Application And Some Characterizations Of Unsteady Open Channel Flow

Open channel flows are unsteady flows basically, so the research of open channel flows' characterizations and laws of movement are very important, which has great significance to river regulation and water storage and flood diversion and levee design. Especially the whole basin flood of the Yangtze River in 1998, through the joint efforts of national people, the whole basin flood was overcame finally. So research of the flood characteristic of the Yangtze River and levee design standard become one of the common discussions.Many papers has researched and analyzed the stage-discharge relationship of middle and downstream reach of the Yangtze River. There are two typical views: the first view copes with the stage-discharge relationship of Luoshan hydropower station by one-valued relation in order to eliminate the influence of water slope, then it thinks sediment deposition is the one of the reasons to the raising of water level in the same discharge; another view thinks the raising of water level in the same discharge is mainly influenced by the characterization of unsteady flow, according to this view the stage-discharge relationship is complicated rope sheath form, whose central axis can variable with different flood, generally it is between 20 to 30 percent, the largest is more than 50 percent.This paper has researched the characterizations of unsteady open channel flow and the 1998 flood's water level characteristic and reason of the typical hydropower stations in the middle reach of the Yangtze River, then analyses the influence of unsteady open channel flow to the flood control standard and crest elevation of levee in the middle and downstream reach of the Yangtze river. The main content is as follows:Chapter 1 mainly discusses the significance of unsteady open channel flow, characterizations of steady open channel flow and unsteady open channel flow.The characteristic of unsteady flow in natural river and flood level in river and flood in Yangtze River are analyzed in the Chapter 2.The fluid characteristic in natural river mainly represents as the unsteadiness of fluid and riverbed, which includes circumfluence, movement of riverbed and riverside and etc, which causes complicated and various numerical value relation between the water level and discharge in natural river. The floodof Yangtze River is mostly caused by rainstorm, the characteristic of flood is associated with the time and the distribution of region of the rainstorm occurred. There are 3 types of special floods in Yangtze River: the regional middle reach flood, the whole basin flood and the regional upriver flood.Chapter 3 mainly discusses the flood in the Yangtze River in 1998. The flood in the Yangtze River in 1998 was another catastrophic and whole basin one since 1954. In 1998 flood's processes, the water level in most hydropower stations in the middle-reach approached or exceeded the corresponding historical records. In some reaches water level in the 1998 flood reached higher than the 1954 record, but the corresponding discharge in the 1998 flood was less than the 1954 record. This paper mainly discusses the reason of this phenomenon. In conclusion influence factors include the heavy storm rain flood, the decrease of flood diversion dam-break, and the worse encounter of flood peaks etc; also analysis the stage-discharge relationship of Luoshan hydropower station with polynomial fitting methods, after influences of stage-discharge relationship is excluded , this paper analyses whether the water level at the same discharge in the typical hydropower stations were raised or not, and the reason for raising of water level, which includes the deposition of sediment and the decrease of flood capacity etc.Thorough the analysis of flood level characteristic, Chapter 4 discusses the importance of levee in the middle and downstream reach of the Yangtze River. This paper suggests that the raising of water level in the same discharge should be considered when the standards to flood control and crest elevation of levee are constituted.Chapter 5 has sum up the whole paper.