Overtopping Characteristics Research Articles

Hydraulic stability and wave overtopping characteristics of Tblock™ armour units on a 3V:4H slope

Tblock™ is a newly developed single-layer regularly placed interlocking concrete block that has been designed to work on breakwaters and revetments. Physical model tests were conducted to assess the hydraulic stability and overtopping of the armour layer under a wide range of wave steepness on a 3V:4H slope. Based on 51 stability tests, it was observed that the stability of the Tblock™ armour layer decreases as wave steepness increases. This pattern resembles the behavior of Tetrapod and Cube armour layers. Furthermore, an extreme case of brittle destruction was observed, where the failure occurred rapidly after the extraction of the first unit. When compared with other interlocking armour units, Tblock™ demonstrated higher stability number (Ns) across a wide range of wave steepness. Based on 27 tests, overtopping performance was unsatisfactory, with a roughness coefficient (γf) of 0.73. Moreover, it was confirmed that increasing wave steepness also reduces the roughness effect of the armour layer. The reflection coefficient was found to be comparable to that of other concrete armour units.

Inundation Characteristics of Solitary Waves According to Revetment Type

Wave absorbers installed in front of revetments are effective in reducing wave overtopping and inundation caused by periodic waves. The wave absorbers’ mechanism of reducing wave overtopping and inundation caused by long-period waves such as tsunamis and storm surges is not clearly understood. This study conducted a physical modeling test and numerical analysis based on a large eddy simulation model using in-house code to examine the characteristics of wave overtopping and inundation according to the revetment type for solitary waves. In a vertical revetment (VR), the dominant vertical velocity of the solitary wave cannot bend at a right angle during overtopping, causing flow separation to occur at the crest, which leads to increased drag and vorticity. In a wave absorbing revetment (WAR), the flow cross-sectional area decreases along the slope of the wave absorber, causing the flow velocity of the solitary wave to increase and the horizontal velocity to be dominant during the overtopping and inundation process. In contrast with the general wave overtopping characteristics of periodic waves, the maximum overtopping water surface elevation in front of the vertical wall is higher in a VR than in a WAR. However, the order of maximum inundation heights reverses as the wave propagates inland.

Numerical evaluation of influences of onshore wind on overtopping characteristics of coastal seawall under solitary wave

To protect the coastal communities and infrastructures from the devastating damages caused by the extreme ocean surface waves during the severe weather conditions, many coastal defense structures, such as seawall, have been widely constructed along the coastline. In fact, huge ocean surface waves and strong onshore winds coexist in the real harsh coastal environment. Hence, it is of significant necessity to accurately evaluate the overtopping characteristics of coastal defense structures under the combined impact of waves and onshore wind. In this paper, overtopping characteristics of the coastal seawalls under the combined impact of onshore wind and solitary wave are numerically studied. Influences of some main factors, such as onshore wind speed, water depth, wave height, beach slope, and seawall slope, are discussed in detail. The results show that the presence of onshore wind can greatly affect the runup and the amount of overtopping water of seawall under the action of solitary wave. It is hoped that the results of this paper will further deepen our understanding of the overtopping characteristics of seawalls during the severe weather conditions.

Prediction of Wave Overtopping Characteristics at Coastal Flood Defences Using Machine Learning Algorithms: A Systematic Rreview

The assessment of coastal defences requires reliable prediction of mean overtopping discharges and acceptable overtopping rates for defined design conditions, an process of increasing importance given that global and regional climate change and associated sea level rises are becoming more acute. Prediction of overtopping discharge is usually computed from physical, analytical, and numerical models. However, the ongoing development of soft computing techniques now offer potential for rapid, relatively simple, and economically attractive methods for predicting overtopping. The application of Machine Learning (ML) algorithms has become increasingly prominent in models for estimating wave overtopping at flood defences. Here we review ML methods as tools for accurate prediction of overtopping and overtopping parameters. A systematic review of 32 publications, published between 2001 and 2021 (last twenty years), underpinned Decision Trees and Artificial Neural Network (ANN) as the most popular ML methods as analysis of wave overtopping datasets. A comparison of estimates of overtopping and overtopping parameters using these models with those from commonly used (empirical) prediction models, highlights the potential of ML methods for these applications. The review, however, highlights important limitations of the methods and identifies future research needs that may serve as an impetus for further development of these ML algorithms for wave overtopping, particularly in applications characterised by complex geometrical configurations.

