Based on sand data of six hydrological stations in the main Yellow River,this paper analyzed the spatial and temporal variation
characteristics of grain size of suspended sediments during 1950s to 1986 and 2002 to 2010. The results show that in the case of significant reduction
of sediment loads,yearly median particle diameter of Lanzhou,Longmen,Tongguan and Huayuankou stations shows decreasing
trend,Hekouzhen ( Toudaoguai) and Lijin stations show increasing trend. Changes of the monthly median particle diameter are different in
the six stations. Monthly median particle diameter of Lanzhou Station becomes smooth,Hekouzhen Station becomes sharp,the others are synchronous
and monthly median particle diameter of peak values increases with time. The relationship between the group sediment and total
load is consistent,which shows that the law of sediment composed has not changed in trend. In summary,the change of grain size of suspended
sediment is mainly caused by water and soil conservation and building of reservoirs on the mainstream.
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