тестування нейронної мережі GoogleNet створено базу даних і розроблено спеціальний додаток у середовищі MATLAB. Можливості розробленої нейронної мережі досліджували для 5 варіантів відстані до об’єкта. Об’єктами виявлення були БПЛА Inspire 2, DJI Phantom 4 Pro, DJI F450, DU 1911, не включені до навчальної бази. Точність розпізнавання БПЛА нейронною мережею склала 98,13 % на відстані до 5 м, 94,65 % на відстані до 20 м, 92,47 % на відстані до 20 м, 90,28 % на відстані до 100 м, а на дистанції до 200 м – 88,76 %. Середня швидкість розпізнавання БПЛА цим методом склала 0,81 с.

Intraslope basins, or minibasins, are topographic features of the continental slope that can be filled with sediment transported by submarine flows. These deposits may contain important hydrocarbon reservoirs. Here we present results of two-dimensional numerical simulations of multiple turbidity currents entering two linked minibasins. The numerical model accounts for the non-uniformity of sediment grain size in the flow and the resulting deposit. Model results reasonably reproduce the evolution of linked minibasins illustrated in the field based “fill-and-spill” conceptual model. The conceptual model was developed for the Brazos–Trinity system from field observations. Further, simulations of two linked minibasins show that the upstream basin traps most of the coarse sediment. This material is deposited in the proximal zone of the basin and fine sediment is transported farther downslope, resulting in the formation of a weak pattern of downstream fining. Model results with different initial and boundary conditions reveal that minibasin geometry and turbidity-current characteristics are important controls on the deposit shape and grain-size distribution.

The widespread distribution of tidal creeks and channels that undertake meandering behaviour in modern coasts contrasts with their limited documentation in the fossil record, where point-bar elements arising from the interaction between a mix of both fluvial and tidal currents are mainly documented. The sedimentary products of tidal-channel bend evolution are relatively poorly known, and few studies have focused previously on specific facies models for tidal point bars present in modern settings. The present study improves understanding of tidal-channel meander bends through a multidisciplinary approach that combines analyses of historical aerial photographs, measurements of in-channel flow velocity, high-resolution facies analyses of sedimentary cores and three-dimensional architectural modelling. The studied channel bend (12 to 15 m wide and 2 to 3 m deep) drains a salt-marsh area located in the north-eastern sector of the microtidal Venice Lagoon, Italy. Historical photographs show that, during the past 77 years, the bend has translated seaward ca 15 m. Results show that the channel bend formed on a non-vegetated mud flat that was progressively colonized by vegetation. Seaward translation occurred under aggradational conditions, with an overall migration rate of 0.2 to 0.3 m/year, and was promoted by the occurrence of cohesive, poorly erodible outer bank deposits. Ebb currents are dominant, and translation of the channel bend promotes erosion and deposition along the landward and seaward side of the bar, respectively. Tidal currents show a clear asymmetry in terms of velocity distribution, and their offset pattern provides a peculiar grain-size distribution within the bar. During the flood stage, sand sedimentation occurs in the upper part of the bar, where the maximum flow velocity occurs. During the ebb stage, the bar experiences the secondary helical flow that accumulates sand at the toe of the bar. Lateral stacking of flood and ebb deposits has caused the formation of localized coarsening-upward and fining-upward sedimentary packages, respectively. This article is protected by copyright. All rights reserved.

High-resolution bathymetry, seismic reflection, and piston core data from a submarine channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above channel thalweg and/or distance from channel centerline. A 5 times decrease in bed thickness and 1–2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for submarine channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.

Large vessels are safety-critical systems where operations, performance and component availability are continuously monitored by means of multiple sensors producing large amount of data. Relevant information is preserved in Event Data Recorders that are fundamental for the reconstruction of scenarios related to serious malfunctions and incidents in technical and legal terms. By considering the state-of-the-art and two important naval accidents we evidence some issues related to the exploitation of recorded data in reconstructing the events timeline and the semantics of the scenarios. These studies motivate our proposal that aims to guarantee strong data integrity and availability of all information registered in Event Data Recorders. Our results are fundamental for the precise identification of the sequences of events and for the correct attribution of human and/or machine responsibilities.

The security of the critical infrastructure requires increasing effort. The protection must consider both: cyber-attack vectors, especially when IoT or hardware attacks are the possibility, as well as physical attack vectors, when cheap unmanned vehicles pose a threat. In such scenarios, the development of more robust and accurate systems is required. In the paper the requirement analysis and as well as demonstrator system performance is presented. Both anti-cyber-attacks tools and detection of foreign physical objects are considered. The study is illustrated with examples and trials of the SCOUT Multitech SeCurity system for intercOnnected space control groUnd staTions. The project has been selected by the Community Research and Development Information Service (CORDIS-EU) as a “promising project with a strong impact” Apart of threat assessment tools, the post incident recovery strategies are also shown. For cyber security, the system mainly relies on a combined use of misuse-based and anomaly-based intrusion detection system that allow for a prompt detection of ongoing attack. The physical protection system include various radio frequency sensors capable of tracking, imaging and identifying the targets. Although the demonstration scenario is defined for the ASI infrastructures in Matera, the SCOUT demonstrator could be easily retuned and deployed in other ground stations, given the similarity between these kinds of infrastructures.

