Wave Overtopping Research Articles

Influence of oblique wave attack on wave overtopping at smooth and rough dikes with a berm

Oblique wave attack can significantly reduce the amount of wave overtopping at coastal structures compared to perpendicular wave attack. Guidelines exist to estimate the influence of oblique waves on wave overtopping. Guidelines to estimate the influence of a berm in the seaward slope are also available. These guidelines for the reducing effects of oblique waves and the reducing effects of a berm are frequently applied in combination, although limited data is available for this combination of reducing effects. To develop a method that can account for the reducing effects of oblique waves and a berm in the seaward slope of a dike, physical model tests have been performed in a wave basin on structures with smooth and rough slopes. Based on these data, wave overtopping guidelines for breaking waves on dikes have been validated and one of the guidelines has been extended to take the influence of oblique waves, berms and roughness into account.

Prediction of Mean Wave Overtopping Discharge Using Gradient Boosting Decision Trees

Wave overtopping is an important design criterion for coastal structures such as dikes, breakwaters and promenades. Hence, the prediction of the expected wave overtopping discharge is an important research topic. Existing prediction tools consist of empirical overtopping formulae, machine learning techniques like neural networks, and numerical models. In this paper, an innovative machine learning method—gradient boosting decision trees—is applied to the prediction of mean wave overtopping discharges. This new machine learning model is trained using the CLASH wave overtopping database. Optimizations to its performance are realized by using feature engineering and hyperparameter tuning. The model is shown to outperform an existing neural network model by reducing the error on the prediction of the CLASH database by a factor of 2.8. The model predictions follow physically realistic trends for variations of important features, and behave regularly in regions of the input parameter space with little or no data coverage.

Wave Overtopping Discharge for Very Gently Sloping Foreshores

The spectral wave period T m − 1 , 0 at the toe of sea-dikes is a crucial parameter to predict wave overtopping discharge over sea-dikes. It is known from literature that this period quickly increases when waves reach shallow foreshores; however, sometimes the assumption is made that the wave period remains constant from offshore to near-shore, leading to an underestimation of the near-shore wave period. Several formulae have been proposed to resolve the underestimation of wave overtopping discharges for very shallow foreshores. These corrective formulations confirm the tendency of underestimating the overtopping discharges over a very gently sloping foreshore but are not validated for foreshore slopes gentler than 1:500. The “equivalent slope” method based on a recent study is inappropriate for these very gently sloping foreshores due to the breaker parameter being much smaller than seven. This study proposes an extension of the correction and finds that spectral wave periods can reach values two times those offshore.

Coral reef islands can accrete vertically in response to sea level rise.

Increased flooding due to sea level rise (SLR) is expected to render reef islands, defined as sandy or gravel islands on top of coral reef platforms, uninhabitable within decades. Such projections generally assume that reef islands are geologically inert landforms unable to adjust morphologically. We present numerical modeling results that show reef islands composed of gravel material are morphodynamically resilient landforms that evolve under SLR by accreting to maintain positive freeboard while retreating lagoonward. Such island adjustment is driven by wave overtopping processes transferring sediment from the beachface to the island surface. Our results indicate that such natural adaptation of reef islands may provide an alternative future trajectory that can potentially support near-term habitability on some islands, albeit with additional management challenges. Full characterization of SLR vulnerability at a given reef island should combine morphodynamic models with assessments of climate-related impacts on freshwater supplies, carbonate sediment supply, and future wave regimes.

UK meteotsunamis: a revision and update on events and their frequency

<scp>UK</scp> meteotsunamis: a revision and update on events and their frequency

Experimental Study on Sand Dike Breaching by Wave Overtopping

A series of large-scale experiments are conducted to investigate the breaching process of sand dikes under wave overtopping. The dikes are constructed with uniform sand, covered with a thin clay layer on the upstream slope to prevent seepage during breaching. Wave height, wave period and dike slopes are systematically varied to examine their effects on the breaching process. Morphological development of the breach is recorded using a 3D laser scanner. The results indicate that erosion starts at the downstream edge of dike crest and the downstream dike slope gradually flattens. The breach cross-section is observed to be of a trapezoidal shape. Breach flow increases at an accelerating rate after initial overtopping until a peak flow is attained. The breach dimension and peak flow rate increase with increasing wave height, wave period, and upstream and downstream dike slopes. A dimensionless dike breach parameter is proposed to establish regression relations for the breach geometry and flow characteristics.

