Extreme Hydrodynamic Conditions Research Articles

Large-Scale Test Of Extreme Hydrodynamic Conditions Over Coastal Salt Marshes

Hard coastal structures such as dikes covered with asphalt or placed block revetments have been widely used in the past for coastal protection in densely populated deltas around the world. Nonetheless, in recent years the effectiveness of hard structures has been questioned in light of the inevitable effects of climate change and their static nature. Decades of research on how salt marshes can play a role within a comprehensive coastal protection scheme suggest that these low environmental impact structures (Maza et al., 2015) might have the capability of dissipating wave energy and hence be technically and formally considered within hybrid coastal erosion and flood protection systems (Borsje et al., 2011). However, only very few studies investigated wave attenuation by real salt marsh vegetation in large-scale laboratories (Ghodoosipour et al., 2022; Maza et al., 2015; Möller et al., 2014) and none of them addressed extreme hydrodynamic design conditions in terms of wave energy and water levels. As a result of this knowledge gap, salt marshes in The Netherlands and all around the world have never been formally considered within the coastal flood protection systems and the underlying risk assessment. With this contribution our aim is to provide an overview of the first worldwide large-scale test focused on the interaction between a salt marsh (i.e. vegetation and shallow foreshore) and extreme hydrodynamic conditions, the adopted measurement techniques and the preliminary results in terms of wave damping, erosion and removed biomass.

Species-specific and seasonal differences in the resistance of salt-marsh vegetation to wave impact

The coastal protection function provided by the vegetation of tidal wetlands (e.g. salt marshes) will play an important role in defending coastlines against storm surges in the future and depend on how these systems respond to such forcing. Extreme wave events may induce vegetation failure and thereby risking loss of functionality in coastal protection. However, crucial knowledge on how hydrodynamic forces affect salt-marsh vegetation and whether plant properties might influence plant resistance is missing. In a true-to-scale flume experiment, we exposed two salt-marsh species to extreme hydrodynamic conditions and quantified wave-induced changes in plant frontal area, which was used to estimate plant damage. Moreover, half of the plants were artificially weakened to induce senescence, thus allowing us to examine potential seasonal effects on plant resistance. Morphological, biomechanical as well as biochemical plant properties were assessed to better explain potential differences in wave-induced plant damage. Our results indicate that the plants were more robust than expected, with pioneer species Spartina anglica showing a higher resistance than the high-marsh species Elymus athericus. Furthermore, wave-induced plant damage mostly occurred in the upper part of the vegetation canopy and thus higher canopies (i.e. Elymus athericus) were more vulnerable to damage. Besides a taller canopy, Elymus athericus had weaker stems than Spartina anglica, suggesting that biomechanical properties (flexural stiffness) also played a role in defining plant resistance. Under the highest wave conditions, we also found seasonal differences in the vulnerability to plant damage but only for Elymus athericus. Although we found higher concentrations of a strengthening compound (biogenic silica) in the plant material of the weakened plants, the flexibility of the plant material was not affected indicating that the treatment might not has been applied long enough. Nevertheless, this study yields important implications since we demonstrate a high robustness of the salt-marsh vegetation as well as species-specific and seasonal differences in the vulnerability to plant damage.

Influence of Tsunami-Driven Shipping Containers’ Layout on Their Motion

This study investigated the interaction between containers under extreme hydrodynamic conditions modeled on tsunamis to assess whether the number and layout of containers affect their motion and to guide future studies on numerical simulations describing tsunami-debris motion. The three-dimensional Fluid–Structure–Sediment–Seabed Interaction Model (FS3M), which can compute tsunami–container interaction, was used as a numerical test model, and numerical results for the specific target of the simulation were compared with experimental data to check the validity and computational accuracy of the FS3M. The study showed that the number of rows (Nx), columns (Ny), and stacks (Nz) in the initial arrangement of containers constitute the main factor affecting the area where the containers spread and their drift motion velocity. An increase in Nx and Nz can effectively reduce the container drift velocity. Conversely, as Ny increases, the drift motion velocity of the center of gravity of the entire group increases. The results of this study can facilitate the development of more realistic building structure scenarios in future research that consider the proposed characteristic damage estimation and comprehensive assessment methods laid out herein.

