The problem of estimating the discharge in open channel flow by a reliable method when the wetted border comprises parts with different rugosity coefficients frequently occurs. A review of pertinent literature on the subject indicated some analytical approaches previously made for solving the problem. The above have been tested in the present investigations the results of which are reported in this paper and their relative utility is discussed. The experiments revealed that it is not merely the lengths and the rugosity coefficients of the component parts of the wetted perimeter that count but also the angle which the sides make with the horizontal.
