Fig. 8. Evolution of channel infilling rate and channel bypassing rate on gravel shore
A simple mathematical model of channel bank encroachment, infilling, and bypassing
by cross-channel sediment transport has been developed. The model represents a
substantial amount of the acting physical processes in a schematic way, producing a set of
two coupled, non-linear first-order differential equations. By making an assumption
compatible with the reality of channel maintenance (i.e., the channel will never be allowed
to fully close), a linear set of coupled equations is obtained that can be solved. The
solution explicitly reveals factors representing channel performance in terms of the
governing physical dependencies of channel geometry, upstream transport rate, and
partition of transport as bed load or suspended load.
In addition of serving as a possible screening tool to quickly and conveniently assess
alternative channel designs, the simplicity of the model in representing fairly complex
physical processes holds pedagogic value for explaining channel sediment processes.
Work is underway in the Coastal Inlets Research Program to provide a convenient interface
for implementing the numerical solution of the channel infilling model. The solution will
allow time-dependent wave information to generate a longshore current, calculate the width
of the surf zone, and channel infilling by sections with different ambient depths along the
channel. Further research in micro-scale processes will allow expression of the partitioning
coefficients (a's) in terms of ambient forcing conditions and channel geometry.
This paper was prepared under the Coastal Inlets Research Program, U.S. Army Corps
of Engineers (USACE). We appreciate a critical review given by Julie Dean Rosati.
Permission was granted by Headquarters, USACE, to publish this information.
Kraus and Larson