Spatio-temopral Evolution Of The Yellow River In Inner Mongolia During The Period From 1962 To 2000,and The Preliminary Study On Its Influence Factors

The Hetao plain is a large energy and grain production base in Northwestern China,accommodates and maintains some minorites,playing a critical role in economical and societal affairs.Its development is closely interrelated to the Yellow River which flowing through this plain.Their relationship is generally described as the maxim that the Yellow River is much more harmful than beneficial but reversal in the Hetao plain.Over the past 50 years,however,the channel of the Yellow River between Linhe and Toudaoguai in the Hetao plain has appeared to be filled up,resulting in the frequent occurrence of flood disasters.Some channels along this reach have been high above surrounding surface,making a severe threat to the public lives and properties.Taking into account these grim problems,reconstructing the spatio-temporal evolution of the Yellow River channel enabling the analysis for the cause of sediment accumulation,thus provides new insight into the regulation of this reach.In this thesis,along the Yellow River in the Hetao plain,the fluvial archive of channel move and the shift between erosion and fill in the past 50 years have been excellently reconstructed and analyzed based on the observed data of cross sections and image data.Moreover,this reach of the Yellow River is divided into two portions according to geomorphic setting.One is named as the Hobq Desert reach from Linhe to Sanhukou,while the other is from Sanhukou to Toudaoguai generally called as the Ten-Watershed reach.The channel move and shift between erosion and fill in the two reaches of the Yellow River is analyzed respectively,and further compared with each other,in order to reconstruct spatio-temporal fluvial archives and probe into the reasons for channel fill in different geomorphic setting.On the basis of the above analysis,this thesis suggests that the channel move and shift between erosion and fill of the Yellow River in the Hetao plain can probably be attributed to the fast invasion of the sediments from Ten-Watershed into the Yellow River channel and a series of dam construction.On the whole,the Yellow River in Inner Mongolia presented a sedimentation tendency from 1962 to 2000.The detailed scenario during this period is that this reach was in a slight sedimentation tendency from 1962 to 1982,a remarkable deposition tendency from 1982 to 1991,and a weak erosion tendency from 1991 to 2000.The fluvial behavior of the Yellow River in different reaches nevertheless fell into a discrepant tendency.The Hobq Desert reach seemed to be in an erosion behavior during the whole investigation period of time,except during the interval of 1982-1991 in which a sedimentation tendency dominated the fluvial behavior.In contrast,the Ten-Watershed reach performed a deposition tendency persistently from 1962 to 2000.The maximum deposited volume occurred in the interval of 1982-1991.Since the sediment runoff from upper stream was roughly equal,the notable difference in fluvial behavior between the two reaches of the Yellow River exactly points to the significant influence of the sediments generated from Ten-watershed on the switch from erosion to fill.The Yellow River channel in the Hetao plain unsmoothly moved northwards during the period from 1962 to 2000,and being companied by channel shrinkage.The northwardly channel migration along the reaches of Hobq Desert and Ten-Watershed can probably be associated with centrifugal pull and the fast invasion of sediments into the Yellow River channel,respectively.In addition,the Ten-Watershed reach of the Yellow River in comparison with the Hobq Desert reach presents a more striking tendency in channel shrinkage.In vertical dimension,the erosion and fill rate along the longitudinal profile of the Yellow River in Inner Mongolia performs an increasing tendency.In the Hobq Desert reach,the erosion and fill rate yet is rather lower than that in the Ten-Watershed reach.On the basis of the comparative analysis for the influence of the sediments invasion from Ten-Watershed,a series of dam construction,discharge variation,and reservoir function on the fluvial behavior of the Yellow River in Inner Mongolia,we can conclude that the deposits transported from Ten-Watershed are the major materials source for the sedimentation along the Yellow River channel.Sediments accumulation along this reach can probably be attributed to a series of dam construction.The function by the reservoirs built along the upper stream of the Yellow River and the reduction in discharge ultimately aggravate the channel sedimentation of the Yellow River in Inner Mongolia.