Current surface/subsurface drainage systems for tsunami-salinized Japanese paddy fields have not been quantitatively evaluated across varying initial salt concentration profiles and hydrological conditions. In this study, the flooding and drainage processes under field weather conditions were simulated using COMSOL Multiphysics and HYDRUS-2D. Three representative initial soil salt concentration profiles were analyzed under varying ponding depths (3–10 cm) and flooding durations (24–120 h). The results showed that desalination effectiveness was strongly influenced by the initial salt concentration profile. Various ponding water depths and flooding durations can be selected to achieve specific desalination targets based on different initial soil salt concentration profiles. And for different initial soil salt concentration profiles, there is a significant difference between the desalination effect of subsurface drainage alone and the combined surface and subsurface drainage. Subsurface drainage alone showed optimal performance at 10 cm ponding depths, achieving desalination rates up to 2.6 times higher than those achieved by the combined surface drainage method. However, for the shallower ponding depths of 3 and 5 cm, the combined surface drainage method improved the desalination rate by approximately 40% when high concentrations were near the soil surface. These findings establish quantitative selection criteria for drainage strategies based on the initial salt concentration profile and hydrological constraints, offering guidelines for post-tsunami soil recovery.
Jia et al. (Fri,) studied this question.