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

Zeyad Ayoob Sulaiman, Mena Ahmed Al Sawaf, Ahmed Shareef Hayder et al.

Many fluvial systems have undergone significant changes in their morphology due to base level fall since the last glaciation. Channels in such transient fluvial systems continuously adjust their morphology and may still be incising until reaching a new equilibrium condition. This study examines morphometric change detection indices and techniques to quantify and analyze the recent variations in the channel properties of the lower portions of the Le Sueur and Maple Rivers, in response to upstream knickpoint migration. The results reveal that channel reaches upstream of the knickzones remain relatively stable, exhibiting low channel bed gradients and minimal morphological change. In contrast, the local channel gradient increases about ∼3 fold near the knickpoints and continues with predominantly high rates into the downstream direction. Together, the morphometric indices indicate that the channel geometry of the Maple and Le Sueur Rivers downstream of the knickpoints is actively adjusting to accommodate the rapid base level drop. Because of incomplete adjustment processes, both rivers experienced remarkable change in channel geometry between 2008 and 2015, albeit with differing adjustment patterns. In particular, the percentage change in channel properties along the knickzone reaches up to 120% for the channel cross-sectional area, 60% for the channel width, and 75% for the mean hydraulic depth. These changes are accompanied by a sharp increase in cross-sectional stream power and impose boundary shear stress along the knickzones which amplify sediment transport capacity and drive further modifications to channel size and shape. This study provides a quantitative framework for assessing geomorphic responses to base level drop and provides insights into the feedback mechanisms between hydraulic forces and channel morphology. The findings have broader implications for understanding channel evolution under non-equilibrium conditions and for guiding river management in similar fluvial systems.

Amir H. Azimi

A new semianalytical model for the prediction of local scour profiles downstream from typical grade-control structures is proposed on the basis of the variation in bed shear stress and the sediment bed curvature concept. The proposed method was applied to a continuous boundary between the flow and sediment regions to predict the scour profile downstream of submerged sharp-crested weirs. By applying the momentum equation, the nappe flow over the weir was modeled as an oblique point force on the bed surface boundary, and the eroded profile was represented by a system of differential equations. The scour length and sediment resistance strength are the two unknowns in the shear stress and sediment bed curvature (SSC) differential equations. A series of laboratory experiments were carried out under clear water conditions to evaluate the accuracy and performance of the proposed model. The scour profile was calculated via prediction equations that are based on the known maximum scour depth, dmax, which was proposed in this study and in the literature. The effects of the submergence ratio and flow intensity on the maximum scour depth and scour profile were investigated, and a model was developed to predict the equilibrium scour depth. The prediction error associated with equations based on the equilibrium scour depth, dmax, resulted in a significant error in scour length prediction. Furthermore, the deviation between the measured and predicted geometrical characteristics was also correlated with predictions of dmax and scour length, L, as functions of flow intensity and submergence.

Lu Zhang, Muhammad Haseeb, Zainab Tahir et al.

The current research aimed to evaluate the severity and distribution of soil erosion in a Swat district, Pakistan, which is vital for sustainable land management and conservation efforts. This study focused on key parameters affecting soil erosion: the length factor (L), slope factor (S), crop management factor (C), rainfall erosivity factor (R), soil erodibility factor (K), and support practice factor (P). Various parameters were quantified via RS data from Sentinel-2 imagery and processed with geographical information system (GIS) tools. The values of these parameters ranged from 0.00% to 38.86%, 0 to 1, 547 to 773 MJ·mm·ha−1·year−1, 0.24–0.33 MJ·mm·ha−1·year−1 and 0.10–1.00, respectively. On the basis of these estimates, the total annual potential soil loss was approximately 173,816 t·ha−1·year−1 with extreme erosion rates exceeding 10,000 t·ha−1·year−1 in specific locations. The study categorized the soil erosion risk into five classes, ranging from very low to extreme, enabling the identification of areas requiring immediate attention and intervention. The findings of this study provide valuable insight for land management and conservation planning while also contributing to the United Nations’ Sustainable Development Goal 2 (Zero Hunger) by identifying areas where soil erosion poses a significant threat to food security. The current study underscores the importance of addressing soil erosion to promote sustainable land use and conservation strategies, ensuring long-term agricultural productivity and environmental health.

