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Abstract Channels with parabola-shaped cross-section are widely used in water conservancy and hydropower engineering, agricultural irrigation and drainage engineering, so it is necessary to determine the accurate normal depth values for design of open channels, operation management and analysis of gradually varied flow. However, the governing equations are nonintegrable for cubic and semi-quintic parabola-shaped channels in terms of the wetted perimeters. In this study, the Simpson's numerical integral method is introduced to approximate the two nonintegrable wetted perimeters for cubic and semi-quintic parabola-shaped channels which can meet the requirements of engineering design well in the commonly using range of engineering. Subsequently, the approximate wetted perimeters are substituted into the uniform flow equation and the uniform flow equation deforms optimal model identically. The optimal model parameters are determined by the 1stOpt software based on Marquardt algorithm and two explicit calculation formulas for the normal depths of cubic and semi-quintic channels are proposed. At the same time, two direct calculation formulas for normal depths of semi-cubic and quadratic parabola-shaped channels are presented as well. Four sets of formulas for normal depths of parabola-shaped channels are presented and their maximum relative errors are 0.52%, − 0.37%, − 0.22% and 0.57%, respectively, which have wide range of application, high precision, concise form and can provide some better guidance for engineering design and operation management. Highlights • The Simpson's numerical integral method is firstly introduced to approximate the two nonintegrable wetted perimeters for cubic and semi-quintic parabola-shaped channels accurately. • Two explicit formulae for normal depths of cubic and semi-quintic parabola-shaped channels are obtained with high precision, wide range of application firstly. • Two explicit formulae for normal depths of semi-cubic and quadratic parabola-shaped channels are obtained with higher precision, wider range of application than those of former studies. [ABSTRACT FROM AUTHOR]

Abstract A Two-stage compound channel section is commonly used in ecological channel design. This paper presents the geometric properties of the compound section and the formulae for calculating the cross-section area, wetted perimeter are obtained. Then, the explicit equations of the best hydraulic section for design are derived. Results show the best width-depth ratio of the compound section is related to some geometric parameters. Furthermore, this type of best hydraulic section is compared with the rectangular and trapezoidal sections. Results indicate that the cross-section area and wetted perimeter are less than those of rectangular and trapezoidal sections for a given flow discharge when the ratios of the compound section's roughness coefficient to those of rectangular and trapezoidal sections are less than 1.017 and 0.855, respectively. It means less lining and excavation cost is required for construction. Highlights • Geometric properties of the two-stage compound channel section are presented. • Formulae for calculating the cross-section area, wetted perimeter of the compound section are obtained. • The explicit equations of the best hydraulic section of the compound section for design are derived. • This type of best hydraulic section is compared with the rectangular and trapezoidal sections. • Quantitative values are obtained used to determine the more efficient section of the compound section. [ABSTRACT FROM AUTHOR]

Highlights • A new approach is applied to estimate the bank profile shape of a stable channel. • Most influential parameters on channel geometry are studied. • A wide-ranging field dataset are used to evaluate the models. • An explicit expression for practical engineering is provided. • The proposed method can be used as an alternative in practical applications. Abstract Accurate prediction of the long-term average dimensions of alluvial stable channels is a significant problem in river engineering. The goal of this research is to investigate the effect of flow discharge (Q), mean sediment size (d 50) and Shields parameter (τ∗) on the stable channel dimensions by employing non-linear regression (NLR) and two Artificial Intelligence (AI) methods, including: Generalized Structure of Group Method of Data Handling (GS-GMDH) neural network and Gene Expression Programming (GEP). Discharge, grain size and Shields parameter from 85 gaging stations situated in three stable Iranian rivers were used as input data for the three methods to estimate the water-surface width (W), average flow depth (D) and longitudinal slope (S) of the rivers. Based on the results, it was found that the GS-GMDH produced more accurate results for simulating the channel width with a Mean Absolute Relative Error (MARE) value of 0.055; and GEP produced better estimations for channel depth and slope with MARE values of 0.035 and 0.03, respectively. Furthermore, by employing Artificial Intelligence (AI) methods (GS-GMDH and GEP), the RMSE values decreased by 22%, 25% and 75% in predicting width, depth, and slope, respectively, compared to NLR method. The overall results showed that the AI methods generally produced better estimations than the non-linear regression method. To determine the effect of each input variable (Q, d 50 , τ∗) on the target variables (W, D, S), a sensitivity analysis comprising various combinations of input variables was conducted. Based on the results, the flow discharge had a dominant role on depth and width estimation of stable channels. In slope estimation, the most important parameter was τ∗ and then d 50 , while the discharge had a weak effect on slope prediction. In general, the Shields parameter was the most effective parameter in depth and specially slope estimation of stable channels. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • We created an intermediate complexity model for simulating channel evolution at watershed scales. • The model matches physical understanding of channel change. • It can also predict erosion processes in accordance with field data sets. • The model is useful for predicting channel evolution and answering relevant management questions. Abstract Excessive river erosion and sedimentation threatens critical infrastructure, degrades aquatic habitat, and impairs water quality. Tools for predicting the magnitude of erosion, sedimentation, and channel evolution processes are needed for effective mitigation and management. We present a new numerical model that simulates coupled river bed and bank erosion at the watershed scale. The model uses modified versions of Bagnold's sediment transport equation to simulate bed erosion and aggradation, as well as a simplified Bank Stability and Toe Erosion Model (BSTEM) to simulate bank erosion processes. The model is mechanistic and intermediate complexity, accounting for the dominant channel evolution processes while limiting data requirements. We apply the model to a generic test case of channel network response following a disturbance and the results match physical understanding of channel evolution. The model was also tested on two field data sets: below Parker Dam on the lower Colorado River and the North Fork Toutle River (NFTR) which responded dramatically to the 1980 eruption of Mount St. Helens. It accurately predicts observed channel incision and bed material coarsening on the Colorado River, as well as observations for the upstream 18 km of the NFTR watershed. The model does not include algorithms for extensive lateral migration and avulsions and therefore did not perform well in the lower NFTR where the channel migrated across a wide valley bottom. REM is parsimonious and useful for simulating network scale channel change in single thread systems responding to disturbance. [ABSTRACT FROM AUTHOR]

