Seasonal shoreline changes of the Prachuap Khiri Khan coast

Abstract

The study of seasonal coastal change is one method to help analyzing the erosion of ht coast. Causes of coastal changes are varied from place to place. Coastal changes around Prachuap Khiri Khan areas have previously defined and orderly ranked mostly based on the spatial calculation from remote sensing data, e.g., the most risky areas of erosion has been reported to have the land lost up to 5m/year at Pranburi area. This rate becomes equivocal in terms of how to analyse the causes of erosion and how much of geological data were taken into account. Thus, the assumption of this research was set up on that the causes of erosion differ from one individual area and might be controlled by specific geological factors. To prove this assumption, the understanding of annual sediment depositional cycle and current movement is the first aim to take into consideration. One important method of this work is the measurement of coastline, beach and shorefaces vertically and horizontally. This research focuses in Pranburi truncated beach ridges plain, Prachuap Khiri Khan Bay, and Wanakorn beach ridge plain where there are difference in morphology. Remote sensing data (series of aerial photographs taken in different period of time) were used to integrate and select the appropriate areas for evaluating sediment cycle and currents. Annual checks and measurement of shoreface profiles were designed in order to understand the changes in sediment budget in different season. Based on geomorphological aspects, the deposition and erosion in Prachuap Khiri (Khan Bay showing the equilibrium or balance of annual sediment gain and loss from the shoreface. Shoreface profiles of Pranburi and Wanakorn areas show similarity that annual depositional rate of shoreface sands seem to have a larger number than erosion. The analysis in shoreface slope was also taken in account. Clearly, shoreface slope relies on the volume of sediment gain and loss from the coast. One conclusion arisen from this research is that the major cause of coastal changes in the study areas is much relied on seasonal monsoon storms. Annual sedimentary cycles are of very important key to explain erosion and deposition along the invidual shoreline areas. The understanding in the annual change of shoreface topography is another important way to analyse the precise short-term and long-term rates of erosional and depositional scenarios rather than using only remote sensing measurement.