Impacts of Long Jetties Construction on Shoreline Change at the Western Coast of the Gulf of Thailand

Abstract

Pranburi Jetties, a pair of long jetties with a length of 800 m and 860 m, have been constructed at the Pranburi River inlet, located on the western coast of the Gulf of  Thailand since 1999 to stabilize the river mouth. The purposes of this study were to evaluate the responses of shoreline due to the construction of Pranburi Jetties, and the accuracy of the One-Line model (OLM) on predicting the shoreline change due to construction. Based on the shoreline positions retrieving from aerial photographs and satellite imagery during 1967-2018, the difference in shoreline evolution before and after the construction of the jetties was evaluated using ArcGIS and Digital Shoreline Analysis System. The predicted shorelines using the One-Line model were compared with the image-analyzed shorelines for evaluating the accuracy of the model. The results indicated that the construction of Pranburi Jetties had caused the shoreline accretion at the vicinity of the jetties with the maximum accretion of up to 300 m in 2018. The land growth of 16.2 and 9 ha took place at the northern and southern coasts, respectively. The percentage of errors between the predicted and the image-analyzed shoreline varied from 2 to 13,000 percent with an average of 250 percent. Misprediction in shoreline change using a numerical model caused unnecessary construction of three detached breakwaters at the northern coast of the jetty.