Abstract A channel head is the upstream-most point of concentrated water flow and sediment transport between definable banks with a longitudinally continuous channel downstream. A channel head can be a relatively diffuse feature, the identification of which is subjective, or a very discrete and prominent break in the surface associated with a headcut. As the formal start of the channel network, channel heads reflect the location of process thresholds and thus differentiate geomorphic process domains for water, solute, and sediment fluxes. Stream order derives from mapped channel networks and the accuracy of stream ordering thus depends on the accuracy of identifying channel heads and associated first-order streams. In the absence of mapped channel heads, remote methods that under- or over-estimate the contributing area necessary to form a channel head can significantly over- or under-estimate, respectively, the extent of first-order streams and erroneously estimate drainage density. This paper reviews the current state of knowledge of the processes that form channel heads, the influences on channel head stability, and the methods used to identify the location of channel heads within a landscape unit. Individual channel heads can result from distinctly different processes, including surface fluvial erosion, surface colluvial erosion, subsurface erosion, or the intersection of subsurface preferential flow with the surface. The location of any channel head over a period of years to decades and longer is best understood as an average location that can and does change through time. The magnitude of change in the location of a channel head over time periods of years to decades will reflect the disturbance regime of the hillslope and the speed with which hillslope-channel processes recover following disturbance. If channel heads form where overland flow exerts a boundary shear stress that exceeds the critical value for substrate erosion, the channel initiation threshold, C , can be expressed as the product of contributing catchment area, A , and hillslope gradient, S : AS α ≥ C. An inverse relation between source area A and local slope S is present to a greater or lesser degree across diverse regions. Substantial variability in values of A and S reflects the influence of factors such as vegetation, slope aspect, surface versus subsurface flow paths, and substrate grain size. Analyses of published data suggest that channel head locations can be predicted with reasonable accuracy where surface runoff dominates channel initiation. Subsurface processes strongly influence the locations of many channel heads, however, and the area-slope relations for these channel heads are much less consistent and predictable. The challenges of channel heads are three-fold for any given drainage basin or portion of a drainage basin: to identify their geographic location, to predict their geographic location, and to determine the relative importance of potential control variables on the multiple processes that can create channel heads. In order to effectively address these challenges, additional research is needed to predict the regional characteristics likely to result in channel heads created by predominantly surface versus subsurface flow; develop envelope curves of A-S relations for different regions; compare channel head locations predicted based on hillslope curvature versus actual channel head locations; evaluate the spatial consistency of channel heads through time; and develop A-S relations for channel heads in little studied regions, including arid and hyperarid environments, karst and permafrost terrains, and grassland and savanna environments. [ABSTRACT FROM AUTHOR]

In this paper, the thermo-hydrodynamics of Al 2 O 3 -water nanofluid in a wavy U-turn channel with hot walls is numerically investigated by means of lattice Boltzmann modeling. At first, the numerical technique is validated by simulating fluid flow in a (non-)wavy straight channel. Then, the effects of various active parameters, e.g. pressure gradient in the channel, nanoparticles volume fraction, and number of sinusoidal waves along the channel, on the flow field and heat transfer is studied. Furthermore, the thermal–hydraulic performance factor is determined to investigate whether heat transfer enhancement outweighs the greater frictional losses caused by both complex wavy wall geometry and nanoparticles. The results show that the heat transfer rises by increasing pressure gradient in the channel while drops by increasing number of waves. Also, the effect of nanoparticles volume fraction on dimensionless Nusselt number becomes more pronounced at higher pressure gradients. The results indicate that the thermal–hydraulic performance factor grows by increasing nanoparticles volume fraction or decreasing the number of waves. [ABSTRACT FROM AUTHOR]

Studying solute dispersion in channel flows is of significance for environmental and industrial applications. Two-dimensional concentration distribution for a most typical case of a point source release on the free water surface in a channel flow with bed absorption is presented by means of Chatwin’s long-time asymptotic technique. Five basic characteristics of Taylor dispersion and vertical mean concentration distribution with skewness and kurtosis modifications are also analyzed. The results reveal that bed absorption affects both the longitudinal and vertical concentration distributions and causes the contaminant cloud to concentrate in the upper layer. Additionally, the cross-sectional concentration distribution shows an asymptotic Gaussian distribution at large time which is unaffected by the bed absorption. The vertical concentration distribution is found to be nonuniform even at large time. The obtained results are essential for practical implements with strict environmental standards. [ABSTRACT FROM AUTHOR]

In this study, we report large eddy simulations of turbulent flow in a periodic compound meandering channel for three different depth conditions: one in-bank and two overbank conditions. The flow configuration corresponds to the experiments of Shiono and Muto (1998). The predicted mean streamwise velocities, mean secondary motions, velocity fluctuations, turbulent kinetic energy as well as mean flood flow angle to meandering channel are in good agreement with the experimental measurements. We have analyzed the flow structure as a function of the inundation level, with particular emphasis on the development of the secondary motions due to the interaction between the main channel and the floodplain flow. Bed shear stresses have been also estimated in the simulations. Floodplain flow has a significant impact on the flow structure leading to significantly different bed shear stress patterns within the main meandering channel. The implications of these results for natural compound meandering channels are also discussed. [ABSTRACT FROM AUTHOR]

This study uses continuous-recording load cell pressure sensors in four, high-elevation (1500–1800 m), Sierra Nevada headwater streams to collect high-temporal-resolution, bedload-movement data for investigating the channel bed movement patterns within these streams for water years 2012–2014. Data show an annual pattern where channel bed material in the thalweg starts to build up in early fall, peaks around peak snow melt, and scours back to baseline levels during hydrograph drawdown and base flow. This pattern is punctuated by disturbance and recovery of channel bed material associated with short-term storm events. A conceptual model, linking sediment sources at the channel margins to patterns of channel bed fill and scour in the thalweg, is proposed building on the results of Martin et al. (2014). The material in the thalweg represents a balance between sediment supply from the channel margins and sporadic, conveyor-belt-like downstream transport in the thalweg. The conceptual model highlights not only the importance of production and transport rates but also that seasonal connectedness between the margins and thalweg is a key sediment control, determining the accumulation rate of sediment stores at the margins and the redistribution of sediment from margins to thalweg that feeds the conveyor belt. Disturbance and recovery cycles are observed at multiple temporal scales; but long term, the channel beds are stable, suggesting that the beds act as short-term storage for sediment but are in equilibrium interannually. The feasibility of use for these sensors in forested mountain stream environments is tested. Despite a high failure rate (50%), load cell pressure sensors show potential for high-temporal-resolution bedload measurements, allowing for the collection of channel bed movement data to move beyond time-integrated change measurements — where many of the subtleties of bedload movement patterns may be missed — to continuous and/or real-time measurements. This type of high-temporal-resolution data provides insight into short-term cycles of bedload movement in high gradient, forested mountain streams. [ABSTRACT FROM AUTHOR]

This paper focuses on simulation and analysis of the Houston Ship Channel vessel traffic and operation, through a discrete event model in Arena. The model is applied to mitigate the consequences of the channel closure for constructing a new bridge over the waterway. To evaluate different closure scenarios, real world data is analyzed, and a single factor ANOVA is used to find significant vessel waiting time differences. In addition, Fisher pairwise comparison method is applied to specify the best closure alternative. The results reveal that the best closure scenario will decrease waiting time up to 70%. The model can be used for assessing the performance of the system under different decision making frameworks. [ABSTRACT FROM AUTHOR]

Experimental study on mixed convection in the entrance region of a one-side-heated narrow rectangular channel has been carried out. We have performed a series of experiments under natural circulation conditions with Re ranging from 1000 to 3000 and inclination angle ranging from 0° to 30°. Meanwhile, we conducted flow visualization experiments to identify secondary flow driven by temperature difference between the lower, heated and upper, unheated plate of the channel. It is found that thermal instability can be enhanced by increasing the inclination angle of the channel. The secondary flow induces the onset of thermal instability (OTI) while increasing in Re delays the OTI. A sudden increase of hear transfer coefficient and friction factor has been observed after the OTI. The traditional identification criteria for mixed convection are not suitable for the inclined, narrow rectangular channel with a heated lower side. However, transverse Richardson number can identify mixed convection in the channel. The experiment results, together with image data for the flow condition in the inclined narrow rectangular channel, offer valuable data to improve the engineering design of plate-type fuel assembly and similar heat exchangers. [ABSTRACT FROM AUTHOR]

