Wind-driven Currents Research Articles

수치실험에 의한 한국 동해 연안용승해역의 영양염 분포 특성

Numerical modeling was conducted to understand characteristics of nutrient distributions caused by wind currents which occur upwelling in the East sea of Korea. Averaged northeastward wind speed of 9.1m per second which occurred upwelling strongly in 2013 was applied in numerical modeling and wind-driven currents was calculated. Water moved northeastward from coastal area to open sea in surface layer, which develop clockwise or counterclockwise eddies. In bottom layer, However, water moved westward to compensate the surface water. Spatio-temporal distributions of nutrient affected by wind-dirven currents were investigated using the numerical model. As time passes, nutrient concentrations increased gradually, spreading to open sea in coastal area from Pohang to Yeongdeok. Highly accumulated nutrients in bottom layer was risen to the surface by upwelling currents. Risen nutrients spread open sea gradually.

Evaluation of wind induced currents modeling along the Southern Caspian Sea

To improve our understanding of the Caspian Sea hydrodynamics, its circulation is simulated with special focus on wind-driven currents of its southern basin. The hydrodynamic models are forced with a newly developed fine resolution wind field to increase the accuracy of current modeling. A 2D shallow water equation model and a 3D baroclinic model are applied separately to examine the performance of each model for specific applications in the Caspian Sea. The model results are validated against recent field measurements including AWAC and temperature observations in the southern continental shelf region. Results show that the 2D model is able to well predict the depth-averaged current speed in storm conditions in narrow area of southern coasts. This finding suggests physical oceanographers apply 2D modeling as a more affordable method for extreme current speed analysis at the continental shelf region. On the other hand the 3D model demonstrates a better performance in reproducing monthly mean circulation and hence is preferable for surface circulation of Caspian Sea. Monthly sea surface circulation fields of the southern basin reveal a dipole cyclonic-anticyclonic pattern, a dominant eastward current along the southern coasts which intensifies from May to November and a dominant southward current along the eastern coasts in all months except February when the flow is northward. Monthly mean wind fields exhibit two main patterns including a north-south pattern occurring at warm months and collision of two wind fronts especially in the cold months. This collision occurs on a narrow region at the southern continental shelf regions. Due to wind field complexities, it leads to a major source of uncertainty in predicting the wind-driven currents. However, this source of uncertainty is significantly alleviated by applying a fine resolution wind field.

Coastal hydrodynamics beyond the surf zone of the south Baltic Sea

The paper presents experimental and theoretical investigations of hydrodynamic processes in a coastal region located close to the seaward boundary of the surf zone. The analysis is based on field data collected near Lubiatowo (Poland) by measuring equipment operated simultaneously by the Institute of Hydro-Engineering of the Polish Academy of Sciences (IBW PAN) and the Maritime Institute in Gdańsk (IMG). The data consist of wind velocity and direction measured at the IBW PAN Coastal Research Station (CRS) in Lubiatowo, deep-water wave buoy records, current profiles and sea bottom sediment parameters. Mean flow velocities measured in the entire water column have almost the same direction as wind. Nearbed flow velocities induced by waves and currents, as well as bed shear stresses, are modelled theoretically to determine sediment motion regimes in the area. It appears that the nonlinear wave–current interaction generates bed shear stresses greater than those that would result from the superposition of the impacts of waves and currents separately. The paper discusses the possibility of occasional intensive sediment transport and the occurrence of distinct seabed changes at greater coastal water depths adjacent to the surf zone. It was found that this can happen under the joint influence of waves and wind-driven currents.

Taylor dispersion in wind-driven current

Taylor dispersion associated with wind-driven currents in channels, shallow lakes and estuaries is essential to hydrological environmental management. For solute dispersion in a wind-driven current, presented in this paper is an analytical study of the evolution of concentration distribution. The concentration moments are intensively derived for an accurate presentation of the mean concentration distribution, up to the effect of kurtosis. The vertical divergence of concentration is then deduced by Gill’s method of series expansion up to the fourth order. Based on the temporal evolution of the vertical concentration distribution, the dispersion process in the wind-driven current is concretely characterized. The uniform shear leads to a special symmetrical distribution of mean concentration free of skewness. The non-uniformity of vertical concentration is caused by convection and smeared out gradually by the effect of diffusion, but fails to disappear even at large times.

