For solving the problems is hydraulic engineering, the velocity used is

ANS:B - average velocity of flow over a section

For solving problems in hydraulic engineering, the velocity used depends on the specific context of the problem and the assumptions made in the analysis. However, in many hydraulic engineering calculations, the average velocity of flow over a given section is commonly used. This average velocity provides a representative measure of the flow velocity within the section and is often employed in computations related to flow rate, discharge, and other hydraulic parameters. The average velocity can be calculated by dividing the total flow rate by the cross-sectional area of the flow. It accounts for variations in velocity across the section and is useful for obtaining a single representative velocity value for the entire cross-section. Therefore, in many cases, the average velocity of flow over a section is used for solving problems in hydraulic engineering.