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Fluid flow over an initially flat granular bed leads to the formation of a surface‐wave instability. The sediment bed profile coarsens and increases in amplitude and wavelength as disturbances develop from ripples into dunes. We perform experiments and numerical simulations to quantify both the temporal evolution of bed properties and the relationship between the initial growth rate and the friction velocity u∗. Experimentally, we study underwater bedforms originating from a thin horizontal particle layer in a narrow and counter‐rotating annular flume. We investigate the role of flow speed, flow depth and initial bed thickness on dune evolution. Bedforms evolve from small, irregular disturbances on the bed surface to rapidly growing connected terraces (2D equivalent of transverse dunes) before splitting into discrete dunes. Throughout much of this process, growth is controlled by dune collisions which are observed to result in either coalescence or ejection (mass exchange). We quantify the coarsening process by tracking the temporal evolution of the bed amplitude and wavelength. Additionally, we perform Large Eddy Simulations (LES) of the fluid flow inside the flume to relate the experimental conditions to u∗. By combining the experimental observations with the LES results, we find that the initial dune growth rate scales approximately as u∗5 ${u}_{\ast }^{5}$. These results can motivate models of finite‐amplitude dune growth from thin sediment layers that are important in both natural and industrial settings. Plain Language Summary: If the flow of water over a flat bed of sand is sufficiently fast, then grains of sand can be picked up, transported and deposited to form sand dunes. Initially, many small dunes form but, as the flow continues, they grow and merge to become a smaller number of larger dunes. We have performed experiments investigating the formation and growth of underwater dunes from an initially flat bed of sediment. In particular, we vary the speed of the flow, the depth of the water and the thickness of the sediment bed. We observe that the dunes initially grow rapidly, before reaching an almost‐constant height that increases with the sediment thickness. In order to relate the initial dune growth rate to the driving flow, we have also performed numerical simulations of the water flow in the experiment. This enables us to better‐constrain the shear stress on the sediment bed, which is quantified through the friction velocity u∗. By combining the experimental and numerical results, we show that the initial dune growth rate is approximately proportional to u∗5 ${u}_{\ast }^{5}$. These results can form a starting point for models describing the growth of underwater dunes. Key Points: Experiments show 2D dune pattern coarsening from a thin sediment bed through dune‐dune interactionsBedform amplitude and wavelength display exponentially saturated growthCombining experiments with Large Eddy Simulations finds a power‐law relation between the friction velocity and the initial growth rate [ABSTRACT FROM AUTHOR]

Abstract Subaqueous landslides are common features at active and passive ocean margins, in fjords and lakes. They can develop on very gentle slope gradients (<2°) and the presence of sandy tephra layers seems to facilitate the development of translational failure. Despite numerous investigations, it remains elusive how different slope preconditioning factors act and interact over time and how different triggering mechanisms can lead to slope failure. In settings of low to moderate seismicity, stratigraphic sequences with sublacustrine mass-transport deposits (MTDs) have successfully been used for constructing prehistorical earthquake catalogs. In high seismicity areas, it is inferred that not all strong earthquakes succeed in triggering landslides on the investigated slope segments, and MTD records do not fully represent their complete recurrence pattern. Here, we present the spatio-temporal distribution of MTDs in two large glacigenic Chilean lakes (Villarrica and Calafquén) based on a detailed seismic-stratigraphic analysis and several radiocarbon-dated piston cores (up to 14 m long). We find a strong influence of slope gradient on the occurrence and volume of landslide events; i.e. most (small) landslides take place on slopes of 5–20°, whereas the few large (potentially tsunamigenic) landslides exclusively occur on slopes of <4°. Liquefaction of sandy tephra layers facilitates the development of thin (<0.5 m) in-situ deformations during earthquake shaking. When sandy tephra layers get progressively buried, liquefaction becomes unlikely, but repeated excess pore pressure transfer to overlying units facilitates the development of translational sliding. The occurrence of voluminous landslides seems to follow a "landslide cycle" which starts with the deposition of a tephra layer and the development of in-situ deformations directly on top. Once the slope sequence reaches a critical thickness, the end of the cycle is indicated by incipient scarp development, and subsequent major sliding event(s). The duration of the landslide cycle is defined by the rate of gradual sedimentation, but may be affected by sudden geological events (e.g., volcanic eruptions), expediting the end of the cycle. Despite the many methodological challenges inherent to the construction of a MTD stratigraphy, we propose that well-dated multiple MTD events can be used as positive evidence to strengthen and specify the regional paleoseismic record, concerning the largest events in a high-seismicity region. This method is most successful when targeting the base of relatively steep slopes (5–20°) with frequent, minor landsliding, and complementing this with seismic-stratigraphic analysis of fluid-escape features and correlation with distal turbidite records. Highlights • Detailed landslide stratigraphy in Chilean lakes • Subaqueous landslide cycle controlled by tephra layers and slope gradient • Limitations and potential of subaqueous paleoseismology in high-seismicity setting [ABSTRACT FROM AUTHOR]

Dune slack wetlands should be relatively unhindered by challenges in recovering the hydrology, geochemistry and biological structure affecting other created habitats, thus presenting a simple exemplar of restoration's success. The Manawatū coast, New Zealand, has one of the most actively prograding parabolic dunefields in the world. In 1992 a study of Tawhirihoe Scientific Reserve, Tangimoana, first described three significant wetlands in dune slacks, the floor of these wetlands containing several rare perennial turf-forming species (<4 cm tall), which were in decline. A practical experiment creating wetlands in 1996 resulted in appropriate turf habitat, and was repeated on a larger scale in 2008. A survey of the vegetation and environment of the 3 natural and 3 created wetlands was conducted in 2009-2010 summer. Seven vegetation communities were identified, the three earliest successional communities containing rare turf species. The largest wetland contained the broadest range of communities, but other natural wetlands were successionally older. The most recently created wetland has only the earliest successional phase. All wetlands progressively infill with aoelian sand over the decades, rates depending on their locations and sizes, accelerating succession to exotic vegetation. Turf communities containing rare wetland plants appear to exist for only about two decades, highlighting their temporary nature. Deliberate wetland creation remains the most promising management strategy for their perpetuation in small reserves within dynamic dunelands, but even in these simple environments, restoration impediments are easy neither to predict nor to forestall. [ABSTRACT FROM AUTHOR]

