ความคิดเห็นที่ 3
Yellow River at Lanzhou
The part of Yellow River between Hekou County in Inner Mongolia and Zhengzhou in Henan constitutes the middle reaches of the river. The middle reaches are 1,206 km (749 mi) long, with a basin area of 344,000 km² (132,820 mi²), 45.7% of the total, with a total elevation drop of 890 meters (2,920 ft), an average drop of 0.074%. There are 30 large tributaries along the middle reaches, and the water flow is increased by 43.5% on this stage. The middle reaches contribute 92% of the river's silts.
The middle stream of the Yellow River passes through the Loess Plateau, where substantial erosion takes place. The large amount of mud and sand discharged into the river makes the Yellow River the most sediment-laden river in the world. The highest recorded annual level of silts discharged into the Yellow River is 3.91 billion tons in 1933. The highest silt concentration level was recorded in 1977 at 920 kg/m³. These sediments later deposit in the slower lower reaches of the river, elevating the river bed and creating the famous "river above ground". In Kaifeng, the Yellow River is 10 meters (33 ft) above the ground level.[12]
From Hekou County to Yumenkou, the river passes through the longest series of continuous valleys on its main course, collectively called the Jinshan Valley. The abundant hydrodynamic resources stored in this section make it the second most suitable area to build hydroelectric power plants. The famous Hukou Waterfall is in the lower part of this valley.
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