EurOCEAN 2000 - Vlaams Instituut voor de Zee

Conference among others, and will be discussed in the coming ICCE 2000 Sydney Conference,
and in an end-users conference “Presentation of Research Results in Coastal Engineering,
Scour Around Marine Structures, and Morphodynamics Around Coastal Structures” in Paris 3-
4. October, 2000 (e-mail to hildur@isva.dtu.dk for information on this latter conference).
The project is organized in two main tasks: Task 1. Flow and scour processes, and Task 2.
Sediment behaviour close to the structure and scour.
FLOW AND SCOUR PROCESSES (TASK 1)
The work in Task 1, led by HR, concentrates on the interaction between the water flow and the
sediment at the toe of the structure. The work is sub-divided into four topics:
TOPIC 1.1. FLOW AND SCOUR PROCESSES AROUND VERTICAL CYLINDERS.
The data on scour around vertical cylinders - slender piles, pile groups and large diameter
cylinders - has been obtained in wave flumes and wave basins. Test conditions have covered
the cases for waves alone, including non-linear shallow water waves and breaking waves, as
well as waves and currents. The work on scour around pile groups has been published Sumer
and Fredsøe (1998) and Mory et al (1999). Additional test results were obtained for the scour
and settlement of a single pile into the sand bed. A 3D numerical model for bed scour around a
slender pile has been devised (Roulund et al, 1998).
TOPIC 1.2. SCOUR AT RUBBLE MOUND BREAKWATER. Experimental results for
the scour development at the toe of a rubble mound breakwater (RMB) have been published
(Sumer et al, 2000). This work investigated the scour development at the trunk section of a
breakwater and the efficiency of scour protection measures. The results have been extended to
the 3D case through test data for scour development around a shore-parallel RMB. The data
was collected in a large 3D wave basin. A total of 5 tests investigated the time development of
scour and the equilibrium morphology around the breakwater for normal and oblique incidence
waves and with a tidal current. Scour protection measures were tested and the influence of
storm (breaking) waves was simulated. The first results have been published (Sutherland et al,
1999a) and a data report written (Sutherland et al, 1999b). Measurements of the pore pressure
field in the bed at a number of locations during the 3D tests will enhance the link with Task 2
of the project.
TOPIC 1.3. SCOUR AROUND SUBMERGED BREAKWATERS. The large-scale 2D
wave flume experiments on scour development at the toe of submerged breakwaters is
underway. The tests show the extent of scour development under different wave conditions
and varying levels of freeboard. Scour protection measures will be tested. In parallel,
mathematical modelling of the wave hydrodynamics and morphodynamics around the
submerged breakwater has been completed. These results are used in conjunction with some
earlier test results to determine both the hydraulic performance of the structure and the seabed
scour. Early results have already been published (Gironella and Sanchez-Arcilla, 1999).
TOPIC 1.4. THE EFFECT OF TURBULENCE ON SEDIMENT TRANSPORT. The
turbulence levels in the vicinity of coastal structures can be high and the flow field non-steady
and non-uniform. The influence of an external (grid) turbulence field on the bed shear stress
and sediment transport has been measured in steady flow flume experiments. The sediment
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