- A pump developing a pressure of 600 kN/m2 is used to pump water (at about 20C) through a 120-mm-ID pipe 300 m long to a reservoir 40 m higher. With the valves fully open, the flow rate is 0.03 m/s. As a result of corrosion and scaling, the effective absolute roughness of the pipe surface increases by a factor of 2. By what percentage is the flow rate reduced