Sand Waves Research Articles

A Salt Tolerant Native plants as a Solution for Mobile Sand and Dust in Kuwait

In this study, a coastal research site north of Kuwait Bay faces sand encroachment, floods, and wave erosion. The plantation project’s infrastructure was improved by fencing 1.2 km2 with barbed wire. The heavily deteriorated environment has coppice dunes of Nitraria retusa and Lycium shawii around single, double, or triple plants. To manage mobile sand and dust and protect the research centre, 21,500 Nitraria and Lycium were planted and irrigated with brackish water (around 7000 TDS). In order to aerodynamically shift and/or trap mobile aeolian sediments, the vegetation was planted in a V-shape facing the north-westerly wind. A closer gap (about 1m between plants) on the side facing the primary wind and widened toward the inner edges of the gated area controls mobile sand and dust. This projected design stabilizes the soil, protects against floods and wave erosion, enhances flora and animals, and controls aeolian activity. Mobile sand and dust yearly rates in the downwind traps were reduced by 94% and 64.5%, respectively. Native vegetation can control mobile sand and dust, according to this. Such systems can be more efficient with proper design and plant spacing.

Geological hazards in the Oujiang estuary in the Zhejiang Province, China: type, distribution, and origin

Introduction: As our understanding of the ocean and its uses continues to advance, countries worldwide with ocean access are implementing new marine strategies. For example, understanding marine geological disasters can help develop the use of ocean resources and oceanic engineering.Methods: Therefore, this study used recent data from the Oujiang Estuary, a nearshore area in China, to determine its geological hazards.Results: The geological hazards were classified as active or restricted based on topography, geomorphology, shallow seismic profile, single-channel seismic profile, and geological drilling data. Active geological hazards primarily include shallow gas and active sand waves, whereas restrictive geological hazards include irregularly buried bedrock, erosion channels, steep submarine slopes, and buried paleochannels. We also evaluated the distribution characteristics and scope, such as the vertical distribution of shallow gas based on the seismic profiles, drilling rock facies, methane, and carbon dioxide contents in the top air, and the isotope values. We found that shallow gas was vertically distributed among multiple layers. The main gas-bearing layers were the clayey silt and sandy (silt) clay layers of the early Holocene and late Pleistocene strata. The shallow gas content was relatively low in the coarse sediment layer at the bottom of the late Pleistocene succession. Generally, the Holocene and late Pleistocene deposits do not contain gas, and the gas content in the middle and late Pleistocene strata (at greater depths) is relatively low.Discussion: The combined effects of the regional geological structure, sea level changes, modern hydrodynamics, and human activities have formed the geological environment of the Oujiang Estuary.

Variational RANS modeling of hydraulic jumps

The hydraulic jump is a phenomenon which frequently appears in nearshore, estuarine and riverine regions; it plays a major role for example in the development and migration of sand waves in mobile beds, and in controlling the propagation of infra-gravity water waves from the nearshore into the river through bar-built, shallow estuaries. Although the prediction of these natural flows becomes crucial in many circumstances, it is difficult because hydraulic jumps are complex flows, and their modeling is far from simple. The steady-state hydraulic jump may be undular or broken, and their physical properties differ significantly. Undular jump profiles are dominated by the deviation of the fluid pressure from hydrostatic conditions, with turbulence playing a secondary role. In contrast, broken hydraulic jumps are determined by the differential advection of momentum due to breaking, and turbulence stresses. Between both types, there is a complex transition involving the interaction of non-hydrostaticity and turbulence, which is difficult to mimic with depth-averaged models. Simulations of these flows are typically conducted by resorting to vertically-averaged models either using the Saint-Venant or the Serre-Green-Naghdi equations, but none of them are fully satisfactory. In this work, an alternative approach for hydraulic jumps is proposed by developing a variational Reynolds-Averaged Navier-Stokes (RANS) model which uses Kantorovich-Krylov expansions of the flow variables, and a novel depth-averaged, eddy viscosity approach suitable for non-hydrostatic flows. The model is validated through results of simulations of both undular and broken jumps compared against detailed experiments. New experiments were conducted in a simplified bar-built shallow river inlet; the variational RANS model was found to reproduce well the flow profile over the bar, the hydraulic jump position and dynamic pressures over the bar surface.