Highlights • We reviewed the state of art of windblown sand effects on civil structures. • Windblown sand is defined as an environmental variable action. • A probabilistic modelling framework for windblown sand action is proposed. • A desert railway protected by two alternative design solutions is tested. Abstract The accurate prediction of windblown sand effects on structures and infrastructures is fundamental for their design and performance assessment in desert and coastal regions. Windblown sand occurs in the form of moving sand dunes, sand drift, sand erosion, accumulation, and avalanching around built structures. Windblown sand is here defined as an environmental variable action, analogously to wind or snow actions. We categorize its effects into Sand Ultimate Limit States and Sand Serviceability Limit States. We propose a framework to assess windblown sand action by means of a probabilistic method because of the inborn variability of the phenomenon. The proposed method is useful for the design of both structures and infrastructures and of sand mitigation measures. It allows to evaluate characteristic values of the sand action and assess related characteristic times of failures. In order to prove its technical feasibility, the proposed framework is then applied to a desert railway because of the particular sensitivity of such kinds of infrastructures to windblown sand action. [ABSTRACT FROM AUTHOR]

Purpose: In sediment transport modeling, several sources of uncertainty exist that impinge on the variability of model results. Therefore, it is essential to conduct an uncertainty analysis to quantify the impact of these uncertainties, to detect regions of enhanced sensitivity and subsequently to determine a range of possible model outcomes.Materials and methods: The first-order second moment method with numerical differentiation is applied to assess the uncertainties of a 2D sediment transport model Hydro_FT-2D at the Lower River Salzach. In comparison to other methods, the first-order second moment method has benefits in terms of total time requirement since it uses considerably less simulation runs to determine model uncertainty. In total, eight uncertain parameters are investigated including both model and river specific parameters. For this purpose, only 2n + 1 simulation runs are necessary leading to a total of 17 simulations. The results are evaluated against a reference simulation regarding bed elevation changes, bed load transport rates, grain size distribution, and total riverbed evolution volume.Results and discussion: The results of the total riverbed evolution volume indicate a large influence of the investigated river specific parameters roughness of river channel (kst), grain roughness (ks), and bed load input rate of the upstream River Saalach (QS SAAL). Among the model specific parameters, the critical Shields parameter (θcrit) and the scaling factor of Meyer-Peter and Mueller equation (MPM) have a significant effect on the model results. Moreover, a spatial evaluation of the maximum and minimum parameter-specific deviation from the reference indicates sensitive areas in regions with poor descriptive data as well as in close vicinity to weirs, ramps, and lateral inflows. In these areas, the model predictions are subject to a high degree of uncertainty and have to be taken with caution.Conclusions: The applied first-order second moment method with numerical differentiation is a powerful method to identify sensitive areas within the numerical model and to gain knowledge on both uncertain model and river specific parameters. Based on the results, the variability of model outputs can be evaluated and assessed with respect to the uncertainty in the input parameters and can thus contribute to a deeper understanding of the model behavior, which is highly beneficial for long-term morphodynamic studies. The method is found to be applicable for sediment transport models especially in an applied engineering context and for long-term simulation runs due to the simplicity of implementation as well as the reasonable total time requirement. [ABSTRACT FROM AUTHOR]

Integration of the geological context, core analysis, and petrographic investigation, together with data from wireline logs, resulted in the recognition of petrofacies types and the representation of facies models characterizing the X-XII sand groups of the K2qn3 Formation in the Daqingzijing area of the Songliao Basin, China. The results show that the lithology of the reservoir’s X-XII sand groups includes shale calcium-bearing siltstone and sandstone, calcareous siltstone and silty sandstone. The petrofacies consist mainly of quartz, feldspar and rock fragments cemented by clay, and some samples include calcite. The studied interval was deposited onto a delta front. Four types of petrofacies were recognized: subaqueous distributary channel, mouth bar, distal bar and subaqueous interdistributary bay. According to background investigation, the study area’s X-XII sand groups have experienced a large-scale decline in lake level. There are many subaqueous distributary channels in layers 36-40, while other layers were mainly deposited in a subaqueous interdistributary bay. [ABSTRACT FROM AUTHOR]

ABSTRACT Birchler, J.J.; Harris, C.K.; Kniskern, T.A., and Sherwood, C.R., 2018. Numerical model of geochronological tracers for deposition and reworking applied to the Mississippi subaqueous delta. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 456–460. Coconut Creek (Florida), ISSN 0749-0208. Measurements of naturally occurring, short-lived radioisotopes from sediment cores on the Mississippi subaqueous delta have been used to infer event bed characteristics such as depositional thicknesses and accumulation rates. Specifically, the presence of Beryllium-7 (7Be) indicates recent riverine-derived terrestrial sediment deposition; while Thorium-234 (234Th) provides evidence of recent suspension in marine waters. Sediment transport models typically represent coastal flood and storm deposition via estimated grain size patterns and deposit thicknesses, however, and do not directly calculate radioisotope activities and profiles, which leads to a disconnect between the numerical model and field observations. Here, observed radioisotopic profiles from the Mississippi subaqueous delta cores were directly related to a numerical model that represented resuspension and deposition using a new approach to account for the behavior of short-lived radioisotopes. Appropriate selection of parameters such as the biodiffusion coefficient, sediment accumulation rate, and radioisotopic source terms enabled a good match between the modeled and observed cores. Comparisons of modelled profiles with geochronological analytical models that estimate accumulation rate and flood layer thickness revealed potential avenues for refining these tools, and highlight the importance of constraining the biodiffusion coefficient. [ABSTRACT FROM AUTHOR]

