Berm Breakwaters Research Articles

Stability of two-class armour berm breakwaters: An experimental study

The recession of a berm breakwater is a key parameter in ensuring its stability, and functionality, to protect coastal areas against wave impacts. Consequently, consideration of the expected recession in structural design is required to ensure the required objectives of the structure. In this study, physical model laboratory experiments were conducted to measure the recession of two-class armour berm breakwaters in response to varying sea state conditions (wave height, wave period, storm duration, and water depth at the structure's toe) and geometrical parameters (berm elevation from still water level, berm width, and rock size). A total of 110 tests were conducted under irregular wave forcing and the results were compared with those of existing formulae, derived specifically for mass armour and Icelandic-type berm breakwaters. Of the existing formulae, the Sigurdarson and Van der Meer (2013) formula that is derived for both mass armour and Icelandic-type berm breakwater outperforms the other formulas. Subsequently, a new empirical formula was developed to estimate the erosion depth based on the dimensionless water depth. The findings from this study could be instrumental for the structural design of two-class armour berm breakwaters under different sea states and geometrical configurations.

AVERAGE OVERTOPPING DISCHARGE PREDICTION FOR BERM BREAKWATERS

The present paper deals with overtopping prediction for berm breakwaters in line with the EurOtop methodology. The basis for the paper is the recent advances proposed for EurOtop for conventional breakwaters with respect to the influence of the wave steepness and the crest width. New model tests have been performed to investigate the applicability of these influence factors to berm breakwaters. To cover a white spot in existing data for berm breakwaters, the model tests included wave conditions with very low wave steepness. The results show that the recently developed influence factors for conventional breakwaters also improve predictions for berm breakwaters. Based heron an additional influence factor for the dimensionless berm width is established. The berm width was in previous studies made dimensionless by the wave height, but the present study indicates that the wavelength is more appropriate.

Reliability evaluation of different models' recession failure in berm breakwaters; case study Shahid Beheshti port breakwater

Reliability evaluation of different models' recession failure in berm breakwaters; case study Shahid Beheshti port breakwater

Genetic programming for the prediction of berm breakwaters recession

The response of berm breakwaters to wave forces has been examined with rebuild and cumulative experiments. In rebuild experiments, the breakwaters were reconstructed after each test, whereas in cumulative experiments the structural damages were examined at the end of the experiment. This study presents a new method to investigate the berm breakwaters recession considering datasets collected of both types of experiments. Cumulative experimental results were converted to their equivalent rebuild experimental results by modifying the number of waves for the reported damage. After homogenizing the data, the datasets were divided into the train, validation, and test subsets. The data were analyzed using the Multi-Objective Genetic Programming (MOGP) approach, and a prediction model was created to evaluate the berm breakwater recession. The results obtained from the MOGP model were compared to outcomes computed using implicit formulas available in the literature showing that the MOGP model is accurate (R2 = 0.911 and RMSE = 0.111) with a relatively broader applicability range. The impact of each input parameter on the berm breakwater recession was examined using parametric and sensitivity analyses. The stability number was the most important parameter impacting the damage on the coastal structure. The results are in line with findings reported in previous studies.

On the General Longshore Transport model for resilient beaches

In the present paper, a set of 319 field and laboratory data on longshore transport rate has been gathered, checked, and finally adopted in order to overcome a noticed limitation in the previous version of General Longshore Transport (GLT) procedure for the estimation of Longshore Transport (LT). In particular, the extensive number of additional data, characterized by a wide mobility range, has allowed to obtain a single equation able to determine the longshore transport rate at coastal slopes consisting of loose not-cohesive materials, from reshaping dynamically stable berm breakwaters to sandy beaches. The reliability of the GLT procedure has been assessed by an independent verification with 39 field and laboratory data, for both offshore and breaking wave characteristics as an input. In addition, the GLT procedure has been compared with the van Rijn (2014) formula.

