Head loss
This is the loss of energy or head (height of water expressing energy per unit weight) occurring in a pipe or channel carrying flows of water. The loss is caused by friction between the water and the conduit’s walls and within the flow, and by turbulence effects (shock losses) occurring at features such as pits.
The following diagram shows the likely to losses that occur along a piped drainage system that is mostly flowing full.
Total energy is illustrated by the energy grade line (EGL) or total energy line (TEL) that becomes lower along a a pipeline due to friction and local (shock) losses at pits, bends and other features. Engineers are usually more interested in the hydraulic grade line (HGL) which is located a distance V2/2g
below the EGL, where V is the flow velocity, as this shows the level to which water rises in pits.
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