长江上游干支流悬移质含沙量的变化及其原因

河流含沙量的变化是流域自然与人文因子变化的反映。以长江上游干支流1956~2000年的水沙和降水资料为基础,运用时间系列分析和统计分析方法进行研究。研究发现,干流宜昌站和4条主要支流含沙量的变化不是同步的,4条主要支流含沙量的变化呈现出复杂变化图形。流域面平均年降水量的变化,仅能解释含沙量变化的15.86%~37.21%,说明气候因素的变化不是长江干支流含沙量变化的主要原因。运用双累积曲线分析方法,研究了人类活动 (如水库修建,交通、矿山和城市建设,水土保持,植被破坏和恢复等 )对含沙量变化的影响。人类活动影响在不同的流域有较大差异。与4条主要支流相比,长江干流宜昌站含沙量的变化较小,反映了尺度效应的影响。多元回归分析表明,屏山 、高场、北碚、武隆4站的年均含沙量变化对宜昌站年均含沙量变化的贡献率分别为28.5%、12.6%、44.2%和14.7%。

Temporal variation in suspended sediment concentration of the upper Changjiang River and its tributaries

Based on water,sediment and precipitation data from the upper Changjiang River and its tributaries,a study has been made of the temporal variation in suspended sediment concentration in relation with the variation in precipitation and human activities.The variations in suspended sediment concentrations in the main stream and tributaries are not synchronic,and some complicated variation can be seen.The variation in precipitation can only explain 15.86%~37.21% of the variation in suspended sediment concentration,and thus variation in precipitation is not the main cause for the variation in suspended concentration.Using the analysis of double-mass curve,the effect of human activities on the variation in suspended concentration has been studied.The suspended concentration of the lower Jinsha River increased ofter 1983.This can be explained by the large-scale mining and road and urban construction,which not only disposes huge quantities of soil and rock debris to the river,but also results in the reactivation and releasing of the previously deposited mass-wasting and debris flow materials.The double-mass curve for the Minjiang River shows three breaks,which may be explained by reservoir construction and deforestation and reforestation.The suspended sediment concentration of the Jialing River decreased after 1984 because marked sediment reduction effect has been achieved by soil and water conservation measures.The suspended sediment of the Wujiang River increased after 1967 and then decreased after 1983,the former can be related to the vegetation destruction that enhanced soil erosion and the latter to the construction of reservoirs that trapped sediment.Compared to the 4 tributaries,the suspended sediment of the main stream of the upper Changjiang River shows smaller variation in suspended sediment concentration.As the suspended sediment concentration of the lower Jinsha River increased after 1983 while that of the Jialing River decreased after 1984,they offset each other and thus the variation in the suspended sediment concentration of the Yichang station is much smaller.The results of a multiple regression analysis shows that the contribution percentages of the variation in suspended sediment of Pingshan,Gaochang,Beibei and Wulong stations are 28.5%,12.6%,44.2% and 14.7%,respectively.