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Hydraulic head (or piezometric head) is a specific measurement of the potential of water above a vertical datum. [7] It is the height of the free surface of water above a given point beneath the surface. [4] Pumping level is the level of water in the well during pumping. [8] Specific capacity is the well yield per unit of drawdown. [8]
Measuring hydraulic head in an artesian aquifer, where the water level is above the ground surface. Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum. [1] [2] It is usually measured as a liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer.
The standard method for measuring pore water pressure below the water table employs a piezometer, which measures the height to which a column of the liquid rises against gravity; i.e., the static pressure (or piezometric head) of groundwater at a specific depth. [6] Piezometers often employ electronic pressure transducers to provide data.
where s is the drawdown (change in hydraulic head at a point since the beginning of the test in units of distance), u is a dimensionless parameter, Q is the discharge (pumping) rate of the well (volume per unit time), T and S are the transmissivity and storativity of the aquifer around the well (distance squared per unit time and dimensionless ...
h = z + p / ρg is the piezometric head or hydraulic head (the sum of the elevation z and the pressure head) [11] [12] and; p 0 = p + q is the stagnation pressure (the sum of the static pressure p and dynamic pressure q). [13] The constant in the Bernoulli equation can be normalized.
The specific storage is the amount of water that a portion of an aquifer releases from storage, per unit mass or volume of the aquifer, per unit change in hydraulic head, while remaining fully saturated. Mass specific storage is the mass of water that an aquifer releases from storage, per mass of aquifer, per unit decline in hydraulic head:
The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N·m −2 or kg·m −1 ·s −2). This special name for the unit was added in 1971; before that, pressure in SI was expressed in units such as N·m −2. When indicated, the zero reference is stated in parentheses following the unit, for example 101 kPa (abs).
Pressure head is a component of hydraulic head, in which it is combined with elevation head. When considering dynamic (flowing) systems, there is a third term needed: velocity head. Thus, the three terms of velocity head, elevation head, and pressure head appear in the head equation derived from the Bernoulli equation for incompressible fluids: