Fluid Mud Research Articles

The effects of flocculation on the entrainment of fluid mud layer

Flocculation is an integral part for cohesive sediment transport processes as it will further influence other processes such as settling, deposition as well as erosion processes. To understand the impacts of flocculation on entrainment process of fluid mud with different salinities, a series of entrainment and sedimentation experiments were conducted. Entrainment experiments were conducted under constant hydrodynamic conditions driven by a shear ring on the top of an annular flume. While the sedimentation experiments were conducted within cylinders with different diameters. Results show that fluid mud samples with different salinities can form different distributions of sediment concentration in the vertical direction, which will significantly influence the entrainment rate of fluid mud. Results also show that entrainment rate of fluid mud with higher salinity (E18) is smaller than that of fluid mud with lower salinity (E4) in the upper layer of fluid mud. Sedimentation tests show that the settling rate of fluid mud sample with higher salinity is enhanced and the gelling concentration is reached at a lower sediment concentration. These two mechanisms cause the different distributions of sediment concentration for fluid mud under different flocculation states. Accordingly, the mud characteristics such as density, viscosity, yield strength, buoyancy effects and eventually the entrainment rate vary with different fluid mud samples (the initial sediment concentrations are the same). An effort has also been made to predict the entrainment rate with existing equation. The good agreement between from equation and experimental results further demonstrates that the flocculation process should be considered when calculating the entrainment rate, as accurate prediction of the entrainment rate of fluid mud requires the details of sediment concentration and rheological properties of fluid mud in the vertical direction.

High‐resolution X‐ray fluorescence profiling of hybrid event beds: Implications for sediment gravity flow behaviour and deposit structure

AbstractHybrid event beds form when turbidity currents that transport or locally acquire significant quantities of mud decelerate. The mud dampens turbulence driving flow transformations, allowing both mud and sand to settle into dense, near‐bed fluid layers and debris flows. Quantifying details of the mud distribution vertically in what are often complex tiered deposits is critical to reconstructing flow processes and explaining the diverse bed types left by mud‐bearing gravity flows. High‐resolution X‐ray fluorescence core scanning provides continuous vertical compositional profiles that can help to constrain mud distribution at sub‐millimetre scale, offering a significant improvement over discrete sampling. The approach is applied here to cores acquired from the Pennsylvanian Ross Sandstone Formation, western Ireland, where a range of hybrid event beds have been identified. Raw X‐ray fluorescence counts are calibrated against element concentrations and mineral abundances determined on coincident core plugs, with element and element log‐ratios used as proxies to track vertical changes in abundances of quartz, illite (including mica), chlorite and calcite cement. New insights include ‘stepped’ (to higher values) as opposed to ‘saw‐tooth’ vertical changes in mud content and the presence of compositional banding that would otherwise be overlooked. Hybrid event beds in basin floor sheets that arrived ahead of the prograding fan system have significantly cleaner sandy components than those in mid‐fan lobes. The latter may imply that the heads of the currents emerging from mid‐fan channels entrained significant mud immediately before they collapsed. Many of the H3 debrites are bipartite with a sandier H3a division attributed to re‐entrainment and mixing of a trailing debris or fluid mud flow (H3b) with sand left by the forward part of the flow. Hybrid event bed structure may thus partly reflect substrate interaction and mixing during deposition, and the texture of the bed divisions may not simply mirror those in the suspensions from which they formed.

