Hasil untuk "Harbors and coast protective works. Coastal engineering. Lighthouses"

Wenbin Wu, Chunliu Wang, Zheng Zhao et al.

Sediments had emerged as a significant repository of MPs (microplastics) and biomass accumulation in eutrophic lakes, yet the mechanisms by which these particles impact sediment stability remained elusive. This study aimed to investigate the effect of MPs on the structural stability of sediments during the accumulation of biomass, as these properties could affect the formation of fluid sediment and trigger resuspension. A coaxial cylindrical rheometer was used to explore changes in the rheological properties of sediments under the influence of MPs. Within 30-day experiments, it was found that MPs could decrease sediment viscosity, yield stress, and flow point shear stress (τtau) by up to 61.2 %, 57.9 % and 54.3 %. In the early stage of the experiment, MP addition led to a significant decrease on sediment rheological properties, but then this effect decreased gradually. Subsequently, the variations in EPS (extracellular polymeric substances), organic matter, and microbial communities influenced by MPs were suggested to relate with the change in sediment rheology properties. These findings suggested that MPs could facilitate the degradation of biomass and decrease sediment rheological properties by altering sediment microbial activities. On this basis, the decline in sediment stability would increase the risk of sediment re-suspension under wind and wave disturbance. Overall, this study sheds light on the environmental challenges posed by MPs under biomass accumulation, offering a fresh perspective that deepens our comprehension of the environmental behavior of MPs in sediment ecosystems.

Ariadna Martín, Robert Jane, Alejandra R. Enriquez et al.

Temporal storm surge clustering refers to a series of events affecting the same region within a short period of time, which can strongly influence coastal flooding impacts and erosion. Here, we analyze global storm surge clustering from tide gauges and a state-of-the-art global model hindcast to identify geographical hotspots of extreme storm surge clusters and assess event frequencies. We study the spatial distribution as well as the contribution of different event intensities to clustering. On average, globally, 92% of coastal locations show significant temporal clustering for 1-year return period events, and 25% for 5-year return level events, although notable spatial differences exist. Our results reveal two distinct clustering regimes: (i) short timescale clustering, where events occur in rapid succession (intra-annual), and (ii) long timescales (inter-annual), providing varying recovery times between events. We also test the validity of assuming a Poisson distribution, commonly used in storm surge frequency analyses. Our results show that >80% of the stations analyzed do not follow a Poisson distribution, at least when including events that are not the most extreme but exceeded, for example, the 1-year return level. These findings offer insights into temporal clustering dynamics of storm surges and their implications for coastal hazard assessments.

Vilmar Leandro Dias Ferreira, Elizabeth Santos Pereira, Lucas Pluvie Souza de Mello et al.

It is estimated that around 10% of the world’s population lives in low-lying coastal areas, with an altitude of up to 10 m: considered vulnerable to unequivocal sea level rise, as result of climate change. This study sought to assess the coastal environmental vulnerabilities of the municipality of Niterói, Rio de Janeiro, Brazil, in these lowlands, through of an analysis matrix, considering sea level rise projections for 2100. The matrix was applied to nine areas along the coast and consisted of assigning values from 1 to 4 (4 being the most critical scenario) to four variables: two to natural indicators and two to socio-economic indicators. The index for each area was obtained from the simple average of the values assigned. In general, the areas facing Guanabara Bay were more sensitive in socio-economic terms, due to population densification and lower per capita income. The areas facing the Atlantic Ocean were more vulnerable in natural terms, due to exposure to waves and the presence of the natural systems protected on land located below the 10-m. These issues highlight the importance of using vulnerability analysis tools, which can enable public authorities to plan and organize the actions in each specific situation.

Mayara de Oliveira Bandeira, Caroline Fiório Grilo, Kyssyanne Samihra Santos Oliveira et al.