Marc Bouzas Sabater, Josep Burch i Rius, Pere Castanyer Masoliver et al.

The River Ter is one of the axes which, in a west-east direction, has historically articulated the population of the extreme north-east of the Iberian Peninsula. Although its upper, middle and part of the lower courses do not present any problems in its course, its mouth in the Mediterrane-an Sea has raised many questions due to the existence of two potential branches, one to the north that would flow into the Gulf of Roses and another to the south that would flow into the Bay of Pals. In 2016, an exhaustive documentary study on the potential southern branch provided exhaustive information on the existence of lake areas and their relationship with the settlement between the 9th and 11th centuries, but raised doubts about the existence of the river in the bay from Pals. Subsequently, between 2020 and 2022, geological studies have been carried out in this area which demonstrate the existence of the river in this area but with a variable course, with changes in the river channel (meandering, diffuse and braided), and with notable changes that conditioned the settlement of this sector of the coast and as was recorded in written documentation between the 9th and 11th centuries.

Omar A. Alharbi, Abdoul Jelil Niang

The coastline is a constantly evolving boundary between land and sea, shaped by natural forces and human activities. Given its significant ecological and economic value, this zone faces increasing pressures, highlighting the need for continuous monitoring and improved understanding to support sustainable management. This study analyses the spatial and temporal changes along the Al Qunfudhah coastline from 1984 to 2020. Using a combination of multi-temporal Landsat satellite images and geographic information system tools—specifically the digital shoreline analysis system—the research tracks changes over time. Shoreline positions were accurately extracted using automated methods, particularly the Canny edge detection algorithm. Over the 36-year period, analysis using the linear regression rate (LRR) and end point rate (EPR) methods revealed a general pattern of slight shoreline advancement. The highest rates of accretion were recorded at 12.43 m/year (LRR) and 13.36 m/year (EPR), with average rates of 3.63 m/year and 4.17 m/year, especially in the northern region where a corniche road was developed along the coast. Conversely, the most significant erosion occurred near the boat port, with maximum rates reaching −24.4 m/year (LRR) and −20.9 m/year (EPR) and average rates of −1.23 m/year and −1.08 m/year. These results offer valuable insights into the factors driving coastal changes and provide a scientific foundation for making informed, sustainable decisions about the future of the Al Qunfudhah coastline.

Holly Muecke, Scott Smithers, Stephanie Duce et al.

Tropical cyclones (TC) can produce waves and water levels that markedly reshape sand cay shorelines. TC Jasper (December 2023) passed near Low Island (Low Isles, Northern Great Barrier Reef [GBF]) as a category 2 storm. Using a combination of remote sensing and ground surveys, we compare detailed, high-resolution digital terrain models created before and after TC Jasper to quantify sediment redistribution around the cay during and after the event. During TC Jasper, net transport of 8,870 m3 occurred to elongate the spits at the eastern and western ends of the cay, but the sediment volume of the cay did not significantly change. Following TC Jasper, the shoreline at Low Island returned to its modal seasonal state within six months. This accords with historical accounts of seasonal shifts in shoreline configuration driven by prevailing wind and wave regimes, as well as the relatively rapid readjustment to a modal form following episodic extreme events. Overall, the documented changes to Low Island following cyclonic events highlight the complex interplay between episodic disturbances and longer-term geomorphic stability, emphasising the importance of ongoing research into these interactions as higher-intensity cyclones increase in frequency due to climate change.

Louis Zadi, Anthony Soive, Philippe Turcry et al.

