Entrainment Depth Research Articles

Influence of wind and waves on ambient noise and bubble entrainment depth in the semi-enclosed Baltic Sea

Semi-enclosed, fetch-limited waters create unique conditions for wind wave development and breaking. Parameters of breaking waves influence bubble entrainment depth and associated noise, which is why they differ in semi-enclosed sea compared to open waters. While the established noise-wind speed relationship holds in oceanic conditions, it differs in land-constrained basins like the Baltic Sea. To explore noise level, bubble entrainment depth and wind speed relationships, we conducted noise and sub-surface bubble measurements, coupled with wind observations, in the selected area of the Baltic Sea during two consecutive summers. A novel method was employed to estimate bubble entrainment depth under conditions of strong backscatter. Model data of wave field parameters were employed to assess their influence on noise level and bubble entrainment depth. Results suggest stronger connections between noise level and wind speed, as well as wave height, compared to wave age and wind sea steepness. The same patterns hold true for the correlation between bubble entrainment depth and both wind speed and wave field parameters. The parameterized noise level-wind speed relationship differs from that obtained for oceanic conditions and also varies across measurement periods. Observed differences were shaped by varying wind-wave conditions, notably differences in wind speed, direction, wave height, and the presence of swell. The noise level-bubble entrainment depth relation is reported for the first time for Baltic Sea conditions. For a thorough analysis of the influence of these factors on noise and bubbles, longer measurements under diverse wind-wave conditions are required to account for site-specific wave field characteristics.

Gaseous Entrainment Dynamics in a Viscous Pool Due to Combined Influence of Asymmetric Rotational Field and Crossflow of Air

Abstract Efforts are made to perform simulations to describe the gaseous entrainment dynamics in a viscous liquid pool due to the combined influence of asymmetric converging rotational field and continuous freestream flow of air. A pair of counter-rotating and equal sized rollers is placed inside the pool along a horizontal line. Gerris is an open-source solver, which is employed to carry out the present computational study. Complex interfacial configurations are illustrated with the influence of relevant input parameters, such as rotation of rollers 1 and 2 (measured by Capillary number, Ca1=Rω1μl/σ and Ca2=Rω2μl/σ, where R=D/2 is roller radius), submersion depth (b*), the gap between the rollers (2a*), and strength of air stream flow (measured by Reynolds number, Reflow=ρgUD/μg). It has been observed that the depth of steady entrainment is reduced at Reflow≠0 compared to Reflow=0 because the hydrodynamic force acts as an opposing force to viscous pumping and rotating inertia. A complete understanding of disintegration of and subsequent accumulation of gaseous bubbles from the cusp tip is characterized in detail. In addition, the influence of viscous drag (specified by Morton number, Mo=gμl4(ρl−ρg)/(ρl2σ3)) and gravitational pull (estimated by Archimedes number, Ar=gD3ρl2/μ2) on the phase contours are also reported. Finally, an analytical formulation is proposed to analyze the structure of entrainment, and this model reports an excellent match with the numerical findings.

The Diurnal Cycle of Entrainment and Detrainment in LES of the Southern Ocean Driven by Observed Surface Fluxes and Waves

AbstractEmpirical rules for both entrainment and detrainment are developed from LES of the Southern Ocean boundary layer when the turbulence, stratification, and shear cannot be assumed to be in equilibrium with diurnal variability in surface flux and wave (Stokes drift) forcing. A major consequence is the failure of downgradient eddy viscosity, which becomes more serious with Stokes drift and is overcome by relating the angle between the stress and shear vectors to the orientations of Lagrangian shear to the surface and of local Eulerian shear over 5 m. Thus, the momentum flux can be parameterized as a stress magnitude and this empirical direction. In addition, the response of a deep boundary layer to sufficiently strong diurnal heating includes boundary layer collapse and the subsequent growth of a morning boundary layer, whose depth is empirically related to the time history of the forcing, as are both morning detrainment and afternoon entrainment into weak diurnal stratification. Below the boundary layer, detrainment rules give the maximum buoyancy flux and its depth, as well a specific stress direction. Another rule relates both afternoon and nighttime entrainment depth and buoyancy flux to surface layer turbulent kinetic energy production integrals. These empirical relationships are combined with rules for boundary layer transport to formulate two parameterizations; one based on eddy diffusivity and viscosity profiles and another on flux profiles of buoyancy and of stress magnitude. Evaluations against LES fluxes show the flux profiles to be more representative of the diurnal cycle, especially with Stokes drift.