Near-seafloor core and seismic-reflection data from the western Niger Delta continental slope document the facies, architecture, and evolution of submarine channel and intraslope submarine fan deposits. The submarine channel enters an 8 km long x 8 km wide intraslope basin, where more than 100 m of deposits form an intraslope submarine fan. Lobe deposits in the intraslope submarine fan show no significant downslope trend in sand presence or grain size, indicating that flows were bypassing sediment through the basin. This unique dataset indicates that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by traditional lobe facies models, and that thickness patterns in intraslope submarine fans do not necessarily correlate with sand presence and/or quality. Core and radiocarbon age data indicate that sand beds progressively stack southward during the late Pleistocene, resulting in the compensation of at least two lobe elements. The youngest lobe element is well characterized by core data and is sand-rich, ~ 2 km wide x 6 km long, > 1 m thick, and was deposited rapidly over ca. 4,000 yr, from 18-14 ka. Sand beds forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location and age of these two compensating lobe elements. A third compensation event would have shifted sand deposition back to the northern part of the fan, but sediment supply was interrupted by rapid sea level rise during Meltwater Pulse 1-A at ca. 14 ka, resulting in abandonment of the depositional system.

The cyber defenses of Critical Infrastructures require early detection of new threats and attacks. This includes defensive systems that are able to learn from novel attacks and to detect 0-day vulnerabilities as early as possible. Honeypots are not defensive systems based on prevention, but they still represent an effective way to gather information about attacks from the source. Nevertheless, most existing solutions operate in a stateless way. As a consequence, they are easily identified by expert attackers, and they are unable to track progress of individual attacks in large applications. We propose a novel approach that enables a so called stateful honeypot. The idea comes from the observation that a typical cyber attack to a Critical Infrastructure is carried out through multiple attempts and intrusions. Hence the main goal is to fingerprint each attacker by observing and registering his adopted methods, tools and actions. Once identified, the adversary is redirected to his specific environment that preserves the history of his previous operations including the installation of rootkits or backdoors. The proposed solution paves the way to a more effective generation of honeypots that are necessary to face the augmented complexity of cyber attacks.

Meandering channel networks exert a fundamental control on hydrodynamic and morphodynamic processes within tidal landscapes. The planform of tidal meanders develops through erosional and depositional processes, which occur along the outer and inner bank of the bend, respectively. The present study describes the internal architecture and morphodynamic evolution of a tidal meander bend in the Venice Lagoon (Italy), by integrating aerial photographs, bathymetric field surveys, three-dimensional high-resolution geophysical investigations, sedimentary cores and numerical modeling. We find that the evolution of tidal channels is punctuated by abrupt changes in channel dynamics, which are triggered here by changes in tidal asymmetry and increase in water and sediment discharge from lateral tributaries. Our results suggest that dynamics at a specific meander can be dependent on events that happen elsewhere in the system, and meandering patterns in the tidal landscape can retain the signatures of processes acting at larger spatial scales.

Knickpoints often form in bedrock rivers in response to base-level lowering. These knickpoints can migrate upstream without dissipating. In the case of alluvial rivers, an impulsive lowering of base level due to, for example, a fault associated with an earthquake or dam removal commonly produces smooth, upstream-progressing degradation; the knickpoint associated with suddenly lowered base level quickly dissipates. Here, however, we use experiments to demonstrate that under conditions of Froude-supercritical flow over an alluvial bed, an instantaneous drop in base level can lead to the formation of upstream-migrating knickpoints that do not dissipate. The base-level fall can generate a single knickpoint, or multiple knickpoints. Multiple knickpoints take the form of cyclic steps, that is, trains of upstream-migrating bedforms, each bounded by a hydraulic jump upstream and downstream. In our experiments, trains of knickpoints were transient, eventually migrating out of the alluvial reach as the bed evolved to a new equilibrium state regulated with lowered base level. Thus the allogenic perturbation of base-level fall can trigger the autogenic generation of multiple knickpoints which are sustained until the alluvial reach recovers a graded state., Earth Surface Dynamics, 2(1), pp.271-278; 2014