Microplastic contamination of sediments across and within three beaches in western Lake Superior

Microplastic pollution of the environment is ubiquitous, but the processes by which microplastics accumulate within beach sediments are not yet well understood. We isolate microplastic pollution from the sediments at three western Lake Superior beaches. Samples of both surface and subsurface sediments are considered. We find that the average microplastic contamination is 65 microplastic particles kg−1 sediment across our sites with significant variability across beaches, but the microplastic composition is always dominated by polyester fibers. The variation across beaches does not seem to relate to the distance from suspected sources of microplastics to the lake. Within each beach, we find no significant variation of the mean microplastic concentration in the cross-shore direction or in the surface vs. subsurface sediments at the wrack line. We interpret this mean microplastic concentration in the sediment as a measure of the bulk microplastic concentration in the nearshore water at each beach. In subsurface sediments, we observe a significant difference in the variance of microplastic concentrations, and we attribute this variation to the intermittency of the extreme hydrodynamic conditions that deposit microplastics deeper into the sediment.

Hydrodynamic drivers of fine‐scale connectivity within a coral reef atoll

AbstractAn accurate representation of physical and biological processes is crucial to resolve larval dispersal pathways and characterize connectivity of coral reef ecosystems. We investigate how hydrodynamic forcings drive larval retention rates during the bi‐annual mass coral spawning of the coral genus Acropora within a coral reef atoll (Mermaid Reef), located off northwestern Australia. By analyzing hydrodynamic conditions during 41 yr of historical spring and autumn coral spawning events, we identify typical and extreme hydrodynamic forcing conditions. Particle tracking using the output from a fine‐scale coupled wave‐flow hydrodynamic model forced with typical hydrodynamic conditions during coral spawning, revealed a mean transport of larvae eastward across the atoll. Transport was mainly driven by a combination of wave and tidal currents, where the residual tidal flow and unidirectional wave flow increased the net export of particles, and the oscillatory tidal (non‐residual) flow reduced the net export of particles from the reef. Importantly, however, numerical simulations forced with extreme hydrodynamic conditions generated by episodic tropical cyclones (11 out of 41 yr) showed large deviations from the typical eastward flow during autumn spawning, generating different connectivity pathways within the reef. Considering the substantial time larvae can be retained within reef systems, overlooking fine‐scale hydrodynamic processes may greatly overestimate larval transport distances between adjacent coral reef atolls. As a result, we emphasize the need to consider fine‐scale hydrodynamic processes within regional connectivity predictions, which is generally not considered yet critical to understand the capacity of reefs to recover following disturbances.

Interconnections between Coastal Sediments, Hydrodynamics, and Ecosystem Profiles on the Mexican Caribbean Coast

The interconnections between hydrodynamics, coastal sediments, and ecosystem distribution were analysed for a ~250 km strip on the northern Mexican Caribbean coast. Ecosystems were related to the prevailing and extreme hydrodynamic conditions of two contrasting coastal environments in the study area: Cancun and Puerto Morelos. The results show that the northern Mexican Caribbean coast has fine and medium sands, with grain sizes decreasing generally, from north of Cancun towards the south of the region. Artificial beach nourishments in Cancun have affected the grain size distribution there. On beaches with no reef protection, larger grain sizes (D50 > 0.46 mm) are noted. These beaches are subject to a wide range of wave-induced currents (0.01–0.20 m/s) and have steeper coastal profiles, where sediments, macroalgae and dune-mangrove systems predominate. The coastline with the greatest amount of built infrastructure coincides with beaches unprotected by seagrass beds and coral reefs. Where islands or coral reefs offer protection through less intense hydrodynamic conditions, the beaches have flatter profiles, the dry beach is narrow, current velocities are low (~0.01–0.05 m/s) and sediments are finer (D50 < 0.36 mm). The results offer a science-based description of the interactions between physical processes and the role played by land uses for other tropical coastal ecosystems.

Impact of Management Regime and Regime Change on Gravel Barrier Response to a Major Storm Surge

Gravel barriers represent physiographic, hydrographic, sedimentary, and ecological boundaries between inshore and open marine offshore environments, where they provide numerous important functions. The morphosedimentary features of gravel barriers (e.g., steep, energy reflective form) have led to their characterization as effective coastal defense features during extreme hydrodynamic conditions. Consequently, gravel barriers have often been intensively managed to enhance coastal defense functions. The Blakeney Point Barrier System (BPBS), U.K., is one such example, which offers the opportunity to investigate the impact of alternative management regimes under extreme hydrodynamic conditions. The BPBS was actively re-profiled along its eastern section from the 1950s to the winter of 2005, whilst undergoing no active intervention along its western section. Combining an analysis of remotely sensed elevation datasets with numerical storm surge modeling, this paper finds that interventionist management introduces systemic differences in barrier morphological characteristics. Overly steepened barrier sections experience greater wave run-up extents during storm surge conditions, leading to more extreme morphological changes and landward barrier retreat. Furthermore, while high, steep barriers can be highly effective at preventing landward flooding, in cases where overwashing does occur, the resultant landward overtopping volume is typically higher than would be the case for a relatively lower crested barrier with a lower angled seaward slope. There is a growing preference within coastal risk management for less interventionist management regimes, incorporating natural processes. However, restoring natural processes does not immediately or inevitably result in a reduction in coastal risk. This paper contributes practical insights regarding the time taken for a previously managed barrier to relax to a more natural state, intermediary morphological states, and associated landward water flows during extreme events, all of which should be considered if gravel barriers are to be usefully integrated into broader risk management strategies.

