EurOCEAN 2000 - Vlaams Instituut voor de Zee

THE OPTIMISATION OF CREST LEVEL DESIGN OF SLOPING
COASTAL STRUCTURES THROUGH PROTOTYPE MONITORING
AND MODELLING
OPTICREST
DE ROUCK Julien 1 , TROCH Peter 1 , VAN DE WALLE Björn 1 , VAN DAMME Luc 2 , BAL
Jan 2
1 Ghent University, Ghent, Belgium; 2 Ministry of the Flemish Community, Coastal Division,
Ostend, Belgium
INTRODUCTION
Sloping coastal structures such as seawalls, breakwaters, sea dikes,… are essential in coastal
protection and harbour sheltering. Although many research has already been carried out, some
aspects of their design still remain unsolved. Actually, crest level design is based on laboratory
scale models solely. In the MAST II-project ‘Full scale dynamic load monitoring of rubble
mound breakwaters’ (MAS2-CT92-0023) it was stated that wave run-up is underestimated by
small scale experiments. Prototype measurements carried out in this project confirm this
conclusion. As overtopping and spray are closely related to run-up, it is expected that prototype
data analysis results from overtopping and spray measurements may deviate from laboratory
experiment results.
The main objectives of the OPTICREST-project are
• to provide end users with improved design rules for the crest level of sloping coastal
structures, based on full scale data and supported by model tests
• to verify and to calibrate scale models and to obtain better scale modelling techniques
• to calibrate numerical models with full scale data in order to improve the numerical schemes
for the simulation of wave interaction with sloping coastal structures
• to upgrade, improve and optimise existing run-up monitoring devices and software
Major emphasis is put on the collection of prototype data on run-up, overtopping and spray.
PROTOTYPE MEASUREMENTS
Prototype measurements are carried out at two different sites. At the northern part of the west
outer harbour of Zeebrugge (Belgium) a rubble mound breakwater (armour layer consisting of
25 ton grooved cubes) is fully instrumented. In Petten (the Netherlands) run-up data is
collected on an impermeable smooth sea dike.
In Zeebrugge a measurement jetty has been constructed. Fig. 1 shows a cross section of the
Zeebrugge breakwater. The wave climate in front of the structure is recorded by two wave rider
buoys which are located at a distance of 150 m and 215 m from the breakwater slope.
Wave run-up is detected simultaneously by a spiderweb system and by run-up gauges. The
spiderweb system consists of a set of vertically placed stepgauges between the measurement
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