Observations and operational model simulations reveal the impact of Hurricane Matthew (2016) on the Gulf Stream and coastal sea level

In October 7–9, 2016, Hurricane Matthew moved along the southeastern coast of the U.S., causing major flooding and significant damage, even to locations farther north well away from the storm’s winds. Various observations, such as tide gauge data, cable measurements of the Florida Current (FC) transport, satellite altimeter data and high-frequency radar data, were analyzed to evaluate the impact of the storm. The data show a dramatic decline in the FC flow and increased coastal sea level along the U.S. coast. Weakening of the Gulf Stream (GS) downstream from the storm’s area contributed to high coastal sea levels farther north. Analyses of simulations of an operational hurricane-ocean coupled model reveal the disruption that the hurricane caused to the GS flow, including a decline in transport of ∼20Sv (1Sv=106m3s−1). In comparison, the observed FC reached a maximum transport of ∼40Sv before the storm on September 10 and a minimum of ∼20Sv after the storm on October 12. The hurricane impacts both the geostrophic part of the GS and the wind-driven currents, generating inertial oscillations with velocities of up to ±1ms−1. Analysis of the observed FC transport since 1982 indicated that the magnitude of the current weakening in October 2016 was quite rare (outside 3 standard deviations from the mean). Such a large FC weakening in the past occurred more often in October and November, but is extremely rare in June-August. Similar impacts on the FC from past tropical storms and hurricanes suggest that storms may contribute to seasonal and interannual variations in the FC. The results also demonstrated the extended range of coastal impacts that remote storms can cause through their influence on ocean currents.

A study on some basic features of inertial oscillations and near-inertial internal waves

Abstract. Some basic features of inertial oscillations and near-inertial internal waves are investigated by simulating a two-dimensional (x − z) rectangular basin (300 km × 60 m) driven by a wind pulse. For the homogeneous case, near-inertial motions are pure inertial oscillations. The inertial oscillation shows typical opposite currents between the surface and lower layers, which is formed by the feedback between barotropic waves and inertial currents. For the stratified case, near-inertial internal waves are generated at land boundaries and propagate offshore with higher frequencies, which induce tilting of velocity contours in the thermocline. The inertial oscillation is uniform across the whole basin, except near the coastal boundaries ( ∼ 20 km), where it quickly declines to zero. This boundary effect is related to great enhancement of non-linear terms, especially the vertical non-linear term (w ∂ u∕ ∂ z). With the inclusion of near-inertial internal waves, the total near-inertial energy has a slight change, with the occurrence of a small peak at ∼ 50 km, which is similar to previous research. We conclude that, for this distribution of near-inertial energy, the boundary effect for inertial oscillations is primary, and the near-inertial internal wave plays a secondary role. Homogeneous cases with various water depths (50, 40, 30, and 20 m) are also simulated. It is found that near-inertial energy monotonously declines with decreasing water depth, because more energy of the initial wind-driven currents is transferred to seiches by barotropic waves. For the case of 20 m, the seiche energy even slightly exceeds the near-inertial energy. We suppose this is an important reason why near-inertial motions are weak and hardly observed in coastal regions.

