Hydrological characteristics of Zijiang River

Zishui River Basin is characterized by low mountains in the south, hills in the east, hills in the middle and plains in the northeast. The southwest is high and the northeast is low. Mountains account for 55%, hills account for 35% and plains account for 10%. The average annual precipitation in Zishui Basin is1483.3mm. The high-value areas are from Dongkou to Longhui and Anhua to Taojiang in the west of the basin. The area from Xinning to Shaoyang in the southeast is a low-value area. The extreme maximum value is 2605.3mm (Robbie Station in Taojiang County 1969). The extreme minimum value is 7 18.8mm (Zhujiating Station, Shaoyang County, 1960). The distribution of precipitation in a year is uneven. The maximum monthly precipitation generally occurs in May or June, and the minimum monthly precipitation generally occurs in 65438+February or 65438+1October. The precipitation in flood season (April-September) accounts for 67.3% of the whole year. The average evaporation of water surface for many years is about 700 mm, and there are frequent rainstorms in Zishui basin during flood season, mainly from Anhua to Taojiang, Ziyuan and the north of Longhui. The number of heavy rains is the most in May-June, but the extreme value mostly appears in July-August. 1991August 26 -27, the 24-hour maximum length of Menggongtang Station in Taojiang is 47 1.5mm ... which is the largest rainstorm actually measured in Hunan Province. Heavy rain causes floods, and the maximum peak discharge mostly occurs in June, July and August. The measured maximum flood peak discharge at Taojiang Station15300m3 per second (1955, August 27th). The average annual runoff in Zishui River Basin is 25.2 billion cubic meters, and the annual distribution corresponds to the seasonal variation of rainfall. The annual average maximum runoff for four consecutive months generally occurs from April to July, accounting for 54% of the total annual runoff. The annual runoff changes greatly, with the maximum annual runoff of 37.48 billion cubic meters (1994) and the minimum annual runoff of14 billion cubic meters (1963).