How natural processes contribute to flood protection - A sustainable adaptation scheme for a wide green dike

Effective adaptation to sea-level rise is critical for future flood protection. Nature-based solutions including salt marshes have been proposed to naturally enhance coastal infrastructure. A gently sloping grass-covered dike (i.e. Wide Green Dike) can be strengthened with clay accumulating locally in the salt marsh. This study explores the feasibility of extracting salt-marsh sediment for dike reinforcement as a climate adaptation strategy in several sea-level rise scenarios, using the Wide Green Dike in the Dutch part of the Ems-Dollard estuary as a case study. A 0-D sedimentation model was combined with a wave propagation model, and probabilistic models for wave impact and wave overtopping. This model system was used to determine the area of borrow pits required to supply clay for adequate dikes under different sea-level rise scenarios.For medium to high sea-level rise scenarios (>102 cm by 2100) thickening of the clay layer on the dike is required to compensate for the larger waves resulting from insufficient marsh accretion. The model results indicate that for our case study roughly 9.4 ha of borrow pit is sufficient to supply clay for 1 km of dike reinforcement until 2100. The simulated borrow pits are refilled within 22 simulation years on average, and infilling is projected to accelerate with sea-level rise and pit depth. This study highlights the potential of salt marshes as an asset for adapting flood defences in the future.

Numerical Simulation of Spatial Distribution of Wave Overtopping on Non-reshaping Berm Breakwaters

This study presents the results of a 2D numerical modeling investigation on the performance of non-reshaping berm breakwaters with a special look at the spatial distribution of irregular wave overtopping using FLOW-3D CFD code. The numerical model is based on Reynolds-Averaged Navier-Stokes solver (RANS) and volume of fluid (VOF) surface capturing scheme (RANS-VOF). The numerical model has been validated using experimental data. The armor and core porosities have been used as calibration factors to reproduce the wave overtopping distribution. The computed distributions of wave overtopping behind the structure agree well with the measurements for a non-reshaping berm breakwater. A formula is derived to relate the spatial distribution of wave overtopping water behind non-reshaping berm breakwaters to non-dimensional forms of wave height, wave period, berm width, berm height, and armor freeboard based on numerical results. This formula model agreed reasonably well with numerical model results.

Experimental Study of Wave Reflection in Breakwater Overtopping Catcher Model

Breakwater overtopping catcher model is a breakwater or shore protection model, which can accommodate or catch wave overtopping. This breakwater model is different from most other conventional breakwater models, at the back of this breakwater model, an opening is made to form a reservoir. This reservoir serves to collect overtopping wave, which is then collected and released back to the sea through an energy conversion process. How many waves overflow at the peak of the breakwater model is strongly influenced by several factors, one of which is the wave characteristics. This research was carried out experimentally to determine the characteristics of the waves, especially the influence of wave steepness to the wave reflection coefficient. The experiment was carried out in a wave flume with regular wave generation. Variations of research carried out on variations in the model that is slope and freeboard and wave variations that is period and wave height. The results of the study show that the wave reflection coefficient decrease with the increase of wave steepness, it is also seen that steep slopes produce the largest wave reflection coefficient.

Risk Modelling in Urban Coastal Areas to Support Adaptation to Climate Change and Extreme Weather Events: Early Warning, Emergency Planning and Risk Management Systems

Duarte, C.M.; Ferreira, J.C., and Fortes, J., 2020. Risk modelling in urban coastal areas to support adaptation to climate change and extreme weather events: Early warning, emergency planning and risk management systems. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 785–789. Coconut Creek (Florida), ISSN 0749-0208.The Portuguese coast is exposed to the Atlantic high-energy storms, endangering populations and coastal infrastructures and causing economic and environmental losses. With climate change and the rise of sea-level, it is expected that these storms became more frequent and violent. For this reason, it is essential to provide the authorities with tools for managing the hazards and risks associated with coastal events. The purpose of the To-SEAlert project is to develop, implement, and validate a set of tools and methodologies based on a WebGIS to monitor, prevent and manage wave overtopping and flooding emergencies caused by coastal events. In this work, XBeach software was used to model the effects of storm induced wave overtopping and sea erosion in a low-lying sandy shore in Costa da Caparica, Portugal. Two experiments were carried out, simulating a storm event in a segment and in a grid area. Results show beach and dune erosion and wave overtopping, similar to recorded effects in past events, and important limitations are discussed. The improvement of these simulations can be essential to input data on the To-SEAlert project model, allowing its objectives accomplishment.

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.

