Wind-induced Flow Research Articles

Pulsed wind-driven control of phytoplankton biomass at a groundwater-enriched nearshore environment

Along some Mediterranean coastal areas and other world regions, nutrient and chlorophyll concentrations often show gradient increases of up to one order of magnitude perpendicular to the coast. This nearshore stripe, extending a few hundred meters from the coast, is enriched by submarine groundwater discharges (SGD) containing elevated nutrient concentrations that may eventually sustain high biomass phytoplankton blooms. During a survey carried out in the summer of 2018, we examined the short-term (hours) variability of the phytoplankton biomass (measured as chlorophyll; Chl) in response to environmental changes associated with SGD and wind forcing in the nearshore waters of Palma Beach (Mediterranean Sea). Continuous CTD records revealed a general salinity decline indicative of SGD along the shoreline. Large and pulsed salinity fluctuations (i.e. 2–3 psu variations, 1–4 h) were observed each day that were consistent with offshore advection episodes of the lower salinity water retained in the nearshore (peak crosshore velocity 5–6 cm s−1). Chl near the shoreline was markedly higher than offshore (3.55 ± 1.29 and 0.68 ± 0.27 mg m−3 respectively) but recurrently fluctuated in the afternoon to up to >7 mg m−3. Primary production estimations showed that despite the higher production in the nearshore (50.29 ± 10.98 μmol O2 L−1 d−1, 4-fold offshore values) productivity per unit chlorophyll did not significantly vary (p > 0.01) therefore suggesting that, at this time scales, high biomass episodes in the nearshore are driven by an accumulation mechanism. Statistical analysis (CCA) demonstrates that Chl variability is largely explained (93 %) by variations in wind and current velocity. Our results provide evidence that the dynamics of this nearshore environment are modulated by the interplay between the shoreward wind-induced flow and the offshore directed density flow. This mechanism could explain the occurrence and episodic nature of high biomass blooms in the nearshore, as well as be an important factor influencing the microbial community structure at the coastal zone.

Effect of Internal Waves on the Hydrodynamics of a Mediterranean Sea Strait

In the present work, the effects of wind- and tide-induced internal waves in the Rio-Antirio Strait in western Greece were studied by using three-dimensional numerical simulations. For the wind-induced flow in the strait, it emerged that the internal waves’ initiation is associated with the direction of the wind. Tidal action, with or without the combined action of wind, also generates internal waves in the strait, with amplitudes higher than 20 m. The action of the internal waves causes a subsurface inflow of colder waters from the Gulf of Corinth to the Gulf of Patras, as has been also simulated for the case of the wind-induced flow, generating strong hypolimnetic currents. The exchange flowrate between the Gulf of Patras and the Gulf of Corinth appeared to undergo significant modification for the wind-induced flow and had little effect for the pure tidal flow (in windless conditions) due to the development and action of the internal waves at the strait. The combined action of the tide and the wind was found to marginally affect the exchange flowrate between the two gulfs compared to the pure tidal flow. The interaction between the Coriolis effect and internal waves, at least away from the strait, forms a characteristic horizontal structure of flow. The structure of turbulence in the near strait area under the action of internal waves generated by the wind and/or tide was also discussed and compared with the corresponding barotropic flow.

Interfacial friction induced capillary flow within nanofiber-supported ionic liquid droplets

As global economic growth increases, the demand for energy sources boosts. While fossil fuels have traditionally satisfied this demand, their environmental influence and limited reserves require alternatives. Fossil fuel combustion contributes substantially to greenhouse gas emissions, with a pressing need to halve these emissions by 2030 and target net-zero by 2050. Renewable energy sources, contributing currently to 29% of global electricity, are viewed as promising substitutes. With wind energy's potential, Zheng's team developed a novel method to harness even low wind speeds using well-aligned nanofibers and an innovative “drop wind generator”. This system, combining moisture-saturated ionic liquid 3-Methyl-1-octylimidazolium chloride with specific nanofiber arrays, exploits wind-induced flows for energy conversion. This study highlights the vast untapped potential of low-speed wind as a sustainable energy source potentially for electronics.

