Correct option is B
The velocity with which water approaches a notch is called the velocity of approach. This term refers to the speed of the fluid as it nears the opening (notch) through which it will flow. The velocity of approach is an important factor in calculating the discharge over a notch or weir, as it affects the flow rate and the resulting measurements.
A notch is an opening in the side of a channel or tank where the liquid surface is below the top edge of the opening. The discharge through a notch or weir is directly related to the water depth or head. The head is affected by the velocity of the approaching stream, the condition of the crest, the contraction, and the elevation of the water surface downstream from the weir.
