Study On The Characteristics And The Coupling Characteristics Of Unsteady Flow In Jinsha River And Minjiang River

The new unsteady flow process is produced in Yibin with the confluence of unsteady flow which produced by the Xiangjiaba hydropower station in the Jinsha River and the cascade hydropower station in the Mingjiang River,and the daily water level reached 3.5 m.The unsteady flow process of the two rivers has brought a number of adverse effects on the construction and maintenance of the downstream channel,and shipping in the upper reaches of the Yangtze River will face these problems in the long term.Therefore,it is necessary to predict the water-level amplitude at Yibin,which is the starting point of the high-level channel in the upper reaches of the Yangtze River.The research on the characteristics of the unsteady flow in the two rivers and coupling laws is a prerequisite for solving the above problems.This paper firstly summarized the flow and water level process of Xiangjiaba in the Jinsha River,Gaochang in Minjiang and Yibin in recent four years and the characteristics of respective unsteady flow were obtained.On this basis,mathematical model is used to analyze the variation of ratio,velocity and wave shape of unsteady flow propagation and confluence of two rivers,obtains the coupling law of the water flow variation and wave-wave and the relationship of wave-flow.The following conclusions are obtained:(1)From 2013 to 2016,the daily regulation time of the XiangJiaba hydropower station increased from 1700 hours to 6000 hours gradually,the daily regulation flow was 1660~4380m~3/s,the daily flow amplitude was 0~1500m~3/s,the diurnal amplitude of water level was mainly in 0~2m;and the flow of Minjiang River was not obvious,distributed in 600~1600m~3/s,and the daily amplitude of flow was concentrated in150~800 m~3/s,The diurnal amplitude of water level is mainly 0.16~1m.The water level in Yibin had an irregular change because influenced by the two rivers,it's average amplitude of the water level is 0.3m and 0.65m in 2015 and 2016respectively.(2)The shape of flow and level in Jinsha River changes from square wave to sine wave,while it keep constant in the Minjiang River when the unsteady flow propaies along the path.Though the wave height rives and falls,it keeps the change trend consistengt in the same position,and the overall trend is gradual reduction.Finally,the distribution of wave height of the two rivers varies greatly,and the wave height of more than 1.8m in Jinsha River and over 1m in Min River is basically disappearing.there is little change in the unsteady flow cycle,the maximan phase of Jinsha River moves forward for 1 hour,while the Min River moves forward 1to 3hours.As for the wave speed,the Jinsha river is 4.17 to 5.18 meters per second,and the MinRiver reaches 1.94 to 3.16 meters per second.(3)The flow factors of the two rivers will change gradually during the confluence process:the water level in Jinsha River increases first and then decreases,to the peak of 4~6km in the upper reaches of the estuary,near 0 in the vicinity of2km;while the water level of the Minjiang River decreases continuously;the closer to the confluence mouth,the smaller the flow velocity of the two rivers.Influenced by the confluence ratio,flow volume and the phase of two rivers,the flow of two rivers have different characteristics.(4)Unsteady flow of Yibin is a comprehensive result of coupling between flow and wave shape process of two rivers,the influence between the waves-wave is larger than that between wave-flow among these factor.During the coupling process of unsteady flow of two rivers,the change of wave shape mainly occurs in the upper reaches of the estuary 6km~2km,and the smaller branches of the wave vary greatly along the path,and even the wave shape will turn over.The larger tributaries of the wave height between the Jinsha River and the Minjiang River have great influence on the wave shape of Yibin,and the greater the two river wave height difference,the closer the wave shape,wave height and cycle of Yibin are with the tributary,however,the wave velocity and wave length are always closer to the Minjiang River.When a branched wave height is higher than the another,the superposition results of the two rivers rising section,wave peak,descending section and trough are consistent with the shapeer.When the difference between the wave height of two river is small,there will be different superposition results between the different phase of the two rivers.