An integrated approach combining swath bathymetry, high-resolution seismic reflection and seabed sediment sampling was performed to characterize a field of sand ridges on the Murcia continental shelf in the western Mediterranean Sea. The aim of this work was to improve knowledge about the formation, evolution and present-day dynamics of these bedforms on a narrow, tideless continental shelf receiving little sediment input. Sand ridges are observed on the middle shelf at water depths ranging between 58 and 78 m. The sand ridges are 1.5 to 3 m high and show a predominant E-W orientation oblique to the present-day shoreline. Smaller-scale subaqueous dunes (0.3–1.3 m high) appear superimposed on the sand ridges and beyond the ridge field. The subaqueous dunes show a NW-SE orientation and asymmetric profiles, with the lee side facing southwest. The comparison of two bathymetric surveys 10 years apart revealed that the subaqueous dunes are migrating towards the southwest at very low rates (~ 3 m yr − 1 ). Internally, both sand ridges and dunes display southwestward dipping oblique reflections, indicating long-term migration in that direction. The morphology, architecture and distribution of the Murcia sand ridges suggest that they were formed in a shallow-water environment during the Holocene transgression and were later detached from the coast due to the subsequent sea level rise. The shallow architecture of the sand ridges reveals the presence of small, mound-like features within the sand ridges, most probably associated with coastal deposits, which could have served as a precursor for the development of the sand ridges. The preservation of these deposits within the sand ridges evidences limited offshore ridge migration. At present, active subaqueous dunes superimposed on the sand ridges suggest that they may play a significant role in the ridge evolution. At a regional scale, the comparison of the Murcia sand ridges with those described in the western Mediterranean allows us to propose a gradation from partially evolved to fully evolved sand ridges with increasing water depth. [ABSTRACT FROM AUTHOR]

The effect of grazing on desert plant species from three distinct habitats i.e. Kot Diji sand dune, Ubhan Shah flat dune and Sorah inter-dunal area of District Khairpur was studied by using quadrat method. We analyzed each plant species for cover, total plant cover of grazed, un-grazed and mean % reduction in cover (cm) from pre-monsoon and post-monsoon seasons. The results revealed a considerable effect of grazing on plant species; however the impact of grazing varied from plant to plant and season to season, in the studied areas. There was highest grazing intensity of Indigofera species leading to endanger in this area. In all sites, maximum reduction in cover was observed in Indigofera oblongifolia and Indigofera argentea, with 62.8 and 57.2cm, respectively during pre-monsoon, and 61.5 and 52.8cm in post-monsoon. Aristida funiculata also possesses high grazing intensity with 40.3 and 54.2cm in pre and post-monsoon seasons respectively. The species Convolvulus protratus, Cassia italica, Dipterygium glaucum and Digera arvensis showed grazing intensities with 47.8, 57.4, 25.2, 42.7 in pre-monsoon season and 44.3, 35.9, 45.7,53.7 in post monsoon seasons, respectively. The low grazing intensity was observed in dominant plant communities Aerva javanica, Calligonum polygonoides, and Leptadenia pyrotechnica in a pre-monsoon season with 7.8, 17.4, 13.2cm, whereas, it was increased in post-monsoon with 11.5, 25.9, 32 in the reduction of cover (cm), respectively. These plant species were grazed by the animals at that time when ephemerals were not available in the desert during a drought period. It is suggested that partial protection and controlled grazing can be beneficial to get positive results and maintain the desert vegetation in the study area. [ABSTRACT FROM AUTHOR]

This is the first part of our study of inertial manifolds for the system of 1D reaction-diffusion-advection equations which is devoted to the case of Dirichlet or Neumann boundary conditions. Although this problem does not initially possess the spectral gap property, it is shown that this property is satisfied after the proper non-local change of the dependent variable. The case of periodic boundary conditions where the situation is principally different and the inertial manifold may not exist is considered in the second part of our study. [ABSTRACT FROM AUTHOR]

This paper reports research estimating the costs of replacing the groundwater that the metropolitan areas of Mexico City, Toluca, and Cuernavaca, in Central Mexico, pump from 10 over-exploited aquifers with 6 supply alternatives of surface water. These aquifers provide about 70% of the water required by more than 28 million people, and their recharge zones in forested areas are increasingly threatened by economic activities. By designing a constrained optimization program that minimizes investment and operation costs, we found that replacing groundwater extraction involves the construction of all six alternatives at an estimated cost of US$25 billion at present values (US$0.6 m-3 over a 26-year period). We designed and analyzed a scenario to combine measures to reduce water leaks in Mexico City; a positive balance was found: every dollar invested in leak control reduces replacement costs by between US$1.9 and US$8.4. Therefore, our results suggest the prioritization of leak control measures in order to reduce extraction from over-exploited aquifers. Local authorities should be warned about the economics of losing ecosystem services that are crucial to sustaining the population and the economic activities in the region of study. [ABSTRACT FROM AUTHOR]

