Abstract:
Simulation of sediment transport rate at the river Ganges and variation of bed level
along the river is carried out by using a one dimensional morphological model. Noncohesive
sediment transport module of MIKEll is used for the simulation. The
upstream boundary of the model is taken at 97 Ian upstream of Mathabhanga offtake
(Ganges 0) and downstream boundary is taken at Padma 100 Ian. The river system
is schematized by five branches, one inflow boundary at upstream, one lateral inflow
and four lateral outflow boundaries and one outflow boundary at downstream (water
level boundary).
In order to make convenient for sediment calculation with hydrodynamic computation,
the river is represented by equivalent cross-sectional shape and longitudinal profile.
This is achieved by considering that the hydraulic properties of the representative
cross-section is the same as that of the actual cross section. Simulation period is taken
from April 1985 to October 1991. Simulation is carried out for hydrodynamic
calibration and for transport rates. The cross-section interval varies from 2 Ian to 10
Ian in the schematization and the total length including the Padma river is 314 Ian.
The time interval used for the morphological computation is four hours for
hydrodynamic computation and four days for sediment transport computation
respectively. Both for hydrodynamic and sediment transport, the results are saved
after every four days. Calibration is carried out against field observations (both water level and discharge)
from 1985 to 1991. Water level comparison for simulated and observed values are
taken at five key locations (Hardinge Bridge, Sengram, Mohendrapur, Baroria and
Mawa) whereas discharge is compared at Baroria only. The results showed
satisfactory agreement with observed values.
For morphological computation, a time series data of sediment flow is used at the
upstream boundary. This time series is generated after a logarithmic transfomation
of observed transport rate and observed water discharges measured by BWDB. With
this generated transport rates at the boundary, the sediment transport calibration is
performed by comparing simulated rates. The results show very good agreement with
the observed rates of sediment transport. The simulated sediment load is again
verified with the loads at Hardinge Bridge as computed by various investigators.
After calibration of the model for both hydrodynamic and sediment transport, the net
amount of erosion and siltation along the river reach is computed. Finally,
longitudinal variation of bottom level for the monsoon season from 1988 to 1991 is
drawn from the model results.