A series of large-scale experiments on nonchannelized, depositional turbidity currents show the evolution and complex stratigraphy of channel-lobe systems developed updip and downdip of a break in slope. Two different sets of experimental turbidity currents with different sediment concentrations were run. The results provided a comparative picture of the gross structure of the fans, with information on their surfaces, growth sequences, and times of activity of the incised channels and lobed features. In particular, data analysis focused on: (a) velocity and suspended-sediment concentration of the flows themselves; (b) time and spatial sequences of channel and lobe construction and modification, and (c) spatial trends in grain-size distribution along the deposit. Significantly, the floor geometry employed in this study allowed investigation of adjustments in deep-sea fan deposition associated with natural changes in bed slope. We show here that the break in slope played a very important role in governing channel aggradation and lobe architecture over the deposit. More specifically, the slope break tended to break up the formation of long channels and enhance the formation of lobate features. A comparison with field submarine lobe analogs demonstrates that the morphodynamics and stratigraphy associated with lobed fans can indeed be modeled, within limits, at laboratory scale. Fil: Fernandez, Rocio Luz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Cantelli, Alessandro. Shell International Exploration and Production; Estados Unidos Fil: Pirmez, Carlos. Shell International Exploration and Production; Estados Unidos. Shell International Exploration and Production; Países Bajos Fil: Sequeiros, Octavio. Shell International Exploration and Production; Países Bajos Fil: Parker, Gary. University of Illinois at Urbana; Estados Unidos

Active and relic channels with extensive levees are common on the seafloor adjacent to the continental margin. Exponential, power-law, and logarithmic functions have been proposed by others to describe the lateral thickness decay of submarine levees. In the present study, experiments have been conducted to study submarine levee growth by flow stripping at a channel bend. Various functions have been fitted to the data. The results show that a third-order polynomial function best describes the levee thickness in the cross-stream direction near a submarine channel bend. Generalized model coefficients are derived as functions of deposit thickness adjacent to the channel bank. The model is applied to experimental data obtained by others as well as levee shapes derived from seismic data. In both cases, satisfactory agreements are found. The proposed model can be a useful tool for stratigraphic modeling of submarine channel–levee systems and fill gaps in field data.

[1] Density underflows in general and turbidity currents in particular differ from rivers in that their governing equations do not allow a steady, streamwise uniform “normal” solution. This is due to the fact that density underflows entrain ambient fluid, thus creating a tendency for underflow discharge to increase downstream. Recently, however, a simplified configuration known as the “turbidity current with a roof” (TCR) has been proposed. The artifice of a roof allows for steady, uniform solutions for flows driven solely by gravity acting on suspended sediment. A recent application of direct numerical simulation (DNS) of the Navier-Stokes equations by Cantero et al. (2009) has revealed that increasing dimensionless sediment fall velocity increases flow stratification, resulting in a damping of the turbulence. When the dimensionless fall velocity is increased beyond a threshold value, near-bed turbulence collapses. Here we use the DNS results as a means of testing the ability of three Reynolds-averaged Navier-Stokes (RANS) models of turbulent flow to capture stratification effects in the TCR. Results showed that the Mellor-Yamada and quasi-equilibrium k-ϵ models are able to adequately capture the characteristics of the flow under conditions of relatively modest stratification, whereas the standard k-ϵ model is a relatively poor predictor of turbulence characteristics. As stratification strengthens, however, the deviation of all RANS models from the DNS results increases. All are incapable of predicting the collapse of near-bed turbulence predicted by DNS under conditions of strong stratification. This deficiency is likely due to the inability of RANS models to replace viscous dissipation of turbulent energy with transfer to internal waves under conditions of strong stratification. Within the limits of modest stratification, the quasi-equilibrium k-ϵ model is used to derive predictors of flow which can be incorporated into simpler, layer-averaged models of turbidity currents.

Turbidity currents traversing canyon-fan systems flow over bed slopes that decrease in the downstream direction. This slope decrease eventually causes turbidity currents to decelerate and enter a net-depositional mode. When the slope decrease is relatively rapid in the downstream direction, the turbidity current undergoes a concomitantly rapid and substantial transition. Similar conditions are found when turbidity currents debouch to fan systems with loss of lateral confinement. In this work a simplified approach to perform direct numerical simulation (DNS) of continuous turbidity currents undergoing slope breaks and loss of lateral confinement is presented and applied to study turbulence modulation in the flow. The presence of settling sediment particles breaks the top-bottom symmetry of the flow, with a tendency to self-stratify. This self-stratification damps turbulence, particularly near the bottom wall, affecting substantially the flow?s ability to transport sediment in suspension. This work reports results on two different situations: turbidity currents driven by fine and coarser sediment flowing through a decreasing slope. In the case of fine sediment, after the reduction in the slope of the channel, the flow remains turbulent with only a modest influence on turbulence statistics. In the case of coarse sediments, after the change in slope, turbulence is totally suppressed. Fil: Cantero, Mariano Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Balachandar, S.. University of Florida; Estados Unidos Fil: Cantelli, Alessandro. Shell International Exploration And Production; Estados Unidos Fil: Parker, Gary. University Of Illinois At Urbana; Estados Unidos

