Do wooden pile breakwaters work for community-based coastal protection?

Abstract

In developing countries, coastal protection with wooden piles may be a low-cost and eco-friendly countermeasure option that can be readily implemented by local communities or even individuals. However, the effectiveness of these piles in a realistic environment has yet to be scientifically proven, and there have been no established design guidelines for this type of improvised coastal protection to date. This study focuses on Phan Thiet City, Vietnam, where local people are resorting to wooden piles to mitigate severe coastal erosion immediately in front of their houses. A 3D hydrodynamic modelling with irregular waves is applied to evaluate complex wave mechanisms and hydrodynamics around and between wooden piles. The complicated interaction mechanisms between incident and reflected waves cannot be adequately evaluated using a common 2D numerical model or mathematical analysis, demonstrating the benefit of using a 3D hydrodynamic model. The performance of wooden piles are simply assessed using two criteria: wave run-up and bending stress. The result shows that wooden piles installed at a severely eroded beach in Vietnam can reduce wave run-up on the beach slope to some extent. The reduction in wave run-up occurs because of the creation of turbulence and oscillation triggered by the partial reflection of waves on the piles, diverting water flows into various directions. A case study shows that wave pressure in the seaward direction is about a half of that in the shoreward direction. However, the pressure in the negative direction can be instantaneously increased due to a significant reflection from a steep shore. This paper discusses whether such a state-of-the art computational fluid dynamics model can contribute to the assessment of wooden pile breakwaters.