A non-deltaic clinoform wedge fed by multiple sources off São Sebastião Island, southeastern Brazilian Shelf

Sao Sebastiao Island (SSI) marks the latitudinal boundary between two sedimentological and geochemical provinces in the Sao Paulo Bight, an arc-shaped sector of the southeastern Brazilian Shelf. The island is separated from the continent by the narrow, deep Sao Sebastiao Channel (SSC). A relatively thick sediment wedge—the Sao Sebastiao Wedge (SSW)—has been formed offshore SSI. This study explores the possible genetic and evolutionary mechanisms of the wedge, bearing in mind that clinoform wedges can form at considerable distances from major fluvial sources. For that, a marine geological database has been interpreted comprising high-resolution seismic data, a surficial sediment map and several sediment cores, from which radiocarbon dates were obtained and sedimentation rates deduced. A wave model was also applied to obtain the dominant wave directions. The SSW is a wedge-shaped deposit, and its internal structure presents three seismic units. The two lowest are wedge shaped and arranged in a backstepping pattern. The most recent unit is mostly aggradational and can be divided into three seismic subunits. Sedimentological data show that at least the most recent unit is composed of a mixture of sands and silts. Modeled wave conditions indicate a major influence from southerly waves that are able to remobilize shelf sediments and to create a bypass sediment zone until the foreset of the deposit is reached at the water depths where the SSW is found. Taken together, these data suggest that the SSW formed through contributions from different sediment sources, and should be regarded as an intermediate case of a non-deltaic clinoform wedge. Sand transport in the area involves wind-driven currents passing through the SSC and sediment remobilization by energetic southerly waves. Fine-grained sediment is derived mostly from the joint contributions of many minor catchments located north of the island, and this sediment is later transported southwestward by the prevailing surface currents. The morphological obstacle presented by the island leads to current veering and subsequent sediment deposition. The internal architecture of the wedge indicates that its deposition was probably initiated during the last part of the postglacial transgression, but its present-day morphology is mostly a product of episodic highstand sedimentation that began under conditions of gently falling sea levels during the last 5 ka, after the Holocene glacio-eustatic maximum.

Dynamic controls on shallow clinoform geometry: Mekong Delta, Vietnam

Compound deltas, composed of a subaerial delta plain and subaqueous clinoform, are common termini of large rivers. The transition between clinoform topset and foreset, or subaqueous rollover point, is located at 25–40-m water depth for many large tide-dominated deltas; this depth is controlled by removal of sediment from the topset by waves, currents, and gravity flows. However, the Mekong Delta, which has been classified as a mixed-energy system, has a relatively shallow subaqueous rollover at 4–6-m depth. This study evaluates dynamical measurements and seabed cores collected in Sep 2014 and Mar 2015 to understand processes of sediment transfer across the subaqueous delta, and evaluate possible linkages to geometry. During the southwest rainy monsoon (Sep 2014), high river discharge, landward return flow under the river plume, and regional circulation patterns facilitated limited sediment flux to the topset and foreset, and promoted alongshore flux to the northeast. Net observed sediment fluxes in Sep 2014 were landward, however, consistent with hypotheses about seasonal storage on the topset. During the northeast rainy monsoon, low river discharge and wind-driven currents facilitated intense landward and southwestward fluxes of sediment. In both seasons, bed shear velocities frequently exceeded the 0.01–0.02m/s threshold of motion for sand, even in the absence of strong wave energy. Most sediment transport occurred at water depths <14m, as expected from observed cross-shelf gradients of sedimentation. Sediment accumulation rates were highest on the upper and lower foreset beds (>4cm/yr at <10m depth, and 3–8cm/yr at ~10–20m depth) and lowest on the bottomset beds. Physically laminated sediments transitioned into mottled sediments between the upper foreset and bottomset regions. Application of a simple wave-stress model to the Mekong and several other clinoforms illustrates that shallow systems are not necessarily energy-limited, and thus rollover depths cannot be predicted solely by bed-stress distributions. In systems like the subaqueous Mekong Delta, direction of transport may have a key impact on morphology.

