Maximum Current Velocity Research Articles

Changes in the suspended floc properties by bed erosion in a macrotidal muddy flat: Case of Asan Bay, Korea

Intertidal flats have closely connected sediment transport systems with tidal channels. The properties of suspended sediments derived by horizontal advection and local erosion were examined under various current and wave. A field campaign was conducted over two weeks (October 17–31, 2021) in the Asan intertidal flat. Suspended sediments were in the form of flocs, which are clumps of particles, with an average floc size (davg) of 70–275 μm. The maximum current velocity and water level at each tidal cycle continuously decreased from 0.19 to 0.04 m s−1 and from 5 to 2 m, respectively. In accordance with the hydrodynamic conditions, continuous decrease in davg from spring to neap tides was superimposed by flood-ebb variations in davg. Geological heterogeneity between channels and flats can be significantly influenced by tide and wind conditions. Under tide-dominant conditions, the spring tidal current was strong enough to transport macroflocs with davg of 200–500 μm into the intertidal flats. The grown macroflocs up to 1.6 times of davg at early flood tide were deposited in the flats during the slack tide and transported back to the channels by ebb tidal current. Under wind-dominant conditions, the suspended flocs originated primarily from the bed by erosion. The deposited macroflocs or microflocs were entrained into water column and transported to adjacent tidal channel as microflocs or flocculi. The structure of the advected flocs had more varied density in the range of 42–147 kg m−3, compared to the eroded flocs. Under severe erosion, the structure of suspended flocs was similar to that of advected flocs despite their smaller size. This suggests that bed erosion supplied more porous flocs into the water column than those transported by advection. Consequently, the intertidal flats are at an increased risk of erosion due to the diverse structure of flocs.

On detailed representation of flood defences and flow-wave coupling in coastal flood modelling

Coastal flooding is projected to become more severe over the 21st century, necessitating effective adaptation, which in turn requires detailed local scale information that can only be provided by detailed numerical modelling. The current lack of information on flood protection measures and the high resource requirements of traditional hydrodynamic models presents concurrent challenges for detailed coastal flood modelling. But how comprehensive do the representation of coastal flood defences and hydrodynamic forcing need to be for adequately accurate modelling of coastal flooding? Here, we attempt to answer this question through strategic numerical simulations of the flooding that occurred at Île de Ré (France) during the Xynthia storm (2010), using the flexible mesh model Delft3D FM, with an over-land grid resolution of ~10 m. The model is validated against the flood extents observed in Île de Ré during Xynthia. We use three levels of detail in flood defence representation: a 5 m resolution DEM (i.e. base case DEM), the same 5 m DEM augmented with defences extracted from a 1 m DEM and Google Earth images (i.e. moderately augmented DEM), and the moderately augmented DEM further augmented with in-situ measurements of flood defences (i.e. highly augmented DEM). Simulations with these three DEMs are performed with and without flow-wave coupling (thus, 6 simulations in total), and results are analysed in terms of four flood indicators: maximum flood depths, flood extents, flood current velocities and flood damages. Our analysis indicates that both detailed representation of flood defences and the inclusion of waves have substantial effects on coastal flood modelling at local scale, with the former having a more pronounced effect. The return on the investment in implementing highly detailed in-situ measurements to represent flood defences appears to be low in this case, and adequately accurate results are obtained with a moderately augmented DEM. The combined effect of using the moderately augmented DEM together with waves, relative to using the base case DEM without waves, is to decrease maximum flood depths (up to 2 m), flood extent (by ~10%), maximum current velocities (in ~50% flooded area) and total flood damage (by ~27% or ~€ 188 million).

Genetic-environment associations explain genetic differentiation and variation between western and eastern North Pacific rhinoceros auklet (Cerorhinca monocerata) breeding colonies.

