Study On The Resistance Characteristics Of The River Channel In The Yellow River Estuary

In response to the underestimation of the water level for low flow rates for a constant Manning coefficient,the current authors,using the data of velocity?v?and Manning coefficient?n?measured in the Yellow River estuarine channel,establish a new formula for channel roughness for the estuary,which takes the form of n=av^-1,a=R^2/3J^1/2 taken as a constant parameter over a certain period.The parameter?a?is found to make the calculated water level processes in the low-flow season and the non-low-flow season match well the measured ones when it is taken as the average of the daily values over the low-flow season and over one year,respectively.The parameter?a?can be easily estimated using the characteristic water levels near the low-flow floodplain within the channel.Bed form in the about 106 km-channel from Lijin to the river mouth tends to be plane bed for larger flow rates,resulting in Manning coefficient varying near the lower bound of 0.01while it tends to be dunes for smaller flow rates,resulting in it changing near the upper bound of 0.035.The significant factors are velocity and hydraulic radius with the sizes of bed materials insignificant in the Yellow River estuarine channel.The method and formula proposed in the paper is applicable to not only fine-bed material-particled estuarine channel but also the coarse material-particled channel such as the Dongxiayuan-Huayuankou channel,the upper part of the Lower Yellow River,with its rougness varing between 0.01 and 0.035.Studies have shown that for a given flow process,the roughness and flow rate,bed surface morphology,specific drop,bed sand grading and other factors interact and interact.