Simultaneous laser-induced fluorescence and capacitance probe measurement of downwards annular gas-liquid flows

This study focuses on the characterisation of downwards annular gas-liquid (air-water) flows, by employing a combination of advanced laser-based and capacitance-based measurement methods. A variant of laser-induced fluorescence (LIF), referred to as structured-planar laser-induced fluorescence (S-PLIF), eliminates biases commonly encountered during film-thickness measurements of gas-liquid flows, due to refraction and reflection of the light at the interface. A bespoke capacitance probe is also assembled to enable temporally resolved film-thickness measurements with high temporal resolution along the circumferential perimeter of the pipe. We compare the film mean thickness, roughness, and probability density functions obtained with each method. We find that both methods are able to measure time-averaged film thickness to within <20% deviations from each other and from results obtained from the available literature. The resulting probe data suggest a biased (suppressed) standard deviation of the film thickness, which can be attributed to its working principle, i.e., measuring the film thickness averaged along the circumferential perimeter of the pipe. The autocorrelation functions of the time-traces provide an insight into the characteristic time-scales of the interfacial phenomena in these flows, which span a range from ∼10 ms for highly gas-sheared flows and increase to about 30 ms for the smoother falling films. The power spectral densities reveal modal frequencies that start from 2.5 Hz for falling films, and increase with the gas Reynolds number by almost an order of magnitude. The turbulent wave activity (slope in the power spectrum) reduces with a decrease in gas shear, and shows similarities to the decay of homogeneous and isotropic turbulence. The sizes of the bubbles entrained in the liquid film are measured from the S-PLIF images, and exhibit log-normal distribution that become flatter with a decrease in the gas Reynolds number. The normalised location of the bubbles (quantified as the relative entrainment depth, i.e., distance of the bubble from the wall over the local film thickness) follows a Gaussian distribution, with the peaks located between 0.5 and 0.6, indicating that the majority of the bubbles accumulate in the middle of the thin film.

Advances in the simulation of debris flow erosion: The case study of the Rio Gere (Italy) event of the 4th August 2017

Debris flows are natural hazards causing fatalities and damages to infrastructures every year. One of the current challenges is to improve the predictability of such events using simulation tools. In this direction, the paper aims to model debris-flow generation starting from the water component and then simulating the motion of the bulked solid-fluid mixture mass flow. The debris component is progressively increased through entrainment of the channel bed material. The simulation has been performed exploiting the tool r.avaflow, which implements a physically-based model (Pudasaini and Mergili, 2019) for the flow propagation and an empirical multi-phase model for the entrainment processes.The investigated study case occurred in the Northeastern Alps of Italy, near the town of Cortina d'Ampezzo (Veneto Region), during the summer of 2017. The debris flow was triggered by a heavy rainstorm that caused extreme surface runoff, leading to entrainment of sediment from the channel bed. The debris flow obstructed the bridge of a regional road and consequently flooded the adjacent areas.Different types of debris flow simulations are performed, testing four specific functions to compute the entrainment rate. The simulated results are then compared against field observations. The analysis considers the differences in volume and depth of entrainment and in the output hydrograph.We conclude that entrainment is correlated with the terrain slope, particularly if it is calculated on a smoothed digital elevation model, which dilutes a less significant local steepness. We calibrate a spatially distributed slope-dependent erosion coefficient that successfully reproduced the observed entrainment volumes. The outcomes highlight the great importance of simulating debris flow entrainment processes adopting a multiphase model, which resulted particularly suitable for an accurate reproduction of the investigated event. The results, corroborated by further verifications, can improve the reliability of challenging predictive simulations on debris flow erosion.

Effects of entrainment phenomenon on the rapid and long-runout movement of landslides in Wenjia gully, Sichuan, China

As a common phenomenon in landslides, entrainment of loose bed material along the sliding path can enhance both the volume and mobility of the sliding mass, posing a great threat to the life and property safety of people in the affected area. For the purpose of revealing the mechanism of entrainment phenomenon of sliding material in the runout process, a dynamic slice-based model was firstly proposed in the present study. In this model, the motion of landslide body is assumed to follow the rheological law proposed by Voellmy. Additionally, through Voellmy model, the increase in kinetic energy, mass and volume of landslide body and entrainment depth caused by the entrainment phenomenon were taken into consideration. Subsequently, on the basis of the dynamic slice-based model, back-analyses were performed on the Wenjia gully landslide. The effect of entrainment phenomenon on the post-failure motion was analyzed. The calculated results shows that the travel distance obtained from proposed model is closer to field data than that resulted from Scheidegger’s empirical method. Moreover, the peak value of the maximum velocity calculated by this model is in good agreement with that get from the dynamic analysis model (DAN3D). When considering the entrainment phenomenon, the volume of sliding mass increases greatly in post-failure motion. This paper provides a new method for analyzing the entrainment phenomenon in landslide motion.

