Civil Engineering - Hydraulics - Discussion

I think the Pitot tube is correct.

It's by pitot tube. It gives velocity then find discharge as velocity*area.

Flow in 3 m dia is measured by pitot tube. But more than 3 m dia measured by the rotameter. Hence the given answer is correct

With the help of pitot tube, we measure the velocity and as the diameter of the pipe is known we find the area. Multiply velocity and area to get flow rate in metre cube per second. If you want in kg/sec multiply discharge with a density of water. Rotameter requires float and tube but such size of tube and rotameter is not economical to construct. Orifice meter consists of a plate with a hole but it is not economical to have a 3 meters dia orifice plate. By considering the above pitot tube is considered to be most economical.