Spatial distribution of wave-by-wave overtopping behind coastal structures: a critical review of the literature and a novel semi-analytical model

While extensive research has been carried out on the management of various types of infrastructure assets, limited research was allocated to coastal structures. The rapid world demographic growth especially in low-lying areas within close range to the shoreline over the past centuryas well as global climate change have given more importance to coastal infrastructure management. Climate change has increased storm intensities while decreasing storm return periods; imposing further risks to life and property. The aim of this research is to provide a modeling methodology for deterioration prediction, and optimization of repair, maintenance, and rehabilitation costs of various sorts of coastal protection structures. The coastal protection structures in Alexandria, Egypt, represent the case study. An Asset Inventory Database for Alexandria's coastal assets was developed, comprising 43 structures occupying an approximate length of 18.50 km. Established visual inspection and condition rating procedures were followed to obtain a current Structural Condition Index and a Structural Condition Matrix for each reach and each structure, considering a single inspection point in 2013. Structural Indices and Structural Condition Matrices (SCM's) are classified into severity ranges. Transition probabilities between structural condition ranges were calculated using backward analysis considering an excellent structural condition at the year of construction. Such probabilities were then utilized to formulate the structure's Markov Chain transition probability matrix, enabling the prediction of future deterioration. Integration of single-time random events, namely intermediate and design storms; was also performed on the future deterioration forecast. Maintenance and repair policies and their associated costs were determined, according to which a Genetic-Algorithm-based Life-Cycle Cost (LCC) optimization modeling was constructed with the aim to optimize maintenance and repair cost for the next 50 years, all while achieving the minimum reliability of structures. Results of the optimization are then presented collectively for the entire group of coastal structures within the study area.

Introduction. The reduction in beach width due to erosion is a significant issue that can either be mitigated or exacerbated by coastal protection structures. Modelling breaking waves near the coast and around coastal structures can be used to determine their impact on the dynamics of the coastal zone. The objective of this study is to model and analyze the dynamics of turbulent structures around a single breakwater, obtained using two turbulence modelling schemes: RANS and LES.Materials and Methods. Turbulence induced by breaking waves was investigated. The modelling was based on bathymetric measurements conducted along the Azov Sea coast and a three-dimensional wave hydrodynamics model supplemented with various turbulence calculation configurations.Results. Modelling results of wave processes generating turbulent flows in the presence of coastal protection structures using different turbulence models were obtained. Results obtained based on Reynolds-averaged Navier-Stokes (RANS) equations are compared with the results of Large Eddy Simulation (LES) approach with Smagorinsky dynamic subgrid-scale model (DSM).Discussion and Conclusions. The results showed that wave heights simulated by LES were higher than those simulated by RANS in the front and leeward regions of the coastal protection structure and were lower in its upper part. Thus, according to LES, a greater amount of wave energy was preserved after passing over the breakwater. Velocity vectors of the water medium showed the formation of a vortex when LES was used, whereas no evidence of such turbulent vortices was detected in the case of RANS, confirming the better performance of LES for turbulence modelling in the coastal zone. According to the presented results, LES is the preferred tool for generating turbulence under incoming wave conditions in engineering practices.

Beach lowering and the effects of scour in front of coastal defences and erosion protection structures are recognised as a principle cause of their failure including collapse/breaching and washing out of fill materials. Both localised scour and more widespread beach lowering can lead to undermining of the Toe (see Figure 1 for definition). This can promote structural instability and result in partial or total collapse with subsequent reduction in, or loss of performance for flood defence or erosion protection. Lowering of the ‘ground levels’ in front of seawalls, revetments or other coastal structures is a common phenomenon not only in the U.K. but also around the world. Toe scour is a serious and costly problem – moreover, it is one which is not limited to any particular coastal environment or to any particular type of defence structure. The prevention of, design for, and management of beach lowering and scour at the Toe of coastal structures is an important factor in the management of those structures. Understanding, designing for and managing toe scour at coastal structures therefore is a key issue for coastal managers, designers and engineers. To date there has been no guidance available tailored specifically to meet these needs. Recognising this, the Defra/ Environment Agency Flood and Coastal Risk Management programme commissioned the development of guidance on the management of the Toe of coastal structures in 2008 (Toe Scour Guide). The guide draws together recent key research and development work on beach lowering and scour including ‘Understanding the Lowering of Beaches in Front of Coastal Defence Structures’ (Sutherland et al, 2006, 2008). It is also integrating work on performance and reliability of coastal structures developed through the Performance-based Asset Management Project (PAMS) including performance analysis and asset inspection methods. This paper reflects on and highlights some of the developments made in the preparation of the guide.