In recent years, seagrass beds in Cam Ranh Bay and Thuy Trieu Lagoon have declined from 800 to 550 hectares, resulting insignificantly reducing the number of fish catch. This phenomenon is due to the effect of the degradation of water environment. Turbidity is one of the most important water quality parameters directly related to underwater light penetration which affects the primary productivity. This study aims to investigate spatiotemporal variation of turbidity in the waters with major factors affecting its patterns using remote sensing data. An algorithm for turbidity retrieval was developed based on the correlation between in situ measurements and a red band of Landsat 8 OLI with R² = 0.84 (p < 0.05). Simulating WAves Nearshore (SWAN) model was used to compute bed shear stress, a major factor affecting turbidity in shallow waters. In addition, the relationships between turbidity and rainfall, and bed shear stress induced by wind were analyzed. It was found that: (1) In the dry season, turbidity was low at the middle of the bay while it was high in shallow waters nearby coastlines. Resuspension of bed sediment was a major factor controlling turbidity during time with no rainfall. (2) In the rainy season or for a short time after rainfall in the dry season, turbidity was high due to a large amount of runoff entering into the study area. [ABSTRACT FROM AUTHOR]

Subaqueous flowstones have been studied in two resurgence caves in Slovak Karst (southern Slovakia), namely Krásnohorská and Drienovská Caves. The flowstones litter streambeds within the distance of several hundred meters upstream from resurgences. They form laminated crusts within channels of the underground streams flowing through the caves. Layers composed of columnar sparry calcite alternate with those composed of microcrystalline calcite. The latter are enriched in fine, detrital, non-carbonate components, which resulted in crystallization of microcrystalline calcite instead of sparry calcite. The growth rate of the studied flowstones reaches 0.96 mg/cm 2 /day, which corresponds to ca. 0.3 mm per year. Seasonal observations conducted between November 2010 and September 2012 reveal that deposition of subaqueous flowstones in the studied caves significantly depends on the local hydrological conditions. During the periods of low flow, SI calc. values of underground stream increase and columnar sparry calcite grows. Conversely, during peak flow periods SI calc. values decrease and subaqueous flowstones are subjected to destruction, both by mechanical erosion and corrosion. The decreasing discharge, just after peak flows, causes deposition of fine-grained particles, which results in precipitation of microcrystalline layers. Subaqueous flowstones grow in complete darkness and in atmosphere with elevated CO 2 content, similarly to typical speleothems, but they are fed with turbulent stream water, similarly to calcareous tufas. Their growth rate is higher than those of ‘normal’ flowstones fed with a film of water seeping down; it falls within a range of growth rate of calcareous tufas, though near the lower limit of this range. Therefore, subaqueous flowstones represent an intermediate link between other speleothems and tufas deposited outside the cave environment. [ABSTRACT FROM AUTHOR]

This study investigates the temporal variability and effects of bio-climatic factors and bridges on local hydro-geomorphic conditions that cause excess sedimentation and flood hazard in ephemeral rivers of the Raya graben (northern Ethiopia). Normalized difference vegetation index (NDVI) was analyzed using Landsat imageries of 1972, 1986, 2000, 2005, 2010, and 2014. Daily rainfall data of three meteorological stations were considered to analyze the temporal trends and return time intervals of rainfall intensity in 24 h. Stream-bed gradient and bed material grain size were measured in 20 river reaches. Results show that the maximum NDVI values were recorded in the time interval from 2000 to 2014. Nevertheless, during this decade, the study bridges experienced the largest excess sedimentation, in some bridges up to 1·6 m. Different factors to account for it are discussed as no evidence of rainfall pattern, accountable for an increase in sediment delivery from the headwaters, is found. The field data show that channel narrowing at bridges is the main cause of thick upstream sedimentation and of increasing frequency of overbank flows during the last 15 years. A simple hydraulic approach is presented to explain the variability of sediment deposition at bridges and change in bed material grain size between the main stem and the reach right upstream of the bridge. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The internal structure of a new subaqueous sedimentary body with a 3D morphology of a fan was studied using an interdisciplinary approach based on geophysical, geomorphological, sedimentological and radiocarbon data. The genesis of the sedimentary body is controlled by two main factors: (1) the presence of a basement ridge that constitutes the Cíes archipelago, acting as a barrier that protects the ria from high-energy marine events; and (2) the W-SW swell direction under stormy conditions, which sweeps the sediment from the platform and introduces it into the ria through the narrow entrance between Faro and San Martiño Islands. The sedimentary body that has grown inside the ria under low-energy conditions progrades in a landward direction (from the shelf to the ria). Sedimentological analysis indicates that the facies associations are coarse-grained bioclastics in the proximal areas of this body, changing laterally to mixed fine-grained sediment in its distal parts. The combination of geophysical and radiocarbon data leads us to establish the beginning of the progradation of the sedimentary body subsequent to the Younger Dryas cold event, associated with the Holocene sea level rise. The seismic analysis of the high-resolution seismic records allows us to recognize five main clinoform sets inside the subaqueous prograding sedimentary body, which can be attributed to sea level changes during the Holocene. [ABSTRACT FROM AUTHOR]

A field of large to very large subaqueous dunes was investigated in the Jade tidal channel, south-eastern North Sea, between January 2006 and October 2011. A ground-truthed sidescan sonar sediment map shows that the dunes, which are located on top of a consolidated clay surface, are composed of medium to coarse sand. A series of 35 consecutive high-resolution bathymetric surfaces collected by multibeam echosounder revealed a complex migration pattern induced by the reversing tidal currents. Various parts of the dune field are under the influence of either ebb- or flood-dominated currents, as indicated by dune asymmetries. Although some dunes migrate at a pace exceeding 100 m/year, the majority are displaced by 30 m/year in the direction of the locally dominant current. In the deepest part of the channel, however, dunes were observed to converge head-on, resulting in practically zero net transport with minor oscillations of symmetrical dunes at the apex. Applying the numerical UnTRIM model for the simulation of the fair-weather hydrology, a simplified map of residual current vectors over the dune field was generated. The residual flow vectors are found to perfectly match the derived dune migration vectors, suggesting that dune convergence is controlled by two counter-rotating residual current vortices caused by the local shape of the tidal channel. As no sediment build-up is observed, a mechanism of sediment bypassing with potential recirculation must exist, but has not yet been identified. [ABSTRACT FROM AUTHOR]

