Reasons for the abnormal channel roughness of the Yellow River and the solution to its problems

The abnormal roughness problem of the Yellow River is expounded in this paper and the reasons why the roughness is taken too small has been analyzed through theoretical analysis and measured data. The main reasons for the abnormal channel roughness of the Yellow River are: (1) using a flow resistance formula for the time averaged flow in the fixed bed conditions, (2) using inadequete representive hydrologic data. It is pointed out that the Manning’s formula is not suitable for movable bed resistance calculation. The existing research results of movable bed resistance are limited in theoretical progress, and it is hard to find a formula with strong practicality or high precision. Further more, a correction solution has been put forward to solve the abnormal channel roughness of the Yellow River by describing the impact factors and their expressions of the depth index, which improved the relation graph of roughness and guaranteed its physical meaning. Finally, according to the adjusted roughness data of the Huayuankou Hydrometric Station, an empirical equation of roughness with flow quantity has been established, by which the average velocity in different incoming water and sediment conditions can be predicted together with the modified resistance formula of movable bed. The test result shows that the prediction accuracy is better in processing the measured data of the Yellow River.