Assessment of Groundwater Loss from the Holocene Aquifer of the Coastal Sand Dune: A Case Study in Tuy An, Phu Yen, Vietnam

Groundwater loss is one of the primary factors contributing to the degradation of water resources in terms of both quantity and quality. This phenomenon is of particular concern in coastal sandy areas where groundwater in sand dunes is a main source of fresh water for human activities and production. This study includes surveys and field measurements conducted throughout 2022 in the coastal sandy area of An Hoa Hai commune, Tuy An district, Phu Yen province, to identify types of groundwater loss in sand dunes and the level of loss of each type. The results based on the analysis of hydrogeological structures, groundwater monitoring, seepage measurements using seepage meters, and groundwater evaporation measurements using lysimeters over the course of a year (2022), it was found that freshwater for domestic use and production in the study area is obtained from a Holocene unconfined aquifer (qh) in coastal sand dunes. The natural recharge source for this aquifer is mainly rainwater. Specifically, the total amount of natural recharge in 2022 for this aquifer is approximately 1,406,261 m3. There are two main types of loss: loss to the sea and loss due to groundwater evaporation. The previous amounts to approximately 413,097 m3, accounting for 29.4% of the natural recharge, and the latter accounts for 537,264 m3, representing 38.2% of the natural recharge. Total groundwater loss in the study year 2022 took over 67.6% of the natural recharge.