Framework of wind joint analysis for different lake regions and its effects on the water quality

Water quality of Lake Taihu (LT) is paid wide attention, and the wind field makes wind-induced flow, significantly impacting the water quality. As a wide lake, the wind field suffers spatial and temporal changes. The correlated relationship among the wind fields for different lake regions has not been studied, and the joint effects of wind field on the water quality is still unknown. Hence, this paper proposed a framework of wind joint analysis for different lake regions and modelling its effects on the water quality, including joint analysis of wind field for different lake regions using Copula function, random time series generation of wind field using Monte-Carlo simulation, and hydrodynamic and water quality numerical simulation. Taking the Lake Taihu (LT) as study case, the joint relationships of wind field for four lake regions were analyzed, and the CODMN, TP and TN distributions under different wind fields were simulated. This paper showed the following: (1) The relationship between the wind speed and direction was weak, and the correlated relationships among the wind fields for four lake regions were significant (ρ > 0.5). (2) The water quality of LT was more influenced by the wind direction rather than the wind speed, with an impacting ratio of ∼4.5. (3) The discharged weighted angle of runoff outflow (DWARO) was a practical index to improve the water quality. When regulating the input/output runoff discharge, water diversion project and water intakes in practice, the administrations should make the DWARO less than or equal to the average wind direction, to decrease the average pollutant concentration and improve the water quality of lake and intake. The proposed framework and results of LT could be extended to other wide shallow lakes to support the environmental management and basin runoff regulation.

Three-Dimensional Numerical Modeling of Flow Hydrodynamics and Cohesive Sediment Transport in Enid Lake, Mississippi

Enid Lake is one of the largest reservoirs located in Yazoo River Basin, the largest basin in the state of Mississippi. The lake was impounded by Enid Dam on the Yocona River in Yalobusha County and covers an area of 30 square kilometers. It provides significant natural and recreational resources. The soils in this region are highly erodible, resulting in a large amount of fine-grained cohesive sediment discharged into the lake. In this study, a 3D numerical model was developed to simulate the free surface hydrodynamics and transportation of cohesive sediment with a median diameter of 0.0025 to 0.003 mm in Enid Lake. Flow fields in the lake are generally induced by wind and upstream river inflow, and the sediment is also introduced from the inflow during storm events. The general processes of sediment flocculation and settling were considered in the model, and the erosion rate and deposition rate of cohesive sediment were calculated. In this model, the sediment simulation was coupled with flow simulation. In this research, remote sensing technology was applied to estimate the sediment concentration at the lake surface and provide validation data for numerical model simulation. The model results and remote sensing data help us to understand the transport, deposition and resuspension processes of cohesive sediment in large reservoirs due to wind-induced currents and upstream river flows.

Carbon dioxide levels and ventilation in Acromyrmex nests: significance and evolution of architectural innovations in leaf-cutting ants.

Leaf-cutting ant colonies largely differ in size, yet all consume O2 and produce CO2 in large amounts because of their underground fungus gardens. We have shown that in the Acromyrmex genus, three basic nest morphologies occur, and investigated the effects of architectural innovations on nest ventilation. We recognized (i) serial nests, similar to the ancestral type of the sister genus Trachymyrmex, with chambers excavated along a vertical tunnel connecting to the outside via a single opening, (ii) shallow nests, with one/few chambers extending shallowly with multiple connections to the outside, and (iii) thatched nests, with an above-ground fungus garden covered with plant material. Ventilation in shallow and thatched nests, but not in serial nests, occurred via wind-induced flows and thermal convection. CO2 concentrations were below the values known to affect the respiration of the symbiotic fungus, indicating that shallow and thatched nests are not constrained by harmful CO2 levels. Serial nests may be constrained depending on the soil CO2 levels. We suggest that in Acromyrmex, selective pressures acting on temperature and humidity control led to nesting habits closer to or above the soil surface and to the evolution of architectural innovations that improved gas exchanges.

