Impact Of The Lawer Weihe River Channel Sedimentation And Shrinkage On The Characteristics Of Flood Routing

Studying on the influence of the lower Weihe river channel sedimentation and shrinkage to the flood routing is not only of important practical significance to the river govemmemt and flood forecasting, but also of important reference value to other similar rivers in the Yellow River valley. Based on the annual hydrologic record from the construction of San men xia dam ,This paper Studys and Analyses the low of the channel scour and silting evolvement, the low of flood lever at different flow discharge, the low of the flood peak propagation time and the change of peak discharge along the lower Weihe River. Then, ID mathematical model for unsteady sediment transport is established.The research of the low about the channel scour and silting evolvement indicated that Tongguan riverbed elevation is the main factor impacting on the riverbed aggradation in the lower Weihe River. In recent years the reduction of oncoming flow and sediment, the small flood with hyperconcetration of sediment frequently occurred also is the important attribute impacting on the riverbed aggradation in the lower Weihe River. The riverbed elevation rises, the main channelwidth reduces and the beach roughness coefficient increases is the main factor which affects the flood level rise. Quantitative analysis shown shat if the main channel width shrinks narrow 100m everytime,the flood level rises about 4~5m at30000m"7s flow dischanrge at Hua xian;if the beach roughness coefficient increases 0.01,the flood level increases 0.2~0.3m.at same flow discharge. The main channel flow discharge becomes weaken, the cross section mean velocity of stream reduces, the beach roughness coefficient increases and the river course gradient changes slow is the main reason which the flood propagation time lengthens. Based on the actual material, though analysis and calculation indicated that it become the inverse relation between the main channel flow discharge and the flood peak propagation time from Lin tong to Hua Xian. If the river course gradient reduces 0.1 %oo every time,The flood propagation time from Lintong to Hua Xian lengthens about 6 hours. If the beach roughness coefficient increases 0.01, the flood propagation time lengthens about 3~4 hours. Rested on the actual record ,though regression analysis, it get the empirical relationship between flood peak clipping rate and the main channel flow discharge from Lintong to Hua Xian and from Hua Xian to Hua yin. It also analyzed the influence to the flood peak clipping rate casused by water sand condition and the human activity. In the article it deeply analysed the reason that caused by the special phenomenon such as the flood level high, the flood propagation time long and so on which appeared in the flood process in 2003.It has carried on the confirmation to sedimentation mathematical model which established in the paper, using actual hydrology sedimentation record which happened in 8-9 month in 2003.The checking result shown that the water level process, the discharge process and the scour and silting process from Lin tong to the Chen village tallies with the measured ones well. It shown that the mathematical model established in the paper is suitable for the river condition in the lower Wei he river.lt can be used to forecast the situation such as the flood routing and the scour and silting changes .