Reproducibility of The Estimation Using Hydraulic Tomography Analysis With In Situ Pumping Test Data.

Although Hydraulic Tomography has been employed to determine the heterogeneous hydraulic properties, there is no particular study yet on the reproducibility of the in-situ hydraulic properties. In this paper, two comprehensive sequential pumping tests on a single site in two different years, 2004 and 2010, are conducted and the drawdown data are analyzed using the specific drawdown (s/Q) to demonstrate the reproducibility of the drawdown and, subsequently, the hydraulic properties.

The results of the pumping tests show that the reproducibility of the drawdown at the single site is validated as the statistical error and the correlation coefficient between the specific drawdown-time data in 2004 and 2010 are < 0.005 and > 0.9, respectively.

The performance statistics of the estimated transmissivity (T) by SSHT indicates that the mean absolute error (L1 norm) is 0.001, the root mean square error (L2 norm) is 0.002, and the correlation coefficient (COR) is 0.424. The performance statistics of the estimated transmissivity (T) by THT shows that the values for L1, L2 and COR are 0.001, 0.002 and 0.424, respectively while on the estimated storativity (S), the values for L1, L2 and COR are 0.013, 0.129 and 0.234, respectively. The result of statistics show that the estimated transmissivity (T) and the estimated storativity (S) have similar trends by both of SSHT and THT between 2004 and 2010. In addition to, the variogram analysis by the exponential regression also suggests that there is a corrlation between the estimated fields in different years by both of SSHT and THT. Consequently, the reproducibility of the heterogeneous hydraulic properties is confirmed. The reproducibility of the in-situ hydraulic properties can be demonstrated by above two results of analysis.

      Additionally, the performance statistics on the predicted drawdown by SSHT show that the values for L1, L2 and COR are 0.167, 0.196 and 0.771, respectively whereas L1, L2 and COR are 0.099, 0.143 and 0.89, respectively in the case of the predicted drawdown by THT. The results of validation between the drawdowns by SSHT in 2004 and 2010, it is noticed that if more pumping test data sets employed, a more accurate predicted drawdown can be generated, and the results are like Huang et al., [2011] mentioned the methods of validation with some charteristics.

Based on the validation result on the drawdown in the different years (in which L1, L2 and COR are  0.084, 0.119 and 0.883, respectively), the result of the cross validation is singificantly dependent on the average pumping rate. In the comparison between Steady State Hydraulic Tomography (SSHT) and Transient Hydraulic Tomography (THT) on the results of estimated fields, HT also appears to be robust and accurate.