Wind and Current Effects on Extreme Wave Formation and Breaking

AbstractWind and current effects on the evolution of a two-dimensional dispersive focusing wave group are investigated using a two-phase flow model. A Navier–Stokes solver is combined with the Smagorinsky subgrid-scale stress model and volume of fluid (VOF) air–water interface capturing scheme. Model predictions compare well with the experimental data with and without wind. It was found that the following and opposing winds shift the focus point downstream and upstream, respectively. The shift of focus point is mainly due to the action of wind-driven current instead of direct wind forcing. Under strong following/opposing wind forcing, there appears a slight increase/decrease of the extreme wave height at the focus point and an asymmetric/symmetric behavior in the wave focusing and defocusing processes. Under a weak following wind, however, the extreme wave height decreases with increasing wind speed because of the dominant effect of the wind-driven current over direct wind forcing. The vertical shear of the wind-driven current plays an important role in determining the location of and the extreme wave height at the focus point under wind actions. Furthermore, it was found that the thin surface layer current is a better representation of the wind-driven current for its role in wind influences on waves than the depth-uniform current used by previous studies. Airflow structure above a breaking wave group and its link to the energy flux from wind to wave as well as wind influence on breaking are also examined. The flow structure in the presence of a following wind is similar to that over a backward-facing step, while that in the presence of an opposing wind is similar to that over an airfoil at high angles of attack. Both primary and secondary vortices are observed over the breaking wave with and without wind of either direction. Airflow separates over the steep crest and causes a pressure drop in the lee of the crest. The resulting form drag may directly affect the extreme wave height. The wave breaking location and intensity are modified by the following and opposing wind in a different fashion.

Analysis and forecast of the surface currents in the Okhotsk Sea on the base of observations on drift of buoys

Data of observations on drifting buoys in the western Okhotsk Sea are presented. Quasi-stochastic mode of the buoys drift under forcing of atmospheric cyclone is noted. The drift is analyzed jointly with analysis of the wind field and the sea surface satellite altimetry. The buoy drift trajectories are modeled under separate influence of the wind-driven and geostrophic flows. There is concluded that both wind-driven and geostrophic currents at the sea surface should be accounted for forecasting of drift for buoys or any floating objects.

Waves and associated currents–experiences from 5 years metocean measurements in the northern North Sea

To acquire sufficient simultaneous data to establish joint distributions of waves and currents for design, an extensive metocean measurement programme has been performed over a period of approximately five years at several locations in the northern North Sea. A brief description of the measurement programme is given. The measured current data have been found to be more inaccurate than the specified accuracy of the instruments. However, the measured current data still give a good over-all description of the current conditions. At the southernmost locations, wind-driven currents, i.e. inertial oscillations, are the governing current conditions and contribute to larger current speed during summer than in the spring and fall, both operational and extreme. At all locations, year-to-year variation in estimated extreme current speeds based on different individual years are larger than expected, indicating that current measurements for considerably more than one year is required for reliable estimates of extreme current conditions for design of offshore structures. Sensitivity studies of the ultimate limit state (ULS) load on a jacket suggest the possible gain of accounting for the simultaneous occurrence of metocean parameters. The Norwegian design regulations seem to be conservative, at least regarding ULS. These results highlight the need for a better understanding of the current conditions in order to account for the uncertainties associated with these in design of offshore structures.

Remote Sensing Studies of Suspended Sediment Concentration Variations in a Coastal Bay During the Passages of Atmospheric Cold Fronts

Mississippi River, the largest river in North America, carries a significant amount of sediment into the northern Gulf of Mexico coastal waters. In this region, recurring wind events associated with atmospheric cold fronts between fall and the following spring dominate resuspension and transport of the sediment. In this paper, based on a time series of the moderate-resolution imaging spectroradiometer satellite images with a moderate spatial resolution of 250 m during the passages of three atmospheric cold fronts in March 2013, considering the entire process of cold fronts, the distribution and variation of total suspended sediment (TSS) concentration and underlying hydrodynamic mechanism were analyzed. The TSS concentration distribution and sediment transport in the Atchafalaya Bay within the Mississippi River estuary were found to be positively correlated with the magnitude of local winds and waves, and negatively correlated with bathymetry. During the prefrontal stage, concentrations in the offshore water always decreased as a result of the wind-induced landward sediment transport. In the shallower water, the variations of TSS concentration are dominated by the intensity of wind stress. In the postfrontal period, the variations of TSS were controlled by wind-driven currents, resuspension, and vertical mixing. Although there were some exceptional situations due to the variations of the characteristics of wind and wind-induce wave, in general, the TSS concentration decreased in the entire region.

