Effects of groundwater evaporation on the natural recharge to groundwater lenses residing in coastal dunes in Southern Central Vietnam

Abstract

Groundwater lenses in the coastal dunes along the South Central coast of Vietnam are often of shallow table. The lithologic composition of the vadose zone in these areas is mainly fine to medium-grained sand, characterised by high porosity. The vegetation is sparse, the annual time of sunrise is long, the air temperature and surface evaporation are high. The above-mentioned conditions are favourable for the evaporation of the groundwater. This study utilised direct evaporation measurement by Lysimeter (LS) according to the principle of water balance. The LS measurement is designed to simulate the groundwater level at a depth of 0.9 m to monitor groundwater loss due to evaporation corresponding to the conditions of natural climate and the vadose zones. Monitoring results showed that the total amount of groundwater evaporation in 2022 at three stations Da Nang, Phu Yen and Binh Thuan is 259.9, 335.6, and 377.0 mm, respectively. With the assumed groundwater level at a depth of 0.9 m, the annual amount of groundwater evaporation has caused the reduction in the groundwater level in the aquifer in Da Nang, Phu Yen and Binh Thuan by 0.64, 0.78, and 0.92 m, respectively.