New Method for Estimating Roughness Coefficient for Debris Flows

Abstract

Flow resistance is a fundamental control of flow hydraulics in streams and rivers. In this paper, five dimensionless factors affecting the Manning roughness coefficient n and attributed to the external roughness coefficient n1 and the internal roughness coefficient n2 were analyzed comprehensively. And then, dimensionless factors affecting n1 and n2 with precise physical meanings were proposed. With a calculation method for roughness coefficient fitted and analyzed based on observation data from published research papers, the analysis results showed that the external resistance coefficient is closely related to the dimensionless factor D84/R. The correlation between the dimensionless factor (D16/D50) and the internal roughness coefficient n2 was not significant. While the factors H/D50, J, and Sv showed significant correlation. In addition, the expression of external roughness n1 is calibrated based on the observation data of 102 cross-sections listed in previous works, while the internal roughness n2 is calibrated by 20 experimental model tests. Finally, an equation describing the Manning’s roughness coefficient is presented and verified based on 24 groups of observation data from Dongchuan Debris Flow Observation Station (DDFORS) in China. This study is contributing toward a comprehensive model for the Manning coefficient, which provide a scientific reference for the research on disaster prevention and mitigation of debris flow.