Coastal Flooding Process: Comparing Different Coastal Typologies Response to Extreme Hydrodynamic Conditions

Freire, P.; Oliveira, F. S. B. F. and Oliveira, J. N., 2020. Coastal flooding process: Comparing different coastal typologies response to extreme hydrodynamic conditions. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 797–802. Coconut Creek (Florida), ISSN 0749-0208.To upgrade the response capability to coastal flood events, hazard predictions need to be improved through integrating the effect of the coastal morphological variability in the nearshore-foreshore-backshore hydromorphological processes induced by waves-tide-wind-atmospheric pressure. In order to evaluate the short-term morphological response of different coastal typologies to potential flood conditions (spring high tide level, storm surge, high wave height), field data acquired in 2019 in three sites in the West coast of Portugal with past flooding episodes are presented and discussed. The preliminary results point out that under the same forcing conditions the short-term response of the cross-shore beach profile that controls the flooding levels is dependent on the beach typology, namely: the nature of the lower and upper limits of the beach face, profile gradient and its alongshore context. This knowledge can be used to develop robust and validated flood prediction tools contributing to improve mitigation and adaptation management strategies.

Study on optimization technology of protective engineering for submerged tube overburden in crossing river tunnel

Under the influence of many complex factors, such as flood, tidal power, ship operation, earthquake and construction quality, the stability of the tunnel’s underwater overburden layer is crucial to the safe operation of the project. A technical line combined with measured data analysisand physical model testing were utilized to study the features of scouring and sediment for tunnel overburden under several extreme hydrodynamic conditions. In order to ensure the rationtity of anti-scouring stability and economy for tunnel engineering project, optimization design for overburden layer of tunnel was proposed after detailed experiments and analysis. The slurry block stone and stone throwing method can be used to protect the slope and the bottom of the embankment downstream of the tunnel line, which can effectively control the possiblescouring of the concave embankment foot and river bed. The technical line and research methods applied in this paper can be extended to statisfy the engineering design optimization for overburden layer of similar tunnel engineering.

Multiple Debris Impact Loads in Extreme Hydrodynamic Conditions

AbstractVideo footage from the 2004 Indian Ocean and 2011 Tohoku tsunamis showed large quantities of debris entrained within the inundating flows. Such extreme debris conditions can lead to a high ...

Electrochemical Corrosion Performance of Aromatic Functionalized Imidazole Inhibitor Under Hydrodynamic Conditions on API X65 Carbon Steel in 1 M HCl Solution

The hydrodynamic corrosion inhibitive performance of two imidazole derivatives 2-ethyl-4-methylimidazole and 1-benzylimidazole was investigated on API X65 steel in 1.0 M HCl solution. Structural features of the molecules derived from density functional theory (DFT) calculations at B3LYP/6-31G(d.p) showed that 1-benzylimidazole possess high electron density due to $$\pi $$ network which lies flat on the surface and tends to form a stronger interaction with the metal. The addition of the inhibitor molecules in 1 M HCl solution shifted the corrosion potential $$({E}_{\mathrm{corr}})$$ in the noble direction. Tafel polarization and electrochemical impedance spectroscopy (EIS) experiments performed at 0–1500 rpm and 50–500 ppm of inhibitor concentration revealed that the corrosion rate was increased with an increase in rotation speed in the absence of inhibitor molecules. However, upon the addition of the inhibitor molecules in the solution minimized the corrosion rate with an efficiency of 82% in the case of 1-benzylimidazole at 500 ppm and 500 rpm electrode rotation. It was concluded that simple imidazole molecules could serve as corrosion inhibitors under extreme hydrodynamic conditions.

