黄河临河辫状河段心滩变化及其影响因素分析

Variation of Mid-channel Bars in Linhe Braided Channel of the Yellow River and Its Influencing Factors

心滩作为辫状河道最主要的微地貌特征,其变化特征的研究对于理解辫状河道的演变具有重要意义。以黄河临河段213km长的辫状河道为研究对象,基于1988—2013年的遥感图像绘制了相应日期的河道平面形态图,分析了该河段心滩数量和心滩面积变化;利用2013年内6幅河道平面图建立了心滩面积与巴彦高勒站水位之间的线性关系式,利用该关系式求取了其他年份1 050m参考水位下的心滩面积并进行心滩冲淤变化对比。结果表明:黄河临河段心滩总个数、心滩总面积、心滩平均面积、中位数心滩面积和最大心滩面积总体上都具有减小的趋势。在1 050m参考水位下,黄河临河段心滩面积在1988—2013年具有不同的冲淤变化特征,其中在2000年以前的变化幅度大,趋势不明显,2000年以后则分布较为集中,且有减小的趋势,并在1990—2000年大幅减小。在龙羊峡、刘家峡等水库运行影响下汛期黄河临河段水量和输沙量占全年的比例在减小,年内分配趋于均衡化,并且输沙量的减幅要大于水量的减幅,这对于研究区心滩的冲淤有重要影响。同时,上游流域来沙系数的变化也在一定程度上影响着该河段心滩的冲淤变化。

As the main micro-geomorphic features of the braided channel,study on variation of the midchannel bars contributes to understanding the evolution of the braided channel.Taking the braided channel with a channel length of 213 km in Linhe of the Yellow River as an example,we drew the channel planform in different years from 1988 to 2013,furthermore,we analyzed the variation of the numbers and sum area of the mid-channel bars based on the remote sensing images.We fitted a relationship between area of mid-channel bars and the water level of Bayangaole gauging station according to six images and the hydrological data in 2013.Then,the areas of mid-channel bars at the reference water level of 1 050 meters in other years during the period from 1988 to 2013 were calculated by the relationship to compare the erosion-deposition of the midchannel bars.The results show that the total numbers,mean area,total area,median area,and the largest area of the mid-channel bars in the Linhe have the decreasing trend as the whole.At the reference water level of 1 050 meters,the erosion-deposition variations of the mid-channel bars from 1988 to 2013 are different.The variation trend of the mid-channel bars was not obvious before 2000.Their distribution was more concentrated and had a decreasing trend after 2000.The significant decrease of mid-channel bar areas occurred in the period from 1990 to 2000.In the river reach,the proportions of runoff and sediment load in flood season accounting for the whole year decreased.This phenomenon was affected mainly by the joint operation of Longyangxia and Liujiaxia reservoirs.The distribution of runoff and sediment load in a year tends to be equal and the sediment load decreased to a greater extent than runoff.This has an important influence on the erosion-accretion variation of the mid-channel bars in the study reach.At the same time,the changes of the sediment delivery coefficient from upstream can affect the erosion-deposition variation of mid-channel bars in this reach to a certain extent.