SILTATION STUDIES OF RESERVOIRS

Abstract

The most important practical and critical problem related to the performance of reservoirs is the estimation of storage capacity loss due to sedimentation process. The problem to be addressed is to estimate the rate of sediment deposition and the period of time at which the sediment would interfere with the useful functioning of a reservoir. Fairly a large number of methods and models are available for the estimation, analysis and prediction of reservoir sedimentation process. However, these methods and models differ greatly in terms of their complexity, inputs and computational requirements.

In the present study, trap efficiency is calculated for different reservoirs using different approaches like Brune’s curve, Gill’s method, Brown’s method, etc. The trap efficiency of Bhadra reservoir(Karnataka) has been found out to be 96% according to brune’s curve, 93.26% according to Heinemann’s curve, 96.88% according to USDS-SCS equations, 96.063% according to Dendy’s method, 99.51% according to brown’s curve, 96.37% according to Gill’s method, 97.93% according to Jothiprakash and Garg method. The trap efficiency of Upper Kolab reservoir(Odisha) has been found out to be 95.5% according to brune’s curve, 92.985% according to Heinemann’s curve, 96.749% according to USDS-SCS equations, 95.67% according to Dendy’s method, 99.27% according to brown’s curve, 96.14% according to Gill’s method, 97.656% according to Jothiprakash and Garg method. The trap efficiency of Panchet reservoir(Jharkhand) has been found out to be 80% according to brune’s curve, 76.166% according to Heinemann’s curve, 80.7% according to USDS-SCS equations, 79.43% according to Dendy’s method, 81% according to brown’s curve, 82.078% according to Gill’s method, 81.86% according to Jothiprakash and Garg method. The trap efficiency of Idamalayar reservoir(Kerala) has been found out to be 96.8% according to brune’s curve, 93.67% according to Heinemann’s curve, 96.987% according to USDS-SCS equations, 96.657% according to Dendy’s method, 99.8% according to brown’s curve, 96.71% according to Gill’s method, 98.335% according to Jothiprakash and Garg method. The values of trap efficiency determined by Heinemann method and Brown method differ from the values v

of trap efficiency obtained by other methods. The reason behind the variation in Heinemann’s curve is because of the fact that it is developed using the data of small ponds while in our case the size of reservoirs is quite large. All the methods used above except Brown’s method uses the relationship between capacity and inflow for the determination of trap efficiency. However Brown’s method relates the trap efficiency with the ratio of capacity of reservoir and watershed area, therefore the variation in the results of Brown’s method is attributed to this factor.