黄河宁蒙河段悬沙冲淤量时空变化及其影响因素

通过对黄河宁蒙河段6个水文站1952~2003年间的实测悬移质泥沙资料,运用输沙平衡方法,对划分的5个时段和5个区段的悬沙冲淤量进行了计算分析,探讨宁蒙河段悬沙冲淤量的时空变化规律。黄河上游无大型水库的1952~1959年间和水库建成坝下河道充分调整后的1994~2003年间,宁蒙河段强烈淤积,年均悬沙淤积量分别为0.9588亿t/a和0.9503亿t/a;而期间的三个时段,年均悬沙分别为净侵蚀0.6127亿t/a、微淤0.0161亿t/a和较强淤积0.7475亿t/a。年均悬沙淤积量在宁蒙河段为0.345亿t/a;在宁夏河段为0.076亿t/a,其中下沿河~青铜峡区段微淤,青铜峡~石嘴山区段冲淤平衡;在内蒙古河段总和为0.269亿t/a,石嘴山~巴彦高乐、巴彦高乐~三湖河口、三湖河口~头道拐三个区段分别为0.0084亿t/a、0.113亿t/a和0.147亿t/a,沿程增大。悬沙淤积量的时间变化主要受到区间支流来沙量变化和水库建设的双重影响,而空间变化主要受到青铜峡水库拦沙以及刘家峡、龙羊峡水库消减洪峰的影响。黄河宁蒙河段处于构造沉降区,淤积是总趋势,人类活动可以引起个别时段、区段发生侵蚀,但无法改变其沉积的总趋势。

Spatial and temporal variations of suspended sediment capacity by erosion or deposition in the Ningmeng Reach of the Yellow River and its influencing factors

The channel variation of the Ningmeng Reach has been very remarkable in the upper Yellow River and has increased flood risk. To reveal the channel variation trend and its influencing factors the sediment budget method was adopted in this study. The Ningmeng channel was divided into 5 sub-reaches, simultaneously, the total time period was divided into the 5 time periods. The mean annual erosional or depositional suspended sediment capacity (SSC) at the 5 different sub-reaches during the different time periods was calculated and analyzed. The results show that, sedimentation strongly occurred during 1952~1959 when there was no big reservoir and during 1994~2003 when the three big reservoirs of Qingtongxia, Liujiaxia and Longyangxia had been built and the downstream channel had been adequately adjusted. The mean annual SSC is 9.588×10⁷ t/a and 9.503×10⁷ t/a for the two periods, respectively. Intense erosion (-6.127×10⁷ t/a), slight deposition (0.161×10⁷ t/a) and stronger deposition (7.475×10⁷ t/a) respectively occurred in the periods of 1960~1968, 1969~1985 and 1986~1993. The mean annual deposited SSC is 3.45×10⁷t/a in the Ningmeng Reach, including 0.76×10⁷ t/a in the Ningxia reach and 2.69×107 t/a in the Neimenggu reach. The annual mean SSC deposited in the 5 downstream channel reaches in the Ningmeng Reach of the Yellow River is 0.73×10⁷ t/a, 0.029×10⁷ t/a, 0.084×10⁷ t/a, 1.131×10⁷ t/a and 1.47×10⁷ t/a, respectively. The temporal variation of the SSC in the Ningmeng Reach of the Yellow River was mostly influenced by the decrease of suspended sediment load from the tributaries and reservoir construction, whereas, the spatial variation was mostly influenced by the interception of suspended sediment load in the Qingtongxia reservoir and adjustment of flood discharge in the Liujiaxia and Longyangxia reservoirs. The Ningmeng Reach is located in a subsidized area and the sedimentation in this river reach is the general trend. Human activities may induce channel erosion in certain periods or sub-reaches, but cannot change the general trend.