The aim of this work was to investigate the evolutionary mechanisms of an artificial sedimentary agglomerate formed by cathodic polarization in natural seawater during its abandonment to a natural environment. Previous studies indicate that the mineralogical evolution of the material is controlled by kinetic factors and/or the local precipitation of aragonite on the brucite surface. However, the observation of the precipitation of metastable phase precipitation during the initial immersion of this material (in powder form) has suggested the possibility of a more complex mechanism. The present study builds upon previous experimental work and includes thermogravimetric analysis and infrared spectrometry. The results are analyzed using numerical experimentation to evaluate the proposed hypotheses. Findings show that the transformation mechanism is characterized by the precipitation of metastable calcium carbonate phases. Under supersaturation conditions, these hydrated phases form on the brucite surface, limiting the mineral’s contact with the solution. The subsequent transformation of these amorphous phases into aragonite further reduces brucite–solution interaction, which explains the persistence of brucite both in the residual powder after 120 h of immersion and in the consolidated material after more than 20 years of exposure to natural seawater.

Nikolas Gomes Silveira de Souza, Jader Lugon, Alexandre Macedo Fernandes et al.

This study addresses the challenge of identifying pollutant sources in aquatic coastal environments using inverse problem techniques hampered by particularities in hydrodynamic and Lagrangian models. An approach is presented employing the General Inverse Problem Platform (GRIPP) coupled with a General Simulated Annealing (GenSA) algorithm for robust backtracking. This methodology was applied to a hypothetical case study in Guanabara Bay, Brazil, using the MOHID Water platform for hydrodynamic and Lagrangian simulations. GRIPP significantly improved emission identification and pathway representativeness compared to traditional backtracking methods by exploring multiple potential particle origins and optimizing seeding parameters. The optimization yielded a solution with a mean error of 0.019 degrees between predicted and observed tracer locations. This demonstrates the potential of GRIPP and GenSA for solving practical environmental problems in coastal regions. The use of GRIPP can bypass eventual numerical errors in cases of long-term pollution source identification when compared to traditional methods. This approach contributes with blended models for the identification of potential sources of Lagrangian tracer emissions, as well as a potential solution to determine the pathways of pollutants.

Junzheng Liu, Jinliang Zhang, Zhe Huang et al.

The prediction of the flow resistance (usually quantified as the hydraulic roughness) of a movable flatbed is a key issue affecting the calculation accuracy of flood levels in river training projects. Bedload motion on a movable flatbed causes additional energy loss and increases hydraulic roughness. Several theoretical and empirical predictors for characterizing this phenomenon have been proposed, but the accuracy and physical basis of these models should be improved. In this study, the total energy dissipation rate is separated into two components: the energy dissipation rate due to grain drag and the additional energy dissipation rate due to bedload motion. Following the energy dissipation rate balance equation, a new predictor was proposed for movable flatbed flows. The water temperature was empirically coupled with the fluid viscosity and its associated physical variables. A new empirical relation between two dimensionless flow‒sediment combination variables was established to demarcate the various bedform transitions induced by the water temperature. The new predictor was compared with other predictors, and the prediction results were compared to the measured data. The error metric showed that the new predictor provided the highest accuracy, with ∼88.5% of the 826 data points falling within the ±30% error band. The new predictor suggested that the additional drag is nonlinearly proportional to the grain drag, and the scale factor between these two parameters is related to five flow‒sediment variables. In addition, the ability of the new predictor to quantify water temperature effects was examined. The predicted resistance exhibited three change modes with increasing water temperature, and the results suitably agreed with the measurements. The effect of the water temperature on the resistance of a movable flatbed is jointly controlled by the suspension number and roughness Reynolds number. This study provides an effective predictor that can be used by decision makers for modeling the hydraulic roughness of a movable flatbed.