Numerical simulation of the propagation process of a rapid flow-like landslide considering bed entrainment: A case study

Bed entrainment plays an important role in the run-out process of a flow-like landslide. A limited number of studies have investigated the influence of entraining loose materials on the mechanical properties of a landslide, and some of them have considered bed entrainment either by mechanical or empirical methods. In this paper, a modified finite difference model was used to analyze the propagation process of a typical flow-like landslide with bed entrainment that occurred in the Jingyang loess tableland, China. In this model, the mechanical parameters of the sliding mass were modified according to the local entrainment depth. Triaxial Consolidated Undrained (CU) tests and ring shear tests were conducted to obtain the mechanical parameters needed in the numerical simulation. The triaxial CU tests were conducted on three intact loess samples taken at the back scarp of the landslide, and the ring tests were conducted on gravelly sand samples taken from the first terrace of the Jinghe River, which includes the landslide deposit. The results show that both the simulated run-out distance and final covering area agreed well with the field data. The modified model revealed the propagation process of this landslide. A major contribution of this study is that entraining the saturated gravelly sand contributed to the flow-like movement of the landslide. The case study investigated here is helpful for better an understanding of the flow-like transformation mechanism. In addition, the numerical model adopted in this paper can be effectively used to assess or predict the propagation processes of similar landslides.

Incipient motion of large wood in river channels considering log density and orientation

ABSTRACT The incipient motion conditions of large wood were tested in flume experiments using 48 handmade cylindrical logs of different lengths, diameters and densities. Their orientation to flow determined the motion: parallel logs slid, while oblique or transverse logs rolled. Log orientation, channel bed roughness, and log diameter had significance influence on entrainment depth. The logs’ density strongly influenced motion for logs parallel to flow. Logs oriented parallel to flow needed large entrainment depth to entrain than similar logs oriented oblique or transverse. Logs denser than water had high correlation with buoyancy, suggesting initial movement by floating, followed by either sliding or rolling downstream along the bed. From the modelled datasets, our results guided by the goodness of fit demonstrate that the floatation thresholds taken from global datasets should be applied with caution under different bed roughness conditions.

Energy dissipation in a deep tailwater stilling basin with partial flaring gate piers

Flaring gate piers (FGPs) have been used to increase energy dissipation in stilling basins downstream of spillways. For projects with a low water head and large unit discharge together with a deep tailwater level, energy dissipation inside a conventional stilling basin is usually insufficient. This paper proposes a new partial flaring gate pier (partial FGP) scheme to intensify the energy dissipation inside the stilling basin. The results for the no FGP scheme, the conventional FGP scheme, and the partial FGP scheme were compared using a physical model study and numerical simulations. It was found that the partial FGP scheme (the alternation of flaring and no flaring gate piers in chambers) can contain the submerged hydraulic jump and high-speed water jet in the upstream region of the stilling basin. Thus, the water jet from the FGP chamber was forced to laterally diffuse, thereby intensifying the shear friction and turbulent kinetic energy and forming a vertical vortex from the bottom to the surface. Compared with the other two schemes, the flow pattern in the partial FGP scheme was improved significantly with much deeper air entrainment depth inside the stilling basin and much lower turbulent kinetic energy in the outgoing flow. The mean velocity of the outgoing flow also decreased by more than 20%. The common problems of secondary hydraulic jump outside the stilling basin were eliminated.

