Effects Of Water And Sediment Of Jinghe River On The Deformation Of Riverbed Of Weihe River

As a channel of hyper-concentration flow, Jinghe River is the main tributary of Weihe River and transports a large amount of sediments to the River. Sediment plays an important role in a streambed formation; hence the situation of water and sediment in Jinghe River means much to the streambed of Weihe River. In the history, Weihe River had been in a long time stable stage of silting and scoring but now is heavily silted and the major trough was seriously shrinking, and the ability of discharging flood through a cross section gets lower. As a result, even the normal flood in Weihe will bring a large flood disaster, which prevails and greatly hinders the development of Shaanxi's economy/, and thus receives wide regards of all levels. All of those mean that it is quite necessary to research on the effects of Jinghe River on the bed deformation of Wei River.This thesis associated with the studying subject, the mechanics of channel shrinking and its influence on the situation of flood control at downstream channel of Weihe River, discusses the influence of Jinghe River on the downstream channel of Weihe River and gets the conclusion that in the past, on the one hand, the boundary of the channel bed at downstream reach of Weihe River could adapt the water and sediment combination of Jinghe River and the other hand, the combination in turn has dynamical force to govern the deformation and keep the lower reach of Weihe River in a dynamic balance between scouring and silting. Nowadays, the combination and the boundary can't adapt each other any more in a short time, which make the downstream riverbed of Weihe River be heavily silted. So the role of Jinghe River has been changed and becomes a harmful river. This change is not because of a spontaneous variation but a passive mode. The major conclusions of this thesis are as follow:(1) The occurring frequency of big flood (Q>2600m~3/s)with hyper-concentration gets small but that of small flood (Q<810m~3/s) with hyper-concentration increases significantly, and a large sediment content presents with high frequency. As to the annul runoff of Jinghe River, it has not changed so much withinperiod from year 1955 to 2003 while the annul sediment runoff coincides with annul runoff before 1982 and less than that slightly after 1982.(2) In the past, flood from Jinghe River can scour more silts laying in the channel around Huaxian hydrometric Station, even if the small flow with hyper- concentration silted the river temporarily, the subsequent big flow with hyper- concentration could scour the silts in major trough by its ability of carrying sediment. This is to say, Jinghe River plays a dynamical role to the lower reaches of Weihe River and keep the dynamic balance between scouring and silting.(3) Now Jinghe River's water and sediment combination has lose its dynamical effect because the water amount and sediment content of Jinghe River have changed and don't adapt to the boundary condition of riverbed of Weihe River. The boundary condition of the lower reach of Wei River have in turn also changed and can't adopt the Jing River's water and sediment. Besides, the situation of water and sediment from Xianyang hydrometric station of Weihe River has changed too, resulting in the percentage increase of water and sediment amount from Jinhe to the total measured at the Huaxian hydrometric station. On the whole, the trance of water and sediment change in Jinhe is not conducive to the scouring of Wei River bed.(4) Analyzing the tendency of annul flood and sediment concentration of Jinghe River through db3 wavelet, the conclusion can be drawn as that the occurring frequency of big flood (Q>2600m~3/s)with hyper-concentration decreases before 1990 but increases a little after 1990; And the frequency of small flood (Q<810m~3/s) with hyper-concentration increases significantly before 1990 and then decreased slightly; the annul runoff and sediment of Jinghe River decreases but the tendency is not obvious.(5) The NewMorlet wavelet was also used to analysis the periods of the floods, annul runoff and sediment runoff of Jinghe River and then simulated and predicted the series by means of the method of list in conjunction with wavelet. The results shows the occurring frequency of small flood (Q<810m~3/s) with hyper-concentration will keep large in recent years, while the frequency of high flood will still stay in the low level. In recent years, the annul runoff increase and the annul sediment amount of Weihe River decrease are also be found.