Investigation of Spatiotemporal Variation of Surface Turbidity along the West Coast of Sri Lanka Using MODIS

Abstract

 This study focuses on use of the Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite data for monitoring of spatiotemporal variation of surface turbidity along the west coast of Sri Lanka, which may be one of effective indicators of the change of sediment transport. We conducted a field survey to obtain in-situ turbidity data of the sea surface, and used these data for evaluations of different models for MODIS-based turbidity estimations. Surface turbidity over the domain was obtained from MODIS over 20 years from 2000 to 2019. Computed monthly mean turbidity showed clear seasonal variation corresponding to the monsoon season in the region. The alongshore variation of the mean and median turbidity over the entire observation period showed clear local peaks at the river outfalls. Around Colombo Harbor, relatively low turbidity was identified. This clear reduction of turbidity may be due to breakwaters constructed at Colombo Harbor and Panadura fishing Harbor. The 5-year-mean turbidity are clearly reduced from the period of 2005-2009 to 2015-2019. Furthermore, exceedance probability curves of the turbidity in these two periods at different locations show clear difference, which reasonably explains the different extent of coastal erosion at each location and time.