Experimental Study On The Hydraulic Characteristics Of Water Flow In The Intersection Area Of Asymmetric River Channels And The Pebble Initiation Under Its Action

Asymmetric river intersections are typical geomorphic units in river systems,often with complex and variable morphological structures and hydrological conditions.Two streams of water converge here,support and mix with each other,resulting in complex and special water flow structural processes,which are crucial for the initiation and transportation of pebbles.Intersection areas often have complex and varied terrain,geomorphological structures,and hydrological conditions,and the water flow structure in the intersection area exhibits strong three-dimensional and complex characteristics;The starting law of pebbles in the non-uniform flow regime of the intersection area is more complex.The commonly used formulas for starting pebbles are generally obtained through hydraulic tests of water flow in a flume under approximate uniform flow conditions,without considering the influence of different water depths and backwater phenomena at different positions along the flume under the non-uniform flow structure.This experiment conducted the following research on the hydraulic characteristics of water flow and pebble initiation in the intersection area of asymmetric rivers:(1)Based on the study of the flow motion characteristics of the reach of asymmetric channel intersection by scholars at home and abroad,this study tested the flow characteristics when tributaries intersected with the main stream of asymmetric channel,designed and established the flume test model.(2)Through the study of the hydraulic characteristics of the flow in the intersection area,the influence of the intersection angle,momentum ratio and width depth ratio on the water surface shape characteristics,the characteristics of the plane flow field and the longitudinal time average velocity distribution is revealed.(3)The influence of pebble feeding rate(volume concentration)in the intersection area on the velocity distribution of pebble particles and the change of pebble particle transport mechanism under different transport mechanisms was studied.(4)After multiple experiments,it has been found that using a particle size with a bed load frequency close to 100%(about 95%)as the starting particle size can achieve higher accuracy in the start-up of bed pebbles.In addition,the results of the flume experiment were used to verify the drag force formula,which showed that it was basically consistent with the Hiltz curve.By applying the starting power formula,an accurate starting power of 0.0191 was obtained,which provides a reliable reference for bed load pebble starting.