Report on DAM BREAK Flood Simulation and Reservoir Sedimentation in Maithon Reservoir : Part I – Reservoir Sedimentation

Abstract

The capacity of reservoir gradually reduces due to silting and hence sedimentation of reservoir is of great concern to all the water resources development projects. Storage loss not only occurs in the dead storage but also encroaches into live storage capacity, which has long and short term impact on the functioning of the project and economics. Correct assessment of the present capacity of reservoir is essential for assessing useful life of the reservoir as well as optimum reservoir operation schedule. The conventional silt and sedimentation surveys are laborious, time consuming and also costly. Remote sensing data plays a significant role in providing information about water-spread areas on different dates. Remote sensing data by virtue of its synoptic viewing of vast terrain features at regular intervals is of immense help and use in capacity surveys. It provides timely, reliable and comprehensive data on various natural resources. Its ability to map inaccessible areas helps in getting information about the reservoir. Reservoir sedimentation surveys are essentially based on mapping of water spread areas at the time of satellite over pass. It uses the fact that water-spread area of the reservoir reduces with the sedimentation at different levels. The water-spread area and the elevation information are used to calculate the volume of water stored between different levels. These capacity values are then compared with the previously calculated capacity values to find out the change in capacity between different levels. In this study, sedimentation in Maithon reservoir has been estimated using IRS 1C satellite data for 6 dates from December 2002 to May 2003. All digital image processing work has been done using ERDAS Imagine software. The total capacity loss has been estimated since last conventional survey of reservoir during 1993-94. Annual rate of siltation has also been computed. The sedimentation below minimum draw down level has been estimated using historical data of hydrographic survey of the reservoir since 1955. The uncertainty and various source of error associated with remote sensing technique have been evaluated.