电站建设对澜沧江-湄公河泥沙年内分配的影响

采用澜沧江漫湾电站上游旧州站和下游允景洪、清盛站1987~2003 年逐月悬移质泥沙含量实测资料, 分析对比了三站年内泥沙分配不均匀系数、集中度和集中期、变化幅度等特性。将上述参数与澜沧江上游干流漫湾与大朝山电站建设的响应进行关联研究, 分析电站建设进程对河道输沙变化的驱动作用。结果表明: (1) 旧州水文站泥沙年内分配与区域气候变化 (降水) 趋势一致, 研究时段内不均匀性系数呈上升趋势, 维持天然河道输沙特性; 允景洪和 清盛水文站的泥沙年内分配不均匀性系数对电站建设等人类活动的响应程度不一致, 允景洪站泥沙含量不均匀系数先减小后急剧增加, 而清盛站呈微弱减小态势。(2) 旧州水文站泥沙年 内分配集中度及集中期基本无变化; 允景洪与清盛水文站的泥沙年内分配集中度变化较大, 泥沙集中期在在电站施工的高峰期(1987~1992 年、1997~2003 年) 后延, 且不同步, 允景洪在漫湾施工期后延5~6 天, 而清盛则后延将近半个月,而在大朝山施工期, 允景洪的后延响应 却明显于清盛。(3) 旧州站相对、绝对泥沙变幅逐时段递增, 允景洪站年内最大与最小月泥沙含量的相对、绝对变化幅度均减小, 清盛站泥沙含量的相对变化幅度却先增后减, 绝对变化 幅度则一直减小。三站泥沙年内极值变幅以及电站建设前后的响应差异, 说明三站泥沙变化的驱动因子有明显不同。这些关于泥沙含量年内分配特征规律的发现, 为研究澜沧江干流电站建设对上下游泥沙变化以及跨境影响的科学评价提供了新的佐证。

Impacts of Dam Constructions on the Annual Distribution of Sediment in Lancang- Mekong River Basin

Annual distribution characteristic of river sediment concentration is closely related to climate change and anthropogenic activities and directly affected by the process of hydraulic resource development in the Lancang-Mekong River basin.Using monthly suspended sediment concentrations in 1987-2003 at the three hydrological stations,Jiuzhou,Yunjinghong and Chiang Saen stations,on the mainstream of Lancang-Mekong River,the uneven distributions coefficient,the concentrated rate and period,and the range of variation of annual distribution characteristics of sediment concentrations at the three stations were studied and then the responses of these characteristics to the progress of upstream dam constructions were analyzed.The research results show that:(1) Annual distribution of sediment concentration at Jiuzhou hydrological station agrees with the variation trend of local climate changes,its uneven distribution coefficients(AUDC) increased at the studied period and maintained the characteristics of natural river;AUDCs at Yunjinghong and Chiang Saen stations seemed to be affected by anthropological activities such as dam constructions rather than climate changes,however,sediments of two downstream stations responded differently to the dam constructions.AUDC at Yunjinghong station decreased from the periods of 1987-1992 to 1993-1996,then abruptly increased during 1997-2003;while AUDC at Chiang Saen took on a trend of moderate decreasing in the whole period.(2) Rates and distribution periods of sediment concentrations at Jiuzhou station almost kept stable during the studied period;but those at Yunjinghong and Chiang Saen changed evidently,their distribution periods delayed asynchronously during the dam construction processes(1987-1992,1997-2003),in the period of Manwan dam construction,distribution periods at Yunjinghong station delayed 5-6 days,while Chiang Saen delayed almost half a month,and in the Dachaoshan dam construction,delayed period at Yunjinghong station was longer than that at Chiang Saen.(3) Relative and absolute ranges of sediment variations at Jiuzhou station both increased against the time phases;those at Yunjinghong decreased,while relative ranges of sediment variation at Chiang Saen decreased in the earlier years then increased later,but absolute range was decreasing all the time.Different responses of annual distributions of sediment concentration at three hydrological stations to dam constructions indicate that their driving factors of sediment variation are absolutely different.These discoveries of annual distribution characteristics of sediment concentrations present new scientific evidences for assessing the impacts of dam constructions on upstream and downstream sediment change as well as its transboundary effects.