三峡水库2003年蓄水对长江悬沙中值粒径的影响

长江三峡水库分别在2003-06-01~06-10和10-25~11-05 2次蓄水,坝前水位分别达到135m和139m(吴淞高程)。通过三峡大坝上下游长江干流主要水文控制站(寸滩、宜昌、沙市、汉口和大通)蓄水后(2003~2005)的年均悬沙中值粒径分别与多年平均值以及蓄水前一年(2002)实测值相比较,分析了三峡水库2003年蓄水对长江悬沙中值粒径的影像。结果显示,与2002年和多年平均值相比,寸滩、宜昌、汉口和大通站蓄水后(2003~2005)年均悬沙中值粒径偏小,而沙市站明显偏大。这很可能说明,三峡水库蓄水引起大量泥沙特别是粗颗粒泥沙在库区落淤,从三峡大坝下泻的非正常清水,导致宜昌站至沙市站之间的长江河道遭受到严重冲刷,从该段河道冲刷起来的粗颗粒泥沙随着变小的河道坡降和河水流速,又逐渐沉降在沙市和汉口之间的河道。这些结果有助于决策者更好地管理三峡水库以及各行业学者更好地了解三峡水库蓄水带来的影响。

EFFECTS OF THREE GORGES RESERVOIR WATER STORAGES IN 2003 ON THE MEDIANGRAIN SIZE OF SUSPENDED SEDIMENT OF THE YANGTZE RIVER

The Three Gorges Reservoir(TGR) on the Yangtze River stored water from 1 June to 10 June and from 25 October to 5 November in 2003,respectively,finally elevating the pool level to 135 m and 139 m(at the altitude of Wusong),respectively.The annual mean median grain sizes of suspended sediment of the Yangtze River at the main hydrological stations(Cuntan,Yichang,Shashi,Hankou and Datong) above and below the TGR Dam during 2002-2005 and the multi-yearly averages were used to examine the effects of the TGR water storages in 2003 on the median grain sizes of suspended sediment of the Yangtze River.The results mainly show that the annual mean median grain sizes of suspended sediment of the Yangtze River at Cuntan,Yichang,Hankou and Datong during 2003-2005 were somewhat reduced compared to those in 2002,or with the multi-yearly averages;however,at Shahsi it was markedly increased.This probably indicates that large suspended sediment especially coarse particulates had settled in the TGR,and resultantly the river channel between Yichang and Shashi was badly eroded by the unnaturally clear water from the TGR Dam,and then,the coarser eroded sediment gradually settled along the channel between Shashi and Hankou due to the decreased slope and flow current.These results are helpful to decision-makers for TGR management and to all field researchers for better understanding the effects caused by the TGR water storage.