Assessment of manning's resistance coefficient in compound channels

In this paper twelve different empirical resistance coefficients expressed in terms of Manning's roughness are used apiece in seventeen known compositing methods. The data obtained from ten different cross-sections of the Sefidrood River, Iran, are used for the evaluation of the empiricalformulas. The present case-study is selected from a reach with gravel bed topology. Then no remarkable bed form exists. Comparison of the calculated discharges and resistance coefficients with measurements shows that the Keulegan formula used simultaneously with the Brownlieformula in different compositing methods results in highly over estimated discharges, while the Meyer-Peter & Muller, Marion, Chien-Mai formulas in conjunction with the total force approach match best with the measurements. Also comparison of the calculated discharges from empirical formulas in individual sections reveals that Chien-Mai and Subramanya formulas have the least discrepancies from measurements.