Winds and the distribution of nearshore phytoplankton in a stratified lake

The distribution of phytoplankton in lakes is notoriously patchy and dynamic, but wind-driven currents and algal buoyancy/motility are thought to determine where algae accumulate. In this study, nearshore phytoplankton were sampled from different parts of a lake basin twice a day for 4–5 consecutive days, in the spring and in late summer, to test whether short-term changes in phytoplankton biomass and community composition can be predicted from wind-driven currents. On windy days, phytoplankton biomass was higher at downwind than at upwind nearshore sites, and the magnitude of this difference increased linearly with increasing wind speed. However, contrary to the generally assumed downwind phytoplankton aggregations, these differences were mostly due to upwelling activity and the dilution of phytoplankton at upwind nearshore sites. The distribution of individual taxa was also related to wind speed, but only during late stratification (except for cryptophytes), and these relationships were consistent with the buoyancy and motility of each group. On windy days, large diatoms and cyanobacteria concentrated upwind, neutrally buoyant taxa (green algae, small diatoms) were homogeneously distributed, and motile taxa (cryptophytes, chrysophytes, dinoflagellates) concentrated downwind. Predictable differences in the biomass and composition of phytoplankton communities could affect the efficiency of trophic transfers in nearshore areas.

Quantifying the impact of the major driving mechanisms of inter-annual variability of salinity in the North Sea

New 67-year long (1948–2014) gridded time series of salinity in the North Sea at all depths allowed to quantify, spatially resolved, the amount of inter-annual salinity variability explained by each of its driving mechanisms: sea level pressure (SLP), precipitation, river run-off, zonal and meridional winds and currents over the eastern North Atlantic. For the current data, not only annual averages but also their deviations, as measure of turbulence, were considered. Our results summarize and expand the knowledge gathered in the last 50years about the mechanisms driving inter-annual variability of salinity in the North Sea. Three mechanisms, uncorrelated with each other and acting over separate regions of the North Sea, arise as most important: (1) River run-off from continental Europe explains 50–80% of inter-annual salinity variations at lag 0 in the Southern and German Bights and the Norwegian Trench up to the connection with the North Atlantic, down to the seabed near the coasts and to the deep Norwegian Trench (100m); (2) Remote variations of salinity in the Rockall Trough explain 70% of salinity variations of the tongue of high salinity in the northwestern North Sea with a lag of one year and down the water column; (3) The Neva discharge explains 60% of salinity changes in Skagerrak and southern Norwegian trench at lag 0. An explanation for this correlation might be the Baltic freshwater outflow being modulated by the Neva discharge through intensification of the estuarine gravitational circulation. We confirmed known relations between river run-off, precipitation over continental Europe, SLP over northern Europe and zonal wind over western Europe. Linked to these changes, we found also changes of meridional wind north of Scotland favoring eastward Ekman transport of salty North Atlantic waters into the North Sea off the Norwegian coast. Excluding this only case, we found no significant correlation between wind-driven currents and North Sea salinity changes. This result supports the notion that the Atlantic inflow into the North Sea is mainly density-driven. Salinity in the region east of Scotland and northern England was alienated from all driving mechanisms tested. An explanation was found in concomitant canceling changes of the intensity of the North Sea circulation and the discharge of the river Tay.