Guang Yin, Sindre Østhus Gundersen, Muk Chen Ong

Pipelines and power cables are critical infrastructures in coastal areas for transporting energy resources from offshore renewable installations to onshore grids. It is important to investigate the hydrodynamic forces on pipelines and cables and their surrounding flow fields, which are highly related to their on-bottom stability. The time-varying hydrodynamic forces coefficients and unsteady surrounding flows of a near-seabed pipeline subjected to a wave-induced oscillatory boundary layer flow are studied through numerical simulations. The Keulegan–Carpenter numbers of the oscillatory flow are up to 400, which are defined based on the maximum undisturbed near-bed orbital velocity, the pipeline diameter and the period of the oscillatory flow. The investigated Reynolds number is set to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>1</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>4</mn></mrow></msup></mrow></semantics></math></inline-formula>, defined based on <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>U</mi></mrow><mrow><mi>w</mi></mrow></msub></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>D</mi></mrow></semantics></math></inline-formula>. The influences of different seabed roughness ratios <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>/</mo><mi>D</mi></mrow></semantics></math></inline-formula> (where <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi></mrow></msub></mrow></semantics></math></inline-formula> is the Nikuradse equivalent sand roughness) up to 0.1 on the hydrodynamic forces and the flow fields are considered. Both a wall-mounted pipeline with no gap ratio to the bottom wall and a pipeline with different gap ratios to the wall are investigated. The correlations between the hydrodynamic forces and the surrounding flow patterns at different time steps during one wave cylinder are analyzed by using the force partitioning method and are discussed in detail. It is found that there are influences of the increasing <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>/</mo><mi>D</mi></mrow></semantics></math></inline-formula> on the force coefficients at large <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi mathvariant="normal">K</mi><mi mathvariant="normal">C</mi><mo>,</mo></mrow></semantics></math></inline-formula> while for the small <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi mathvariant="normal">K</mi><mi mathvariant="normal">C</mi></mrow></semantics></math></inline-formula>, the inertial effect from the oscillatory flow dominates the force coefficients with small influences from different <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>/</mo><mi>D</mi></mrow></semantics></math></inline-formula>. The FPM analysis shows that the elongated shear layers from the top of the cylinder contribute to the peak values of the drag force coefficients.

Ishfaq Hussain Malik, James D. Ford, Ian Winters et al.

The Arctic is at the forefront of climate change, undergoing some of the most rapid environmental transformations globally. Here, we examine the impacts of climate change on the livelihoods in the coastal Inuit community of Hopedale, Nunatsiavut, Canada. The study examines recently evolved adaptation strategies employed by Inuit and the challenges to these adaptations. We document changing sea ice patterns, changing weather patterns and the impact of invasive species on food resources and the environment. Utilising knowledge co-production and drawing upon Indigenous knowledge, we monitor the changes and multiple stresses through direct observations, engagement with rights holders and community experiences to characterise climate risks and associated changes affecting livelihoods. We use both decolonising research and participatory methodologies to develop collaboration and partnership, ensuring that monitoring reflects local priorities and realities while also fostering trust and collaboration. We showcase that monitoring environmental trends involves more than data collection; it includes observing and analysing how environmental changes affect community well-being, particularly in terms of food security, cultural practices, economic activities, mental health, sea ice changes and weather patterns. The paper contributes to a nuanced understanding of Inuit resilience and experiences in confronting climate risks and the broader implications for Indigenous communities confronting climate challenges.

Andrea Lombardo, Giuliana Marletta

For almost all the Sicilian islands, there are no faunistic data concerning marine Heterobranchia, which is one of the most sought-after groups of marine critters by photographers and diving enthusiasts all over the world. With the present study, carried out through underwater photography at various dive sites and stretches of coastline in the island of Marettimo, we made the first contribution to the knowledge of the marine Heterobranchia fauna present on this island of the Egadi archipelago. Through data collection, it was possible to document the presence of 43 species of marine Heterobranchia. Data analysis showed a remarkable homogeneity in the number of species between the examined sites. This is probably due to the peculiar environmental homogeneity present in the sites of this island, which are almost all rich in the presence of both benthic suspension feeders (the favorite prey of many groups of marine Heterobranchia) and environments full of crevices, grottos, and vertical walls, which are the preferred habitats of the majority of these mollusks. The higher number of marine heterobranch species found in Marettimo compared to the smaller number of species found on the other recently examined Sicilian islands (Pantelleria, Lipari, and Vulcano) is probably due to the massive presence of rich coralligenous biocoenoses and the particular hydrodynamic regime to which Marettimo is subject.