This study represents the first characterization of sand microbiota in migrating barchan sand dunes. Bacterial communities were studied through direct counts and cultivation, as well as 16S rRNA gene and metagenomic sequence analysis to gain an understanding of microbial abundance, diversity, and potential metabolic capabilities. Direct on-grain cell counts gave an average of 5.3 ± 0.4 x 105 cells g-1 of sand. Cultured isolates (N = 64) selected for 16S rRNA gene sequencing belonged to the phyla Actinobacteria (58%), Firmicutes (27%) and Proteobacteria (15%). Deep-sequencing of 16S rRNA gene amplicons from 18 dunes demonstrated a high relative abundance of Proteobacteria, particularly enteric bacteria, and a dune-specific-pattern of bacterial community composition that correlated with dune size. Shotgun metagenome sequences of two representative dunes were analyzed and found to have similar relative bacterial abundance, though the relative abundances of eukaryotic, viral and enterobacterial sequences were greater in sand from the dune closer to a camel-pen. Functional analysis revealed patterns similar to those observed in desert soils; however, the increased relative abundance of genes encoding sporulation and dormancy are consistent with the dune microbiome being well-adapted to the exceptionally hyper-arid Qatari desert. [ABSTRACT FROM AUTHOR]

The Grado lagoon is among the largest in the Mediterranean sea and is characterized by salt marshes, where tides influenced the development of a complex micromorphology coupled to a micromosaic of vegetation covers. This study represents the first contribution to the understanding of the main processes governing formation, development and spatial transitions between hydromorphic and subaqueous soils in an Adriatic lagoon ecosystem. Physicochemical characteristics and development of soils were investigated in three salt marshes differing for their proximity to the open sea, textural composition and age of formation. Soils of back barrier salt marshes had A/C profiles and were mostly characterized by a sandy coarse texture that allows rapid drainage and subsurface oxygen exchanges. Soil sequences from the inner salt marsh to its submerged border slope or to a brackish waterhole do not simply represent a hydrosequence, but also reflect erosion/sorting/accumulation processes. The soils in the central part of the lagoon have finer texture and in displayed transition or cambic horizons. Silty clay loam textures and low positions allowed the development of more severe anoxic conditions and accumulation of sulphides. The tide oscillation strongly contributed to formation of redoximorphic features, intensity of anaerobic conditions but also colonization by different plant communities. Discriminant analysis was performed to identify physicochemical properties which discriminate the different soils according to geo-morphological position and prevailing plants. It confirmed that differentiation of plant communities occurred according to distinct morphological and physicochemical soil properties, but also acted as a primary affecting factor of pedogenesis. [ABSTRACT FROM AUTHOR]

The Swiss plate geophone system is a bed load surrogate monitoring technique that is used to quantify bed load transport in steep streams. The amplitude of the signal recorded by the Swiss plate geophone contains information about the grain-size distribution of the transported bed load. To extract this information, the authors computed the number of impulses and packets (representing a single particle impact) registered for different amplitude ranges, the so-called amplitude histograms, for 46 samples when bed load was measured independently with automatic basket samplers at the Erlenbach. Amplitude histograms can be interpreted as a statistical distribution of the signal's amplitude over a given time interval. Using the number of bed load particles per unit mass, absolute bed load masses for each grain-size class can be calculated. The results show that the grain-size distribution of the transported bed load for particles larger than 9.5 mm can be continuously monitored at the Erlenbach with the Swiss plate geophone system. [ABSTRACT FROM AUTHOR]

The aim of this paper is to compare the usefulness of equipment employed for foredune ground surveys in different environmental conditions based on literature and field experience from the Polish coast. This article contains a description of recently used methods of coastal dunes monitoring for management and scientific purposes. It presents issues of coastal dunes mapping that are a part of long-term research conducted along the Polish coast since 1997. The employed methods and techniques are briefly described and evaluated. Subsequently, a description and assessment of these field surveys is provided. The description of techniques is focused on the aim of the research and on the types of morphological coastal forms and vegetation cover. Those full descriptions may allow the choice of a proper method for field investigation suited to the researcher's need. The precision of measurement techniques and collected data is presented. Those data fulfill the need for geomorphologic investigation in coastal dune areas. The described experiences are based on 20 years of investigation of coastal dunes on the Polish Baltic coast, with additional data originating from other field investigations of many global coastal areas. [ABSTRACT FROM AUTHOR]

