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.