Animals are strongly connected to the environments they live in and may become adapted to local environments. Examining genetic-environment associations of key indicator species, like seabirds, provides greater insights into the forces that drive evolution in marine systems. Here we examined a RADseq dataset of 19,213 SNPs for 99 rhinoceros auklets (Cerorhinca monocerata) from five western Pacific and 10 eastern Pacific breeding colonies. We used partial redundancy analyses to identify candidate adaptive loci and to quantify the effects of environmental variation on population genetic structure. We identified 262 candidate adaptive loci, which accounted for 3.0% of the observed genetic variation among western Pacific and eastern Pacific breeding colonies. Genetic variation was more strongly associated with pH and maximum current velocity, than maximum sea surface temperature. Genetic-environment associations explain genetic differences between western and eastern Pacific populations; however, genetic variation within the western and eastern Pacific Ocean populations appears to follow a pattern of isolation-by-distance. This study represents a first to quantify the relationship between environmental and genetic variation for this widely distributed marine species and provides greater insights into the evolutionary forces that act on marine species.

Experimental study on mooring system of tunnel element subjected to current loading during the standby period before its immersion

ABSTRACT The safety of mooring system during the standby period is important for the follow-up immersion of tunnel elements. In this study, performance of a typical four-point mooring system, subjected to the current loading alone, was experimentally investigated. The latter is characterised by different direction, tidal elevation, and velocity, reaching the magnitude up to 2.5 m / s . The experimental results of motions of the tunnel element and tensions of the mooring lines were presented, based on which the safety of the mooring system and its correlation with the motions of the tunnel element are discussed. The results indicate that the magnitude of both the tensions of the mooring lines and the motions of the tunnel element increase with increasing current velocity, which is particular visible after reaching the 1.5 m / s -threshold. Whereas their relative values are governed by the current direction. The current loading is mainly carried by the mooring lines on the front side of the incoming current, among which the auxiliary lines generally governs the safety status of the mooring system. In this study, the maximum allowable current velocity can reach 1.5 m / s at the low tidal elevation of 12.016 m , where the safety factor of the mooring system keeps no smaller than 1.0, irrespective of the current direction. However, the maximum current speed is limited to 1.0 m / s at the high tidal elevation of 20.084 m . This maxima can be increased by strengthening the auxiliary mooring lines, in order to prolong the time window for construction of the immersed tunnel.

Modeling investigation of wave-induced longshore current distribution patterns on barred beaches

A three-dimensional coupled wave-current model was employed to investigate the wave-induced longshore currents on barred beaches. The modeling system was developed by coupling the finite-volume community ocean model (FVCOM) and the simulating waves nearshore (SWAN) model to fully describe wave-current interactions in the nearshore region. The three-dimensional radiation stress, surface rollers and wave-enhanced turbulent mixing were incorporated as the major wave effects on currents. The model was first evaluated against data collected from multiple sets of laboratory experiments. Diagnostic simulations demonstrated that the contributions of the wave rollers and wave-induced mixing, in addition to the radiation stress, were important for ensuring accurate calculations. Then, the longshore current patterns on barred beaches were investigated through simulations of a series of test cases under controlled conditions. The cross-shore distribution of wave-induced longshore currents, which predominantly occurred within the barred beach surf zone, usually exhibited bimodal characteristics. The maximum peak longshore current velocity was positively correlated with the incident wave height and period. As the bar height and width increased, the first velocity peak of the longshore current strengthened, while the second peak weakened. In most cases, the maximum longshore current velocity on a barred beach coincided with the first peak, which could occur anywhere from the bar-trough region to the bar-crest region, depending on the wave and bar heights. This finding could be used to clarify the cross-shore location discrepancies in the maximum peak longshore current velocity reported in previously published studies.

Assessment of Ocean Circulation Characteristics off the West Coast of Ireland Using HF Radar

Research on coastal ocean circulation patterns over long time periods is significant for various marine endeavors: environmental protection, coastal engineering construction, and marine renewable energy extraction. Based on sea surface current data remotely observed using a shore-based high frequency radar (HFR) system for one year (2016), spatiotemporal characteristics of surface flow fields of sea surface flow fields along the west coast of Ireland are studied using harmonic analysis, rotary spectral analysis and representative flow fields over different seasons and the whole year. Coastal surface currents in the study area are strongly affected by tidal dynamics of the M2 constituent, showing significant characteristics of regular semidiurnal tide, such as M2 and S2. The energy spectrum distribution indicates that the tidal constituents M2 and S2 are the dominant periodic energy constituents in a counterclockwise spectrum, which mainly presents rotating flow; the representative diurnal tidal constituents is the constituent K1, and its energy spectrum distribution is mainly clockwise. A comparison between probable maximum current velocity (PMCV) and measured maximum current velocity (MMCV) is presented. It shows that although tidal current characteristics in the study area are significant, the main driving force of the currents at the time of the maximum currents is wind energy. These results provide new insights into a region of huge societal potential at early stages of sustainable economic exploitation where few data currently exist.

