长江流域泥沙特点及对流域环境的潜在影响

泥沙是流域系统中的一个重要的物理通量,对流域环境具有直接影响。近40年来,长江上游流域的植被覆盖率减少近一半,水土流失扩大了一倍多。金沙江下游干支泥沙80年代较60年代增加了12％－60％,而通过长江宜昌站的泥沙年平均输沙量则没有增加。由水土流失、山地灾害等带给流域系统的泥沙大部分堆积在各支流的中下游河道。50％以上的支流河道出现了严重的泥沙加积,加积速率可达5－20cm/a,部分支流因泥沙过只而呈辫状河特点。支流河道泥沙的过度液积,构成长江环境的巨大隐患。当发展到一定程度或环境突然变化,堆积在支流的泥沙必然会进入主河道。一旦爆发,将严重影响到长江环境的安全。应尽快开展长江流域上游和支流泥沙的运移和淤积现状及规律调研。

SILT TRANSFORM CHARACTERISTICS AND LATENT EFFECT ON FLUVIAL SYSTEM ENVIRONMENT IN YANGTZE RIVER

Silt, as an important physical flux, has a direct effect on fluvial environment system, Over the last forty years, the vegetation coverage has declined almost a half, and the soil erosion has expanded. Although in the 80th the silt concentration in main stream and tributary of Jinshajiang River increased 12-60 percent compared with that in the 60th, yet the sediment runoff per year through Yichang hydrological station did not increase, In the upper reaches, the large amount of silt coming from the soil erosion and the mountain gravity disaster was brought into fluvial system and piled up in middle and lower courses of the tributary streams. In over 50 % affluent channel, there has occurred severe silt accetion with its yaring ratio 5 - 20 centimeters per year. As a result, parts of the tributary are the charactersistic of braided river because of over-silting, and this has become the great incipient fault of environment in the Yangtze River. When the silting reaches to a limit or the environment changes abruptly, the silt deposited in tributaries must flow into main channel, which will greatly affect the safety of the environment in the Yangtze River. It is thus important to investigate the current conditions and the patterns of silting and silt movement in tributaries in the upreaches of the Yangtze River.