High flow variability and storm events shape the ecology of the Mbhashe Estuary, South Africa

The possible impacts of extreme events on the ecology of selected aquatic biota within the Mbhashe Estuary were investigated during a four year (2010–2013) spring sampling programme. During periods of low to average flow conditions the estuary is shallow, turbid and characterised by the presence of fluid mud and the build-up of mud and clay deposits. During these conditions, extremely high biomasses of intertidal microalgae and zooplankton are present. Fish and macroinvertebrate abundance and diversity are also highest during low-flow conditions. Flood events can reset, or partially disrupt, the sediment erosion/depositional cycle and decrease the biomass and diversity of plankton, fish and macroinvertebrate species. The Mbhashe Estuary’s unique fluid mud habitat is therefore subjected to regular resetting, which potentially contributes to the fluid nature of the muds. A storm surge in 2011 resulted in the temporary dieback of an area of mangroves, as a result of the deposition of marine sediment. Although extreme events seem to play an important role in the deposition and erosion cycle of the estuary, an increased frequency of both types of extreme events may ultimately result in estuarine habitat loss, which will adversely affect the biota of the estuary.

Comparison of different turbulence models in predicting cohesive fluid mud gravity current propagation

A numerical study of propagation of cohesive fluid mud gravity currents in the form of lock-exchange was done using the OpenFOAM open source toolbox. An Eulerian approach solution for three separate phases was developed by incorporating a rheological model to predict the front position of cohesive fluid mud gravity currents. The model also simulates features in the complete movement phases including slumping, self-similar, and viscous in which the dynamics of propagation are affected by the balance of viscous and buoyancy forces, and the inertia force is negligible. The influence of using different turbulence models containing sub-grid scale (SGS), modified SGS, detached eddy simulation (DES), delayed-detached eddy simulation (DDES), Launder-R eece-Rodi (LRR), and k-ɛ models on the accuracy of simulation results was evaluated by comparing with available experimental data. The results show that the selection of the proper turbulence model is one of the most important issues for this type of the numerical modeling. The more efficient turbulence model was suggested and tabulated for each stage of propagation and different selected concentrations of 1,045, 1,140, and 1,214 g/L. Although different turbulence models (except k-ɛ) lead to front propagation dynamic simulation results that are in good agreement with the experimental measurements in the early stage of propagation for low concentrations, only DES, SGS, and modified SGS are able to capture the Kelvin-Helmholtz instability vortex shapes at the dense fluid interface, which is the main characteristic of the gravity current through the slumping phase. The calculated accuracies of SGS and modified SGS in predicting gravity current propagation for the both self-similar and viscous phases also are slightly better than DES, DDES, and LRR model results. The results of this study confirmed the performance and efficiency of the modified SGS model in which the interaction coefficients between phases are calibrated for the numerical modeling of fluid mud gravity current propagation.

Fluid Mud Induced by Super Typhoon and Fluvial Flood in a Deep-Dredged Waterway of Xiamen, China

Abstract The mechanisms of fluid mud formation and its characteristics are far from clear in the deep-dredged waterway in Xiamen estuarine bay. Some experiments were conducted in the muddy estuarin...

Dynamic Response of the Fluid Mud to a Tropical Storm

AbstractFluid mud (FM) is a unique sedimentary feature in high‐turbidity estuaries, where it can make a rapid contribution to morphodynamics. Insufficient field measurements and fixed‐point monitoring lead to deficient understandings of the formation, transport, and breakdown of the FM under extreme weather conditions. A field survey was conducted in the Changjiang Estuary during the period of turbidity maximum, just after Typhoon Haikui. The measurements captured the formation of the FM beneath the suspended layers, particularly around the lower reach of the North Passage. The thickness of the observed FM gradually decreased landward along the channel, with the maximum value reaching ~0.9 m. The major features of the observed storm‐induced FM were simulated using the Finite‐Volume Community Ocean Model. The results indicated that the initial appearance of the FM was the result of a typhoon‐intensified, salinity‐induced stratification in the outlet region. The subsequent landward propagation of the FM was driven by the combined effects of the FM‐induced mud surface pressure gradient force and saltwater intrusion near the bottom. Weak mixing during the subsequent neap tidal period sustained the FM as it rapidly extended into the middle region of the North Passage. This produced a large velocity shear at the interface of the FM and upper suspension layer, increasing the entrainment from the FM to the upper suspension layer. As a result of the increased tidal mixing, the FM weakened and then finally broke down in the subsequent spring tidal period.