Multi-criteria analysis to evaluate tidal energy potential in France

France benefits from an important tidal energy resource, with the second largest potential in Europe, and one of the biggest in the world. In addition, France has an important industrial and academic fabric, with several tidal developers, shipyards, and research centers, creating, theoretically, an attractive environment. However, though some tidal turbines already installed, such as Sabella demonstrator at Ouessant Island, or Guinard energy turbine in the Etel river, the sector still has a large development potential. One limitation of such a development is the lack of available data to assess the total potential. Previous studies mainly focused on the most energetic sites, such as the Alderney Race or the Fromveur Passage, while other sites are neglected. Yet, those sites, such has rivers or estuaries, offer softer conditions, lowering the risks. Moreover, although identifying a suitable area for tidal array implementation requires technical criteria (maximum current velocity, water depth, installable potential, etc.), it should also consider other aspects such as ecological indicators (migratory fishes, specific habitats, etc.), regulation specificities (Natura 2000, ZNIEFF, etc.) or human activities conflicts (fishery, UXO, etc.). On top of that, socioeconomic indicators, such as potential local content or partnerships with relevant academic stakeholders, are encouraged by authorities, and must be accounted for.
 Hence, this study proposes an extensive multi-criteria analysis methodology, to assess tidal energy potential of ten sites in France, including five nearshore locations (Alderney race, Fromveur passage, Raz-de-Sein, Raz-Barfleur, Paimpol-Bréhat), and five estuaries, river or similar (Gironde estuary, Gulf of Morbihan, Adour river, Etel river, Arcachon Bay). The analysis is limited to ten sites, selected based on a pre-screening analysis, which will be detailed in the study.
 The different criteria used will be presented, including their weight to the final score which reflect their importance during project development, and the 3-level grading system used to discriminate sites. The methodology developed to assess full-time equivalent employments created by a tidal array, using world input-output tables and other economic parameters will also be detailed. A specific focus will be proposed on methodology used to assess the installable capacity, relying on data from MARS 2D model for nearshore sites and public data for the others.
 First analysis shows that Raz-de-Sein and Paimpol-Bréhat are the two most suitable sites for tidal arrays implementation, while the Alderney Race is the most energetic one. Those results are driven by high scores obtained by these sites in categories such as ecological or human activities. Direct, indirect, and induced employments created during construction and operational phase by each project are also calculated, as well as potential growth value added. Hypothesis and sensitivity to them will be discussed.
 This research was funded by the H2020 projet ELEMENT, grant number 815180.

Development of a Tool to Optimise Tidal Stream Energy Sites

Several prospective tidal energy sites have been identified around the UK, however, little is known about the specific, and often complicated, hydrodynamics in many of these area [1]. Many sites comprise complicated seabed and coastline configurations, which can not only give rise to fast-flowing currents, but also results in highly turbulent and spatially-varying currents. These latter features are undesirable characteristics for devices.
 Tidal stream energy developers seldom design devices to suit a particular site, rather devices are designed and suitable sites located subsequently. This reduces the number of viable sites as each device has its own design constraints, e.g. minimum water depth, minimum velocity, etc. In order to maximise the exploitability of these sites, where space is generally limited, it would be more beneficial for developers to design devices once site conditions/constraints are better understood.
 An open-source tool is being developed that determines the physical constraints of a site based primarily on bathymetry and current velocities (measured and/or modelled). This tool aims to optimise a site to help developers understand what conditions need to be met in order to maximise energy generation – it will also identify which areas are unsuitable depending on the device design. The flexibility of the tool ensures two key aspects:
 
 For existing devices, the device design parameters can be selected to show which areas are viable that meet these parameters (e.g. maximum bed slope, maximum current velocity, etc.);
 For devices yet to be designed, different design parameters can be selected to optimise a site to help maximise the energy that can be extracted from a particular site.
 
