Publication
Specific yield (Sy) is an essential hydrogeological parameter in groundwater-related modeling and estimation. In this study, we proposed several new analytical expressions of Sy to characterize the nonlinear variations of Sy under shallow groundwater environments, encompassing Sy for three-layered soil, transition zone Sy, and flux-dependent Sy (in Boussinesq-type equation). The proposed Sy expression for three-layered soils expanded the applicability of previous expressions for homogeneous soil. The result indicated that different from the trend for homogeneous soil, Sy for three-layered soils may also decrease with the increase of water table depth. Besides, Sy corresponding to the transition zone (Sy,tz) was analytically quantized to improve the previous empirical method, and we found that Sy,tz was not dependent on initial water table depth but the increment of depth. Moreover, flux-dependent Sy in the Boussinesq-type equation was proposed by considering the vertical fluxes in the unsaturated zone, which effectively improved the modeling behavior of the previous Boussinesq-type equation with Sy under the hydrostatic assumption. Sensitivity analysis of analytical expressions showed that saturated moisture content, shape parameter α, and water table depth were the three most important variables for Sy expressions. Overall, our study expanded the applicability of the previous analytical expressions of Sy and offered valuable analytical approaches for sustainable groundwater management.