Comparison of solitary wave overtopping characteristics between vertical and wave absorbing revetments

In this study, the wave overtopping characteristics of the solitary wave were investigated in the vertical revetment (VR) and the wave absorbing revetment (WAR) through hydraulic experiment and numerical analysis. In the case of WAR, the horizontal flow velocity significantly increased on the crest as the solitary wave passed through the inclined wave absorbing region and the flow cross-sectional area decreased. In terms of VR, the water level rose and the vertical flow velocity developed, as it was blocked by the impermeable vertical wall and the wave overtopping progressed. As a result, the WAR and VR wave overtopping rates were larger under the conditions of a relative solitary wave height of <0.272 and >0.272, respectively. Furthermore, the wave overtopping discharge per unit time was calculated in VR and WAR by applying the effective period of solitary waves, and a dimensionless overtopping formula for solitary waves was proposed.

SPATIAL DISTRIBUTION OF WAVE-BY-WAVE OVERTOPPING AT VERTICAL SEAWALLS

Over the years, many physical and numerical modelling research has been carried out to investigate the wave-structure interactions and the resulting mean overtopping characteristics at sea defences. The most reliable empirical predication formulae for prediction of mean overtopping rates have been reported in the overtopping manual, EurOtop (2018). In addition to average overtopping rates, in recent years, the spatial distribution of overtopped water has become an important topic of research to understand the safe zone behind coastal defences. The existing empirical formulae for spatial distribution of overtopping provide conservative predictions, as it has been derived from the mean overtopping volumes. The extreme wave overtopping hazards in generally originate from individual overtopping events rather than the mean overtopping volumes. This study presents comprehensive laboratory investigations on the spatial distribution of wave-by-wave overtopping at vertical seawalls.

Wave overtopping of smooth impermeable seawalls under unidirectional bimodal sea conditions

Reduction of risks due to overtopping of coastal defences is an essential requirement for the design, management and adaptation of coastal structures. Extensive knowledge is available on the prediction of overtopping of smooth, sloping and vertical impermeable seawalls. The existing prediction methods provide less certain guidance for combined wind and swell conditions. This experimental study focuses on overtopping characteristics of coastal seawalls under random bimodal waves. Both unimodal and corresponding bimodal conditions were simulated under different slopes and crest freeboards. Proportions of swell in the bimodal sea were varied in each test. Mean wave overtopping discharges were calculated for non-breaking random waves over at least 1000 waves. EurOtop formulae agree closely with our measurements from the unimodal experiments whereas they underpredict the observed wave overtopping rates for bimodal conditions even when using the recommended Tm−1,0 period for such cases. A modification to the EurOtop formula is proposed on the basis of the experimental results, to better capture the overtopping discharge under bimodal conditions.

Video-based Monitoring of an Artificial Beach Nourishment Project

Cao, Z.; Zhang, C.; Chi, S.; Zhuang, L., and Zheng, J., 2020. Video-based monitoring of an artificial beach nourishment project. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1037-1041. Coconut Creek (Florida), ISSN 0749-0208.This paper presents a case study on field observation of a new artificial beach nourishment project in Rizhao Coast, China. Using video-based monitoring technique combined with beach profile surveying, wave overtopping features prior to nourishment, shoreline change during the construction, and short-term post-fill morphological evolution of the artificial beach are observed and analyzed. Results show that wave overtopping characteristics and nourishing process can be quantified through video imagery analysis. Two-month post-fill profile and shoreline data reveal that little sand has been moved to the deep water and overall sand volume above -6 m elevation remained stable. The northern beach evolution was dominated by alongshore sediment transport and the eroded sands from central beach were mainly transported to the north, while the southern beach evolution was affected by both alongshore and cross-shore processes due to sheltering effect of the southern breakwater. Attention is recommended to be paid to the relationship between overwash-driven onshore sediment transport and berm/backshore evolution, as well as the future evolution of beach morphology close to the northern breakwater. The present study suggests that integrating the video-based and the conventional monitoring approaches can be helpful to capture and interpret in more details the physical processes involved in different phases of a beach nourishment project.