 
 The tool is being written in Python with a QGIS front end to allow the user to make changes readily and choose which parameters are important. Not only will the tool identify suitable sites based on user-defined parameters, it will also calculate how much power is available (in kW/m2) based on velocity data.
 Given the data availability and interest from tidal energy developers in Ramsey Sound (Figure 1) and to the west of Ramsey Island in West Wales, UK, this site has been chosen as a case study. This site also experiences significant spatial and temporal variation in flow, caused in part by a narrowing of the Sound, which accelerates flow [2]. Once this tool has been proven it will be expanded to assess the viability of other tidal energy sites, both in the UK and overseas. Sensitivity testing is currently underway to determine how sensitive the tool is to data resolution. For example, do higher resolution bathymetry and velocity datasets provide a marked difference in the areas that are viable. 
 This tool will demonstrate that developers (and other relevant parties in the supply chain) cannot rely on first-order appraisals, which may make energetic tidal straits attractive sites for development since their resource potential depends on flow conditions that are fundamentally local.

Numerical Modeling of Nearshore Wave Transformation and Breaking Processes in the Yellow River Delta with FUNWAVE-TVD Wave Model

The presence of wave coherence, which contributes to the inhomogeneity of wave characteristics and significantly affects wave processes over nearshore regions of the Yellow River Delta (YRD), was simulated and analyzed in this study. A phase-resolving Boussinesq-type wave model, FUNWAVE-TVD, was used to simulate waves with desirable coherency effects. Bathymetry and topography data were obtained from the Chinese nautical chart and E.U. Copernicus Marine Service Information. After the model configuration, spatial distributions of the root mean square and significant wave heights, and the maximum cross-shore current velocity and vorticity over the domain with respect to different degrees of wave coherence and energy spectrum discretization were investigated. The results indicate that the complexity of the spatial distribution and magnitude of longshore variations in wave statistics are proportional to the degree of coherence. Waves with higher coherency exhibit more complex variabilities and stronger fluctuations along the longshore direction. The influence of morphological changes on wave height in the YRD was discernible by comparing the results with and without coherency effects. The cross-shore current velocity decreased as the waves moved toward the surf zone, while the vorticity accelerated, indicating a higher shear wave magnitude. The simulated wave dissipates more than 60% (80%) of its energy when it reaches water depths of less than 5 m (2 m) and completely dissipates when it breaks at the shore.

Seasonal hydrodynamic pattern and effect of marine sediment distribution in Banten Bay

This study aimed to see the pattern of current velocity and direction at the time of high tide, high tide, low tide, and lowest low tide during the west and east monsoons as well as to see an increase in sedimentation. Oceanographic and environmental baseline data used in this study consisted of bathymetry, tides, winds, waves, ocean currents, and sediment. The model used was DHI MIKE 21 Flow Model FM. Based on the calculation of determining the type of tide using the Formzahl formulation 1.54, the tides in the study area were classified as single dominant mixed tides. In the west season, the maximum current velocity was 0.112 m/s with the dominant current direction coming from the northeast to the southwest and approaching the coast. In the east season, the maximum current velocity was 0.112 m/s with the dominant current direction coming from the northeast to the southwest and approaching the coast. The highest concentration of suspended sediment in December was when the seawater conditions were nearing low tide. The highest concentration of suspended sediment was in the eastern part of Pier 3 at 1120 g/m3. The most significant change in bed level in December was at Pier 3 on the east side where the elevation increase was +0.30 m and the elevation decrease was -0.40 m. From the information regarding the location of the abrasion and sedimentation of the jetty development, it is possible to know in advance the anticipation of the dredging plan and the mitigation of coastal abrasion.