Mechanism of wave-induced flow in reshaping breakwaters

The aim of this work was to investigate the reshaping mechanisms of a reshaping berm breakwater (BB) by assessing the results of a two-dimensional numerical model in OpenFoam. The flow inside and outside the breakwater was numerically simulated. The initial and reshaped form of the breakwater was modelled using the Darcy–Forchheimer equation and k–ϵ closure model. The numerical model was calibrated with and validated against experimental data of wave-induced pressure and water-level fluctuations inside and outside the breakwater. Both the initial and reshaped BB were evaluated for calibration and validation processes. The results show that the minimum run-down level on the breakwater slope is a critical area for armour instability due to outward driving forces caused by the critically synchronised outward flow and excess pressure gradient. Moreover, parallel downward flow occurs during a wave run-down, which can push the displaced armour down the slope. After reshaping, the breakwater profile has a milder slope than the initial profile, and the outward forces due to the excess pressure gradient are reduced to less than one-half of their initial amount, a result of the change in breaker type. Accordingly, the reshaped profile is modified to harmonise with the new flow field conditions.

The effect of sequential storms on the performance of homogeneous berm breakwaters

Reshaping of homogeneous berm breakwaters have been experimentally investigated using 2D physical tests. Berm recession depends on storm duration in addition to breakwater geometry and other storm parameters such as significant wave height and peak period. Furthermore, a berm breakwater may experience some recessions prior to exposing to a design storm for which the breakwater is designed. In this study, 109 tests have been conducted totally to investigate the enhancement of berm recession during design storms and also to study the effect of sequential storms on the ultimate berm recession during the life span of berm breakwaters. The measured cumulative recessions have been compared with direct recessions obtained from a breakwater with no initial reshaping. According to the results, the effect of earlier sea states on final berm recession depends on the design stability index and it can be neglected only if the design storm is too weak ( H 0 T 0 < 40 ) or it is too strong ( H 0 T 0 > 80 ). For weak design storms, earlier reshaping is negligible, while for strong design storm, the final reshaped profile will be governed only by such design storms regardless of earlier sea states. The results show that the predicted berm recession against design storms can be maximum 10% less than the actual recession in the case of missing the effect of earlier sea states. Since this conclusion is valid for both statically and dynamically stable berm breakwaters (the maximum value occurs around H 0 T 0 = 70 ), it is suggested finally that designers consider 10% more recession than the predicted values by existing design formulae to be sure about the endurance of berm width against the cumulative berm recessions during design life of reshaping berm breakwaters. The observations showed also that this width can efficiently dissipate the wave energy and protect underneath layers. • Homogenous reshaping berm breakwaters are studied using 109 physical tests. • A new formula is proposed to calculate berm recession during storms as a function of modified stability index. • Cumulative recession during design life of berm breakwater is investigated and an applicable suggestion is provided. • A modified stability index is proposed for measuring the influence of design storms.

On berm design of Icelandic-type breakwaters (case study: Sirevåg berm breakwater)

An experimental model of an Icelandic-berm breakwater has been set up in the hydraulic laboratory of Tarbiat Modares University using irregular waves. Experimental model tests have been carried out using a wide range of sea-state conditions and geometrical parameters to measure different parameters, such as the eroded area (Ae), the berm recession (Rec) and the depth of the intersection point of initial and reshaped profiles (hf). A stability formula is proposed to establish the relationship between the damage parameter of the Icelandic-berm breakwater (Sd) and the non-dimensional form of Rec and hf. The application of the given formula for estimating the berm recession in the phenomenon and practical cases was evaluated employing the Sirevåg berm breakwater. The results of the evaluation highlight the appropriate estimation of berm recession. Moreover, some recommendations are suggested to consider berm parameters, such as the berm width, the berm elevation from still water level and the height of class I stones, as an Icelandic-type berm breakwater design criterion for future engineers. Eventually, taking all the proposed formulae and recommendations into consideration, a design tool for engineers in berm design of berm breakwaters has been provided.