Submarine channels with intricate meandering patterns and extensive levees are recognized as products of density-driven flows known as turbidity currents. Compared to the fluvial meandering channels, understanding of the flow and morphodynamics of submarine channels is limited. In this paper, we present experimental results on the morphodynamic and stratigraphic evolution of a submarine channel from sedimentation due to the passage of successive flow events. A pre-formed sinuous channel with multiple bends, a trapezoidal cross section, and an initial thalweg slope of 0.43° was emplaced in a large tank. A total of 29 runs, each lasting an hour, were made by releasing heavier fluids containing salt and silica powder at a constant rate in the tank filled with fresh water. The overbank flow was restricted to curvature-induced flow stripping. The following observations were made from the experimental measurements; (i) asymmetric channel cross sections developed due to higher deposition rates on the outer bank of the channel bends, (ii) an apron or sediment wedge with overlain bedforms appeared near the channel entrance that prograded and aggraded with successive runs, (iii) overbank flow due to flow stripping at bend apices resulted in lobe-shaped deposits, (iv) a higher concentration of solute resulted in flow confinement, and (v) the flow velocity during later runs increased due to channel narrowing and steepening of the gradient.

A three-dimensional unsteady numerical model is applied to simulate turbidity currents in deep submarine canyons located on the continental slope of the Niger Delta. In one of the few attempts to compare field core data to numerical simulations, we conduct several high resolution flow simulations with various boundary conditions to predict the grain size and deposition rates and compare the results to grain size and bed thickness from 22 piston cores collected at different elevations above the canyon thalweg. The model solves the Reynolds-averaged Navier–Stokes equations (RANS), the Mellor–Yamada turbulence closure equations, and the sediment conservation equations for different grain size classes. The bed evolution is modeled using the Exner equation of sediment conservation allowing adjustment of the numerical grid due to bed level changes caused by sediment entrainment/deposition during each time step. The simulated flow fields suggest that turbidity current dynamics is strongly controlled by the seafloor topography. Simulated mean bed thickness and grain size show trends where values of bed thickness and grain size are fining upwards with the elevation above the channel thalweg.

Submarine turbidity currents are controlled by gravity acting on suspended sediments that pull water downslope along with them 1 . In addition to suspended sediments, turbidity currents also transport sediments at the base of the flow 2 , which causes the reorganization of basal sediments prior to the settling of suspended grains 3‐6 . However, as turbidity currents reach areas with minimal slope, they cross a fall-velocity threshold beyond which the suspended sediments begin to stratify the flow. This process extinguishes the turbulence near the bed 7,8 . Here we use direct numerical simulation of turbidity currents to show that this extinction of turbulence eliminates the ability of the flow to re-entrain sediment and rework the sediment at the base of the flow. Our simulations indicate that deposits from flows without basal reworking should lack internal structures such as laminations. Under appropriate conditions, then, sustained delivery of fine sediments will therefore result in the emplacement of massive turbidites. We suggest that this mechanism can explain field observations of massive deposits 9 that were emplaced gradually by dilute but powerful turbidity currents. We also conclude that turbulence in submarine turbidity currents is more fragile than river systems, and more sensitive to damping by the stratification of suspended sediment in the flow. Turbiditesareoftencharacterizedintermsofcompleteorpartial manifestations of the Bouma sequence 10 . Units Ta to Te in Fig. 1a correspond to a single flow event, with flow waning from bottom to top. Intervals Ta and Tb, tend to be sand. Interval Tb has parallel laminations, indicating bedload reworking as sediment settles 3 . Interval Ta is ‘massive’, that is, lacking sedimentary structures. Massive deep-sea turbidites are prominent features of channelized and unchannelized submarine fans. They are enigmatic in that they show little or none of the internal structure used to interpret emplacement mechanisms. Parallel laminations are seen in fluvial deposits as well as turbidites, and have been reproduced in the laboratory 36 . Their formation is due to the organization of sand grains into streaks according to size and orientation by bedload. Mechanisms for the emplacement of massive turbidites are more speculative. These units are common in the ancient rock record of deep-water deposits, as well as in deeper parts of modern continental margins. Individual event beds can be up to metres in thickness (Fig. 1b), and extend for tens to hundreds