Sustainable Membrane Distillation Coupled with Solar Pond

Abstract The necessity for fresh water is at the top of the international schema of serious issues. As the fresh water shortage becomes an issue, the application of desalination plants is rapidly rising on a large scale. Also, membrane technologies are gaining high importance for their great performance and their economic viability. Membrane distillation as a novel thermally-driven separation process can be adapted for water desalination, due to its simplicity and ability to couple with a sustainable source of energy. In this paper, study was conducted to develop a Sustainable Water Desalination (SWD) system by combining direct contact membrane distillation with solar ponds. A brief explanation of the solar pond concept and the concept of the membrane distillation (MD) system was illustrated. Additionally, the possibility of desalinating high saline water with zero brine discharge was investigated. Moreover, an alternative source of energy which is from the heat stored in the lower zone of the solar pond was investigated by using the combination of MD and salinity gradient solar pond (SGSP). In this work, the idea of using the surface of the solar pond as heat sink for the permeate water was considered, by introducing floating cooling pipes that are also acting as wave suppressors to reduce the surface mixing in solar pond caused by wind-driven currents. Furthermore, the present understanding and contribution to the research efforts to build a SWD technology system was analysed. In addition to the concept illustration, an indoor study was also conducted about the performance of MD with variation of the feed temperature. It concluded that as the feed temperature increases, the heat flux, mass flux, heat transfer coefficients and evaporation efficiency will increase as the temperature polarization coefficient decreases.

Sedimentary constraints on the development of a narrow deep strait (São Sebastião Channel, SE Brazil)

The Sao Sebastiao Channel (SSC), which separates Sao Sebastiao Island from the continent, is a deep elongated strait on the inner shelf of the Sao Paulo Bight (SE Brazil). The aim of this study is to explain why it is presently sediment starved, instead of forming a tombolo. Wave data were obtained from both a WW3 model database and buoy records, and wave propagation patterns from the SWAN numerical model. Grain size trend analysis of 579 surficial sediment samples from the strait and the surrounding region served to estimate the residual transport directions. Bedload sediment transport was computed considering in situ currents and bottom sediment grain size. Moreover, six seismic profiles and one gravity core were obtained in the strait in order to evaluate the hickness of the sedimentary deposits. The geometry of the SSC (X/B=0.3, where B is the breakwater or island diameter and X is its cross-shore distance to the mainland) predicts that a tombolo should be formed, and wave patterns confirm that it is a zone sheltered from both S and NE waves. Previous studies have shown that the hydrodynamics of the SSC is controlled by wind-driven currents, which are more intense in the eastern and central sectors of the strait. The western sector is currently covered by sandy mud, whereas very coarse to fine sand prevails in the deeper eastern sector. Sediment patterns show a trend to deposition of fine sediment in the western sector of the SSC and two main depocentres located at the northern limit of the study area and at the southern mouth of the strait. Sandy mud in the western sector forms a 40-m-thick deposit close to the outer limit of Araca Bay, whereas the remainder of the SSC is covered by a very thin layer of sandy sediments. Dominance of mud in the depositional western sector suggests low availability of sand in the area. Therefore, despite the geometry and wave patterns of the SSC favouring the formation of a tombolo, the dominance of wind-driven currents and the low availability of sand determine that such a sedimentary feature cannot be formed, resulting in a deep strait.

The Longshore Transport Enigma and Analysis of a 10-Year Record of Wind-Driven Nearshore Currents

Burnette, C. and Dally, W.R., 2018. The longshore transport enigma and analysis of a 10-year record of wind-driven nearshore currents.Previous analysis of a 10-year record of nearshore directional wave spectra collected with an Acoustic Doppler Current Profiler (ADCP) installed outside the surf zone in Melbourne Beach, Florida, unexpectedly revealed that the long-term average wave-induced radiation stress (Sxy) was nearly balanced between northerly and southerly forcing. More than 4 years of wind data collected at the site with a directional anemometer also showed a nearly balanced net longshore wind stress. However, shoreline offsets at nearby jettied inlets clearly indicate a predominant north-to-south net sediment transport. This enigma was investigated by analyzing the nearshore currents measured by the ADCP, and examining their correlation with the wind and incident waves. Significant correlation was found between the depth-averaged wind-driven longshore current and the incident wave conditions; e.g., the average energy-based significant wave height ___mo is typically larger (0.95 m) when the current is directed to the south than when the current is directed to the north (0.73 m). Guided by the classic Coastal Engineering Research Center (CERC) formula for longshore sediment transport, it is found that is significantly more correlated with southerly directed longshore currents (r = 0.47) than northerly currents (r = 0.21). Also, if a “storm” is defined as whenever Hmo exceeds 1.75 m, 40% of this time, the mean wave direction is out of the northeast quadrant, 33% is from the southeast, and 27% approaches shore-normal. Additionally, during storms, a stronger correlation between Sxy is found with southerly directed wind-driven currents (r = 0.51) than with northerly directed currents (r = 0.32). These findings indicate that net longshore sediment transport may in fact be heavily influenced by the correlation of the local wind with the waves, a feature not included in traditional longshore sediment transport formulas.

