The annual distribution of runoff is more even than that of all rivers in the province. The monthly maximum value appears in May-June (the main tributaries are different, the tributaries are mostly in May, and the main stream is mostly in June), accounting for about 20% of the annual total, and the flood year can account for 35-45% of the annual total, which has obviously decreased since June, so the maximum water volume of Xin 'anjiang River is relatively concentrated and lasts for a short time. In the six months of the second half of the year, the monthly average water volume is lower than the annual water volume 10%, and the monthly minimum is generally 65438+65438 from February to 10 of the following year, accounting for 2-3% of the annual total.
Xin 'anjiang is a mountainous river, and the rainy season is concentrated in April-July. The flood surges and falls suddenly, and the flood peak lasts for a short time, but it occurs many times in a year, and each flood usually lasts for 3 to 5 days. The flood season is consistent with precipitation, and its water volume accounts for 65% of the total annual amount. According to the measured time period at Tunxi Station, the maximum peak flow is 5780 seconds cubic meters (1May 5, 969), and the minimum peak flow is 965 seconds cubic meters (1May 7, 968), with six annual changes. In normal years, the peak flow is 2760 seconds cubic meters. In flood year, the maximum measured flood volume in each period is less than the normal annual total, which is really rare in all rivers in the province. Only the maximum flood volume 15 and 30 days are close to and greater than the annual total in dry years, but the multiple is also the lowest value of all rivers in the province.
The dry season is from September to March of the following year, and the dry season is also one of the largest rivers in the province. In the 35-year measured data of Tunxi Station, there is no interruption (except man-made interruption caused by 1978 stage-by-stage pumping irrigation along the river), with the minimum flow of 1.09 cubic meters, the average minimum flow of ten days of1.5 ~1.4 cubic meters, and the average daily flow of half a year. This is also unique among all rivers in the province, which is obviously the role of high vegetation coverage in water conservation in Xin 'anjiang River Basin.
Xin 'anjiang is originally a river with little sand, and the water is clear to the bottom. Since 1958, due to the blind slogan of one-sided emphasis on grain production and "self-sufficiency in mountain rations", the hills have been reclaimed to the top and the hills to the waist, which has increased the sediment in Xin 'anjiang River year by year. Especially in Nanxiang area of Shexian County, soil erosion is extremely serious, covering an area of 257.9 square kilometers. The siltation in some sections of Changyuan, Yangzhishui, Fengleshui and Jinxi River is 2m higher than that before 1958. The same is true of Hengjiang River in the upper reaches of Xin 'an River. Serious soil erosion, on the one hand, makes people live in poverty. In the 1970s, when people's communes engaged in collective production, the work score was only 5 cents. At that time, a popular song "A six-foot man is not as good as an old hen laying eggs" most vividly explained the harm of soil erosion to people's lives. On the other hand, the high sediment in the riverbed caused heavy shipping losses in Xin 'anjiang. Before 1958, a boat can reach Hangzhou from the fishing pavilion, and the boat can only reach Tunxi above the middle water level. Since 1984 ~ 1985, the main stream of Xin 'anjiang River has been channelized in three phases, with movable barrage at lakeside, Mushilin and Meitan respectively, and light bulb power station and water slope boat crossing facilities to achieve navigation and power generation. The movable dam has less backwater and is flexible to use. It is suitable for flood discharge and water storage in mountainous rivers and solves the contradiction between flood control and power generation. Light bulb power station is suitable for low head power generation; The water consumption for crossing the water slope is small, so the contradiction between power generation water and crossing the water should be solved. After the high dam ship lift of Xin 'anjiang Power Station is completed (under construction), it can be reached by one boat from Tunxi to Hangzhou. This plan has not yet been completed.