The erodibility of natural cohesive sediments and artificial mixtures was investigated through controlled laboratory experiments and used as a basis to discuss seabed mobility and suspended particulate matter on the Continental Shelf adjacent to a river mouth. Changes in the erodibility of cohesive seabeds can influence resuspension and erosion rates and impact suspended particulate matter dispersion patterns and even the benthic community. For the experiments, sediment samples with sand content ranging from 0% to 90% were tested using an erosion testing chamber to evaluate the relationships among sand content, settling, consolidation, critical shear stress, and erosion rate. Critical shear stress values ranged from 0.31 to 0.42 N/m², and erosion rates varied up to 30 times between the most mud-rich and sand-rich samples. Natural samples exhibited lower erodibility, evidenced by higher critical shear stress and lower erosion rates compared to Industrial Clay, highlighting the role of organic matter in enhancing sediment stability. Additionally, although the sand addition reduced the critical shear stress required for sediment motion, it resulted in lower erosion rates. Results were also compared with sediment samples collected from the Continental Shelf adjacent to the Doce River mouth, a region impacted by a large-scale mining tailings spill in 2015. Although the frequency of sediment mobilization did not differ significantly between pre- and post-disaster conditions, mud-rich sediments exhibited greater erosion potential once the threshold was surpassed. This suggests that the dam failure impacted the sediment dynamics of the Continental Shelf adjacent to the Doce River mouth. These findings can be used to improve sediment transport models and environmental management strategies in disturbed coastal systems.

Abu Reza Md Towfiqul Islam, Abu Hena Md Fazla Rabbi, Amit Hasan Anik et al.

In the context of transboundary rivers, which constitute intricate fluvial ecosystems, the persistent threat of heavy metals (HMs) contamination poses significant risks to ecosystem health. In this study, ecotoxicological hazards, governing factors, and the distribution of nine HMs (uranium (U), lead (Pb), cadmium (Cd), nickel (Ni), chromium (Cr), manganese (Mn), iron (Fe), zinc (Zn), and copper (Cu)), as well as sediment characteristics (sand, silt, clay, organic matter, and pH) are assessed within the sediment. The current investigation encompasses the analysis of twenty-seven sediment samples, utilizing inductively coupled plasma mass spectrometry, in the transboundary river basin of Bangladesh, specifically the Teesta River. Notably, the findings underscore the predominance of Cd as a contaminant, responsible for 51.85%, 81.84%, and 100% of the geo-accumulation index, contamination factor, and enrichment factor, respectively. The Teesta River emerges as moderately to highly polluted, with cumulative probabilities of 7.4%, 85.2%, and 7.4% denoting “medium”, “high”, and “priority” pollution levels, respectively. Regions in the upstream and downstream middle sections of the study area exhibit relatively higher pollution levels, particularly in proximity to Kaunia Upazila in the Rangpur district. Ecologically, the potential risk index indicates a low likelihood of ecological impacts at 77.8%, alongside a moderate risk observation of 22.2%. The current results attribute the distribution of these HMs to the pH and organic matter content within the sediment, serving as pivotal factors. To unravel the origins of the HMs, the positive matrix factorization (PMF) model successfully identifies four contributing factors, primarily from geogenic sources. Validation of the PMF model through Spearmen correlation and principal component analysis (PCA) reveals a consistent pattern, affirming its efficacy in this analysis. Within the region, HM sources are identified as originating from anthropogenic activities such as irrigation, industrial discharges, and domestic effluent, in addition to substantial inputs from geogenic sources. Recognizing the transboundary nature of metal pollution, the current study underscores the imperative for continuous and vigilant monitoring, coupled with the implementation of robust management practices. The interplay of both anthropogenic and geogenic factors necessitates a comprehensive approach to effectively and sustainably combat HM contamination.

Trevor R. Tubbs, Robert Marlin Smith, Adam B. Catasus et al.

