The Reduction of Wave Overtopping by Means of a Storm Wall (original) (raw)

EurOtop wave overtopping of sea defences and related structures: assessment manual

2007

P r e f a c e Why is this Manual needed? This Overtopping Manual gives guidance on analysis and/or prediction of wave overtopping for flood defences attacked by wave action. It is primarily, but not exclusively, intended to assist government, agencies, businesses and specialist advisors & consultants concerned with reducing flood risk. Methods and guidance described in the manual may also be helpful to designers or operators of breakwaters, reclamations, or inland lakes or reservoirs. Developments close to the shoreline (coastal, estuarial or lakefront) may be exposed to significant flood risk yet are often highly valued. Flood risks are anticipated to increase in the future driven by projected increases of sea levels, more intense rainfall, and stronger wind speeds. Levels of flood protection for housing, businesses or infrastructure are inherently variable. In the Netherlands, where two-thirds of the country is below storm surge level, large rural areas may presently (2007) be defended to a return period of 1:10,000 years, with less densely populated areas protected to 1:4,000 years. In the UK, where low-lying areas are much smaller, new residential developments are required to be defended to 1:200 year return. Understanding future changes in flood risk from waves overtopping seawalls or other structures is a key requirement for effective management of coastal defences. Occurrences of economic damage or loss of life due to the hazardous nature of wave overtopping are more likely, and coastal managers and users are more aware of health and safety risks. Seawalls range from simple earth banks through to vertical concrete walls and more complex composite structures. Each of these require different methods to assess overtopping. Reduction of overtopping risk is therefore a key requirement for the design, management and adaptation of coastal structures, particularly as existing coastal infrastructure is assessed for future conditions. There are also needs to warn or safeguard individuals potentially to overtopping waves on coastal defences or seaside promenades, particularly as recent deaths in the UK suggest significant lack of awareness of potential dangers. Guidance on wave run-up and overtopping have been provided by previous manuals in UK, Netherlands and Germany including the EA Overtopping Manual edited by Besley (1999); the TAW Technical Report on Wave run up and wave overtopping at dikes by van der Meer (2002); and the German Die Küste EAK (2002). Significant new information has now been obtained from the EC CLASH project collecting data from several nations, and further advances from national research projects. This Manual takes account of this new information and advances in current practice. In so doing, this manual will extend and/or revise advice on wave overtopping predictions given in the CIRIA/CUR Rock Manual, the Revetment Manual by McConnell (1998), British Standard BS6349, the US Coastal Engineering Manual, and ISO TC98. The Manual and Calculation Tool The Overtopping Manual incorporates new techniques to predict wave overtopping at seawalls, flood embankments, breakwaters and other shoreline structures. The manual includes case studies and example calculations. The manual has been intended to assist coastal engineers analyse overtopping performance of most types of sea defence found around Europe. The methods in the manual can be used for current performance assessments and for longer-term design calculations. The manual defines types of structure, provides definitions for parameters, and gives guidance on how results should be interpreted. A chapter on hazards gives guidance on tolerable discharges and overtopping processes. Further discussion identifies the different methods available for assessing overtopping, such as empirical, physical and numerical techniques. In parallel with this manual, an online Calculation Tool has been developed to assist the user through a series of steps to establish overtopping predictions for: embankments and dikes; rubble mound structures; and vertical structures. By selecting an indicative structure type and key structural features, and by adding the dimensions of the geometric and hydraulic parameters, the mean overtopping discharge will be calculated. Where possible additional results for overtopping volumes, flow velocities and depths, and other pertinent results will be given. Intended use The manual has been intended to assist engineers who are already aware of the general principles and methods of coastal engineering. The manual uses methods and data from research studies around Europe and overseas so readers are expected to be familiar with wave and response parameters and the use of empirical equations for prediction. Users may be concerned with existing defences, or considering possible rehabilitation or new-build. This manual is not, however, intended to cover many other aspects of the analysis, design, construction or management of sea defences for which other manuals and methods already exist, see for example the CIRIA/CUR/CETMEF Rock Manual (2007), the Beach Management Manual by BRAMPTON et al. (2002) and TAW guidelines in the Netherlands on design of sea, river and lake dikes. What next? It is clear that increased attention to flood risk reduction, and to wave overtopping in particular, have increased interest and research in this area. This Manual is, therefore, not expected to be the 'last word' on the subject, indeed even whilst preparing this version, it was expected that there will be later revisions. At the time of writing this preface (August 2007), we anticipate that there may be sufficient new research results available to justify a further small revision of the Manual in the summer or autumn of 2008.

Wave overtopping of sea defences and related structures: assessment manual

This Overtopping Manual gives guidance on analysis and/or prediction of wave overtopping for flood defences attacked by wave action. It is primarily, but not exclusively, intended to assist government, agencies, businesses and specialist advisors & consultants concerned with reducing flood risk. Methods and guidance described in the manual may also be helpful to designers or operators of breakwaters, reclamations, or inland lakes or reservoirs Developments close to the shoreline (coastal, estuarial or lakefront) may be exposed to significant flood risk yet are often highly valued. Flood risks are anticipated to increase in the future driven by projected increases of sea levels, more intense rainfall, and stronger wind speeds. Levels of flood protection for housing, businesses or infrastructure are inherently variable. In the Netherlands, where two-thirds of the country is below storm surge level, large rural areas may presently (2007) be defended to a return period of 1:10,000 years, with less densely populated areas protected to 1:4,000 years. In the UK, where low-lying areas are much smaller, new residential developments are required to be defended to 1:200 year return.