Chris T. Perry, Ines D. Lange, Marleen Stuhr

Ama Wakwella, Amelia Wenger, Aaron Jenkins et al.

David S. Schoeman, Jessica A. Bolin, Sarah R. Cooley

Few coastal ecosystems remain untouched by direct human activities, and none are unimpacted by anthropogenic climate change. These drivers interact with and exacerbate each other in complex ways, yielding a mosaic of ecological consequences that range from adaptive responses, such as geographic range shifts and changes in phenology, to severe impacts, such as mass mortalities, ecological regime shifts and loss of biodiversity. Identifying the role of climate change in these phenomena requires corroborating evidence from multiple lines of evidence, including laboratory experiments, field observations, numerical models and palaeorecords. Yet few studies can confidently quantify the magnitude of the effect attributable solely to climate change, because climate change seldom acts alone in coastal ecosystems. Projections of future risk are further complicated by scenario uncertainty – that is, our lack of knowledge about the degree to which humanity will mitigate greenhouse-gas emissions, or will make changes to the other ways we impact coastal ecosystems. Irrespective, ocean warming would be impossible to reverse before the end of the century, and sea levels are likely to continue to rise for centuries and remain elevated for millennia. Therefore, future risks to coastal ecosystems from climate change are projected to mirror the impacts already observed, with severity escalating with cumulative emissions. Promising avenues for progress beyond such qualitative assessments include collaborative modelling initiatives, such as model intercomparison projects, and the use of a broader range of knowledge systems. But we can reduce risks to coastal ecosystems by rapidly reducing emissions of greenhouse gases, by restoring damaged habitats, by regulating non-climate stressors using climate-smart conservation actions, and by implementing inclusive coastal-zone management approaches, especially those involving nature-based solutions.

Mehrnaz Farzingohar, Zabihollah Khakpour, Mohammad Ahmadizadeh Shaghooei et al.

Bandar Abbas fish quays activities impacted on chemical compounds of the coasts. Three stations as Posht e Shahr (Ps), Sayadan (Sa) and Shilat (Sh) were selected to investigate the oil spill pollution and heavy metal concentrations in the regions. The sediment samples were collected in June and November 2017 then extracted. The highest concentrations were Fe>Zn> Pb>Cu>Cd respectively in the Sh quay. The cluster results indicated that Ni and Zn have the same sources but Pb, Cu and Cd were from different sources. Ni and Zn entered the environment due to the activities of ship repairs and coastal construction. Pb, Cu and Cd sources were from oil spills of fishing boats. The ERLQ and ERMQ toxicity rates of Ni at Ps and Sa were at the occasional but the Sh was at the frequent occurrence level. In November, the Cd toxicity at Sh was at occasional level. The new rules needed to control the pollution of quays operation.

Mohammad Mohammad Beigi Kasvaei, Mohammad Hossein Kazeminezhad, Abbas Yeganeh-Bakhtiary

A three-dimensional numerical simulation of regular waves passing over a monopile with square and circular cross-sectional shape was carried out to investigate flow field and vortex induced vibration. The rectangular wave flume and monopile are modeled with a solver; available in the open-source CFD toolkit OpenFOAM®. This solver applies the Reynolds-Averaged Navier-Stokes (RANS) equations with the volume of fluid technic (VOF) for tracking free surface. The motion equation together with mesh deformation was applied to capture monopile displacement. To validate the numerical model, results were compared to experimental data, and an admissible agreement was seen. Computations were conducted for four cases with two different wave characteristics and different Keulegan-Carpenter (KC) numbers for square and circular cross-sectional shape. Vorticity field and Q criterion around the square and circular pile were depicted. It was seen that when KC increased, the difference in vortices around the square and the circular pile was more distinct. Investigations continued on transverse force coefficient and its oscillations. It was seen that by increasing KC, this coefficient and its frequency increased. When KC=20, the lift coefficient is larger for square pile compared to the circular pile. For both square and circular cross-sectional shape, the number of pile oscillation increased by increasing KC number. Also, the Strouhal number and vortex shedding frequency were larger for the circular pile compared to that of the square pile in vortex shedding regime. However, cross-flow vibration frequencies of the square and circular pile were close together.