New approaches for assessing site formation of submerged lithic scatters

This study investigates the hydrodynamic processes that affect site formation of a submerged lithic scatter located at Cape Bruguieres Channel (CBC) in the NW of Western Australia through a combination of in situ, experimental and modelling approaches. A pressure sensor and current meter were deployed on the site and recorded hydrodynamic data over a three month period with maximum current speeds of 0.55 m/s recorded during spring tides. To test the potential for artefacts to be transported away from their original depositional context, a representative selection of submerged archaeological artefacts collected from the site and natural stone were subjected to a range of current speeds within a controlled flume environment. This demonstrated that all artefacts and natural stone remained stable within the flume even when experiencing current speeds approaching the maximum current velocities recorded at the site, regardless of lithic orientation relative to the current direction. In addition it was seen that mass alone did not control the hydrodynamic stability of the lithics tested, rather the hydrodynamic properties of a lithic are highly dependent on both its shape and orientation relative to current flow direction. This is a significant finding and suggests that the smaller the mass of a lithic does not necessarily correspond with preferential transport by currents caused by tides or waves. To test the potential for lithics to be transported during extreme cyclone events, a fine 30 m resolution bathymetric grid was constructed for CBC and current speeds modelled for Tropical Cyclone (TC) Damien which crossed the archipelago as a Category 3 (severe tropical cyclone) in February 2020. Modelled currents during this event reached a maximum velocity of 0.8 m/s and would be capable of transporting the smallest mass lithic but only if it was orientated in its most hydrodynamically unstable position relative to the current direction. These results suggest the Cape Bruguieres lithic scatter site has effectively remained in situ following sea level inundation at approximately 7,000 years BP.

Dramatic loss of seagrass Zostera marina L. suitable habitat under projected climate change in coastal areas of the Bohai Sea and Shandong peninsula, China

Seagrass is an important foundational species in marine ecosystems that plays an important role in providing ecosystem services. However, seagrass distribution and suitable habitat have rapidly declined in recent decades because of climate change and human-mediated disturbances. To achieved better conservation and management of the seagrass Zostera marina, an important representative seagrass in northern China, studies must investigate how this species responds to climate change. Here, we used an ensemble species distribution model to forecast the potential distribution and future suitable habitat change for the eelgrass Z. marina in coastal areas of the Bohai Sea and Shandong Peninsula, China. Two future climate scenarios, RCP 4.5 and RCP 8.5, were considered, which represent stable and high levels of greenhouse gas emissions, respectively. The ensemble model accurately predicted the current Z. marina distribution and performed better than the single-algorithm methods of random forest, generalized boosting model and maximum entropy according to performance matrices (AUC and TSS). The distance to land (78.50 ± 3.51%) and the maximum sea surface temperature (11.90 ± 0.25%) were the most important variables determining the distribution of Z. marina, while the contributions of other variables, maximum sea surface current velocity (3.80 ± 0.33%), minimum surface salinity (2.15 ± 0.22%) and water depth (1.74 ± 0.24%) were relatively low. Under future climate scenarios, the suitable habitat of Z. marina was predicted to decrease by more than half by the 2050s, whereas under the pessimistic greenhouse gas emission scenario (RCP 8.5), suitable Z. marina habitat was predicted to decrease by nearly 80% by the end of this century. The loss of Z. marina seagrass beds will have important ecological effects on the marine ecosystem. Our results not only provide valuable information to assist in identifying potential Z. marina meadows, but also have important implications for guiding conservation and management of Z. marina in the northern coastal region of China.

Ongoing Development of the Bass Strait GNSS/INS Buoy System for Altimetry Validation in Preparation for SWOT

GNSS equipped buoys remain an important tool in altimetry validation. Progressive advances in altimetry missions require associated development in such validation tools. In this paper, we enhanced an existing buoy approach and gained further understanding of the buoy dynamics based on in situ observations. First, we implemented the capability to separate the ambiguity fixing strategy for different constellations in the processing software TRACK. A comparison between GPS and GNSS solutions suggested up to 3 cm reduction in the root mean square of the buoy minus co-located mooring SSH residuals over the selected sidereal periods. Then, comparison between double differencing and precise point positioning solutions suggested a possible common mode error external to GNSS processing. To assess buoy performance in different ocean conditions and sea states, GNSS and INS observations were used during periods where external forcings (waves, current and wind) were not interacting substantially. For the deployments investigated, no significant relationship was found, noting the maximum significant wave height and current velocity was ~2.3 m and ~0.3 m/s, respectively. In the lead up to the validation required for the SWOT mission, these results place important bounds on the performance of the buoy design under real operating conditions.

