GIS as a Tool to Identify a Coastal Sediment Management Option using Remote Sensing - A Study of Songkla Bay in Southern Thailand Wijesekera N.T.S. Tel: +66 2 524 6184 Fax: +66 2 524 6147 Email: sohanw@ait.ac.th Picton Phillipps G.P. Tel: +66 2 524 6148 Fax: +66 2 524 6147 Email: gppicton@ait.ac.th GIS Application Center, Asian Institute of Technology Bangkok, Thailand 1. Introduction Throughout the world coastal sediment management is an issue that has attracted the attention of many governments. Sediments in the coastal zone interact with the sea waves and get transported in either a long-shore or cross-shore direction. This phenomenon causes either coastal erosion or accretion and has been an ongoing challenge for coastal managers, engineers, planners and the like. Since most countries coastal zones stretch for hundreds or thousands of kilometers, it is not an easy task to identify the coastal reaches that require early attention. Remote sensing images that have the coverage of significant spatial extents are excellent tools to provide information with respect to beach sections that need attention. Multi-temporal remote sensing images over a particular region provide straightforward information about the beach profile changes. However efforts to manage beach profile changes using RS have to be supported with associated sediment quantities so that useful decisions on coast management and financing options can be made.  Fig. 1 Landsat Image of Songkla Coastline (1999). Inset – location of Songkla in Southern Thailand Geographic information systems incorporating temporal changes in the bathymetry of a region can be effectively used to identify the volumetric change of coastal sediments over time together with the associated beach profile change. In the present work, the bathymetry of a coastal reach near Songkla bay of Thailand for the years 1955, 1977 and 1990 were used to identify the sediment change and the beach profile change. The present work is based on a dataset that has been previously used for training activities (GACR 2001). Report of a related previous work raises many concerns (Lacoul, Samarakoon & Honda 2001). A critical analysis, based on previous experience, was performed on the same base data to identify the nature of any relationship between the volumetric changes of sediment in a beach section over time and the linear shift in the coastal extent over the same period of time (GACT 2002). Sound theoretical reasoning and achieving rational delineation of shoreline cells with uniform thickness, establishing a logical long shore direction suitable for spatial analysis, method of delineation and spatial demarcation using true GIS potential while avoiding visual ambiguities, a critical evaluation of results etc., are some of the differences of the present study. The present study also critically looks at results over different spatial and temporal resolutions.
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