Key Subjectsin Flow Motion Studies I.Review of Roughness Study

The study of Manning's roughness coefficient is closely related to the progress of hydrology and hydraulics.The difficulties in the determination of roughness are mostly arisen from the wrongly introduction of the Chezy formula which was established in steady uniform flows to unsteady and nonuniform flows.Roughness coefficient has quite different physical reasonings when it is taken as an ajustable parameter reflecting various influences including the surface roughness,land use, hydraulic characteristics,and even boundary conditions,etc.. This paper presents the disadvantages of the treatments which prevails in the numerical study and hydraulic analysis during the passed decades since Chezy formula was developed in the end of last century.It is indicated that new methodologies should be developed to enhance the study of hydraulic drag as well as the roughness instead of taking it as a"comprehensive"parameter covering numerous factors and without any clear physical meaning.