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Articles | Volume 19, issue 7
https://doi.org/10.5194/hess-19-2971-2015
https://doi.org/10.5194/hess-19-2971-2015
Research article
 | 
01 Jul 2015
Research article |  | 01 Jul 2015

Analyses of uncertainties and scaling of groundwater level fluctuations

X. Y. Liang and Y.-K. Zhang

Abstract. Analytical solutions were derived for the variance, covariance, and spectrum of groundwater level, h(x, t), in an unconfined aquifer described by a linearized Boussinesq equation, with random source/sink and initial and boundary conditions. It was found that in a typical aquifer, the error in h(x, t) at an early point in time is mainly caused by the random initial condition, and the error reduces as time progresses to reach a constant error at a later time. The duration for which the effect of the random initial condition is significant may be a few hundred days in most aquifers. The constant error in h(x, t) at a later time is due to the combined effects of the uncertainties in the source/sink and flux boundary: the closer to the flux boundary, the larger the error. The error caused by the uncertain head boundary is limited to a narrow zone near the boundary and remains more or less constant over time. The aquifer system behaves as a low-pass filter which filters out high-frequency noises and keeps low-frequency variations. Temporal scaling of groundwater level fluctuations exists in most parts of a low permeable aquifer whose horizontal length is much larger than its thickness, caused by the temporal fluctuations of areal source/sink.

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The error or uncertainty in head, obtained with an analytical or numerical solution, at an early...
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