Crimean coastal protection structures play a key role in preserving coastal areas from erosion, storm surges and other natural impacts. Their condition directly affects the sustainable development of coastal zones. The author examines the features of coastal zone formation. Understanding the formation affects the ability to manage coastal ecosystems. The results of research in the field of coastal protection in recreational areas are presented. The factors influencing the state of coastal zones, such as natural and anthropogenic, which include relief forms, sea level rise, the influence of the biological environment, as well as the development of coastal zones by humans (construction of settlements, construction of port infrastructure, coastal protection structures) are analyzed. Subject: The state of coastal protection structures in the coastal zones of Crimea and the factors influencing their state. Materials and methods: The study used the method of analyzing data obtained during field surveys of coastal territories. To identify patterns in the development of recreational territories, a comparative analysis of the state of development factors is used. This study uses an integrated approach based on the analysis and systematization of data identified in scientific and regulatory literature, information resources and the media. Results: The marine coastal protection structures of Crimea are a complex system of engineering structures designed to protect the coastline from the destructive effects of waves, storms and erosion. The results of the conducted research allowed to identify key problems related to their integrity, as well as to determine the factors affecting their stability. Conclusions: The features of the formation of the coastal zone, the typification of the coast of the Crimean Peninsula, as well as the features of the coast in recreational areas have been identified. An integrated approach to organizing research aimed at a more in-depth study of the factors influencing the formation of the ecological state of recreational areas, as well as the development of coastal protection structures, is needed. Also, research should be based on the insufficient study of the morphological and exogenous processes of the sea coast, which leads to difficulties in carrying out design, construction and repair work on coastal protection structures. It is necessary to analyze and generalize existing research in the field of environmental safety of the construction of coastal protection structures, as well as an in-depth study of the morphological and exogenous processes of the sea coast.

Gabion-based coastal structures are being adopted frequently in recent times due to its energy dissipation characteristics and reduction in construction time. The coastal defense has become an essential aspect for maritime facilities and for the places prone to erosion. Reef breakwaters (also called Low crested structures) are seen to cause less environmental impact which makes them popular in recent past. The present investigation involves the study of hydrodynamic stability aspects of gabion-based reef breakwaters. Though these coastal protection structures are meant for wave attenuation, a study on the stability aspects of the structure to resist wave action is essential. This knowledge on the hydrodynamic stability is essential to come out with the design basis for construction of such coastal structures in a wave environment. This investigation on gabion-based reef breakwaters is performed using physical model tests with varying wave parameters and reef geometries. The study is aimed at fetching knowledge on the determination the weight of the gabions to resist the wave action by obtaining a relation between the weight of the gabion, geometrical parameters and to that of the wave parameters. This determination of the weight of the gabions to resist wave action is essential if gabion-based structures are deployed as low crested coastal structures or reef breakwaters. This paper is based on the experimental study conducted in the shallow water wave flume facility in the Department of Ocean Engineering, IIT Madras.

The work describes research of wave processes in the presence of shore protection and coastal structures using 3D wave hydrodynamics model. The model presented in the article gives realistic description of the physical wave process near the coastline. The influence of coastal protective structures on the diffraction and reflection of waves is investigated on the basis of 3D wave hydrodynamics model.

