Conceptual experiment on wave attenuation due to mangrove root systems

Abstract

As waves propagate into a mangrove forest, the waves energy will be reduced due to two main factors, i.e. the bed friction and the drag force from the trunks and roots of mangrove trees, particularly in case of prop root system of Rhizophora. This paper presents a conceptual experiment in the laboratory to study the hydrodynamic and botanical factors affecting wave attenuation when moving through prop root system of Rhizophora models. The experiment was carried out in a 16-m long, 60-cm wide, 80-cm deep wave flume, in which regular waves were generated. The stems and roots of Rhizophora models were made with steel bar. The independent variables of interest were the wave steepness, the water depth relative to root height, the width of root line and the density of mangrove trees, as well as the dependent variable was the wave reduction. As the wave steepness, the width of root line and the density of mangroves increased, the wave reduction also increased. While as the water depth relative to the root height increased, the wave reduction decreased. This study also presents an empirical formula to predict the wave reduction from the aforementioned factors.