Design Of Coastal Structures Research Articles

RELATION BETWEEN SHAPE OF EXTREME WAVE HEIGHT DISTRIBUTIONS AND WEATHER SYSTEM

The extreme value analysis of wave height has been used to estimate design value of coastal structure design. The procedure of extreme value analysis is standardized but distributions change highly depending on target locations. A long-term atmospheric reanalysis is useful for engineering applications to complement observation data. Although the reanalysis dataset was insufficient for coastal engineering applications due to shorter length of period and sparse spatial resolution of modeling, recent reanalysis (e.g. CFSR) give reasonable performance for engineering applications as wave climate both accuracy and length of periods (e.g. Menendez and Losada, 2017). This study analyzes characteristics of extreme wave heights and understands relation between extreme wave height distribution and its dependence on weather systems based on long-term analysis and observed data.

Integrating short- and long-term statistics for short-crested waves in deep and intermediate waters

The main objective of the present study is the combination of short- with long-term wave statistics in deep waters in order to achieve a more accurate description of the long-term wave climate in shallower waters. Such a description would provide vital information for many engineering applications in deep and intermediate waters, including design of coastal structures. This task can be accomplished by accumulating the statistics for all short-term sea conditions, considering the frequency of occurrence of each sea state during a certain period of years. A modification of an existing relationship has been developed aiming at achieving this purpose. More specifically, by using the relative frequencies of occurrence of the significant wave height (Hs) and mean zero-crossing wave period (Tm), measured at a specific location, as well as the short-term joint distributions of wave height (H) and period (T) associated with each sea state, the long-term joint distribution of H and T can be produced at that location in deep waters. Then, the long-term joint probability density function of Hs and Tm and the long-term joint probability function of H and T can be estimated at any intermediate water depth by considering wave directionality in deep waters and wave transformation of each individual wave, as waves propagate from the open sea towards shallower waters. Wave measurements obtained at three different locations in the Aegean (Greece) have been examined and compared. The results showed that, as waves propagate from deep to shallower waters, wave statistics differ from those in deeper waters, especially when waves become significantly depth limited. It is noted that this individual wave analysis refers to short-crested waves, thus wave directionality and refraction have been considered. However, in this approach, the nonlinear wave – wave interactions have not been taken into account.

Statistical modelling of extreme storms using copulas: A comparison study

Coastal risk assessment and structure design heavily rely on the statistical analysis of the extreme wave climate, such as the wave height, storm duration, wave period and surge height. Due to the dependence among these variables, the multivariate dependence structure should be taken into account for statistical simulation of the storm events. Here, three modelling framework are described and compared for probabilistic modelling of extreme storms, i.e. the Gaussian copula, conditional mixture method and entropy copula. This paper demonstrates the functionality of the approaches in simulating the sea storm while maintaining their statistical characteristics. None of the three methods can fit all the bivariate cases best, and the Gaussian copula gives the best overall fitting quality for the four dimensional data in the case study, while the conditional mixture method gives the lowest fitting quality. The entropy copula gives a comparable simulation results and shows its great potential to be universally applicable for modelling the multivariable joint distribution by avoiding the procedure of assigning any copula family before fitting data.

Landslide Tsunami Hazard Along the Upper US East Coast: Effects of Slide Deformation, Bottom Friction, and Frequency Dispersion

Numerical simulations of Submarine Mass Failures (SMFs) are performed along the upper US East Coast to assess the effect of slide deformation on predicted tsunami hazard. Tsunami generation is simulated using the three-dimensional non-hydrostatic model NHWAVE. For rigid slumps, the geometry and law of motion are specified as bottom boundary conditions. Deforming slide motion is modeled using a depth-integrated bottom layer of dense Newtonian fluid, fully coupled to the overlying fluid motion. Once the SMFs are no-longer tsunamigenic, tsunami propagation simulations are performed using the Boussinesq wave model FUNWAVE-TVD, using nested grids of increasingly fine resolution towards shore and employing a one-way coupling methodology. Probable maximum tsunamis are simulated for Currituck SMF proxies sited in four areas of the shelf break slope that have enough sediment accumulation to cause large failures. Deforming slides have a slightly larger initial acceleration, but still generate a smaller tsunami than rigid slumps due to their spreading and thinning out during motion, which gradually makes them less tsunamigenic. Comparing the maximum envelope of surface elevations along a 5 m isobath, consistent with earlier work, the bathymetry of the wide shelf is found to strongly control the spatial distribution of tsunami inundation. Overall, tsunamis caused by rigid slumps are worst case scenarios, providing up to 50% more inundation than for deforming slides having a moderate level of viscosity set in the upper range of debris flows. Tsunamis from both types of SMFs are able to cause water withdrawal to the 5 m isobath or deeper. Bottom friction effects are assessed by performing some of the simulations using two different Manning coefficients, one 50% larger than the other. With increased bottom friction, the largest tsunami inundations at the coast are reduced by up to 15%. Selected simulations are rerun by turning off dispersion in the model, which leads to moderate changes in maximum surface elevations nearshore (− 10 to + 5% changes), but to more significant effects in the far field (− 40 to 80% changes). Onshore, dispersion causes the appearance of short period undular bores that eventually break nearshore without significantly affecting inundation at the coast. However, these bores increase wave-induced maximum flow velocity and impulse forces, the latter by up to 40%, which may affect the design of coastal structures.

