Modeling Roughness Coefficients in Vegetated Canals Based on Bed Particles Diameters

The indirect variables such as bed particles diameters could be applied to estimate roughness coefficients (RC) to decrease measurement costs. Bed particles diameters based relations were developed for non-vegetated channels. Therefore, the current study was conducted to evaluate bed particles diameters based relations (BPBR), to estimate roughness coefficients in vegetated canals for irrigation and drainage network of Moghan (in North-west of Iran) and to compare acquired RC from BPBR and RC from experiments and to model roughness coefficients in vegetated canals as a function of bed particles diameters. In irrigation and drainage network of Moghan 181 canals sections were selected to measure water flow velocity (with a flow meter) and canal cross sections. The Manning coefficients were estimated via water velocities, hydraulic radius and canal slopes. Results revealed that RC varied from 0.005 to 0.41 and averaged at 0.076 in vegetated channels. Also, Applying Strickler, Henderson, Garde and Raju and Bray (relations based on D50) and Ravdkivi, Bray, Lane and Carlson and Henderson (relations based on D65 and D75) did not produce a suitable value for RC in vegetated channels. The particle diameters (D50, D65 and D75) were applied to model roughness coefficient as a function of bed particles diameters in vegetated channels. Relative to the results from developed relations, the model results were relatively precision and recommendable. The correlation coefficient of RC with the particle diameters of D50, D65 and D75 were 0.91, 0.83 and 0.66, respectively. The advantages of developed models were accuracy, simplicity and facility in application.