The average annual runoff depth of Songhua River Basin for many years is 134.3mm, which is equivalent to 73.3 billion cubic meters of runoff. The area south of the mainstream is larger. The maximum value in mountainous areas can reach about 500 mm, such as the Daojiang river basin at the upstream source of the second Songhua River. Followed by Mudanjiang tributary Hailang River, Hulan River tributary Ikimi River, Tangwang River tributary Yong River Verdon River basin, the annual runoff depth is above 400 mm, and Songnen Plain annual runoff depth is only 20 ~ 30 mm. The regional distribution trend of annual runoff and annual precipitation is basically the same. The water in Songhua River basin is mainly supplied by atmospheric precipitation and supplemented by meltwater, so the annual distribution of runoff also has obvious seasonal changes. More than 90% of the inflow of rivers is concentrated in April ~ 65438+1October in the free flow period, and the runoff from June to September accounts for about 55~80% of the whole year. Floods are mostly concentrated in July and August, and the main stream can be extended to the beginning of September, and the floods last for about 60 days. Because of the large basin area, the flood propagation time is long. The flood in Songhua River basin is mainly caused by rainstorm, followed by the flood peak caused by the simultaneous rise of several tributaries. With the replenishment of seasonal meltwater in spring, rivers generally form different degrees of spring flood. The runoff from April to May accounts for about 15~30% of the whole year, while the runoff in winter is the smallest, which forms the obvious characteristics of abundant summer and low water in winter. Runoff changes greatly during the year, showing obvious periodic changes of continuous high and low, but the cycle length is different. The annual runoff of the basin is getting worse, and the CV value is generally 0.4~ 1.0, and the upstream of the second Songhua River is smaller, only 0.2 ~ 0.5. However, the western region is the largest, and the small inflow areas such as Wuyuer River, Shuangyang River and Taoer River can reach 0.9~ 1.0. The runoff difference between wet season and dry season is several times to dozens of times. For example, the catchment area of Shuangyang Station of Shuangyang River 186 1 km2, the water volume in wet season 1969 is 236 million cubic meters, and the water volume in dry season 1968 is only 0.04190,000 cubic meters, and the water ratio in dry season is 56.3. After the flood season of 1998, the precipitation in Nenjiang River basin in the upper reaches of Songhua River was obviously too high, and three consecutive floods occurred. The first flood occurred from the end of June to the beginning of July, the second flood occurred from the end of July to the beginning of August, and the third flood occurred in mid-August, which was a major flood in Nenjiang River Basin. Affected by the inflow of water from various tributaries, the water level in the main stream of Nenjiang River rose rapidly, and the highest water levels at Tuanjie, Qiqihar, Jiangqiao and Dalai hydrological stations exceeded the historical measured highest water levels by 0.25, 0.69, 1.6 1 and 1.27 meters respectively. Under the condition of execution of the 6 th outlet of Nenjiang levee, the flood peak discharge of Qiqihar, Jiangqiao and Dalai stations all exceeded 1932.
The highest water level 120.89 m in Harbin, the main stream of Songhua River, was 0.84 m higher than the historically measured highest water level, and the flow rate 16600 cubic meters per second, which was the largest flood in the 20th century. There are two kinds of floods in Songhua River basin: one is caused by heavy rain in flood season; Secondly, there is continuous rainy weather in a certain area in the flood season, and the time can be as long as 1 month. In this continuous rainy day, heavy rain occurs and floods form.
Floods in Songhua River basin include spring floods and summer floods. The flood time in spring flood season is basically the same as that in ice flood season in early spring, which occurs in April-May every year. Ice dams often appear in glacial floods. According to the statistics of Yilan Station, ice dams occurred in 13 years from 1956 to 1976. The height of an ice dam is generally 4 ~ 6 meters, the highest is 15 meters, and the length of the ice dam is 5 ~ 10 kilometers. Floods in summer and autumn occur in June-August, sometimes postponed to September. The total amount of water resources in the whole basin is 88.028 billion cubic meters, of which the total amount of surface water resources and groundwater exploitation is 85/kloc-0.50 billion cubic meters. The total surface water resources are 73.47 billion cubic meters, of which Nenjiang River is 22.73 billion cubic meters, accounting for 30.9%. The Songhua River is 65.438+072 billion cubic meters, accounting for 23.5%. The main stream of Songhua River is 33.48 billion cubic meters, accounting for 45.6%.
The Songhua River basin is rich in hydropower resources, concentrated in the mainstream of Songhua River, Nenjiang River and Mudanjiang River. There are 7 trunk and tributary rivers with theoretical hydropower reserves of over 65,438+100000 kilowatts in the basin, and the total theoretical hydropower reserves are 6,598,500 kilowatts, of which the trunk and tributary of the West Songhua River 1.39 million kilowatts, accounting for 2 1.2% of the whole basin. The main and tributary of Nenjiang River is 2.2710.2 million kilowatts, accounting for 34.4%; The main stream of Songhua River and its tributaries are 292.9 1 10,000 kilowatts, accounting for 44.4%.