Piezometry

Piezometry is the measurement and interpretation of pressure distribution within a fluid-saturated porous medium, most commonly groundwater in soils and rock. It relies on devices called piezometers to access pore water pressure at specific depths. In saturated conditions, the hydraulic head H is the sum of the vertical elevation z and the pressure head p/γw, and the resulting piezometric surface reflects the energy state of the groundwater. Changes in piezometric levels indicate groundwater flow and changes in recharge, pumping, or subsurface conditions.

Piezometers come in several forms. Standpipe or open-tube piezometers measure static pore pressure by the height of water column in a small-diameter tube installed within a borehole. Piezometers can be vented or non-vented; closed or vibrating-wire piezometers enclose a sensing element that translates pressure to a digital or analog signal. Other types include pneumatic or liquid-filled pressure transducers connected to probes. Proper installation includes a screened interval at the depth of interest, sealing to prevent surface water entry, and venting for accurate pore-pressure measurements.

Applications include assessing groundwater flow directions by constructing piezometric head maps, evaluating pore pressures beneath embankments or retaining structures, monitoring aquifers during pumping tests, mine dewatering, dam and slope stability, and geotechnical investigations. Piezometric data are used to estimate hydraulic gradients and to calibrate groundwater flow models.

Interpretation considerations: measurements reflect local pore pressure and can be affected by well efficiency, screen length, temperature effects, and pore pressure dissipation after loading. Time-series data capture transient responses; static readings require equilibration. Piezometry provides a direct, localized measure of subsurface hydraulic conditions complementary to other hydrological and geotechnical methods.