Considering slug tests for aquifer characterization, the phase of the hydraulic head variation in the well, starting from the instant in which it is generated, until the initial (undisturbed) hydraulic head condition is reached, has a duration determined by the initial volume of slug and the particular characteristics of the aquifer related to the use of field or laboratory scale. In this time range, it is necessary to acquire a number of hydraulic head values able to guarantee a reliable estimate of the aquifer parameters, specifically of the hydraulic conductivity. Various methodologies were developed to smooth out unwanted high and low frequency oscillations such as decimation, statistical methods, the use of convolution formulas based on simplified procedures of the least squares method and spectral analyses both in time and time-frequency domain. The aim of this study is to highlight the opportuneness to carry out smoothing in cases where the data series obtained by the tests commonly used to characterize the aquifer parameters, specifically by slug tests, are particularly extensive. The main purpose, of great usefulness and of which there is no trace in the literature, is to provide valid guidance in this field, regarding the choice of the specific smoothing method to be used, in the constant search to reduce times and costs. The present work is based on a 3D experimental investigation carried out on a physical model reproducing a confined aquifer. Seven slug tests were performed by the injection of a specific water volume in the central well of the aquifer. The hydraulic head variation was recorded by a pressure transducer placed in the injection well. The raw data were processed using a Savitzky-Golay filter, a Fourier Transform, and Mexican hat and Morlet Wavelet Transform were used. The performances of the adopted techniques to smooth the hydraulic head data were analyzed in terms of correlation coefficient to well reproduce the canonical Cooper’s equation. An analysis of the time variation of the shape and the frequency oscillation of the hydraulic head variation was conducted in the time-frequency domain by means of Wavelet Transform. The results deduced from the smoothed hydraulic heads were adopted to perform a sensitivity analysis in determining a stable value of the hydraulic conductivity of the confined aquifer.
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|Titolo:||ON THE SMOOTHING OF HYDRAULIC HEAD DATA OBTAINED BY LABORATORY SLUG TESTS|
|Data di pubblicazione:||2018|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|