Resistance Coefficients for Steady Spatially Varied Flow

In spatially varied flow three coefficients in Weisbach f form are involved which are sometimes termed resistance coefficients. They are the frictional resistance coefficient, the dissipated energy coefficient, and the total head-loss coefficient. In general these three coefficients are not equal whether there is lateral flow or not. Only for steady uniform flow without lateral flow are these three coefficients equal to one another and to the corresponding f in the Moody diagram. Theoretical solution of steady two-dimensional Stokes flow with lateral flow is obtained to show the difference among these three coefficients. Experimental data for steady two-dimensional sheet flow under simulated rainfall are also analyzed to illustrate numerically the variations of these coefficients. In practice, hydraulic engineers should keep in mind the difference in these different resistance coefficients, to avoid unnecessary errors.