Effect of combining biogeotextile and vegetation cover on the protection of steep slope of highway in northern China: A runoff plot experiment

Abstract

Biogeotextiles can be used to facilitate the formation of vegetation cover and to reduce soil erosion. Studies have demonstrated that only biogeotextile or vegetation cover can greatly reduce soil erosion. However, information about the effects of the combination of biogeotextile and vegetation cover on soil erosion is still limited, despite that the combination is the commonly practical form for bare road slope protection. Experimental plots, consisting of a relatively loose surface layer and a compacted sublayer, were constructed using movable soil-bin trolleys (200 × 100 × 40 cm3) filled with silt loam sieved through 1-cm screen. The plots were seeded with a seed mixture of tall fescue (Festuca elata Keng ex E. Alexeev) and alfalfa (Medicago sativa L.) as a grass-legume regime. Then the plots were covered with three types of biogeotextile, i.e., coir blanket (CB), mixed coir-straw blanket (MB), and straw blanket (SB). A bare slope (BS) was constructed as the control experiment. Irrigation was applied to ensure vegetation germination and growth. Plant characteristics were measured after every 20 days. Laboratory simulated rainfall of 71 mm/h intensity was applied to each plot for 60 min after 20, 40, and 60 days. Surface runoff and sediment were collected every 5 min during rainfall. The results showed that the MB and SB promoted increased total emergence density of plants by 47% and 23%, respectively, compared to case of vegetation growth without biogeotextiles. The dense structure of the CB impeded the emergence of alfalfa, leading to 9% lower total emergence density. Compared with bare slope (0 day BS), biogeotextiles increased runoff by 3% (MB)–19% (CB) and reduced erosion by 96% (MB and SB)–98% (CB). After 60 days, vegetation cover reduced runoff by 54% and reduced erosion by 81% compared with the BS case. The combination of biogeotextile and vegetation cover reduced runoff by 44% (CB)–62% (SB) and reduced erosion by no less than 99% compared to the BS case. Compared with biogeotextile alone, the combination reduced runoff by 53% (CB)–64% (SB). Compared with vegetation cover alone, the combination reduced erosion by 94% (MB)–99% (CB). The combination takes advantages of vegetation cover for long-term protection and of biogeotextile for facilitating the formation of vegetation cover and immediate erosion control. Thus, the combination is a better choice for road slope protection in northern China. These findings may promote the understanding of how biogeotextiles and vegetation cover work together for runoff and erosion control on bare slopes. In future research more attention should be paid to the selection of plant species and biogeotextile types to avoid impediment by the biogeotextile on the formation of vegetation cover like CB affected alfalfa in this study.