Monitoring the Functional Performance of Coastal Protection Structures Along the Eastern Coast of Thailand

The Map Ta Phut deep-sea port, the largest industrial port in Thailand, was constructed in the middle portion of the Rayong bay located in the eastern coast of Thailand. The construction of the port caused a severe shoreline erosion on the east side of the port. Various structural measures such as systems of segment breakwaters, Y-shaped groins, and straight groins were built as a component of coastal protection project to mitigate the beach erosion. The objective of this study is to monitor the functional performance of those beach erosion control structures. Historical shoreline positions of the Rayong bay between 1956 and 2016 were extracted from aerial photographs and satellite imagery using ArcGIS release 10.4 software, and the digital shoreline analysis system (DSAS) was used to calculate the shoreline change rates of pre- and post-construction of those coastal protection structures. The results show that the Rayong Bay was relatively stable with an average rate of shoreline change less than 1 m/y before the port construction. After the completion of the first phase of the Map Ta Phut port in 1992, about 6 % of the Rayong coast experienced a severe erosion up to 6 m/y. A significant shoreline accretion was found at both eastern and western ends of the port (approximately 1% of the total coastline). However, the shoreline retreat increased to 17 % of the coast since the construction of the second phase Map Ta Phut project was completed in 1999. Based on the analysis of shoreline changes after the construction of coastal protection measures, it was found that multiple breakwater systems with the exposure ratio of 0.6 have successfully stabilized 5 km of the protected beach. Ten Y-shaped groins with the length to spacing ratio of 2:5 have been placed along the 3 km coast adjacent to the multiple breakwater systems. A segmented breakwater with the length of one-fifth of the groin spacing was placed between each pair of groins to lessen the significant shoreline retreat between the Y-shaped groins. However, it still was not sufficient to protect the coastline of the project area. Additionally, using a short straight groin system with the ratio of groin length to the spacing of 2:5 was not adequate to diminish the erosion effects due to constructions of the port and its coastal protection scheme.