A progressive entrainment runout model for debris flow analysis and its application

A progressive entrainment model has been incorporated into an energy-based runout model to calculate the kinematic characteristics of debris flow. The progressive entrainment model considers both rolling and sliding motions of erodible material. To study the effect of the controlling parameters in the entrainment model, sensitivity analyses have been carried out by varying model parameters such as the internal friction angle of the debris, the basal friction angle of the channel, the turbulent flow coefficient, and the mean value of the probabilistic density function (PDF) for the resting angle. The results are evaluated by calculating the change of the maximum entrainment rate, the maximum frontal velocity, the final total volume, the longitudinal length of deposition, the maximum debris flow height, and the runout distance of the debris. The progressive entrainment runout model is sensitive to the characteristic particle size, basal friction angle and turbulent coefficient. Measurements from the 1990 Tsingshan debris flow, Hong Kong, China, are used to validate the model. Velocities at different channel sections estimated using the super-elevation method and entrainment depth are used to evaluate the simulation results. Comparing the results between simulated and observed maximum velocity and entrainment depth indicate that the progressive entrainment model together with the runout model can capture the erosion characteristics of the granular material. The results are also compared with that using a dynamic entrainment model. The results demonstrate that the progressive entrainment model provides a more realistic calculation of entrainment for this case compared with the dynamic entrainment model.

Model test on the entrainment phenomenon and energy conversion mechanism of flow-like landslides

A reduced-scale physical model test with a scale of 1:2000 is designed based on the Wenjia Gully landslides. By changing the volume and kinetic energy of the sliding mass, we find that the material grading and bed-sediment thickness exert an important effect on the movement process of the landslide. To investigate the dependence of the entrainment on the grade of the sliding material and bed-sediment thickness, a series of comparison experiments with sliding masses of different grades and loose sediment bed materials of different thickness values are conducted. Furthermore, a high-speed camera is used to record the runout process. The experimental results indicate that because of the entrainment effect, the erosion depth of the substrate increases when the grade of the sliding mass increases. In addition, different characters appear in the erosion depth, volume of the accumulated area and entrainment length with the increase in bed-sediment thickness. Furthermore, the entrainment depth may increase when the bed-sediment thickness increases. The velocity of the sliding mass is reduced with the increase in basement thickness. Finally, based on the analysis of landslides and the previous experimental results, the energy conversion can be calculated to analyze the process of substrate entrainment for each sliding phase.

Modeling of Entrainment in Debris Flow Analysis for Dry Granular Material

Debris flow entrainment refers to the increase in mass by way of erosion of the channel beds or undermining the channel banks. Entrainment makes the calculation of travel distance and velocities of debris flow much more complex and difficult. Shear failure of the material in the channel bed is usually considered to be the dominant mechanism in entrainment analysis. However in granular flow, material at the surface of the channel bed can be eroded by progressive scouring under the base of the debris. This may result in more material being eroded and entrained than just considering the shear failure mechanism. A new analytical model is proposed to calculate entrainment in debris flow analysis by considering both rolling and shearing motion. Newton’s Law of Motion is used to calculate accelerations, velocities, and displacements of granular particles. To study the entrainment process inside granular flow and to verify the new entrainment model, numerical experiments have been carried out using the Discrete Element Method (DEM). Velocities, including translational velocity, rotational velocity and average velocity, total volume, shear stresses are monitored using measurement circles in the numerical experiment. Variations of the depth of erosion at specific locations along the debris flow channel are monitored and the average entrainment rates are calculated. By comparing the numerical experimental results with the analytical solutions, it is found that results from the analytical model agree well with that from the numerical experiments. In order to use the new entrainment model into debris flow runout calculation, the new entrainment model has been incorporated in a runout model based on an energy approach. Entrainment calculation governed by a second order partial differential equation is solved using the finite difference method. The total mass and profile of the channel bed are adjusted during the entrainment calculation. Sensitivity analyses have been carried out on the new model by varying the model parameters including internal friction angle, basal friction angle, turbulent coefficient and mean of Probability Density Function (PDF) etc. Back analysis of historical cases is carried out using the new model. Several case histories have been studied which include the Tsingshan debris flow, Niumian Rock Avalanche, Fjaerland debris flow, Faucon debris flow and Zymoetz River rock avalanche. An extremely large rock avalanche occurred on April 9, 2000 at Yigong is also studied in the thesis. Measurements obtained from site investigation, including flow velocity, flow height, entrainment depth at specific locations, run-out distance and total volume at deposition fan, have been used to evaluate the model. The results are encouraging based on comparisons of the run-out distance, front velocity and total volume of the debris. Improvements are required on the entrainment depth and total volume in some cases when lateral spreading of the debris is significant.

