Response in the Mekong Deltaic Coasta to Its Changing Sediment Sources and Sinks

The coastal zone of Mekong delta is suffering under intense pressures from climate change as well as human intervention. Currently, the coastline evolution of Mekong delta is a complex combination of impacts due to (1) relative sea level rise i.e. the sum of eustatic sea level rise, natural and human induced subsidence (2) sediment transport rate changes at some sections due to change of wave condition by climate change (3) change of sediment sources from the Mekong estuaries by dam construction and sand mining and (4) mangrove degradation. A coastline monitoring is the basis to understand and manage coast. This study utilizes integrated techniques of remote sensing, geographic information system and statistics to monitor coastline change over the period of 1973 to 2015 from Landsat images of Multispectral (MSS), Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), Operational Land Imager (OLI) at coastal area of Mekong delta. An advanced toolbox is developed for the work of atmospheric and radiometric correction of Landsat images as well as influence of tidal range is taken into account to obtain mean water level. Tasseled Cap and Normalized Difference Water Index (NDWI) algorithm is applied to separate land-water interface for extracting shorelines. Besides, a digital shoreline assessment system (DSAS) tool is used to analyze shoreline rate by statistic parameters as Shoreline Change Envelope (SCE), End Point Rate (EPR) and Linear Regression (LRR). Furthermore, uncertainty assessment for this methodology based on topographic surveying and Google Earth images. Moreover this research explored relationships between the accretion and erosion of land and the sediment load of the Mekong River. The results revealed a general pattern of accretion and erosion. The eastern coast, which is fragmented by 9 estuaries, was significant accretion and erosion, especially annual erosion rate of around 40 meter at Bo De estuary is noted. Meanwhile the western coast is rather stable, particularly annual accretion rate of up to 90-95 meter at Datmui commune of Camau province. This study indicated there is relative difference of coastline change rate among periods of 1973-1990, 1990-2005 and 2005present. And the study illustrates the rate of shoreline change is significantly associated with sediment discharge on Mekong River through statistic approach, especially the phase of sediment flow decrease by dam and sand mining on Mekong River in recent 15 years. The results of methodology and maps from this research may be useful in planning and management of this exposed coastline.