ACOUSTIC CHARACTERISTICS OF SIDESCAN SONAR ALONG PROPOSED POWER CABLE ROUTE, DUMAI – RUPAT ISLAND

Cable power installation along the route with bedforms-sediment structures sometimes potentially to have problems in the future or near future. In order to mitigate the cable from exposure because of currents, it is important to know a detailed understanding of the seabed and its mobility. Seabed characteristics, either textures or sediment structures, could be interpreted from acoustic characters, one of which is based on sidescan sonar images. An automatic interpretation to classify seabed characteristics can be done by using an image processing software. Image processing has been done on sidescan sonar images along power cable route between Dumai and Rupat Island. The image processing was using simple textures and Grey-Level Co-occurrence Matrix (GCLM) textures. Manual interpretation of sidescan sonar images classifies the acoustic characters into six; (1) fine sand waves with ripple marks, wave length 2.5-4 meters, (2) fine sands, (3) fine sand waves with ripple marks, wave length 5-9 meters, (4) fine sand with ripple-mega ripples, (5) coarse sands with ripple-trawl marks, and (6) very fine sands. The results of automatic classification show that image processing with simple textures is unable to identify the textures and structures of sediments properly, but by combining simple texture classification and GCLM types of sediment textures and sediment structures are better identified. This classification results are in agreement with the results of manual interpretation of sidescan sonar images.

Experimental Study on Wide-Graded Soil Transport in Unsteady Flow

A special study on the interaction mechanism between flow and soil is of great significance for revealing the macro breaching mechanism of barrier dams. To study the scouring characteristics of wide-graded sediment under different flow conditions, flume scour tests were conducted regarding the grading curve of dam material and the discharge process of the Tangjiashan barrier dam. The results show that: (1) The scouring process of narrow-graded or uniform sediments is the formation and movement of the sand wave, while the scouring mode of wide-graded sediment is mainly the formation, expansion, and movement of the scouring pit. (2) Under the condition of weak unsteady flow, the surrounding and shielding effect of coarse particles on fine particles is obvious, and the erosion resistance of the material is strong. However, under the condition of strong unsteady flow, the erosion resistance is weak. (3) The erosion of wide-graded sediment is mainly caused by slope angle collapse at the initial stage, and mainly reflected by traceable erosion at the later stage. Therefore, in the initial stage of erosion, the downstream erosion intensity is high, and the bed surface can easily form a slope inclined downstream. (4) The scouring intensity under the condition of unsteady flow is greater than that under the condition of steady flow. The sediment transport formula based on the condition of steady flow cannot be used to calculate the dam break process directly.

Exploring distinct types of intertidal bars on either side of a small estuary using a multifaceted approach

Multiple intertidal bars are common sedimentary landforms found on low-gradient sandy coasts exposed to low to moderate wave energy with a significant tidal range. However, studying the factors that influence their morphology can be challenging due to limited high-resolution field data and tools for bedform analysis. To address this, a multifaceted approach was used to investigate the morphology of intertidal bars at two adjacent tidal beaches on the north and south coasts of a small estuary on the Lianyungang coast of China. This approach included repeated real-time kinematic-global positioning system (RTK-GPS) leveling, unmanned aerial vehicle (UAV) surveys, surface sediment sampling, satellite remote sensing analysis, and automated bedform analysis. The study revealed two distinct types of intertidal bars on either side of the estuary with similar hydrodynamic settings. The north coast presented low-amplitude ridges (also called ridges and runnels), while the south coast had sand waves. The north coast displayed 2–5 oblique, asymmetrical, and dynamic bars that appeared at the seaward end of the intertidal zone and migrated landward to eventually attach to the steep beach on the landward end of the intertidal zone, representing a life cycle. The south coast had 6–9 parallel, continuous, symmetrical, and stable sand bars occupying the lower part of the intertidal zone. Due to the nearly identical hydrodynamic background, the alongshore variability in sediment supply is suggested as a key factor driving the formation of distinct types of bars.

