SEDIMENTATION STUDIES IN RESERVOIRS USING MATHEMATICAL MODELLING

Abstract

An attempt has been made to study the applicability of the FCM (Fully Coupled Mobil Boundary Model) developed by Correia to the problem of sedimentation in Indian reservoir: This model is a one-dimensional, unsteady and fully coupled model. The basic feature of th model is the flexibility in choosing the resistance and sediment relationships and taking variable bed roughness into account. In the present thesis the work of Anjana Kumari (1996) on FCM application in reservior sedimentation is extended by studying the effect of non-equilibrium transport on deposition profiles. The FCM model has been used for study of the sedimentation process in four Indian reserviors namely, Hirakud, Matatila, Nizamsagar and Gobingsagar. The model was used by taking into account the temporal variation in the downstream (i.e reservoir levels) and the upstream (i.e. inflow discharges) boundary conditions. The deposition profiles have been computed by running the model for large time durations varying from four years for the Gobinsagar to thirty four years for the Nizamsagar reservoir. It was noticed that for obtaining realistic results the model parameters pertaining to transport; resistance etc. need to be judicionsly chosen. Effect of non-equilibrium transport on the computed deposition profiles was also studied. It was noticed that in some cases (Hirakud for example), the computed deposition profiles are widely different under the conditions of equilibrium and non-equilibrium transport. This is considered to occur mainly because of the significant difference in transport rates under these two situations. As a net result, the values of energy slopes are different for given inflow under these two conditions. Qualitatively, good agreement is found between the observed and computed profiles for Matatila reservoir. However, the obseved profiles for the Nizamsagar and Hirakud were not available and so no comparisons were possible. Poor agreement is noticed between computed and observed profiles in the downstream segment of the Gobindsagar reservoir.