Wave Overtopping Rate Research Articles

주기영향을 고려한 직립식 구조물의 월파량 산정 : 비쇄파조건

Two-dimensional hydraulic experiments for wave overtopping under non-breaking wave condition are conducted. The wave overtopping formula for vertical structure is suggested and the results are compared with EurOtop (2007). The relative water depth coefficient () shows that almost the same coefficient is obtained for certain range (kh > 1.55) regardless of relative water depth, that is, although the relative water depth becomes larger, the relative water depth coefficient is almost same. When the wave steepness becomes larger the wave steepness coefficient decreases. The overtopping formula are expressed by relative freeboard(R) and non-dimensional wave overtopping rate(Q) and this formula has the form of exponential function. In this formula, the effects of wave period on wave overtopping are quantitatively investigated and suggested through the relative water depth coefficient() and wave steepness coefficient().

Wave Transformation and Runup on Dikes and Gentle Slopes

ABSTRACT Kobayashi, N.; Pietropaolo, J.A., and Melby, J.A., 2013. Wave transformation and runup on dikes and gentle slopes. Coastal flood-risk mapping requires the prediction of wave runup and overtopping of dikes and beaches. The cross-shore numerical model CSHORE is adjusted to predict irregular wave runup on impermeable dikes. The model is compared with 137 wave runup tests and 97 wave overtopping tests. The seaward boundary of the computation is taken at the location where wave setup is negligible. The spectral period and peak period at this boundary location are specified as input. The model predicts the measured cross-shore variation of the spectral significant wave height on the barred and sloping beaches in front of the dikes. The measured 2% and 1% exceedence runup heights are predicted within errors of about 20% for the spectral period used as input to CSHORE. The model predicts the threshold of wave overtopping, but the minor wave overtopping rates can be predicted only within a factor of 10. T...

Derivation of a New Model for Prediction of Wave Overtopping at Rubble Mound Structures

Prediction of wave overtopping is a key task in the design and safety assessment of coastal structures. In this study, M5' model tree as a new soft-computing approach was used to develop a model for the prediction of the wave overtopping rate at rubble mound breakwaters. The main advantages of model trees are that they are easier to deploy and more importantly, they produce understandable formulas. Selected data from the CLASH database were used for training of the model, and the conventional governing parameters were used as the input parameters. The obtained results were also compared with those of previous models. The accuracy of the model was evaluated by statistical measures, and it was shown that the developed model is more accurate than previous models. Furthermore, the model was validated with the prototype overtopping measurements in three sites. Results indicated that the developed model outperforms the previous models in predicting the full scale overtopping rates as well. DOI: 10.1061/(ASCE)WW.1943-5460.0000099. © 2012 American Society of Civil Engineers. CE Database subject headings: Wave overtopping; Breakwaters; Databases; Predictions; Coastal structures; Safety. Author keywords: Wave overtopping rate; M5' model tree; Rubble mound breakwaters; CLASH database.

Evaluation of a coastal flood inundation model using hard and soft data

Observed data of coastal inundation are very rare, yet are essential for testing the performance of simulation models for this significant natural hazard. In this paper we therefore examine the extent to which observed data can constrain predictions of a typical flood inundation model for a coastal flood event that affected the Somerset Levels in the UK on 13th December 1981. In doing so, a detailed reconstruction is made of the flooding that occurred along a 20 km stretch of the North Somerset coast, potentially providing a benchmark data set for comparative model analysis. Information on the extent of flooding was gathered from photographs taken on the day following the storm (‘hard’ or quantitative data), and contemporary newspaper reports and interviews with a number of people who had first hand experience of the storm and the consequent flooding (‘soft’ or qualitative data). Data on tidal levels and wave overtopping rates were collated from contemporary reports. Information on the topography of the study area and the configuration and heights of the sea defences at the time was determined from a variety of sources. Across the whole domain the model correctly predicted 85% of the flooded area; a level of performance comparable to fluvial applications of inundation models. The performance of the model in areas where flooding was dominated by wave overtopping was shown to be very sensitive to relatively small changes (±50%) in the specified flux rate, yet this parameter can plausibly vary by as much as ±300%. The overtopping flux rate was shown to be a much more sensitive control on the model performance than friction parameters. Finally, the study shows that 2D hydraulic models with relatively simple physics can closely simulate real coastal flood events given the availability of high resolution, high accuracy terrain data such as LiDAR. These conclusions mirror those arrived at over the last decade for fluvial flooding and suggest that the hydrodynamics of coastal and fluvial floodplain inundation are similar, if not identical.

