Evaluating Flow Resistance in Straight Channels Using 2-Point Velocity Measurements

Accurately measuring Manning’s roughness coefficient is crucial for enhancing the precision of hydraulic models and supporting informed decision-making in water resource management. Traditionally, this coefficient is determined using the cross-sectional mean velocity, which may introduce inaccuracies due to its approximate nature. However, estimating Manning’s roughness coefficient through flow velocity distribution analysis remains a relatively underexplored approach. This study aims to improve the accuracy of estimating Manning’s roughness coefficient by analyzing the velocity distribution at two vertical positions within the flow: z/H = 0.2 and z/H = 0.8. Secondary velocity data were obtained from four locations to support this investigation: a laboratory flume, the Selokan Mataram irrigation channel, the Kuning River, and the Opak River. The research methodology involves simplifying and applying analytical equations needed to determine Manning’s roughness coefficient based on the velocity profile. The results indicate that, in natural river systems, Manning’s roughness coefficient ranges from 0.035 to 0.095 at z/H = 0.8 and z/H = 0.2 and from 0.032 to 0.085 at z/H = 0.4 and z/H = 0.2.