Microbial communities play a crucial role in coastal ecosystem function, yet their seasonal and spatial dynamics in response to environmental change remain underexplored in tropical and subtropical regions. This yearlong study investigated microbial composition in water, sinking particles, and sediments along an inshore–offshore gradient influenced by the Caloosahatchee River Estuary in southwest Florida. The region has been altered by rapid coastal development and was struck by Hurricane Ian in September 2022. Environmental parameters exhibited significant spatiotemporal variation, shaping microbial beta diversity in all habitats. Sediment communities showed the greatest hurricane-induced disruption but returned to pre-disturbance conditions within six months. Dominant microbial classes included Alphaproteobacteria, Bacteroidia, and Gammaproteobacteria. Biogeochemical cycling taxa displayed strong habitat specificity, such as Desulfobulbia which dominated sinking particles, Desulfobacteria which was abundant in sediments, and Nitrosomonadaceae and Nitrosopumilaceae which were key nitrifiers in water and sediments, respectively. Particle–sediment taxonomic overlap suggests resuspension processes. Several inshore microbial indicators were consistently present across microbial habitats, especially at estuarine sites, suggesting the estuary as a microbial diversity reservoir for the coastal zone. These results highlight the value of long-term microbial monitoring to understand ecosystem change and resilience in dynamic coastal environments.

Thi-Kim-Anh Do, Nicolas Huybrechts, Isabel Jálon-Rojas et al.

Simulating sediment dynamics in a large and energetic estuary system remains challenging, primarily due to the spatial and temporal complexities of the interaction between flow and sediment transport, especially for sand-mud mixtures. This study uses a three-dimensional (3D) numerical model, based on the open TELEMAC system, to investigate the dynamics of suspended sediment concentration (SSC) in the Gironde Estuary, a complex estuarine environment characterized by an estuarine turbidity maximum (ETM) and significant variations in river discharge. The main contributions of this study include addressing the challenges of coupling bed friction with sediment transport of the sand-mud mixture for feedback on bed roughness and bottom depth changes and the ability of the model to capture the migration of ETM from high to low flow. Additionally, the current study analyzes the ability of the model to capture the migration of ETM from high to low flow, and it utilizes a calibration strategy that minimizes parameters by using in situ data and encompassing hydro–morpho-sedimentary interactions. A sensitivity analysis was done using different settling velocity approaches and sediment classes to establish an optimal model configuration and the uncertainty associated with the reduced model parameterization is discussed. The model satisfactorily reproduces the hydrodynamic features, particularly when the hydro-sedimentary feedbacks are taken into account, the seasonal trend of SSC, spring-neap variations, and the development of a well-defined ETM. The selection of a specific formulation for the settling velocity influences the location and magnitude of ETM. The van Leussen formula not only predicts a broad movement of ETM from high to low river flow, but also predicts high turbidity for extended periods during low river flow. Conversely, two empirical formulas from Le Hir and Defontaine predicted the highest turbidity during neap tides but sediment losses during prolonged simulations. The results of this study contribute to a deeper understanding of sediment dynamics in the Gironde Estuary, providing valuable information for future estuarine modeling and management.

Yanan Zhu, Yibao Lou, Wenlong Wang et al.

Dump slopes have experienced severe rill erosion and threaten the safety of the ecological environment. Although vegetation restoration has improved the ecological environments of mining areas, because dump slopes have unique soil properties, the mechanism by which roots impact rill erosion on dump slopes remains unclear. Based on the in-situ runoff scouring experiment of the dump slope and the use of bare land as the control (CK), the influence of roots on rill erosion characteristics (RECs) of the dump slopes were analyzed for three root types of vegetation, specifically, tap root–Artemisia ordosica (AO), fibrous root–Elymus dahuricus (ED) and tap + fibrous root–Artemisia ordosica + Elymus dahuricus (AE). The results indicated that, compared to the CK, the roots reduced the rill erosion rate (Ts) by 75.61%–86.64% and the rill depth (Rd) by 64.62%–81.06% on the dump slopes. However, they increased the runoff depth (h) and Reynolds number (Re) by 2.02%–37.14% and 36.1%–172.0%. Among them, AO significantly increased Manning roughness coefficient (n), Darcy–Weisbach friction factor (f) and shear stress (τ), whereas ED and AE were most effective in reducing h and Ts, respectively. 59.9% of the RECs of dump slopes were explained by roots and hydraulic characteristics together. Furthermore, PLS-SEM analysis revealed that roots affect hydraulic characteristics by changing surface roughness and runoff friction resistance, ultimately leading to differences in the RECs of dump slopes, which explained 98.5% of the RECs on dump slopes with a 72.2% goodness-of-fit. The above results further enhance the understanding of the role of roots in controlling rill erosion on dump slopes.

