FLOOD-PLAIN MODELING OF RIVER BRAHMAPUTRA, ASSAM, INDIA

Abstract

The art of modeling an alluvial river of multi-channel configuration is still in a developing stage and a lot of ground yet remains to be covered. A number of contributions have been made for simulating flood routing, overland flow and related time-dependent transient flow problems by solving the gradually varied unsteady flow equations numerically however, invariably in all the existing models the solutions are obtained based on certain simplifications of geometric properties such as The geometric properties of all the irregular sections of a natural stream over the entire reach are averaged with respect to the flow depth to form a single representative cross-section. The cross-sectional areas and the top widths of the representative cross-section are then fitted by a polynomial. The above simplifications can work satisfactorily only when natural stream consists of single channel at all the stages of flow. However, in an alluvial stream of multi-channel configurations these simplifications can introduce serious error and the simulation results based on this cannot be relied upon. The objectives of this study were to develop a methodology to delineate flocd plain, to develop the simple mathematical equations for cross-sectional area and perimeter of river, to develop the hydraulic and viii morphological characteristics of the river during floods, to develop the stage discharge relation for the river Brahmaputra. A first effort is made to extract the floodplain section of the River during floods. For this purposes satellite images and field data were combined to extract the flooding extent which is further used in developing the mathematical equation for area and perimeter which can be used in flood routing problems. The hydraulic characteristics of the river during floods were developed. For this, Lacey's equations were modified to develop the new equations, applicable to river Brahmaputra. Subsequently, the development of stage-discharge equation for the river is carried out, which is applicable at any section of the river Brahmaputra. The comparison of calculated results and the observed data are in reasonably good agreement .This proves the feasibility of applying the mathematical models for prediction of flooding extent, regime flow conditions and gauge-discharge relationship for river Brahmaputra at any section.