MODELLING OF RIVER MORPHOLOGY USING REMOTE SENSING TECHNIQUES

Abstract

A river is a dynamic system. It adjusts its channel roughness, geometry, pattern and profile with changing climate, geological, hydrological, hydraulic, sediment and man-made constructions. Thus fluvial hydraulics and river morphology form one of the most complicated subjects. The plan-form of a reach of an alluvial river reflects the hydrodynamics of flow within the channel and the associated process of sediment transport and energy dissipation. Braided streams occur in high energy environments with large and variable discharges carrying heavy sediment loads on steeper gradients. These streams are characterized by a random pattern of multi-thread channel network due to appearance of braided bars within the overall water way of the river. The presence of braid bars increases the total flow resistance and the energy losses along the boundary, thereby promoting the development of a network of hydraulically inefficient channels. The river Brahmaputra is one of the largest braided streams of the world. The river discharge varies along the river and carries a high concentration of sediment load. The river is widening subsequently.. Keeping the above in view, a 640 km reach of the river which is passing through Assam has been adopted for morphological study using satellite images and hydrographic data. The objective of the present study is to study the pattern of changes in river morphology and lateral extent of channel migration to define the intensity of braiding over different time space. The stability of channel geometry has also been studied using the modeling concept of HEC-RAS. With the help of the study of changes in river pattern and stability of river banks, suitable river training works may be proposed at the unstable iii and vulnerable points to control the erosion and thus inhibit the shifting of the river. The functional relationships have been developed between braide indicators and suitable thresh hold numbers have been adopted for the river Brahmaputra.