Using in situ density and strength measurements for sediment maintenance in ports and waterways

PurposeFluid mud layers can be substantial in waterways and they can jeopardise navigation when the ship’s keel comes in its vicinity. The nautical bottom has therefore to be properly characterised. Mud density and yield stress are used as criteria to characterise the nautical bottom. For a decade, measuring these parameters in situ has been a challenging task. The goal of this paper is to compare the parameters obtained from recently developed in situ measuring instruments.Materials and methodsTwo vertical profilers (Graviprobe and Rheotune) were used in this study. The Graviprobe measures the undrained shear strength, whereas the Rheotune measures the Bingham yield stress and density of mud layers. Four different locations at the Port of Hamburg were used to test the Rheotune. Bingham yield stresses obtained from Rheotune measurements were compared with the laboratory rheological measurements. The mud layer thicknesses profiled by Graviprobe and Rheotune at the Port of Hamburg and at the Port of Rotterdam were compared. The measurements were also compared with a model that predicts the consolidation of weak mud.Results and discussionThe Rheotune data match well with the laboratory experiments at two of the four tested locations at the Port of Hamburg. For the other two locations, the Rheotune data underestimates the Bingham yield stress, as compared with the laboratory data. The reason for the discrepancy is discussed. The comparison between the Graviprobe’s and Rheotune’s profiles showed that the thickness of the fluid mud layer, found from each device, for all locations, is similar. The in situ density measurements were confirmed by the laboratory experiments. It was found that the standard model for consolidation of mud could reproduce the in situ strength and density measurements as a function of time relatively well. The mismatch between model and experimental data is most probably due to a change in constitutive parameters over time.ConclusionsOur results show that the correlation between density and yield stress measurements, as a function of different measuring equipment, strongly depends on the type of mud. Therefore, a proper calibration should be performed by establishing a reference database for each equipment. In order to decrease the amount of in situ survey, it is also necessary to develop models that can accurately predict the consolidation over time.

Detection of fluid mud layers using tuning fork, dual-frequency echo sounder, and chirp sub-bottom measurements

Many ports and navigation channels around the world suffer from silting and the presence of fluid mud layers, which can cause reductions in nautical depth. In this context, the existence of fluid mud layers makes the definition of the bottom ambiguous because the location of interfaces between water, fluid mud, and consolidated mud is dynamic. The present paper presents an integrated approach to analyzing the fluid mud layers in different port regions of South America and under controlled conditions in a laboratory column. In situ measurements were obtained with acoustic equipment, a chirp sub-bottom profiler and density profiles. The laboratory experiment was operated in a sedimentation column 4.3 m high, and dual-frequency echo sounder and density measurements were used to monitor sedimentation and resuspension events. Concerning the detection of the mud layers through dual-frequency echo sounder measurements, the high frequency return (HF) is associated with the water mud interface (lutocline), and the low frequency return (LF1) is more difficult to interpret. The high frequency recorded the position of the upper layers formed, either by resuspension or by the presence of diluted suspension. The depth measured by the low frequency can be either related to higher densities or associated with a second density gradient observed in the profiles. It is recommended to interpret and visualize the echograms when there is interference in the signal due to suspensions. The combination of techniques to detect and measure the fluid mud layers is a promising approach to empower and develop tools using fluid mud for navigation, with a potential increase in draft, as well as to define critical densities for port and channel areas, for safe navigation.