In the present work, an integrated coastal engineering numerical model is presented. The model simulates the linear wave propagation, wave-induced circulation, and sediment transport and bed morphology evolution. It consists of three main modules: WAVE_L, WICIR, and SEDTR. The nearshore wave transformation module WAVE_L (WAVE_Linear) is based on the hyperbolic-type mild slope equation and is valid for a compound linear wave field near coastal structures where the waves are subjected to the combined effects of shoaling, refraction, diffraction, reflection (total and partial), and breaking. Radiation stress components (calculated from WAVE_L) drive the depth averaged circulation module WICIR (Wave Induced CIRculation) for the description of the nearshore wave-induced currents. Sediment transport and bed morphology evolution in the nearshore, surf, and swash zone are simulated by the SEDTR (SEDiment TRansport) module. The model is tested against experimental data to study the effect of representative coastal protection structures and is applied to a real case study of a coastal engineering project in North Greece, producing accurate and consistent results for a versatile range of layouts.

Integrated Simulation Model for Maintenance and Repair Optimisation for Rubble Mound Coastal Structures Using Markov Chains, Regression and Genetic Algorithms Ayman El Hakea, Soliman Abu-Samra, Ossama Hosny, Moheb Iskander, Hesham Osman Pages 1-8 (2015 Proceedings of the 32nd ISARC, Oulu, Finland, ISBN 978-951-758-597-2, ISSN 2413-5844) Abstract: The significant increase in the world population living within close proximity to coastlines has assigned further importance to coastal protection structures. This importance has been even ascertained given the increasing risks posed by climate change. from this standpoint comes the importance of maintenance and repair strategies for coastal protection structures especially in low-lying coastal areas. This research provides an integrated model for the optimisation of maintenance and repair for rubble-mound breakwaters, revetments and groins under simulated climatic conditions. The model starts by establishing an Asset Inventory Database (AID), a Markov-Chain (MC) Deterioration Engine, and a Genetic Algorithm (GA) repair and maintenance Optimisation Engine. The AID includes the coastal structures within any particular study area, along with their design attributes and hydrodynamic data. The database divides coastal structures into structural reaches for ease of management. The MC deterioration engine predicts future condition of the structure based upon actual visual inspection results, while taking into account the single-time condition drop caused by seasonal storms. The GA Optimisation Engine includes a set of decisions that are triggered when the structure's Priority Index (PI) -- a factor of the condition and the magnitude of failure impact- attains the defined threshold. MC deterioration patterns are expressed using best-fit regression to enable the integration between MC's and the GA Optimisation Engine. The case study consists of a group of rubble-mound structures in Alexandria, Egypt. The Optimisation Engine simulates repair and maintenance scenarios for various climatic conditions at a preset PI threshold, and results are compared and discussed. Keywords: Optimization, Maintenance, Repair, Cost, Rubble Mound, Coastal, Structures, Markov Chains, Genetic Algorithms DOI: https://doi.org/10.22260/ISARC2015/0118 Download fulltext Download BibTex Download Endnote (RIS) TeX Import to Mendeley

