FIGURE 2. Water table data from 11 observation wells vs rainfall rate
every month
The flowchart of this study can be seen in Figure 3. The coefficient of
skewness can be derived from the statistical tools in GIS. Based on the
coefficient of skewness, the original data from each well is transformed
using logarithmic transformation. The purpose of the logarithmic
transformation is to gain a better coefficient of skewness and to
stabilize the variance. The limit of the excellent coefficient of
skewness is ±2 (Rubin, 2012), therefore if it is outside the threshold,
the data is highly skewed, and logarithmic of transformation must be
considered. In this case, the original data is within the range ±2;
however, by the log-transformation, it is slightly improved. Therefore,
it has been decided to use the log-transformation for better
predictions.