Entrapment of an estuarine fish associated with a coastal surge barrier can increase the risk of mass mortalities

Estuarine storm surge barriers are designed to prevent the flooding of human-developed landscapes. While such barriers may have a range of ecological impacts, including the fragmentation of aquatic habitats and the alteration of water quality, their impact on obligate estuarine fishes is largely unknown. The sparid, Acanthopagrus butcheri, was used as a model species to determine how surge barriers may influence the movements of solely estuarine species and fish kill events. Individual A. butcheri were monitored for one year using passive acoustic telemetry in the Vasse-Wonnerup Estuary (south-western Australia), in which fish kills occur regularly during summer and autumn. Hydrological data and surge barrier operational information were used to make inferences on the movements and habitat use of A. butcheri. Individuals were largely restricted to the waters downstream of the surge barriers. The fish tended to occupy deeper sites in proximity to complex structure with the distribution also influenced by changes in salinity during the spawning period. A strong seasonal trend existed in the daily distance travelled by the fish and this was positively associated with the annual flow period. The majority of fish that successfully passed upstream through one of the surge barriers did so through a fishgate that operated outside of the spawning period. All those fish were then likely trapped with no downstream fish passage occurring in summer and autumn at a time when water quality was characterised by low dissolved oxygen and cyanobacterial blooms. The surge barrier therefore acts as a seasonal trap and increases the risk of mass mortalities. Given a projected increased need to combat flooding and storm surges associated with climate change in low-lying coastal areas, the study highlights the necessity of ensuring that the life-cycles and movement requirements of estuarine fishes are considered in the design and operation of coastal flood mitigation structures.

Estimation of significant wave period from wave spectrum

Although the significant wave period is one of the key parameters in the design of coastal structures, it is not calculated by the spectral wave model because it is obtained by the zero-crossing analysis. The present paper examines several formulas that relate the significant wave period to wave spectral parameters such as peak period, mean period, and peakedness parameter. The formulas are derived based on the wave measurements in two locations in the Japan/East Sea (JES). The derived formulas are then compared with the measured significant wave periods in other locations in JES. It is shown that the formula using the mean wave period, Tm−1,0, is the most accurate. This formula is further used in a spectral wave model, the significant wave periods from which are compared with the measurement. Additionally, the relationship between the significant wave height and period is obtained based on the wave hindcasting, from which the most probable significant wave period can be determined for a specific significant wave height. A comparison with the measurement shows that the relationship is relatively inaccurate in the locations where southerly swell waves are significant, which are not accurately taken into account in the numerical model.

A Bayesian Quantile Regression Approach for Nonstationary Frequency Analysis of Annual Maximum Sea Level in a Changing Climate

ABSTRACT Uranchimeg, S.; Kim, J-G.; Kim, J.-G.; Kwon, H.-H., and Lee, S.-O., 2018. A Bayesian Quantile Regression Approach for Nonstationary Frequency Analysis of Annual Maximum Sea Level in a Changing Climate. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 536–540. Coconut Creek (Florida), ISSN 0749-0208. Sea level rise is primarily caused by global warming and has been a key consideration in design practices in coastal engineering. The design of coastal structures is currently based on a frequency analysis of the local sea level under the stationary assumption, meaning that the maximum sea level will not vary significantly over time. However, the stationary assumption for sea levels might not be valid in a changing climate. In such a context, this study proposes a systematic approach to investigate nonstationarity in annual maximum sea levels (AMSLs) and of...

