Estimation of groundwater evaporation based on lysimeter experiment and analytical solution in the Mu Us sandy land

Groundwater evaporation is one of the important discharge item in the calculation of water balance in arid areas. Due to the highly non-linear soil water transport in the vadose zone and the complexity of water dynamic at the atmospheric-surface interface, estimation of groundwater evaporation has been the difficult issue of groundwater resources evaluation. In this study, the E601 type lysimeter was used in the Henan Township equilibrium test site in Wushen County of Inner Mongolia, and the in-situ experiment on surface water evaporation and groundwater evaporation for four typical vadose zone lithologies (sandstone K₁, Salawusu sand Qp^al+l, sandy loam Qh^l, and aeolian sand Qh^eol) were established in the Mu Us sandy land. Combined with the long-term field observation data, the relationship among surface water and groundwater evaporation, groundwater evaporation and extinction depth were examined, and the estimation approach of groundwater evaporation was investigated. The results show that (1) the ratios of saturated evaporation to surface water evaporation are 0.60, 0.77, 0.47 and 0.88 for four typical vadose zone lithologis (sandstone, Salawusu sand, sandy loam, and aeolian sand), respectively, indicating that the surface water evaporation value cannot be used to estimate groundwater evaporation, if used, the surface water evaporation value must be corrected. (2) Based on the observation data of lysimeter and the steady-state analytical solution of soil water movement equation, the key empirical coefficients c of four typical vadose zone lithologies (sandstone, Salawusu formation sand sand, sandy loam, aeolian sand) are Obtained, which are 628932.63, 165058.71, 48948.21 and 1525104.031 m⁻², respectively. (3) According to the stable evaporation formula, the groundwater extinction depth of four typical vadose zone lithologies (sandstone, Salawusu sand, sandy loam, and aeolian sand) is about 60 cm in the Ordos Basin. The results are verified by unsteady evaporation experiment in the laboratory, which may provide important parameter basis for water resources assessment in the study area.