Sedimentation Mechanics: Trap Efficiency and Brune’s Curve Analysis

 Reservoir storage capacity gradually diminishes over time due to sediment retention. The proportion of incoming sediment trapped within a reservoir is defined as Trap Efficiency ($\eta$), which depends on the ratio of reservoir capacity ($C$) to annual water inflow $(I).$

​Brune’s Empirical Curves estimate trap efficiency based on the C/I ratio:

$$\eta = f\left(\frac{C}{I}\right)$$

​For high C/I ratios ($\ge 0.1$), trap efficiency typically exceeds $90\%,$ meaning almost all coarse and fine sediments settle out. As sedimentation reduces effective storage capacity ($C$), the C/I ratio decreases, leading to a progressive reduction in trap efficiency until an equilibrium condition is reached.

​Heavy silt loads in Himalayan rivers cause rapid storage loss in major Indian reservoirs, impacting long-term hydropower generation and flood control capacity.

​To mitigate sedimentation, dam operators under the National Hydrology Project (NHP) execute periodic bathymetric surveys using multi-beam echo sounders and satellite remote sensing (SRS). Integrated catchment area treatment (CAT), sediment flushing through low-level sluices, and targeted dredging are dynamically scheduled based on updated elevation-capacity curves.

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