Porous Aquifers and Groundwater Circulation - Hydrogeology: Objectives, Methods, Applications - page 44

Figure 19 Topographic calibration of piezometry.
The curves interpolating the elevation of the water table between
measurement points (called isohypses, isopiestic lines, or pressure curves)
present the appearance of a topographic map of a drainage basin at the
surface, groundwater fl owing perpendicular to the curves, from the tops
of the aquifer towards its low points.
Analysis of the piezometric surface (Figure 20) allows the determination
of an aquifer's limits, as well as of zones of high or low transmissivity in the
case of a heterogeneous environment, and of zones of infl ow and outfl ow
in a homogeneous environment.
Figure 20 Appearance of the piezometric surface with fl ow lines.
The aquifer's reaction to events such as precipitation and fl ooding can
be followed with piezographs, limnigraphs installed in piezometers. The
measurements thus obtained, called piezograms, allow the determination of
the best time periods for piezometric surveys and the cautious interpolation
of their values.