Soil salt drainage efficiency is of significant interest in quantifying soil remediation, related to external environment, soil properties, and amendment. This study mainly discusses the mechanism of slope gradients and rainfall intensities affecting water-salt transport in saline soils. Laboratory investigations were made to measure the key parameters including the wetting front, water content, and salinity in a flume of almost 1.2 m long under four slope gradients (0°, 5°, 10°, and 15°) and five rainfall intensities (10, 30, 50, 75, and 100 mm/h). The results show that the migration rate of water in soils increased with higher rainfall intensity and at lower slope gradients, in turn resulting in a substantial decrease in soil salinity. The rainfall intensity grew from 10 mm/h to 100 mm/h, and the water content growth rate and salinity decrease rate increased from 0.59%/min to 0.93%/min and 0.044%/min to 0.060%/min, respectively. The rainfall intensity has less influence on the time of salinity stabilization, which is approximately 420 to 480 min. Higher slope gradient and shorter distances from the slope top caused decrease in water-salt migration rate. The wetting front and water content showed a significant linear and exponential relationship with rainfall time respectively, while soil salinity as a function of rainfall time are piecewise functions. The results explicate the water-salt transport behavior of saline soils, and provide a scientific reference for soil remediation.

To understand the water-salt transport process of saline soils in the Yellow River Delta region under traditional hydraulic remediation measures and to determine its engineering parameters, this study made laboratory investigations to measure the soil salt content using three remediation practices under simulated rainfall conditions. The results indicated that under the rainfall intensity of 100 mm/h, 6-8 h are needed for the soil salt content to tend to be constant. The distribution of the salt content presents a typically symmetrical shape regardless of the position of the saline soil relative to the concealed pipe, the open ditch, or the vertical shaft. The two-parameter exponential function indicates the relationship between the soil desalination rate and the horizontal distance from the pipe, ditch, or shaft. The maximum spacings to build the salt drainage engineering projects of the concealed pipe, open ditch, or vertical shaft in the laboratory are 4.79 m, 2.88 m, and 2.19 m, respectively. The effectiveness of salt drainage for coastal saline soils can be ranked from highest to lowest as first the concealed pipe, then the open ditch, and finally the vertical shaft. The findings provide an experimental basis and reference for the application of hydraulic measures to remediate saline soils in this region.