Knowing of flow resistance in channels is necessaryfor many purposes such as the estimation of stage-discharge relationship, and the evaluation of sediment transport from the hydraulic characteristics of the channel by means of transport formulas.All relationships between Froude number (Fr)andMainning’s roughness coefficient(n)lead to obtain useful information in design, implementation, minimization the construction cost, and design the economical section.
The goal of the present work is to investigateexperimentally theeffect ofManning roughness on Froude number in open channel in subcritical flow, as well as, to establish some relations between different parameters, like Froude number with Manning’s Roughness coefficient,velocity and head, inorder to findusefulrelations.
Two different cases have been adopted in this study. The first one is to predict relationships from the concrete lining irrigation canal, andthe second is to procedure conducted in a selected reach of a natural streamMain Outfall Drain Project (M.O.D.) with two sectors of Mahmudiya, and J׳balaas a case study.
In this invistgation on lined irrigation canal, the relationship between Fr and n appears as a polynomialrelation of the fourth degree and a moderate relationship between of them.
In the second case,the relationship betweenFr andngave a significantrelationship in the two regions, and gave a good agreement with the observed value.This study reveala general equation that can correlatethe Froude number with friction factor (n).