Tropical Storm Event of 4 January 2019 in the Gulf of Thailand: Sedimentological Comparison to Other Extreme Cyclones and Coastal Impacts on Different Shorelines

A tropical storm named Pabuk impacted the coastal areas of the Gulf of Thailand on January 4th, 2019, generating a high storm surge and leaving behind prominent washover sediments. Soon after the storm, we recorded sedimentological characteristics in relation to geomorphology and hydrodynamic intensities to understand the flow conditions and the coastal impact on different shoreline patterns. Pabuk’s sediments consist of very fine to very coarse sand, poor sorted and thinning landward. The general thickness is 25–30 cm with a maximum of 40 cm. At Chao Samran Beach and Thung Tako sites, 500 and 200 km away from the landfall site, the lowest unit contains planar laminations with reverse grading that resulted from traction load or grain flow transportation during the initial stage of the storm event. The middle unit contains a large number of shell fragments with inclined laminations reflecting the grain flow transportation during the high and intense currents. The uppermost unit consists of normal grading that indicates the deposition during the stagnant water after the inundation regime. At Talumphuk sand spit, 15 km from the landfall site, washover lobes including planar lamination, massive and cross lamination were dominated. In comparison to the other extreme tropical cyclones, the prominent factors generating different washover geometry and thickness of Pabuk included local high tide level, storm surge height, wave runup height, elevations of dune crest, artificial structure, and amount and type of sediment supply rather than the distances from the landfall.