A boundary-value problem arising in the modelling of equatorial wind-drift currents

We investigate the boundary-value problem that models wind-induced equatorial flows, establishing the existence and uniqueness of solutions. We also discuss some special cases that were studied in recent geophysical research.

Optimisation of the Geometric Parameters of Longitudinally Finned Air Cooler Tubes Operating in Mixed Convection Conditions

The results of optimisation calculations presented in the article are related to longitudinally finned tubes of a heat pump evaporator operating under natural wind-induced flow of outdoor air conditions. The finned surface is characterised by an unusual, wavy fin shape. The article presents the methodology applied to seeking optimal geometric parameters of the finned tube in which thermal calculations were performed by modelling a mixed convection process on the finned surface using the finite volume method. In the case of maximising the heat flow with the minimum mass of the fins, the optimal solution was dominated by the minimum mass of the fins and thus geometric parameters correspond to the number of fins n = 6, fin height h = 0.065 and fin thickness s = 0.0015 m. Optimisation calculations made for maximum efficiency of the exchanger at constant mass indicated that the tube with ten fins (n = 10) with a height of h = 0.11 m and a thickness of s = 0.0018 m allowed maximum heat flow at the assumed mass of the fins in the exchanger tube model. The article proposes a simplified method of determining the optimal geometric parameters of the profile for any mass and maximum thermal efficiency.

A methodology for quantifying flow patterns in a water-table apparatus for naturally ventilated buildings

Wind-driven ventilation in buildings is an effective way of diluting the indoor air for maintaining thermal comfort and acceptable indoor air quality. Visualization of the wind-induced flow patterns in a building using a water-table apparatus is a relatively convenient method that produces instantaneous results. The present study focused on the quantification of the flow patterns generated in and around buildings using water-table experiments. The flow patterns were analyzed photographically to derive different ventilation metrics, such as dead spots, ventilation efficiency, etc., which would reveal quantitative information regarding the flow in the different zones of the building. Experiments were conducted using different configurations in order to verify the results obtained with the photographic method. The method used in the present study could be useful in the prediction of flow patterns for complex geometries, which would assist in undertaking early decisions for the proper orientation of a building and its openings. Abbreviations: ACH: Air Changes per Hour (h−1); AS: Room with windows on adjacent walls configuration; AVE: Absolute Ventilation Efficiency; BHK: Bedroom, Hall, Kitchen; C: dye concentration at a point after t, s (g/l); CFD: Computational Fluid Dynamics; Ci: average inside concentration(g/l); Cmax: maximum dye concentration at a point (g/l); Co: initial concentration at a point (g/l); Cs: concentration in the outdoor supply air (g/l); d: characteristic length (mm or m); D: Dining room; dC: change in concentration (g/l); DS: Dead Spots; Ea: Absolute Ventilation Efficiency; fps: Frames per seconds; IAQ: Indoor Air Quality; k reactivity rate (h−1); K: Kitchen; L: Living Room; MATLAB: Matrix Laboratory; OS: Room with windows on opposite walls configuration; P: Dimensionless penetration factor; P1: Passage 1; P2: Passage 2; P3: Passage 3; Pix: Pixel value (px); PNG Portable network graphics; R1: Room 1; R2: Room 2; R3: Room 3; Re: Reynolds Number; RGB: Red, Green, Blue; S: indoor source emission rate (μg/h); SS: Room with single-sided window configuration; T1: Toilet 1; T2: Toilet 2; T3: Toilet 3; U: Utility room; V: Room volume, m3; v: velocity (m/s); VLC: VideoLAN Client

Numerical investigation of Typhoon Kai-tak (1213) using a mesoscale coupled WRF-ROMS model — Part Ⅱ: Wave effects

Continuing along the path of previous papers in this series, this paper describes numerical work to investigate seven different computational schemes of wave impact on the typhoon processes. Investigations showed that the wave dynamics factor is the most severe impact factors and should therefore be considered for coupling atmosphere-ocean interaction during a typhoon. The simulation results reveal the temporal and spatial distribution of typhoons field, pressure field, typhoon waves, storm surges, wind-induced flow field, sea surface stress and heat flux. Typhoon waves have a spatial asymmetrical distribution, the storm surges and flow field have asymmetrical distribution in space and has lag in time. This paper is a companion paper to “Numerical investigation of Typhoon Kai-tak (1213) using a mesoscale coupled WRF-ROMS model”.