The velocity distribution in natural channels is of considerable interest for streamflow measurements to obtain information on discharge and flow resistance. This study focuses on the comparison of theoretical velocity distributions based on 1) entropy theory, and 2) the two-parameter power law. The analysis identifies the correlation between the parameters of the distributions and defines their dependence on the geometric and hydraulic characteristics of the channel. Specifically, we investigate how the parameters are related to the flow resistance in terms of Manning roughness, shear velocity and water surface slope, and several formulae showing their relationships are proposed. Velocity measurements carried out in the past 20 years at Ponte Nuovo gauged section along the Tiber River, central Italy, are the basis for the analysis. [ABSTRACT FROM AUTHOR]

The present study combines numerical and experimental approaches to investigate cross flow problems in the entrance channel of a harbor. The combined numerical-experimental approach is illustrated by an application to Lanshan Port (Shandong, China) where large tidal ranges and a newly planned harbor layout may give rise to strong cross flow in the entrance channel of the planned harbor. The resulting flow field with the numerical prediction shows that the layout of newly planned harbor has a major impact on the cross flow speeds in the entrance channel. This will affect the navigation safety of ship entering or leaving the harbor. A corresponding protective scheme related to breakwaters was put forward. A series of physical model experiments under the given flow provided by the numerical approach, were conducted to design the length and crest elevation of a previously proposed breakwater. Results from a series of laboratory model tests show a significant reduction of flow velocities across the entrance channel with longer breakwater length and higher crest elevation. However, a longer or higher breakwater obviously can expand the cross flow influenced zone into the entrance channel. The acceptable breakwater length and crest elevation were determined by taking account the maximum cross flow speed and cross flow influenced zone in addition to the construction cost. [ABSTRACT FROM AUTHOR]

This paper experimentally investigates the effects of rotation, turning vane, trailing edge ejection, and channel orientation on heat transfer (HT) in a typical turbine blade three-passage internal cooling test model. The cross section of the first and second passage are rectangular with aspect ratio 1:1 (AR = 1) and 2:1 (AR = 2) respectively, while the third passage is wedged shaped with slot discharge configuration to simulate the trailing edge ejection design. The flow direction in the first passage is radial outward, after the 180° tip turn, the flow turns radial inward at the second passage. The flow finally redirected to radial outward by the 180° hub turn and discharges through the slot configuration at the third passage. Data measurements are conducted in the second and third passages (includes the hub turn regions). The first passage is not instrumented and serves as flow inlet only. The effects of rotation on the heat transfer coefficients (HTC) were investigated at rotation numbers ( Ro ) up to 0.32 and Reynolds numbers ( Re ) from 10,000 to 40,000. This study concludes that the rotating utilizes a positive and negative effect on HT on the radial inward flow leading and trailing surfaces respectively. A reverse trend is concluded for radial outward flow. Rotation also suppresses HT in the turn portion. The effect is most severe at the hub turn side wall. The effect of turning vane slightly reduces and increases HT on all interested surfaces in radial inward and outward flow passages respectively. The turning vane effect is diluted in the hub turn area under rotation. Radial outward flow (third passage) HT is substantially impacted by the channel orientation. Combine with the discharge configuration, under rotating scheme, HT levels in β = 45° is significant lower then β = 90°. Regional HTCs are correlated with rotation numbers for multi-pass rectangular smooth channel with hub turning vane and trailing edge ejection. [ABSTRACT FROM AUTHOR]

This work presents an assessment of the potential use of hydrokinetic turbines in the discharge channels of large hydroelectric power plants in Colombia. The assessment is performed at a pre-feasibility stage in order to evaluate the technical and financial potential of using hydrokinetic devices as a way to exploit kinetic energy in such channels. As a case study, two large hydropower plants were selected, one operated by a Francis turbine and the other operated by a Pelton turbine. The analysis assessed the hydraulic characteristics of the channels and the corresponding discharge flows. A prefeasibility financial analysis in an environment of uncertainty was also carried out using Monte Carlo simulation. The results show that the technology is not currently feasible for the Colombian market conditions, but the situation should be monitored in order to identify the right time for its optimal use in the future. The proposed methodology can be applied to research the feasibility of hydrokinetic energy for other kinds of applications. [ABSTRACT FROM AUTHOR]

Tidal channels with narrow constrictions are attractive sites for electricity generation due to energy dense, high velocity flow through the constricted zones. This work uses a 1D model to systematically examine the effect of constriction on channel potential (theoretical maximum power) and transport in channels connecting two large water bodies (Type I) and channels connecting a large water body to an embayment/lagoon (Type II). Type I channels showed a monotonic decrease in potential and transport with increasing constriction due to enhanced bottom drag from the resultant high velocity zone. The effect of constriction on potential and transport in Type II channels varies depending on the relative geometries of the channel and embayment. Type II channels may be geometrically modified to increase power and in some instances this would simultaneously produce a high velocity zone. The flow reduction required to achieve a channel’s potential was invariant to changes in constriction for Type I channels and also Type II channels if a “lagoon geometry factor” is less than about 4. A simple approximation for potential provided in the literature for unconstricted channels is extended for use with constricted channels and an approximation for the drag coefficient required to achieve potential is provided. [ABSTRACT FROM AUTHOR]

Due to the ringing and side-lobe interference, acoustic Doppler current profiler (ADCP) is unable to accurately capture the complete velocity profile in open channels near the water surface and channel bottom, which are usually called unmeasured areas. At present, the flow velocities through the unmeasured areas are most commonly estimated using the power law with the power set to be the default value. However, since the flows are unsteady and nonuniform in tidal reaches, the velocity distribution model and corresponding parameters will vary with the bathymetric, tide period, etc. Therefore, the most common estimation with the power law may not be suitable in tidal reaches. In this paper, a simple determination method of the best model is proposed. Firstly, the parameters in three classical velocity distribution models, which are called power law, logarithmic law and parabolic law models, are solved by least squares based on the ADCP measured velocity cells. Then, the corresponding root-mean-square error (RMSE) of each model is used for the quantitative indicator that the model with the minimum RMSE is chosen as the best model. At last, the flow velocity and discharge of the unmeasured area are estimated by the best model. The experiments carried out in the tidal reach of Yangtze Estuary showed that vertical flow velocity distribution various with the bathymetry and tide period, and the best models averagely improved about 2.0% of the relative standard deviation (RSD) relative to the power law method in the discharge estimation, especially at some tide period the RSD of the best model was several times better than that of power law model. For Yangtze River with an annual average discharge of 3.0×10 4 m 3 /s, the improvement should not be ignored. Therefore, it will be necessary to use the best model with minimum RMSE to estimate the flow velocity in tidal reach. [ABSTRACT FROM AUTHOR]