Innovative methods for dike construction – An overview

Various methods are employed to investigate the effects of coastal structures in coastal areas on marine environments and transport phenomena. These methods can be categorized into physical models and numerical simulations. Due to the lack of long-term wave height data in Türkiye, numerical models are utilized to estimate wave heights generated by wind based on long-term measured wind speeds. These wave heights generated in deep sea conditions can be transported to the coast by wave transformation and interactions between coastal structures and waves, turbulence, currents induced by wind and breaking waves, coastal sediment transport rates, and changes in the coastline can be successfully predicted with the assistance of numerical models. In the scope of this study, the new “Integrative Probabilistic Design Approach of River Jetties” was developed. 3D numerical models were used for the optimum design, considering the sediment transport near the jetties and aiming to protect the coastal environment in the long term. 3D numerical modeling has been conducted to investigate the transport phenomena occurring at the outlet of the Kabakoz River in the Şile District of İstanbul Province to acquire the optimum layout and design of the coastal structures. The study presents the “Integrative Probabilistic Design Approach” for coastal protection structures by wind and wave climate, wave transformation, coastal sediment transport, shoreline change, and coastal structure probabilistic design sub-models. Monte Carlo Simulation of Hudson Limit State function conducts probabilistic design for the jetties. The greatest advantage of probabilistic design (Monte Carlo Simulation) is the prediction of uncertainties, such as wave height changes under design conditions. Following the completion of the construction of groins, the effect of probabilistic design on both design and coastal morphology can be evaluated precisely. In conclusion, in the study area, 146,237.55 m3 of sediment is transported annually from west to east and 221,043.49 m3 from east to west. In the absence of coastal structures, sediment transport from east to west is approximately 1.5 times greater than from west to east. The annual net coastal sediment transport from east to west is approximately 74,805.94 m3, while the total transport is estimated to be 367,281.04 m3. The coastline is expected to reach sediment balance within approximately two years. In this study, the coastal structure of a jetty is designed from an innovative probabilistic design perspective. The aim is to ensure the reliability of the structure and, at the same time, protect the morphology of the coastline where the structure will be constructed. The region’s wind and wave climate were initially determined using Hydrotam 3D software. Following this procedure, the length of the jetty is predicted considering the closure depth. The model parameters were calibrated from coastline morphology using satellite images and Google Earth over the past twenty years. These parameters are defined to Hydrotam 3D as input data; a trial-and-error model application procedure calibrates the coastline’s accumulation and erosion. Finally, the probabilistic design is conducted with Monte Carlo Simulation using the Hudson Equation as the limit state function. Det Norske Veritas developed a design code for marine structures in 1992, where the target reliability is 10-3 for structures with less serious failure consequences. This reliability level validated the Level IV model presented in this paper. The class of failure depends on the possibility of timely warning, and these standards can be revised by the model presented to address the effects of climate change on the design of maritime structures.

Evaluating the effectiveness of coastal protection structures in flood mitigation using hydrodynamic modeling: A case study in a tropical environment.

The analysis of the surrounding coastal relief of the North Caucasus Railway section, which is promising in terms of high-speed traffic development, and the coastal protection structures traditionally used on this section was carried out, and a three-dimensional map of the sailing directions near the section under study was constructed. A computer experiment was carried out using numerical modeling tools to examine the impact of storm waves on coastal protection structures and railway track structures in areas of intense coastal storm tide impact.The intensity of the impact of hydrodynamic factors on structural elements and the indirect impact of traditional coastal protection structures on coastal erosion were estimated. Computer modeling was carried out using the smoothed particle hydrodynamics method.A map of the distribution of flow velocities and excess pressure for the incident and reflected wave was constructed using a section of the coast as an example, and numerical indicators of the impact of hydrodynamic factors on the coastal structures of the railway were obtained. The study showed the advantages of integrating these structures into the natural landscape due to a significant reduction in the impact of reflected waves on coastal erosion. A comparative analysis of the impact of the specified hydrodynamic factors on the classical and alternative designs of the substructure of the track in the coastal zone, ensuring maximum use of the natural protection of the coastline, was carried out.