The formative mechanisms of many geologic features attributed to the passage of turbidity currents are still obscure due to the difficulties in documenting the dynamics of turbidity currents in the field. Submarine channels and lobes have been extensively documented using seismic tools and outcrops. The actual morphodynamics of their emplacement remain, however, only poorly understood. In this paper we present experimental research that documents the morphodynamic and stratigraphic evolution of self-channelized subaqueous fans emplaced by turbidity currents. A large-scale facility is used to document the fan structure and internal stratigraphy that developed after repeated flow events. The fan surface tended to prograde and aggrade from event to event. Within this general pattern, the experiments exhibited the formation, migration, and abandonment of well-defined depocenters that tended to stack compensationally. These depocenters were typically characterized by one or more channels bounded by levees. The deposits of successive runs showed a tendency to cyclically expand–contract in the strike direction, and extend–backstep in the dip direction. The overall pattern of grain-size variation consisted of downstream fining. The sediment in the channels, however, tended to be coarser than in the levees bounding it. As the fan evolved from flow event to flow event, successively more of the sediment fed in bypassed the platform on which it developed. The evolution of morphologic and stratigraphic patterns observed in the experiments shows several key similarities with channelized fans at field scale.

Channel-levee systems are frequently interpreted as having a long history of cut-and-fill by channel-shaped features of different scales. Results from a simple geometric model based on a centerline migration algorithm combined with a vertical channel trajectory show that an incising-to-aggrading trajectory of a single channel can produce realistic morphologies similar to systems observed on the seafloor and subsurface, including features such as a basal erosional surface, coeval inner and outer levees, internal erosional boundaries, and terraces draped by inner levee deposits. Channel migration results in composite erosional surfaces that are distinct from topographic surfaces, and their formation does not require larger than usual erosional flows. Many submarine channels interpreted as underfit were probably carved by flows similar to the ones that eroded and deposited the entire channel system. We suggest that the features of most submarine channel-levee systems do not require large temporal variations in flow magnitude but can be explained by a simpler model whereby incision, migration and aggradation of a single channel form over time results in an apparently complex system.

Incised valleys are critical stratigraphic features for unraveling long-term Earth-surface processes and depositional history, and commonly exhibit stratigraphic attributes that make them desirable fluid reservoirs. While there is much descriptive documentation on architecture of incised-valley fills and paleoenvironmental regimes, relatively little work has focused on quantitative modeling of the dynamics of incised-valley evolution. Here we use well-constrained observations of incised valleys in experiments and the field to explore controls on valley geometry and develop a simple valley model to quantify the primary dynamics of incised-valley evolution. We document a strong tendency for incised valleys to widen downstream independent of the details of the relative base-level curve or initial surface profile, due primarily to the effects of increased sediment flux. This is in general agreement with measurements of experimental and natural incised valleys, though the degree of widening is less in natural systems due to greater sidewall resistance and smaller water discharge (relative to valley size). A first-order model of incised-valley evolution highlights three important trends: valley aggradation and widening; valley incision and widening; and valley incision and narrowing. The model reproduces the primary geometric responses to valley formation as measured from experiments: valley width and depth both increase in response to increases in (1) local relative base-level fall and (2) the initial offshore water depth. Finally, we generalize the first-order controls on valley geometry via dimensional analysis to show that long-term valley narrowing is not readily produced from relative base-level fall alone.

As a river-carrying sediment mixture aggrade, it creates a stratigraphic signature that records this evolution. This stratigraphy is characterized by the vertical/horizontal variation of substrate grain size distribution. If a river degrades, it mines this stratigraphy, and transfers the sediment so accessed farther downstream. Although several numerical models tracking the creation/consumption of stratigraphy are available, none has been tested against experiments under plane bed regime conditions. Here nine physical experiments modelling the creation/consumption of stratigraphy are described. These are compared with nine corresponding numerical experiments using a model that tracks stratigraphy. The results justify the numerical model, and in particular the scheme to track stratigraphy. This scheme can be used at field scale to characterize e.g. the response of a river to an increased/decreased sediment supply. The numerical model shows a discrepancy with the experiments, however, whenever a distinct de...

This paper reports on a laboratory study that aims to reproduce a tidal channel network, in order to enhance the understanding of the morphodynamic evolution of the channel characteristics as the network expands and finally reaches equilibrium. A high-resolution laser system scanned the bed topography at different time steps creating multiple digital elevation models of the channel network. Two hundred and seventy individual channel segments are analyzed and cross-correlated in terms of their width, depth and length. The laboratory results show positive linear correlations between depth and width as well as between length and width of channel segments of the network configuration at final equilibrium. In a downstream direction, channels appear to widen more than they deepen, indirectly a sign that discharge has a stronger control on channel width than on depth. In contrast to fluvial drainage networks that commonly display fractal and scale-invariant behavior, the geometric properties of the experimental tidal creek network shows scale dependence. Channel attributes exhibit consistent patterns of exponentially decreasing abundance, with increasing creek length, depth and width. The nature of the observed exponential distributions within creek attributes (width, depth, length) allows for statistical predictability of relative creek attribute dimensions downstream and through time. Copyright © 2010 John Wiley & Sons, Ltd.

