Abstract
The flow and sediment condition in the middle and lower reaches of Yangtze River (MLYR) was changed a lot after the impoundment of Three Gorges Reservoir (TGR), and further, the evolution process of the sandbars and shoals were affected, both of which have obvious influence on the navigation in the MLYR. Based on the field data, the analysis shows that the changes of flow and sediment favored the waterway condition, which includes the elevation of the lowest water level, the extension of the scour time of shoals, the increase of the erosion speed of shoals caused by the reductive sediment. After the operation of TGR, the frequency of the bank collapse and the sandbar cutting is increasing, and the shoal tends to shrink. However, not all the deformation of sandbars and shoals will obstruct the waterway, only the Critical Width of Returning to Channel (CWRC) is more than the critical river width, the channel will not be unimpeded. The CWRC is about 900–1900m, varying with the navigation base surface and the channel dimension.
Highlights
The main stem of the Yangtze River is a transportation artery communicating East part – West part of China, known as the golden waterway (Gao et al, 2013; Chen et al, 2010; Zhang et al, 2006; Xu et al, 2011)
If the sandbar deforms rarely after impoundment of Three Gorges Reservoir (TGR), and the duration of the critical flow of returning to channel (CFRC) turns longer, the channel average flow increases, the lowest water level raises, the shoal deposition slows down but the erosion accelerates, the CFRC tends to increase, which are all advantageous to the improvement of the channel condition, namely the change of the flow and sediment conditions is favorable for the channel
Arranging of the field terrain data in the middle and lower reaches of Yangtze River (MLYR) and combining the change of navigation condition over the years, analysis shows that the effect on the channel by sandbar deformation can be divided into two kinds: the channel condition obstructs the navigation after the deformation as well as doesn’t impede navigation after the deformation
Summary
The main stem of the Yangtze River is a transportation artery communicating East part – West part of China, known as the golden waterway (Gao et al, 2013; Chen et al, 2010; Zhang et al, 2006; Xu et al, 2011). The impoundment of TGR changes the downstream flow and sediment condition and has an influence on the navigation condition of MLYR (Dai et al, 2013; Xia et al, 2014). The field data shows that the channel condition in the MLYR turns better as a whole after the impoundment of TGR, though part of them deteriorates. Based the analysis of the changes of flow and sediment condition and the deformation of sandbars and shoals, combining with the field data before and after the operation of TGR, dissect their impact on the channel condition, so as to provide a reference for the waterway remediation and the upstream reservoir regulation. The Impact on Flow & Sediment Condition & Sandbar Deformation by Impoundment of TGR
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