Experimental investigation of manning's equation coefficient in open channels with coarse bed

Determination of flow resistance is an essential parameter for flow hydraulic computation in open channel. Flow resistance in open channels with coarse materials on bed is mostly due to grain roughness. Over the past decades many studies have been conducted to estimate the flow resistance coefficient to the particle size but the effects of particle shapes are not clear so far. In this experimental research for determination of flow resistance coefficient eight types of particles; four naturally nearly rounded and four angular particles have been tested under different hydraulic conditions in a flume of 10 meter long، 25 cm wide and 50 cm height and constant bed slope of 0. 0005. By applying experimental data، the manning roughness coefficient has been calculated and equationes for prediction of roughness coefficient have been proposed. The results showed that parameters such as relative submergence (R/Ks)، Froude number (Fr)، energy grade line (Sf) and flow hydraulic radius (R) have significant effects for precise estimation of flow resistance coefficient.