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

Jae-In Lee, Chang-Hee Lee, Chang-Gu Lee et al.

This study investigated the potential application of dredged sediments as a medium for cultivating landscape plants, assessing plant performance in contaminated dredged sediment (CDS) and remediated dredged sediment (RDS), using commercial horticultural soil as a control. Three ornamental plant species, Korean lawn grass (KLG), Aster arenarius Nemoto, and English poppy, were grown under distinct soil conditions both with and without the addition of organic and biochar-based amendments. Soil quality indices and responses in plant growth were measured to determine the influence of sediment remediation and amendment application. The findings demonstrated that RDS created a more suitable substrate for plant development compared to CDS, with KLG exhibiting the most pronounced growth improvement, especially when supplemented with wood-derived biochar and soil conditioner (SC). Incorporating SC into CDS markedly improved KLG biomass, with dry weight increases of 7.4 % and 136.9 % at 2 % and 5 % SC, respectively. Significant correlations (p < 0.05) were observed between soil and leaf Ni concentrations. Additionally, the study analyzed how soil properties impacted heavy metal(loid) accumulation in KLG, showing that soil pH, electrical conductivity, and cation exchange capacity exerted significant effects on Pb and Zn levels in plant tissues. Overall, these results indicate that adequately remediated and amended RDS has the potential to be utilized as a sustainable medium for landscape plant production and may play a role in environmental restoration initiatives.

Hulan Badde Gedara Dilshan Madubhashana Padminda Ekanayaka, Nimal Shantha Abeysingha, Tusita Amarasekara et al.

Soil erosion is a significant environmental threat, impacting water quality and the siltation of the productive capacity of reservoirs. To prioritize soil conservation areas for sustainable land management, quantitative spatial assessment of soil erosion is essential, particularly in the catchment of a reservoir. The current study aims to evaluate the soil erosion severity and sediment generation in the closer catchment of a proposed reservoir, the lower Malwathu Oya Reservoir in Sri Lanka. Erosion modeling has proven cost-effective in assessing the spatial distribution of soil erosion severity. This current study utilized the Integrated valuation of ecosystem services and tradeoffs sediment delivery ratio (InVEST-SDR) model to analyze the spatial distribution of soil erosion and sediment export. A digital elevation model (30 m × 30 m), 22 years of rainfall data, land use and land cover data, soil map, and cropping factors were used as model inputs. The results revealed an average annual soil loss ranging from 0 to 15.55 t/(ha·y) in the catchment and a mean annual sediment export of 0.016 t/(ha·y). Erosion severity was classified into four hazard classes, i.e., insignificant (<0.5 t/(ha·y)), weak (0.5–3 t/(ha·y)), considerable (3–12 t/(ha·y)), and severe (12 < t/(ha·y)). A critical 0.12% area was identified as a considerable soil erosion hazard area, necessitating urgent measures for erosion control. High-risk areas were at Galpottegama, Asirikgama, Puleliya, Navodagama, and Thuppitiyawa Grama Niladari. These findings provide valuable insight for formulating and implementing soil conservation practices in the catchment to reduce the siltation of the proposed lower Malwathu Oya reservoir. The study is an example of using InVEST-SDR to evaluate the sedimentation of a proposed reservoir.

Gerd Masselink, Tim Poate, Timothy Scott et al.

Low-lying atoll islands are among the world’s most vulnerable coastal environments to sea-level rise (SLR). Global application of coastal flooding models suggests that centennial flood events may become annual events by 2050 in tropical regions. This article addresses this claim by modelling an island flooding event that occurred in the Maldives on 1 July 2022 as a result of a distant-swell event coinciding with an extra high spring tide. Hydrodynamic data collected after the event on one of the affected islands were used to calibrate and validate a one-dimensional non-hydrostatic XBeach model. The model overpredicted wave setup and underpredicted the water motion at frequencies <0.05 Hz, but the wave run-up elevation was predicted reasonably well. The 1 July flood event was considered in a decadal context using modelled wave data and measured tide data. It was concluded that the 1 July event represents a c. 1:25-year flooding event, but, due to SLR, such flooding could occur every few years by 2050. This prediction ignores natural or anthropogenic adjustments to the island morphology. The expected increase in frequency of coastal flooding in the Maldives requires atoll and island authorities in the Maldives to act swiftly in adapting to future flood risk.

