Siltation and Erosion Control | Rapu-Rapu Polymetallic Project

Silt mainly comes from runoffs laden with sediments and silt washed off from erodible areas such as open slopes, unlined drainage system and access roads. During the development stage of the project where road networks and major facilities were being constructed, silt control structures like gabion check dams and silt fences were installed at several sections of the tributaries and creeks affected by silted runoffs to control siltation of the sea. Regular desilting activities and repair or replacement of silt fences effectively controlled siltation especially during storm events.

Progressive planting of cover crops and trees provide cover and slope stability. Slopes of embankments are covered with vetiver (Vetiveria zizanoides), para grass (Brachiaria mutica Forssk), and torpedo grass (Panicum repens) for erosion control. Other slopes are planted with native ipil-ipil trees (Leucaena glauca). Where vegetative cover is not possible, i.e., steep slopes, cocomatting and shotcreting are employed. Cocomattings installed in 2005 are now covered with grass and shrubs. Major access roads are sheeted with base course and gravel. Drainage systems are lined with concrete and provided with mini sumps to settle sediments.