Min Li, Jing Ou, Zhihe Chen

The aggregation of microplastics (MPs) with sediments in natural water plays a crucial role in the general deposition and transport of plastic particles. However, the effect of salinity changes on the settling behavior of aggregates remains unclear. In this study, the aggregation and settling processes of sediment particles with spherical MPs were investigated using a settling tube and a microphotography device, in deionized water (pH 8.0) with 10–35 practical salinity units (PSU). Two-particle and three-particle aggregates were most commonly observed in the experiments. Increasing the salinity promoted the aggregation of MPs, reaching the largest average particle size at 25 PSU, but the mean Corey shape factor values exhibited minimal variations at different salinities. Meanwhile, the settling velocity of the aggregates was directly proportional to their particle size, and thus the average settling velocity also reached a maximum at 25 PSU. Although the settling velocity can be predicted with high correlation coefficients using existing formulas developed for static conditions, dynamic flow may reduce the settling velocity of aggregates and cause overestimation. Herein, a reduction coefficient was used to revise the settling velocity formula and predict the measured values with higher accuracy. This study provides insights into the aggregation and settlement of MPs in estuarine environments with varying salinity, which affect the fate and distribution of plastic particles in natural waters.

William A. Gough, Zhihui Li

A day-to-day temperature (DTD) variability metric was used to detect marine coastal climates in the province of Ontario, Canada. Eleven of fourteen climate stations on islands, most in the Great Lakes and two in other large water bodies, displayed marine characteristics using a day-to-day temperature metric threshold developed for ocean coastal locations in China and Canada with values below 2.35 for the daily minimum temperature variability. Detailed comparisons with neighbouring coastal stations were conducted for six focal areas in the Great Lakes and the marine effect on the local climate was unambiguously demonstrated in a statistically significant manner. Those displaying marine characteristics were all island climate stations, usually at an elevation close to the lake level, and the marine influence, as measured by day-to-day temperature variability, dropped off rapidly with distance and elevation from the local water body. The DTD metric was compared to a diurnal temperature range (DTR) metric. While DTR was able to distinguish in a statistically significant manner between islands and inland stations, an unambiguous threshold between the two was not possible, unlike DTD.

Karen A. Alexander, Ingrid Kelling

Sustainability and sustainable development are the buzzwords of our era. Nowhere is this clearer than in primary production/extraction industries, such as aquaculture and fisheries. Yet in the seafood sector (as with many others), the term continues to be used most commonly in relation to the environmental dimension; much less is known about social and economic sustainability. In this review, we explore what is known about social sustainability in the seafood sector. We identify seven key thematic areas: livelihoods and human development; human rights; social, psychological, and cultural needs; equitable access to resource and benefit sharing; a voice in public issues; flow-on benefits for local and regional economies and improved infrastructure and access. We reveal that while there has been a clear focus on developing social sustainability indicators, this has largely missed more relational and subjective aspects of social sustainability. We also show that some thematic areas of social sustainability also remain underdeveloped. Overall, we argue that it is imperative that we address the knowledge gaps and incorporate what we already know about social sustainability into existing industry and governance processes. If we do not, not only risk not achieving the Sustainable Development Goals, but we also risk moving closer towards environmental and societal collapse.

Marcus Lange, David Cabana, Anna Ebeling et al.

