Coastline changes in Mantanani Besar Island, Sabah, Malaysia

Coastline dominated by sandy beaches tends to change due to the processes of beach erosion and accretion. However, the coastline of an island is continuously changes due to direct exposure to physical forces from the sea and anthropogenic activities. At Mantanani Besar Island (west coast of Sabah), continuous beach erosion is among the major threats and a matter of concern by both islanders and tour operators. Therefore, this study aim at identifying the long-term coastline changes and the most dynamic coastline processes by detecting the pattern of beach modifications based on remote sensing images and photographs. The island was divided into four segments following the cardinal directions namely westward (seg 1), southward (seg 2), eastward (seg 3) and northward (seg 4). Aerial photos (1986, 1990, 2001 and 2013) and satellite image (2010) were analysed using ArcGIS Software Version 9.3. Results revealed that the island has undergone long-term coastline erosion (1986 to 2013) with the estimated total beach loss area of 168,113 m2 . All these segments experienced more beach erosion than accretion where seg 2 had the highest beach loss, approximately 71,590 m2 followed by seg 4 (57,558 m2 ), seg 1 (23,008 m2 ) and seg 3 (15,957 m2 ). The most dynamic areas were at seg 3 which had experienced more beach processes. Impacts from both natural phenomenon and anthropogenic activities lead to different rates of erosion at each segment. Further study on hydrodynamic forces (winds, waves and currents) at Mantanani Besar Island is recommended to better understand the coastal processes. Studies on hydrodynamics and beach changes would provide baseline data that might be helpful in planning measures for protecting the island from further erosion