milad zabihi, said mazaheri, masoud montazeri namin

Supplying world future energy is tied with renewable energies and wave energy is one of the biggest resources of renewable energy which is somehow untapped. Oscillating Water Column (OWC), one of the most familiar devices in harnessing wave energy, is still not being properly commercialized due to the complicated hydrodynamic behavior. Offshore OWCs are exposed to higher wave energy; however, the researches on this kind of OWCs is limited. Hence, in this paper, a fully nonlinear two phase flow model of a fixed offshore OWC is developed using Ansys Fluent. Unlike the previous studies, the developed numerical model has the merit of being validated against a relatively large scale physical model (1:15). The results of the model are compared by those obtained in experimental campaign conducted by the authors. Results of both free surface elevation and air pressure in the OWC chamber are compared. Generally, the results showed an admissible accordance between numerical and experimental model. Some discrepancies could be detected in the free surface elevation in the chamber especially for short wave period. This can be attributed to the increase of nonlinear effects in the chamber by increase of wave steepness. The developed model can be applied for further researches on OWCs such as optimization or improving OWC performance.

Mahmood Reza Akbarpour Jannat, Ehasn Rastgoftar, Toshyuki Asano

In this study two numerical models, one a regional generation and propagation model and the other an inundation model, have been applied to the problem of examining the impact that a large, locally generated tsunami could have on Chabahar Bay facilities in Iran. To achieve a realistic outlook of tsunami hazards in the area, the generation, propagation and interaction of tsunami waves with Chabahar Bay coasts is being numerically modeled for specific events. The modeling is performed using the numerical code which solves the nonlinear Boussinesq wave equations. Results of numerical simulations performed in this study considering past tsunami occurrence records indicate that the multipurpose Chabahar Port is expected to experience the tsunami events with heights ranging between 8 to 10 meters. The model gives approximately the observed maximum area of flooding of Chabahar City. The large amount of flooding of Chabahar city coasts, Iran from the 9.1 magnitude earthquake and small amount of flooding from the 8.3 magnitude earthquake achieved and extensively flooding Chabahar City was reproduced by the numerical model. The effect of the tide was modeled and found to be small. The results of this study are intended for emergency planning purposes. Appropriate use would include the identification of evacuation zones. The results are used also to find a best configuration advice for the urban facilities in order to mitigate tsunami related risks, with positioning such facilities at the Western Cape of the bay.

Mahdi shabani, Abdolrahim taheri

Free-span in subsea pipelines occur at manmade supports, uneven seabed or pipeline crossing. Free spanning may induce pipeline vibration due to vortex shedding which makes pipeline susceptible to some failures such as fatigue, fracture, etc. Free spanning analysis is an important subject because fatigue is the most effective factor in reducing the pipeline design life. Free spanning analysis includes static analysis and dynamic analysis. DNV-RP-F105 suggests a methodology of dynamic analysis for long pipeline with multi-mode responses, but the fatigue analysis method for multi-modes is not detailed. In addition, the fatigue analysis of multi-spanning pipeline is not clear. Based on the methodology of DNV-RP-F105 fatigue life relates to natural frequencies of pipeline, the method of determination of effective natural frequencies still is not clear. In this paper, a fatigue analysis for multi-spanning pipeline in Persian south gas field is performed based on VIV analysis. ABAQUS FE model is developed to obtain the stress distribution and the natural frequency of each vibration mode for spanning pipeline on seabed with three multi-spans, then the fatigue analysis of VIV is carried out for the spanning pipeline based on DNV-RP-F105.