Debris impact forces on flexible structures in extreme hydrodynamic conditions

Field surveys of recent major flood events have emphasized the need for an in-depth examination of debris loading. Debris loading occurs when solid objects entrained within the flow interact with a structure in its movement path, exerting loads through direct impacts or damming. Until now, the focus of research into debris impacts has concentrated on single debris impacting a rigid structure. This study extends to examining the influence of debris impacting a flexible structure. A two degree-of-freedom (2DOF) system was used to model the debris–structure interaction. The model is compared with two experimental data sets using a rigid body and the effective stiffness model. The proposed 2DOF model was shown to be more accurate in estimating the impact force than those to which it was compared to. However, due to difficulties in estimating the stiffness and inertia of the structure and the debris, the proposed model under predicted the maximum measured impact loads. The effective stiffness model was shown to represent the maximum measured impact loads, and should therefore be implemented in the design process when considering debris impacts on flexible structures.

Debris impact under extreme hydrodynamic conditions part 2: Impact force responses for non-rigid debris collisions

Historical tsunami events have resulted in extreme damage to coastal regions worldwide. Among the various loads associated with tsunami waves, debris impact has been shown to cause major damage to nearshore infrastructure. As a result, debris impact loads have been included prominently in existing design guidelines and standards, such as the FEMA P-646 [11] and ASCE7 Chapter 6 [6]. In the present study, single debris impacts on structures was experimentally investigated under tsunami-like wave conditions. Eccentric and oblique impacts of a model shipping container (length scale 1:40) on a non-rigid structure were examined. The experimental results of the non-rigid impacts are discussed in the context of the existing force equations which were derived under the assumption of rigid-body impact theory. As expected, the elasticity of the structure was determined to influence and, specifically, reduce the magnitude of the debris impact forces. Existing impact force equations are herein critically discussed through comparison with the experimental results and, finally, modifications to existing force equations to account for non-rigid collisions are proposed.

Debris impact under extreme hydrodynamic conditions part 1: Hydrodynamics and impact geometry

In field investigations of major flooding events, debris impact has been identified as a critical load and has thus been included in various building codes, such as FEMA P-646 and ASCE7. However, the evaluation of debris loading solely based on field data is challenging. Therefore, to address the uncertainties related to debris loading, an experimental program investigating debris impacts on structures was performed using a dam-break wave. The debris were down-scaled 6.1 m (20 ft) shipping containers (1:40 geometric scale) which were entrained and displaced by the transient wave conditions. The study presented here examines the influence of the transient flow conditions and the flow features around the structure due to the impinging wave on the debris impact conditions. The influence of the impact geometry (obliqueness, eccentricity) on the impact force is also discussed and possible parameters to describe the impact geometry are introduced.

Probabilistic Investigation and Risk Assessment of Debris Transport in Extreme Hydrodynamic Conditions

Probabilistic Investigation and Risk Assessment of Debris Transport in Extreme Hydrodynamic Conditions

Entrainment and Transport Dynamics of Shipping Containers in Extreme Hydrodynamic Conditions

An experimental study was performed to examine multiple debris entrainment and transport in tsunami-like flow conditions. The study was performed in the Tsunami Wave Basin at Waseda University. The wave basin used a falling-head driven elongated solitary wave that broke at the edge of a horizontal apron to generate a tsunami-like surge. The debris, modeled as scaled-down (1:40 length scale) 20-foot standard shipping containers, was placed on the horizontal apron. The debris was tracked using a camera-based object tracking algorithm. The study examined the effect of the debris configuration, the number of debris, and orientation of debris on the entrainment and transport within the inundating surge. In examining the transport of multiple debris, the debris tended to be transported within the surge as an agglomeration. Using a previously derived model of debris transport, the study determined experimentally derived coefficients to explain the difference in debris transport between various configurations.

Estimation of extreme hydrodynamic environments of Puti Island wind farm in Bohai Sea

In order to manifest the extreme hydrodynamic environments for Puti Island wind farm in Bohai Sea, flow and wave climates in the area induced by cold waves are investigated. According to the historical meteorology statistics and taking the global climate change into account, three typical paths (NNE, ENE and NNW) with four high wind speeds for cold waves in Bohai Sea are presumed. After calibrated with field data, the Princeton Ocean Model (POM) and the third-generation wave model, SWAN, are employed to delineate possible extreme hydrodynamic conditions in the area of Puti Island wind farm. The dependence of the extreme current and water wave parameters to the wind speed and wind direction is investigated. The distribution of the extreme current and water wave parameters in the wind farm is discussed.

Pipelines Stability under Extreme Hydrodynamic Conditions

At the current level of technical development of subsea pipeline systems a probability of their damage during construction and operation due to various causes may not be excluded.In the regions of high seismic activity the soil destruction may occur in the weak layers forming seabed deformations. Hazard management practice has advanced in recent years, due to several factors: global pipeline expansion in areas of difficult terrain (tectonic/seismicity; permafrost area, landslides) coupled with a greater understanding of the prevalence of hazard.Formal risk assessment is relatively immature in most industries, including pipelining. A better solution is to establish guidelines of essential ingredients necessary in any pipeline risk assessment. Critical would be identified and it would be left to the operator subject matter experts to detail those elements.This article focuses on the problem of imposing special (seismic) loads; the subject matter of the article also includes the issues of the marine pipeline safety (risk) evaluation.

