What is the term for the line joining the points of highest elevation of water in a series of vertical pipes connected to a pressurized pipeline?

The correct answer is the hydraulic gradient. This term specifically refers to the slope of the energy line in a fluid flow system and represents how the pressure and elevation energy changes along the flow path. In a series of vertical pipes connected to a pressurized pipeline, the hydraulic gradient connects the points of highest elevation of the water, indicating how the energy associated with fluid pressure and gravitational potential varies throughout the system.

The hydraulic gradient is crucial for understanding fluid behavior in engineering applications, as it affects flow rates and pressure at different points in the system. In contrast, while the water table relates to the surface where the soil or rock is saturated with water, it is not relevant to the context of pressurized pipelines. The pressure gradient, on the other hand, describes how pressure changes over distance, which, although related, does not directly link the specific elevations of water in the vertical pipes. Lastly, the elevation line could potentially refer to various elevation points but lacks the specificity that the hydraulic gradient provides regarding fluid flow.