黄河内蒙古段支流“十大孔兑”侵蚀产沙的时空变化及其成因

“十大孔兑”来沙造成黄河干流强烈淤积.为了通过流域治理来减轻泥沙灾害,研究“十大孔兑”侵蚀产沙过程具有重要意义.基于1960—2005年的河流输沙量、径流量和降雨量资料,运用统计方法进行了研究.结果表明:“十大孔兑”输沙量高度集中于几个大水大沙年份,其余年份对46年总输沙量的贡献很小.最大1年、最大3年、最大5年和最大10年的累积输沙量分别占到46年总输沙量的21.26%、37.18%、47.92%和69.29%.1960—1991年和1992—2005年两个时段相比,后一时段输沙量年均值减少了37%.这一差异可以用暴雨特征的差异和下垫面(如植被)的变化来解释.1991年以后,年降水量无明显变化,但最大1日降雨量在p<0.10的水平上呈现减小的趋势.虽然20世纪90年代西柳沟并未大规模实施水土保持治理,但由于农村富余劳动力转移,对土地的压力减轻,对植被的破坏大大减弱,使得植被逐渐恢复,NDVI呈增大趋势,因而侵蚀产沙减弱.“十大孔兑”产沙模数具有明显的空间分异特征,从西向东增大,在西柳沟达到最大值,然后再减小.流域自然地理因素具有明显的变化,从西向东,沙尘暴频率减小,降雨量增大.沙丘类型也发生了变化,由以流动沙丘为主变为以半固定沙丘为主,进入河道风沙的输沙强度减小.另一方面,水力驱动的侵蚀和泥沙输移从西向东增强.上述两种作用叠加的结果,在区域中部西柳沟附近出现了侵蚀产沙的峰值区.

Temporal and Spatial Variations in Erosion and Sediment Yield and the Cause in the Ten Small Tributaries to the Inner Mongolia Reach of the Yellow River

Sediment supply from the ten small tributaries causes strong sedimentation in the upper Yellow River. For the purpose of reducing sediment-related disasters through soil erosion control measures in the ten small tributaries, we studied the soil erosion regularity in the ten small tributaries based on data of sediment load, runoff and precipitation from 1960 to 2005. The total sediment supply in the 46 years was highly concentrated in a few years with large sediment load and runoff, and the sediment yield from the remaining years made little contribution. The cumulative maximum 1-year, 3-year, 5-year and 10-year sediment yield accounts for 21.26%, 37.18%, 47.92% and 69.29% of the 46-year's total, respectively. Comparison with during1960-1991, the annual sediment yield from the Xiliugou River during 1992-2005 decreased by 37%. This difference can be explained by two factors, the difference in rainstorms and the variation of vegetation. After 1990, although annual precipitation shows no significant change, the maximum 1-day rainfall has a decreasing trend (p<0.10). The NDVI shows an increasing trend (p<0.01), which is caused by the transfer of surplus rural labors out of the land. The specific sediment yield shows clear spatial difference. In the ten small tributaries, it increases from west to east, reaching the maximum in the Xiliugou River, and then decreases. In the same direction, annual precipitation increases, the frequency of sand-dust storms decreases, and the types of sand dunes gradually change from movable to semi-fixed ones. Thus, the wind-blown sand to the rivers decreases, while the erosion and sediment transport by water increases. The superposing of these two processes leads to the occurrence of a peak of specific sediment yield near the Xiliugou River.