There is a complex interaction between pollution, climate change, the environment and people. This complex interplay of actions and impacts is particularly relevant in coastal regions, where the land meets the sea. To achieve sustainable development in coastal systems, a better understanding is necessary of the role and impact of pollution and the connectedness of the elements, namely, pollution, climate and the people, as well as associated impacts unfolding in an integrated social–ecological system (SES). In this context, the enabling capacity of tools connecting scientific efforts to societal demands is much debated. This paper establishes the basis for climate-smart socially innovative tools and approaches for marine pollution science. The goal of developing a set of innovative tools is twofold: first, to build on, integrate, and further improve the well-founded strengths in diagnosis and process understanding of systemic environmental problems; and, second, to provide decision-making with usable information to create actionable knowledge for managing the impact of marine pollution on the SES under a changing climate. The paper concludes by establishing the scope for a ‘last mile’ approach incorporating scientific evidence of pollution under climate change conditions into decision-making in a SES on the coast. The paper uses case studies to demonstrate the need for collaborative tools to connect the science of coastal pollution and climate with decision-making on managing human activities in a SES.

Ehsan Sarhadizadeh, Mehrnaz Farzingohar, Niusha Mostoli

In this study, the performance and efficiency of 12 ports in the Persian Gulf, Oman and Caspian seas in Iran is evaluated using data envelopment analysis (DEA) method. DEA allows comparing the efficiency in revenue generation of ports with different economies. Two different modeling approaches were presented in this study; based on relating earnings to port operational capability and activity, and based on land indicators, infrastructure, and equipment. The results of this study showed that most of the ports in the Persian Gulf region had a relative efficiency in the field of petroleum products. On the other hand, a significant difference was observed between the nominal capacity of acceptance of petroleum products of ports and the volume of oil product exchanges.

Jalal Mofidi, Akbar Rashidi Ebrahim Hesari

A three-dimensional primitive equation model has been developed to study wind-driven currents in the Caspian Sea (CS). The equations were solved in the spherical coordinate system with a vertical array of pressure-sigma using a finite difference Method on a staggered modified Arakawa c grid. Simulations showed that there is an anticyclonic eddy over the deep water of South Caspian Basin (SCB), which extended from surface to subsurface and persist throughout the year. The model successfully produced the coastal current along the eastern coast of the Middle Caspian Basin (MCB) with a prevailing southward component, resulting in upwelling on these coasts to compensate the surface drift. The results indicate that the bottom topography has a key role in steering currents and generated a divergence in the surface Ekman layer which balanced by convergence in the frictional bottom Ekman layer in deepest areas of the CS.

Alireza Sadat Hosseini, Mehdi Shafieefar, Omid Alizadeh

Berm breakwaters are used as protective structures against the wave attack where larger quarry materials as armor stone is scarce, or large quarry materials are available but using berm breakwater lowers the costs considerably. In addition, wave overtopping in berm breakwaters are significantly lower than the traditional ones for equal crest level because of the wave energy dissipation on the berm.The most important design parameter of berm breakwaters is its seaward berm recession which has to be well estimated. In this paper a method has been developed to estimate the front slope recession of berm breakwaters using artificial neural networks with high accuracy. Four different available data-sets from four experimental tests are used to cover wide range of sea states and structural parameters. The network is trained and validated against this database of 1039 data. Comparisons is made between the ANN model and recent empirical formulae to show the preference of new ANN model.

Saeed Imani Bidgoli, Shahab Shahriari, Pedram Edalat

Structural response of different types of conventional deep water riser affected by mooring systems in harsh environment is focused in this study. With increasing water depth, the mooring system design of a floating-type production platform becomes more important and complicated from cost as well as safe operation point of view. With the development of offshore oil and gas exploitation, FPSO with many advantages can better adapt to the complicated environment of deep sea. According to the current mooring system development, this study compares the effect of spread mooring system and turret mooring system on riser structural response. Both systems consists of 12 mooring lines and each line is made from two components. Three types of more conventionally used deep water risers have been selected and applied with the mooring systems, resulting in 6 different case studies. The case studies have been modeled in OrcaFlex software with same extreme environmental conditions. Comparing bending moment in the risers, as one of the main design parameter, shows the effect of proper selection of the riser and mooring system.

