The correlation between groundwater level data of Jeju Island and altitude was analyzed. The hydraulic watershed was established based on groundwater surface of the equipotential lines. The 3D numerical analysis model was used to interpret flow characteristics of the watershed, and the results of analyzing
hydraulic conductivity computed from the model are as follows. The range of average annual fluctuation of ground water level in Jeju Island was 0.16 ∼ 48.84m. The basal groundwater distribution area was changed to 0.16 ∼ 2.73m, the parabasal groundwater area was changed to 0.47 ∼ 12.56m and the high level groundwater area was changed to 0.62 ∼ 48.84m. Based on analysis of the correlation between altitude and groundwater level for every 100m of altitude, the value of R2 was 0.1653 ∼ 0.8011. There was no
clear correlation between altitude and groundwater level. Especially, the eastern and western areas showed an inversely proportional relationship between altitude and groundwater level. Only a portion of the southern and northern areas showed the inversely proportional relationship. The Kriging technique was used to analyze underground water level data and construct the equipotential lines for all areas of Jeju Island. Eight groundwater watersheds were established by considering the direction of groundwater flow, positions of groundwater level observation wells and long and short axes of the watersheds. Groundwater recharge considering rainfall characteristics, hydraulic conductivity of each spot and observation data were supplemented for the groundwater watersheds to perform 3D numerical analysis. The groundwater flow simulation showed RMSE of 0.554 ∼ 6.177 and the direction of groundwater flow was similar to the equipotential lines, increasing reliability of flow analysis. Based on analysis of hydraulic conductivity distribution according to the results of the groundwater flow simulation in all areas of Jeju Island, hydraulic conductivity was 100m/d or above in the coastal area and 1 ∼ 45m/d in the upstream area. Especially, hydraulic conductivity was 500m/d or above in the lowlands of the eastern area, and it was relatively high in some northern and southern areas. Such characteristics were found to be related to distribution of the equipotential lines and type of groundwater occurrence.