Improvements to the statistical theoretical model for wave breaking based on the ratio of breaking wave kinetic and potential energy

An improvement was proposed for the statistical theory of breaking entrainment depth and surface whitecap coverage of real sea waves in this study. The ratio of the kinetic and potential energy was estimated on a theoretical level, and optimal constants were determined to improve the statistical theory model for wave breaking. We also performed a sensitivity test to the model constants. A comparison between the model and in situ observations indicated that the level of agreement was better than has been achieved in previous studies.

Analytical estimation of mixing coefficient induced by surface wave-generated turbulence based on the equilibrium solution of the second-order turbulence closure model

Based on the equations of motion and the assumption that ocean turbulence is of isotropy or quasi-isotropy, we derived the closure equations of the second-order moments and the variation equations for characteristic quantities, which describe the mechanisms of advection transport and shear instability by the sum of wave-like and eddy-like motions and circulation. Given that ocean turbulence generated by wave breaking is dominant at the ocean surface, we presented the boundary conditions of the turbulence kinetic energy and its dissipation rate, which are determined by energy loss from wave breaking and entrainment depth respectively. According to the equilibrium solution of the variation equations and available data of the dissipation rate, we obtained an analytical estimation of the characteristic quantities of surface-wave-generated turbulence in the upper ocean and its related mixing coefficient. The derived kinetic dissipation rate was validated by field measurements qualitatively and quantitatively, and the mixing coefficient had fairly good consistency with previous results based on the Prandtl mixing length theory.

Complex mantle flow around heterogeneous subducting oceanic plates

The foundering of oceanic lithospheres controls the circulation patterns of the mantle around subducting slabs. Here, we investigate the sensitivity of the mantle flow to slab buoyancy variations along convergent margins using three-dimensional numerical models of subduction in a viscous mantle. The models illustrate that in a buoyancy-driven system varying subduction velocity arising from negative buoyancy variations effectively drives pressure gradients and confers a general flow component sub-parallel to the margin's strike, allowing for material transport over large distances around the slabs. The along-slab velocity component introduces widespread horizontal simple shear in the mantle flow which is maximized beneath the slab between ∼100 and ∼350km. Mantle flow complexities develop rapidly, although not instantaneously, upon subduction of heterogeneous plates. The resulting slab pull gradients are mostly accommodated by internal slab deformation, decoupling the mantle flow from motions at surface. Moderate slab pull variations have a minor impact on plate velocity, and might not result in trench motions, although effectively rearrange the flow. Slab buoyancy heterogeneities are firstly associated with age-dependent thickness variations, but also with slab break offs and windows, varying depth of subduction and entrainment of buoyant blocks. Because these are observed at all subduction zones, the process shown here should have a global relevance for the flow around slabs.

Depth profiling 137Cs and 60Co non-intrusively for a suite of industrial shielding materials and at depths beyond 50 mm

A phantom has been used to position two radiation sources, separately, when buried under dry-silica sand at depths between 5 and 50mm. A γ-ray energy spectrum was then measured at every 1mm depth. Principal component analysis has been conducted, which has led to a non-linear fit being established, allowing the depth of entrainment to be accurately inferred. The technique has been expanded for additional shielding media: water, aggregate and both wet and dry soil. The technique has also been expanded beyond the previous depth constraint of 50mm.

Axial Wind Effects on Stratification and Longitudinal Salt Transport in an Idealized, Partially Mixed Estuary*

Abstract A 3D hydrodynamic model [Regional Ocean Model System (ROMS)] is used to investigate how axial wind influences stratification and to explore the associated longitudinal salt transport in partially mixed estuaries. The model is configured to represent a straight estuarine channel connecting to a shelf sea. The results confirm that wind straining of the along-channel salinity gradient exerts an important control on stratification. Two governing parameters are identified: the Wedderburn number (W) defined as the ratio of wind stress to axial baroclinic pressure gradient force, and the ratio of an entrainment depth to water depth (hs/H). Here W controls the effectiveness of wind straining, which promotes increases (decreases) in stratification during down-estuary (up-estuary) wind. The ratio hs/H determines the portion of the water column affected by direct wind mixing. While stratification is always reduced by up-estuary wind, stratification shows an increase-then-decrease transition when down-estuary wind stress increases. Such transition is a result of the competition between wind straining and direct wind mixing. A horizontal Richardson number modified to include wind straining/mixing is shown to reasonably represent the transition, and a regime diagram is proposed to classify the wind’s role on stratification. Mechanisms driving salt flux during axial wind events are also explored. At the onset and end of the wind events, barotropic adjustment drives strong transient salt fluxes. Net salt flux is controlled by the responses of subtidal shear dispersion to wind forcing. Moderate down-estuary winds enhance subtidal shear dispersion, whereas up-estuary winds always reduce it. Supporting observations from upper Chesapeake Bay are presented.

