Abstract
The Yellow River (YR) covers three climatic zones including arid region, semi-arid region and temperate monsoon region, with frequent appearance of flow intermittence in the Lower Yellow River (LYR) before 1999. Channel migration occurs frequently in braided rivers, which is a major focus of study in geomorphology and river dynamics. The braided reach in the LYR is featured by a complexly spatio-temporal variation in channel migration parameters owing to the varying condition of flow and sediment. It is crucial to investigate the migration characteristics of channel centerline for the sake of fully understanding channel evolution. A detailed calculation procedure is proposed to quantify migration rates and intensities of channel centerline at section- and reach-scales, using the measurements of remote sensing images and cross-sectional topography. Migration rates and intensities of channel centerline at section- and reach-scales from 1986 to 2016 were calculated, with the characteristics and key factors to control the migration intensity of channel centerline being identified quantitatively. Calculated results indicate that: (i) the mean probability of centerline migrating toward the left side was approximately equal to the probability of rightward migration from a long-term sequence; (ii) the mean reach-scale migration rate of channel centerline was reduced from 410 m/yr in 1986–1999 to 185 m/yr in 1999–2016, with a reduction of 55% owing to the Xiaolangdi Reservoir operation in 1999, and the mean reach-scale migration intensity of channel centerline was decreased from 0.28 to 0.16 m/(yr·m), with a reduction of 43%; (iii) the incoming flow-sediment regime was a dominant factor affecting the degree of channel migration, although the channel boundary conditions could influence the intensity of channel migration; and (iv) the reach-scale migration intensity of channel centerline can be written as a power function of the previous two-year average incoming sediment coefficient or fluvial erosion intensity, and the reach-scale migration intensities of channel centerline calculated using the proposed relations are generally in close agreement with the measurements over the period of 30 years.
Highlights
Braided channel pattern is one of the common river patterns of natural rivers, which is widely distributed throughout the world
The annual water volume entering the Lower Yellow River (LYR) changed slightly with a reduction of 8%, whereas there was a huge reduction of 92% in annual sediment discharge
This study, a characteristic condition in and a study is generally expressed by a specifiedInfunction of the mean water parameter termed as fluvial erosion intensity (Fi ) is used toIndepict the incoming condition discharge and the corresponding sediment concentration
Summary
Braided channel pattern is one of the common river patterns of natural rivers, which is widely distributed throughout the world. Yellow River (LYR) in China and the Jamuna River in Bangladesh belong to typical braided rivers [1,2]. These rivers have a number of central bars or islands, which lead to multiple channels at low flows, and such a planform geometry usually results in frequent lateral channel shifting. The main-channel near the Liuyuankou section of the braided reach in the LYR shifted to and fro along the north-south direction during the 1954 flood season, with the migration amplitude greater than 6 km within 24 h [3]. The channel shifts frequently, with lateral migration rates greater than 500 m/yr [4] These fluvial processes of braided rivers can cause unfavorable effects
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