Computational Procedures for Flow Resistance Laws

After stressing the essentially empirical nature of all fluid resistance laws for turbulent flow, it is demonstrated that the normal discharge is the only quantity which is always explicitly calculable in channel flow problems. It is therefore suggested that computer programs should not depend on a specific resistance law but should rather be designed to use any one of a number of normal discharge function subroutines which operate on a standard list of parameters. Other quantities implicitly defined in a flow resistance equation, such as depth, energy gradient or roughness, may then be found by iterating on the explicitly determinable normal discharge. The application of such routines is demonstrated with reference to shape effects and experimentally determined friction laws. Flow diagrams of the basic routines are given.