Field Tests on Sea Defences Subject to Wave Overtopping

Coastal Structures 2007 - Proceedings of the 5th Coastal Structures International Conference, CST07, 2009

As a response to ongoing sea level rise, crest levels of sea defences need to be raised in future at huge expenditure and with increased risk. As an alternative, dikes can be strengthened as to accommodate for increased wave overtopping. Within the ComCoast program (a European project between governments along the North Sea for innovative solutions for the safety of sea defences) research has been done on overtopping-resistant sea defences and ideas for different types of reinforcements have been generated. A concept with a specific geosynthetic that reinforces the crest and inner slope of the dikes was awarded for installation at a sea dike in the Netherlands in 2006. The actual field tests took place early 2007. These tests are unique in their kind as they have been carried out on a real dike under full scale wave overtopping conditions, far beyond present standards. As a result, the erosive impact of wave overtopping on the natural grass covered dike section, on the reinforcement section, as well as on a bare clay layer section, has been investigated under representative wave overtopping conditions. This paper describes the results of these field tests, i.e. the strength response of the dike slopes and indicates the follow-up and potentials of the results obtained thus far.

Van Doorslaer et al. REDUCTION OF WAVE OVERTOPPING: FROM RESEARCH TO PRACTICE

The present paper shows the purpose, the test results and the practical implementation of two innovative crest designs, based on scale model test with mainly non-breaking waves. First, the parapet and its geometrical parameters are shown. Second, the reduction of a dike with stilling wave basin is presented. Both crest designs will be built along the Belgian coast in order to fulfill current and anticipate future safety norms. Alternatives and/or performance are discussed within the present paper. INTRODUCTION To ensure the safety in Belgian coastal regions now and in the future (up to 2050, including the sea level rise) a Coastal Safety Plan 3 is being worked out, in which is declared that cities near the coastline have to be protected against storms with a return period of 1000 year (which is a minimal acceptable protection level). If this storm would appear now, theoretical and physical models have shown that the safety of one third of the Belgian coastal zone is insufficient. Su...

Investigating the Effect of Wind and Current on Wave Run-Up and Wave Overtopping

2009

This study describes the experimental work and preliminary results of investigations made on the effects of wind and currents on wave run-up and wave overtopping. The tests were carried out in the shallow water wave basin at the DHI (Hørsholm / Denmark). A detailed description of the set-up and measurements will be given followed by a parametric and a regression analysis which aims at the development of reduction factors for wind, current and obliquity. This is done with respect to the existent design formulae in the Eurotop-Manual (2007) and the results are discussed with regard to former investigations. INTRODUCTION In the past, a variety of structures was built to protect the hinterland during high water levels from coastal flooding or river flooding. Common use in practice is the application of smooth sloped dikes as well as steep or vertical walls. Today the knowledge of the design water level, wind surge, wave runup and/or wave 1 Institute for Hydraulic Engineering and Water R...

Wave Runup and Overtopping at Seawalls Built on Land and in Very Shallow Water

Journal of Waterway, Port, Coastal, and Ocean Engineering, 2013

The current study proposes prediction formulas both for random wave runup and mean overtopping discharge at seawalls constructed on land or in very shallow water. Although several existing formulas for runup and overtopping use the incident wave characteristics at the toes of seawalls, this study adopts the equivalent deepwater wave characteristics and an imaginary seawall slope for easy application of the formulas, especially in relation to seawalls constructed on land. The prediction formulas for overtopping use the predicted runup values. For the wave runup prediction formulas two sets of experimental data are used; i.e., a new set of data and the data obtained in a previous study. For the wave overtopping prediction formulas, the experimental data measured in a previous study are used. Comparisons with measurements show good performances of both new prediction methods.

Wave overtopping and overflow hazards: application on the Camargue sea-dike

2021

Dike breaches occurs regularly during storm events. This phenomenon contributes to amplify considerably the impact of floods on coastal areas. It represents an important cost for repairing existing infrastructures in the vicinity of the seadike. Then, they must be upgraded to prevent breaches. In the present study, ANEMOC and REFMAR dataset were analysed, off Camargue coasts, to quantify the storm hazards in terms of wave height and sea level wind setup. Repartition laws were adjusted on dataset to build a 2D-copula which is used to estimate events return periods. As we were interested in the physical parameters around the seadike, waves were propagated from the deep water by using TOMAWAC module which takes into account the actual bathymetry. As a first approximation, only a 1D propagation was considered. From estimated local parameters, overtopping formula were used to estimate the overtopping discharge, the crest velocity, and the water level over the sea-dike. These latter were used to assess a potential erosion on the dike rear-side. A set of several wave heights-sea-level wind setup couple were tested and each of them were relied to a probability of occurrence given by the 2D-copule. I.

Effectiveness of Recurve Walls in Reducing Wave Overtopping on Seawalls and Breakwaters

Coastal Engineering 2004 - Proceedings of the 29th International Conference, 2005

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.