Research on the fluid dynamics interaction between submarine sand waves and seawater by seismic oceanography

IntroductionThe seafloor is an important interface between the lithosphere and the hydrosphere, where processes related to circulation and energy exchange happen along with various marine processes widely developed in the water column near the seafloor. These processes are still not yet completely understood as there are constraints of submarine detection technology and the interdisciplinary nature of these complex environments. Seismic reflection data have been a preferable tool to study and image these processes due to their characteristics in terms of spatial resolution. In seismic reflection data, submarine sand waves show hair-like reflection configurations with low continuity and wearing-hair style, appearing with an angle with the seafloor. Investigation of the relationship between the characteristics of submarine sand waves induced hair-like reflection configuration and hydrodynamics is crucial for understanding hair-like reflection configuration generation and spatiotemporal evolution. MethodsThis study combines fluid dynamics numerical simulation and seismic oceanography to discuss the seismic response characteristics and formation mechanisms of the hair-like reflection configuration. First, we create a seawater time-variant fluid-dynamical model followed by the numerical simulation of seismic oceanography data. This procedure results in seismic oceanography numerical simulation sections with hair-like reflection configurations for different constant flow conditions forced on the boundary. Optimal matching method is then applied to interpret field seismic reflection sections given the results obtained with the numerical experiments. Results and discussionAs consequence, the fluid dynamic explanation for the formation mechanism of the hair-like reflection configuration due to differences in seawater thermohaline is proposed. The study provides additional comprehension and further insights into the dynamic process of submarine sand waves induced hair-like reflection configuration using the seismic oceanography method.

Sand wave migration near the southeastern corner of Martha's Vineyard, Massachusetts, USA

Sand waves of approximately 2 m in height were observed to migrate nearly 40 m with counterclockwise rotation between two bathymetric surveys performed three months apart near the southeastern corner of Martha's Vineyard, Massachusetts. The region is characterized by strong tidal currents, intermittent energetic surface wave events, and shallow water with local depth ranging from 2 to 7 m. This study uses the process-based model, Delft3D, with a three-dimensional approach to examine the sand wave dynamics by incorporating surface waves, winds, currents, and bathymetric observations. The model successfully simulates sand wave migration in comparisons to observations. Model sensitivity analyses show that the sand wave migration reduces by 65% with the absence of the surface waves. The modeled sand wave migration speed is correlated with the tidal current Shields parameter, and sharp increases in migration speed occur when the wave-driven Shields parameter increases in response to energetic surface wave events. The combined effect of tides, surface waves, and bathymetry is the origin of the rotational aspect of the sand wave, using the Shields parameter as an indicator of tidal currents and surface wave influence on sand wave dynamics.

Bed forms under the combined action of waves and wind-driven currents in the remote foreshore of the non-tidal sea

The paper presents a prediction of bed form parameters (length and height) in the remote foreshore of the non-tidal sea. The study site is located in the south Baltic region, near the Coastal Research Station (CRS) in Lubiatowo, Poland (ca. 1–2 Nm off the shoreline at depths of around 16–20 m). The study site is an area with hydrodynamics and lithodynamics typical of the south Baltic coast, built of fine sands. Predictions are based on numerical modelling with an input of measured data. Numerical modelling uses assumptions of specific relations of sand wave height and length with shear stress, grain size, kinematic viscosity, or storm event frequency. To establish these relations for the study area, wave, sea temperature and wind data were collected near CRS Lubiatowo. To verify the predictions made in this research, bathymetric data from a field survey in the study area was used. The results show that the flow is mostly current-dominated. Sand waves formed by hydrodynamic conditions in this area have a steepness of 0.01 to 0.02, a length of 40 to 70 m and a height of 0.6 to 2.3 m.

Numerical Investigations on the Transient Behavior of Sand Waves in Beibu Gulf Under Normal and Extreme Sea Conditions

Numerical Investigations on the Transient Behavior of Sand Waves in Beibu Gulf Under Normal and Extreme Sea Conditions

A Numerical Simulation of Internal Wave Propagation on a Continental Slope and Its Influence on Sediment Transport

Significant current velocity near the sea bottom can be induced by internal waves, even for water a few hundred meters in depth. In this study, a nonhydrostatic ocean model was applied to simulate the generation and propagation of internal waves on the continental slope of the northern SCS. Based on the analyses of the vertical profiles of the currents, the propagation of internal waves along the continental slope can be categorized into six modes. The bed shear stress and the bedload transport were calculated to analyze the general characteristics of sediment transport along the continental slope of the northern SCS. Generally, there was no sediment transport on the sea bottom induced by the internal waves when the water depth was deeper than 650 m or shallower than 80 m. The downslope sediment transport dominated the slope at a water depth range of 200~650 m, while the upslope sediment transport dominated the slope at a water depth range of 80~200 m. The predicted directions of the bedload transport are coincident with the field observations of sand wave migration on the continental slope, which further confirms that the main cause of the generation and formation of sand waves on the continental slope of the northern SCS is the strong bottom current induced by the shoaling process of internal waves.

