Effect of soil hydrological conditions on rainfall erosion on coastal saline soil slopes

Soil erosion on bare slopes in coastal reclamation areas reduces the efficiency of water conservation projects and poses a threat to the water environment in saline tidal flats. Slope shape and soil hydrological conditions are affected by severe soil detachment and rapid sedimentation processes during rainfall, which in turn influence soil erosion processes. In this study, the influences of slope gradient, slope length, initial soil water content and groundwater depth on slope erosion processes of saline sodic soils were investigated through simulated rainfall experiments. We found that the effect of slope gradient on soil loss varied with slope length. For the long-slope treatments with the same total length of initially air-dried soil (AD), the unit width sediment yield rate (Rs) significantly (p = 0.05) increased with increasing slope gradient from 30° to 60°. For the short-slope treatments with different total lengths, opposite trends were observed for the runoff rate and Rs variation with increasing gradient. The Rs values of the slopes with initially saturated surface soil (SS) and a groundwater depth of 0.8 m (GW) were significantly (p = 0.05) greater than that under the AD treatment. On the 60° SS treatment slopes and 45° and 60° GW treatment slopes, soil erosion induced distinct collapse failure and altered the original slope shape, yielding lower gradients and larger lengths, which significantly (p = 0.05) increased Rs in turn. Canonical correlation analysis (CCA) revealed that 71.6% of the variance in the set of dependent variables (sediment yield and runoff) could be explained by the first pair of canonical variables, which mainly represented slope topography factors, and 12.1% of the variance could be explained by the second pair, which mainly represented soil hydrological conditions. The conclusions of this study could provide a theoretical foundation for slope protection in coastal reclamation areas.