The Effects of Changes in Manning’s Roughness Coefficients and Eddy Viscosity on a Constrained Flume

Abstract

Any numerical model is designed to address a specific class of problems. The results of these numerical models are often sensitive to the values of Manning’s roughness and eddy viscosity. This study analyzes the effects of changes in Manning’s roughness coefficients and the eddy viscosities on a constrained flume. Understanding these effects is useful in model calibration. A computer program called RMA2 has been used for this purpose. The effects of five values of Manning’s (n) and five values of eddy viscosity (E) are investigated, for determining the water depth and flow velocities. The results indicate the fact that as the roughness increases, the upstream water depth increases and the eddy viscosities have a much larger effect when there are large longitudinal velocity gradients. For realistic values of eddy viscosity, differences in depth at the upstream end of the channel are small. The effect of Manning’s roughness and eddy viscosity in model calibration are presented by an equation. This equation involves the dimensionless parameters (Peclet No. and Froude No.) and for different values of Manning’s (n). In this study and for subcritical flow, the Peclet No. was less than 28.0 and a good agreement was found between the result of the present work and that of the published studies.

Keywords

• Manning’s Roughness
• Eddy Viscosity
• Constrained Flume
• RMA2 Computer Program