Numerical investigation on the impact of wind-induced hydraulics on dissolved oxygen characteristics in a shallow stormwater pond

Abstract Stormwater ponds (SWPs) are widely utilized for flood and water quality control. Low-flow rates are common in SWPs, sometimes causing wind-driven currents to become the dominant hydrodynamic force during ice-free periods. Hence, it is essential to understand the influence of the wind-induced flow on stratification and dissolved oxygen (DO) concentrations in shallow SWPs to predict the performance and water quality of these systems. The objective of this study is to evaluate the influence of wind-driven circulation on the spatial distribution of DO in an SWP using a numerical model. A bottom-mounted acoustic Doppler current profiler (ADCP) was utilized to measure small wind-induced currents and to validate a hydrodynamic model, which suggested that a wind-dominated circulation was generated even with the moderate wind speed. Countercurrents opposite in the direction to surface wind-generated flow were also present. The DO model demonstrated that complete mixing can be produced by higher wind speed, leading to fully oxic conditions throughout the water column (7.00 mg/L DO or higher), wherein low DO water at depth was carried to the surface by upwelling circulation and was possibly replenished during the surface transportation. This sheds some light on the impact of wind-induced mixing on the water quality in shallow SWPs.

ON THE TOPOGRAPHY-DRIVEN VORTICITY PRODUCTION IN SHALLOW LAKES

We analyse the vorticity production of lake-scale circulation in wind-induced shallow flows using a linear elliptic partial differential equation. The linear equation is derived from the vorticity form of the shallow-water equation using a linear bed friction formula. The features of the wind-induced steady-state flow are analysed in a circular basin with topography as a concave paraboloid, having a quadratic pile in the middle of the basin. In our study, the size of the pile varies by a size parameter. The vorticity production due to the gradient in the topography (and the distance of the boundary) makes the streamlines parallel to topographical contours, and beyond a critical size parameter, it results in a secondary vortex pair. We compare qualitatively and quantitatively the steady-state circulation patterns and vortex evolution of the flow fields calculated by our linear vorticity model and the full, nonlinear shallow-water equations. From these results, we hypothesize that the steady-state topographical vorticity production in lake-scale wind-induced circulations can be described by the equilibrium of the wind friction field and the bed friction field. Moreover, the latter can also be considered as a linear function of the velocity vector field, and hence the problem can be described by a linear equation.

Numerical investigation of Typhoon Kai-tak (1213) using a mesoscale coupled WRF-ROMS model

The Typhoon Kai-tak that occurred in August 2012 produced strong winds, heavy rain, extreme wave, and storm surge, which also had a significant impact on the coastal areas of China and Vietnam. Studying the formation and tracking the movement mechanism of this typhoon will help reduce future coastal disasters, as well as have important scientific significance. The impact of a typhoon creates strong mass transport and energy exchange between the atmosphere and the ocean which produces a strong interaction between the wind field and the flow field. A coupled atmosphere-ocean model in the South China Sea was established based on the mesoscale atmospheric model WRF and the regional ocean model ROMS. Typhoon Kai-tak was simulated using this model. The simulation results show that the coupled WRF-ROMS model indicate high simulation accuracy with respect of storm surge in the South China Sea under the influence of Typhoon Kai-tak. The simulation results also reveal the temporal and spatial distribution of Typhoon Kai-tak's field, storm surge, and wind-induced flow fields. The spatial asymmetry and time lag in the spatial–temporal distribution of sea surface temperature during Typhoon Kai-tak have been discussed. The heat exchange at the air-sea interface was very strong under the influence of Typhoon Kai-tak, and the latent heat generated by water vapor evaporation plays a dominant role in the heat exchange at the air-sea interface, which shows that the heat carried by the vaporization of the sea surface is one of the important factors for the decrease of sea temperature under the influence of a typhoon.

