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.