Performance enhancement of low speed current savonius tidal turbines through adding semi-cylindrical deflectors

Qeshm channel between the Persian Gulf and Oman Sea with a maximum tidal current velocity of about 2 m/s is unsuitable for installing conventional tidal turbines. This study aims to introduce a new turbine with semi-cylinder deflectors, which is added to a Savonius tidal turbine to make feasible power extraction from this low-speed tidal current. For this purpose, Computational Fluid Dynamics analysis is done on the Savonius turbine with 2,3, and 4 blades in two cases (with and without deflectors). The results show an increase in power coefficient (CP) to 0.38 at an optimum TSR of 0.68 for two-blade Savonius Rotor by implementing semi-cylinder deflectors. In comparison, the maximum CP is 0.14 for a two-blade Savonius rotor without deflectors. Power coefficient decreases by increasing the number of blades in rotors with obstacles. CP has an upward trend by increasing the speed of water flow in the absence of deflectors. However, CP has an upward trend till 1.5 m/s current speed and after that has a downward trend in rotors with deflectors. As a general result, the Savonius turbine with semi-cylinder deflectors is very consistent with the conditions of the Qeshm channel, in which the tidal current speed is always fewer than 2 m/s.

Interspecific differences in the flow regimes and drag of North Pacific skate egg cases.

Skates are a diverse group of dorso-ventrally compressed cartilaginous fishes found primarily in high-latitude seas. These slow-growing oviparous fishes deposit their fertilized eggs into cases, which then rest on the seafloor. Developing skates remain in their cases for 1-4 years after they are deposited, meaning the abiotic characteristics of the deposition sites, such as current and substrate type, must interact with the capsule in a way to promote long residency. Egg cases are morphologically variable and can be identified to species. Both the gross morphology and the microstructures of the egg case interact with substrate to determine how well a case stays in place on a current-swept seafloor. Our study investigated the egg case hydrodynamics of eight North Pacific skate species to understand how their morphology affects their ability to stay in place. We used a flume to measure maximum current velocity, or "break-away velocity," each egg case could withstand before being swept off the substrate and a tilt table to measure the coefficient of static friction between each case and the substrate. We also used the programming software R to calculate theoretical drag on the egg cases of each species. For all flume trials, we found the morphology of egg cases and their orientation to flow to be significantly correlated with break-away velocity. In certain species, the morphology of the egg case was correlated with flow rate required to dislodge a case from the substrate in addition to the drag experienced in both the theoretical and flume experiments. These results effectively measure how well the egg cases of different species remain stationary in a similar habitat. Parsing out attachment biases and discrepancies in flow regimes of egg cases allows us to identify where we are likely to find other elusive species nursery sites. These results will aid predictive models for locating new nursery habitats and protective policies for avoiding the destruction of these nursery sites.

Seasonal variability of ocean circulation near the Dotson Ice Shelf, Antarctica

Recent rapid thinning of West Antarctic ice shelves are believed to be caused by intrusions of warm deep water that induce basal melting and seaward meltwater export. This study uses data from three bottom-mounted mooring arrays to show seasonal variability and local forcing for the currents moving into and out of the Dotson ice shelf cavity. A southward flow of warm, salty water had maximum current velocities along the eastern channel slope, while northward outflows of freshened ice shelf meltwater spread at intermediate depth above the western slope. The inflow correlated with the local ocean surface stress curl. At the western slope, meltwater outflows followed the warm influx along the eastern slope with a ~2–3 month delay. Ocean circulation near Dotson Ice Shelf, affected by sea ice distribution and wind, appears to significantly control the inflow of warm water and subsequent ice shelf melting on seasonal time-scales.

