Effects of vegetation on the hydraulic properties of soil covers: Four-years field experiments in Southern China

Vegetation is essential in constructing eco-slopes for environmental protection and restoration, as well as in minimizing soil erosion and landslide. The effects of vegetation on the hydraulic properties of the underlying soil cover, especially the saturated-unsaturated hydraulic properties during long-term drying-wetting cycles, are extremely important to assess the performance of an eco-slope, which have not been intensively investigated. This study investigated the infiltration and hydraulic conductivity of the vegetated covers by continuously monitoring the hydraulic properties of three different vegetated layers for a period of four years. Thirty-three sensors were set up to monitor the hydraulic properties of a Vetiver grass cover, a Bermuda grass cover and a bare cover in-situ. The results demonstrate that the infiltration rate through the Vetiver grass cover is almost two times that of the cover without vegetation. In contrast, the infiltration rate through the Bermuda grass cover is only half of the bare cover. The hydraulic conductivity of the Vetiver cover is larger than that of the bare cover and increases up to 3 orders of magnitude. The unsaturated hydraulic conductivity of the Bermuda cover is the smallest, which only increased by 1–2 orders of magnitude under the same matric suction in four years. The field study indicates that the Bermuda grass can effectively reduce the increase in percolation of a soil layer. This study provides valuable field data to clearly demonstrate the influence of vegetation on the covers, paving the way for a more sustainable ecological slope design.