What is hydraulic gradient and how is it used in pipeline design?

Hydraulic gradient is the slope of the hydraulic grade line (HGL), representing energy loss per unit length due to friction. HGL = elevation + pressure head; it drops along flow direction due to friction. For gravity-driven flow, the HGL slope determines flow rate. In pump systems, the pump adds energy, creating a step up in HGL. Pipeline profile is plotted against HGL to ensure positive pressure throughout (HGL above pipe centerline) and identify potential problems like vapor pockets at high points.