Observations of the lateral structure of wind-driven flow in a coastal plain estuary

Wind-stress is one of the main drivers of estuarine circulation. The lateral structure of wind-induced flows in estuaries has been described mainly with analytical and numerical models. The aim of this study is to investigate, with observations, the lateral structure of wind-induced flow in a coastal plain estuary, the James River, Virginia. Such structure was explored with the first Empirical Orthogonal Function (EOF1) mode derived from month-long moored ADCPs deployed at two cross-sections in the estuary. Mode 1 explained 53% of the variance and was attributed to wind forcing. Its lateral structure (eigenvectors) consisted of upwind flow centered in the channel at middle depth, downwind flow over the shoals, and a vertically sheared bidirectional flow over the channel slope. Wavelet coherence analysis showed that along-estuary wind was highly coherent with mode 1 (coherence squared > 0.9), especially at the period band between 4 and 6 days. The along-estuary wind stress and the temporal variation of mode 1 showed an anti-phase coherence, with the wind stress leading mode 1 persistently. In addition, an analytical solution showed a lateral structure similar to the eigenvectors obtained with EOF1. The conclusion is that the lateral structure described by EOF1 was induced by wind-stress and was consistent with analytical and numerical model results. These results are among the handful available that confirm the theoretical structure of wind-driven flows over laterally varying bathymetry.

Driving forces of sandy sediment transport beyond the surf zone

The paper deals with experimental and theoretical investigations of forces that drive sediment motion beyond the surf zone of the southern Baltic Sea. The study site is located in the sandy coastal zone at Lubiatowo (Poland). Field surveys were carried out by the Institute of Hydro-Engineering of the Polish Academy of Sciences (IBW PAN) and the Maritime Institute in Gdańsk (IMG). The measurements comprise parameters of wind, waves and currents. The wind velocities and directions were recorded at the IBW PAN Coastal Research Station (CRS) in Lubiatowo, while the wave and current data were collected near CRS Lubiatowo, ca. 1.5 Nm from the shoreline, at a depth of 17 m. Theoretical investigations concern wind-induced currents, nearbed wave-induced oscillatory velocities and wave-current interactions. The concept of the apparent roughness related to the wave bed boundary layer is used in the description of wind-induced steady flow. A theoretical model of the wind-induced current is proposed in two variants, depending on the predominance of wave or current impact. The wind-induced flow model is successfully verified using measured current velocity profiles. Previously developed at IBW PAN, a three-layer sediment transport model is adapted to the study site and applied in calculations of sediment transport rates.

Wind-induced flow velocity effects on nutrient concentrations at Eastern Bay of Lake Taihu, China.

Shallow lakes are highly sensitive to respond internal nutrient loading due to wind-induced flow velocity effects. Wind-induced flow velocity effects on nutrient suspension were investigated at a long narrow bay of large shallow Lake Taihu, the third largest freshwater lake in China. Wind-induced reverse/compensation flow and consistent flow field probabilities at vertical column of the water were measured. The probabilities between the wind field and the flow velocities provided a strong correlation at the surface (80.6%) and the bottom (65.1%) layers of water profile. Vertical flow velocity profile analysis provided the evidence of delay response time to wind field at the bottom layer of lake water. Strong wind field generated by the west (W) and west-north-west (WNW) winds produced displaced water movements in opposite directions to the prevailing flow field. An exponential correlation was observed between the current velocities of the surface and the bottom layers while considering wind speed as a control factor. A linear model was developed to correlate the wind field-induced flow velocity impacts on nutrient concentration at the surface and bottom layers. Results showed that dominant wind directions (ENE, E, and ESE) had a maximum nutrient resuspension contribution (nutrient resuspension potential) of 34.7 and 43.6% at the surface and the bottom profile layers, respectively. Total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) average concentrations were 6.38, 1.5, and 0.03mg/L during our field experiment at Eastern Bay of Lake Taihu. Overall, wind-induced low-to-moderate hydrodynamic disturbances contributed more in nutrient resuspension at Eastern Bay of Lake Taihu. The present study can be used to understand the linkage between wind-induced flow velocities and nutrient concentrations for shallow lakes (with uniform morphology and deep margins) water quality management and to develop further models.

