Analysis of the Roughness Coefficient of Overflow in a Drainage Pipeline with Sedimentation

Abstract

Flow resistance is a critical calculation parameter in hydraulic engineering. In this study, the roughness coefficient of a circular drainage pipe with sedimentation was investigated under open-channel flow conditions using experimental measurements and numerical calculations. The ratio of the height of the sediment placed in the pipe to the diameter was defined as the sedimentation degree. The Manning roughness coefficient (n) was determined for pipes with different sedimentation degrees. Moreover, numerical simulations were performed for circular pipes with diameters of 0.152 m and a slope of 0.003, with discharges varying between 1 and 8 L/s. The results of the numerical calculations were validated in terms of the water surface and Manning’s n using the corresponding experimental data. Accordingly, an equation in the form of the Moody formula was proposed to estimate the roughness coefficient. Subsequently, the predicted Manning roughness coefficient obtained through the proposed equation was compared with independent experimental results. The results indicate that the equation accurately predicts Manning’s n in a pipe with sedimentation, which can provide a theoretical basis for the design of drainage pipelines.