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Modelling of coastal and nearshore structures and processes
Published in P. Novak, V. Guinot, A. Jeffrey, D.E. Reeve, Hydraulic Modelling – an Introduction, 2010
P. Novak, V. Guinot, A. Jeffrey, D.E. Reeve
When waves meet a dune or wall, they will run up the slope. If the waves are large enough, the wave will run up to the crest level and over the top. This is known as wave ‘overtopping’ and can lead to damage of the structure, erosion of the dune and flooding. When waves meet a structure, they may be unbroken, already broken or actually break on the structure. This last case provides the most spectacular displays of overtopping, like the one shown in Figure 12.7. For the majority of coastal structures it is the amount of overtopping that determines the elevation of the crest of the structure. Modern design practice uses the mean overtopping rate as a criterion rather than wave run-up, whereas early designs, in the absence of reliable experimental measurements, used wave run-up as a surrogate for overtopping.
Prediction of wave overtopping discharges at coastal structures using interpretable machine learning
Published in Coastal Engineering Journal, 2023
With continuous population growth and coastal area development, protecting people and infrastructure assets is becoming an increasingly important concern for coastal engineers (Koosheh et al. 2021). In addition, an increasing number of swell-like high waves and typhoons due to climate change have been resulting in coastal inundation and flooding damage in low-lying coastal areas and marine city areas. The impact of climate change is expected to significantly increase the vulnerability of coastal zones owing to the uncertainties of future predictions. Thus, technology to accurately analyze and predict potential risks is required to reduce the damage caused by coastal disasters induced by climate change. Overtopping is a phenomenon in which seawater flows inside port structures when their crest freeboards, such as breakwaters, revetments, and berthing, are lower than the wave run-up. It may interfere with the functions of coastal structures and cause structural or physical damage. To reduce this risk, coastal structures need to be designed to ensure that the maximum allowable wave overtopping discharge is not exceeded.
2018 Typhoon Jebi post-event survey of coastal damage in the Kansai region, Japan
Published in Coastal Engineering Journal, 2019
Nobuhito Mori, Tomohiro Yasuda, Taro Arikawa, Tomoya Kataoka, Sota Nakajo, Kojiro Suzuki, Yusuke Yamanaka, Adrean Webb
During Typhoon Jebi, the storm surge around Osaka Bay equaled or slightly exceeded the design storm surge levels that were based on Typhoon Nancy. While large-scale flooding did occur on waterside land, confirmed overflows of storm surge into protected urban areas were limited due to lower tide levels. For instance, a portion of a national highway (Route 2 between Sannomiya and Motomachi) that flooded during Typhoon Songda (2004; known locally as Typhoon No. 18) was protected during Typhoon Jebi due to subsequent measures. However, high waves in conjunction with the storm surge damaged many coastal breakwaters, and there were many instances where flood damage was caused by wave overtopping.
Characteristics of wave attenuation due to roughness of stepped obstacles
Published in Ships and Offshore Structures, 2020
Ruey-Syan Shih, Wen-Kai Weng, Chi-Yu Li
Recently, with changes in the patterns of leisure and the increasing demand for activity spaces, many energy dissipation technologies for the maintenance of natural underwater ecology and landscapes and new energy dissipation structures have been extensively developed and investigated to reduce wave energy and coastal erosion effectively. Scholars have studied various offshore embankments, including changes to the shape of submerged embankments (Shih and Weng 2016a), the permeability characteristics of submerged embankments, the number of submerged embankments and the distances between submerged structures (Shih et al. 2013, 2014; Shih and Weng 2016b), to explore the interaction between waves and structures and their dissipation effectiveness. In addition to reducing the visual barriers of coastal protection facilities, such understanding can be applied to further enhance the utilisation of coastal spatial resources. Among the most important considerations in the design of coastal protection techniques and structures are the characteristics of wave run-up, wave overtopping, and energy dissipation. Ahrens and Titus (1985) analysed some of the existing formulas for calculating wave run-up and methods that can be widely applied to various conditions for making accurate predictions. By using various methods to increase the surface roughness of coastal protection structures, it is possible to moderately reduce the wave run-up height and the volume of wave overtopping. Coastal areas have traditionally been protected by throwing down blocks, ramps, or gravel. In the past, stepped energy-dissipating structures were applied to solid-bed works on spillways and riverbeds with concrete blocks, which could be divided into sub-drop water consumption (as energy-dissipating units) to stabilise the riverbed. Chanson (2015) explored the associated dike overflow spillway and precast concrete block protection systems and emphasised that the safe operation of a dike-overflow protection system depends on good structural design and periodic maintenance that is easy to perform. Ward (2003) determined the range of storm conditions for several design configurations based on aesthetics and safety factors to determine the basic seawalls and stepped revetments of existing coastlines; his experiments on gravel and concrete step-by-step bank revetment showed that concrete step revetment is more durable than the gravel-type step revetment.