This paper will discuss the problem of retaining fine sand in reclamations protected by rubble mounds with geotextile filters. It formed part of a wider study that will be presented at this conference by Dimakopoulos et al., where the hydraulic gradient at the reclamation / landfill will affect retention of the sand. In particular, we will describe the design and application of a novel test device to identify sand retention in experiments on an example sand sample and geotextile subject to reversing heads. It also directly follows on from the work by Cantelmo et al 2011 and Polidoro et al 2015, where hydraulic gradients in the core were examined during the assessment of the extent / suitability of the retention method. The paper will summarise numerical modelling to derive appropriate hydraulic gradients (Dimakopoulos et al.), the design of the test device using relatively easily obtained materials, and the use in a forensic failure study.

Recent land reclamation projects where maximization of land use is crucial have resulted in the appearance of types of coastal defenses that have not been extensively studied. Rubble mound breakwaters with open filters or geotextiles are increasingly used in reclamation projects. Due to placement of landfill material (e.g. dredged sand with silt) close to the rubble mound, these structures are potentially vulnerable to internal erosion and material loss through the coarser breakwater layers, a process which is often characterized as suffusion. Several past studies have highlighted these issues (Cantelmo et al 2011; Polidoro et al 2015). Incipient of sediment motion in the landfill area is highly dependent of the pressure gradients developing and reliable prediction of pressures is of great importance. This work presents a methodology for modifying existing formulas for estimating internal pressures in rubble mound breakwaters in the presence of reflective surfaces. The methodology follows a relatively simple concept and is applied to correct predictions of the formula proposed by Burcharth et al (1999). The corrected formula is compared against numerical modelling predictions published in Dimakopoulos et al (2023). Comparison and further verification of the formula will be performed following additional numerical (CFD) model simulations and experimental data.

A series of physical model tests were performed to explore what, if any, functional benefits in wave protection and damping are associated with various structural augmentations to a traditional breakwater intended to also serve as habitat creating or enhancing. The augmentations are in structural and geometric form and are intended to make large- scale alterations to wave behavior and transmission, and as such, do not involve secondary small-scale measures such as fronting seagrass meadows of vegetated edges. Those would be considered “opportunities” to further increase the ecological value but were felt to have limited functional impact or likely value given the scale of wave aggression. The model test results revealed significant performance deviations from traditional overtopping transmission formulas and experience. Raising the interior breakwater core allowed for significant lowering of the required breakwater crest height for the same incident wave conditions. Flattening of front face slope, combined with a reduction in armor size to better achieve bio compatibility, gave improved results but reached a limiting beneficial level. The biggest impact on reduction of wave overtopping and transmission was found with the introduction of quasi-two-dimensional protruding fronting reef ridges. Similar beneficial results were noted for lee side habitat ponds where perched pools of water intended as juvenile fish nurseries co-serve as stilling basins in severe wave events before transmitting onward to shore. Incorporating these new design elements into the design of a breakwater offers opportunities to improve visual aesthetics by lowering breakwater crest heights and creating breakwater geometries which better emulate natural landforms. Such solutions are more conducive to recreating habitat while still retaining the needed wave mitigating properties of the breakwater.

Beach management through nourishment and annual recycling has been applied for over 37 years to manage flood and coastal erosion risk to 1700 properties at Eastoke, Hayling Island, UK. This form of natural flood risk management has proved successful in avoiding the annual flooding that blighted this area previously. However, there have been unexpected storm events that have caused beach erosion and localised flooding. Using long-term nearshore wave datasets and state-of-the-art statistical methods, new multi-variate extreme wave conditions were derived and applied to assess beach performance. Eastoke beach was found to meet its original design criteria of a 0.5% AEP standard of protection for unimodal wave conditions. However, it experiences greater rollback erosion, wave overwash and therefore flood inundation under certain (but not all) bimodal wave conditions, causing uncertainty around the future standard of protection. Communicating these inconsistencies to practitioners and a non-specialist audience is challenging as we tend to oversimplify, despite every beach and storm being unique. Better understanding of mixed beaches, both in situ and through parametric and numerical models, would reduce uncertainty to ensure communities are resilient to climate change.

Wave overtopping of sea defences poses a hazard to people and infrastructure. Rising sea levels and limited resources mean accurate prediction tools are needed to deliver cost-effective shoreline management plans. A dearth of in-situ data means that the numerical tools used for flood forecasting and coastal scheme design are based largely on data from idealised flume studies, and the resulting overtopping predictions may have orders of magnitude uncertainty for complicated structures and some environmental conditions. Furthermore, such studies usually only provide data on the total volume of overtopping water, and no data on the speed of the water. Here we present WireWall, an array of capacitance-based sensors which measure the speed and volume of overtopping water on a wave-by-wave basis. We describe the successful validation of WireWall against traditional flume methods and present results from the first trial deployments at a sea wall in the UK. WireWall results are also compared with numerical predictions based on EurOtop guidance. WireWall technology offers an approach for reliable acquisition of the data needed to develop resilient coastal protections schemes.

