COMPARISON OF GROUNDWATER FLOODING INTENSITY (GFI) AND FLOOD VULNERABILITY INDEX (FVI) AND THEIR APPLICABILITY IN SOUTH KOREA

Groundwater level’s rise to the land surface causes a groundwater(gw) flooding combined with an inundation, soil wetting, and a decrease of infiltration rate. Gw levels before a large barrage construction in 2012 were generally 20~30 cm deeper than river water levels due to a long period of pumping. However, they are now increased up to the land surface in some riverside regions due to water-filling at the barrages along the river. Groundwater flooding intensity (GFI) is developed using two factors calculated from time series of groundwater monitoring wells; an increasing rate of groundwater levels (tanα) and the shallowest depth to groundwater (DTW_min) for each rising event. Flood vulnerability index (FVI) is also developed using a multiplication of standardized GFI and a high water level’s duration. The trend of GFIs’ magnitude calculated from gw monitoring wells located at the riverside basins exists generally according to the river location, from up to down streams, and is also similar to FVIs’ magnitude trend. Both of them are assumed to be affected by a distance from a well to the river, average gw level, river water level, and land elevation of monitoring site. However, they show an opposite feature at some sites due to a duration factor of high water levels. Large deviation at the duration of high water level exists at these sites, according to the distance from a well to the nearest river. High correlation between the affecting factors and a distance from a well to a river also exists at these sites. Again, it is revealed that GFIs’ magnitudes become opposite to FVIs’ as far as the distance is. Similarly, the irrigation channels to control surface water levels also affect above two values at the sites. Finally, GFIs and FVIs can be used to assess and forecast the flooding possibility, but many factors including river topography, irrigation channel, and a distance from a well to the river should be carefully considered. Except these abnormal sites, gw flooding situation can be estimated and determined by three factors, a distance from a well to the river, average gw level, river water level, and land elevation of monitoring site.