The irrigation area under the jurisdiction of the office is located between the Wu River and Zhuoshui River, and covers 26 townships and cities in Changhua County, Nantou City and Mingjian Township. It starts from Pinglin River and Maoluo River in the east, borders the Taiwan Strait in the west, reaches Zhuoshui River in the south, and is bounded by Wu River in the north. The terrain slopes from southeast to northwest and is about 43 km in length from north to south and 30 km wide from east to west. The terrain is wide in the south and narrow in the north, in an equilateral triangle shape.
Annual rainfall is about 1,300-2,200 mm. Although there is an abundance of rain it is unevenly distributed in time and space; the annual average temperature is about 22°C, and the climate is subtropical island type; there is a northeast monsoon from October to March and typhoons are most common from July to October.
Bagua Mountain terrace is composed of a Pleistocene laterite soil terrace deposit layers, and the Changhua plain is a modern alluvial layer. Most of the soil is silty loam or sandy loam and fertile.
- Irrigation water source
a. Natural river flow: the main irrigation water sources used are the Zhuoshui River and Wu River.
b. Surface water as a supplementary water source: drainage channels are used to build control water gates, rubber dams or pumps and other facilities to intercept and pump water for irrigation or recycle water for use.
c. Groundwater as a supplementary water source: Deep wells and shallow wells were dug to pump groundwater, with 76 wells, 2,736 horsepower and total water output of 56,470 GPS. - The main irrigation channels are: Babao Canal, Jizaipi Canal, Fuma Canal, Tongyuan Canal, Jiji Joint Water Diversion Plan North Bank Communicate Channel.
- Drainage channels: The main drainage channels within the jurisdiction of Changhua County and include 11 drainage main channels; Shengang River Bottom Drainage Main Channel, Liugu Drainage Main Channel, Tianwei Drainage Main Channel, Panyagou Drainage Main Channel, Yangzicuo River Drainage Main Channel, Lugang Drainage Main Channel, Yuanlin Large Drainage Main Channel, Old Zhuoshui River Drainage Main Channel, Wanxing Drainage Main Channel, Erlin River Drainage Main Channel, Yuliao River Drainage Main Channel.
Changhua area (including Nantou irrigation area) has a cultivation area of 75,298 hectares and a current irrigation area of 46,714 hectares or 62.0% of total cultivated land. The area includes double cropped fields, single cropped fields, single late cropped in two years fields, double cropped in two years among four-year fields, sugarcane fields, post second crop fields and miscellaneous crop fields. The rice seedling days in this area are first crop 40 days, second crop 15-20 days, staggered days, first crop 50 days or 60 days, and second crop 30 days or 20 days. The number of irrigation days for first crop fields is 109-120 days and second crop fields 90-102 days. The field irrigation rate (unit ha/CMS) is seedling field preparation 43.2, water irrigation 432, field preparation 57.6 ~ 48.0, growing field 864~720 or 617.