Development of monthly seawater intrusion vulnerability assessment method using GALDIT

Abstract

Accurate diagnoses of vulnerability of seawater intrusion (SWI) into aquifers are required to ensure sustainable utilization of groundwater resources in coastal areas. GALDIT was selected to assess the SWI vulnerability on western coastal areas of South Korea. Climate change trends are updated every year. The existing GALDIT method has various scores to express the changing observed values. However, they are limited because of their sensitivity in the assessment of regional characteristics or climatic change due to low weight flexibility. Therefore, this study assessed vulnerability to SWI by classifying the existing GALDIT into static and dynamic parameters. The static parameters include groundwater occurrence (G), aquifer hydraulic conductivity (A), and distance from the shore (D), whereas the dynamic parameters include height to groundwater level above sea level (L), impact of existing status of seawater intrusion (I), and aquifer thickness (T). The monthly mean was used as the dynamic index to reflect monthly variations. To indicate the temporal trend of parameter L was calculated based on the data observed at the sea level station adjacent to the groundwater level station. To sensitively reflect the monthly changes in values, the range of scores was divided into 10 parts. The calculated GALDIT index showed that the most vulnerable month was September. In the progress of SWI, vulnerability was assessed monthly to highlight the differences in parameters that fluctuate seasonally. The proposed method can be used to apply intensive countermeasures to vulnerable sites and build an operation plan considering the vulnerability period.