3.1 Static GALDIT parameters
In this section, we examine the analysis results for parameters with
slight changes over time, i.e., groundwater occurrence (G), aquifer
hydraulic conductivity (A), and distance from the shore (D). The
histogram colors in Figure 3 represent the ratings divided by the decile
method, and the values were divided into 11 levels by adding 7.5 of the
unconfined included in G. The y-axis represents the cumulative ratio of
the area according to the rating, the secondary y-axis represents the
score of the index, and the values indicated by the broken line
represent the total average of the study area.
G or aquifer types are classified into confined aquifers, unconfined
aquifers, leaky aquifers, and bounded aquifers. The most vulnerable
aquifer type is the confined aquifer. The scores of groundwater
occurrence were divided into four levels in the same way as the existing
scoring method, and the theoretical weight was one. This study assessed
the alluvial layer in a free-surface aquifer of a shallow area. The
aquifer type in all areas was an unconfined aquifer, and the G score was
7.5. Figure 4 (a) shows the G index.
Higher A induces smoother groundwater flow and exhibits larger
vulnerability to the SWI. The theoretical weight was three in this case.
When the aquifer hydraulic conductivity exceeds 40 m/day, it is the most
vulnerable, and it is attributed to a score of ten. When the aquifer
hydraulic conductivity was less than 4 m/day, a score of one was given.
Examination of the area ratios of each score yields A below 4 m/day at
the largest ratio of 94.23 %. Some areas have a high aquifer hydraulic
conductivity near Pyeongtaek. The total average score of the study area
was determined as 1.07. Figure 4 (b) shows the distribution of A.
D was determined based on the observed coastline. Areas below 500 m away
from the shore are most vulnerable to SWI, and areas more than 1,300 m
away from the coast are given a score of one. The theoretical weight, an
index that can intuitively show vulnerability, was four. Most parts of
the study area, accounting for 84.14 %, were 1,300 m from the shore.
Areas 1,000 m or less away from the shore with a score of less than five
accounted for 10.88 %, and areas less than 500 m away from the shore
accounted for 2.46 %. The average score for the study area was 1.86.
Figure 3 shows the percentages and average scores of static GALDIT
parameters. Figure 4 (c) shows the distribution of the D index.