Chiayi–Tainan Plain  The Chiayi–Tainan, Chianan or Jianan Plain (), is an alluvial plain located at the central-southern region of western Taiwan. It is the largest plain of the island, and lies in Tainan City and Chiayi County/Chiayi City, from which the name of the plain derived. It also includes some portions of Yunlin County, Changhua County, and Kaohsiung City. There are several rivers flowing through it, such as the Zengwun River. Historically, the plain was mostly inhabited by Taiwanese Aborigines, a small fraction of the population today. Since the era of the Qing Dynasty, the Chianan Plain became a main destination of Han immigrants. This area also supplies many food crops to the whole island of Taiwan since the Japanese-ruled era. The Chianan Plain faces the Taiwan Strait on the west, Taichung Basin on the north, Pingtung Plain on the southeast, and lies to the west of foothills that extend from the Alishan Mountains. The area determined by dividing the groundwater zones of Taiwan is about . Between broadest points, the plain is about wide and long. Average rainfall in this area is about 1600 mm, lowest in the whole island of Taiwan, and the rainy season is in summer, thus the plain lacks rain in winter. Rivers which pass through this region are the Peikang River, Putzu River, Pachang River, Chishui River, Tsengwen River, Yenshui River and Erhjen River. These rivers flow over the plain roughly from the eastern mountainous area to the western seacoast, and discharge into the Taiwan Strait. About 6000 years ago, the lands near the seacoast of the Chianan Plain were flooded by seawater, and emerged gradually since 5000 years ago. Several archaeological sites are located here, including some late neolithic cultures such as the Tahu Culture, which existed between 3500 and 2000 years ago. The Iron Age Niaosung Culture appeared from 2000 to 500 years ago. The Hoanya people are known in written history to have lived in the northern part of Chianan Plain, and the Siraya people lived in the south. Han Chinese began to immigrate to the Chianan Plain since the European-ruled era of Taiwan. After the Koxinga defeated the Dutch to claim Taiwan in 1662, Han people ruled this region, and became the majority later.