Russian Journal of Earth Sciences Russian Journal of Earth Sciences Russian Journal of Earth Sciences 1681-1208 49080 10.2205/2022ES000775 ОРИГИНАЛЬНЫЕ СТАТЬИ ORIGINAL ARTICLES ОРИГИНАЛЬНЫЕ СТАТЬИ Estimation of Groundwater Recharge from Rainfall for Arid Coastal Plain of Ninh Thuan Province, Vietnam Estimation of Groundwater Recharge from Rainfall for Arid Coastal Plain of Ninh Thuan Province, Vietnam Nguyen Van Hoang Nguyen Van Hoang Trinh Thu Trinh Thu Shakirov Renat Shakirov Renat Tran Thi Thuy Huong Tran Thi Thuy Huong Syrbu Nadezhda Syrbu Nadezhda Institute of Geological Sciences VAST Вьетнам Institute of Geological Sciences VAST Vietnam Institute of Marine Geology and Geophysics VAST Вьетнам Institute of Marine Geology and Geophysics VAST Vietnam Il’ichev Pacific Oceanological Institute FEB RAS Россия Il’ichev Pacific Oceanological Institute FEB RAS Russian Federation Institute of Marine Geology and Geophysics VAST Вьетнам Institute of Marine Geology and Geophysics VAST Vietnam Il’ichev Pacific Oceanological Institute FEB RAS Россия Il’ichev Pacific Oceanological Institute FEB RAS Russian Federation 17 02 2022 17 02 2022 22 1 1 16 18 06 2020 25 08 2021 https://rjes.ru/en/nauka/article/49080/view

Estimation of groundwater recharge from rainfall is a key factor for determining groundwater resources in water development and management for supporting sustainable socio-economic development, especially for arid areas. The paper presents finite element modeling in the simulation of moisture transfer in unsaturated soils through the relationship between soil moisture, soil suction, unsaturated permeability and soil-moisture dispersivity. Those parameters required for soil moisture transfer are derived from the soil-water characteristic curve functions. Element sizes and time steps used in the modelling have been selected based on a detailed analysis of numerical simulation errors. The methodology had been applied to arid coastal plain area of Ninh Thuan province, Vietnam. Five subsurface soil types in the study area have been collected and analyzed, for saturated permeability, porosity, saturated soil water content, field moisture content, etc. Hourly rainfall data of the years 2014–2018 have been analyzed and grouped into different-duration rainfall events (1-hour, 2-hour, 3-hour and so on). The different rainfall durations and depths of rainfall events and temporal infiltration determined by the moisture transfer modelling have allowed determining the groundwater recharge from the rainfall data. The results show that during the rainy months from May to December 2014–2018, the groundwater recharge from the rainfall is very varying through the modeled soil profiles, from 0.280 m (silty clay) to 0.470 m (sandy silt), which is equivalent to 33.3%–55.2% of the rainfall depth during May–December. Lower infiltration in silty clay is due to low permeability and in the sand is due to low suction, and higher infiltration in silt and sandy silt is thanks to their higher moisture dispersivity. On average, in terms of annual rainfall and soil properties, the average infiltration during May–December is 0.380 m which is equivalent to 44.9% of the rainfall depth, which is about 289 x 106 m3 of rainwater infiltrated into the Quaternary aquifer over 760 km2 of the coastal plain of Ninh Thuan province. The results would be very useful for effective water resources development and management in a given specific hydrogeological condition for such a severe drought area where water is extremely essential.

Estimation of groundwater recharge from rainfall is a key factor for determining groundwater resources in water development and management for supporting sustainable socio-economic development, especially for arid areas. The paper presents finite element modeling in the simulation of moisture transfer in unsaturated soils through the relationship between soil moisture, soil suction, unsaturated permeability and soil-moisture dispersivity. Those parameters required for soil moisture transfer are derived from the soil-water characteristic curve functions. Element sizes and time steps used in the modelling have been selected based on a detailed analysis of numerical simulation errors. The methodology had been applied to arid coastal plain area of Ninh Thuan province, Vietnam. Five subsurface soil types in the study area have been collected and analyzed, for saturated permeability, porosity, saturated soil water content, field moisture content, etc. Hourly rainfall data of the years 2014–2018 have been analyzed and grouped into different-duration rainfall events (1-hour, 2-hour, 3-hour and so on). The different rainfall durations and depths of rainfall events and temporal infiltration determined by the moisture transfer modelling have allowed determining the groundwater recharge from the rainfall data. The results show that during the rainy months from May to December 2014–2018, the groundwater recharge from the rainfall is very varying through the modeled soil profiles, from 0.280 m (silty clay) to 0.470 m (sandy silt), which is equivalent to 33.3%–55.2% of the rainfall depth during May–December. Lower infiltration in silty clay is due to low permeability and in the sand is due to low suction, and higher infiltration in silt and sandy silt is thanks to their higher moisture dispersivity. On average, in terms of annual rainfall and soil properties, the average infiltration during May–December is 0.380 m which is equivalent to 44.9% of the rainfall depth, which is about 289 x 106 m3 of rainwater infiltrated into the Quaternary aquifer over 760 km2 of the coastal plain of Ninh Thuan province. The results would be very useful for effective water resources development and management in a given specific hydrogeological condition for such a severe drought area where water is extremely essential.

 tropical savannah climate drought moisture transfer finite element (FE) higher-order element function This paper has been completed within the implementation of the grant research project KHCBTD.01/19-21: “Groundwater quality and quantity assessment for the coastal area of Ninh Thuan province for groundwater resources management under the context of drought and climate change” and with the financial support of the grant FEB RAS 18-1-008 (QTRU02.01/18-19). A number of registration AAAA-A18-118121090011-9, Grant of the FEB RAS “Abnormal gas-geochemical fields and petrochemical features as indicators of a hydrocarbon fluid, deep permeable zones, active tectonics and geoecology of Central Vietnam and the adjacent shelf” (No. 20-BAHT-010) and project VAST-FEB RAS code QTRU02.02/21-22. The research was carried out as part os State Program for basic scientific research AAAA-A19- 119122090009-2 and 121021500055-0.

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