人类活动影响下长江上游水沙条件变化趋势

长江是中国最重要内陆水运通道之一。近年来,人类活动(梯级水库建设和人工采砂)严重影响了长江上游河道河床演变规律。通过分析长江上游2005至2017年的水沙实测资料,对比长江上游梯级水库联合运行前后(2012年前后)发现,梯级水库群下游年内水文过程与泥沙输运量受水库群运行的影响较大。梯级水库拦沙作用使长江上游河段年均推移质和悬移质较水库群建成前分别减少了87%和98.5%,水库群下游泥沙补给大幅减小引发河床冲刷、粗化,河床表层床沙中值粒径较水库群建成前明显增大。人工大面积采砂破坏长江上游河道河床粗化表层,形成局部挖沙坑,造成河床形态异常演变。总体来看,梯级水库清水下泄与采砂监管将使水库群下游河道表层粗化层更加稳定,河床演变逐渐趋近稳定。

The Impact of Human Activities on the Variation of Water and Sediment Conditions in the Upper Reaches of the Yangtze River

The Yangtze River waterway is the most important in Southwest China.In recent years,human activities have seriously affected the riverbed evolution of the upper reach of the Yangtze River.By analyzing the measured data of water and sediment in the upper reaches of the Yangtze River from 2005 to 2017,and comparing the combined operation of cascade reservoirs in the upper reaches of the Yangtze River(around 2012),it is found that the hydrological process and sediment transport volume in the lower reaches of cascade reservoirs are greatly affected by the operation of cascade reservoirs.As a result,the average annual bedload and suspended load in the upper reaches of the Yangtze River have decreased by 87%and 98.5%,respectively,compared with that before the completion of the reservoir group.The sediment supply in the lower reaches of the reservoir group is greatly reduced,leading to riverbed scouring and coarsening,and the median particle size of riverbed bed sand is significantly increased compared with that before the completion of the reservoir group.Artificial large-scale sand mining destroys the surface layer of the riverbed of the upper reaches of the Yangtze River,forming local sand pits and resulting in the abnormal evolution of riverbed morphology.Under the continuous construction of cascade reservoirs and the gradual strengthening of sand mining supervision measures,the channel bed downstream of reservoirs is becoming stable.