Pattern of reservoir sedimentation (silting) over time How does the rate of silting in a reservoir usually vary during its service life?

Introduction / Context:
Sedimentation progressively reduces reservoir capacity. The temporal pattern of deposition influences dead storage sizing, sluicing provisions, and long-term operation strategies.

Given Data / Assumptions:

• Typical alluvial sediment inflow with initial trapping efficiency high.
• No exceptional sediment management measures at start-up.

Concept / Approach:
At commissioning, the reservoir has maximum trapping efficiency and ample low-level volume, causing higher initial silt deposition rates. Over time, as delta progrades and storage geometry changes, effective trapping for finer fractions can reduce, and deposition rates tend to decline or shift location within the pool.

Step-by-Step Solution:

Verification / Alternative check:
Observed capacity surveys of many reservoirs show early rapid losses followed by slower capacity decline as the delta advances.

Why Other Options Are Wrong:

• Less at beginning: contrary to typical trapping efficiency behavior.
• Constant: unrealistic given evolving geometry/hydraulics.
• More in beginning (alone): incomplete without noting later reduction.

Common Pitfalls:
Assuming linear capacity loss over time; in practice, deposition patterns and management actions change the rate.

Final Answer:
It is more in the beginning and reduces towards the end