Numerical simulation of solitary waves overtopping on a sloping sea dike using a particle method

Sea dikes, as a commonly used type of coastal protection structures, are often attacked or damaged by violent waves overtopping under tsunamis and storm surges. In this study, the behavior of solitary waves traveling on a sloping sea dike is simulated, and solitary wave overtopping characteristics are analyzed using a complete Lagrangian numerical method, the moving particle semi-implicit (MPS) method. To better describe the complicated fluid motions during the wave overtopping process, the original MPS method is modified by introducing a new free surface detection method, i.e., the area filling rate identification method, and a modified gradient operator to provide higher precision. Meanwhile, the approximation method for sloping boundaries in particle methods is enhanced, and a smooth slope approximation method is proposed and recommended. To verify the improved MPS method, a solitary wave traveling over a steep sloping bed is studied. The entire solitary wave run-up and run-down processes and exquisite water movements are reproduced well by the present method, and are consistent with the corresponding experimental results. Subsequently, the improved MPS method is applied to investigate the overtopping process of a single solitary wave over a sloping sea dike. The results show that the hydraulic jump phenomenon is also possible to occur during the run-down motion of the solitary wave overtopping. Finally, the characteristics of the propagation and overtopping of two successive solitary waves on a sloping sea dike are discussed. The result manifests that the interaction between adjacent solitary waves affects wave overtopping patterns and overtopping velocities.

Laboratory investigation of overtopping at a sloping structure with permeable shingle foreshore

The vast majority of overtopping data applied in EurOtop (2018) has been made from small-scale measurements with impermeable foreshore slopes. This article describes a comprehensive two-dimensional experimental study conducted in a small-scale 1:50 wave flume. Results are presented for the overtopping performance at a 1 to 2 sloping wall, undertaken on both impermeable and permeable foreshore slopes. Within experimental limitations, the results demonstrated that the mean overtopping rate is reduced by up-to a factor of 4, when compared to the predictions reported for the impermeable slope. However, when comparing maximum individual wave-by-wave overtopping volumes, no significant differences were observed. These results are intended for practitioners and researchers predicting wave overtopping characteristics at sloping structures with permeable gravel foreshores.

Semi-automatic detection of the overtopping waves and reconstruction of the overtopping flow characteristics at coastal structures

This paper proposes a semi-automatic and customizable procedure for the identification of the overtopping waves based on a threshold-down-crossing analysis of the sea surface elevation signals. The procedure can be applied to 2D experimental and numerical signals, to emerged and submerged structures, with the same accuracy of a human-supervised analysis. The procedure includes an original and innovative algorithm to compare the water level signals at consecutive gauges and couple the waves propagating in between. The coupling algorithm implies a series of original applications of practical relevance, such as: i) the computation of the wave celerity, which is a crucial parameter for the assessment of the structural stability and the hydraulic vulnerability of the landward area; ii) the estimation of the wave overtopping discharge, which can be obtained by integrating the wave celerities with the surface elevations; iii) the description of the wave overtopping characteristics and their evolution over the structure crest; iv) the evaluation of the volumes lost for percolation in permeable structures. The application to new and literature data and the comparison with well-established formulae prove that the results obtained from the identification and coupling procedures are accurate and reliable.