Side weirs have been used for centuries in urban drainage and flood control for their ability to divert high incoming flow rates. The flow along a side weir may be studied by means of different approaches. However, although the question of side weir has been debating for many decades, there are few studies on the local hydraulic characteristics of the flow along these structures in circular channels. An experimental study of the flow field in a circular channel along a side weir using a commercial TSI Particle Image Velocimetry (PIV) system is shown in this paper. Weakly supercritical flows running into different geometric configurations of the weir were investigated, with Froude numbers varying from 1.1 to 1.6. Free surface profiles have been obtained by an image processing technique. An empirical equation has been proposed for their representation. Longitudinal velocity profiles along the side weir can be well predicted by an entropic approach. Local outflow along the side weir may be represented by an asymmetric curve. The peak outflow generally occurs between the 30% and the 50% of the weir length. The elementary discharge coefficient significantly increases from upstream to downstream. An energy head reduction was observed under the investigated configurations. Most of the head variation occurs in the central part of the weir. Finally, the flow power decreases along the weir according to a non-linear function. A thorough knowledge of the flow field features should allow to improve side weir analysis and design, whatever approach is used for the study. [ABSTRACT FROM AUTHOR]

Summary Closely related to the solar photocycle, plankton growth in eutrophic waters displays a diurnal variation because of photosynthesis and respiration. Presented in this paper is an analytical study of the diurnal variation of mean concentration of plankton and nutrient in an open channel eutrophic flow initiated by an instantaneous emission. The evolution of the concentration is shown driven by the combination of hydraulic dispersion and diurnal reaction between plankton and nutrient. The analytical solution for longitudinal distribution of concentration is rigorously derived and illustrated, based on the time dependent hydraulic dispersivity. Numerical results are presented and characterized by the reaction rate, yield factor and period for the diurnal reaction and the P e ́ clet number of the flow. For typical applications such as ecological risk assessment and environmental impact assessment, the upper and lower limits of critical length and duration of five typical pollutant concentrations are concretely illustrated for given concentration criterions. Remarkable diurnal variations are revealed up to around one third in the critical length and duration for plankton, and about ten percent for nutrient. [ABSTRACT FROM AUTHOR]

The air and water flow distribution are experimentally studied in a test section simulating a heat exchanger composed by a round header and 16 parallel upward channels. The effects of the tube protrusion depth as well as the gas and liquid superficial velocities are investigated and the results are compared with previous data. A new fitting solution to be inserted in the header has been developed based on previous findings by the Authors. The fitting geometry belongs to the family of the protruding pipes but the protruding depth has been varied along the header in order to cope with expected liquid and gas mass flow rates in the parallel channels. The flow at the header inlet is intermittent and annular and water and air have been employed as two phase mixture. The new header fitting demonstrated to yield meaningful improvements in phase distribution in terms of either dimensionless liquid and gas flow ratios or standard deviation of phase flow ratio (the overall performance parameter STD 2 here presented decreased by 64%) when compared to the previous configurations. [ABSTRACT FROM AUTHOR]

An optical method is developed in order to measure the top and bottom liquid film thicknesses during evaporative annular flow in a horizontal minichannel. This method is based on the detection of liquid–vapor and liquid–solid interfaces. For each flow condition, about 4000 frames (corresponding to an observation time of 2 s) are recorded with a high-speed camera. Thus, these frames are processed with an image processing algorithm to obtain the average liquid film measurement. Three different configurations of the camera are tested. The chosen solution ensures a good reliability and accuracy of film measurements. The view section is a 2.95 mm glass circular channel and the working fluid is R-245fa. The tests are performed in annular flow, for different vapor qualities. A test facility allows reaching the desired conditions of the flow at the inlet of the test section. The examined saturation temperatures are 40, 60, 80 and 100 °C, whereas the mass velocities are 300 and 400 kg/m 2 s. A parameter of eccentricity is introduced to characterize the stratification effect. The influence of the saturation temperature, mass velocity and vapor quality is physically discussed through the Froude and Bond numbers. Finally, by using the top and bottom liquid film measurements, the cross-sectional void fraction is estimated. [ABSTRACT FROM AUTHOR]

The friction factor f is a crucial parameter for scaling friction resistance and energy loss in open channel flows [11,16] . We propose an auxiliary bed for the distinctive flow structure arising from mutual effects of flow and vegetation. Using the auxiliary bed, a two-layer dynamic model with meaningful physical significance is established to modify equations for channelized flows with vegetation. This new approach divides the vegetated flow into two parts: a basal layer and a suspension layer. A parameter named ‘effective relative roughness height’, analogous to the relative roughness height of unvegetated open channels, is proposed to predict the friction factor of the suspension layer. By analyzing hundreds of datasets, a series of formulae are proposed based on the application of the effective relative roughness height. Comparisons show that the new formulae yield more precise estimates of the flow rate, Manning coefficient and Chezy coefficient than previously published formulae on the subject. [ABSTRACT FROM AUTHOR]

The objective of this paper is to discuss the results of a combined physical and computational analysis of the dynamics of large deformable bubbles in conduits of different geometries and orientations. The situations analyzed included a vertical circular pipe and a narrow rectangular channel of different inclination angles. Three-dimensional simulations were performed at a DNS-scale using the PHASTA code combined with the level set method for interface tracking. The results of computer simulations for Taylor bubble flow in a vertical pipe have been verified against a simplified theoretical model and validated against available general evidence deduced from various experimental studies. The predictions for bubbles flowing along inclined rectangular channels have been validated against experimental data. Several modeling and numerical issues have been investigated, including the effect of a liquid microfilm between the bubble and the wall above it, and the impact of the blending region arising from the level-set model formulation on the accuracy of results. [ABSTRACT FROM AUTHOR]

Summary Sediment concentration ( SC )–water discharge ( Q ) relations in rivers are typically governed by multiple and relatively complex processes. Due to hysteresis effects, sediment discharges can differ for similar or equivalent water discharges, which causes scatter in empirical datasets and may decrease the predictive power of SC rating curves. Such hysteresis effects must therefore be understood and accounted for to make dependable predictions for river system management. The overall objectives of this study are to develop modelling approaches suitable for reproducing and predicting hysteresis effects at larger scales and to investigate the possible contribution of in-channel processes (erosion and deposition) to sediment concentration hysteresis loops. To investigate relevant field-scale conditions, we develop a one-dimensional dynamic sediment transport model of the downstream Tuul River (northern Mongolia), investigating in-channel processes along a 141 km stretch during a hydrological year. The results show that the present modelling approach can reproduce both anti-clockwise and clockwise hysteresis effects. Importantly, in-channel processes alone can cause considerable anti-clockwise hysteresis effects without being reinforced by catchment processes such as hillslope erosion. Such specific contributions from in-channel processes introduced data scatter into the sediment rating curves, decreasing their R 2 -values from unity to approximately 0.5 to 0.6. More generally, possible changes in the number or magnitude of high-flow events, caused by climatic or other anthropogenic factors, could influence total sediment deposition, which was primarily found to occur during relatively short high-flow events. Such potential changes also have important implications for the possible spreading of polluted sediments. [ABSTRACT FROM AUTHOR]

