ANS:B - half the depth of flow

For a rectangular channel, the hydraulic mean depth (D) is defined as the ratio of the cross-sectional area (A) to the top width (T) of the channel. It is given by: D=TA​ In a rectangular channel, the cross-sectional area (A) is equal to the product of the flow depth (y) and the channel width (B), and the top width (T) is simply the channel width (B). So, we have: A=y×B =B Therefore, the hydraulic mean depth (D) can be expressed as: D=By×B​=y So, the hydraulic mean depth (D) for a rectangular channel is equal to the depth of flow (y). Hence, the correct option is: the depth of flow.