A Bivariate Frequency Analysis of Extreme Wave Heights and Periods Using a Copula Function in South Korea

Kim, Y.-T.; Park, J.-H.; Choi, B.-H.; Kim, D.H., and Kwon, H.-H., 2018. A Bivariate Frequency Analysis of Extreme Wave Heights and Periods Using a Copula Function in South Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 566–570. Coconut Creek (Florida), ISSN 0749-0208.Sea storms are generally described by a set of variables such as wave height, wave period and wave direction, and these random variables are typically treated as independent of one another. Moreover, univariate wave frequency analysis has been applied to estimate design wave heights corresponding to various return levels (e.g. 20, 50 and 200-year) using significant wave heights under stationary conditions. However, it has been acknowledged that these variables are often correlated with each other, and such dependence structure needs to be considered in the estimation of extreme quantiles. More specifically, a joint estimation of quantiles for different combinations of these variables such as wave heights and wave periods is required to reliably assess optimal design of coastal (or offshore) structures. Over the last several decades, accelerated sea level rise (SLR) and its impact on coastal areas have been reported in many parts of the world. Estimation of extreme quantiles of SLR as a nonstationary process play a crucial role in assessing these impacts. In these contexts, a multivariate frequency model using a copula function approach is introduced to describe sea storm risk, which is mainly characterized by wave heights and periods. The proposed multivariate frequency analysis offers several advantages over widely used univariate stationary frequency analysis including uncertainty estimation, improved representation of inter-dependency and significant improvement of compound risk estimation.

THE PLANFORM STABILITY OF EMBAYED BEACHES ON THE WEST COAST OF PENINSULAR MALAYSIA

Embayed beaches can be found along the West coast of Peninsular Malaysia and they are subject to beach’s dynamic changes. Some part of the coast along the West coasts have experienced severe erosion for several decades, in spite of the construction of various coastal defence structures. Therefore, it is crucial to predict the stability of embayed beaches along the West coast of Peninsular Malaysia. The planform stability of embayed beaches was established by applying the MEPBAY model. It was found that the total number of embayed beaches along the West coast of Peninsular Malaysia is 139 with 73 % were natural embayed beaches and 27 % were artificial embayed beaches. From the analyses, out of the 139 embayed beaches; 82 % were in static equilibrium and 18 % were in dynamic state. The causes of the instability of embayed beaches are the topography of the embayed beach, discrepancies in the design of previous coastal structures, influenced by wave climate as well as human intervenes without prior investigation of the biological and physical effects towards the beach. Furthermore, the applicability of engineering solutions applied on embayed beaches that are in either dynamic equilibrium can be predicted using MEPBAY programme.

Experimental study on the hydrodynamic impact of tsunami-like waves against impervious free-standing buildings

ABSTRACTTsunamis, landslide-generated waves, and dam failures are rare, but highly destructive phenomena, associated with extreme loading on infrastructure. Recent events showed that specific measures must be taken to guarantee safety of both people and the built environment. This experimental study investigates the forces and moments exerted on free-standing buildings that are induced by both surges and bores. The hydrodynamic impact was characterized by high splash, subsequently followed by a quasi-steady flow around the structure. For dry bed surges, the time history of the horizontal force was proportional to the momentum flux per unit width. For wet bed bores, an attenuation of the peak force due to the presence of an aerated front was observed and the introduction of a reduction coefficient was necessary to achieve a realistic force estimation. Additional force analysis in terms of peak time, wave height at maximum force and impulse also pointed out some key differences between forces exerted by dry bed surges and wet bed bores. The occurrence of the maximum tilting moment on the building coincided with the maximum horizontal force and an evaluation of the cantilever arm was possible. These findings provide engineers with practical information for the design of safer coastal structures.

Shape optimisation of wall structures located in solitary wave flows

ABSTRACT In this paper, we present a shape optimisation method for wall structures due to the wave force induced by a solitary wave. The fluid is assumed to be incompressible. Introducing the adiabatic assumption in addition, the acoustic velocity method presented by the author's group, the SUPG finite element method, is effectively used. To evaluate the wave force, we use the performance functional, which consists of the sum of the square of the wave force integrated between the starting and final times. The coordinates of the wall structure are regulated to obtain the minimum performance functional. The adjoint equation method is utilised to derive the gradient of the performance functional with respect to the coordinates. The simple weighted gradient method is employed as the minimisation procedure. Two numerical studies show that the results are consistent with existing structures and provide useful information on the practical design of coastal structures.