Depositional Facies and Palynofacies Provenance of Clastic Deposits: Insight from Paleocene Strata in Southeast Region, Nigeria

Detailed sedimentary facies and palynofacies provenance studies were carried out on clastic deposits outcropping around the Awka area within the Imo Formation (Paleocene) of the Niger Delta Basin. Seven facies were systematically recognized based on the textural parameters, sedimentary structures and palynological constituents. Interpretation of the prevailing paleoenvironments, palynofacies provenance and depositional mechanisms were derived from the hydrodynamic controls. The sedimentary facies include shales, mudstones, siltstones, heteroliths, cross-bedded sandstones and matrix-supported conglomerates. The palynofacies showed preponderance of amorphous organic matter, marine taxa, opaque particles, with few structured phytoclasts and terrestrial microflora. These palynological microflora constituents are grouped into palynofacies association A and B based on the composition and proportion of the organic particles, stratigraphic position and paleoenvironments of the strata. Facies analysis indicates that the mudrock facies (e.g. shale, mudstone and siltstone) are deposits of deep marine depositional settings with terrestrial input while the sandstones mimic deposits associated with tidal sand waves in shallow sandy seas, braided river and tidally influenced distributary channels. The facies and palynofacies provenance model suggest dominance of terrestrially influenced shallow to deep marine environment evidenced from the abundance of amorphous organic matter and presence of gonyaulacacean dinoflagellate species, Glaphyrocysta ordinata, G. exuberans, and pollen of Proxapertites operculatus, Retitricolporites irregularis with other accompanying marine forms. In addition, the presence of texturally mature coarse- to fine-grained sandstones, variable sedimentary structures, internal bed geometries and nature of bedding are suggestive of tidally dominated shallow marine settings including distributaries channel network deposits.

CAGE20-3 Cruise Report: Geochemical and Sedimentological Investigation into Ingøydjupet, Håkon Mosby Mud Volcano and the Sorvestnaget Sand Waves

This expedition ran between July 28 and August 3 2020, targeting three sites in the Barents Sea, an area of glacial landforms in Ingøydjupet trough, the Håkon Mosby Mud Volcano and the Sorvestnaget Sand Wave area. Our short but productive expedition gave three post-doctoral researchers the opportunity to follow a research hypothesis from conception through planning and data collection aboard the research vessel, as well as plan and lead a research expedition. At the Ingøydjupet and Håkon Mosby Mud Volcano study areas, our objectives were to collect cores for geochemical analyses of the area and bathymetry data for geophysical analyses while the objectives at the sand waves are were to collect a time-lapse multibeam survey and grab samples for sedimentological analysis
 The cruise may be known as: CAGE20_3

Shorter estuarine dunes and upstream migration due to intratidal variations in stratification

Estuarine dunes are large-scale subaqueous rhythmic bed patterns, and differ from river dunes and marine sand waves in that they exist in environments characterized by several estuarine-specific processes. One of these processes is the tidally varying salinity stratification, with stratified conditions inhibiting vertical mixing. This causes an asymmetry between ebb and flood tide, leading to the strain-induced circulation. Here, we show through a morphodynamic linear stability model that reduced turbulent mixing in partially mixed environments leads to significantly shorter dunes compared to well-mixed environments. Furthermore, intratidal variations in stratification are a driver of upstream migration of dunes due to the tidal straining circulation. Our results constitute one explanation for differing dune wavelengths between two positions in the Elbe estuary. This study stresses the importance of (variations in) stratification for estuarine dunes, and hence improves our understanding of dune characteristics.

