The flood of the Nenjiang river and the Songhua river in 1998 and the comprehensive management of the river basins

In the summer of 1998, an exceptionally serious flood, with the characteristics of high water level, large volume of flow, long duration and serious losses caused by the disaster, occurred in the Nenjiang River basin and the Songhua River basin. Greater flood peak occurred three times in the trunk stream of the Nenjiang River for the floods occurred in its tributaries one after another. At Jiangqiao Hydrometric Station, the water level was 141.90 m and the rate of flow was 12 000 m³/s. The flood is ranged to a catastrophic one, which occurs once in 50 years. Ranged to a catastrophic flood at Qiqihar Hydrometric Station that occurs once in 400 years, its water level, 0.89 m higher than the former alltime highest, was 149.30 m and the corresponding rate of flow was 14 800 m³/s. The water level that exceeded the all-time highest lasted for 7 days. At Harbin Hydrometric Station, the water level, 0.59 m higher than the former all-time highest, was 120.89 m and the corresponding rate of flow was 17 400 m³/s. The water level that exceeded the all-time highest lasted for 9 to 10 days. The flood here is ranged to a catastrophic one, which occurs once in 150 years. The flood of the Nenjiang River damaged 456 × 10⁴ ha of crops and 115 × 10⁴ rooms and the direct loss of economy exceeded 40 billion yuan(RMB). The main reasons of the flood are great rainfall, long flood season, unreasonable land use, regional ecological environment degradation and lack of water control projects. It is obvious that the following measures are greatly needed: the comprehensive management of the river basins; the formulation of development planning of the river basins, especially the water control projects; the development of agriculture based on ecological security.