The role of breakwaters on the rehabilitation of coastal and mangrove forests in West Kalimantan, Indonesia

Abstract The breakwaters, which were built by the government of West Kalimantan, Indonesia in late 1993 were aimed to protect the coast and mangrove forest. However, the effectiveness of building the breakwaters is not known because no measurement has been done. This study aimed to reveal the effectiveness of building breakwaters to protect the coast and its role in the rehabilitation of mangrove forest. The role of breakwaters in protecting the coast and rehabilitating the mangrove forest were assessed by comparing differences between the condition when there were no breakwaters versus condition after the breakwaters built. Beside building breakwaters, the government plant Rhizopora to restore the mangrove forest. The success rate of mangrove rehabilitation effort was determined by measuring density and distribution of Rhizophora and colonization of Avicennia marina . The study conducted using survey method with a landscape approach conducted in three bays of the South China Sea, West Kalimantan, Indonesia, which are: Penibung, Sungai Duri, and Karimunting. The measurement of parameters was conducted with purposive sampling technique based on perpendicular toward the sea area. The parameters measured were shoreline differences, the distribution of bottom and drift sediment, and the prediction of longshore sediment transport alongside the shore. The result showed that the breakwaters built in Karimunting and Penibung Bay were successful to reduce the amount of coastal erosion up to 70% within 22 years. On the contrary, the breakwaters built in the Bay of Sungai Duri could not reduce the coastal erosion. The effects of breakwaters on mangrove rehabilitation were clear, which can be observed on the colonization rate of Avicennia marina and reforestation of Rhizophora sp. in Karimunting Bay. The abrasion of shoreline still occurred although there were breakwaters built. It might be caused by the construction of breakwaters were segmented. The condition worsens by activities of beach sand excavation.