Eranga K. Galappaththi, Sithuni M. Jayasekara, Chrishma D. Perera et al.

Coastal systems are a major source of food for Indigenous communities. Climate change poses a high risk to coastal communities’ food security. Successful climate change adaptation practices are essential to ensure food security among Indigenous peoples. Yet, limits and constraints challenge climate change adaptation practices. Our study seeks to identify these limits and constraints in the context of food security among coastal Indigenous peoples. We performed a global scale systematic literature review using 155 scholarly articles to examine the constraints and limits to climate adaptation in the coastal food security and Indigenous peoples’ context. The three research questions are as follows: (i) What are the key constraints? (ii) What are the limits? (iii) What are the ways of overcoming the constraints? First, we found that, globally, the main constraints to adapting to climate change in coastal food security settings are related to governance, institutions and policies. Second, most limits are soft, to be solved, compared to hard limits on coastal systems. Third, we unveiled ways of overcoming the constraints, such as restoring coastal food system resilience, improving food accessibility and building the adaptive capacity of Indigenous peoples. The findings of the study provide valuable insights for policymakers, researchers and other relevant stakeholders involved in decision-making regarding coastal food security in the climate change adaptation context.

Matthew Cole Tillman, Robert Marlin Smith, Trevor R. Tubbs et al.

Tropical cyclones can severely disturb shallow, continental shelf ecosystems, affecting habitat structure, diversity, and ecosystem services. This study examines the impacts of Hurricane Ian on the Southwest Florida Shelf by assessing water quality, substrate type, and epibenthic and microbial community characteristics at eight sites (3 to 20 m in depth) before and after Ian’s passage in 2022. Hurricane Ian drastically changed substrate type and biotic cover, scouring away epibenthos and/or burying hard substrates in mud and sand, especially at mid depth (10 m) sites (92–98% loss). Following Hurricane Ian, the greatest losses were observed in fleshy macroalgae (58%), calcareous green algae (100%), seagrass (100%), sessile invertebrates (77%), and stony coral communities (71%), while soft coral (17%) and sponge communities (45%) were more resistant. After Ian, turbidity, chromophoric dissolved organic matter, and dissolved inorganic nitrogen and phosphorus increased at most sites, while total nitrogen, total phosphorus, and silica decreased. Microbial communities changed significantly post Ian, with estuary-associated taxa expanding further offshore. The results show that the shelf ecosystem is highly susceptible to disturbances from waves, deposition and erosion, and water quality changes caused by mixing and coastal discharge. More routine monitoring of this environment is necessary to understand the long-term patterns of these disturbances, their interactions, and how they influence the resilience and recovery processes of shelf ecosystems.

Elizabeth Basha, Stephanie N. Vaughn, Jacqueline C. Pavlovsky et al.

Despite being low-resource environments, sandy beaches can contain diverse bacterial assemblages. In this study we examined the spatial heterogeneity of bacterial communities in sand on a beach on the Mississippi Gulf Coast, USA. 16S ribosomal RNA gene sequencing was used to characterize bacterial communities in surface sand along 10 m transects from dry sand towards the upper beach to fully submerged sand, as well as up to 0.4 m deep into the sand. There were clear gradients in bacterial community structure based on position on the beach and depth, and community richness and diversity was greater in moist sand subject to tidal influence than drier sand. Bacterial communities in sand higher up the beach were characterized by members of the phyla Bacillota and Actinomycetota, whereas there was an increased presence of picocyanobacteria (phylum Cyanobacteriota) in sand closer to the water and greater diversity overall. Along with gradients in community structure, microbial activity also showed spatial patterns, with microbial extracellular enzyme activity being greatest in surface sand at intermediate positions along the beach transects that were subject to tidal influences but not fully submerged. This research supports the idea of beaches containing diverse bacterial communities and demonstrates that the existence of gradients in beach environments means that these communities show clear patterns in their spatial distribution.

