Narrow Results

Designers of vertical seawalls and breakwaters have often included some form of seaward overhang (recurve / parapet / wave return wall / bullnose) as part of the structure with the design motivation of reducing wave overtopping by deflecting back seaward uprushing water. Despite a lengthy track record in the field and relevance to current design issues, very little generic guidance is available for their incorporation into seawall / breakwater design. This paper reports a study whose aim is the formulation of generic guidance for recurve structure design. Particular attention is given to high freeboard and / or wave breaking conditions under which the recurve / parapet gives very large reductions (recurve k-factor < 0.05). The paper presents tentative guidance in the form of a decision chart. Finally, overtopping and loading results from a case study into a wall of particularly complex geometry are presented and compared with earlier studies. Forces on the vertical wall are found to be highly impulsive in nature and approximately double the magnitude of those expected on a simple wall, with additional forces of a similar magnitude measured on the underside of the parapet.

In this paper, the influence of changes on the slope, foreshore and position of armour units on overtopping discharges based on small scale model tests is analyzed. The Zeebrugge breakwater (Belgium) was tested in the Universidad Politécnica de Valencia (UPVLC) and the Leichtweiss-Institut (LWI) of the Technischen Universität Braunschweig. A 2-D model of the Zeebrugge breakwater was modelled at a 1:30 scale in the wind and wave test facility of the UPVLC. The influence of spatial variability and foreshore was studied by varying the model conditions from a standard situation which can be accurately reproduced in terms of overtopping discharges. The experiments and the corresponding model conditions are also described herein.

Within two European projects – FLOODsite and COMRISK – detailed risk analyses have been applied to two case studies to test new methods developed within these projects and to identify gaps in present knowledge. For both case studies, the risk analysis has been performed in two major steps comprising (i) a hazard analysis and (ii) a vulnerability analysis. This paper presents the results of both studies, discusses the practicability of risk analysis applications as a common tool and pinpoints the demand for further investigations.

The performance of laboratory experiments is one of the most appropriate methods to investigate beach profile development under storm surge conditions. However, physical models are subjected to scale and laboratory effects. Scale effects can be eliminated in large scale research facilities if both the profile form and sediment characteristics are reproduced in a near prototype scale. Regarding the assessment of laboratory effects on the beach profile evolution in two-dimensional wave flumes and the quantitative transfer-ability of experimental results to natural conditions, there is still some controversy. In order to be able to make statements on the magnitude of laboratory effects, experimental data from large wave flumes are analysed and compared with field data. The results of data analyses and additional numerical computations show that the development of natural beaches during storm surges can principally be reproduced correctly in large scale two-dimensional experiments. Only after changing the beach profile layout or water level and wave conditions, relocations of sand from the side walls to the centre of the flume, which are not encountered under prototype conditions, are observed.

A model system for the simulation of the breaching process induced by wave overtopping and optionally combined wave overtopping and overflow, has been developed and herein described. The model system is made of a preliminary model and a detailed model. These models have been using to simulate the breach formation and growth in a real coastal dike, including the effects of waves and grass protection. Details of the preliminary model are given together with discussion on input parameters, model uncertainties and first results. Further improvements to be achieved in the detailed model are also briefly addressed.

A tiered modeling approach for the prediction of dike breaching initiated by breaking wave impact on the seaward slope is being developed, including a preliminary and a detailed model. This paper addresses the preliminary model that will provide an overall first picture of the breach development and reveal the critical issues, before embarking into the detailed modeling. The model is based on a semi-empirical approach for the calculation of hydrodynamic forces on the dike slope and applies the wave impact theory and empirical erosion coefficients for grass and clay for the prediction of breach initiation and formation.

The International Organization for Standardization (ISO) is going to issue a new standard concerning “Actions from Waves and Currents on Coastal Structures,” which becomes the first international standard in coastal engineering. It is composed of a normative part (29 pages), an informative part (80 pages) and Bibliography (17 pages). The normative part describes what is considered as the norm of the matters in concern, while the informative part provides the information on recommended practice. The paper introduces the main points of the normative part and discusses the influence of the new standard on coastal engineering practice.

Input parameters and models (in the form of limit state equations) in coastal engineering are influenced by uncertainties. In many cases, it is not possible to avoid or to determine model uncertainties, inherent uncertainties and human errors exactly. Hence a questionnaire was set-up to ask experts in coastal engineering to estimate uncertainties required for the design of coastal structures. Results of this expert judgement are discussed in the present paper. Estimated uncertainties of key input parameters show a dependency of the professional background, the professional experience and the professional age of the experts asked.

A detailed analysis of failure modes for seadikes has been performed and was used to derive a complete set of limit state equations for the description of failure scenarios of seadikes. These models and scenarios were then used to calculate the respective failure probabilities and the overall failure probability by a fault tree approach. A simple example of a non-existing seadike was used to illustrate the procedure. Details of parameters, model uncertainties and their influences on the results as well as further information required for the aforementioned procedure are also discussed.

