TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
Drawdown or head differential, or residual drawdown after a pump test
Drawdown expressed as Hz-H2o
Head dimension in the measurement of flow with a Parshall flume
Average head loss in header pipe to pump intake
Friction head loss in screen entrance or filter and screen entrance
Friction head loss in riser pipe and connections
Friction head loss in well screen
Velocity head loss in well
Total hydraulic head loss in well or wellpoint
Distance from bottom of sheet pile or cutoff wall to impervious boundary
Head at a specific point P, head on permeability test sample in constant head permeability test; final
head on permeability test sample in falling head permeability test; pressure drop across an orifice; ob-
served head on crest in weir flow measurement; or head at a specific time during a pump test
Height of free discharge above water level in a gravity well
Head at center of a group of wells
Maximum head landward from a drainage slot or line of wells, or maximum head between two slots or
lines of wells
Head in an artesian drainage slot, average head at a line of wells, or height of bottom of excavation in
computing the creep ratio
Head midway between wells, or height of mercury for pipe orifice flow measurement
Head in a gravity drainage slot or at equivalent drainage slot simulating a line of wellpoints or sand
drains, or initial head on permeability test sample in the falling heat permeability test
Head at point P
Height of free discharge above water level in drainage slot
Velocity head in measuring flow with a Pitot tube
Head at well, wellpoint, or sand drain
Wetted screen length
Head in a wellpoint that can be produced by the vacuum of a wellpoint pump
Electric current or rate of flow
Hydraulic gradient of seepage, well number, intensity of rainfall
Electrical gradient between electrodes
Drawdown at any well
Constant used in jet-flow calculations
Coefficient of permeability of homogeneous isotropic aquifer
Transformed coefficient of permeability
Coefficient of permeability for the flow of air
Vertical coefficient of permeability of a sand drain
Coefficient of electroosmotic permeability
Effective permeability of transformed aquifer
Horizontal coefficient of permeability
Vertical coefficient' of permeability
Distance from drainage slot, well, or line of wells or wellpoints to the effective source of seepage, length
of permeability test sample, or seepage length through which Ah acts in determining a seepage gradi-
ent
Distance from drainage slot to change from artesian to gravity flow
Distance from well j to source of seepage
Half the distance between two parallel drainage slots or lines of wells; long dimension of a rectangular
drainage slot, or number of strata penetrated by a well in calculating effective well screen penetration
Height of pump intake above base of aquifer
Mean sea level
Number of equipotential drops in a flow net
Number of flow channels in a flow net
Number of wells in system or group, or porosity, number of strata in an aquifer for transformed section
calculations, or number of concentric rings in measuring flow with a Pitot tube
Number of equipotential drops from seepage exit to point P
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