Resistance to flow determines several hydraulic parameters in streams and rivers that should be properly
represented for estimating water discharges and sediments transport. In this research, a combination between
experimental and numerical models study were carried out to investigate the influence of bed roughness of flow
characteristics. Seventy two (72) runs were conducted physically and verified numerically. 6 bed materials were
used (Gravel, Cement, Interlock, Grass, Formica, and Vegetations). 4 discharges and 3 tail gate water levels
were tested with each bed material. Results were analyzed and were graphically presented and the percentages
of errors between the obtained results from the used models were reported to define the sufficient compatibility
between the used models. The Manning roughness coefficient was estimated for each bed material using the
experimental and numerical models. The percentages of errors between them were reported and were under
estimations. The models proved that for a given bed material, the roughness coefficient was inversely proportional
to the discharge and directly proportional to the tail gate water levels.