The wind effect on the efficiency of a coastal defense structure is studied in this paper. It is normally assumed that the strength of the wind impact is characterized by the impulse parameter. If it is lower than a certain value, the wind is expected to have a dominant effect on the wave overtopping rate. In contrast to the regular observation, this study reports a new regime of wave overshoot when a low value of the impulse parameter does not lead to increased importance of wind. It is argued that the new regime appears due to the triplet instability previously studied by others. The variation of the standing wave height and the overshooting jet between the sequential cycles results in independence of the overtopping rates of the wind speed.

Wind effects on wave overtopping over a fully impermeable vertical sea wall were studied numerically using the open-source computational fluid dynamics library OpenFoam. A pressure gradient correction term was incorporated in the momentum equations. In recent studies, it was found that, in the absence of wind, an increase in wave steepness results in a reduction of wave overtopping. This is related to the instability of the standing wave formed at the front of a vertical structure. Such instability was noticed in the range of steepness 0.285-0.443 from previous physical experiments for a regular wave interacting with a vertical structure. The existence of this regime was confirmed in the current study. It was also found that the stability of the standing wave determines the shape and volume of the overshooting jet, which has a strong effect on wave overtopping. When the wind is relatively weak (e.g. a wind speed of 10 m/s) it is unable to alter the overshooting jet very much, meaning a weak wind effect on wave overtopping. When the wind is strong (e.g. a wind speed of 30 m/s) it completely deforms the overshooting jet resulting in overtopping discharge almost three times that without wind.

Wave overtopping formulae, which often underlie coastal hazard early warning systems, are typically parameterised using wave conditions at the toe of the structure. For very shallow conditions where significant wave breaking occurs over the foreshore, this usually requires computationally-demanding numerical models—and practitioners skilled in their application—to accurately transform offshore waves to the structure toe. An additional concern is that overtopping formulae are scarcely validated in the field due to the very limited availability of in-situ overtopping data obtained at actual structures. Here, we validate a set of deep-water-parameter-based formulae for mean overtopping discharge (q) at smooth slopes, which remove the need for nearshore measurements or additional numerical modelling but require that a single representative foreshore slope angle (m) be defined. The validation is carried out against field data gathered at Crosby (UK) using two novel approaches: i) a new overtopping measurement system called “WireWall”; and ii) crowd-sourced data in the form of overtopping images obtained from a community Facebook page (social media). A method is introduced to define m for irregular bathymetries, based on the location where the local water depth is equal to the offshore significant wave height. The overtopping formulae proved accurate—with estimates of q being within a factor of 4 of observations—when compared to both 1-h averaged and 15-min averaged overtopping data, suggesting that the approach can be used for both design and assessment and now-casting hazard information. Finally, hindcasts made using the newly validated formulae for the events reported by the community indicate that q can exceed 10 l/s/m under yearly winter conditions, posing a serious hazard to pedestrians. This highlights the pressing need to update the current hazard warning system at Crosby, which estimates q to be a factor of 3 lower than the deep-water-parameter-based approach, on average.

The impact of rising sea level on the flood hazard from sea defence overtopping means new coastal schemes need to remain resistant to changing wave and water levels over the next 100 years. The design of new coastal flood defences and the setting of tolerable hazard thresholds requires site-specific information of wave overtopping during storms of varying severity, which are combined with future projections in sea level. By converting an existing wave measurement technology into an overtopping monitoring system "WireWall", observations of wave-by-wave overtopping velocity and volumes have been made. Prior to field tests this winter at our study site Crosby, in the North West of England, the system was validated and refined in HR Wallingford’s physical modelling laboratories. During August and September we collected our first measurements of wave overtopping distribution for a scale model of the Crosby beach system; designed using available data from the North West Regional Coastal Monitoring Programme. These results were shared with our followers @WireWall_NOC and the #FlumeFriday community. Together the new flume and field system has collect measurements that will provide site-specific data to:

Mean wave overtopping discharge is generally accepted to be a primary design criterion for assessing the performance of coastal structures. It is a boundary condition for many coastal flood risk assessments. Modern methods for assessing wave overtopping discharges and their consequences are well documented and reported. Among the various tools available for assessing wave overtopping, the use of artificial neural networks has become increasingly popular. This paper introduces the next stage in the development of these models. Using the same source data, the new generic meta-modelling overtopping model reduces uncertainties and gives clear guidance on the range and validity of the outputs.

