Lagoon degradation and management in Yanuca channel on the Coral Coast of Fiji

Abstract

Yanuca Channel is a narrow marine lagoon separating a low limestone island in Cuvu Bay from the south west Viti Levu mainland in Fiji, known as the “Coral Coast”. Historical air photographs show significant changes in the drainage configuration of the lagoon and local Fijian landowners give accounts of degrading environmental conditions in the lagoon due to sediment infilling. This investigation found several processes were responsible for the aggradation. Large quantities of terrigenous sediments are discharged by streamwaters into the lagoon, as a consequence of the removal of estuarine mangroves and agricultural practices such as burning and grazing in adjacent catchments. A previous outlet into the bay became blocked in the 1980s after inappropriate sand mining and vegetation clearance caused accelerated coastal erosion. The altered lagoon drainage pattern has led to lagoon eutrophication and aggradation. Developed on the island is a large international resort complex; the resort causeway constructed across the lagoon to the island has a significant dam effect, impeding the flow of currents and preventing the periodic scouring of sand from the lagoon floor. Several modern and traditional management options have recently been implemented to improve lagoon conditions, through partnerships between NGOs, traditional landowners and the resort management. These include riparian reforestation and the establishment of marine protected areas to conserve coral reefs.