Seyed Masoud Mahmoudof, Fatemeh Hajivalie

In this study, a simple and efficient approach based on nonlinear wave interaction fundamentals is theoretically proposed to generate surface profile of the cnoidal waves. The approach includes Newton-Raphson algorithm to calculate the Ursell parameter and using a simple formulation. The wave profile resulted by means of introduced approach is determined as a superposing of limited number of cosine harmonics without encountering difficulties of using elliptic or hyperbolic functions, or any complex and complicated differential equations. It is demonstrated that a cnoidal wave profile is a result of high order self nonlinear interaction of primary frequency. Some definite energy is transmitted to higher harmonics due to nonlinear interactions. The amount of transmitted energy is controlled by Ursell parameter. The desirable accuracy determines the number of included harmonics in the proposed formulation and relative error of approach can be predicted based on Fourier and least square analysis techniques. The outputs of the proposed method are verified with cnoidal resulted from elliptic functions and the high efficiency of new approximation is revealed for engineering applications. The calculation of wave parameters such as energy flux, volume flux and radiation stress for cnoidal wave can be approximated using the proposed method. Using this approach, a physical interpretation of the Bm parameter (introduced in the first order of cnoidal wave theory) is presented. The calculation of several parameters such as velocity vectors and dynamic pressure duo to cnoidal waves is very simple by means of proposed approach.

Mojgan Ghazi Mirsaeid, Mehdi Mohammad Mehdizadeh, mohammad reza Bannazadeh

The tropical Indian Ocean forms the major part of the largest warm pool on Earth, and its interaction with the atmosphere plays an important role in shaping climate on both regional and global scales. Three dimensional temperature and velocity fields are calculated analytically for an ocean forced by wind stress and surface heat flux. A basic thermal state involving a balance of lateral and vertical heat diffusion is assumed.  The wind stress is chosen such that a tropical mass transport gyre is generated. An effect of nonlinear heat advection is calculated by a perturbation method. This circulation is closed through thin up and downwelling layers at the sides. Superimposed there is a barotropic wind driven circulation, with a transport field of the type described by Munk. The interior temperature field to the next order is affected not only by interior heat advection but by heat advection in the Ekman layer, in the up and downwelling layers and in the main western boundary current. We have compared Sepherical and Cartesian computational results.

Sirous Yasseri, Hamid Bahai

The oil and gas pipelines are significant assets in Iran. However, these assets are subject to degradation from corrosion.  Corrosion causes gradual thinning of the pipelines’ wall leading to leaks or bursts. Allowing a corroding pipeline to continue operation may lead to a finite risk of exceeding the limit state of burst. Codes of practice, such as Modified ASME B31G [1] and DNV F101 [3], among others, have developed relationships to determine the bursting pressure of corroded pipelines.  The purpose of this paper is to develop, test, and illustrate a simple spreadsheet-based probabilistic procedure that can be used by practicing engineers to determine the Remaining Useful Life (RUL) of a corroding pipeline, following its first inspection.  Modified ASME B31G and DNV F101 equations are used to illustrate this method. As new inspection data regarding the extent of corrosion becomes available, the results can be updated and a new probability of failure obtained. The calculated probability of failure is then compared with the target values to determine the remaining life. The approach is equally applicable to both onshore and offshore oil and gas pipelines.

Milad Zabihi, Said Mazaheri, Ahmad Rezaee Mazyak

Developing numerical tanks to study wave structure interaction drew engineers’ attention in last decade. Numerical wave tanks are absolutely essential for investigating wave-structure interaction. This paper presents two different numerical software capabilities to generate regular gravity waves in a wave tank. The wave generation was performed using the FLUENT package and Flow-3D. Both models are based on Navier-Stokes and VoF equations. The results of the mentioned models were compared with theoretical results. Free surface elevation and horizontal component of wave particle velocity were the two parameters which have been considered for comparison. Results indicate that Flow-3D in some cases is a bit more accurate than Fluent in capturing free surface elevation. In numerical models it is important to dissipate wave energy and prevent wave reflection. In this way four different slopes were evaluated to determine the minimum slope needed for wave energy dissipation. The results showed that a minimum slope of 1V:35H is needed to avoid wave reflection. The variation of streamlines and velocity potential are also studied. The pattern of horizontal and vertical velocity variation in the fluid domain is similar to stream function and potential velocity function variation, respectively.