A LABORATORY STUDY ON WAVE OVERTOPPING AT VERTICAL SEAWALLS WITH A SHINGLE FORESHORE

The existing empirical prediction formulae to determine the wave overtopping characteristics are mainly based on the laboratory measurements with the use of an impermeable foreshore slope in front of the structure. Recently, EurOtop (2016), an updated version of previous overtopping manual has been published with revised empirical equations to estimate mean overtopping discharge rates at plain vertical walls with and without foreshore.As past studies were mostly carried out at vertical seawalls on a fixed impermeable bed, little knowledge is available on the performance of these processes at coastal structures on a permeable shingle beach. This study presents the baseline overtopping characteristics at a plain vertical wall on an impermeable 1:20 foreshore slope, and compares the results with existing empirical predictions (EurOtop, 2016). In this paper, only the results on mean overtopping discharge and mean sediment rate at vertical walls are reported.

Wave overtopping and toe scouring at a plain vertical seawall with shingle foreshore: A physical model study

This paper describes a physical model study to investigate the wave overtopping and toe scouring at a plain vertical wall with a shingle foreshore. A matrix of 180 experimental test conditions were performed in a 2D wave flume, with an approximate scale of 1:50. The study investigates the baseline overtopping characteristics at a plain vertical wall on an impermeable 1:20 foreshore slope and compares the results with two permeable 1:20 shingle beach foreshores with prototype d50 values of 13 mm, and 24 mm respectively. For impulsive wave conditions, it was found that the mean overtopping rate was reduced by factor 3 for the d50 of 13 mm, and a factor of 4 for the d50 of 24 mm. For non-impulsive waves, the reduction factors were 1.5 for d50 of 13 mm and 2 for d50 of 24 mm. Prior to this study, limited design guidance was available to predict the mean overtopping discharges and mean sediment rates at vertical seawalls on permeable shingle foreshores. Therefore, a new set of prediction formulae are proposed in this study, based on the new laboratory test results, and a comparison with the available prediction methods in literature for vertical seawalls subjected to both impulsive and non-impulsive wave conditions.

Application of Grass Cover Failure Models Following in Situ Wave Overtopping Experiments in Belgium

In situ wave overtopping tests were performed on typical dike structures along the Schelde in Flanders (Belgium) with the Dutch Wave Overtopping Simulator. For a storm duration of 2 hours, wave overtopping characteristics were derived for significant wave heights ranging from 0,75 to 1 m and peak periods between 3 and 4 s. Prior to the in situ experiments, soil investigations were executed together with a detailed study of the quality of the grass cover. During the tests, video recordings were made and detailed pictures of the damage were taken. Water content and evolution of the grass cover were monitored. At one location, no failure was experienced up to 50 l/s per m, even after applying initial damage to the surface protection. Other locations failed after facing 30 l/s per m. Besides the cumulative overload method, available failure models are derived for steady overtopping conditions. Assuming erosion equivalence with unsteady overtopping conditions, different erosion resistance as well as (superficial) slip models are applied. Outcomes of the models are compared to the results of the in situ wave overtopping tests in Flanders (Belgium). Different approaches for describing the load term are discussed. Whether for unsteady overtopping conditions, erosion is predominant determined by the front velocity or an approximation of the average velocity of consecutive waves still needs further investigation. However, this discussion is maybe rather philosophical, because one's choice has a direct influence on the threshold values under which waves are not accounted for. For all methods, the determination of threshold values given different qualities of covering is at-the-time still questionable.

