Tim Pullen

Violent Wave Overtopping: CLASH Field Measurements at Samphire Hoe

As part of a major European research project into wave overtopping at coastal structures, overtopping discharges have been measured at full-scale on a vertical seawall in Southern England. The measurement site, Samphire Hoe, is an area of reclaimed land just west of Dover on the English channel coast, and is an ideal location for monitoring overtopping. The site is described in detail and the design and operation of the measurement equipment are also outlined in the paper. Overtopping was measured on three occasions and the storms and their results are discussed. It is shown that the field measurements compare will with empirical prediction methods. Additional discussion interprets the hazardous nature of each of the storms.

Use of field measurements to improve probabilistic wave overtopping forecasts

The paper investigates the practicalities and potential value of coupling offshore to nearshorewave models, and nearshore-wave and surge models to coastline overtopping models and floodrisk indicators. The available coupled models include Ensemble surge models, offshore wave models, hydrodynamic wave transformation models and empirical wave overtopping formulae. The uncertainty associated with an individual model output, and the propagation of this incertainty forward through the modelling chain is handled through Monte Carlo simulation from either discrete or continuous probability distributions, based on the information available on each of the variables involved. The paper will concentrate on the collection and analysis of measured overtopping discharges at a site in North-west England. At the same site inshore wave measurements will be recorded for selected high tide events. The results from these field measurements will be used to calibrate and refine the Monte Carlo simulations.

Jet velocities of overtopping waves on sloping structures: measurements and computation

Current empirical methods often predict inadequately the overtopping discharges of waves on shallow sloping seawalls. As part of the DEFRA / EA funded research project FD2410, Coastal Flooding Hazard by Wave Overtopping, physical model studies have been undertaken for structure configurations of 1:2, 1:10 and 1:15. For 1:10 and 1:15 sloping structures, no data or method is currently available for predicting accurately the overtopping discharge. Although discharge quantities are widely used for analysing the hazard of overtopping, this may not be the best way of defining a violent overtopping event. Discharge velocities may also be of key importance and it is these velocities that are reviewed here for overtopping of waves on sloping structures. Two numerical non-linear shallow water models have also been used for comparison against the physical results to see whether they can be implemented as a valid prediction tool.

The Uncertainty in the Prediction of the Distribution of Individual Wave Overtopping Volumes Using a Nonlinear Shallow Water Equation Solver

ABSTRACT Williams, H.E.; Briganti, R.; Pullen, T., and Dodd, N., 2016. The uncertainty in the prediction of the distribution of individual wave overtopping volumes using a nonlinear shallow water equation solver. This work analyses the uncertainty of the prediction of individual overtopping volumes using the nonlinear shallow water equations. A numerical model is used to analyse the variability from seeding. The effect of the incident wave height distribution on the distribution of individual overtopping volume is also considered. The numerical results are then compared with both the laboratory tests and available empirical methods. A large variability was found across the distributions, which produced some results showing significant diversion from the empirical prediction methods. The magnitude of that departure was directly related to the accuracy of the numerical model in reproducing the incident wave height distribution at the toe of the structure in the physical model.

WAVE OVERTOPPING AT VERTICAL SEAWALLS: FIELD AND LABORATORY MEASUREMENTS OF SPATIAL DISTRIBUTIONS

Guidance on levels of safe overtopping discharge that can be tolerated by members of the public are often based on arbitrarily set values with little validation. Generally these values will indicate a mean discharge, but will not take into account how the overtopping is distributed across the seawall. This paper presents guidance for the design of vertical or steeply battered seawalls, that describes how the discharges are distributed spatially. Recent field and laboratory measurements of violent overtopping during storms at Samphire Hoe, Kent, UK, have been conducted as part of the EU 5th framework and Defra / EA funded CLASH project. Accurate measurements of individual wave-by-wave volumes have provided new data on how overtopping discharges are distributed under different conditions. The results show a good generic agreement between the field and laboratory measurements, and the paper provides a method for determining the distributions.

Hazards Resulting from Wave Overtopping--Full Scale Measurements

The objective of this paper is to describe the recently installed full scale measurement infrastructure to quantify hazards resulting from wave overtopping at the Zeebrugge rubble mound breakwater. First, the measurement site and the specific set-up used for wave overtopping measurements is briefly described in section 2. Section 3 contains the description and design of the instrumentation to quantify hazards and finally in section 4 preliminary conclusions are drawn.

Overtopping of Seawalls under Oblique and 3-D Wave Conditions

The majority of prediction methods for overtopping of seawalls are based on physical model tests under simple 2-dimensional conditions. There is some evidence (not unambiguous) that overtopping may increase at small degrees of obliquity, and that corners (in plan) may give local concentrations of overtopping. This paper, produced as part of the VOWS project on impulsive (violent) overtopping of vertical seawalls, describes experiments to measure mean and wave-by-wave overtopping discharge under conditions of oblique wave attack and at 3-d corners. Results analysed in the first phase of this 3-d study suggest that mean overtopping discharges reduce significantly with increasing angle of wave attack and that the occurrence of impulsive overtopping diminishes rapidly with obliquity of wave attack > 30°. It is also observed that overtopping may not increase in corners with an approach beach or berm.

Wave Overtopping at Vertical and Steep Structures

Wave overtopping prediction at vertical structures in earlier days was mainly based on caisson-type structures in relatively deep water. Recent research in many EU-projects has been concentrated on shallower water with waves breaking onto the structure as well. It has led to the definition of two situations: nonimpulsive and the most severe impulsive condition. This chapter relies on the EurOtop Overtopping Manual, as well as the two previous chapters, 14 and 15, in this handbook. It first describes the mean overtopping discharges for many configurations of vertical and composite vertical structures. Later sections quantify influences such as oblique wave attack, wind effects, model, scale effects, etc.