Velocity and water-layer thickness of overtopping flows on sea dikes: Report of measurements and formulas development
The study aims to establish a set of formulas estimating velocity and depth of overtopping flows at sea dikes including seaward-side slope, crest and landward-side slope. These formulas are applicable to flows which are generated by natural waves and the simulator giving associated characteristics of any arbitrary value of exceedance probability. Note that the probability is based on the total number of incident waves and not to be confused with the total number of overtopping events. The difference between the fictitious wave run-up level and the crest level (Ru2% - Rc) is widely considered as a measure of the (potential) energy of wave overtopping. This term is therefore used to estimate values of the mean overtopping discharges, ow velocities, water-layer thickness and overtopping volumes. In line with many existing research works and guidelines, the potential term is crucial to derive other parameters. Experimental data of Van Gent [2002] is reanalyzed with a slightly different perspective to achieve the study objective. The analysis procedure basically consists of three main steps:  from wave conditions and dike cross-section to calculate wave run-up levels;  from wave run-up levels to estimate flow parameters on the dike crest;  from flow parameters on the dike crest to further compute the corresponding parameters on the landward slope. The obtained equations are verified with flow measurements of the simulator on real dike slopes. Consequently, feasible values representing the roughness of different grass coverings are determined.
Destructive tests with the wave overtopping simulator
Report on destructive overtopping tests executed with the wave overtopping simulator along the coast of Vietnam to investigate the strength of the inner slopes of grass dikes. This report presents measurement and observation results obtained during destructive tests with the simulator in Do Son, Thinh Long and Thai Thuy. After the first chapter, Chapeter 2 discribes all test sections in detail and test scenario. The method and results of hydraulic measurements are presented in Chapter 3. Chapter 4 and Chapter 5 introduce the slope profiles and photograph of grass slopes. The formation and development of the damages induced by wave overtopping are discussed in Chapter 6. Chapter 7 deals with the resistance against wave overtopping and critical velocity of different grass covered slopes which were tested with the simulator. Finally, Chapter 8 are conclusions and future research, respectively. Detail of hydraulic measurement performed at three sea dikes are given in Appendix A. Data of the slope profiles measured at Thinh Long and Thai Thuy are presented in Appendix B. Appendix C contents of the photograph of the damages on the slope sections at Thinh Long and Thai Thuy sea dike. Characteristics of soil and grass taken at test sections are given in Appendix D. Appendix E summarises brief specifications of all test sections.
Layer thicknesses and velocities of wave overtopping flow at seadikes
Abstract Seadikes often fail due to wave overtopping and a failure of the landward slope. Therefore, these aspects have to be taken into account for the design of seadikes. In present design, the calculation of the crest height of seadikes is essentially based on using a design water level and the corresponding wave run-up height. An average overtopping rate is generally considered for wave overtopping which can not account for the stresses and other effects due to extreme individual overtopping events. Landward slope design is more or less based on experience. It can be concluded from failure analysis that dike failures on the landward slope are rather initiated by individual overtopping events, in particular by the related overtopping flow velocities and layer thicknesses which are relevant for the prediction of erosion, infiltration and slip failure. Therefore, overtopping flow velocities and layer thicknesses are required in addition to average overtopping rates as hydraulic boundary conditions for the geotechnical stability analysis of seadikes. The objective of the present paper is the theoretical and experimental determination of overtopping flow velocities and layer thicknesses on the seaward slope, the dike crest and the landward slope of a seadike. Overtopping parameters are derived on the basis of small scale model tests which are required for the design of the landward slope and to avoid dike failures by wave overtopping in the future. For the prediction of the layer thicknesses and the velocities of the overtopping flow on the seaward slope, the dike crest and the landward slope, a set of theoretical formulas is derived and validated by hydraulic scale model tests.