Abstract
The fluvial river is a kind of open system that can interact with its outside environments and give response to disturbance from outside on the earth. It can adjust itself to the disturbances outside the system and reflects new characteristics in the process of reaching a new equilibrium. The TGD (Three Gorges Dam) constructed at the Yangtze River Upstream was set up to operate in 2003. And it has changed the boundary conditions of the downstream reaches and has broken the long term equilibrium of the Yangtze River system. The reaches alter the river regime to response the disturbance from the TGD. In this paper, the case study Shashi Reach is selected to analyze the variations of the river regime in a river system. The discharge is becoming smoother without large peak or lower discharge for the regulation of the reservoir. The sediment diameter becomes coarser downstream of the TGD and the sediment transport rate decreases as the sediment concentration becomes lower, in spite of the sediment erosion along the reach downstream. The thalweg moves in plane dramatically to adjust itself to reach a new equilibrium. And the topography changes a lot since there are different sediment and flow conditions. The disturbed river system is in the process of reaching a new equilibrium.
Highlights
Rivers are large natural streams flowing in channels on the earth
This paper describes the disturbance from the construction of the Three Gorges Dam (TGD) and its influence on the Yangtze River system
The river system has to adjust itself to the disturbance and reflects new river regime characteristics till it reaches a new equilibrium
Summary
Rivers are large natural streams flowing in channels on the earth. Generally, river systems are open as other systems in the nature. As a sub-system of Yangtze River, Shashi Reach system is facing the change of system boundary, i.e., the incoming flow and sediment transport. Shashi Reach downstream from the TGD is selected to study the river regime responses to the disturbance from the TGD’s operation. For the operation of the TGD, the upstream incoming flow and sediment transport change a lot with that in the past [14] This reach can be seen as a river sub-system. The water quantities are used to generate the electricity This operation scheme gives a continuous disturbing influence on the whole river system, and the disturbance will push the river regime to change downstream the TGD and have a long term influence. The developments of the shoals are induced by the disturbance outside the river system, i.e., by the variables of incoming sediment and flow downstream from the TGD. The changes of thalweg and topography indicate the process of system’s adjustment to the disturbances
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