diverging part of the channel, as the flow velocity decreases, accretion of the sediment occurs and
a mound or shoal develops in time. It can be noted the scour and accretion patterns occurring in
the center of the channel are slightly larger than those occurring toward the sides of the channel
across the width of a given cross section. This can be explained by the fact that the velocity field
is not entirely uniform across the width of the channel with somewhat higher velocities occurring
in the center. These small variations in the velocity field across the width of the channel produce
variations in the morphology of the bed across the width of the channel given the fact that the
sediment transport is a function of U3. We also note that the velocity field evolves along with the
Finally, we remark that the computed results of the evolution of the bed compare well
qualitatively to an analytical solution given by Exner (1925) for a problem of the same geometry.
Exner's results, as shown in Figure 10, are the solution of a simplified model similar to that of
Section 2 but modified accordingly to account for variations in the width of the channel (see Graf,
1971 for details). Specifically, it can be seen that the numerical and analytical solutions show the
same general evolution of the bed, i.e. scour in the converging section of the channel and
accretion in the diverging section.