Recently, because of the shortage of natural rock, traditional forms of the river and coastal structures have become very expensive to build and maintain. Therefore, the materials used in hydraulic and coastal structures are changing from the traditional rubble and concrete systems to the cheaper materials and systems. One of these alternatives employs geotextile tube technology in the construction of coastal and shore protection structures, such as embankment, groins, jetties, detached breakwaters and so on. Geotextile tube technology has changed from being an alternative construction technique and, in fact, has advanced to become the most effective solution of choice. Erosion problems in coastal zones are become increasingly serious due to the development of artificial activities related to the expansion of city functions, industrial complexes and harbour facilities, as well as the removal of sea sand for use in This erosion motion accelerates the regression of the coastal cliff due to the regression of the dunes or the shoreline. In addition, the regression leads to loss of real estate in the hinterland and ruins the shock-absorbing zone between land, and sea. Therefore, the destruction of the dunes may lead to a loss of the habitat or egg-laying grounds of living creatures. In addition, the erosion motion of coastal beach zones destroys the living sites of inhabitants who live in coastal beach zones, and the erosion problem harms the local economy by decreasing the number of visitors. The sea dikes can be easily damaged by the attack of seismic sea wave (Tsunami) due to massive earthquake like the Great East Japan Earthquake in 2011. For these reasons, concern is increasing for the protection of coastal line. Many nations are striving to prevent damage to such zones, as are private organizations and local self-governments. One such preventive effort is beach nourishment or construction of the coast structures. Geotextile containment such as small sandbag has been adopted for the construction of civil structures in the past, large volume geotextile containers are being applied widely in consideration of economical and easy installation, and also for the minimization of environmental effects. Especially, contaminated soil and sediments dredged from port area are utilized to fill in geotextile containment for reclamation. Geotextile containment is widely classified into geotextile bag, geotextile tube, and geotextile containment, and they are filled with soil to be shaped of structure. The filling method is normally hydraulic filling by means of pumping, and also mechanical method can be applied according to the site condition. Thus, Shore erosion is currently causing millions of dollars worth of damage to shorelines and public properties not only along the east coast of Korea but also around the world. Little else needs to be said to emphasize that, without adequate protection, a very significant part of our coastline will fall prey to the ravages of the sea and to man himself.

A breakwater is a coastal structure that breaks the wave energy coming towards the beach. When a wave hits an object, it will be reflected entirely or partially. Initially, the primary layer units on the coastal protection structure were only composed of large piles of natural stone. It is becoming increasingly difficult to find a natural stone of the right size, and to prevent its scarcity; natural stones are commonly replaced with concrete blocks. This study conducted the reflection coefficient analysis on the BPPT Lock concrete armor unit. Physical model testing was carried out on the wave channel of the Coastal and Port Infrastructure Laboratory, Department of Ocean Engineering ITS. From this study, it was found that the reflection coefficient on BPPT Lock ranges from 0.512 to 0.828 at a wave steepness of 0.002088 to 0.0117 with a structural slope angle of 1: 2. The reflection coefficient value is influenced by wave height, wave period, and the slope angle of the structure.

Coastal zone is a central attraction for coastal engineers, scientists and coastal community due to economic and developmental activities of the coast. Kerala has 593 km of coastline. More than 50% of the coast is occupied with artificial structures such as ripraps, groins, seawall, ports and fishing harbours. These coastal protection structures and developmental activities played a major role in altering the shoreline position significantly. Therefore, periodical analysis and monitoring of shoreline change is the primary requirement for effective planning and management of the coast. This paper provides the primary requirement of shoreline change rate for the past 26 years using geo-spatial technology and field investigation for proper management of the coast. Landsat 5 and 7, Resourcesat 1 and 2 and Cartosat-1 data set were used as primary data source. Long-term shoreline change rate (1990–2016) was calculated using weighted linear regression statistical method. The morphological study was carried out to substantiate the shoreline change pattern. For detailed investigation, the study area was divided into five sediment sub-cells. The analysis revealed that the maximum erosion of 54% was noticed in sediment sub-cells II, followed by IV (52%) and III (43%) respectively. The result also indicated that the accretion/erosion pattern of shoreline change on either side of breakwaters was varying from place to place. The effectiveness of the coastal protective seawall was very minimal. This indicates that proper planning of any artificial structures is the basic requirement for effective management of the coast. The overall shoreline change status of Kerala coast indicates that 45% of the coast is eroding and 34% of the coast is in stable condition. Only 21% of the coast is of accreting nature. The field survey was carried out to validate the analysed results for entire coast, specifically along the coastal structures. The study demonstrates that the combined effect of satellite data and field investigation can be a reliable approach for shoreline change analysis for these complex environments.