Diffusional mass transfer coefficient at the water–sediment interface for wind-induced flow in very shallow lagoons

Very shallow lagoons that are a few centimeters deep are common in the arid Andes of Northern Chile, Argentina, Bolivia and Peru. The dynamics of these lagoons are dominated by the water–sediment interface (WSI) and strong afternoon winds. Although many studies have examined the diffusional mass transfer coefficients (k t ) of open channel flows, estimates for wind-induced flows are still unknown. The aim of this article is to propose and validate an analytical expression for computing k t at the WSI for wind-induced flow. The laboratory measurements were conducted in a wind tunnel with a water tank of variable depth located at its downwind end. Natural muddy sediments were placed in the middle of the tank so that the dissolved oxygen (DO) was consumed in the sediments. The diffusional mass transfer coefficient that characterizes the DO uptake in the sediment was obtained from DO micro-profiles measured with an OX-25 Unisense microelectrode. Water velocity profiles were measured with a 2D side-view Sontek acoustic doppler velocimetry (ADV), and the wind shear velocity was computed based on wind velocity profiles that were measured with an Extech hot-wire anemometer. A total of 16 experiments were conducted with different water depths and wind shear stresses. The constants required by the model were determined from these experiments, and the analytical expression was successfully validated by the laboratory observations. The analytical expression obtained for computing k t was also validated with field observations that were conducted in October, 2012, in Salar del Huasco, Northern Chile (20.274° S, 68.883° W, 3800 m above sea level). The comparison between the observed and predicted values of k t provides a determination coefficient of r 2 = 0.48 and a p value < 0.01. The results show that the value of k t for wind-induced flow is proportional to the wind shear velocity and the inverse of the Reynolds number of the wind-induced current.

ВЛИЯНИЕ ДЕЯТЕЛЬНОСТИ ГОРНО-МЕТАЛЛУРГИЧЕСКИХ ПРЕДПРИЯТИЙ НА ХИМИЧЕСКИЙ СОСТАВ ДОННЫХ ОТЛОЖЕНИЙ ОЗЕРА ИМАНДРА, МУРМАНСКАЯ ОБЛАСТЬ

Крупнейший водоем Мурманской области – озеро Имандра – более 80 лет испытывает загрязнение промышленными сточными водами горнодобывающих и металлургических предприятий и коммунально-бытовыми стоками населенных пунктов, что сказалось в значительных преобразованиях химического состава воды и донных отложений озера, ухудшении экологического состояния озера и изменении структуры гидробионтов. Для оценки современного экологического состояния оз. Имандра и изучения истории развития и загрязнения озера был исследован химический состав донных отложений, для чего отбирались их колонки, и проводился послойный анализ накопления элементов. Определялись содержания тяжелых металлов (Ni, Cu, Co, Zn, Cd, Pb, As, Hg, Mn, Fe, Cr), щелочных и щелочноземельных металлов (Na, K, Ca, Mg, Sr), а также Al и P. Установлено, что геохимический состав донных отложений оз.Имандра претерпел значительные изменения по всей акватории вследствие как прямого поступления сточных вод предприятий горно-металлургического комплекса и коммунально-бытовых стоков, так и аэротехногенного загрязнения водосбора озера и ветровых нагонных течений. Наибольший вклад в эти преобразования оказывают горнометаллургические, горнодобывающие и горноперерабатывающие предприятия – комбинат «Североникель», ОАО «Апатит» и «Олкон». Самые значительные преобразования химического состава произошли на акватории поступления стоков металлургического комбината «Североникель», где в поверхностных слоях донных отложений происходит лавинное увеличение концентраций всех исследуемых тяжелых металлов. Концентрации Ni и Cu увеличились на три и два порядка соответственно по сравнению с глубокими фоновыми слоями – до 3 и 0,6%. Увеличение содержания более чем на порядок зафиксировано и для остальных тяжелых металлов – Co, Zn, Cd, Pb, As, Hg, Cr, которые являются сопутствующими металлами в медно-никелевой руде. Влияние стоков предприятий ОАО «Апатит» сказалось в увеличении концентраций элементов, содержащихсяв апатитонефелиновых рудах и в скрышных породах (Ca, P, Na, K, Al, Sr). Обнаружилось также аномальное увеличение содержания Hg, связанное с проведением взрывных работ на рудниках.

