COMPUTER APPLICATION OF ENTROPY BASED RIVER MORPHOLOGICAL STUDIES

Abstract

In hydraulic studies element of uncertainty is invariably involved in estimation of model parameters and variables, as flow velcoties, sediment concentration , shear stress and energy gradient. The uncertainties can b6 attributed to both inherent randomness and man's ignorance or inability to understand their intricacies and cope with them. However, the traditional approach to hydraulic studies using. the conservation laws i.e. the equation of continuity, momentum and energy of fluid mechanics is deterministic. Despite the advances made with the deterministic approach, major barriers exists in hydraulics at many front. Leopold and Langbein (1962) introduced the theoretical concept of entropy in the evaluation of stream morpholgoy which later on extended by CHIN TED YANGi (1971) using thermodynamical entropy concept. However, they did not consider the physical parameters like flow, sediment discharge, bed material size distribution which play a vital role in the evolution of near equilibrium state of an alluvial river. Howard H. Chang introduced the minimum stream Power Criterion for alluvial river modelling. Adopting Chang's criterion, a simple computer model is formulated in this dissertation for quasy steady case. The aforesaid model makes use of Garde Ranga Raju resistance law and Modified Eienstein sediment discharge predictor for simulation of flow resistance and sediment load respectively. The incorporation of above two components in the above model is a modification to Chang's approach for more realistic simulation in an alluvial river. Lastly V.P. Singh et al. tried to explain morophology of river basin network system using primary entropy concept but without taking into account the physical features of the system such as flow,sediment discharge bed material size distribution etc. Primarily using the formulation of V P Singh as a basis, anew model named WRDTC-1 has been developed for evolving equilibrimum state of an alluvial river after duly accounting for the dominant physical parameters of river. In 4WRDTC-1 model Garde Ranga Raju resistance law is adopted for determination of energy slope in a relatively equilibrium state. The primary, objective of this dissertation is to investigate a few applications of the theory and concept of "entropy" for an alluvial rivers. "Entropy" seems to provide the foundation and the bridge between the familiar, deterministic world and the realm of probability that is less familiar in hydraulics. Based on the concept of entropy, a new algorithm has been proposed to determine the equilibrium condition• -of an alluvial river considering dominent physical feature which governs the morphology of an alluvial river. All three model formulated in this dissertation were tested for some of the rivers of Indian subcontinent and satisfactory results were obtained. The mathemetical model MEANDER have very recently been developed by a panel of - expert from the Delft Hydraulic Reseach Institute and applied to study the morphology of Mekong River in LAO PDR. The input to the model MEANDER has also taken as the input for the models formulated, as part this dissertation and the obtained results are being presented in Chapter®IV which shows close conformity with the output of mode1.MEANDER. In the light of the findings of the present study it is recommended that "entropy" based river morphological analysis may fruitfully extended for transient condition of flow.