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Reservoir Capacity and Sedimentation: Trap Efficiency and Useful Life Determination

 Reservoirs are designed with distinct storage zones: dead storage (below the lowest outlet level), live storage (available for regular supply), and flood storage. Over time, sediment-laden river flows drop their load upon entering the low-velocity reservoir pool. The proportion of sediment retained is defined by the Trap Efficiency $(\eta)$, which is primarily a function of the reservoir capacity to annual inflow ratio (C/I), typically evaluated using Brune’s Empirical Curves:

$\eta = f(C / I)$

​As sediment accumulates, dead storage fills first, followed by gradual reduction of live storage, ultimately determining the functional life of the reservoir.

​Monsoon-fed Indian rivers carry heavy silt loads, causing many large reservoirs across the country to lose storage capacity faster than original design estimates.

​To address this, the Central Water Commission (CWC) mandates periodic hydrographic and bathymetric surveys using modern dual-frequency acoustic echo sounders and Satellite Remote Sensing (SRS) techniques. These digital surveys update Elevation-Capacity-Area curves accurately, enabling dam authorities to optimize desilting schedules and implement catchment area treatment (CAT) to slow down reservoir sedimentation.

​Note: This technical content was curated and structured with AI assistance to support technical education.

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