Substratum type affects recruitment and development of marine assemblages over artificial substrata: A case study in the Alboran Sea

There are more than 27,000 harbours along coasts worldwide and construction is expected to increase. The development and application of new ecological engineering ideas, for both old and new structures, is now imperative in order to reduce perturbation on marine coastal biota and to avoid the spread of non-native species. In this study, the early benthic assessment of subtidal and intertidal communities is tracked on five artificial substrata differing in origin, roughness, and chemical composition: Oyster Sandstone, Limestone, Gabbro, Slate and Concrete. Within substrata, Sandstone was the roughest on a 1–2 mm scale. Also, Sandstone and Limestone had predominantly calcareous composition while silicon was abundant in Concrete, Gabbro and Slate. In the intertidal zone, results showed that primary productivity and diatom abundance markedly increased with substratum roughness. In the subtidal zone, species richness and diversity over experimental substrata were lower than in adjacent rocky reefs. Nonetheless, during the first year of colonization communities varied within the experimental substrata. Coverage was higher on Sandstone than Concrete and Gabbro, and species richness was higher on Sandstone than Limestone. The differences are related to intrinsic substratum-type characteristics and showed Limestone, Gabbro and Concrete hold relatively poor ecological benefits in the first phases of ecological succession. The results may help to promote future research in this field and to test different substrata combinations and heterogeneities, for more environmentally sustainable surfaces in design of coastal structures.

Climate and extrema of ocean waves in the East China Sea

Wave climate plays an important role in the air-sea interaction over marginal seas. Extreme wave height provides fundamental information for various ocean engineering practices, such as hazard mitigation, coastal structure design, and risk assessment. In this paper, we implement a third generation wave model and conduct a high-resolution wave hindcast over the East China Sea to reconstruct a 15-year wave field from 1988 to 2002 for derivation of monthly mean wave parameters and analysis of extreme wave conditions. The numerical results of the wave field are validated through comparison with satellite altimetry measurements, low-resolution reanalysis, and the ocean wave buoy record. The monthly averaged wave height and wave period show seasonal variation and refined spatial patterns of surface waves in the East China Sea. The climatological significant wave height and mean wave period decrease from the open ocean in the southeast toward the continental area in the northwest, with the pattern generally following the bathymetry. Extreme analysis on the significant wave height at the buoy station indicates the hindcast data underestimate the extreme values relative to the observations. The spatial pattern of extreme wave height shows single peak emerges at the southwest of Ryukyu Island although a wind forcing with multi-core structure at the extreme is applied.

The Benefit of Wind Distribution Analysis for Coastal Construction Design in East Java Province

To create a safe and durable coastal structures design, a comprehensive data including minimum, maximum, and significant sea wave’s height are needed. Normally, to obtain such massive data, engineers need to elaborate specialized consultant to carry out direct measurement on site, which typically consumes enormous financial resources and involves exceptionally rare experts. In such case, engineers can use a set of 10 to 20 years’ wind data as a substitution. The suggested duration is expected to ensure that the set of data has sufficient information, which includes extreme wind speed and its fluctuation along the respective years. Therefore, it is common to adopt available data at the nearest wind stations, such as airports and harbors, to estimate the wind features on site. This paper presents a normative wind speed distribution model based on 16 years’ wind data at a location obtained from National Oceanic and Atmospheric U.S. Department of Commerce (NOAA). The outcomes of the research show that the maximum sea wave height prediction in Sidoarjo Regency East Java with respect to analytical and graphical method are 0,465 m and 0,840 m, respectively. The results are considered satisfactorily reliable to be used as primary data to design coastal structures.

Effects of Crown Wall and Berm on Wave-Overtopping Discharge over a Seawall

ABSTRACT Liu, S.; Ju, Q.; Huang, W.; Hu, X.; Qi, D., and Zhong, G., 2018. Effects of crown wall and berm on wave-overtopping discharge over a seawall. Reliable estimation of wave-overtopping discharge over a seawall is important in the crest-height design and safety assessment of coastal structures. Crown wall and berm have been widely used to reduce the wave overtopping over a seawall. According to recent literature, the influence of crown wall under breaking wave conditions has not been discussed precisely, and the reductive effect of an intermediate berm has not been clarified under nonbreaking wave conditions. In this study, 650 experiments have been conducted to investigate the influence of crown wall in breaking wave conditions and the influence of berm under breaking and nonbreaking wave conditions on the wave-overtopping discharge. New empirical equations have been derived from the analysis of experimental data to provide more accurate estimations of the reduction of wave overtopping on a seawall ...