The stability of berm breakwaters, state of art and sensitivity analysis

Berm recession plays a significant role in the design and assessment of berm breakwaters. In this study, different recession formulas were first thoroughly reviewed. Most of these formulas were developed based on mass armour berm breakwater tests, and some of the existing models contain many variables, while others have only a few parameters. Therefore, to determine the most significant parameters in these formulae, a comprehensive sensitivity analysis was conducted. It was found that the sensitivity of the recession to a particular parameter can be a function of several influencing parameters, and under some circumstances, some formulae are very sensitive to input variables. A comparison was made between the predicted recession and the measured one of the Sirevåg breakwater to investigate the performance of different formulas, which shows that Sigurdarson and Van der Meer (2013) formula performs better than others in this case.Furthermore, the impact of each governing parameter on the predicted berm recession was investigated. Results showed that the stability number is the significant parameter influencing the recession. However, there is an inconsistency between the formulae regarding the influence of T0 on the recession. Finally, experimental data was used to evaluate the sensitivities (of recession) obtained from different formulas, noting that these experimental data were obtained from research carried on a mass armour berm breakwater. The study revealed that Moghim et al. (2011) formulae showed reasonable performance regarding the influence of wave period T0 on the sensitivity of the recession, while Tørum et al. (2003) formulae was underestimating the sensitivity to T0. Moreover, it was found that Lykke Andersen (2006) formula is better fitted to the experimental data regarding the influence of the berm heigh (hbr) on recession.

SPH modeling of wave interaction with reshaped and non-reshaped berm breakwaters with permeable layers

A berm breakwater may reshape during storms while its hydraulic performance depends on its reshaping status. Some experimental studies have been done to evaluate berm recession and to suggest the final reshaped breakwater section. Some numerical models have also been developed in the recent years especially by taking into account the permeability of breakwater layers and these powerful models cab be utilized efficiently to simulate wave interaction with permeable reshaping breakwaters. In this study, a numerical model based on SPH technique is developed to compare the hydraulic performance of a non-reshaped with a reshaped breakwater. To validate this model, wave transmissions from a permeable submerged breakwater as well as wave penetration through a reshaping breakwater are modeled and the calculated wave profile as well as wave pressure inside the porous breakwater are compared with the recorded data in available experimental studies. Then, by modeling both reshaped and non-reshaped breakwaters with different porosities, different hydraulic responses such as wave reflection, dissipation, transmission and run-up are calculated for these cases. It has been shown that the hydraulic performance of a berm breakwater depends on both its reshaping status and permeability of armor layer. In addition, either modeling the reshaped geometry or neglecting the permeability of armor layer results in overestimated responses such as overestimated wave run-up and overtopping. Therefore, it is necessary to model a reshaping section with actual permeability to evaluate hydraulic performance of a berm breakwater accurately. However, for initial design purposes, a reshaped impermeable breakwater can be applied conservatively.

WAVE REFLECTION FROM BERM BREAKWATERS

Wave reflection from berm breakwaters is an area less focused as these structures are generally considered to have relatively low reflection levels. However, the reflected waves may compromise the stability of the structure by inducing scour at the toe and may enhance harbour access risk (Zanuttigh et al., 2013). Hence, it is necessary that the reflection coefficients are predicted accurately. Several empirical formulas such as Postma (1989), Alikhani (2000), Zanuttigh and Van der Meer (2008) and Van der Meer and Sigurdarson (2016) have been suggested for the prediction of wave reflection, Kr. In this study, physical model tests were conducted to supplement the existing berm breakwater data sets in the CLASH database (Zanuttigh et al., 2016). The measured reflection coefficients were then compared with those of the existing formulas to evaluate their performance.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/WXIoa_ae-1Y

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.

