Tha Chin River Project: A solution for salt intrusion in the Tha Chin River mouth

Abstract

The Tha Chin River is a river in central Thailand, which starts in Chainat province as a branch of the Chao Phraya River and flows into the Gulf of Thailand at about 35 km southwest of Bangkok. The Tha Chin is one of Thailand’s most important rivers and it plays a vital role for the lives of over two million people living in this basin. Near the river mouth, it serves as a traffic route for about 4000 ships, mostly used for fishing, located in the area. More upstream, the river is used for both shrimp farms and fisheries, as well as fruit and flower farming and paddy fields. Al these fields are irrigated using a vast and complex network of increasingly smaller irrigation channels, controlled by water gates. The use of river water is however not limited to irrigation only. Besides the agricultural users, the industrial and domestic users are two other major consumers of water from the Tha Chin. Currently the river basin is experiencing serious problems regarding water quality. One of these problems is the high amount of pollution in the river. Multiple factors (e.g. waste water dump from several sources, oil spillage and water hyacinths) contribute to lower dissolved oxygen levels, higher levels of chemicals and algae blooms. Resulting in considerable damage to the ecosystem in the last decades. Another major water problem is salt intrusion. The tide in the Gulf of Thailand brings saline water into the river. Currently this water is pushed back by increasing the river discharge, which is controlled by the Pho Praya water gate in the Suphanburi Province. However, during the dry season the river discharge is often too low to effectively push back salt water and therefore salinity in the Tha Chin becomes too high. The salt water threatens the agricultural production, it decreases the amount of yearly grown crops or even destroys them complete, causing major economic damage. Additionally, it decreases the river capacity with respect to its function to provide fresh water. One of the major institutions involved in managing and controlling the Tha Chin River is the Royal Irrigation Department (RID). This is a department of the Thai Ministry of Natural Resources \& Environment. The RID is responsible for the development and maintenance of the main irrigation systems. As such, it controls the irrigation network in the Tha Chin Basin. Part of their mission is developing water resources and in their search for solving the salt intrusion problem in the Tha Chin, they asked the TU Delft project team to find with a solution. Two solutions are proposed. The first solution is building a barrier in the river at 12 km upstream from the river mouth. This solution is the only one that can solve the salt intrusions problem, however due to negative experiences in other rivers this solution is likely to encounter much opposition. The second solution is the construction of Balance Islands in front of the river mouth. The principal of this solution is to alter the tidal flow such that saline water flows less into the river while the river discharge is not obstructed. In order to implement this solution further research is needed. Also this solution is not able to solve the salt intrusion problem entirely, but will make the problem less severe.Civil Engineering and GeosciencesHydraulic Engineering / Structural EngineeringMultidisciplinary Project CIE4061-0