Initial filling of the project reservoir

The initial filling of Tehri dam reservoir had started w.e.f. October 29th, 2005 after the closure of the last diversion tunnel T-2 which remained in operation for almost 4 years. Since the filling upto Minimum Draw Down Level (MDDL) i.e., El 740 m was unrestricted, the issue of adopting, the specific criteria for further filling to accomplish a pre-determined monitoring programme needed deliberations. The major factors to be considered for establishing initial filling criteria for a dam are the geology of the dam foundation and reservoir, landslide potential along the banks of the reservoir, inflow characteristics whether controlled or uncontrolled, hydrology of the river and time taken to fill the reservoir etc. In addition to this, other factors like the releases for project requirements, flood release and emergency evacuation requirements, if necessitated, also needed to be considered. The time to be kept for intermediate stoppage depends on the type of instruments installed in the dam, provisions for monitoring the readings and evaluation time needed etc.

The paper provides the specified Central Water Commission criteria for initial filling of reservoir, reservoir operation during initial filling for the specified criteria, its implications on overall filling schedule, actual reservoir filling in monsoon 2006 and proposed filling schedule up to Full Reservoir Level.