The interaction of flow with an erodible bed in alluvial rivers and deep-sea channels gives rise to a wide range of self-formed morphologies, including channels, ripples, dunes, antidunes, alternate bars, multiple-row bars, meandering and braiding. As the flow is invariably turbulent in field manifestations of these morphologies, there has been a tendency to assume that turbulence is necessary for them to form. While turbulence undoubtedly has an important influence when it is present, it is not necessary for any of these features. Indeed, all of these features can be formed by the morphodynamic interaction of purely laminar or nearly laminar flow with an erodible bed. This paper provides a survey and synthesis of a wide range of laminar or near-laminar flow analogues of morphologies observed in the field. Laminar-flow analogues of turbulent-flow morphologies cannot and should not be expected to satisfy dynamic similarity in terms of all relevant dimensionless parameters. What is of more significance is the convergence of the underlying physics. It is illustrated in this paper that many existing theoretical frameworks for the explanation of turbulent-flow morphodynamics require only relatively minor modification in order to adapt them to laminar flows.

A model of modified Bingham fluid is used to investigate uniform mudflows in narrow cross sections of the kind typical of hillslope incisions. The problem is tackled both numerically and experimentally. Experiments were performed using carboxymethylcellulose, a shear thinning fluid whose rheological behavior can be interpreted by a modified Bingham fluid model. For narrow rectangular, trapezoidal, and triangular cross sections, the capability to flow has been expressed by a general relationship that defines a dimensionless coefficient (f) as a function of two dimensionless parameters: the Bingham number and an aspect ratio of the channel. We also derive plots for the critical Bingham number for incipient flow of modified Bingham fluids as a function of the aspect ratio of the channel. The present calculations and the experimental results demonstrate that the narrow character of the channel as well as its shape strongly affect the flow conductance and the critical value of the Bingham number.

Deposits of turbidity currents induced by subaqueous volcanic eruptions are increasingly recognized in settings ranging from lakes to the deep sea. These “eruption‐fed density currents” have high current temperatures and low‐density particles, which affect current dynamics and deposit features. Field data indicate that deposit thickness and grain size decrease downflow at a changing rate. This trend is similar for deposits of noneruptive turbidity currents, but with volcanic activity, the deposits often exhibit a break in slope of the profile of deposit thickness and grain size distribution. Here we present laboratory results on density currents that address the effects of variations in grain density and water temperature on flow properties and depositional processes. Parallel runs were performed under identical flow conditions using quartz sand and pyroclastic sediment. Each grain type was used in one series of runs in which a hot density current enters a cold environment and one series in which...

Laboratory studies are commonly used to improve our understanding of physical processes that are very difficult or almost impossible to investigate in their natural settings. Erosion impacts on large-scale submarine morphology are good examples. We present the results of a preliminary laboratory study focused on submarine knickpoints, which are bed depressions bounded by steep walls upstream and a gentle slope downstream, originated by the passage of a turbidity current over an erodible bed. Eight experiments using different materials were performed in a facility capable of running continuous turbidity currents. The sediments used in these experiments were: kaolin clay, two different silica flours, and fine sand. Silica flours and fine sand were each used as single sediments in four experiments. The other four experiments were performed using a mixture of these sediment types. The bed deposit was formed by a net-depositional turbidity current. The total sediment concentration by volume in the experiments was 5% in one experiment and 10% in the other seven. The discharge ranged from 0.009 to 0.055 l/s. Each experiment started with an initial slope in the channel bed of 15% (8.53°). As the experiments progressed, the bed deposit inside the flume built up. Knickpoints were observed in four of the eight experiments. Knickpoints formed under a wide variety of conditions; they were found when one material or a combination of materials was used in the tests and when the turbidity current was partially and totally distributed over the channel. Measured width of the bed depressions ranged from 2 to 4 cm, length ranged from 3 to 6 cm, and the estimated maximum depth was close to 0.5 cm. Calculations of the speed of upstream migration indicate values in the vicinity of 0.5 mm/s. Upscaled geometric dimensions based on these laboratory experiments fairly reproduce bed depressions observed on a field scale in earlier studies. These laboratory observations suggest that the body of the turbidity current is responsible for the upstream migration of the knickpoint.