Network analysis indices reflect extreme hydrodynamic conditions in a shallow estuarine lake (Lake St Lucia), South Africa

Food web structure and function in ecosystems are a reflection of environmental conditions, this is especially apparent during extreme circumstances. The St Lucia estuarine-lake system in South Africa has recently experienced an unprecedented prolonged period of desiccation and hypersaline conditions caused by climatic variability and anthropogenic impacts. This has had a significant impact on species diversity, abundance and biomass. The system has received significant research attention over the past 70 years; however, little research has been conducted to understand how the system responds to changing environmental conditions as a whole. The aim of this study was to quantitatively assess the ecosystem response to different physico-chemical conditions and mouth states using ecological network analysis. The biomasses and trophic exchanges of various biotic species were estimated and used to establish ecological networks from which several ecosystem indices were calculated. Results indicate that the water level, salinity and mouth state have a significant impact on the total system biomass and productivity and the number and weight of energy flow pathways. These influence the biological structure and functioning of the St Lucia system. The substantial increase in the total living standing stock and species diversity during an intermittent open phase indicates that the system responds rapidly to such favourable conditions. This was reflected in the ecosystem indices calculated for before, during and after a breach which highlighted the importance of the short open mouth period after several years of mouth closure. Not only were biomass and productivity increased, but also the organisation of pathways to ensure more efficient energy transfer. At the same time adequate pathway redundancy was invigorated, resulting in a more robust and efficient functioning of the food web even after the re-closure of the inlet.

Studies on settling, traction and entrainment of larger benthic foraminiferal tests: implications for accumulation in shallow marine sediments

AbstractSettling and traction velocities were measured on optimally preserved tests of larger foraminifera using a settling tube and flume tank. Within larger foraminifera with porcelaneous tests, the peneroplids, Peneroplis antillarum, P. planatus, P. pertusus and Dendritina cf. D. zhengae, are distinguished by low test densities (ca 1·2) that do not change with growth. Buoyancy is high because of low Reynolds numbers and increases in large individuals because of the allometric change of test shape. The fusiform Alveolinella quoyi, with test densities ca 1·6, is characterized by high Reynolds numbers, inducing the weakest buoyancy within porcelaneous larger foraminifera. The highest buoyancy was recorded for the three soritids, Parasorites orbitolitoides, Sorites orbiculus and Amphisorus hemprichii, because of their low test densities (ca 1·25) and the extremely flat, biconcave, plate‐like shape. Flat tests, however, reduce traction and entrainment from smooth surfaces. Within hyaline larger foraminiferat, the amphisteginids show thick‐lenticular (Amphistegina lobifera, A. radiata) to thin‐lenticular tests (A. bicirculata, A. papillosa), influencing buoyancy. Here, high test densities (ca 1·8) decrease with growth in A. lobifera, A. lessonii and A. bicirculata, and remain constant in A. radiata and A. papillosa. Minimum velocities required for entrainment are lower for thick‐lenticular tests and higher for thin‐lenticular tests. Test densities remain constant with growth in the calcarinid Baculogypsina sphaerulata (ρ ∼ 1·78) and decrease slightly in Calcarina gaudichaudii and Neorotalia calcar (starting at ρ ∼ 1·85), all living under extreme hydrodynamic conditions. Density decreases the most in Baculogypsinoides spinosus (starting at ρ ∼ 1·8), resulting in higher buoyancy through low Reynolds numbers. Traction is promoted in spherical tests of Baculogypsina and Baculogypsinoides. Within nummulitids, the thick‐lenticular Palaeonummulites venosus (test density decreasing with size; starting at 1·78) is less buoyant, expressed in high Reynolds numbers, but easily entrained. Thick‐lenticular juveniles and extremely flat adults distinguish Operculinella cumingii, Heterostegina depressa and the giant Cycloclypeus carpenteri. Test densities increase during growth, starting from ca 1·6 and attaining a maximum of 1·8. Buoyancy is low in small tests and high in large tests, while entrainment velocities are reduced as the tests flatten. High buoyancy is also a characteristic of the entirely flat tests in Operculina ammonoides (from deeper regions) and Planostegina operculinoides, which is expressed in the lowest Reynolds numbers within larger foraminifera.