Wave attenuation in mangrove wetlands. Red River Delta, Vietnam

Abstract

Mangrove forests cover the shores of many tropical and sub-tropical coast lines. These trees are tolerant to saline environments which enables them to grow in the tidal zone. They are known for their often complex and impressive root system. From a Civil Engineering point of view, mangrove forests are interesting for since they reduce transmitted wave energy of incident waves and thus serve as a natural coastal protection. In Vietnam, mangroves grow in the deltas of the Red river Delta and Mekong River where they protect valuable aquacultural and agricultural lands. Although awareness on the value of mangrove forests has risen in recent years, there is still little known about how (much) waves are reduced in these forests and how to investigate this effect. This study deals with the physical processes involved in the dissipation of wave energy by vegetation and with wave measurements in mangrove forests. From the analysis of the physical processes, it followed that the dissipation of wave energy is relative to the vegetated cross-area exposed to waves and the third power of the amplitude of horizontal particle velocities. It also turned out that the effect of shoaling was very small on slopes, typical in mangrove forests, which makes calculation less complicated. This study also included a trip to Vietnam for wave measurements in a mangrove forest. This fieldwork was carried out together with the Hanoi Water Resource University. Unfortunately, no wave measurements were carried out successfully. However, the fieldwork did yield interesting information about mangrove vegetation and its habitat that is useful for future measurements.