Designing bamboo wave attenuators for mangrove plantations

Abstract

The design of a cost-effective method for attenuating wave energy to protect coastal mangrove plantations is examined. The design makes use of bamboo, a material that is strong, environment-friendly, and widely available and cheap in most developing countries. It is suggested that bamboo poles are pushed into the sediment offshore from the coastal mangrove plantation, presumably unconsolidated mud. In order to determine the performance in reducing incident wave energy, a numerical model was developed that is capable of predicting wave attenuation due to isolated cylinders of various spatial densities, i.e. number of bamboo per m², and various diameters. A design in which an 8 cm bamboo diameter arranged within a density of 1 bamboo per m² to 4 bamboos/m² is shown to be the most economical way of attenuating 50% of incident wave energy, costing as low as US$ 22.5 per 1m length of coastal protection. This is significantly lower than conventional breakwaters, which cost over US$ 1,000/m. A field experiment on a mud-bank and review of various studies suggested that the bamboo embedment depth be no less than 60 cm to avoid dislodging and scouring, with 100 cm of bamboo protruding above the bed surface.