Influence of toe berm geometry on stability of reshaping berm breakwaters

Reshaping berm breakwaters have been mainly designed and built for water depth less than 20 m. In such conditions, a toe structure may be needed to reduce bottom settlements and increase geotechnical stability in the loose subsoil condition. Also, a toe berm can be deployed to reduce the berm recession and increase the stability of the Reshaping berm breakwater, especially in deep water. Although many studies have been conducted to study the effects of toe berms on stability of conventional breakwaters, investigations on the influence of a toe berm on stability of reshaping berm breakwaters are rare. This paper presents results of an experimental work that has been carried out to investigate the influence of a toe berm on the hydraulic stability of reshaping berm breakwaters. In a 2D physical test setup in a wave flume, a total of 207 tests were conducted to systematically examine the effects of toe berm configuration on the reshaping of berm breakwaters with three types of armor stones. The experimental program covers the influence of different geometrical parameters of the toe berm on the berm recession under various sea state conditions. Comparing results of berm recession of the cases having a toe structure with the cases without a toe berm shows that the amount of berm recession with toe berm is considerably less than the analogous amount for without toe structure. It is observed that an increasing toe berm width and thickness both have considerable influence on recession reduction. However, the toe depth has a relatively larger influence on recession than the toe width, and the influence is larger for higher stability numbers. It is concluded that a toe berm in front of reshaping berm breakwater not only does have influence on recession due to the depth influence and the changing wave conditions, but also the toe depth has a direct influence on the reshaped profile by preventing the displaced rocks to fall down to deeper parts. Using the test results, a new formula is developed for estimation of berm recession by taking into account the influence of the toe berm configuration. Given an acceptable stability number (Ho) as a design criterion for reshaping berm breakwaters, the present method predicts that the recession can be reduced up to 35% by the application of a toe berm. Thus, the main berm width can be shortened, resulting in reduction of the required armor stones volume. So, by using a smaller stone size for the toe berm, the stability of the structure is secured and also the total cost of the breakwater can be reduced.

The Effect of Stone Class I Characteristics on Hydraulic Stability of Multi-Layer Berm Breakwaters

The Effect of Stone Class I Characteristics on Hydraulic Stability of Multi-Layer Berm Breakwaters

An experimental study on the hydraulic stability of Icelandic-Type berm breakwaters

One of the key aspects of breakwater design and safety assessment is their stability evaluation. In the present paper, hydraulic stability of a multi-layer berm breakwater (MLBB) has been studied through varying the parameter of eroded area. To this end, a 2-D experimental model has been carried out in the wave flume of Tarbiat Modares University using irregular waves with a JONSWAP spectrum. A total of 150 tests have been performed to cover a wide range of sea state conditions and geometrical parameters such as wave height, wave period, water depth, berm width, berm elevation, stone class I height, front slope and nominal diameter of stone class I. In this study, a new dimensionless parameter is introduced to indicate that the wave breaking type plays a fundamental role in stability of MLBBs. Eventually; a new formula is derived to estimate the damage of MLBBs, based on different sea state conditions and various geometrical parameters. Comparisons are made between the estimated damage parameter of MLBBs by the proposed formula and those estimated by existing formulae. The results denote that the present formula not only performs well for MLBBs experimental data, but also indicates a reliable performance for some of Lykke Andersen's (2006) data in statically homogenous berm breakwaters (HBBs) outside the range of given formula. Furthermore, an innovative approach is presented to examine the eroded area based on the berm recession and the intersection point of reshaped and initial profile from SWL, which performs faultlessly rather than the existing one.

Effect of Sea Level Rise on the Wave Overtopping Rate at Berm Breakwater

This study quantitatively assessed the risk in the overtopping performance of berm breakwaters due to sea level rise (SLR). To achieve this, a recent overtopping prediction formula that includes the influence of water depth on the estimated overtopping rate was used for the analysis. Additionally, the probabilities of failure in terms of the overtopping rate for different SLR scenarios were estimated using the Monte Carlo simulations, and the optimal maintenance intervals were determined. The increase in the crest freeboard, required to maintain the design overtopping rate, was estimated to be less than the increase needed in berm width for the different sea level rise scenarios considered. Furthermore, the required crest freeboard was influenced less by the initial configuration of the berm width. Shorter maintenance intervals were required for structures with an initially wide berm compared to those with a high crest freeboard. The results indicated that the future design and maintenance of berm breakwaters need to consider the effects of SLR on the overtopping performance, especially in shallow water zones.