Large asymmetric bedforms known as dunes commonly dominate the bed of sand rivers. Due to the turbulence generation over their stoss and lee sides, dunes are of central importance in predicting hydraulic roughness and water levels. During floods in steep alluvial rivers, dunes are observed to grow rapidly as flow strength increases, undergoing an unstable transition regime, after which they are washed out in what is called upper stage plane bed. This transition of dunes to upper stage plane bed is associated with high transport of bed sediment in suspension and large decrease in bedform roughness. In the present study, we aim to improve the prediction of dune development and dune transition to upper stage plane bed by introducing the transport of suspended sediment in an existing dune evolution model. In addition, flume experiments are carried out to investigate dune development under bed load and suspended load dominated transport regimes, and to get insight in the time scales related to the transition of dunes to upper stage plane bed. Simulations with the extended model including the transport of suspended sediment show significant improvement in the prediction of equilibrium dune parameters (e.g. dune height, dune length, dune steepness, dune migration rate, dune lee side slope) both under bed load dominant and suspended load dominant transport regimes. The chosen modeling approach also allows us to model the transition of dunes to upper stage plane bed which was not possible with the original dune evolution model. The extended model predicts change in the dune shapes as was observed in the flume experiments with decreasing dune heights and dune lee slopes. Furthermore, the time scale of dune transition to upper stage plane bed was quite well predicted by the extended model. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Measurements of topography at the segment of bifurcation between the South Channel and North Channel in the Yangtze Estuary were conducted, and a new type of subaqueous dune was discovered. This structure, newly defined as a catenary-bead dune, consists of a catenary dune and its associated elliptical pit bedform. Based on this finding, the nomenclature of 'morphology of dune associated with accompanying bedform' is first proposed. The measured data indicate a mean height and wavelength of 1.29 m and 31.89 m, respectively; wavelength/height ratio (L/H) of 14 to 56; and elliptical pits of mean and maximum depth 0.98 m and 1.98 m, respectively. Flow information was obtained using an Acoustic Doppler Current Profile (ADCP), and the bed material components were gathered with a bottom sampler. The results show mean flood and ebb velocities of 0.27 and 0.78 m s, respectively, with shorter duration of flood tide than ebb tide. The silt, very fine sand, and fine sand fractions were within the ranges 21.6-23.4%, 28.2-32.2%, and 39.7-41.6%, respectively, revealing complex bed material composition. Water depth at the study site varies from 13 to 17 m. This finding will enrich the study of dunes and provide important data for geomorphological research. Moreover, the results are significant for engineering applications to estuaries. [ABSTRACT FROM AUTHOR]

Chang, J.I. and Yoon, S., 2016. The Economic Benefit of Coastal Erosion Control in Korea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1317 - 1321. Coconut Creek (Florida), ISSN 0749-0208. The Korean coastal zone is regarded as a highly valuable environmental asset and provides important space for human life. Korean counties with a coastline have a deep interest in finding the most appropriate and sustainable management policy for their coastal resources and ecosystems. Korean coastal zone is now experiencing environmental pressure and is under threat from a diverse range of destructive forces. Thus, this study analyzes the economic benefits of Korea's coastal erosion control project (CECP). The main results of the study are as follows. (1) First, the study identifies the benefit factors of coastal erosion control, such as damage control services, recreational services, and other coastal ecosystem services. (2) Second, this study assesses the economic benefits of the CECP in Korea by applying choice experiment, a non-market valuation method. The annual benefit is estimated at 31,824 KRW (26.56 USD) per household, and the total annual economic benefit of the CECP is estimated at 587.7 billion KRW (490.8 million USD). The findings provide policymakers with a useful methodological framework and quantitative information for decision making on costal management policy. [ABSTRACT FROM AUTHOR]

Numerous approaches to local scour forming studies have been developed. This paper presents different scientific approaches to the scour phenomenon using Lane's relation [1] in its modified form during laboratory studies. The original Lane's relation is applicable in dynamic balance conditions in alluvial rivers context, and it is not an equation, but a qualitative expression which cannot be directly used to estimate the influence of a change in one parameter on the magnitude of others. Lane's relation, despite its qualitative and simplified character, serves well to describe the nature of the process of forming alluvial stream channels, while modified relation allows transforming it into an equation for laboratory studies of local scour forming in prearranged clear-water equilibrium conditions and gives a new opportunity for this principle application. [ABSTRACT FROM AUTHOR]

The practical finite-analytic (PFA) method was applied to the solution of the one-dimensional advection–dispersion equation (ADE) for solute transport in porous media under advection-dominated (high Peclet number, Pe) conditions. Several PFA spatial-temporal computational molecules were developed for Cauchy and pulse loading boundary conditions. The PFA solutions were compared with solutions from the upwind method and quadratic upwind differencing (QUICK) scheme. For all boundary conditions the trapezoidal explicit PFA (EPFA) computational molecule gave the most accurate results at very high Pe number as long as the Courant number (Cr) was close to one. Stability analysis shows that the PFA molecules are always stable for high Pe number. [ABSTRACT FROM AUTHOR]

Sediment structures including submarine banks and dune fields are ubiquitous on tide-dominated continental inner shelves such as in the Iroise Sea. These are of current interest to human activities in several respects: they constitute an obstacle to navigation, they are dredged for beach nourishment or exploited for marine aggregates. In addition, the morphodynamic characterising of these sedimentary structures improves the knowledge of the sediment transfers that occur in coastal areas. This study documents a submarine sand dune field located along the northern flank of the Goulet channel connecting the Bay of Brest to the Iroise Sea and the Bay of Biscay. Subject to a macrotidal regime with strong currents, and to large waves during storm events, this sedimentary system features large dunes with very high migration rates. The analysis of six bathymetric datasets (from March 2013 to October 2019) allows specifying the morphodynamic characteristics of this small dune field about 3.5 km in length and 500 m in width. These dunes have heights on the order of 0.5 m–3.7 m with migration rates that can vary significantly within the range from 10 m/yr to 70 m/yr. The results highlight that the ebb tidal current and slope of the channel are the main factors controlling the evolution of these biogenic sandy structures migrating offshore (SW). Furthermore, seasonal variations in coastal hydrodynamics forcing, driven by tidal currents, appear to affect the temporal and spatial evolution of the dunes at this shorter time scale. This paper proposes a model of sediment transport patterns at the mouth of the bay of Brest according dune field characteristic, strong ebb current and residual tidal gyre. • Channelised tidal currents in macrotidal environment induce large variation in dune migration rates across a dune field at the outlet of the Bay of Brest. • Tidal gyre in the shallower nearshore terrace contributes to the recirculation of sediment from dune field through external pathways. • The steep slopes of the channel impact dune migration rates, with reduced rates on the negative slopes and increased rates on the positive slopes. [ABSTRACT FROM AUTHOR]

