Statement (I): The trap efficiency of a reservoir increases with age as the reservoir capacity is reduced by sediment accumulation. Statement (II): The trap efficiency is a function of the ratio of reservoir capacity to the total inflow. A small reservoir on a large stream has a low trap efficiency.

Factors affecting the trap efficiency

Reservoir Capacity or Sedimentation: The reservoir capacity and the sedimentation rate are inversely connected. The amount of sediment deposited will rise as time goes on even though the pace of silting or sediment deposition slows down, decreasing the reservoir's capacity. Consequently, trap efficiency is also affected. Statement I is untrue.

Reservoir and stream sizes: A larger reservoir on a smaller stream has a lower capacity inflow ratio and, as a result, has a higher trap efficiency.

Stream flow velocity: Lower trap efficiency, and higher flow velocity results in less sediment accumulation.

Summary:

Statement (I): The trap efficiency of a reservoir increases with age as the reservoir capacity is reduced by sediment accumulation. Statement (II): The trap efficiency is a function of the ratio of reservoir capacity to the total inflow. A small reservoir on a large stream has a low trap efficiency.

Although statement (I) is untrue, statement (II) is accurate. The relationship between reservoir capacity and total inflow determines a reservoir's trap efficiency.