**Related Resources: hydraulic**

### Hydraulic Head Pressure

**or piezometric head is a specific measurement of liquid pressure above a geodetic datum. It is usually measured as a liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer. In an aquifer, it can be calculated from the depth to water in a piezometric well (a specialized water well), and given information of the piezometer's elevation and screen depth. Hydraulic head can similarly be measured in a column of water using a standpipe piezometer by measuring the height of the water surface in the tube relative to a common datum. The hydraulic head can be used to determine a hydraulic gradient between two or more points**

*Hydraulic head pressure*Fluid flows from the tank at the top to the basin at the bottom under the pressure of the hydraulic head. |

*- In fluid dynamics, head is a concept that relates the energy in an incompressible fluid to the height of an equivalent static column of that fluid. From Bernoulli's Principle, the total energy at a given point in a fluid is the energy associated with the movement of the fluid, plus energy from pressure in the fluid, plus energy from the height of the fluid relative to an arbitrary datum. Head is expressed in units of height such as meters or feet.*

**Fluid Dynamics Head**Elevation head is due to the fluid's weight, the gravitational force acting on a column of fluid.

Pressure head is due to the static pressure, the internal molecular motion of a fluid that exerts a force on its container.

Resistance head (or friction head or Head Loss) is due to the frictional forces acting against a fluid's motion by the container.

*Equations used in Hydraulic Head Calculations:*= Pressure head, in terms of the elevation difference of the water column relative to the piezometer bottom (Length in m or ft), and

z = Elevation at the piezometer bottom (Length in m or ft)

= Unit weight of water (Force per unit volume, typically N�m−3 or lbf/ft�)

p = Density of the water (Mass per unit volume, frequently kg�m−3)

g = Gravitational acceleration (velocity change per unit time, often m�s−2)

*Fresh Water Head*= is the density of fresh water (Mass per unit volume, typically in kg�m−3)