Hong-wei Fang

Gabrielle P. Quadrado, Katherine A. Serafin

Effectively managing coastal impacts requires understanding how hydrodynamic processes interact with beach morphology and alter sandy beaches. Sallenger’s Storm Impact Regime classification provides proxies for identifying these interactions by classifying potential coastal changes into impact regimes based on the elevation of total water levels (TWLs), the combination of waves, tides and nontidal residuals, compared to the elevation of beach morphology features. Here, we evaluate spatiotemporal variations in TWL drivers during storm impact regimes across sandy beaches along the continental U.S. coastlines. TWL magnitude and composition vary across impact regimes and regions. Although impacts are identified using consistent definitions, the processes contributing to regimes are location-specific, influencing where and how often impacts occur. Wave runup is the dominant contributor to TWLs in all regimes, but its contribution is gradually offset by increases in the nontidal residual as storm impacts intensify, despite waves becoming more energetic during storms. The Pacific and Atlantic coasts show the highest susceptibility to coastal impacts due to high average TWLs relative to morphological thresholds. Our findings identify regional differences in TWLs with potential for coastal impacts, offering critical insights into how large-scale changes in individual processes may influence local coastal hazards along open sandy coastlines.

Edilson Freitas da Silva, José Tasso Felix Guimarães, Gabriel Negreiros Salomão et al.

Over the last several decades, extensive changes in land use and land cover (LULC) have caused substantial environmental impacts in the watersheds of southeastern Amazonia, such as the Verde River Watershed (VRW). The effects of anthropogenic activities on soil cover loss rates in the VRW were evaluated to estimate soil loss over time by applying the revised Universal Soil Loss Equation (RUSLE) in a geographic information system (GIS) environment via rainfall erosivity (R), soil erodibility (K), topography (LS), and LULC (CP) data. The VRW experiences strong seasonality, with the most significant R concentrated from January to April, which coincides with a relatively high rainfall index reaching approximately 42% of the annual total. Most of the VRW has gently undulating to flat relief (88.9%) and low LS values (0.02–0.025), but its upper course has a sandy soil texture with high K values (0.02–0.073). Pastureland has replaced forested areas during the past 40 years, dramatically changing the landscape with more significant changes in LULC rates in the upper VRW. Estimates of annual and average soil losses and areas at high and very high risk of erosion increased by more than 200% from 1984 to 2021. In conclusion, deforestation is the main factor influencing erosion patterns and volume in the VRW and has accelerated soil degradation, increasing the risks to human health and the maintenance of tropical rainforests. Additionally, simply stopping deforestation is insufficient to prevent the expansion of areas with high and very high erosion risk. It is crucial to implement reforestation projects to recover forested areas.

Ana Vila-Concejo, Thomas E. Fellowes, Shari Gallop et al.

There is a relative lack of research, targeted models and tools to manage beaches in estuaries and bays (BEBs). Many estuaries and bays have been highly modified and urbanised, for example port developments and coastal revetments. This paper outlines the complications and opportunities for conserving and managing BEBs in modified estuaries. To do this, we focus on eight diverse case studies from North and South America, Asia, Europe, Africa and Australia combined with the broader global literature. Our key findings are as follows: (1) BEBs are diverse and exist under a great variety of tide and wave conditions that differentiate them from open-coast beaches; (2) BEBs often lack statutory protection and many have already been sacrificed to development; (3) BEBs lack specific management tools and are often managed using tools developed for open-coast beaches; and (4) BEBs have the potential to become important in “nature-based” management solutions. We set the future research agenda for BEBs, which should include broadening research to include greater diversity of BEBs than in the past, standardising monitoring techniques, including the development of global databases using citizen science and developing specific management tools for BEBs. We must recognise BEBs as unique coastal features and develop the required fundamental knowledge and tools to effectively manage them, so they can continue providing their unique ecosystem services.

