Royal Irrigation Department started irrigation work in the Southern region since B.E.2492 (A.D.1949). According to the Department’s order No. 28/2492 on 10 March B.E. 2492, it defined to establish an irrigation office in the Southern region by equivalent function as Construction Project Division in that time. It was responsible for controlling irrigation works in 14 provinces in the Southern region. In B.E.2517 (A.D.1974), due to an extensive expansion of irrigation activities in every year, Royal Irrigation Department restructured its organization in the Southern region to be appropriate and flexible for implementation by dividing into 2 irrigation offices as follows: Regional Irrigation Office 11, responsible for water management of 7 provinces in upper southern region and its head office located in Pakpanang district, Nakhon Si Thammsrat province; and Regional Irrigation Office 12, responsible for water management of 7 provinces in lower southern region e.g. Songkhla, Phatthalung, Satun, Trang, Patani, Yala and Narathiwat, and its head office located in Hat Yai district, Songkhla province. Later, Royal Decree Organizing Royal Irrigation Department, Ministry of Agriculture and Cooperatives B.E. 2540 (A.D.1997) defined to rename Regional Irrigation Office 12 to "Regional Irrigation Office 12" by raising its structure. After that, Royal Decree Organizing Royal Irrigation Department B.E. 2545 (A.D.1997) defined to change Regional Irrigation Office 12 to Regional Irrigation Office 16 since 11 November B.E. 2545 until present. This office is responsible for irrigation works of 4 provinces in lower southern region e.g. Phatthalung, Songkhla, Trang, Satun.