Abstract:
Aggradation and degradation are ubiquitous phenomena that occur in most alluvial
channels. The complete Saint Venant equations describe the unsteady open channel
/low conditions. The continuity equation for the conservation of sediment mass needs
to be solved along with the hydrodynamic equations to determine aggradation and/or
degradation of channel bottom. In these viewpoints, a one-dimensional mathematical
model has been developed that computes the aggradation-degradation of channel bed.
The MacCormack explicit finite difference scheme has been used in the model. This
scheme is second-order accurate, handles shocks and discontinuities in the solution
without any special treatment, and allows simultaneous solution of the water and
sediment equations, thereby obviating the need for iterations.
The developed model has been applied to two different case studies. The first case is a
laboratory investigation where experimental results were obtained due to imposing
extra sediment load. The sediment overloading produces aggradation in the channel. It
has been found that the model simulates most of the test runs with a reasonable
accuracy.
In order to verify the ability of the model to real field situation, it has been applied to
simulate Jamuna river reach from Bahadurabad to Sirajgang. A test run for three years
has been done using field data for that period. The agreement between the computed
results and measured data is quite satisfactory.
The successful application of the model strongly demonstrates that the model is valid
in solving unsteady open channel flow problems in conjunction with sediment
transport. The different problems just require incorporating the appropriate initial and
boundary conditions .