Spatial variability of organic matter degradability in tidal Elbe sediments

PurposeThe microbial turnover of sediment organic matter (OM) in ports and waterways impacts water quality, sonic depth finding and presumably also rheological properties as well as greenhouse gas emissions, especially if organic carbon is released as methane. As a consequence, sediment management practices as a whole are affected. This study aimed to discern spatial OM degradability patterns in the Port of Hamburg and investigated correlations with standard analytical properties as a basis for future predictive modelling.Materials and methodsSediments in the Port of Hamburg were repeatedly sampled at nine locations along an east-west transect using a 1-m corer. In a stratified sampling approach, layers of suspended particulate matter (SPM), fluid mud (FM), pre-consolidated sediment (PS) and consolidated sediment (CS) were identified and individually analysed for long-term aerobic and anaerobic degradation of organic matter, DNA concentration, stable carbon isotope signature, density fractions and standard solids and pore water properties.Results and discussionThe investigation area was characterised by a distinct gradient with a 10-fold higher OM degradability in upstream areas and lower degradability in downstream areas. Concomitantly, upstream locations showed higher DNA concentrations and more negative δ13C values. The share of bulk sediment in the heavy density fraction as well as the proportion and absolute amount of organic carbon were significantly larger at downstream locations. A depth and hence age-related gradient was found at individual locations, showing higher degradability of the upper, younger material, concomitant with higher DNA concentration, and lower OM turnover in the deeper, older and more consolidated material. Deeper layers were also characterised by higher concentrations of pore water ammonium, indicative of anaerobic nitrogen mineralisation.ConclusionsOrganic matter lability is inversely linked to its stabilisation in organo-mineral complexes. The observed degradability gradient is likely due to the different OM quality in relation to its origin. Downstream OM enters the system with the tidal flood current from the direction of the North Sea whereas upstream locations receive OM originating from the catchment, containing more autochthonous, plankton-derived and more easily degradable components. At individual sampling points, depth-related degradability gradients reflect an age gradient, with easily degradable material in top layers and increasing stabilisation of OM in organo-mineral compounds with depth.

New insights into fluid-rock interaction mechanisms at mud volcanoes: Implications for fluid origin and mud provenance at Bahar and Zenbil (Azerbaijan)

Understanding the fluid-rock interactions occurring in terrestrial mud volcanoes is a premise for elucidating the (bio)geochemical processes involved in the release of aqueous fluids, mud and gases to the Earth's surface and atmosphere. For the first time, fluid and mud ejecta from the mud volcanoes at Bahar and Zenbil, located in eastern Azerbaijan and in the shallow coastal water of the South Caspian, were collected and analyzed for their mineralogical, textural and chemical composition. The expelled aqueous fluids have a Na-Cl-(HCO3) composition and are generated by the mixing of evaporitic Caspian seawater and ancient, low- to high-salinity, sedimentary pore water at temperatures of 32 ± 3 °C and 42 ± 5 °C for the mud volcanoes at Bahar and Zenbil, consistent with mud chambers to be situated in the Pliocene sediments at 2–3 km depth. These aqueous fluids are strongly enriched in major solutes, like Na, Cl, HCO3, B, Br, NH4 and DOC, as well as in some trace elements (As, Ba, Cu, Fe, Li, Sr and Zn), with concentrations up to 220 times that of the current Caspian seawater. This chemical concentration is caused mainly by a combination of (i) strong surface evaporation, ion exchange and adsorption-desorption involving smectite clays, redox-driven reactions and carbonate mineral precipitation at relatively shallow depths (not deeper than 4 km) as well as (ii) thermal breakdown of organic matter and methane production in deeply buried (4 to 7 km depth) organic-rich strata. Biogenic processes are only of minor importance. The mud is sourced from all horizons the mud volcanoes are cross-cutting, partly altered by diagenetic processes. Alteration is comprised of illitization of smectite during burial diagenesis (120 to 150 °C), replacements of feldspar by kaolinite and smectite, weathering of sulfide minerals, Fe-(oxy)hydroxide formation, as well as oxidation of methane and organic matter in the near sub-surface environments at low temperature (<40 °C). Our results indicate that fluid-mud mixtures expelled from mud volcanoes of the South Caspian basin can influence the chemistry of local surface and ground water as well as of (sub-)surface sediments.