Measured and modeled wave overtopping on a natural beach

The rate of wave overtopping of a barrier beach is measured and modeled. Unique rate of wave overtopping field data are obtained from the measure of the Carmel River, California, lagoon filling during a time when the lagoon is closed-off with no river inflow. Volume changes are based on measured lagoon height changes applied to a measured hypsometric curve. Wave heights and periods are obtained from directional wave spectra data in 15 m fronting the beach. Beach morphology was measured by GPS walking surveys. Three empirical overtopping models by Van der Meer and Janssen (1995), Hedges and Reis (1998) and Pullen et al. (2007) with differing parameterizations on wave height, period and beach slope and calibrated using extensive laboratory data obtained over plane, impermeable beaches are applied in a quasi-2D manner and compared with the field observations. Three overtopping events are considered when morphology data were available less than 2 weeks prior to the event. The models are tuned to fit the data using a reduction factor to account for beach permeability, berm characteristics, non-normal wave incidence and surface roughness influence. In addition, the run-up model by Stockdon et al. (2006) based on field data is examined and found to underestimate run-up as the calculated values were too small to predict any of the observed overtopping. The three overtopping models performed similarly well with values of 0.72–0.87 for the two narrow-banded wave cases, with an average reduction factor of 0.78. The European model (Pullen et. al., 2007) performed best overall and in particular for the case of the broad-banded, double peaked wave spectrum.

WAVE-INDUCED OVERWASH AND DESTRUCTION OF SAND DUNES

Numerical modeling of the rapid dune profile changes that may occur due to wave overtopping and sediment overwash during a storm is challenging. One of the reasons is the limited amount of available field and laboratory data related to the problem. Another reason is the complex interaction of hydrodynamics, morphological changes and sediment transport in the intermittently wet and dry zone of the dune profile. We modified the cross-shore numerical model CSHORE on the basis of three laboratory overwash tests with different dune geometries in front of a low-crested vertical wall to include the capability to predict profile evolution due to wave overtopping and overwash. Experimental results show that the transition from minor to major overwash is fairly rapid and that the resilience of the dune against destruction by wave-induced overwash is dependent on its geometry. Computed results compare well with the measured hydrodynamics, profile changes, wave overtopping rates and sediment overwash rates, requiring only one empirical parameter to be calibrated. Only the erosion in front of the vertical wall in the last phase of each test is not predicted well by the model. Additional comparisons with field data on profile evolution involving overwash verifies the field capabilities of CSHORE.

Three Dimensional Simulation of Hydraulic Phenomenon around Wave-Dissipating Blocks by MPS method

In this study, hydraulic phenomenon around wave dissipating blocks is simulated by a three dimensional MPS method with a precise gradient operator and penalty method. This MPS method solves the pressure oscillation and the fluid particle that penetrates through the wall. As an accuracy verification, the authors simulate wave overtopping rate by this MPS method and obtain a similar result compared with two dimensional CADMAS-SURF. In the simulation of wave breaking on seawall of complex shape, the authors obtained good result. The study suggests that this three dimensional MPS is useful to simulate hydraulic phenomenon around wave-dissipating blocks.

Wave Overtopping and Damage Progression of Stone Armor Layer

A probabilistic hydrodynamic model for the wet and dry zone on a permeable structure is developed to predict irregular wave action on the structure above the still water level. The model is based on the time-averaged continuity and momentum equations for nonlinear shallow-water waves coupled with the exponential probability distribution of the water depth. The model predicts the cross-shore variations of the mean and standard deviation of the water depth and horizontal velocity. The model is compared with four test series in which measurement was made of the wave overtopping rate and probability as well as the water depth, velocity, and discharge exceeded by 2% of incident 1,000 waves. The agreement is mostly within a factor of 2. Damage progression of a stone armor layer is predicted by modifying a formula for bed load on beaches with input from the hydrodynamic model. The damage progression model is compared with three tests that lasted up to 28.5 h. The model predicts the eroded area of the damaged armor layer well but overpredicts the deposited area because it does not account for discrete stone units deposited at a distance seaward of the toe of the damaged armor layer.

Numerical Experiments on Appearance Frequencies of Wave-overtopping due to Random Waves and Its Variations

Generally, it is extremely difficult to determine the exact wave-overtopping rate by random waves because of the irregularity of waves. In this study, the influence of the number of waves acting a seawall on the wave-overtopping rate was investigated by conducting a large number of computations with a numerical simulation model CADMAS-SURF based on VOF method. The main conclusions obtained from the results of numerical experiments are: 1) it is necessary to measure about 500 overtoppings to obtain the convergent wave-overtopping rate in a wave train. 2) However, if the appearance frequency distribution of overtopping quantity by individual waves is sufficiently expressed with an exponential distribution, the reliable wave-overtopping rate can be obtained, even if the number of overtopping is about 50 or 60 times.

Prediction Formula of Wave Overtopping Discharge Including Wave Runup

The height of seawall is determined based on allowable wave overtopping rate or wave runup height for the design of surge and wave prevention facilities. Although a design method based on wave overtopping rate takes into account of wave randomness, a design method based on wave runup height does not consider the wave randomness but uses equations and figures obtained from regular waves. Therefore, a unified prediction formula for random wave overtopping and runup is required for establishing the design scheme of seawalls. This study proposes prediction formula for random wave overtopping discharge including wave runup for seawalls with composite cross section installed near shoreline.

