Influence of Suspended Sediment Load on Roughness Coefficient and Intensity of Flow Turbulence (Case study: Haraz, Rostamabad and Beheshtabad Rivers)

Estimating the effect of sediment transport, especially suspended load, is important in river planning and management. The aim of this study was to investigate the effect of suspended sediment load on the roughness coefficient and the intensity of flow turbulence in Haraz, Rostamabad and Beheshtabad Rivers. In order to better understand these relationships, the geometric characteristics of the sections, the flow velocity and the suspended load were measured in different sections of these rivers. Then shear stress, Manning coefficient and Von karman coefficient were calculated using related equations in each section. The intensity of turbulence was also determined by measuring velocity fluctuations. The study of the effect of suspended load on roughness coefficient and Van Carmen coefficient showed that in most sections roughness coefficient and Van Carmen coefficient have decreased due to the presence of suspended load. In Haraz, Rostamabad and Beheshtabad Rivers, the ratio of roughness coefficient in the presence of suspended load to roughness coefficient without suspended load was 0.9, 0.94 and 0.6, respectively. The results of this study showed that the turbulence intensity distribution is independent from the flow rate and the distribution is always convergent and its maximum value occurred not in the bed but above the bed. Besides, the distribution of turbulence intensity in the presence of suspended load in gravel-boulder rivers is convergent and can be analyzed based on the boundary layer equation. Quadrant analysis was performed on the dominant events at three flow depths. In the areas close to the bed, the predominant phenomena were inward, outward and ejection, respectively, and the contribution of the sweeping event in this section was negligible.