Mud deposits at Cassino beach: role of dredging

Mud deposits on Cassino beach are associated with waves generated from storms during cold front passages and extratropical cyclones from the southern quadrant. During such episodes fluid mud deposited at the shoreface and surf zone is transported towards the surf zone and the sandy beach prism. The first mention on the origin of mud has always attributed a source exclusively natural for the deposits. However, new interpretations and recent data indicate that the increase in dredged volumes over the years increased the frequency of mud depositions. In order to verify this association, records of dredged and discarded volumes in the Port of Rio Grande and Cassino beach shoreface were analyzed. Maps of bottom types, silt and clay ratio, and fluid mud thickness obtained from superficial samples and sediment cores between 4 and 15 m water depth at the time of the 1998 impact were also reanalyzed. Current conditions near the dumping sites in the estuary and inner shelf in 1998 were reconstructed by hindcast based on reanalysis data and an ADCP anchored 15 m off the Rio Grande coast. In order to verify the effect of the passage of a cold front on the bottom near the ocean dumping site, data from two mooring stations made on the crest and swale of a sand ridge field were considered. To further understand the disposal of the dredged material, a particle transport model was created for two periods related to the depositional events. In the period of 1998, it was simulated the disposal of dredged material on two locations, one with the disposal of 640,000 m3 of sediment inside the estuary at 8 m of depth and, the other, with 2.3 million m3 of disposal material, at 13 m depth in the shoreface. The simulation at depth of 19 m, for the dumping site of 2014 considered the disposal of 1,000.000 m3 at 19 m water depth. The occurrence of massive concentrations of an estuarine gastropod associated with the deposits at the beach led to a literature search on their occurrence in the area after researches carried out for more than three decades on the fauna ecology of sandy beaches. From the 1970s onwards, dredged volumes intensify and were deposited into the estuary and ocean using Hopper dredges. There was an increase in episodes of mud deposition at CB. The sedimentation patterns after dredging operations indicate that natural sedimentary processes are altered in a transient way. Currents generated by winds and storms in both quadrants north and south provide conditions of instability of fine sediments in the disposal sites with flow components parallel and also direct to the coast regardless of wave action. Hydrodynamic modeling indicates that sediments disposed into both the estuary and the shoreface during northeast and southern winds have the potential to be driven towards the beach. The massive deposition of millions of organisms after dredging events is not a natural process and is an indication of the dredging activities. Dredging can be an important part of the environmental impact because the natural accumulation process is enhanced by intense pulses of fine sediments in short time favoring more frequent depositions since the historical and current disposal sites are not appropriate. Negative environmental impacts are related to beach usage since it affects sunbathers, surfers, vehicle traffic, morphodynamic changes, and massive mortality of the benthic fauna.

Two-dimensional modeling of fine sediment transport with mixed sediment and consolidation: Application to the Gironde Estuary, France

In order to optimize ship navigation in the macrotidal Gironde Estuary, a recent project funded by the port of Bordeaux aims at better understand and forecast hydrodynamic and fine sediment transport within the estuary. In the framework of this project, a two-dimensional hydro-sedimentary model is built. The model includes hydrodynamic forcings, mixed-sediment transport, and consolidation processes. The harmonic analysis of the astronomical tides reveals a strong distortion of the tidal wave inducing the growth of overtide constituents and the non-significant effect of tide-surge interactions in annual-scale prediction. Depending on hydrological conditions, river discharge can considerably alter the model accuracy due to the migration of the turbidity maximum zone modifying the bottom roughness. Comparison with measurements shows the ability of the model to reproduce suspended-sediment concentrations in the central Estuary. Sensitivity of the model to sediment features has also been discussed in regard of suspended-sediment concentrations and fluid mud deposits. The model will be further coupled with ship squat predictions and a morphodynamic model.