Notorious Ocean Current Is Far Stronger Than Previously Thought

The Antarctic Circumpolar Current is the only ocean current to circle the planet and the largest wind-driven current on Earth. It's also 30% more powerful than scientists realized.

Effect of wave-current interactions on sediment resuspension in large shallow Lake Taihu, China.

The disturbance of the water-sediment interface by wind-driven currents and waves plays a critical role in sediment resuspension and internal nutrient release in large, shallow lakes. This study analyzed the effects of the interactions between wind-induced currents an1d waves on the driving mechanism of sediment resuspension in Lake Taihu, the third largest freshwater lake in China, using acoustic and optic techniques to collect long-term, high-frequency, synchronous in situ measurements of wind, currents, waves, and suspended solid concentrations (SSCs). The results suggested that water turbidity started to increase at wind speeds of approximately 4m/s and significantly increased when wind speeds exceeded 6m/s. In most cases, wind-induced waves were the main energy source for changes in turbidity. Wave-generated shear stress contributed more than 95% to sediment resuspension and that only in weak wind conditions (<4m/s) did the lake bottom shear stresses generated by currents and waves contributed equally. The relationship between SSC and bottom shear stress generated by wave was established by fitting the observed results. The processes of sediment dynamics were divided into four stages (A through D) according to three shear-stress thresholds. In stage A, SSC remained stable (about 45mg/L) and τw was less than 0.02N/m2. In stage B, the sediment bed was starting to be activated (SSC 45∼60mg/L) and τw was in the range of 0.02∼0.07N/m2. In stage C, a medium amount of sediment was suspended (SSC 60∼150mg/L) and τw ranged from 0.07 to 0.3N/m2. In stage D, large amount of sediment was suspended (SSC 150∼300mg/L) and τw was larger than 0.3N/m2. The findings of this paper reveal the driving mechanism of sediment resuspension, which may further help to evaluate internal nutrient release in large shallow Lake Taihu.

Effect of Wind and Hydrographic Conditions on the Transport of Vistula Lagoon Waters Into the Baltic Sea: Results of a Combined Experiment

The influence of wind and hydrodynamic processes on the spreading of turbid waters from the Vistula Lagoon into the Baltic Sea was studied. Our research is based on joint analyses of remote sensing data and those from concurrent in situ measurements of the three-dimensional structure of the outflow. A strong difference in the water optical properties of the Baltic Sea and the Vistula Lagoon caused by an intense summer bloom of cyanobacteria allowed studies of the evolution and transformation of the outflow in mid-July–early August 2014 using Ocean Color satellite data. Our in situ measurements revealed that waters from the Vistula Lagoon were exclusively present in the upper water layer. The study was conducted under various wind and, therefore, under different upwelling/downwelling conditions, thereby determining different patterns of wind-driven currents, which enabled us to assess their impact on the propagation of the lagoon outflow. One of these patterns was reaching to the south, along the Vistula Spit, and another one reaching to the north, along the Sambia Peninsula. We show that the main spreading direction of the plume strongly coincides with that of wind-driven currents. However, if vortical structures are present in the Bay of Gdansk, they also affect the plume transformation, and that should be taken into account when the propagation of water pollution is forecasted.