Alexandra Rodrigues Finotti, Elisa Ferreira Pacheco, Patricia Kazue Uda

Operation of source control measures (SCM) in urban drainage in tropical/transitional climates are still a challenge because of higher rain volumes and more intense rains, as well as constraints from sea-level interference. In this study, the performance of a swale to control runoff was detailed and monitored in such an environment. The data on rain, runoff, and sea levels were acquired at a site located in an island in the south coast of Brazil. The results showed that even with higher rain volumes and more intense rains, the mean capture of the swale was 51.7% of the entrance runoff volume, but it depended on seasonal rain variation and interference of sea/tide level. As a result, the swale might be undersized in summer and oversized in winter. Peak flow retardation was observed in 97% of monitored events. The interference of sea/tide level was not directly correlated with infiltration volumes, but in the principal component analysis, the parameters of sea/tide level, along with the hydrological parameters of rain duration, height, and intensity, explained 60% of the variance in the data. In conclusion, the application of SCMs in tropical regions is suitable, but seasonality should be incorporated in the design. The interference of sea/tide level must be further investigated to verify how to incorporate its influence in the design.

Sean Vitousek, Daniel Buscombe, Kilian Vos et al.

Satellite remote sensing is transforming coastal science from a “data-poor” field into a “data-rich” field. Sandy beaches are dynamic landscapes that change in response to long-term pressures, short-term pulses, and anthropogenic interventions. Until recently, the rate and breadth of beach change have outpaced our ability to monitor those changes, due to the spatiotemporal limitations of our observational capacity. Over the past several decades, only a handful of beaches worldwide have been regularly monitored with accurate yet expensive in situ surveys. The long-term coastal-change data of these few well-monitored beaches have led to in-depth understanding of many site-specific coastal processes. However, because the best-monitored beaches are not representative of all beaches, much remains unknown about the processes and fate of the other >99% of unmonitored beaches worldwide. The fleet of Earth-observing satellites has enabled multiscale monitoring of beaches, for the very first time, by providing imagery with global coverage and up to daily frequency. The long-standing and ever-expanding archive of satellite imagery will enable coastal scientists to investigate coastal change at sites vulnerable to future sea-level rise, that is, (almost) everywhere. In the past decade, our capability to observe coastal change from space has grown substantially with computing and algorithmic power. Yet, further advances are needed in automating monitoring using machine learning, deep learning, and computer vision to fully leverage this massive treasure trove of data. Extensive monitoring and investigation of the causes and effects of coastal change at the requisite spatiotemporal scales will provide coastal managers with additional, valuable information to evaluate problems and solutions, addressing the potential for widespread beach loss due to accelerated sea-level rise, development, and reduced sediment supply. Monitoring from Earth-observing satellites is currently the only means of providing seamless data with high spatiotemporal resolution at the global scale of the impending impacts of climate change on coastal systems.

Pablo Sanchez-Jerez, Nuria Casado-Coy, Jesus Souza Troncoso et al.

Ecosystem engineers are organisms that cause changes in the physical state of biotic and abiotic structures that modulate the availability of resources to other species, thus affecting biochemical cycles. Molluscs, especially bivalves such as mussels, are widespread in coastal environments and they are excellent ecosystem engineers because of the durability of their shells, which add complexity and heterogeneity to benthic environments. The presence of mussel farms favours the accumulation of shells in benthic environments and may influence surrounding bare sediments, with potential legacy effects on benthic communities. We studied the effects of the accumulation of mussel shells at finfish farms and mussel farms by experimentally comparing bare sediment and sediment with fragmented shells in terms of the abundance of the most relevant faunal groups, specifically polychaete families as well as physical–chemical variables in sediment water samples, specifically organic matter (OM), redox potential, and acid-volatile sulphides (AVS) NH₄⁺ and PO₄³⁻. The experiment was replicated under two environmental conditions over a period of 35 days: eutrophic muddy sediments and oligotrophic sandy sediments. The OM and AVS values were significantly higher in the eutrophic sediment with mussel shells. Only NH₄⁺ was positively affected by the mussel shells in the oligotrophic conditions. Differences between the two environments were observed, and the effect of the mussel shells on the polychaete assemblages was more significant in the oligotrophic conditions. Mussel shell accumulations affected the structure of benthic assemblages by modifying their heterogeneity and complexity, which suggests that the presence of mussel farms above bare sediment may affect ecosystem functioning. Aquaculture has potentially negative or positive effects that must be addressed on a large scale, considering the increased input of organic matter and also the simultaneous presence of mussel shell waste, both of which alter the surrounding environment. This is particularly important in oligotrophic sandy sediment.