Nanoparticle-based drilling fluids as promising solutions to enhance drilling performance in Egyptian oil and gas fields

Over the years, the discovery of petroleum in various regions of the world has led to the development of different techniques and equipment to enhance and optimize the drilling and production operations in this vital industry. Egypt is both one of the major oil-producing non-OPEC countries and one of the oldest energy producers in the Middle East. Recently, the Egyptian government have signed several agreements for the exploration of oil and gas in several provinces/regions including; the Mediterranean, the Western desert, the Nile Delta, and the Gulf of Suez. Petroleum companies have given great attention to Egypt’s new discoveries such as Zohr Gas Field, and Nour exploration prospect. Successful drilling operations to reach the oil and gas targets depends strongly on the effectiveness of the drilling fluids. Drilling fluids can be considered as the heart of the drilling process. They are used to fulfil several functions, such as controlling pressure, carrying cuttings and cooling bit and drill strings, stabilizing wellbore as well as controlling fluid losses. Drilling fluid technology is one of the most targeted and developed technologies worldwide. Several studies have examined the use of various types of nanoparticles (NPs) as additives to enhance the properties and improve the performance of the drilling fluid to mitigate the drilling problems. NPs can be defined as a simplest structure with a size in the range of nanometers. The effectiveness of NPs can be accredited to their small sizes and thus, high surface-area-to-volume ratio. NPs were also showed promising enhancements on the rheological and filtration characteristics of the drilling fluid (mud). Additionally, swelling and collapse of shale formations is expected under drilling with water-based mud, which might result in complicating the drilling operation. Adding NPs to the drilling mud was found to minimize the shale permeability and thus, promote the wellbore stability. This research paper discusses the latest applications and presents the most valuable findings concerning the efficient use of NPs in the drilling fluid industry. Based on that, different recommendations are stated. This might help researchers to better understand NPs’ functionality in this area of application and promote using NPs-based drilling muds as cost-effective and environmental-friendly fluids to drill the Egyptian oil and gas wells.

Suspended sediment properties in the Lower Mekong River, from fluvial to estuarine environments

The Mekong river is one of the largest rivers in the world, which flows through six countries of Southeast Asia (China, Myanmar, Laos, Thailand, Cambodia and Vietnam). Its hydro-sedimentary regime is changing rapidly, as a consequence of a regional shift of land use (agriculture, road, etc.), damming, sand mining and climate changes, among others. This study assesses the behavior of particles transported in suspension in the Lower Mekong River (LMR), along approximately 1700 km from fluvial to estuarine environments. Suspended sediment properties were estimated, simultaneously with hydrodynamic conditions, during three field campaigns. In addition, further investigations were performed in the laboratory to assess the structures of particles (flocculated or not), their capacity to flocculate (and the impacts on siltation), under a wide range of sediment concentration (20–30,000 mg.L−1). This study confirms that suspended sediment transported in the LMR are predominantly (75% by volume) flocculi (or freshly eroded soils aggregates), with median aggregated particle size in the range 10–20 μm and median settling velocity of the order of 0.01–0.1 mm s−1. These flocculi are robust under the hydrodynamic conditions (turbulence and suspended sediment concentration – SSC) existing in the LMR. Laboratory investigations reveal the existence of a threshold sediment concentration (400 mg.L−1), beyond which flocculation and sedimentation increase of orders of magnitudes. Thus, concentration that exceeds this threshold might promote the formation of so-called fluid mud layers. Because of the nonlinear response of flocculation and sedimentation with SSC and considering the ongoing changes at a regional scale in the LMR, higher occurrence of fluid mud layers in the fluvial upstream waterbodies might be anticipated, and a lower occurrence in estuaries and alongshore where the concentration decrease. The geomorphology could be impacted, with an over-siltation in dams and an exacerbated erosion of the muddy-mangrove coast.