Wave run-up on bermed coastal structures

Reliable estimation of wave run-up is required for the effective and efficient design of coastal structures when flooding or wave overtopping volumes are an important consideration in the design process. In this study, a unified formula for the wave run-up on bermed structures has been developed using collected and existing data. As data on berm breakwaters was highly limited, physical model tests were conducted and the run-up was measured. Conventional governing parameters and influencing factors were then used to predict the dimensionless run-up level with 2% exceedance probability. The developed formula includes the effect of water depth which is required in understanding the influence of sea level rise and consequent changes of wave height to water depth ratio on the future hydraulic performance of the structures. The accuracy measures such as RMSE and Bias indicated that the developed formula is more accurate than the existing formulas. Additionally, the new formula was validated using field measurements and its superiority was observed when compared to the existing prediction formulas. Finally, the new design formula incorporating the partial safety factor was introduced as a design tool for engineers.

A CASE STUDY ON PERFORMANCE OF RESHAPING BERM BREAKWATERS: ORDU GIRESUN INTERNATIONAL AIRPORT, TURKEY

In this study, the stability and serviceability (wave overtopping) of hardly-reshaping berm breakwater of Ordu-Giresun International Airport and four alternative cross-sections of fully- and partly-reshaping berm breakwaters are assessed by physical model experiments. Ordu-Giresun International Airport is a public airport constructed on an approximately 1.77 km-square reclaimed land at the eastern Black Sea coast of Turkey. The reclaimed land area is protected with a 7345 m long hardly reshaping rubble mound berm breakwater at a depth of 11 m (MSL). The design high water level (HWL) corresponding to 100-yr return period is calculated as +1.12 m. The bottom slope from deep water up to 20 m water depth is around 1:50 and becomes steeper (1:20) towards the shore. The design wave characteristics at the toe of the structure (100-yr return period) is determined as Hs = 6.68m, Tm= 10.80 sec.

BATTLING THE BERING SEA: ST GEORGE ISLAND’S BERM BREAKWATER

St. George Island, Alaska is located in the Bering Sea more than 320 kilometers (200 miles) north of the nearest Aleutian Island. During original design and construction of the fishing harbor at St. George Island in the early 1980’s, stone large enough for a conventional breakwater was not available to quarry on the island, so the project utilized a berm breakwater approach with the available local stone. The long-term performance and service life of the berm breakwaters is reviewed in this paper. Construction of the berm breakwater was completed in 1987 and the breakwaters remained functional for nearly 20 years with little maintenance. In the winter of 2015/2016, approaching 30 years since initial construction, significant damage occurred during a winter storm. Repairs utilized a berm breakwater approach similar to the original design. Repairs were completed in 2 phases due to the short construction seasons at the project site.

Numerical Modeling of Berm Breakwater Optimization With Varying Berm Geometry Using REEF3D

Harbors are important infrastructures for an offshore production chain. These harbors are protected from the actions of sea by breakwaters to ensure safe loading, unloading of vessels and also to protect the infrastructure. In current literature, research regarding the design of these structures is majorly based on physical model tests. In this study a new tool, a three-dimensional (3D) numerical model is introduced. The open-source computational fluid dynamics (CFD) model REEF3D is used to study the design of berm breakwaters. The model uses the Volume-averaged Reynolds-averaged Navier-Stokes (VRANS) equations to solve the porous flows. At first, the VRANS approach in REEF3D is validated for flow through porous media. A dam break case is simulated and comparisons are made for the free surface both inside and outside the porous medium. The numerical model REEF3D is applied to show how to extend the database obtained with purely numerical results, simulating different structural alternatives for the berm in a berm breakwater. Different simulations are conducted with varying berm geometry. The influence of the berm geometry on the pore pressure and velocities are studied. The resulting optimal berm geometry is compared to the geometry according to empirical formulations.