Comparison of Depositional Dynamics among the Braided, Meandering and Straight Channel Reaches in the Lower Yellow River

Key words: 
• depositional dynamics

Abstract: There are braided, meandering and straight channel reaches along the lower Yellow River. The difference in channel planform certainly is influenced by different depositional dynamics. In this work, according to a series of data collected from the yearbook of the water and sediment of the Yellow River, the different indexes of representative channel depositional dynamics has analyzed. The results show that, there are evident differences in depositional dynamics among the braided, meandering and straight channel reaches in the lower Yellow River. The channel gradient is the maximum for the braided reach, which ranges 0.20.14, is moderate for the meandering reach, which ranges0.140.10 , and the minimum for the straight reach, which less than 0.10%. The flow velocity of the bankfull discharge is also larger for the braided, moderate for the meandering and least for the straight reaches. Its variational extent decreases downwards along the three channel patterns. The gross power of stream flow is decreases from the braiding via meandering to straight reaches and its ratio is 2.31∶〖KG-*2〗1.35∶〖KG-*2〗1. The specific power of stream flow is minimum for the braided, maximum for the meandering and moderate for the straight reaches and its ratio is 0.52∶〖KG-*2〗1.18∶〖KG-*2〗1. The channel bed sediment is relatively fine and generally lacks the roll component. The median grain size is 3.0, 3.2 and 3.67 for the braided, meandering and straight reaches, respectively, furthermore, the sediment sorting is also enhanced along the different channel reaches downwords. Be enslaved to the abovemationed depositional dynamics, the sedimentation rate on channel bed is different among the three channel pattern reaches. It is the minimum for the braided, maximum for the meandering and moderate for the straight reaches when discharge is moderate to large, and it is approximative among the three channel pattern reaches, but a decrease tendency downwards, when discharge is small. In addition, the sedimentation rate on braided channel bed evidently depends on the variation of discharge, and decreases with increasing discharge. 
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