Remote-sensing observations of Typhoon Soulik (2013) forced upwelling and sediment transport enhancement in the northern Taiwan Strait

The Taiwan Strait plays an important role in water and sediment exchange between the East China Sea and the South China Sea. On 13 July 2013, Typhoon Soulik crossed the Taiwan Strait, causing a significant impact on the strait’s marine system. In this article, we document the use of remote-sensing data to study this impact by comparing sea surface temperature (SST), spatial distributions and concentrations of chlorophyll (Chl-a), and total suspended matter (TSM) in the strait over different time periods. During and after the typhoon, the TSM of the waters near the Minjiang estuary dramatically increased, while Chl-a and SST significantly decreased. To the southeast of Pingtan Island, the SST decreased and Chl-a significantly increased, causing strong upwelling that lasted eight to ten days. To the northwest of Taiwan Island, Chl-a and the TSM of the coastal waters dramatically increased. The strong cyclonic wind-stress of the typhoon enhanced heat exchange between the water and the atmosphere, and a large amount of rainfall and run-off significantly decreased the SST. During the typhoon, the increased sediment discharged into the strait by rivers, and the re-suspension of seafloor sediment, increased the concentration of TSM in the coastal waters. Seawater with relatively high sediment concentration was transported to the middle of the strait after being carried by wind-induced flows. In the waters near the typhoon’s path, especially in the upwelling area, nutrient-rich bottom water stirred by the typhoon promoted an outbreak of aquatic organisms and significantly increased the probability of a red tide occurrence.

Impact of submerged herbaceous vegetation on wind-induced current in shallow water

A combined wind tunnel and water flume experiment was performed to study the effect of an aquatic herbaceous plant patch on the turbulent structure and flow field of wind-induced currents. Eel grass was chosen as the test plant. The plants were settled in patch form. Three-dimensional instantaneous velocities were measured using an acoustic doppler velocimeter (ADV). The results indicate that in the non-eel grass patch flow, turbulent shear stress −u′w′¯has a local minimum near the flow reverse point, turbulent intensity has the tendency to decrease continually from surface to bottom, and the dominant turbulent event is sweeping. In the eel grass patch with wind-induced flow, reverse flow occurs more quickly than in the non-eel grass patch case, and the reverse point shifts downward. Turbulent shear stress −u′w′¯ has two maxima below the canopy. Turbulent intensity u′2¯ decreases generally from water surface to flume bed, but there are maxima below the canopy. The dominant turbulent event is the fourth quadrant event below the canopy, and the two relative contributions of the second and the fourth quadrant event have similar values above the canopy. The mean bias and RMS values at centre of the eel grass patch are almost as two times larger as that at other measuring lines in non-eel grass region. This indicates that not only the shear stress and turbulent intensity become larger, and the vertical variations of the shear stress and turbulent intensity are also larger due to the effect of vegetation. The differences in the effects of submerged herbaceous vegetation on open channel flow and wind-induced flow were discussed in relation to time averaged velocity, turbulent shear stress, turbulent intensity and coherent structure based on the present test data and previous data.