A conceptual framework based on probabilistic risk analysis (PRA) is proposed for the design of coastal flood defences which meets the sustainability requirements. The overall framework includes the management of the remaining risk as an integral part of the design process. The implementation of the risk analysis requires (i) the prediction of the flood risk, (ii) the evaluation of the acceptable flood risk and (iii) the evaluation of the flood risk level which is obtained through comparison of the predicted and acceptable flood risk.

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

Wave overtopping and to a lesser extent wave run-up for armored rubble slopes and mounds have been subject to a number of investigations in the past. The objective of the present chapter is to summarize existing information to be present as a closed guidance on the use of wave run-up and wave overtopping formulae for a wide range of possible applications in practice. Therefore, guidance is given first on the use of wave run-up and wave overtopping formulae for simple slopes, excluding the effects of composite slopes, direction of wave attack, roughness, wave walls, etc. Then, formulae are presented to include these parameters in the calculation procedure. Guidance is also given on wave overtopping volumes, overtopping velocities, and the spatial distribution as well as for wave overtopping for shingle beaches. Finally, the effect of model and scale effects on the calculation of average overtopping rates are discussed. This chapter has mainly been composed from Chap. 6 of the EurOtop Overtopping Manual (2007), with some additions from Chap. 5. The present chapter is related to the previous Chap. 14 and the next Chap. 16 of this manual.

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.

Wave overtopping and to a lesser extent wave run-up for armored rubble slopes and mounds have been subject to a number of investigations in the past. The objective of the present chapter is to summarize existing information to be present as a closed guidance on the use of wave run-up and wave overtopping formulae for a wide range of possible applications in practice. Therefore, guidance is given first on the use of wave run-up and wave overtopping formulae for simple slopes, excluding the effects of composite slopes, direction of wave attack, roughness, wave walls, etc. Then, formulae are presented to include these parameters in the calculation procedure. Guidance is also given on wave overtopping volumes, overtopping velocities, and the spatial distribution as well as for wave overtopping for shingle beaches. Finally, the effect of model and scale effects on the calculation of average overtopping rates are discussed. This chapter has mainly been composed from Chap. 6 of the EurOtop Overtopping Manual (2007), with some additions from Chap. 5. The present chapter is related to the previous Chap. 14 and the next Chap. 16 of this manual.

Coastal flood disasters due to storm surges generally occur as a result of dike breaching. The latter may be initiated either from the landward side by wave overtopping and overflow or from the seaward side by breaking wave impact, including wave up and down rush induced flow on the outer slope. A reliable prediction of the breach initiation, widening and deepening is essential to properly assess the initial conditions for the computation of the flood wave propagation and thus the warning time. In this paper, the detailed computer model for the simulation of a breach initiated from the seaward slope by wave impact is addressed.

This paper presents selected results of small scale model tests performed to determine the mean overtopping rates on the historical sea wall of Baltrum, an Island in the German North Sea. The oldest parts of the coastal defence system of Baltrum can be retraced to the end of the 19^th century. The present situation is characterized by two complex cross sections comprising berms and wave walls. The necessity for model tests, the model test setup, the test programme and the resulting overtopping rates are discussed.

The 'Crest Drainage Dike' (CDD) is an innovative crest design for sea dikes to reduce wave overtopping discharge on the inner side of the dikes by installing an "Overtopping Buffer Basin" on the crest, where parts of the overtopping water are captured and discharged either to the shoreward side or seaward side in a controlled manner. This paper focuses on the feasibility of using the CDD concept, proposes an alternative recurve wave wall design with or without a buffer basin and the combination of both CCD and the recurve wave wall concepts to enhance the safety of the existing sea dikes based on the results of two dimensional physical model tests.

The paper attempts to discuss the most important gaps in the scientific knowledge and modelling encountered in the practical implementation of an integrated framework for risk-based design and management of coastal flood defences. Previous research gaps (Oumeraci, 2004) were rediscussed from the 2008 perspective, i.e. shortly before the completion of the EU FLOODsite project. Therefore, the paper primarily aims at focusing on some of the key achievements in FLOODsite and other related research projects, followed by the perspective of the scientific and modelling challenges for the practical implementation of flood risk analysis and management frameworks. It also discusses requirements from political levels such as the European Flood Directive and further needs formulated by other groups. Finally, these points are brought together and remaining gaps and research needs as well as a possible way ahead for flood risk analysis and management has been sketched.

Dike breaching is a main cause of coastal flooding and associated disastrous damages, but reliable and process-oriented models for dike breaching induced by wave overtopping are still not available. A model system, i.e. a combined preliminary and detailed model, as a first step toward a fully process-oriented description of dike breaching, has been developed. The preliminary model provides qualitatively correct results. The detailed model builds the basis for a full simulation of dike breaching removing assumptions and including new processes. Model uncertainties are quantified through sensitivity and reliability analysis. A tentative validation of the model system with available laboratory data and experienced prototype dike failures shows very encouraging results.