Abstract
Approximate formulae of friction coefficient as well as phase difference under wave-current coexistent motion are derived for laminar, smooth turbulent and rough turbulent flow on the basis of Tanaka and Shuto's theory (1981). By considering flow regime criteria, these formulae for each flow regimes are combined to yield full-range equations, which are in explicit form and reqire no iteration to find solutions. A practical method is also presented to calculate time-variation of bottom shear stress under waves and current with an arbitrary angle of intersection.