Cost and Benefit Analysis of Climate Change Adaptation Strategies in Coastal Areas at Risk

Cardona, F.S.; Ferreira, J.C., and Lopes, A.M., 2020. Cost and benefit analysis of climate change adaptation strategies in coastal areas at risk. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 764-768. Coconut Creek (Florida), ISSN 0749-0208.This paper addresses a cost analysis and evaluation of the benefits associated with different climate change adaptation strategies in coastal areas, considering high risk scenarios. For that, a cost analysis of adaptation strategies was carried out over a period of 50 years for Furadouro Beach, Ovar Portugal, a low-lying coastal area with high coastal erosion and frequent overtopping. The results show that cumulative costs of adaptation measures in the combination of defense and accommodation strategies are € 276M, € 164M in accommodation, € 112M in defense and € 75M in retreat. These results are an example of the importance of evaluating adaptation strategies in high-risk areas and show the usefulness of the approach taken as a support to decision making for processes that involve urban management and territorial planning of coastal zones vulnerable to the coastal erosion, wave overtopping and coastal flooding.

Random wave overtopping of vertical seawalls on coral reefs

Reliable estimations of overtopping rates are necessary for the design of vertical seawalls. Although many studies have been carried out to address this, few have paid attention to vertical seawalls built on coral reefs. In this study, a physical model was constructed with an idealized coral reef topography and vertical seawalls located on the middle or inner reef flat. A steep fore-reef slope in combination with a shallow and horizontal reef flat led to significant changes in wave heights, periods, spectra, and shapes across the reef. State-of-the-art overtopping formulas were tested against the experimental data, but none of them produced satisfying results. The reasons for the inapplicability of these formulas in this regard were discussed, which highlighted the necessity of distinguishing the significant influence of coral reefs on incident waves reaching engineered structures from structures fronted by relatively deep water and foreshores. A new formula for estimation of overtopping rates of vertical seawalls on coral reefs under non-impulsive conditions was derived. This formula is a function of the relative wave height at the seawall toe and the relative crest freeboard, whereas the spectral period is not incorporated. The performance of the new formula was investigated using various combinations of dimensional and dimensionless parameters.

Benchmarking of numerical models for wave overtopping at dikes with shallow mildly sloping foreshores: Accuracy versus speed

Practitioners often employ diverse, though not always thoroughly validated, numerical models to directly or indirectly estimate wave overtopping (q) at sloping structures. These models, broadly classified as either phase-resolving or phase-averaged, each have strengths and limitations owing to the physical schematization of processes within them. Models which resolve the vertical flow structure or the full wave spectrum (i.e. sea-swell (SS) and infragravity (IG) waves) are considered more accurate, but more computationally demanding than those with approximations. Here, we assess the speed-accuracy trade-off of six well-known models for estimating q, under shallow foreshore conditions. The results demonstrate that: i) q is underestimated by an order of magnitude when IG waves are neglected; ii) using more computationally-demanding models does not guarantee improved accuracy; and iii) with empirical corrections to incorporate IG waves, phase-averaged models like SWAN can perform on par, if not better than, phase-resolving models but with far less computational effort.

Correction: Molines, J., et al. Influence of Parapets on Wave Overtopping on Mound Breakwaters with Crown Walls. Sustainability 2019, 11, 7109

The authors would like to make the following corrections about the published paper [...]

Advantages of an innovative vertical breakwater with an overtopping wave energy converter

This paper presents an innovative vertical breakwater cross-section integrating an overtopping wave energy converter, named OBREC-V, and the analysis of its hydraulic performance and stability response to hydraulic loading. The structure is composed of a vertically-faced caisson with a sloping ramp on the top, a reservoir and a set-back crown-wall. The analysis of the structure is carried out by performing numerical simulations based on the Volume-Averaged Reynolds Averaged Navier-Stokes (VARANS) equations. The numerical simulations are performed to compare the performance of a traditional and innovative vertical caissons under the action of irregular waves, in terms of wave reflection, overtopping and wave acting forces. Results show that the reflection coefficients are lower than those computed in front of the traditional breakwater, with a reduction of up to the 40%. New formulations are proposed to better estimate the reflection coefficient and the wave overtopping at the rear side of the structure taking into account the non-conventional geometry of the device. The analysis of the forces indicate that the non-conventional geometry of the innovative OBREC-caisson increases the overall stability of the structure. The values of the safety factor against sliding, Cs, on innovative caissons are similar or greater than those calculated on the traditional vertical structure for almost all the tests. The downward force on the ramp and reservoir and the time lag between the vertical and horizontal forces, lead to a significant reduction of the maximum destabilizing forces Fs in the innovative breakwater, whose values range between 60 and 80% of the ones computed on the traditional structure. The obtained results show the co-benefits, in terms of functionality and hydraulic stability, that an OBREC-V entails with respect to a traditional vertical breakwater.

