Study On The Law Of Flood Routing In The Wide Reach In The Lower Yellow River

Based on the surface runoff and sediment load and changing characteristic of river boundary in different period in the Lower Yellow River, the regulating mechanism of cross section and riverbed withered and its influence to the flood propagation were researched systematically. It is shown that the deep point of river bed lowing and bed material coarsening occurred simultaneously at the beginning of sustained scouring period. And riverbed changed toward V type bed form. Then river width increased and the intensity of deep point lowing and bed material coarsening decreased and water level lowed continuously. So the bed form changed toward to U type. The bed regulation is realized through sediment silting in different parts in cross section during silting period and the deformation of bed form changed from broad U type channel to narrow and deep V type channel. The characteristic of bed regulating is that the width and area of main channel and medium flowing channel increased greatly during the sustained silting period and decreased during scouring period. The width of main channel would influence the water level rising rate greatly in flood events. When the discharges in main channel increased to 8000 m'/s from 3000 m3/s the water rising amplitude at hydrometer stations in the Lower Yellow River was correlative well with the exponent (-0. 65) of main channel width and theexponent (-0.33 ) of river longitudinal slope. The velocity of flood propagation was great and flood deformation was slightly when flood peak increase to bank full discharge. As the discharge increased to 2-2.5 times of bank full discharge the velocity reduced to the lowest value and the greatest flood deformation occurred. The formula of calculating flood peak at downstream stations according to upstream flood peak at hydrometer station was proposed in this research. In the formula river boundary and flood type factors etc. were main factors and the formula can reflect the impacting factors of flood deformation. In addition according to the comparison of typical floods the impact of floodplain morphology to the flood propagation was studied. No continuous water body in main channel and floodplain and the change of floodplain morphology and the increased flood detention capacity caused the time of flood propagation increasing and the flood types changing in abnormally.Based on the measured field data the interaction between water and sediment and river boundary in fluvial rivers was illuminated in this research. The understanding on the law of river variation and flooding in wide and shallow reach in the Lower Yellow River was improved. This research can direct the flood defense in the Lower Yellow River in some extent...