Study of flow characteristics in a compound channel

Abstract

The flow characteristics in a compound channel, with the faster flowing main river and slower moving flood plain, is very complex and inadequately understood. The present thesis consists of two parts - development of a 1-D steady uniform flow numerical model and experimental verification. The governing equation of the 1-D steady uniform flow model is obtained from the general continuity and momentum equation. Then the governing equation is converted into finite difference equations. The solution technique considers total symmetry for the compound section. Because of the difficulty in obtaining sufficiently accurate and comprehensive field measurements of velocity and shear stress in compound channels under unsteady and non-uniform flow conditions, considerable reliance must still be placed on well focused laboratory experiments under steady and uni form flow conditions. The experimental set-up consists of a symmetrical compound section with fixed bed slope. The width of the flood plain is varied. Then for the widest flood plain, the roughness in the flood plain is varied by introducing artificial roughness strips. The total discharge increases with the increase in depth and width of the compound section. The model discharge overestimates the experimental discharge for higher depths of flow and underestimates for lower depths of flow. The discharge decreases with the increase of flood plain roughness for the same depth ratio. Discharge in both the flood plain and main channel decreases with the increase in flood plain roughness. Due to the I lateral transfer of longitudinal momentum, the point velocities, in a vertical at the main channel, increase from the bed upto some level and then decrease continuously until the water surface is reached." The channel bed shear stress decreases from a maximum value at the mid section towards a minimum value at the wall of the flood plain. Further studies will help in better understanding of the phenomena with 2-D or 3-D unsteady numerical models.