Mohammad Akbarinasab, Iman Paeen Afrakoti

Wave height forecasting is very important for coastal management and offshore operations. In this paper, the accuracy and performance of three soft computing techniques [i.e., Multi-Layer Perceptron (MLP), Radial Basis Function Neural Network (RBFNN) and Adaptive Neuro Fuzzy Inference System (ANFIS)] were assessed for predicting significant wave height. Using different combinations of parameters, the prediction was done over a few or a two days’ time steps from measured buoy variables in the Caspian Sea (case study: Anzali).  The data collection period was from 03.01.2017 to 06.01.2017 with 30-minute intervals. The performance of different models was evaluated with statistical indices such as root mean squared error (RMSE), the fraction of variance unexplained (FVU), and coefficient of determination (R2). Different simulations of performance assessment showed that the ANFIS techniques with requirements of past and current values of atmospheric pressures and height waves has more accuracy than the other techniques in the specified time and location. Meanwhile, in high lead times, the friction velocity decreases the accuracy of wave height forecasting.

Behrooz Tadayon, Hamid Dehghani, Cyrus Ershadi

One of the most important issues in the area of coastal structures design is determination of forces and loadings resulted from shallow water wave breaking. In the process of wave breaking, the subsequent particle motion is transformed from irrotational to rotational motion and due to this matter, vorticity and turbulence are generated and the sediment transport is affected by this phenomenon. Therefore, it is necessary to know about the location of wave breaking and other parameters such as the breaker height, breaker depth, etc. Over the last century, several formulas have been presented for predicting the wave breaking onset. These formulas depend on many parameters (e.g. seabed slope, water depth at the location of breaking, offshore wave height, etc.) that need to be known in order to obtain the desired wave breaking parameter (e.g. breaker height). In this study, some of the formulas for predicting wave breaking onset proposed in the recent decade are evaluated using the available laboratory data and it is tried to find out which formula is more suitable in different cases and conditions. A refinement process is carried out for choosing the appropriate data points out of all the available compiled laboratory data. The comparison is carried out in two phases. In the first one, the formulas are compared using all the data and in the second one, the comparisons are made based on the breaker type. These two phases yield to different outcomes. In the first phase, the formula proposed by Delavari et al. has the lowest values of bias, relative error, scatter index and root mean square error and the coefficient of determination of Goda’s formula is the highest. In the second phase, the data are categorized based on the plunging and spilling breaker types and the comparisons are made based on this categorization. The outcomes derived from the first phase are different from the ones derived from the second one.

Milad Zabihi, Said Mazaheri, Masoud Montazeri Namin

Increasing problems due to supplying energy demand conveyed researchers to find a solution in renewable energy resources and consequently marine engineers drew attentions towards wave energy which has the merit of higher energy density than the other resources. Oscillating Water Column (OWC) is one of the most propitious devices for capturing wave energy. Researchers have studied the device under different wave height and period conditions and they investigated various geometric parameters such as front wall draft and the chamber length. However, the effects of wave spectrum type or shape has not been investigated deeply yet. Different wave spectra have been developed for different places around the world but the focus of this study is on the two well-known spectra called JONSWAP and Pierson-Moskowitz to see how the type of the spectrum can impact on inner chamber fluctuation, pressure variation and reflection response of an offshore OWC. To achieve this goal, a 1:15 scale model of an offshore OWC was constructed in National Iranian Marine Laboratory. The results show that inner chamber free surface spectrum is affected by the type of incident wave spectrum. In another word, energy content at peak frequency was approximately 50% higher when the incident wave spectrum is of JONSWAP type. However, energy corresponding to sloshing frequency and total energy content in the chamber were almost the same for both types of the spectra. Pressure spectra inside the chamber showed a similar trend as free surface elevation. Although there was a little difference in reflection response of an OWC influenced by the type of spectra, this discrepancy was more pronounced in high frequency waves.