Validation of Visually Observed Waves with the Recorded Waves on the Southwest Coast of India

The wave climate, pre-requisite information for planning and design of coastal engineering structures, can be obtained by different methods. Coastal protection works require wave climate in the nearshore region; deployment of wave sensors and visual observation of the waves from the shore are among the methods that can be adopted for collecting the wave data. On the southwest coast of India (Kerala), wave data have been collected by visual observation from the shore, at 18 stations located along the entire coastline since 1973. The pressure type wave sensors were installed in the nearshore region at four stations, almost equally spaced along the coast and data acquired for a period of 4 years. Of the four instrument stations, two were located at the visual observation station itself, the third one was about 7 km from the nearest visual observation station and the fourth station midway between two visual observation stations—the distance between the instrument station and the visual observation stations being about 20 km. Study revealed that the visually observed wave parameters are comparable with the wave parameters acquired by the instrument, particularly with respect to the wave height.

An Integrated Numerical Model for the Design of Coastal Protection Structures

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.

Experimental modeling of horizontal and vertical wave forces on an elevated coastal structure

A large-scale physical model was created in Oregon State University's Large Wave Flume to collect an extensive dataset measuring wave-induced horizontal and vertical forces on an idealized coastal structure. Water depth was held constant while wave conditions included regular, irregular, and transient (tsunami-like) waves with different significant wave heights and peak periods for each test. The elevation of the base of the test specimen with respect to the stillwater depth (air gap) was also varied from at-grade to 0.28 m above the stillwater level to better understand the effects of raising or lowering a nearshore structure on increasing or decreasing the horizontal and vertical wave forces. Results indicate that while both horizontal and vertical forces tend to increase with increasing significant wave height, the maximum and top 0.4% of forces increased disproportionally to other characteristic values such as the mean or top 10%. As expected, the horizontal force increased as the test specimen was more deeply submerged and decreased as the structure was elevated to larger air gaps above the stillwater level. However, this trend was not true for the vertical force, which was maximized when the elevation of the base of the structure was equal to the elevation of the stillwater depth. Small wave heights were characterized by low horizontal to vertical force ratios, highlighting the importance of considering vertical wave forces in addition to horizontal wave forces in the design of coastal structures. The findings and data presented here may be used by city planners, engineers, and numerical modelers, for future analyses, informed coastal design, and numerical benchmarking to work toward enabling more resilient nearcoast structures.

A Development of Nonstationary Frequency Analysis Model using a Bayesian Multiple Non-crossing Quantile Regression Approach

Global warming under the influence of climate change and its direct impact on glacial and sea level are known issue. However, there is a lack of research on an indirect impact of climate change such as coastal structure design which is mainly based on a frequency analysis of water level under the stationary assumption, meaning that maximum sea level will not vary significantly over time. In general, stationary assumption does not hold and may not be valid under a changing climate. Therefore, this study aims to develop a novel approach to explore possible distributional changes in annual maximum sea levels (AMSLs) and provide the estimate of design water level for coastal structures using a multiple non-crossing quantile regression based nonstationary frequency analysis within a Bayesian framework. In this study, 20 tide gauge stations, where more than 30 years of hourly records are available, are considered. First, the possible distributional changes in the AMSLs are explored, focusing on the change in the scale and location parameter of the probability distributions. The most of the AMSLs are found to be upward-convergent/divergent pattern in the distribution, and the significance test on distributional changes is then performed. In this study, we confirm that a stationary assumption under the current climate characteristic may lead to underestimation of the design sea level, which results in increase in the failure risk in coastal structures. A detailed discussion on the role of the distribution changes for design water level is provided.

Measuring hydraulic properties of geotextiles after installation damage

Since geotextiles have been progressively incorporated into coastal protection structures, the influence of installation damage on them has been the primary concern. During installation/construction, geotextiles are repeatedly subjected to high mechanical stresses which often exceed service stress. It is therefore vital to evaluate the mechanical and hydraulic damage and determine the consequences of these damages to better develop criteria for selection of suitable products. As these damages could reduce the material's mechanical strength and hydraulic efficiency, or in the severest form of damage, puncturing, would end the separation function. The properties investigated in this paper include the permittivity and apparent opening size (AOS) of geotextiles. Generally, the greater the drop energy of armour units applied to geotextiles, the greater the potential for damage. Findings show that the residual permittivity could increase significantly, 45% during installation. The preliminary design of coastal structures will be optimised as engineers and designers can better estimate the amount of damage on geotextiles upon installation.