A Study on Current Characteristics Based on Design and Performance Test of Current Generator of KRISO's Deep Ocean Engineering Basin

To build an environment facility of a large-scale ocean basin, various detailed reviews are required, but it is difficult to find data that introduces the related research or construction processes on the environment facility. The current generator facility for offshore structure safety evaluation tests should be implemented by rotating the water of the basin. However, when the water in the large basin rotates, relatively large flow irregularities may occur and the uniformity may not be adequate. In this paper, design and review were conducted to satisfy the performance goals of the DOEB through computational numerical analysis on the shape of the waterway and the flow straightening devices to form the current in the large tank. Based on this, the head loss, which decreases the flow rate when the large tank water rotates through the water channel, was estimated and used as the pump capacity (impeller) design data. The impeller of the DOEB current generator was designed through computational numerical analysis (CFD) based on the lift surface theory from the axial-type impeller shape for satisfying the head loss of the waterway and maximum current velocity. In order to confirm the performance of the designed impeller system, the flow rate and flow velocity performance were checked through factory test operation. And, after installing DOEB, the current flow rate and velocity performance were reviewed compare with the original design target values.</br>Finally, by measuring the current velocity of the test area in DOEB formed through the current generator, the spatial current distribution characteristics in the test area were analyzed. Through the analysis of the current distribution characteristics of the DOEB test area, it was confirmed that the realization of the maximum current velocity and the average flow velocity distribution, the main performance goals in the waterway design process, were satisfied.

Numerical models of hydrodynamics and marine debris in the Malacca Strait

The Malacca Strait is a very strategic world trade route and the potential for environmental pollution is also very large, especially pollution from ship and people activities. This study aims to perform numerical simulations to determine the movement of marine debris particles around the waters of Rupat Island, Malacca Strait. The modelling was carried out from June to December 2020 using a modelling application with the basic principles of mesh discretization and the Lagrangian method. The results showed maximum current velocity during the simulation around the distribution area of debris is a maximum of 0.92 m/s. Marine debris around the waters of Rupat Island, the Malacca Strait has the potential to be stranded on the mainland of Rupat Island, mainland Riau, Bengkalis Island and also mainland Malaysia.

An observational study of hydrodynamic impact on water mass transport due to tidal power generation

The world's largest Sihwa Tidal Power Plant (TPP), located on the west coast of Korea, was built in 2011 for the purpose of improving water quality and producing renewable energy. After several years of actual operation, most of the original purpose was achieved, but unexpected coastal environmental changes such as tidal flat damage and sediment accumulation also occurred. In this study, in order to understand the causes of these environmental changes, field observations were conducted near TPP, and spatial and temporal variability of flow structure and water exchange process were investigated. Three-dimensional velocity data were collected along the closed line surrounding the outside of the TPP for 11 h during spring tide and analyzed according to two discharge phases: power generation phase (PGP) and drainage phase (DP). The results show that the depth-averaged maximum current velocity was more than three times greater at DP than at PGP. Jet-like flow during DP caused very high horizontal shear, whereas vertical shear was relatively weak, indicating that the horizontal and vertical flow structures were very different. The most notable result is that the mass transport patterns between PGP and DP are significantly different, i.e., during PGP, mass transport is dominated on the left side of the TPP, whereas during DP, it occurs at the front of the TPP. This means that there is a strong spatiotemporal asymmetry between the inflow from the downstream (outside of the TPP) during PGP and the outflow from the upstream (inside of the TPP) during DP. These asymmetric processes can have a significant impact on the material exchange and sediment transport near the TPP. Since observational studies on TPP are extremely rare, this study is expected to contribute to future TPP related research, such as numerical modeling.

Surface currents modeling based on tidal cycles and monsoon in tropical estuary, Indonesia

The modeling uses a software-based numerical model DHI MIKE user interface developed by The Danish Hydraulic Institute (DHI) Water and Environment, Denmark. Simulation of current uses a 2-dimensional model (averaging to depth) with a finite element approach. Modeling of currents was conducted to know current dynamics by tidal cycle and seasonal variation (west and east monsoon). The models were validated using correlation coefficient value (r) by comparing direct measurement and model output. The r-value for current velocity during west monsoon was 0.653 and east monsoon was 0.697 and for current direct during west monsoon was 0.887 and the east monsoon was 0.857. While the r-value for the tide was 0.858. All these r values showed a strong correlation and these indicated the models were valid. The result of the simulation of the current models showed that the surface currents were strongly influenced by the tidal cycles. The currents direct flowed to the south at flood tide and to the eastern at ebb tide. The maximum current velocity during the west monsoon was 0.50 m/sec and during the east monsoon was 0.40 m/sec. The averages of currents direct were more dominant eastward of Jeneberang estuary.