Piezometers and Groundwater Levels

Science Center Objects

Measurements of elevations, aquifer-system compaction, and water levels are used to improve our understanding of the processes responsible for land-surface elevation changes. Elevation or elevation-change measurements are fundamental to monitoring land subsidence.


Graph showing depth to water and vertical displacement at CGPS station P304 in Mendota, CA

Water-level and CGPS data for Delta-Mendota Canal CGPS site P304. Vertical displacement is relative and 0.0 datum is a reference point. CGPS data provided by UNAVCO. Groundwater data provided by Luhdorff & Scalmanini Consulting Engineers. (Public domain.)

When extensometer or CGPS data are paired with groundwater-level data from a nearby well, some storage properties of the affected aquifer system can be calculated. The CGPS data and water-level data are used for stress-strain analysis. If water levels fluctuate in the elastic range of stress, the elastic skeletal storage coefficient will be computed. The elastic skeletal storage coefficient is a standard measure of aquifer storage that is directly related to the compressibility of the aquifer-system skeleton and largely governs the recoverable (reversible) deformation of the aquifer system. If water levels continue to decline beyond historically low levels (the inelastic range of stress), it may be possible to compute the inelastic storage coefficient that governs the permanent compaction of the aquifer system. If water levels are fluctuating in both ranges of stress (fluctuating seasonally and declining annually), both the elastic and inelastic storage coefficients can be computed.