Application of elastic parabolic equation solutions to acoustic reverberation in ice-covered underwater environments

Parabolic equation solutions can be obtained for underwater acoustic environments where elastic boundaries affect the acoustic propagation. One example of this situation is in the Arctic where a (potentially rough) ice layer is on top of the water column. The parabolic equation method shown here rigorously applies the zero-traction and fluid-elastic interface boundary conditions to obtain full field Green’s function estimates near the ice-water interface. This solution is crucial for calculation of recently derived reverberation estimates that require both horizontal and vertical derivatives of the complex acoustic field. Monostatic reverberation estimates for a rough under-ice interface are calculated for an upward refracting water sound speed profile and an elastic ocean bottom with a nearly fluid mud layer. These calculations could be used, for example, to estimate areal distribution of the ice layer roughness from azimuth-time dependence of acoustic reverberation measured in Arctic environments. Performance of the Pade rational function approach in the presence of thin ice cover and low shear speed ocean bottom layers will be addressed.

Pumping effect of wave-induced pore pressure on the development of fluid mud layer

Fluid mud widely exists in the movement of fine sediment, which is an important potential cause of marine geological disasters. It is important to understand the generation and migration mechanism of fluid mud. The purpose of this study is to investigate the vertical migration response of fine-grained sediments by wave-fluid test of pore pressure response of silty seabed under wave action. The results show that the adhesion between the silt particles and the additional pressure of the film water have a significant effect on the liquefaction characteristics of the silt. Even if the liquefaction degree is far more than 100%, the soil does not completely liquefy. The experiment result show that, there is concentrated movement of the split channel, and mesoscopic migration of fine particles between the gaps of the particles, pumping effect provides an effective source of supply for the development of the floating mud layer, it also exacerbates modern sedimentation when strengthening the vertical exchange of shallow soil in the seabed. Besides, the blending of the middle and lower layers of the previous soil with the recent sediments has increased the difficulty of identifying the time series of the modern sedimentary layer to some extent.

Contribution of Pumping Action of Wave-Induced Pore-Pressure Response to Development of Fluid Mud Layer

To investigate the vertical migration response of fine sediments, the pore pressure response of the silty seabed under the action of waves was tested. Under the action of waves, there is an obvious pumping phenomenon in the sludge accumulated by pore pressure. The excess pore water pressure caused by the waves in the seabed is unevenly distributed with respect to depth and there is an extreme value of up to 1.19 kPa. The pressure affects the liquefaction properties of the sludge. According to instantaneous-liquefaction judgment, the liquefaction of surface soil occurs, but the soil is not completely liquefied. Using theoretical calculations, the vertical source supply of floating mud development was analyzed. The pumping effect of the wave-induced excess pore pressure manifests in two aspects, as follows: (1) The centralized migration of splitting channels, which is visible to the naked eye, and (2) the general migration of fine particles between particle gaps at the mesoscopic level, which accounts for up to 22.2% of the migration of fine particles.

Rheological analysis of mud from Port of Hamburg, Germany

PurposeAn innovative way to define navigable fluid mud layers is to make use of their rheological properties, in particular their yield stress. In order to help the development of in situ measurement techniques, it is essential that the key rheological parameters are estimated beforehand. Is there only one yield stress? In which shear rate/shear stress range is yield expected to occur? How is yield stress dependent on depths and locations in the harbor? In order to answer these questions, we investigated the changes in the rheological properties of mud from along the river stream in the Port of Hamburg, Germany, using a recently developed laboratory protocol.Materials and methodsIn this study, a detailed rheological analysis was carried out on the mud samples collected from different locations and depths of the Port of Hamburg. A variety of rheological tests was performed including: stress sweep tests, flow curves, thixotropic tests, oscillatory amplitude, and frequency sweep tests.Results and discussionThe yield stresses of sediments from different locations were significantly dissimilar from each other due to differences in densities and organic matter content. Two yield stresses (termed static and fluidic) were observed for every sample and linearly correlated to each other. The thixotropic studies showed that all mud samples, except from one location, displayed a combination of thixotropic and anti-thixotropic behaviors. The results of frequency sweep tests showed the solid-like character of the sediments within the linear viscoelastic limit. The yield stresses, thixotropy, and moduli of the mud samples increased by going deeper into the sediment bed due to the increase in density of the sediments.ConclusionsThis study confirmed the applicability of the recently developed protocol as a fast and reliable tool to measure the yield stresses of sediments from different locations and depths in the Port of Hamburg. The fluid mud layer, in all the locations it was observed, exhibited relatively small yield stress values and weak thixotropic behavior. This confirms that despite the fact that rheology of fluid mud is complex, this layer can be navigable.