Regions with subaqueous sand dunes have been discovered on the upper continental slope of the northern South China Sea. These large subaqueous sand dunes are expected to cause errors in the measurement of normal incidence reflection. This letter presents experiment results of two normal incidence survey tracks conducted in 2013, and the errors in reflection coefficient estimation and the resulting sediment properties induced by sand dune bedforms. The results demonstrate that the reflected energy is focused and scattered by different parts of sand dune bedforms and that they produce significant variation in the estimated reflection coefficients and the inverted geoacoustic properties. [ABSTRACT FROM AUTHOR]

Jackson, D.W.T.., Cooper, J.A.G., Green, A.N., 2014. A preliminary classification of sand dunes of the KwaZulu-Natal coast. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 718-722, ISSN 0749-0208. The 550 km-long KwaZulu-Natal coast broadly divides into a bedrock-framed southern section and northern coastal plain section, each of approximately equal length. Seven types of coastal dune are identified on this coast: estuary barrier dunes; mainland beach foredunes; prograded beachridge dunes; headland bypass dunes; transverse dune fields; parabolic/migrating dunefield; and climbing dunes. The development and distribution of the various dune forms is more strongly controlled by the geological setting, than the aerodynamic regime. [ABSTRACT FROM AUTHOR]

The large subaqueous sand dunes on the upper continental slope of the South China Sea are expected to couple acoustic propagating normal modes. In this letter, the criterion of adiabatic invariance is extended to the case of a waveguide possessing bedforms. Using the extended criterion to examine mode propagation over the bedforms observed in the sand dune field in 2012, results demonstrate that bedforms increase mode coupling strength such that the criterion for adiabatic propagation is exceeded for waveguides with small bedform amplitude to water depth ratios; increasing bedform amplitude enhances mode coupling. Numerical simulations confirm the extended criterion parameterization. [ABSTRACT FROM AUTHOR]

Economic development of the São Francisco River basin has increased by building seven river dams since the 1950s. Subsequently, strong coastal erosion reaching maximum rates of 98.6 m/year has been recorded at the river mouth, also leading to the destruction of a coastal village. This work combines discharge data with new sediment and hydro-acoustic records, collected in January 2009, to verify the impact of river damming on processes, controlling coastline evolution. Data analysis is focused on discharge evolution, morphology and sediment composition of subaqueous dunes as well as on the impact by tidal currents. Discharge has been strongly regulated since 1986, when the last river dam was implemented. Again, bedform morphology seems to be not affected neither by reduced river-discharge nor by reduced sediment supply. However, migration rates of these dunes, as calculated, are lower due to decreased discharge. At the same time, tidal impact is strengthened at the lowermost part of the river. From this we assume, that the replenishment of sediment at the coast near the river-mouth might be time-delayed, which could support coastal erosion. [ABSTRACT FROM AUTHOR]

In-situ geotechnical measurements of surface sediments were carried out along large subaqueous dunes in the Knudedyb tidal inlet channel in the Danish Wadden Sea using a small free-falling penetrometer. Vertical profiles showed a typical stratification pattern with a resolution of ∼1 cm depicting a thin surface layer of low sediment strength and a stiffer substratum below (quasi-static bearing capacity equivalent: 1-3 kPa in the top layer, 20-140 kPa in the underlying sediment; thickness of the top layer ca. 5-8 cm). Observed variations in the thickness and strength of the surface layer during a tidal cycle were compared to mean current velocities (measured using an acoustic Doppler current profiler, ADCP), high-resolution bathymetry (based on multibeam echo sounding, MBES) and qualitative estimates of suspended sediment distributions in the water column (estimated from ADCP backscatter intensity). The results revealed an ebb dominance in sediment remobilization, and a general accretion of the bed towards low water. A loose top layer occurred throughout the tidal cycle, likely influenced by bedload transport and small events of suspended sediment resettlement (thickness: 6 ± 2 cm). Furthermore, this layer showed a significant increase in thickness (e.g. from 8 cm to 16 cm) related to periods of overall deposition. These findings imply that dynamic penetrometers can conveniently serve to (1) quantify potentially mobile sediments by determining the thickness of a loose sediment surface layer, (2) unravel sediment strength development in potentially mobile sediments and (3) identify sediment accumulation. Such data are an important complement and add a new geotechnical perspective during investigations of sediment remobilization processes in highly dynamic coastal environments. [ABSTRACT FROM AUTHOR]

Abstract: Very large subaqueous sand dunes were discovered on the upper continental slope of the northern South China Sea. The dunes were observed along a single 40km long transect southeast of 21.93°N, 117.53°E on the upper continental slope in water depths of 160m to 600m. The sand dunes are composed of fine to medium sand, with amplitudes exceeding 16m and crest-to-crest wavelengths exceeding 350m. The dunes'' apparent formation mechanism is the world''s largest observed internal solitary waves which generate from tidal forcing on the Luzon Ridge on the east side of the South China Sea, propagate west across the deep basin with amplitudes regularly exceeding 100m, and dissipate extremely large amounts of energy via turbulent interaction with the continental slope, suspending and redistributing the bottom sediment. While subaqueous dunes are found in many locations throughout the world''s oceans and coastal zones, these particular dunes appear to be unique for two principal reasons: their location on the upper continental slope (away from the influence of shallow-water tidal forcing, deep basin bottom currents and topographically-amplified canyon flows), and their distinctive formation mechanism (approximately 60 episodic, extremely energetic, large amplitude events each lunar cycle). [Copyright &y& Elsevier]