The Statistical Theory of Breaking Entrainment Depth and Surface Whitecap Coverage of Real Sea Waves

Abstract Some basic statistics for wave breaking have been derived based on the statistical model of real sea waves. The analytic expressions of breaking entrainment depth and surface whitecap coverage involved with both sea wave characteristics and surface wind velocity have been derived on the basis of the whitecap formation model. The concept of the upper envelope for all the whitecap coverage data versus wind speed has been proposed, and it is assumed to correspond to the whitecap coverage in the case of the infinite wind duration and fetch to determine the model constants. The analytic expressions of breaking entrainment depth and whitecap coverage have been compared with the observations in several ways, and consistently favorable agreement can be found for most observations.

Lithosphere formation in the central Slave Craton (Canada): plume subcretion or lithosphere accretion?

Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate positively with NiO and negatively with CaO contents, consistent with variable partial melt extraction. Alumina and Cr2O3 contents are broadly positively correlated, suggestive of melt depletion in the absence of a Cr–Al phase. Garnet modes are high at a given Al2O3 content (a proxy for melt depletion), falling about a 7 GPa melt depletion model. These observations, combined with high olivine Mg# and major-element relationships of FeO-poor peridotites ( 3 GPa (residual FeO content being a sensitive indicator of melt extraction pressure), and similar high pressures of last equilibration (∼4.2 to 5.8 GPa), provide multiple lines of evidence that the mantle beneath the central Slave Craton has originated as a residue from high-pressure melting, possibly during plume subcretion. Apparent low melt depletion pressures for high-FeO peridotites (>7.5 wt%) could suggest formation in an oceanic setting, followed by subduction to their depth of entrainment. However, these rocks, which are characterised by low SiO2 contents (<43 wt%), are more likely to be the result of post-melting FeO-addition, leading to spuriously low estimates of melt extraction pressures. They may have reacted with a silica-undersaturated melt that dissolved orthopyroxene, or experienced olivine injection by crystallising melts. A secular FeO-enrichment of parts of the deep mantle lithosphere is supported by lower average Mg# in xenolithic olivine (91.7) compared to olivine inclusions in diamond (92.6).

Sediment transport by sea ice in the Chukchi and Beaufort Seas: Increasing importance due to changing ice conditions?

Abstract Sediment-laden sea ice is widespread over the shallow, wide Siberian Arctic shelves, with off-shelf export from the Laptev and East Siberian Seas contributing substantially to the Arctic Ocean's sediment budget. By contrast, the North American shelves, owing to their narrow width and greater water depths, have not been deemed as important for basin-wide sediment transport by sea ice. Observations over the Chukchi and Beaufort shelves in 2001/02 revealed the widespread occurrence of sediment-laden ice over an area of more than 100,000 km2 between 68 and 74°N and 155 and 170°W. Ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed, multiple layers of rafted nilas, indicative of a flaw-lead environment adjacent to the landfast ice of the Chukchi and Beaufort Seas. This is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern Chukchi Sea in February of 2002 as well as formation of sediment-laden ice along the Beaufort Sea coast as far eastward as the Mackenzie shelf. Moored upward-looking sonar on the Mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment. Analysis of Radarsat Synthetic Aperture (SAR) imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment (>20 m for the Chukchi Sea). Sediment loads averaged at 128 t km–2, with sediment occurring in layers of roughly 0.5 m thickness, mostly in the lower ice layers. The total amount of sediment transported by sea ice (mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment) is at minimum 4×106 t in the sampling area and is estimated at 5–8×106 t over the entire Chukchi and Beaufort shelves in 2001/02, representing a significant term in the sediment budget of the western Arctic Ocean. Recent changes in the Chukchi and Beaufort Sea ice regimes (reduced summer minimum ice extent, ice thinning, reduction in multi-year ice extent, altered drift paths and mid-winter landfast ice break-out events) have likely resulted in an increase of sediment-laden ice in the area. Apart from contributing substantially to along- and across-shelf particulate flow, an increase in the amount of dirty ice significantly impacts (sub-)ice algal production and may enhance the dispersal of pollutants.