Hydrodynamic simulation of the river Jamuna

Abstract

This research deals with the morphological analysis of Jamuna river using finite element method. RMA2, a hydrodynamic model and SED2D, a sediment transport model, have been used to simulate the morphology of the Jamuna. Models have been applied using SMS (Surface-water Modeling System) environment, which gives the pre- and post- processing options for input and output data. The finite element mesh has been developed using LANDSAT image of the Iih November 2000. Initial bed elevations for the nodes of the mesh have been composed from the scattered survey data of April 2001 by BIWT A. Once the mesh and bathymetry have been obtained, the models are ready thereby to incorporate boundary conditions, initial conditions and material properties. The hydrodynamic model developed in this study has been satisfactorily calibrated and validated against the observed water surface elevations at Aricha for 2001 and 2002, respectively. Sediment model has also been calibrated using measured bathymetry by BIWTA with the simulated bathymetry of 23rd August 2001. The model has been validated with the measured bathymetry of November 2002 and November 2003. Sediment rates at Baruria have been generated from the SED2D model and compared with the FAP-24 data (FAP, 1996). Results reveal that erosion takes place in the outer bend of the meandering Eastern anabranch. In Western ana branch, severe deposition has been observed near the confluence due to backwater effect of Jamuna-Ganges flow. Velocity reduction in the confluence significantly diminishes their sediment transport capacity, and hence inducing deposition. Three morphological years have shown much similar type of erosion/deposition patterns, which occur mainly in August and September of each year. An investigation, using surveyed bathymetries from 1996 to 2003, shows that the 1998 flood initiates drastic changes in its Western anabranch near Nagarbari, which indeed may have an impact on the shifting of flow more towards left bank at Naradaha. These observations of measured data are further substantiated by the results obtained from the present simulation models.

To find a suitable location for ferry ghat and also for a sustainable navigable channel, three options have been investigated. Existence of a deep pocket near Naradaha motivates this study to take those options and among them Option 2, which is a dredging option in the upstream channel connecting upper segment of the deep pocket, has appear to show very little deposition compared to other options. Thus the option in question presents a prospective alternative for developing a sustainable ferry route.