黄河内蒙河段河床冲淤演变特征及原因

利用黄河内蒙段1962-2000年间4期大断面观测资料,计算了各期河床冲淤和河槽形态指标。发现从1962-2000年间前20年、中间9年及后9年,内蒙河段河槽500m²过水面积下河底高程发生了降低-升高-再升高的过程;河槽漫滩过水面积经历了升高-降低-再降低的过程,2000年只有1982年的大约一半;滩地经历了持续淤积过程,平均抬升0.25m;河槽宽深比值经历了变化不显著-增加-减小的过程。分析结果表明:气候变化、引水、水库拦沙和重点产沙支流来沙变化在河床冲淤和河床形态调整中作用较大;水库对径流的年内调节对1982年后河槽淤积贡献较大;来水来沙变化下河流多要素自动调整是造成河槽形态变化过程复杂的原因。

Channel change of the Inner Mongolian reach of the Yellow River and its causes

Using measurements of channel cross sections along the Inner Mongolian reach of the Yellow River made by 4 times during the period 1962-2000,the authors computed the thicknesses of scouring and silting of the main channel bed and flood land,and indexes of channel cross-section geometry.Some characteristics of channel adjustment in the Inner Mongolian reach were revealed.The channel bed of 500 m² wet area experienced a process from being scoured of 0.9 m before the year 1982 to being accumulated by 1.6 m thereafter on average,so did the thalweg with scouring and silting thicknesses slightly different from those of the channel bed of 500 m² wet area.Also,the channel capacity increased before 1982 and decreased thereafter,and the channel capacity in 2000 was only about half of that in 1982.The floodland was silted up continuously and increased by 0.25 m on average.The width of the main channel did not change at a significant level from 1962 to 1982,but increased significantly from 1982 to 1991 and decreased significantly from 1991 to 2000.The depth of the main channel increased at first,then decreased and increased again all at a significant level from the early to the later periods.The ratio of square root of the width to depth changed following the same direction as the width.Through analyses of the hydrological data,climate change and water diversion were recognized as the main factors which altered the water discharge and sediment carrying capacity and led to obvious channel changes in the Inner Mongolian reach,and runoff reduction due to climate change was found to be the main cause for serious sediment accumulation and channel shrinkage during the period 1992-2000.Among the factors influencing sediment input,sediment detaining behind dams and variations in sediment load of three main tributaries,i.e.,the Zuli,Qingshui and Kushui rivers,played an important role in sediment erosion and accumulation and in channel adjustment,and they were the main causes for channel erosion in the period 1963-1982.The inner-annual runoff regulation by reservoirs was a main contributor to sediment accumulation in channel during the period 1982-2000.The complex temporal changes in channel adjustment could be attributed to multiple dimensions of channel adjustment.