B = 250 m
B = 500 m
B = 500 m
x = 1000 m
x = 2000 m
x=0
Fig.8: Computational grid of test case 2
4.2
Test Case 2: Converging channel
In this problem, we return to the full morphodynamic modelling system and examine the
morphological evolution of an initially flat bed in a converging channel. A plan view of the
channel showing the computation grid is shown in Fig. 8. The channel tapers in from a maximum
width of 500 m at the edges to 250 m in the center over a distance of 2 km. The boundary
conditions for the hydrodynamics are specified in such a way that a maximum velocity of
approximately 1 m/s occurs in the center of the channel. The evolution of the bed is examined
over a 90 day period. The sediment density and median grain size of the bed are taken to be 2000
kg/m3 and 0.2 mm, respectively. The time step used in the hydrodynamic model is 2 seconds and
the bed is updated every 50 hydrodynamic time steps. Figs. 9a-9c show plots of the bed elevation
surface and velocity contours at 30, 60, and 90 days. The bed changes have been scaled in the
vertical for easy visualization.
The velocity throughout the channel varies from approximately 0.50 m/s at the ends of
the channel to approximately 1 m/s in the center of the channel. The bed experiences erosion in
the converging part of the channel due to the increase in the flow velocity. Conversely, in the
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