Variation of Mid-channel Bars in Linhe Braided Channel of the Yellow River and Its Influencing Factors
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.
国家科技期刊平台
NSTL
万方数据
维普