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

Three-dimensional numerical simulation of regular waves passing over cylindrical monopile has been conducted to investigate the hydrodynamic force and vortex dynamics. To do so, the rectangular wave flume and monopile is modeled on a solver; available in the open-source CFD toolkit OpenFOAM®. The solver applied RANS equations with VOF method for tracking free surface. Model validation has been done by comparison numerical results with the experimental ones and admissible agreement has been seen. Computations have been done for four cases with different wave characteristics consequently for different Keulegan-Carpenter numbers (KC). Hydrodynamic in-line force acting upon pile was studied and the results indicated that the total in-line force increases as KC number increases. In addition, when vortex shedding develops, drag force component increases and inertia force component decreases. The vortex dynamics around the pile was investigated by means of Q criterion and vorticity field. It was seen that by increasing KC number larger than 6, vortex shedding will be happened. Moreover, variation of bed shear stress around the pile has been investigated and it was seen that the bed shear stress is influenced by KC number which is result of existence of horseshoe vortices. The bed shear stress near the pile is negative due to existing of the horseshoe vortex. It begins when KC exceeds 6 and by increasing KC up to 20, the magnitude of negative values of bed shear stress near the pile increased which implies horse shoe vortices are completely formed. This also complies the experimental results.

Younes Komachi, Said Mazaheri, Mohammadreza Tabeshpour

Many procedures suggest for reduction of responses of riser to Vortex Induced Vibrations (VIV). Natural frequencies of marine risers is an important parameter that can affect the responses of riser to VIV. Change of riser properties such as top tension and bending stiffness can alter natural frequencies. In this study effects of riser specifications on the responses and fatigue damage of marine risers were investigated analytically and numerically. For numerically analysis 2D wake-structure coupled model is used for modeling of VIV of riser in two directions of Cross Flow (CF) and In Line (IL). The wake dynamics, including IL and CF vibrations, is represented using a pair of non-linear Van der Pol equations that solved using modified Euler method. The Palmgren–Miner Rule is used for evaluation of fatigue damage. Riser of Amir-Kabir semisubmersible placed in Caspian sea is used for case study. Because VIV is self-limiting, it is showed that lower modes have lower curvature, that in some cases this is lead to lesser stress and also fatigue damage. The results show that for tension dominant modes of vibration, natural frequencies was increased with top tension and for a certain Strouhal frequency, dominant modes of vibration was reduced which leads to reduction of stress and fatigue damage. The results show that stress and fatigue damage increased with module of elasticity of riser and reduction of this leads to reducing of stress and fatigue damage. Therefore suitable procedure for reduction of VIV responses of riser should be selected based on the current velocity.

Hamid Malah, Yuri Sergeyevich Chumakov, Sara Ramzani Movafagh

The system consisting of two rigid bodies in a viscous fluid is considered. The main body with mass M is placed in a viscous incompressible fluid, and the body with mass m moves inside the main body. This system is known as vibrobot which can be used in arbitrary inspection fluid mechanic objects such as oil industries pipes and tanks, as well as marine industries, medicine, etc. In this paper, the interaction between the vibrobot and viscous fluid is studied to achieve the motion laws of the vibrobot with the harmonic oscillation of internal mass. Also the flow structure around vibrobot and its effects on the hydrodynamic force acting on the vibrobot are investigated. Analyses are carried out by direct numerical simulation of the vibrobot motion in a viscous fluid by OpenFOAM package. Calculations are performed for the following combinations of control parameters; The ratio of the viscous fluid mass to the vibrobot mass μ_1=0.35, the ratio of the internal mass to the vibrobot mass μ_2=0.325 and dimensionless oscillation frequency f=1/5, when Reynolds number takes values in the range of 50<Re<250. Calculations have been performed with different initial approximations, determined by different initial velocities of the incident flow.

Hassan Sayyaadi, Ramin Yekta, Abolfazl Motekallem

Today, the rolled products, i.e. sheet, plate and foil is used in marine applications, including platforms, hatch covers, mast, hulls of boats and superstructures on pleasure boats and the bridges and superstructures of passenger ships and merchant ships. In this paper, simulation of asymmetric cold rolling is presented by using explicit analysis procedure. In asymmetric cold rolling, the workpiese if often bent downwards or upwards. A two dimensional explicit dynamic finite element model with adaptive meshing technique has been employed to simulate asymmetrical condition are here due to different roll radii. To validate the simulation, the results of simulation and experiment are compared. Effects of asymmetry due to roll radii ratio and speed ratio mismatch on sheet curvature variations are discussed. Finally, optimum roll speed ratio in various of roll radii ratio could be found to produce flat sheet.