Pilot Study on the Erosion and Rehabilitation of a Mangrove Mud Coast

This pilot study describes an analysis of the erosion processes of the Bang Khun Thien mangrove mud coast situated at the Upper Gulf of Thailand, and discusses measures to stop this erosion process and to rehabilitate the area. The rapid erosion observed is the result of the decimation in intertidal area by the dikes directly behind the coastline, constructed to protect the fish and shrimp ponds in the coastal area. The decrease in sediment yield from the Chao Phraya River as a result of the construction of the Bhumipol and Sirikit dams, and the local subsidence due to ground water withdrawal and natural settling will augment the observed coastal erosion, but at a much smaller rate. The latter effects are expected to become important on a time scale of about a hundred years only.The key to stop the erosion processes and rehabilitate the area is therefore the restoration of the intertidal area. This can be done either entirely within the current coastline, but by sacrificing part of the fish and shrimp ponds, or partly within the current coastline and partly in the coastal zone, i.e. in the coastal area recently lost. In the latter case, the coastal area has to be protected from lateral transport of sediment by permeable groynes perpendicular to the coast. It is estimated that an intertidal mangrove belt of about 300 to 500 m is required to re-initiate sedimentation processes, hence to restore a favourable habitat for mangrove forest.