Can rock fragment cover maintain soil and water for saline-sodic soil slopes under coastal reclamation?

•Rock fragment cover effect on soil loss from saline-sodic soil slopes was studied.•Steady-state infiltration rate and rock fragment cover had a logarithmic relation.•Optimum rock fragment cover to reduce soil loss from gentler slopes was identified.•Temporal variations in rock fragment placement situations requires more attention.

Seeking a potential erosion control method for saline-sodic soil slopes under coastal reclamation is essential. We investigated the effect of rock fragment covers (RC) on the rainfall partitioning, infiltration and runoff processes, and the erosion processes for saline-sodic slopes of 15° and 30° subjected to a 50-min simulated rainstorm with an intensity of 92 mm h− 1. Six rock fragment covers (0%, 10%, 20%, 40%, 60% and 80%) were investigated. Soil was packed in 200 cm × 100 cm × 30 cm flumes, divided into two to create two replicates for each treatment. Two sequential soil erosion events, E1 followed by E2, were induced under two rainstorms that were 24 h apart. Results showed that, in general, RC had a positive effect on the runoff rate for both slopes. A logarithmic relationship existed between the steady-state infiltration rate and the RC. For the gentler slopes, an RC between 40% and 60% could protect the soil from erosion for E2 and E1 + E2 events, but did not do so for the E1 events alone. For the steeper slopes, the RC had no effect on soil losses for the E2 and E1 + E2 events, but increased the soil losses for the E1 events. As the situation of rock fragment changed from Situation 1: well embedded into the soil surface to Situation 4: submerged in water, the relationship between RC and soil loss became more complex and might change over time from a positive to a negative one. The results suggested that the effect of RC on runoff and soil losses was influenced by the change of rock fragment situations over time during individual rainstorms. The benefits of RC might be augmented by using them in combination with another protective measure.