Some of the current methods of geological modeling cannot imitate the order and complexity that is observed in nature. It's been recognized among the geoscientist community how a process-based modelling may facilitate a step change in reservoir building capabilities. The advantage in decoupling the grid design from the facies distribution poses a tremendous opportunity to close the gap between the static and dynamic reservoir model. A major advantage is capturing fine-scale heterogeneities (shale drape, amalgamation, etc) which are hard to capture with pixel-based techniques. The goal of process-based geological modeling is to simulate that order by generating rules. These rules make possible to create high-fidelity 3D geological models representing more realistic depositional and stratigraphic events than those that are randomly generated using conventional geostatistical techniques. In this paper we illustrate the use of surface-based modeling within a submarine-turbiditic environment and the procedure followed to deliver a dynamic model conditioned to production data. The procedure follows development of physics-based methods and rule-base stacking of events to reconcile geological complexities and uncertainties with well performance. We'll present a process combining Design of Experiments and gradient-based techniques to assimilate production data. The method generates complex geometries comparable to those observed in high resolution near-surface seismic datasets. The case under consideration is an oil field offshore Brazil developed with horizontal wells and state of the art surveillance. The proposed workflow has delivered a simulation model that has achieved a good history match to production data in the form of water cuts and pressures.

The passage of turbidity currents over submarine fans often results in intense channelization. The channels are typically bounded by levees, and they vary from mildly to strongly meandering. The process of self-channelization remains, however, somewhat obscure. Preliminary experiments reported here demonstrate for the first time that self-channelization of subaqueous fans by turbidity currents can be reproduced at laboratory scale. The same experiments also illustrate self-channelization by dilute mudflows. The resulting weakly sinuous channels can be predominantly depositional, predominantly erosional, or some combination of the two. The channels can elongate to the length of the entire reach available for their formation. They can show both gradual shift and avulsion. A necessary condition for the formation of intricate channelization in the laboratory experiments appears to be a turbidity current that is insufficient to cover the entire area of the fan at any given time. Loose field analogs to the experimental channelized fans (i.e., analogs that are imprecise but contain many similarities) can often be found at the distal end of submarine fans. Two possible examples are cited, one from the Pochnoi system, Bering Sea, and one from the Gulf of Cadiz.

[1] In the present work, we use a three-dimensional numerical model to simulate turbidity currents in a large-scale submarine environment. The model solves the Reynolds Averaged Navier–Stokes equations, along with a two-equation turbulence closure model, the sediment conservation equations for multiple grain-size classes and the Exner equation of bed sediment conservation. Four different grain-size classes (30, 64, 125, and 250μm) are considered. The model is applied to a modern seafloor environment in the continental slope of the Niger Delta where bathymetric data and seven piston cores were collected in and around a sinuous channel. Detailed analyses show the grain-size distribution for different beds within each core. Since the flow events responsible for the formation of this modern depository are unknown, we perform simulations with different inflow conditions in order to match the grain-size data. The model realistically predicts the flow field and its evolution over the complex topography and shows the spatial distribution of different grain-size classes. A strong lateral flow from the inner to the outer bank is observed at the bends of the low-relief channel. From the computed deposition rate, we obtain the fraction of each grain-size class at the core locations and compareD50 and D90 predicted from the model with the core data. The discrete values predicted from the model fall within the range of D50 and D90observed in different beds in the cores. The results demonstrates that a 3-D numerical model can be a useful tool for understanding the distribution pattern, thickness, and grain size of the turbidity currents and their deposits at the field scale and can help constrain the variabilities of reservoir architecture.

[1] This study focuses on a numerical model of turbidity currents with reversing buoyancy, i.e., flows that are rendered heavier than the ambient water due to the presence of suspended sediment but that as sedimentation progresses become lighter than the ambient water due to a difference in temperature or salinity. The flows considered here may be either pulsed events or continuous flows. It is well known that these flows are subject to a buoyancy reversal. Flows issuing upstream with a sufficient load of suspended sediment are heavier than the ambient water and thus form a bottom underflow. As sediment deposits in the downstream direction, however, the flow gradually loses its density excess, and eventually reverses its buoyancy, detaching upward from the bed. The nature of the sediment deposit emplaced near and downstream of the point of lofting can thus differ significantly from that emplaced upstream. A novel aspect of the work reported here is a mechanistic description of the tendency for the current to sort in the downstream direction a sediment mixture containing a wide range of grain sizes. The numerical model, which is based in the κ − ɛ closure for turbulence, is verified with a unique set of experimental data intended to model sediment sorting associated with turbidity currents created by explosive undersea eruptions. Both cases with nonreversing buoyancy and reversing buoyancy are considered. As such, the model not only provides a detailed description of flows with reversing buoyancy, but also provides a tool to aid sedimentologists in back-calculating the flow emplaced by turbidity currents from the downstream variation in the grain size distribution of the bed deposit.

