This irrigation area is located in the Chianan Plain in southwest Taiwan, reaching from the Central Mountains in the east to the Taiwan Strait in the west. It is about 71km wide from east to west, from Beigang River in the north to Erren River in the south, and about 86km long from north to south. The terrain is flat, spanning Tainan City and Chiayi County and has a subtropical climate, with an average annual temperature of 21-24°C, average annual rainfall of 1,600mm, with 80% of rainfall falling from May to September.

1. Reservoir : 32 reservoirs including Zengwen Reservoir, Wushantou Reservoir, Baihe Reservoir, Hutoupi, Deyuanpi, Neipuzipi, Yanshianpi Reservoirs, etc.
2. River water intake: 114 locations including Daojiang Canal, Zhongxing Canal, Liuzigou Canal and Xuxian Canal
3. Surface water is used as a supplemental water source: Water is diverted from water intakes on rivers, drainage channels and other facilities, pumps or natural guiding methods as supplementary irrigation water in 80 locations
4. Groundwater is used as a supplemental water source: There are 37 deep (shallow) underground wells and 37 deep wells for pumping as supplementary irrigation water source.

The jurisdiction of Jianan Management Office includes general irrigation areas such as Zengwen Reservoir and Wushantou Reservoir irrigation areas in Chiayi and Tainan city and county (including combined water source areas), and Baihe Reservoir irrigation area etc.

The irrigation water for the Zengwen and Wushantou Reservoir irrigation areas are supplied by the Zengwen and Wushantou Reservoirs. The Baihe Reservoir and Daojiang Canal System irrigation areas are irrigated by their own ponds, reservoirs or rivers other than the Wushantou Reservoir. According to geology and water sources, the farming methods in each irrigation area can be divided into double cropping fields, single cropping fields, three-year two crop fields, sugarcane crop fields, and rotational crop fields. Irrigation dates are set according to the crop planting date and physiological characteristics during the growth period.