The main hazard of the Yellow River is floods.
Floods in the upper reaches of the Yellow River mostly occur in September, mainly from Lanzhou and above. Lanzhou floods mainly come from Guide and above. Due to the long duration and low intensity of rainfall, and the better vegetation above Lanzhou, grassland, swamps, etc. have a strong stagnant effect on rainfall, resulting in gentle rise and fall of floods in the upper reaches of the Yellow River, long flood duration, low flood peaks, and short flood process lines. Fat type.
The average duration of a flood at Lanzhou Station is 40 days, with the longest being 66 days and the shortest being 22 days. The measured peak flow rate is generally 4,000 to 6,000 cubic meters per second.
The upper reaches of the Yellow River are mostly canyon sections. Regardless of the size of the flood, the general propagation time does not change much. It takes about 1.5 days from Guide to Lanzhou and about 10.5 days from Lanzhou to Hekou Town. Floods from the upper reaches of the Yellow River reach the middle and lower reaches and generally become base flow.
The actual measurement data of floods in the upper reaches of the Yellow River began after the flood in 1933, when hydrological stations were set up in Lanzhou, Baotou and other places. The largest measured flood occurred in 1946. The peak flow rate at Lanzhou Station reached 5,900 cubic meters per second, and the total flood volume in 15 days was 6.5 billion cubic meters.
Although the peak flow rate of the Lanzhou Station in the 1981 flood was only 5,600 cubic meters per second, without the cofferdam construction of the Longyangxia Reservoir and the retention of the Liujiaxia Reservoir, the peak flow rate of the Lanzhou Station could reach 7,090 cubic meters per second. Second. According to investigation and research, the largest historical flood in the upper reaches occurred in 1904, and the peak flow rate at Lanzhou Station reached 8,600 cubic meters per second.
Extended information:
Irrigation project
1. Inner Mongolia Yellow River Irrigation District
One of the famous large irrigation areas in China. Its scope starts from the eastern edge of the Ulan Buh Desert in the west to the eastern suburbs of Hohhot City in the east. It is bounded by Langshan Mountain, Wula Mountain, and Daqing Mountain in the north. It leans on the Ordos Platform in the south, including the Hetao, Tumo River, and the irrigation area on the south bank of the Yellow River. It spans 19 banners (counties and districts) in Yikezhao League, Bayannaoer League and the three cities of Hohhot, Baotou and Wuhai.
2. Ningxia Yellow River Irrigation District
One of the four ancient irrigation districts in my country, it has an irrigation history of more than 2,000 years. Known as the "fortress of Jiangnan", it is the main grain, cotton and oil production area in Ningxia and one of the 12 commercial grain bases in the country.
The irrigation area involves Qingtongxia City, Yongning County, Yinchuan City, Helan County, Pingluo County, Taole County, Huinong County, Shizuishan City and Zhongwei County, Zhongning County, Wuzhong City, Lingwu City, etc. The Yellow River diversion irrigation part in 4 counties (cities) includes 12 counties (cities) and more than 20 state-owned agriculture, forestry and pasture lands.
3. Fenhe Irrigation District
Located in the Taiyuan Basin in central Shanxi Province, the area is distributed on both sides of the Fenhe River, starting from Shanglan Village in the northern suburbs of Taiyuan City in the north to Jiexiu in the central Jinzhong area in the south. Hongxiang Village in the county is about 140km long and 20km wide from east to west. It is bounded by Taiyuan (Taiyuan) Fen (Fenyang) Highway and Ciyao River in the west, and Taiyuan (Taiyuan) San (Sanmenxia) Highway and South Tongpu Railway in the east.
The irrigation area spans the three cities of Taiyuan, Jinzhong and Luliang, 12 counties (cities, districts) and 488 villages in 56 beneficiary townships (towns). The entire irrigation area controls a land area of ??2.0555 million acres. Among them, the cultivated land area is 1.5684 million acres. The designed irrigation area is 1.4955 million acres, and the benefited area accounts for nearly one-tenth of the province's water land area. It is one of the largest artesian irrigation areas in Shanxi Province.
Baidu Encyclopedia-Yellow River