[1] In this work we present direct numerical simulations (DNS) of sediment-laden channel flows. In contrast to previous studies, where the flow has been driven by a constant, uniform pressure gradient, our flows are driven by the excess density imposed by suspended sediment. This configuration provides a simplified model of a turbidity current and is thus called the turbidity current with a roof configuration. Our calculations elucidate with DNS for the first time several fascinating features of sediment-laden flows, which may be summarized as follows. First, the presence of sediment breaks the symmetry of the flow because of a tendency to self-stratify. More specifically, this self-stratification is manifested in terms of a Reynolds-averaged suspended sediment concentration that declines in the upward normal direction and a Reynolds-averaged velocity profile with a maximum that is below the channel centerline. Second, this self-stratification damps the turbulence, particularly near the bottom wall. Two regimes are observed, one in which the flow remains turbulent but the level of turbulence is reduced and another in which the flow relaminarizes in a region near the bottom wall, i.e., bed. Third, the analysis allows the determination of a criterion for the break between these two regimes in terms of an appropriately defined dimensionless settling velocity. The results provide guidance for the improvement of Reynolds-averaged closures for turbulent flow in regard to stratification effects. Although the analysis reported here is not performed at the scale of large oceanic turbidity currents, which have sufficiently large Reynolds numbers to be inaccessible via DNS at this time, the implication of flow relaminarization is of considerable importance. Even a swift oceanic turbidity current which at some point crosses the threshold into the regime of relaminarization may lose the capacity to reentrain sediment that settles on the bed and thus may quickly die as it loses its driving force.

[1] Intricately meandering channels of various scales constitute a major morphological feature of the submarine slope and fan systems. These channels act as conduits of density-driven gravity underflows and in turn are shaped by these underflows. The relationship between channel curvature and the dynamics of sediment-laden underflows commonly known as turbidity current has been an enigma, and recently, a subject of controversy. This contribution unravels the flow field of turbidity current at submarine channel bends captured from large scale laboratory experiments. The experimental results show that a mildly sloping channel bank greatly enhances the tilt of the turbidity current-ambient water interface, so much so that the current completely separates from the convex or the inside bank. We also show that irrespective of the shape of the channel cross section, two cells of helical flow appear in confined submarine bend flow. The near-bed cell has a circulation pattern similar to that observed in fluvial channels; the other cell has an opposite sense of rotation. If, on the other hand, a portion of the flow detaches from the body of the current and spills to the concave or outside overbank area, the upper circulation cell becomes suppressed by the resulting lateral convection.

[1] This paper is devoted to a morphodynamic model of incision into a reservoir deposit driven by partial or total removal of the associated dam. The model considers the erosional processes upstream of the position of the former dam, rather then the deposition that occurs downstream. A theory is developed to predict the evolution of both the width and depth of the incisional channel that develops as erosion progresses. The theory is implemented in a numerical model, which is tested against and verified with flume experiments on sudden, complete removal of a dam. In these experiments a channel of a given initial width is allowed to freely incise into a noncohesive reservoir deposit after sudden dam removal. These experiments show a phenomenon that we refer to as “erosional narrowing.” That is, as a channel of a given initial width rapidly incises into the deposit, it can become narrower. As the rate of incision slows, this short period of rapid narrowing is followed by a longer period of widening. In the model the incisional channel is abstracted to a trapezoidal channel with well-defined bed and bank regions, both of which are allowed to erode. Balance between bed and bank erosion plays a key role in the morphodynamics of the channel. More specifically, rapid erosion of the bed can cause the channel to narrow even as bank erosion progresses. As the rate of bed erosion slows, bank erosion causes channel widening. This observed pattern is explained in the context of a theoretical model tested against the experiments.

[1] A one-dimensional mathematical model of mudflow dynamics is formulated assuming mud to behave rheologically as a Herschel-Bulkley fluid. Novel features of the present contribution regard the propagation of mudflows over a curvilinear bottom. A set of nonlinear partial differential equations is found to govern the unsteady, nonuniform flow of such fluids. Following the approach of Huang and Garcia (1998), a depth-integrated form of the continuity equation and shear-integrated and plug-integrated forms of the momentum equations are derived. A perturbation analysis is also carried out under the assumption of “slender” flow. The leading-order problem takes the form of a kinematic wave equation. One straightforward application of this simplified model is the evaluation of the maximum run-out extension of a mud which flows over a bed with a variable topography. This solution is obtained by solving the steady state problem. Dynamics information are obtained by numerically solving the hyperbolic conservative equation by means of a free oscillating numerical method. The effects of bottom curvature either on the equilibrium solution or mudflow dynamics are analyzed. Experiments are also performed releasing a given volume of kaoline and water mixture from a reservoir into both a constant slope and an upward concave channel. Comparisons between the numerical solution and the experimental data are generally satisfactory, though suggesting limitations typical of any approach that neglects convective accelerations and assumes gradually varied flow.