Tidal current is a periodic movement of unsteady and non-uniform, which owns obvious acceleration and deceleration process. The vertical distributions of velocity and shear stress in tidal flow possess the extraordinary features from the unidirectional flow. From the fundamental tidal movement equation, a simple-structure velocity profile formula is deduced which is capable of describing the velocity states from bypass to fully-developed, and it can express the velocity distribution of which the maximum velocity is not near the water surface. Based on the velocity profile, the tidal shear stress profile expression is derived and it can depict the characteristics commendably that the shear stress obeys the concave distribution within accelerating flow and a convex distribution within decelerating flow. Meanwhile, the computed values of the surface shear stress, on the conditions of acceleration or deceleration, conform to the fact the surface shear stress is not always equal to zero. Following the results of field observations, indoor experiments and numerical models, the bed shear stress is rather a variable dominated by tidal phase than a constant during the tide. The bed shear stress formula in the tide is derived with the definition raised by Soulsby, which is verified with the measured materials. The results are good agreeing with the field data. [ABSTRACT FROM AUTHOR]

Sedimentary basins occur within a variety of tectonic settings, both within plates and near plate boundaries. We explore the complex history of the Mesoproterozoic Ragged Basin, located in the eastern Nornalup Zone of the Albany–Fraser Orogen, which is part of the West Australian Craton. Sediments of the Ragged Basin were deposited within a shallow basin by a large fluvial system dominated by shifting, sandy braided channels, forming a quartz-rich succession defined as the Mount Ragged Formation. The gradual coarsening upwards sequence indicates a distal fluvial environment characterised by channel migration and abandonment, changing to a proximal fluvial environment characterised by rapid periods of sedimentation and coarser deposits. Ion microprobe (SHRIMP) U–Pb analysis of detrital zircons constrain a maximum depositional age of 1314 ± 19 Ma for the Mount Ragged Formation, so it is feasible that deposition started during the latter part of Stage I (c. 1330–1260 Ma) of the Albany–Fraser Orogeny. The detrital zircon U–Pb data demonstrates that the Mount Ragged Formation contains c. 1810–1320 Ma detritus, most of which appears to be derived locally from the reworked craton margin that forms the Albany–Fraser Orogen basement. However, the smaller c. 1560 and c. 2490 Ma zircon age components have no known source within the West Australian Craton, and were potentially originally sourced from the Gawler Craton or other unknown sources beneath the Eucla and Bight Basins. These exotic ages support the interpretation that outboard accretion occurred prior to Stage II of the Albany–Fraser Orogeny. New structural data, field observations and aeromagnetic image interpretation indicate that the Mount Ragged Formation was deformed by a northwest-vergent fold and thrust system. A minimum age for deposition, and structural emplacement, is provided by a crystallisation age of 1175 ± 12 Ma for a cross-cutting monzogranite exposed at Scott Rock, part of the Esperance Supersuite. Upper-crustal thrusting in the Mount Ragged Formation can be linked to deeper, large-scale regional structures such as the Tagon and Rodona Shear Zones, the latter of which represents the eastern edge of the Albany–Fraser Orogen. [ABSTRACT FROM AUTHOR]

This paper develops a new numerical scheme for flash floods based on the one-dimensional shallow water equations in channel networks, referred to as the dual finite volume method (DFVM) scheme. The scheme uses an upwind spatial discretization based on staggered meshes so that the flows in multiply connected channel networks are consistently handled without complicated treatment at junctions. The scheme is firstly examined with a series of test cases including idealized and experimental dam break problems to demonstrate its accuracy and versatility. The scheme is then applied to numerical simulation of a flash flood resulting from an earthquake-induced complete dam failure in Japan. Channels from a reservoir to the downstream rivers are modelled as a multiply connected channel network with non-prismatic cross-sections, steep slopes, and bends. The computational results agree well with the field observations and eyewitness reports. Numerical simulation of alternative scenarios as possible cases is also performed to analyze potential risks of the downstream area. [ABSTRACT FROM AUTHOR]

Characteristics of flow in a micro-channel with patterned superhydrophobic surfaces were simulated by using an incompressible lattice Bhatnagar–Gross–Krook (LBGK) model. By the simulation, it can be seen that the depth-to-width ratio of the cavities between adjacent micro-ridges is an important effect parameter for the flow in the micro-channel. For the larger depth-to-width ratio, it is easy to keep the air in the cavities. Because of the influence of the air, there is no vortex phenomenon downstream of each micro-ridge. Such vortices are a common phenomenon in macro flows. The simulated results coincide with those of experiments. Moreover, keeping the air in the cavities, one can also find that the smaller the solid area fraction, the greater the slipping velocity at the air–water interface. With a decrease of the solid area fractions, the average exit velocity increases and the flow drag coefficient decreases. [ABSTRACT FROM AUTHOR]

Extensive use of arsenic-contaminated well water for irrigation of rice fields in Bangladesh has led to elevated arsenic concentrations in rice plants, decreased rice yields, and increased human exposure to arsenic. The goal of this study was to investigate whether arsenic removal from irrigation water could be improved within distribution channels by amending them with physical structures that both induce water treatment and maintain water-conveyance capacities. Chemical and hydraulic effects of amending channels with jute-mesh structures were characterized within 27 m-long experimental channels at a Bangladesh field site. Removal of total arsenic, iron and phosphorus from solution was enhanced within amended channels over unamended channels, with 7% of total As removed in amended channels vs. 3% in unamended channels. Increased elemental removal in amended channels was largely due to increases in residence time and particle-trapping efficiency, but removal via oxidative particle formation did not appear to be substantially enhanced. Results suggest that in-channel structures could be a useful tool for decreasing arsenic loading to rice fields, particularly where constrained channel spatial geometries limit the ability to overcome hydrogeochemical thresholds for enhanced arsenic removal. To improve the practical utility of structure-amended channels, future work could optimize structure designs and establish the season-long sustainability of enhanced arsenic-removal strategies. [ABSTRACT FROM AUTHOR]

The main objective of the study was to present the applicability of the limiting current method for investigating of mass/heat transfer in minichannels. The paper provides an overview of results of mass transfer measurements. Some factors influencing the mass transfer experiment were discussed including the state of the electroactive surface, change in ion concentration and thickness of the diffusion layer. The author has based her conclusions on the results of her own electrochemical measurements and on available literature data. The issues examined concerned mass transfer during laminar flow through channels with small hydraulic diameter. The flows with mass transfer through the first of all circular channels (short, d = 1.5 mm and long, d = 0.2 mm) were discussed. A similar analysis for rectangular narrow channels was made. Since the aim of the work was to assess the validity of applying the mass/heat transfer analogy method using the limiting current technique in the study of heat transfer in minichannels, the literature data about the accuracy of the other measurements procedure - thermal balance method - was presented and compared with accuracy of the method considered. Conclusions about the achieve the most suitable procedure for electrochemical measurements in the case of mass transfer in minichannels were formulated. [ABSTRACT FROM AUTHOR]

Abstract: This paper examines the effect of the local support conditions at the ends of the constituent plates of plain channel section columns when subjected to uniformly compressed loading. The buckling and post-buckling interactive response of the columns have been determined through the development of suitable finite element modelling strategies and solution procedures which take due account of the influence of material nonlinearity and geometrical imperfections. Uniformly compressed loading means, of course, fixed conditions at the column ends with respect to global rotations and the ends of the constituent plates of the cross-section can be treated as either locally rotationally constrained or locally rotationally free. These two conditions are shown to lead to quite different characteristic interactive responses of the columns due to amplitude modulation in the buckling mode for the rotationally constrained case. [Copyright &y& Elsevier]