Experimental Study on Wave Overtopping Rate of Long Period Swell on Seawall

Recently, coastal disasters due to swells induced by heavy storms increase at any harbors. The wave overtopping rate of long period swell banded narrow spectra is different from that of wind wave because of the characteristics on the wave grouping and the wave height distribution. In the study, the model experiments were conducted to measure the wave overtopping rate of the long period swell on seawall and to propose the countermeasure to be able to be efficiently decreased the wave overtopping rate. As a result, it is possible to estimate the wave overtopping rate of the long period swell by applying the existing design method and to reduce the wave overtopping rate of long period swell by placing the permeable dethatched breakwater formed in concrete blocks in front of the seawall.

Random Wave Runup Formulae for Seawall with Composite Cross Section

The height of seawalls is designed based on allowable wave overtopping rate or wave runup height in design of surge and wave prevention facilities. Although a design method based on wave overtopping rate takes into account of wave randomness, a design method based on wave runup height does not consider the wave randomness but uses equations and figures from regular waves' theories and experiments. There is an urgent need for establishing estimation schemes of random wave runup height and incorporating the schemes into a seawall design. This study proposes equations for predicting random wave runup heights for seawalls with composite cross section installed near shoreline, aiming at elaborating a seawall design scheme.

Effect of Reef Topography and Wave Condition on Wave Overtopping of Vertical Seawall

It is well known that wave deformation around Okinawa Islands is very complicated because of reef topography. The objective of this study is to investigate the effects of reef length and wave condition on wave overtopping rate of a vertical seawall in an irregular wave field by conducting hydraulic model experiments. The experimental results showed the dimensionless wave overtopping rate decreases exponentially with an increase in the dimensionless reef length. It was revealed that the amplitude of long wave components in front of the seawall tends to increase with the dimensionless reef length R/h and the Ursell number Ur . Moreoverthe results indicated that the dimensionless wave overtopping rate is affected by not only the relative crown height of the seawall but also the amplitude of long wave components.

A Method to Predict Flooding Caused by High Waves

The purpose of this study is to establish a method to predict flooding caused by high waves. The method includes an estimation of the highest waves and storm surges generated by a depression and a typhoon, a numerical simulation on flooding caused by wave overtopping, and an effective output of the flood expectation. The method was examined through a case study on the flooding in the Shimonikawa Coast in February 2008 by considering short-term wave overtopping rates.

Reduction Effect of Wave Overtopping of Upright Seawall with Countermeasure and Wave Pressure Characteristics

The purpose of this study is to examine the reduction effect of wave overtopping of an upright seawall with a triangle-shaped countermeasure and wave pressures exerting on the seawall and the countermeasure throughout hydraulic experiments. As a result, the countermeasure placed on the seawall was found to have a great effect on the reduction of wave overtopping rate. It was evident that the reduction effect is mainly governed by the wave steepness, the relative water depth and the relative crown height. Especially, the relative crown height had the most influence on the reduction effect. It was also found from the experimental results that large wave pressure acts on the countermeasure.

Derivation of unified wave overtopping formulas for seawalls with smooth, impermeable surfaces based on selected CLASH datasets

A set of unified formulas for prediction of the mean rate of wave overtopping at coastal structures with smooth, impermeable surfaces have been derived through the analysis of the selected CLASH datasets. The mean wave overtopping rate is expressed as the function of the significant wave height at the structural toe and the relative freeboard. The formulas are applicable for both vertical walls and inclined seawalls with smooth transition between them. The formulas are simple but cover the full range of water depth from the shoreline to deep water. The effects of the toe depth and the seabed slope on wave overtopping rate are duly incorporated in the formulas. Prediction performance of the new formulas is better than the EurOtop formulas for both vertical walls and inclined seawalls.

Study on Applicability of a Numerical Wave Flume for Overtopping by Irregular Waves

CADMAS-SURF is a useful tool to evaluate wave actions for coastal structures. However, there are few studies concerning irregular waves by using CADMAS-SURF. The aim of this paper is to examine the applicability of CADMASSURF for the wave overtopping rate caused by irregular waves. The wave overtopping rate was calculated for uniform and sloped bottom conditions by using CADMAS-SURF. The calculated wave overtopping rate was compared with existing formulae. It is shown that CADMAS-SURF is capable of estimating the wave overtopping rate by irregular waves under broad condition with almost the same accuracy of existing formulae. It is also possible to determine the short-term overtopping rate caused by wave irregularity.

Experiment on Reduction of wave Overtopping Rate by Seawall with Double Parapet and Permeable Layer

Several offshore airports in the Japanese coasts are often damaged+these days by the wave overtopping due to storm s. One of the problems in such offshore airports is the limitation of seawall crown height derived from the width, height and distance of runway. Minami et al.(2007) have proposed a new typ. seawall with a wide permeable layer behind the front parapet to reduce the wave overtopping rate. In this paper, an experiment in a directional wave basin is carried out to determine the most appropriate width of permeable layer and height of its backward parapet. The experimental results reveal that the wave overtopping rate becomes smaller than the allowable level as the permeable layer becomes wider than 6m. The backward parapet has to be higher than 2.5m to prevent the overflow into runways.

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.

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.