Development of Wave Overtopping–Overflow Transition Model Based on Full-scale Experiments

Development of Wave Overtopping–Overflow Transition Model Based on Full-scale Experiments

Individual wave overtopping volumes on mound breakwaters in breaking wave conditions and gentle sea bottoms

Mound breakwaters are usually designed to limit the mean wave overtopping rate (q) or the maximum individual wave overtopping volume (Vmax). However, rarely do studies focus on wave overtopping volumes on breakwaters in depth-limited breaking wave conditions. This study analyzes 2D physical tests on mound breakwaters with relevant overtopping rates (0.33 ≤ Rc/Hm0 ≤ 2.83) and three armor layers (Cubipod®-1L, rock-2L and cube-2L) in depth-limited breaking wave conditions (0.20 ≤ Hm0/hs ≤ 0.90) and with two bottom slopes (m = 1/25 and m = 1/50). The 2-parameter Weibull distribution was used to estimate Vmax* = Vmax/(gHm0T012) with coefficient of determination R2 = 83.3%. In this study, the bottom slope (m = 1/50 and m = 1/25) did not significantly influence Vmax or the number of overtopping events, Now. During the design phase of a mound breakwater, q is required to use the methods given in the literature to estimate Vmax. Thus, q must be estimated for design purposes when measured q is not available. In this study, CLASH Neural Network (CLASH NN) was used to estimate q with R2 = 63.6%. If the 2-parameter Weibull distribution proposed in this study is used to estimate Vmax with q estimated using CLASH NN, the prediction error of Vmax* is R2 = 61.7%. With the method presented in this study, the ratio between estimated and measured Vmax* falls within the range 1/2 to 2 (90% error band) when q is estimated with CLASH NN. The new estimators derived in this study provide good predictions of Now and Vmax with a method simpler than those in the literature on overtopped mound breakwaters in depth-limited breaking wave conditions on gentle sea bottoms (1/50 ≤ m ≤ 1/25).

Coastal impacts of super typhoon Hagibis on Greater Tokyo and Shizuoka areas, Japan

ABSTRACT A post-event survey of the coastal impacts of Typhoon Hagibis was conducted in the Greater Tokyo and Shizuoka areas. The typhoon’s intensive landfall generated the highest-level storm surges recorded in the study area with a maximum sea-level anomaly of nearly 2 m at the head of Tokyo Bay. Highly populated coastal areas in the inner sheltered part of Tokyo Bay were subject to only minor damage partially because the peak storm surge occurred during a low spring tide. High water levels along the coastline facing the Pacific Ocean mostly measured 4–8 m above the mean sea level, the exception being the Seisho coast, where extreme wave runup reached over 10 m above the mean sea level. The high water levels predominantly caused by energetic swells were comparable with the crest heights of defense structures in a broad range of the study area. The intensive typhoon did not trigger catastrophic flood damage, but caused minor flooding due to wave overtopping, and there was substantial damage to coastal infrastructures along the coast. This paper presents both an overview of and detailed information regarding the coastal impacts of the intensive typhoon along the highly altered coastline with complex geometry.

Crown Wall Modifications as Response to Wave Overtopping under a Future Sea Level Scenario: An Experimental Parametric Study for an Innovative Composite Seawall

The overtopping phenomenon at the rear side of breakwaters has particular importance in harbor protection. Undoubtedly, this topic needs to be taken even more seriously, considering the sea level rise. The present study focuses on the effectiveness in the reduction of the wave overtopping of a triangular parapet placed on the top of an innovative concrete superstructure. The last is part of the OBREC device (Overtopping BReakwater for wave Energy Conversion), an overtopping structure which is integrated into a traditional rubble-mound breakwater, to convert wave energy into electricity. Parametric laboratory tests, including the influence of water depth, have led to the evaluation of the accuracy of the main literature formulations and to the introduction of a new overtopping formula to take into account the influence of the parapet geometry. The results highlight the capability of the parapet in significantly increasing the hydraulic protection compared to a breakwater with a traditional crown wall. The findings from this work are expected to support in promoting and developing adaptive management strategies for existing coastal defenses and smart approaches in the construction and maintenance of new ones, with special reference to future sea-level-rise scenarios.