Highlights: [•] Stability of stratified inclined flows in the multiple solution regions is analyzed. [•] Stability boundaries on flow-pattern maps for various systems are obtained. [•] There are systems and conditions where the multiple solutions are stable. [•] Expressions for the shear stresses in phase with the wave slope are derived. [•] These should be considered even in the framework of long wave stability analysis. [Copyright &y& Elsevier]

Abstract: This paper describes a new simplified model for controller design of open water channels that are relatively short, flat and deep: the integrator resonance model (IR model). The model contains an integrator and the first resonance mode of a long reflecting wave. The paper compares the integrator resonance model to the simplified models: integrator delay, integrator delay zero and filtered integrator delay and to the high-order linearized Saint-Venant equations model. Results of using the integrator resonance model in a model predictive controller applied in closed loop on a high-order non-linear Saint-Venant model of the first pool of the laboratory canal at Technical University of Catalonia, Barcelona are compared to the results of using the other simplified models in MPC. This comparison shows that the IR model has less model mismatch with the high order model regarding the relevant dynamics of these typical channels compared to the other simplified models. It is demonstrated that not considering the resonance behavior in the controller design may result in poor performance of the closed loop behavior. In order to demonstrate the validity of the simulation model used in this study, the controller using the IR model is also tested on the actual open water channel and compared to the results of the high-order non-linear Saint-Venant simulation model. The results of this comparison show a close resemblance between simulation model and real world system. [Copyright &y& Elsevier]

Highlights: [•] The final uncertainty of the StreamPro ADCP discharge measurements was estimated. [•] We evaluate the elemental uncertainty sources of the discharge measurement process. [•] We show the GUM can be applied for practical measurements pertaining to hydrometry. [•] The presented UA is generic and can be applied to other measurement situations. [Copyright &y& Elsevier]

Abstract: The thermal hydraulic system code MERSAT has been applied to model the Brazilian IEA-R1 research reactor. The developed MERSAT model consists of detailed description for the primary loop including reactor core, bypass, reactor pool, main pump and coupling valve. The developed model is verified through the simulation of the steady state operation at the nominal power of 5MW. According to the safety significance of postulated initiating events two selected design basis accidents corresponding to loss of flow accident (LOFA) with reactor scram and reactivity insertion accident (RIA) without scram have been analyzed. The results of LOFA simulation demonstrate the phenomena of flow reversal characterizing the flow turnaround from forced downward to natural upward circulation. The prevailing natural circulation after the flow reversal guarantees the removal of residual decay heat. The maximum clad temperature of the hot channel reaches its maximum of about 73°C after 35s after the initiation of the transient. The step reactivity insertion of 2mk leads to increasing the reactor power up to 1.7 times the nominal value. Consequently, the maximum clad temperature of hot channel reaches about 99°C which is still far below the onset of subcooled boiling. Hence, the established thermal hydraulic conditions ensure a considerable safety margin even if the reactor protection system should fail to shutdown the reactor 400s after the begin of the reactivity insertion event. The results of LOFA and RIA demonstrate the safety features of IEA-R1 under the investigated conditions. In both cases the thermal hydraulic design limits have not been exceeded. However, for the RIA case the maximum clad temperature exceeds the limit of 95°C being chosen as operation criteria for limiting corrosion on the surface of the fuel elements. [Copyright &y& Elsevier]

Abstract: The engineering process of the IFMIF high flux test module (HFTM) demands concurrent optimization with respect to neutronic, mechanical and thermal-hydraulic issues. The cooling technology of the HFTM makes use of helium gas flowing in mini-channels along the specimen capsules. The coolant gas flows in these mini-channels are characterized by transitional Reynolds numbers, high velocities and high heating rates. Further, the flow in the short channels is influenced by entrance effects on a relevant part of the full length. The present study addresses these issues by experimental and numerical simulations. To this end, the experimental facility ITHEX has been constructed, and several mini-channel test sections were investigated using a variety of experimental techniques. The numerical methods are validated against the experimental data, and general conclusions on the HFTM thermal-hydraulic layout are presented. [Copyright &y& Elsevier]

Abstract: Theoretical investigations on solitary waves interacting with a surface-piercing concentric porous cylinder system are presented in this paper. The outer cylinder is porous and considered thin in thickness, while the inner cylinder is solid. Both cylinders are rigidly fixed on the bottom. Following Isaacson''s [Isaacson, Micheal de St. Q., 1983. Solitary wave diffraction around large cylinder. Journal of the Waterway, Port, Coastal and Ocean Engineering 109(1), 121–127.] approach, we obtained the solutions for free-surface elevation and the corresponding velocity potential in terms of Fourier integrals. Numerical results are presented to show the effects of incident wave condition, porosity of the outer cylinder and radius ratio on wave forces and wave elevations around the inner and outer cylinders. [Copyright &y& Elsevier]

Abstract: In this study, turbulence and mixing are investigated in a constricted channel at the mouth of Tokyo Bay, using two instruments: a microstructure profiler, TurboMAP-L, and an ADCP. We observed three different stratified conditions, i.e., SSC (Strongly Stratified Condition), MSC (Moderately Stratified Condition) and WSC (Weakly Stratified Condition) over a complete tidal period. The water exchange at the mouth of Tokyo Bay was in the transitional regime between the hydraulic and the diffusive limit with SSC and MSC close to the hydraulic limit and WSC close to the diffusive limit. For SSC and MSC, the enhancement of the stratification and vertical mixing showed asymmetry over a semidiurnal tide cycle. Mixing was stronger during ebb than during flood for SSC. On the other hand, mixing was elevated during flood for MSC. For WSC, weak stratification and strong mixing occurred during both flood and ebb. The SSC asymmetry resembled the strongly stratified condition of Columbia River (Kay and Jay, 2003a, 2003b), and the MSC asymmetry resembled the Strain-Induced Periodic Stratification condition (Simpson et al., 1990). A principle component analysis applied to the observed velocity profiles showed that both barotropic and baroclinic flow played a role during SSC and MSC, and in turn, barotropic flow dominated during WSC. The probability density function of the turbulent kinetic energy dissipation rate is practically expressed as a single lognormal population for all three conditions. [Copyright &y& Elsevier]

Abstract: Numerical modelling is used to assess the effect of a turbine array on tidal currents in the Tory Channel, New Zealand. The Tory Channel is the smaller of two entrances from Cook Strait to the Queen Charlotte Sound with a large island separating the narrow Tory Channel from the main entrance. The 2D depth-averaged finite element model is validated against velocities from shipboard ADCP transects from a survey during spring tide conditions, and water levels recorded at the study site. Turbine drag is introduced to the model as a stress term in the momentum equations, and includes both the turbine thrust and the structural drag. Turbine array drag is a function of the number and size of turbines, which can be parameterised in a non-dimensional number. This non-dimensional turbine drag number D can be used to represent the drag of several different turbine designs. Restrictions are placed on the size of the array to ensure that turbines are placed in realistic locations. In this study, turbines are restricted to areas with water depths greater than 30 m, and where spring tide currents (in the absence of turbines) are greater than 2.0 m s−1, and consequently the turbine array does not span the entire channel width or length. The modelling shows turbines will reduce current speeds both within the turbine array, and also throughout much of the Tory Channel, with local increases in speed immediately adjacent the array. Cut-in and maximum or rated turbine speeds are also incorporated to compare how these factors influence both the power production and effect on currents. The study shows that, due to the restrictions placed on the array location, the likely power production that can be achieved is considerably less than what an analytical prediction suggests might be obtained from the channel. Due to the effects of turbines on current speeds, optimising the area occupied by an array is likely to be an iterative procedure. The power produced per turbine unit could be substantially improved, with little impact on total power produced by the array, by removing turbines from areas where power produced was low. Turbine operational limits, applied in the form of cut-in speeds below which no power is produced, and design speeds above which load shedding occurs, affect both the magnitude and spatial distribution of power production and thus need to be considered in array design. [Copyright &y& Elsevier]

