it is best to use _______ to determine the hydrolic grade line

• A. Thermometers
• B. Pressure gauges
• C. Flow meters
• D. Valves

Answer: (B)

To determine the hydraulic grade line, you need the pressure head at various points because the HGL is formed by the elevation plus the pressure head (z + p/γ). Pressure gauges give you the static pressure in the pipe, and by converting that pressure to head and adding the local elevation, you can map the piezometric head to draw the hydraulic grade line. Thermometers measure temperature, which isn’t used in calculating HGL; flow meters assess how much water is moving rather than the pressure driving the line; valves influence pressure but don’t provide a measurement. So measuring pressure with a pressure gauge is the right approach.