Detailed studies of flow over subaqueous dunes in laboratory flumes were used to suggest a virtual near-bed layer of twice the dune height in which the mean velocity is accelerated towards the crest by contraction. The mean flow velocity in this layer above the crest, transformed into friction velocity by means of the surface skin roughness, is shown to give values consistent with measured values. The resulting dimensionless shear stress due to skin friction is depth-independent, in contrast to that derived by means of often cited traditional methods. As a result of the relationship between dune height and the thickness of the near-bed layer, an expression for the expansion loss behind dunes was formulated and used to relate form resistance directly to dune height. [ABSTRACT FROM AUTHOR]

Multibeam sonar data provide new high-resolution characterization of morphological and sedimentological features on the upper slope of the Roberts Bank section of the Fraser River delta. Subaqueous dunes are more abundant and broadly distributed over the slope than previously documented and include large asymmetric two-dimensional dunes (sinuous crested and straight crested), large asymmetric three-dimensional dunes (high relief, low relief) and irregularly- spaced dunes. The two-dimensional and three-dimensional dunes fall within the typical range of subaqueous dune heights and wavelengths and show dimensions that do not universally scale to water depth but are probably scaled to the dynamic conditions. The irregularly-spaced dunes fall outside the typical scaling, having excessively low height to wavelength ratios. Current data indicate that these irregularly-spaced dunes form under conditions where the ratio of suspended to bedload transport is too high to maintain fully-scaled bedforms. The orientation of the dunes indicates predominant alongshore transport to the northwest, in the direction of the flood tidal current, although a small patch of ebb-oriented dunes is present near Point Roberts, where the ebb-flow is accelerated. [ABSTRACT FROM AUTHOR]

In the course of two regional side-scan sonar surveys on the continental shelf off southern Vietnam after the winter monsoon seasons of 2003 and 2004, and covering a total distance of over 1,000 km, the widespread occurrence of large and very large subaqueous dunes was discovered. On the basis of their size, shape, depth of occurrence and orientation, the dunes were grouped into five spatially distinct regions. In each case, a different height/wavelength relationship is observed. With the exception of region no. 3 where dune dimensions follow the mean global trend, the dimensions in the other regions lie below the mean global trend. The most plausible explanation for this is sediment starvation and/or insufficient time for the larger dunes to fully adjust to changing flow conditions. A good correlation is observed between average dune height in each region and water depth, although this is not the case for dune length. The orientation of the dunes corresponds to the direction of the current pattern induced by the regional winter monsoon winds (NE to SW and S). The generally well-developed asymmetrical shapes and the large size of the dunes suggest that the wind-induced currents are strong enough to reactivate most of the dunes during the winter monsoon season, a conclusion supported also by theoretical calculations of critical current velocities. The largest dunes, which seem to have reached their maximum sizes for the local water depths, may not be reactivated regularly but rather only by exceptionally strong episodic flows. [ABSTRACT FROM AUTHOR]

The impact of dredge spoil disposal on asymmetrical large-scale dunes has been studied at a disposal site in a shallow subtidal area of the outer Weser Estuary (German Bight, southeastern North Sea). Between June and December 1998, this site was used for the disposal of ~3×106 m3 dredge spoil. Repeated bathymetric surveys with a multibeam echosounder system reveal that the artificial supply of sediment provoked significant morphological changes in the dune field, including the infill of dune troughs and even the complete burial of individual dunes. However, even completely buried dunes began to regenerate within a few months. In addition, slow migration of the dunes toward the open sea was observed, indicating net seaward sediment transport in the survey area. Since the dumped sediment does not appear to have a persistent effect on the bedforms and, in all likelihood, will be exported from the estuarine system on medium- to long-term timescales, the investigated area constitutes a suitable disposal site. [ABSTRACT FROM AUTHOR]

Abstract This experimental investigation examined the controls on the geometry of cross-sets formed by subaqueous dunes. A range of steady, unidirectional flow conditions spanning the field of dune existence was investigated, and aggradation rate ranged from 0 mm s-1 to 0·014 mm s-1 . Data from an ultrasonic depth profiler consist of high-resolution temporal and spatial series of bed profiles from which dune height and length, migration rate and the depth of trough scour were measured. Cross-set thickness and length were measured from sediment peels. The size and shape of dunes from an equilibrium assemblage change continuously. Individual dunes commonly increase in height by trough scouring and, occasionally, by being caught-up by the upstream dune. Both types of behaviour occur suddenly and irregularly in time and, hence, do not appear to depend on dunes further upstream. However, dune climbing or flattening is a typical response of dunes that disappear under the influence of the upstream dune. All types of behaviour occur at any flow velocity or aggradation rate. Successive dune-trough trajectories, defined by dunes showing various behaviours, affect the geometry of the preserved cross-sets. Mean cross-set thickness/mean dune height averages 0·33 (±0·7), and mean cross-set length/mean dune length averages 0·49 (±0·08), and both show no systematic variation with aggradation rate or flow velocity. Mean cross-set thickness/mean cross-set length tends to decrease with increasing flow velocity and Froude number, therefore allowing a qualitative estimation of flow conditions. Quantitative analysis of the temporal changes in the geometry and migration rate of individual dunes allows the development of a two-dimensional stochastic model of dune migration and formation of cross-sets. Computer realizations produced stacks of cross-sets of comparable shape and thickness to laboratory flume observations, indicating... [ABSTRACT FROM AUTHOR]