Since the past few decades erosion has been observed at
various locations along the southern coast of the Mekong Delta,
where sedimentation has been observed in the past. Planting
mangrove forest is so far the best solution to mitigate coastal
erosion in the southeastern coast and the eastern coast of the
MDRS since the coast is rich in sediment supply from the
Mekong River system. Mangroves can reduce wave energy and
trap sediment, and therefore enhance sedimentation. It was
found that the southeastern coast and the eastern coast of the
MDRS was stable with a mangrove width range of approximately 30 to 250 m and 140 m on average. This result is
estimated on the basis of our empirical relationship of mangrove
forest width and coastline evolution from 1989 to 2002.
Results from the XBeach model for the Soc Trang case study
show the effectiveness of short-wave attenuation in a mangrove
forest. After passing through less than 100 m of mangrove
width, the short-wave height is significantly reduced to
virtually zero. Therefore it is hypothesized that short waves
do not really play a role in the health of a mangrove forest.
Long waves, on the other hand, need more distance for
attenuation. Even for the case of dense mangrove, long waves
can still penetrate in the order of 1000 m into the forest, but
after 300 to 400 m the long-wave energy is only 10% of the wave
height at the seaward edge of the mangroves. A qualitative
explanation could be that the long-wave energy needs to be
attenuated (reflections should be limited) to create a sedimentation-friendly environment. In addition, wave reflections will
potentially increase long-wave energy within the mangrove
forest, dependent on the position of a sea dike.
We hypothesize that long waves play an important role in
creating a favorable environment for seedlings and sedimentation. Future work will concentrate on validating our model
results by both fieldwork and laboratory experiments, both in
terms of hydrodynamics and of sedimentation.