Samenvatting

When waves interact with surfaces of different structures they are reflected, and these reflections are mainly caused due to less wave energy being dissipated by the surface of the structure. Naturally, rock slopes or permeable structures (mangroves forests, brushwood material, etc.) are used around the world to dissipate wave energy. Generally, wave energy in hydraulic facilities is dissipated using passive absorption methods as they are economical and efficient in reducing reflections. In hydraulic basins, that are used for replicating ocean/sea waves and conditions, ARC (Active reflection compensation) is also used, however, wave dampening beach slopes are still widely popular due to the high costs of ARC devices.

The Atlantic basin, a facility in Deltares, has a beach slope consisting of large rocks in the wave dissipation zone. To improve the wave dissipation zone’s efficiency for minimizing wave reflections, certain methods consisting of several models with different configurations were investigated in a small-scale flume to find the best performing method, that improves the energy dissipation ability. Hence, the main research question reads as:

What optimizations can be made in the wave dissipation zone to enhance wave absorption and minimize wave reflection in the Atlantic Basin?
To answer this question, the current situation, geometry, and different wave energy absorption methods were examined. During the research, a few hydraulic specialists from Deltares were interviewed. In addition, the measures taken in similar hydraulic facilities around the world were investigated. Based on the gathered information, three variants were devised that would optimize wave energy dissipation by minimizing wave reflections. In the 1st variant, smaller and uniform rock sizes are used for a 1:4 rock slope. In the 2nd variant, a parabolic damper slope is used and lastly, in the 3rd variant, a 10cm layer of the permeable mattress is placed over a 1:4 rock slope.

Experiments were conducted in the 7-meter long wave flume inside the Pacific basin, located at the hydro-hall in Deltares, Delft. Various tests were concluded for two different water depths, and several different wave conditions, to analyse and examine the variants based on reflection performance. The winning variant is a decision based on an assessment using an evaluation matrix, for which the criterion are performance, cost-efficiency, and viability. With the help of these criteria, it was concluded that in given boundary conditions and limitations, variant 3 is an effective solution for enhancing wave absorption and minimizing wave reflection in the Atlantic Basin.

Possible future research could be to analyse the effect of different rock sizes on permeability and wave reflections and to examine milder slopes in a longer flume.