Shelf-wide analyses of sand wave migration using GIS: A case study on the Netherlands Continental Shelf

Shelf seas often display rhythmic bedforms, of which tidal sand waves are the most relevant to study from an engineering point of view due to their dimensions and dynamic nature. Environmental conditions such as water depth, flow velocities and grain size vary across entire shelf regions, consequently influencing the characteristics of tidal sand waves, including migration rates. However, as opposed to site-specific analyses, shelf sea-wide analyses on sand wave migration are scarce. Through the use of timeseries of bathymetric data, we investigate the spatial variability of sand wave migration on the scale of the Netherlands Continental Shelf (NCS). Two existing data-driven techniques, Pairs of Source and Target Points (PSTP) and Spatial Cross Correlation (SCC), were implemented in a Geographic Information System (GIS). Through testing at four sites on the NCS, PSTP was deemed the preferred technique for a shelf-wide analysis and was hence used to quantify the NCS-wide migration rates and directions. To illustrate the spatial variability, the quantified migration rates and directions were averaged per km2. For the NCS in general, migration to the south-west or north-east at typical rates between 0 and 3 m/year was found. The south-western region of the NCS demonstrated migration rates below 0.5 m/year with migration directions alternating over short distances. The north-eastern region exhibited uniform migration to the north-east at rates which gradually increased when in closer proximity to the Wadden Islands. Typical rates in this region were found to be between 2 and 8 m/year. The highest migration rates were observed near coastal regions and on top of sandbanks. The presence of these sandbanks strongly deflects the migration directions of superimposed sand waves at a number of locations. The analysis performed within this study demonstrates valuable insights into methods that can be used to evaluate shelf-wide regions of interest. A deeper understanding of the dynamic nature of the North Sea bed assists in optimising hydrographic re-survey policies, critical infrastructure planning and subsequent monitoring. Furthermore, this study may offer a wider set of tools that could be used for correlating sand wave migration to its governing physical mechanisms and environmental parameters.

An online path planning algorithm for autonomous marine geomorphological surveys based on AUV

This paper proposed a data-driven bi-pattern (DDBP) path planning algorithm for ocean geomorphological surveys based on Autonomous Underwater Vehicles (AUVs). When an AUV conducts surveys in unknown areas, it uses the observation data of real-time side-scan sonar to conduct environment modeling to drive independent online path re-planning (PRP) according to the feature density of the interesting targets. Based on the DDBP algorithm, the AUV can autonomously focus on regions with rich target distribution and deviate from regions with sparse target distribution without prior knowledge of the task region. The quality and efficiency of the AUV-based surveys can be improved by focusing on the underwater detection area with high feature density. The DDBP algorithm includes two patterns: rough and fine scan, and the corresponding planning pattern is selected according to the distribution of the detected targets. AUV performs online PRP in the corresponding pattern according to the pre-identified strategy set. We conducted simulation experiments and selected sand waves and fish reefs as natural and artificial structures to conduct typical marine survey tests. Compared with the traditional marine survey method, the survey efficiency was increased by 33.6% and 29.6%, respectively, in the two DDBP survey experiments for sand waves; the efficiency increased by 32.9% and 36.7%, respectively, in the two groups of DDBP survey experiments on artificial reefs. The proposed general technical framework for online path planning driven by real-time observation data has good application prospects in underwater archaeology, rapid understanding of specific targets on the seafloor, and search of specific targets.

Calibration and Validation of Two Tidal Sand Wave Models: A Case Study of The Netherlands Continental Shelf

Tidal sand waves form a dynamic bed pattern, widely occurring in shallow shelf seas such as the North Sea. Their importance to coastal engineering has inspired many advances in process-based sand wave modelling, aimed at explaining physical mechanisms in the formation stage (‘linear regime’) and capturing the finite amplitude evolution to equilibrium states (‘nonlinear regime’). However, systematic validation of particularly the nonlinear sand wave models is still lacking. Here, we perform a two-step calibration and validation study of a sand wave model (specifically, their linear and nonlinear model versions) against field data from the North Sea. In the first step, the linear model is calibrated by seeking overall values of two uncertain input parameters (slip parameter, wave period) for which the modeled and observed wavelengths show the best agreement. In the second step, using the calibrated input parameters and preferred wavelengths from the linear model, equilibrium heights from the nonlinear sand wave model are validated against the observed sand wave heights. Our results show satisfactory agreement between observed and modeled sand wave lengths (from the linear sand wave model) and a systematic overprediction of sand wave heights (using the nonlinear model). Regression analysis can be used to rescale the nonlinear model results to obtain realistic predictions of sand wave heights.