Abstract: In this paper we examined spatial patterns of bed texture, bed mobility, and channel hydraulics in four reaches of a mountain stream with moderate gradient (<0.02) and linked them to availability and disturbance of potential spawning substrate for small resident cutthroat trout (body size 200mm). Within-reach spatial distribution and extent of potential substrate and disturbance risk enabled us to identify between-reach differences, which pointed to existence of two distinct domains within the study area. In two cobble–gravel reaches bed was generally too coarse for spawning and potential substrate appeared to be limited to small areas protected by flow obstructions. These hydraulically sheltered sites promoted accumulation of large quantities of fine sediment that seemed to pose high disturbance risk to the associated substrate patches. In contrast, general bed fining resulted in development of extensive areas of spawning substrate, unaffected by excess fine sediment deposition, in the unobstructed portions of gravel-dominated reaches. In all study reaches bed mobility and risk of scour disturbance was generally limited, even though its significance was sensitive to the adopted value of eggs burial depth. Abrupt transition between the two contrasting domains in response to relatively modest changes in channel texture led us to hypothesize that small-bodied salmonids in similar mountain streams may be vulnerable to habitat fragmentation that prevent fish movement between reaches but also to climate and land use changes that alter inputs of water and sediment into the channels. Overall, our within-reach analyses illustrated that between-reach differences in potential substrate availability and disturbance risk may be strongly dependent on small-scale hydro-geomorphic processes and their configuration in space relative to one another. [Copyright &y& Elsevier]

Abstract: This study extends earlier contributions on dynamic adjustments of fluvial channels to base level changes. We have investigated an in situ response of self-formed cohesive channels to a base level drop, conditions analogous to a gradual change in uplift and/or climate. Empirical hydraulic geometry equations for clayey-cohesive natural streams are presented using data from eight channels draining perennial brackish springs and discharge into the Dead Sea. Investigation of downstream variations in gradient and stream power relations suggests existence of three distinct reaches in which channel adjustment to base level drop is shared inequitably among hydraulic geometry variables. Values of the flow velocity exponent m are low (0.11≤ m ≤0.24), the mid-channel reach having the lowest exponent. The depth exponent f has the lowest value (f ≈0.3) for the uppermost channel reaches, the rest having higher values (f ≈0.4). The smallest width exponent (b =0.35) characterizes the upper reaches. These values and their spatial distribution exhibit a regular pattern. We show that the lowermost channel reach adjusts by profile steepening and channel narrowing (f > b); the prevailing mechanism in the mid-channel reaches is lateral (width) adjustment, cross sections transiently transforming toward equilibrium; the uppermost reaches have wide and shallow channel cross sections because of series of bank collapses and resultant sediment aggradation, bringing rise to decreased local gradient, forcing further channel widening. The results of this study not only allow inference about how cohesive channels regulate their geometry, but also reveal the means by which hydraulic forces overcome substrate resistance, adjusting slope and channel dimensions and, as such, have implication for reach-scale channel morphology and models of stream power. [Copyright &y& Elsevier]

Abstract: Channels with parabolic cross-section are widely used in water conservancy projects, so it is necessary to determine the accurate conjugate depth value in hydraulic design. In order to seek a simple method, the iterative formula of conjugate depth for parabolic channels is derived and the convergence of which is proved theoretically. Moreover, the direct calculation formula to determine the initial iterative value is derived in order to speed up the convergent rate. And finally an example proves that the method in this paper is simple, fast and clear in physical concepts. [Copyright &y& Elsevier]

Highlights: [•] We examined differences in transient storage metrics between restored and non-restored reaches, using transient storage as a proxy for ecosystem function. [•] Transient storage in restored reaches was dominated by fast exchanging surface transient storage zones while non-restored reaches may have been dominated by shallow hyporheic exchange zones. [•] Restoration did not show significant differences in transient storage metrics. [•] River steering restoration structures created dynamic and diverse flowpaths causing solute from tracer injections to become laterally unmixed. [Copyright &y& Elsevier]

Abstract: Due to the impedance mismatch happening at the terminals and ports of components (splitters, taps, etc.), the frequency-selective fading characteristic exists in the coaxial cable channel. In this paper, the transfer characteristics of each component of coaxial cable network is analyzes. Moreover, a new algorithm to calculate the frequency responses is proposed. This algorithm can estimate all responses of any point-to-point channel accurately at one time. The results have been verified successfully by measurement on actual network, the absolute error of attenuation at any frequency point is less than 0.5dB. This modeling approach can be used to model any coaxial cable network, so long as the construction and dimension are known. It is helpful to analyze the performance of different distribution networks and to identify potential difficulties. It is also useful in the fault diagnosis and location for the further study. [Copyright &y& Elsevier]

Abstract: A laboratory scale flexible rubber blade water wheel has been investigated at the hydraulic laboratory of University of Southampton. The effect of channel width on water wheel performance has been studied. Different upstream and downstream channel widths are set for the tests. In this paper, the experimental set up, tested water wheel and the measurement procedure are described and the experimental results are shown. Results show significant improvement in power output and efficiency in reduced channel width. [Copyright &y& Elsevier]

