A distributed water balance approach to groundwater recharge estimation for Jeju volcanic island, Korea

Groundwater is a major source of water use in Jeju volcanic island of Korea. Due to highly permeable surface conditions, the island does not have any perennial streams or rivers. Therefore, accurate estimation of groundwater recharge and understanding groundwater system are critical to make a reliable water budget in the island. A distributed quasi steady state water balance model, WetSpass (Water and Energy Transfer between Soil, Plants and Atmosphere under quasi Steady State) was adopted to estimate spatially-varying groundwater recharge considering soil type, land use, topography, and groundwater depth. The results from the study using weather data from October 2006 to September 2007 indicated that the eastern and northern parts of the island showed relatively higher rate of recharge as compared with the western region. A total of 69% of recharge occurred in the middle of the Island where topographic elevation is greater than 200 m from the mean sea level. The total amount of recharge was 1,935.6 million tons, 41.8% of the total precipitation. The higher rate of recharge was observed in the watersheds where forest and bare soil as land uses, and sandy loam and clay loam as soil types are dominant. The total runoff was 1,142.7 million tons (24.7%) and the total evapotranspiration was 1,555.7 million tons (33.5%). The zonal hydraulic conductivities estimated with groundwater flow modeling and parameter estimation process showed a wide range of values from 1.2 m/d to 5,380 m/d. The results of groundwater flow modeling indicated that the crest of groundwater table is off-centered from the peak of Mt. Halla toward south.