黄土高原泾河流域1960—2000年的年输沙量时空变化

为制订合理有效的水土流失治理政策,需定量了解流域的泥沙输移总量及其时空变化。以黄土高原多泥沙的典型流域泾河为例,按有连续水文观测数据的11个水文站的控制范围,把流域划分为11个河段,统计分析1960—2000年间的年均输沙量和输沙模数在不同年代的变化和空间上的差异。结果表明:1)20世纪60年代泾河流域年均输沙量为3.024 9亿t/a,年均输沙模数为6 672 t/(km2.a);输沙等级为强度,但空间分布不均匀,其中输沙等级为极强度和强度的河段面积占流域面积的72.6%,其年均输沙量占流域总量的86.0%;输沙等级为中度和轻度的河段面积占流域面积的27.4%,其年均输沙量占流域的14.0%。2)20世纪70年代以来,泾河流域年均输沙量开始减少,90年代已减至2.657 8亿t/a,较60年代下降了12.1%,减沙主要发生在输沙等级为极强度的河段,其减沙量占流域总减沙量的93.5%,尤其以降水较高、植被较好的西部地区为主要贡献区,而其他输沙等级河段的年输沙量基本保持不变。因此,在侵蚀性暴雨增加的气候变化背景下,植被稀疏、抵抗暴雨侵蚀能力差的半干旱地区应列为水土保持重点地区。

Spatial-temporal variation of annual sediment yield during 1960-2000 in the Jinghe Basin of Loess Plateau in China

Quantitative estimation of river sediment yield and its spatial-temporal variation within a river basin is prerequisite to develop an effective strategy for soil erosion control.In this study,the Jinghe basin,where high soil erosion exists,was chosen as representative research area.Based on existing long-term records of 11 hydrological stations,the total river basin was divided into eleven river courses to quantify the spatial-temporal heterogeneity of annual sediment yield during the period of 1960—2000.The results indicated that there was a strong annual sediment yield in Jinghe Basin in the 1960＇s,it was 302.49 million t/a for the total river basin and the corresponding annual sediment modulus was 6 672 t/（km2·a） on average.There was a visible spatial heterogeneity of annual sediment yield within the basin.The total area of river courses with sediment yield intensity grades of ＂extreme＂ and ＂severe＂ accounted for 72.6% of the total basin area,which contributed 86.0% of the annual sediment yield of the total basin.The river courses with sediment yield intensity grade of ＂moderate＂ and ＂slight＂ covered 27.4% of the total basin area and contributed 14.0% of annual sediment yield of total basin.Since 1970＇s,the annual sediment yield in Jinghe Basin reduced.Compared with that of 1960＇s,the average of annual sediment yield for the whole basin in 1990＇s decreased to 265.78 million t/a,with a reduction ratio of 12.1%.However,93.5% of this sediment reduction took place in the river courses with ＂extreme＂ grade of sediment yield intensity.This demonstrated that the river courses with ＂extreme＂ grade of sediment yield intensity made a substantial contribution to the sediment reduction in Jinghe Basin,especially the river courses in the west region of Jinghe Basin with higher precipitation and better vegetation coverage;while the sediment yield and contribution from the areas with other grades of sediment yield intensity was basically unchanged.Under the future regional climate change with increasing erosive rain-storms,the semi-arid regions of the Jinghe Basin with lower vegetation coverage and resistance against rainfall erosion should be listed as the key area for erosion control.