Figure 7. The concept of "hydraulic head" or "head" at a point in an aquifer.

Consider the elevations above sea level at points A and B in an unconfined aquifer and C in a confined aquifer. Now consider the addition of wells with short screened intervals at these three points. The vertical distance from the water level in each well to sea level is a measure of hydraulic head or head, referenced to a common datum at each point A, B, and C, respectively. Thus, head at a point in an aquifer is the sum of (a) the elevation of the point above a common datum, usually sea level, and (b) the height above the point of a column of static water in a well that is screened at the point. When we discuss declines or rises in ground-water levels in a particular aquifer in this report, we are referring to changes in head or water levels in wells that are screened or have an open interval in that aquifer.
https://pubs.usgs.gov/circ/circ1186/html/gen_facts.html

What drives groundwater flow?

gravity is the dominating driving force
water flows from high elevation to low elevation and from high pressure to low pressure, gradients in potential energy (hydraulic head) drive groundwater flow
recharge and discharge (Fig 7.2)
in recharge areas water is added to groundwater
in discharge areas water is lost from groundwater
in recharge (discharge) areas, the hydraulic head decreases (increases) with depth
recharge occurs from the unsaturated zone or from surface waters
the hydraulic head along any equipotential is equal to the elevation of its intersection with the water table (Fig 7.3)
https://www.ldeo.columbia.edu/~martins/hydro/lectures/gwf.ht...


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Note added at 55 мин (2020-09-27 08:47:51 GMT)
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"напорный" -> high-head (?)
https://rb.gy/azlf8l

"безнапорный" -> gravity-driven (?)
https://rb.gy/qhhzch


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Note added at 1 час (2020-09-27 09:35:28 GMT)
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zero-head groundwater не гуглится абсолютно