越波特性を考慮した透水性二重護岸の最適断面選定法

越波特性を考慮した透水性二重護岸の最適断面選定法

EFFECTS OF CROSS SHORE PROFILES ON THE SUSTAINABLE DESIGN OF COASTAL STRUCTURES

The performance of the existing coastal structures at different locations along Alexandria coastline, Egypt was re-examined. These coastal structures have been constructed (1998-2002) on Alexandria coastline during the phase of widening the coastal road. The constructions of these coastal structures, although protected the coastal road but didn’t maintain the sandy beaches. El-Sharnouby and Soliman (2011) studied the behaviour of these structures during a storm. This paper investigates the benefits of complementing the existing structures by adding limited modification. Three areas of different profiles and types of coastal protective works along Alexandria shoreline were selected to investigate their performance. The first area “Shatby” has a narrow sandy beach that is protected by a vertical seawall of 3-5 m above sea water level. The second area “Sporting” was protected by a revetment of 20-30 width with 10 ton concrete cubic blocks. In the third area “Loran”, revetment protected the shoreline against further erosion with beach profile completely covered by blocks, &#x0D; Reeve et el. (2008) used a two dimensional Reynolds-Averaged Navier-Stokes (RANS) numerical model to obtain wave run-up and overtopping characteristics. This model was based on the work of Liu et al. (1999) and Lin and Xu, (2006). A proposed artificial offshore submerged breakwater was introduced to determine its impact on wave runup. Beach profile data were collected by Coastal Research Institute monitoring program for the Alexandria coastal area. Profiles‘surveying were carried out from a constructed land baseline to a water depth of 10.0 m below the M.W.L. The wave characteristics used at the three surveyed profiles are: significant wave height Hs = 1.00 m, dominant wave period = 6.0 sec with wave direction from N to NW. &#x0D; &#x0D; Several coastal protection schemes were explored; submerged sills, T-groins,..etc. The objectives were to determine their effects on the reduction of wave breaking heights, wave run up as well as maintaining nourished sandy beaches. &#x0D; &#x0D; The numerical model showed the reduction of wave runup (20%) by submerged reefs, however other design analyses would indicate that coupled systems could fulfil the sustainable design targets. However cost optimization as well as design risk level should play a rule in the final system selection. Detailed results are provided in the poster session as well as final paper.

Smoothed Particle Hydrodynamics Simulation of Wave Overtopping Characteristics for Different Coastal Structures

This research paper presents an incompressible smoothed particle hydrodynamics (ISPH) technique to investigate a regular wave overtopping on the coastal structure of different types. The SPH method is a mesh-free particle modeling approach that can efficiently treat the large deformation of free surface. The incompressible SPH approach employs a true hydrodynamic formulation to solve the fluid pressure that has less pressure fluctuations. The generation of flow turbulence during the wave breaking and overtopping is modeled by a subparticle scale (SPS) turbulence model. Here the ISPH model is used to investigate the wave overtopping over a coastal structure with and without the porous material. The computations disclosed the features of flow velocity, turbulence, and pressure distributions for different structure types and indicated that the existence of a layer of porous material can effectively reduce the wave impact pressure and overtopping rate. The proposed numerical model is expected to provide a promising practical tool to investigate the complicated wave-structure interactions.

Wave Overtopping Characteristics of Double Seawall with Permeable Bottom

Wave Overtopping Characteristics of Double Seawall with Permeable Bottom

Wave Force and Wave Overtopping Characteristics of High Mound Composite Seawall for Oblique Wave Conditions

A high mound composite seawall, which has a permeable front wall with a dissipation chamber on the superstructure, was newly developed as a revetment for reclaimed land. Several studies have focused on the hydraulic characteristics of high mound seawall; however sufficient examination has not been carried out on the oblique wave conditions. Threedimensional hydraulic model experiments were conducted to investigate the wave force characteristics and wave overtopping characteristics under oblique wave conditions. Based on the phase difference of impulsive wave force acting on superstructure, wave force reduction coefficients for oblique waves were proposed. Furthermore, influence of incident wave angle on wave overtopping rate and wave run-up height were studied.

Effect of Bottom Topography and Revetment Configuration on Wave Overtopping Characteristics of Coastal Revetment in Regular/Irregular Wave Field

The purpose of this study is to investigate the effect of bottom topography and revetment configuration on wave deformation and wave overtopping characteristics around a revetment in regular or irregular wave field by conducting hydraulic model experiments and numerical computations with a CADMAS-SURF. The results revealed thatwave deformation over a reef has an effect on wave overtopping rate and a semi-circle type revetment is efficient in reducing wave overtopping rate. It was, therefore, confirmed to be important to consider the wave deformation so as to take countermeasures against wave overtopping in a coral reef sea area. The computational results also showedthat the CADMAS-SURF is a useful tool to estimate the wave overtopping rate of specially-shaped revetment over complicated bottom topography.