: Abstract The design of breakwaters and other coastal structures around the UK requires the assessment of the joint probability of extreme waves and sea levels. There is a standard simplified approach applied within the UK that uses joint exceedance contours of waves and sea levels. This simplified approach can be non-conservative and lead to the under-design of coastal structures unless correction factors are applied. These limitations have been known for a number of years and alternative, more robust, methods have been applied in the past. These alternative methods are risk-based as they enable the probability of the consequence (structural or serviceability failure) to be established. The more robust methods are not, however, widely used in current practice. This paper describes the development of a statistically robust nearshore multivariate extremes data set around the coastline of England. The dataset can, in principle, be used to undertake risk-based design of structures, thereby overcoming the limitations of existing practice.

The south coast of the UK is identified as a location where significant wave swell components are present within the regional wave climate. During the winters of 2006 and 2014, several sites along the south coast of the UK were subject to significant damages where flood events were recorded. These sea states were characterised by having a double-peaked wave spectra, observing a connection between wave spectrum shape and beach response. A two-dimensional (2D) physical model study was carried out to investigate the effect of gravel beach profile response under wave spectra characterised by swell-wave and wind-wave periods in various combinations. The physical model results showed the effect of bimodal wave spectrum on beach crest erosion and were compared with the parametric model Shingle and the numerical model XBeach-G. Based on this 2D physical model study, a new parametric model, Shingle-B, was derived and an online tool developed and made available on the website for the National Network of Regional Coastal Monitoring Programmes of England. This new tool has been validated at two sites in the south of England where field data of both waves and profiles were available.

In their 2010 paper, Allsop et al (2010) sought to bring together the latest methodologies for predicting waves and wave overtopping for the dams and reservoirs community and modernise the extant approach. In particular, they argued that the reservoir community should move away from the out-dated wave-run up and freeboard allowance approaches and embrace better-validated approaches that limit overtopping, as used by the coastal community. This followed publication of the EurOtop overtopping manual (Pullen et al, 2007), and included many of the methods discussed there. Since the original publication of EurOtop, there have been several improvements to the principal prediction methods and also to methods to improve predictions in cases where the crest includes a promenade and/or a wall that may include a bull-nose. These updates are especially pertinent with regard to bank full reservoirs or where there is a parapet wall at the crest of the embankment. As such, this paper provides an update to Allsop et al (2010) to incorporate the new methods in EurOtop II (van der Meer et al, 2016).

: Abstract This preliminary investigation by HR Wallingford examines how the overall crest level of a caisson structure used as a seawall to front a reclamation in relatively exposed conditions may be lowered, and how the resultant overtopping discharge can be controlled and efficiently drained back to sea. The study pre-selects a cross section and test conditions in order to perform 2D physical hydraulic model testing in order to measure overtopping performance and examine the influence on results on the positioning of crest elements. For the highest incident waves the crest level on the front face of the caisson is seen to govern the trajectory of the resultant overtopping flow.

Presently our understanding of gravel beach response under wave attack is limited and approaches to predict gravel beach response rely on formulae and models based on a few physical modelling studies. Field and laboratory studies (Hawkes, Coates, and Jones (1998)) indicate the importance of complex wave spectra (combining swell and wind sea) in the design of gravel beach recharge schemes. The objective of the study was to develop a data-set and a new parametric model, Shingle-B, to analyse the generic profile response of shingle beaches under bimodal wave conditions in order to increase confidence in beach cross section design. A mobile bed flume study was therefore carried out at HR Wallingford. This paper describes both the design and the results of the 2D physical model study.

