There are many blue lines indicating the rivers of Northern China on the map, such as Fenhe river, Sanggan river, Daqing river, Hutuo river, Zihe river and the Yellow River, but most of these rivers are dry from autumn to the beginning of summer. One reason is the uneven distribution of water resources, which is rich in south-east part and poor in north-west part. The rainfall in Huabei area is lower than 500 mm and concentrates in three months of summer. Backward to 60 years ago these rivers had flow, and the water in river was clean, but now rivers are dry and water is polluted. As environmental scientists always have a dream that is blue sky and clean water. River is a natural system, which has a capacity for self-purification (assimilation) by the actions of dilution, oxygen dissolution and bio-decomposition. However, where is the way to get clean river water if there is no flow? A primary discussion is presented as following based on the situation of the Yellow River.
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