Geotextile tubes for protection of mangrove coast in Malaysia

Abstract

Coasts bordered by mangrove trees are common along the west coast of Peninsular Malaysia and many regions of Sabah and Sarawak. The shore and near shore regions are generally composed of fine grained material. Wave energy reaching mangrove-fringed coasts is usually low allowing silt sized material to remain at or near the shore. Fetches and wave approach directions of mangrove-fringed coasts limit wave energy reaching the shore. Mangrove forests are the natural vegetation of many tropical coasts and tidal inlets. The mangroves form a highly productive ecosystem, maternity and nursery for many marine species. Mangroves survive in the upper tidal zone; approximately above Mean Sea Level to High Water (Spring). Mangroves exist on gentle sloping coasts with moderate wave climate. A striking feature of mangroves is the root system, which offers protection against erosion of the coast by dissipating wave energy. They also provide support and protection of low-lying agricultural land from flooding. Detached geotextile tubes as one of the soft engineering methods were conceptualised to moderate incident waves and mitigate coastal erosion at mangrove areas. The geotextile tube is basically a close-ended tubular geotextile with filling ports. Sand is hydraulically pumped in through the filling ports. The geotextile tubes are constructed to a height of 1.5m and 50m length. They are spaced 5m apart and aligned parallel to shore. Each tube sits above a scour apron against scouring of the seabed that might undermine the stability of the geotextile tubes installed. The installed geotextile tubes are partially exposed during low tides and completely submerged during high tides. This paper will describe the design and construction of the geotextile tubes.