What is meant by the term “hydraulic grade line”?

The term "hydraulic grade line" refers to a representation of pressure head in a water distribution system. It signifies the height to which water would rise in piezometric tubes connected to the system, indicating the available energy at any point in the water distribution system due to pressure. The hydraulic grade line is crucial for understanding how water flows through the system, as it accounts for the static pressure head and the elevation head at that particular point.

When visualizing the hydraulic grade line, you can see how changes in elevation and pressure affect the water's potential to flow. If the hydraulic grade line is above the physical pipe, gravity will assist the flow, while if it's below, additional energy, such as from pumps, may be needed to move the water effectively. This understanding is fundamental in designing and assessing water distribution systems to ensure efficient and adequate water delivery.