Abstract
Numerical simulations were carried out to investigate the so-called Noordbergum effect (i.e. reverse water-level fluctuation) resulting from groundwater withdrawal. Two specific cases were analyzed: a three-layer aquifer system composed of two permeable aquifers separated by a semi-impermeable aquitard, and a corresponding single-layer aquifer system composed of an equivalent lumped material. In the numerical simulation of the layered aquifer system, the Noordbergum effect is observed during the early time period of pumping in the overlying aquitard and unpumped aquifer while the underlying aquifer is pumped. In contrast, the numerical simulation results of the lumped aquifer system do not show such a reverse water-level fluctuation throughout the entire domain. These results strongly suggest that the Noordbergum effect can be explained by the difference in poroelastic responses of the layered (heterogeneous) and lumped (homogeneous) aquifer systems to the hydraulic pumping stress. The Noordbergum effect is caused by two mechanisms: a faster mechanical propagation (deformation) of the pumping stress than its hydraulic propagation (drawdown) from the pumped aquifer into the adjacent aquitard and unpumped aquifer due to relatively lower hydraulic conductivity of the aquitard, and a mechanical amplification (excessive compression) in the lower part of the relatively soft aquitard. However, the pumping stress is evenly distributed throughout the entire domain of the lumped aquifer system without such mechanisms since it has homogeneous hydraulic and mechanical properties.
Published Version
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