Waved-Shape Accumulation of Ice Jam—Analysis and Experimental Study

Ice jam is a unique hydrological phenomenon in rivers in cold regions. The appearance of an ice jam in a river results in an increase in the wetted perimeter of the flow cross-section, and thus an increase in flow resistance as well as water level. It may cause ice flooding sometimes. Similar to the “sand wave” phenomenon in riverbed, it has been observed in laboratory experiments that the waved-shape accumulation of ice particles (termed as “ice wave”) under an ice jam occurred. In this study, an Equation for describing the relationship between the approaching flow Froude number (Fr) and the ratio of ice jam thickness to flow depth (t/H) has been proposed. Taking the inflection point value of the equation under different flow depths, a characteristic curve has been developed to judge whether ice waves under an ice jam occurs. When the flow Froude number in front of an ice jam is below the value at the inflection point of the curve, the ice jam can maintain a mechanical stability within the ice jam thickness in a range from the lower limiting value to the upper limiting value, which were close to the ice wave trough thickness and the ice wave crest thickness, respectively. An Equation for calculating the ice wavelength has been derived and verified by using results of laboratory experiments. The relationship between the migration speed of ice wave and the ratio of ice discharge to water flow rate (Qi/Q) has been also analyzed. At last, case studies have been conducted with respect to ice accumulation in the St. Lawrence River, the Beauharnois Canal and the La Grande River. Results of case studies show that the shoving and ice dam have been dominated by mechanical factors, which would be accompanied by the ice wave phenomenon during the ice jam accumulation process. Results of case studies about ice accumulation in natural rivers also show that the relative thickness of an ice jam (t/H) of 0.4 is the criterion for assessing whether an ice jam in a river belongs to an ice dam.

Effects of vortex formation and interaction on turbulent mass transfer over a two-dimensional wavy wall

Turbulent flow over a wavy wall represents many physical processes in natural environmental flow, such as aeolian sand or wind waves. We focus on the vortex generation and interaction in the two-dimensional wavy wall turbulent mass transfer. The centrifugal instability interprets the formation of the streamwise vortices. The spanwise vortices are verified to be generated through a Kelvin--Helmholtz instability deviating from the crest. A correlation of vorticity production with the statistics of the turbulent momentum (mass) flux demonstrates the likely mechanism of the vortex interaction and its effects on these statistics.

Characterizing bedforms in shallow seas as an integrative predictor of seafloor stability and the occurrence of macrozoobenthic species

AbstractIn soft‐bottom marine ecosystems, bedform variation is induced by wind‐ and tidal‐driven hydrodynamics. The resulting megaripples, sand waves and sandbanks form a spatially and temporally heterogeneous seafloor landscape. The strong physical forces imposed by the migration of these bedforms are important determinants for the occurrence of different macrozoobenthic species. Quantifying the effect of these forces can help in differentiating natural‐ and anthropogenically induced physical stressors. However, large‐scale mapping of seabed morphology at high resolution using multibeam echosounder is challenging, costly and time‐consuming, especially in shallow seas, prohibiting wide swaths. Instead, their bathymetry is typically studied using single‐beam transects that are interpolated to bathymetric grids with a relatively coarse resolution (20 m). However, this leaves out information on smaller scale (<20 m) bedforms that can be ecologically relevant. In the Dutch Wadden sea, a shallow tidal system, we characterized bedform variation at high resolution using single‐beam data for the first time. We calculated a 2‐D Terrain Ruggedness Index (TRI) at sub‐meter resolution along the single‐beam transects and interpolated the results to a full 3‐D grid. We then validated the result by relating TRI to independently modeled hydrodynamic parameters and to the distribution of macrozoobenthic species. We found that TRI successfully integrates the variation of tidal‐driven bed shear stress and wave‐driven orbital velocity. In addition, we found TRI to be a good predictor of the occurrence of macrozoobenthic species. The inferred small‐scale bedforms provide valuable information for separating the relative importance of natural dynamics versus anthropogenic disturbances such as dredging and bottom trawling activities. We discuss that by repurposing already available single‐beam data in this way, bedforms can be characterized at high resolution without the need for additional equipment or mapping campaigns, yielding novel input to decision‐making on marine management and conservation.