Reservoir sedimentation concepts Which combination of statements about trap efficiency, capacity–inflow ratio, and siltation tendency is correct?

Introduction / Context:Understanding how reservoirs trap sediment is crucial for estimating useful life and planning desilting strategies. Two key measures are trap efficiency and the capacity–inflow ratio, which together indicate how effectively a reservoir captures incoming sediment.

Given Data / Assumptions:

• Sediment inflow varies with watershed characteristics.
• Trap efficiency generally increases with capacity–inflow ratio.
• We compare relative tendencies, not precise percentages.

Concept / Approach:Trap efficiency = (sediment retained) / (total sediment inflow). Capacity–inflow ratio = (reservoir capacity) / (annual inflow). A small reservoir on a large river has a small capacity–inflow ratio, hence lower trap efficiency and less percentage of inflow trapped (appearing to “silt less” per unit inflow). Conversely, a large reservoir on a small river has a higher capacity–inflow ratio and traps a larger fraction, appearing to “silt more” relatively.

Step-by-Step Solution:

Verification / Alternative check:Empirical curves (e.g., Brune’s) show trap efficiency rising with capacity–inflow ratio, supporting statements C and D.

Why Other Options Are Wrong:Since A–D are all correct, selecting any single option alone would be incomplete; “All the above” captures the full, correct set.

Common Pitfalls:Confusing absolute silt volume with percentage trapped; a large river can still deliver enormous absolute silt volumes even if the fraction trapped is low.

Final Answer:All the above