Tapi River (Thailand)  The Tapi (or Tapee) river (, , ) is the longest river in southern Thailand. The river originates at Khao Luang mountain in Nakhon Si Thammarat Province, and empties into the Gulf of Thailand at Bandon Bay near the town of Surat Thani. It has a length of . The river drains an area of and in 1997 had a yearly discharge of or per year. The Phum Duang River (or Khiri Rat River), which drains another west of the Tapi watershed, joins the estuary west of Surat Thani in Amphoe Phunphin. The river was named on 29 July 1915, after the river Tapi in Surat, India, shortly after the town of Surat Thani was named after the town Surat in Gujarat, India. The island of Ko Lamphu (เกาะลำพู) is in the Tapi River, about from its mouth, near Surat Thani town center. In 1975, an area of of swamp land on the east bank of the river in the Khian Sa District was declared the Nong Thung Thong non-hunting area.