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Experimental Investigation on the Efficiency of Porous Media Such as Brushwood Fences on Damping of Waves

Author(s): Selim M. Sayah; Jean-Louis Boillat; Anton J. Schleiss

Linked Author(s): Anton J. Schleiss

Keywords: Shore protection; Wave transmission; Wave damping; Brushwood fences

Abstract: Adequate scientific basis for the design of soft measures such as brushwood fences used in shallow coastal zones are still lacking. Thus, protections often do not provide efficient results, like stopping shoreline from moving backward, or substantially damping waves during major wind events or high water levels. By means of experimental modelling, the main goal of the research was therefore to study the interactions of a selected soft shore protection measure (i. e. brushwood fences) with the incident waves and evaluate its effect on wave damping. It is measured by the transmission coefficient of the structure. Its response regarding the transmission coefficient has been evaluated using five dimensionless variables: the relative freeboard of the structure, its relative height, the relative wave number, the wave steepness, and finally the porosity of the structure. It was proven that the response of the structure is different in relation to its immersion condition. Its efficiency decreases rapidly when the structure is totally submerged. The relative freeboard, the wave steepness and the porosity play a major role in the response of the structure regarding wave damping. The effect of the relative height and the wave number is not significant and can be disregarded. The effect of the relative freeboard and the porosity of the structure on the transmission coefficient are nonlinear while the effect of the wave steepness could be considered as linear. This parametric investigation approach provided a better understanding of the behaviour of the brushwood fences and, as a result, helped to establish technical recommendations for their design.


Year: 2007

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