Abstract: In open channels, free overfall can be used as a discharge measuring structure by a single measurement of depth at the end of the channel. If the slope of channel is negative, zero or mild, the flow at upstream of end section will be critical and end depth value depends only on the shape of the approach channel and its critical depth. This research presents a theoretical end depth–discharge (EDD) relationship for free overfall (end section) in a horizontal open channel with generalized trapezoidal section. The generalized trapezoidal shape reduces to the commonly used trapezoidal section as well as to the Δ-shaped section. Two direct discharge equations in terms of end depth for subcritical flows are proposed by simulating free overfall as a weir without crest. Experimental data are then used to verify the proposed EDD relationships. The calculated discharges, using the proposed EDD relationships, show excellent agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: The present study brings new insights on the small-scale characteristics of relatively distal turbidite deposits (classically defined as depositional lobes or sheets) from the deep-water clastic slope system of the Annot Sandstones (Grès d''Annot), in the Trois Evêchés area. This “seismic scale” outcrop has been studied in detail to characterize sedimentary geometries and facies associations within and between sheet-like sandstone-bodies. In terms of facies, their internal architecture is dominated by numerous erosional features, variable scale cross-bedding and dewatering structures. Facies range from gravelly sandstones to fine-grained sandstones and their spatial distribution inside sandstone-bodies is provided, allowing us to discuss the spatial changes in flow behaviour. A detailed dataset, made of very high-resolution correlations in thick to thin-bedded sheet-like sandstone-bodies, enables to identify five main types of architectural elements, composed of both channelised and unchannelised depositional bodies. Gravelly-filled channel-elements, laterally stacked channel-elements (interpreted as being related to sinuous channel migrations) and wing-like channel-elements constitute the channelised sheet systems whereas tabular sandstones (sheets sensu stricto), prograding and/or dome-shaped units constitute layered sheet systems. Sinuous channels are represented by the association of erosive-based, laterally stacked bedsets and very coarse-grained, low-angle cross-bedded facies. These latter facies are interpreted as the result of flow deconfinement and overbanks above channel margins. The stratigraphic relationships between these architectural elements permit establishing a conceptual model of the distribution and organisation of the components. This distribution scheme is based on the longitudinal differentiation of gravity processes, which are directly linked with architectural element types. This model is composed of proximal confined units where channelization processes, amalgamation and bypass dominate, to more distal and less confined units where compensation, constructive structures and high deposition rates control sedimentary architectures. The Trois Evêchés sub-basin may be considered as a good example of a channelised lobe to unchannelised lobe transitional environment, which explains the lateral and vertical high variability during its infill. The widespread apparition of residual facies, such as cross-stratified sandstones as well as basal lags, suggests significant bypass. The appearance of both channelised and unchannelised units is consistent with this transitional environment. The provided detailed dataset in this paper displays the associated wide range of architectural elements in these settings, and highlights the significant heterogeneities of sand-rich confined turbidite sheet systems. These heterogeneities are under the seismic resolution and may influence fluid migration in sand-rich deep-water reservoirs. [Copyright &y& Elsevier]

Abstract: Large scale channel systems are commonly imaged using seismic data and classified hierarchically. Where exposed at outcrop, similar scale ancient channel systems provide an opportunity to investigate subseismic scale architectures, produced for example through short duration autocyclic processes, and assess how they contribute to larger seismic scale architectures. In this study, a seismic scale slope-confined channel system from the Numidian Flysch Formation of northern Sicily is described using a hierarchical classification scheme. The channel system is 5.7 km wide and is organised within 3 hierarchical levels, comprising; 2 channel complex sets, 16 channel complexes, and >30 channel elements. channel complexes are mappable bodies and reach 500 m wide and 90 m thick. Slope confined sinuous channel complexes contain stacked channel elements which show a progression of incision and bypass to fill with massive sandstones interspersed with graded turbidite deposits. Flows are interpreted to predominantly deposit during quasi-steady flow conditions although flow non-uniformity produced beds with complex grading patterns. Lateral expansion of channel elements produced terracing within the complex margin and had the capacity to alter flow rheology through incorporation of large mud volumes. Sinuosity of channel element thalwegs and offset stacking produced asymmetric channel complexes with heterogeneous internal architectures and lithofacies distributions. Both channel complexes and channel elements thicken with younging indicating increased entrenchment through allocyclic forcing. The frequency distribution of channel-element thicknesses also shows a positive skew centred around 12 m as with published data global datasets. We question whether this distribution similarity may result from a fundamental process at the channel-element scale such as substrate armouring through coarse grained sedimentary deposits exceeding the capacity limits of transiting flows. The use of a hierarchical classification scheme therefore highlights the importance of subseismic scale processes on mappable architectures. The quantification of specific hierarchical elements also allows the role of allocyclic forcing to be investigated in an area of complex palaeogeography. [Copyright &y& Elsevier]

Abstract: The Pleistocene slope clinoform succession of the Pescara Basin foredeep (Central Adriatic Basin, Italy) has been investigated combining the analysis of the rollover point trajectories with 2D seismic facies analysis and 3D seismic geomorphology approach and visualization techniques. The study documents two different types of slope clinoforms, each of which is characterized by a specific slope turbidite system with distinctive morphologies, internal geometries and architectural elements. Type 1 clinoforms are characterized by rectilinear, slope-confined gullies which develop during a phase of margin growth. Type 1 clinoforms are characterized by a rise of the trajectories of the rollover points, which can be indicative of intervals of relative sea level rise. In type 1 clinoforms most of the coarse-grained sediments are stored in the shelf. The slope-confined gullies barely indent the shelf break, are not connected to rivers, and develop thin (<30 m) frontal splays at the base of the slope. All these evidences indicate that the gullies are inefficient pathways to transfer sandy sediment basinward. The gully depressions are net-erosional and also the inter-gully sectors are sites of dominant sediment bypass. The infill deposit of the gullies consists of channel-wide high-amplitude reflectors (HARs) wedging-out downslope. The origin of the slope-confined gullies is interpreted to be linked to mass wasting processes affecting the upper slope and the shelf-edge during conditions of relative sea level rise. Longshore drifts and storm-driven turbidity currents rework the outer shelf, promoting the maintenance of gully systems, which become filled during the ensuing high-stand of the sea level. Type 2 clinoforms are characterized by a negative trajectory of the rollover points, and develop during a lowering of the sea level and during lowstand periods. Type 2 clinoforms develop sinuous, aggradational slope channels which are river-connected, with incised valleys that supply sediment directly to the head of the slope channel. The slope channels are fed through sustained turbidity currents possibly associated with hyperpycnal flows. Type 2 slope channels develop in a net-aggradational setting, forming erosive based channel-fill deposits about 150 m thick which are characterized by high-amplitude reflectors (HARs). Type 2 slope channels are able to transfer larger amount of sediment to the basin, comparing with type 1 gullies, as the presence of thick (∼150 m) channelized frontal–splay complexes seems to confirm. The combination of 2D and 3D data analysis has lead to the reconstruction of a sedimentological model which has the potential to be applied as analogue for seismic or outcrop-based studies of slope channels in supply-dominated, mud-prone margins. [Copyright &y& Elsevier]

Abstract: Studies of modern submarine slope to basin floor systems suggest a smooth concave upward long profile is normal for channel systems where down-dip development is unhindered by bathymetric irregularities. Deviation from this ideal may occur where channel systems encounter positive or negative relief that drives down-dip incision and creation of a knick point. The Unit D system, exposed in the Karoo Basin, South Africa, provides a rare opportunity to examine the long profile of a submarine channel where the effects of bathymetry on geometry are evident over a down-dip distance of over 30 km. The Geelbek area, the focus of this paper, is located at the distal end of the study area. Four phases of stratigraphic development are recognised; D1, a distributary lobe complex incised by a younger genetically related high aspect ratio channel; D2, an accumulation of external levee deposits sourced from a channel unrelated to D3, which is a late-stage entrenched low aspect ratio channel, which incised from near the top of the D2 levee, through older Unit D deposits and into the underlying mudstones, before being partially removed by a late-stage slide (D4). Both D1 and D3 channel systems are oriented at a high angle to the regional palaeoslope of the Laingsburg depocentre. The accumulation of earliest Unit D deposits is thought to have influenced the orientation of the D1 channel and lobe, whereas the direction of the D3 channel is consistent with the maximum depositional gradient of the D2 levee. The depth of incision of the D3 channel at Geelbek suggests that connection to a bathymetrically deeper part of the basin was established late in D time, which locally steepened the channel gradient generating a knick point. [Copyright &y& Elsevier]