Impacts of variations in the time series of flow discharge and sediment transport rate on main channel switches: Case of Jianli anabranching reach
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Abstract:
Many anabranching reaches in the middle and lower Yangtze River have been experiencing frequent switches of main flow from one channel to another, while the mechanism and influencing factors of the phenomenon are still elusive. To examine how the phenomenon is related to the changes in hydrological process, this study applies rescaled range analysis, Mann-Kendall test and anomaly analysis methods and examines in detail the changes in the time series of annual flow discharge and annual sediment transport rate based on observations from 1951 to 2009 at Jianli hydrological station in the Middle Yangtze River. It is shown that the Hurst exponents of the time series for flow discharge and sediment transport rate take respective values of 0.9430 and 0.9239, implying that both time series have long-memory or persistent characteristics. Man-Kendall detection shows that a significant abrupt change in flow discharge time series occurred in 1967, mainly resulting from river cutoffs taking place upstream, while there is not any significant abrupt change in sediment transport rate time series during the same period. Both rescaled range analysis and Mann-Kendall test methods show that there is no match between the time of each channel switch and variations in the time series of either flow discharge or sediment transport rate. Nevertheless, it is found that when the time series of flow discharge in a flood-dominated regime while the time series of sediment transport rate in a low regime, the right-hand side channel functions as the main channel, while flow discharge in a low regime but sediment transport rate in a high regime, the left-hand side channel serves as the main channel. This demonstrates that it is the matching regimes of flow discharge and sediment transport rate that determines if main flow switches from one channel to the other.
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