Instability Analysis of the Jamuna River, Bangladesh

Major changes take place in the planform and bed topography of the Jamuna River, Bangladesh, particularly during the flood season, and the effect of these changes are investigated in this paper in the form of a stability analysis by perturbation technique. A two-dimensional model of flow and sediment transport in an alluvial river with erodible bed and non-erodible banks is developed and applied to the Jamuna River, Bangladesh. The effect of transverse slope resulting from the effect of secondary currents, the effect of spiral motion due to curvature of the channel on the bed shear stress, and the effect of frictional resistance occurring from pure skin friction and friction due to bedforms, are considered in the model. The 2-D model can be used to check the instability due to the dunecovered alluvial bed. A stability theory has been developed which determines the most unstable mode, the celerity and propagation of the sand dunes, and the wave number corresponds to maximum instability. The theory is also capable of differentiating between braiding and meandering phenomena. Several implications of the proposed model are also discussed. The proposed model is used to analyze both the meandering and braided patterns of the river. The results from the analyses of the Jamuna River show that instability always exists in the Jamuna River under maximum instability conditions because of its very low aspect ratio (...1/1000) and more than three braids.

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