Winter storms induced high suspended sediment concentration along the north offshore seabed of the Changjiang estuary

Fine-grained sediments suspended in coastal waters play an important role in submarine topography evolution and associated environment changes. The convergence of suspended sediments concentrated near the seabed results in high sediment concentration, and contributes significantly to sediment transport. In order to investigate the mechanism triggering high suspended sediment concentration (SSC), we deployed a tripod to the seabed to obtain in situ bottom boundary layer measurements of sediment dynamics and a buoy to the sea surface to collect meteorological and wave data at the northern Changjiang River mouth from December 20, 2015 to January 20, 2016. The high SSC (e.g. >3 g/L) events were observed together with fluid mud (thicknesses of 4–16 cm) near the seabed during neap tides when cold air intrusion generated winter storms and strong waves. Further, we found that the high SSC event was mainly resulted from wind waves and sediment resuspension supported by local benthic fluid mud, which was associated with three stages. At the setting up stage, the winter storm brought long duration of strong-waves (e.g. significant wave height >1.5 m) more than 15 h, resulting in a maximum wave-current combined bottom shear stress of 3.2 Pa and the increase of SSC to >1 g/L. At the reinforcement stage, the strong waves and bottom shear stress lasted for several hours, and further increased the SSC to >3 g/L. At the final decay stage, wind waves and the maximum wave-current shear stresses decreased significantly, with the disappearance of high SSC. Thus, there was no high SSC event observed even with strong wind waves during spring tides because strong wave duration was too short for the reinforcement process. The sediment source for the high SSC events was mainly from bottom fluid mud resuspension, as well as the advection transport from the adjacent subaqueous Changjiang River delta.

Mud dynamics in the Port of Zeebrugge

This paper presents the mud dynamics in the harbor basin of Zeebrugge in the Southern North Sea based on an analysis of field data. Mud is typically transported into and within the harbor basin through advection of suspended particulate matter (SPM). Three important timescales have been identified. On the intratidal timescale, sediment import occurs from 2 h before high water to high water. Flood currents in the North Sea (directed northeastward along the Belgian coast) drive the primary gyre in the harbor mouth which is advected into the basin during rising tide. This results in water inflow near the eastern breakwater and outflow near the western breakwater. Because of sediment settling in the harbor, this results in a net import of SPM. During spring tide, the SPM flux into the harbor basin is two to four times higher than during neap tide. However, the volume of sediment removed from the port by maintenance dredging is kept constant over the spring-neap cycle, causing the amount of mud in the harbor basin to grow around spring tide conditions. On the seasonal timescale, mud volume within the harbor basin is larger in winter and reaches a minimum at the beginning of autumn. Moreover, the measured densities within the deposited mud layers are lower in winter than in summer. The most shallow point of the 210-kHz reflector is also more shallow in winter. Finally, the profile of the interface of the mud layer in the sheltered Albert II dock is more horizontal in winter than in summer, suggesting seasonal variations in the strength of the mud layer. The question to what degree the seasonal variation of thickness and density of the fluid mud layer is related to differences in the suspended sediment input, to differences in the settling rates of suspended flocs, or to the mud consolidation rate remains open however. The data do not show a strong influence of meteorological conditions (waves, freshwater inflow) on siltation rates in the harbor basin.