Handbook of Coastal and Ocean Engineering, pp. 341-382 (2009) No AccessPrediction of OvertoppingJentsje van der Meer, Tim Pullen, William Allsop, Tom Bruce, Holger Schüttrumpf, and Andreas KortenhausJentsje van der MeerVan der Meer Consulting, P. O. Box 423, 8440 AK Heerenveen, The Netherlands, Tim PullenHR Wallingford, Howbery Park, Wallingford, Oxon, OX10 8BA, UK, William AllsopHR Wallingford, Howbery Park, Wallingford, Oxon, OX10 8BA, UK, Tom BruceSchool of Engineering, University of Edinburgh, King's Buildings, Edinburgh, EH9 3JL, UK, Holger SchüttrumpfRWTH-Aachen University, Institute of Hydraulic Engineering and Water Resources Management, Mies-van-der-Rohe-Str. 1, 52065 Aachen, Germany, and Andreas KortenhausLeichtweiss-Institute for Hydraulics, Technical University of Braunschweig, Beethovenstr, 51a, 38106 Braunschweig, Germanyhttps://doi.org/10.1142/9789812819307_0014Cited by:2 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: This chapter describes the processes of wave overtopping at sea defense and related coastal or shoreline structures. It introduces a range of methods to calculate mean overtopping discharges, individual and maximum overtopping volumes, and the proportion of waves overtopping a seawall. It describes the principal hazards from wave overtopping and will help engineers by suggesting limiting tolerable discharges for frequent, design, and extreme wave conditions. This chapter is supported by more detailed material in Chaps. 15 and 16 which focus on the methods to predict overtopping for rubble mound structures (with partly sloping embankments), and on vertical structures and battered walls. All of these three chapters have been based closely on the new EurOtop Overtopping Manual.5 FiguresReferencesRelatedDetailsCited By 2A methodological approach for the development and verification of artificial neural networks based on an application to wave–structure interaction processesSara Mizar Formentin and Barbara Zanuttigh22 August 2018 | Coastal Engineering Journal, Vol. 60, No. 3Full scale study of combined wave and surge overtopping of a levee with RCC strengthening systemLin Li, Yi Pan, Farshad Amini and Cuiping Kuang1 Nov 2012 | Ocean Engineering, Vol. 54 Handbook of Coastal and Ocean EngineeringMetrics History PDF download

This paper will explore the process of ‘suffusion’–the movement of fine material through the voids of a granular matrix with particular reference to the retention of sand-fill by a rubble bund. Guidance on suffusion has hitherto been derived for rock-fill dams, where hydraulic gradients are steep, and persist for the life of the dam. In contrast, sand protected by rubble mound bunds will experience hydraulic gradients that are much smaller, and intermittent. The paper presents a series of empirical analyses and physical model tests for an idealised defence in which detailed pressure measurements within the rubble bund were used to define representative hydraulic gradients. Test data from studies on onset of movement of fine materials reported in 1991 were then used to identify where hydraulic gradients were sufficiently reduced to avoid significant loss of sand-fill.

It is widely recognised that coastal flood events can arise from combinations of extreme waves and sea levels. For flood risk analysis and the design of coastal structures it is therefore necessary to assess the joint probability of the occurrence of these variables. Traditional methods have involved the application of joint probability contours, defined in terms of extremes of sea conditions that can, if applied without correction factors, lead to the underestimation of flood risk and under-design of coastal structures. This paper describes the application of a robust multivariate statistical model to analyse extreme offshore waves, wind and sea levels around the coast of England. The approach described here is risk based in that it seeks to define extremes of response variables directly, rather than the joint extremes of sea conditions. The output of the statistical model comprises a Monte Carlo simulation of extreme events. These distributions of extreme events have been transformed from offshore to nearshore using a statistical emulator of a wave transformation model. The resulting nearshore extreme sea condition distributions have the potential to be applied for a range of purposes. The application is demonstrated using two structures located on the south coast of England.

Quite some new insights on wave overtopping were achieved since the first submission of the EurOtop Manual in 2007, which have now resulted in a second edition of this Manual. A major improvement has been made on the understanding of wave by wave overtopping and tolerable wave overtopping that is connected to it. Many videos are available on the overtopping website that show all kind of overtopping discharges and volumes and may give guidance for the user of the Manual. The EurOtop Neural Network and the EurOtop database are improved and extended versions of the earlier NN and CLASH database. New insights and prediction formulae have been developed for very low freeboards; for very steep slopes up to vertical walls; for run-up on steep slopes; for overtopping on storm walls on a promenade; and for overtopping on vertical walls, where overtopping has been divided in situations with and without an influencing foreshore and where the first situation may be divided in non-impulsive and impulsive overtopping.

It has long been recognised that extreme coastal flooding can arise from the joint occurrence of extreme waves, winds and sea levels. The standard simplified joint probability approach used in England and Wales can result in an underestimation of flood risk unless correction factors are applied. This paper describes the application of a state-of-the-art multivariate extreme value model to offshore winds, waves and sea levels around the coast of England. The methodology overcomes the limitations of the traditional method. The output of the new statistical analysis is a Monte-Carlo (MC) simulation comprising many thousands of offshore extreme events and it is necessary to translate all of these events into overtopping rates for use as input to flood risk assessments. It is computationally impractical to transform all of these MC events from the offshore to the nearshore. Computationally efficient statistical emulators of the SWAN wave transformation model have therefore been constructed. The emulators translate the thousands of MC events offshore. Whilst the methodology has been applied for national flood risk assessment, it has the potential to be implemented for wider use, including climate change impact assessment, nearshore wave climates for detailed local assessments and coastal flood forecasting.