Flow hydraulic responses to near-soil surface components on vegetated steep red soil colluvial deposits

Abstract

The effects of vegetation restoration on the hydraulic processes of steep colluvial deposits at collapsing gullies in South China have rarely been evaluated. This study quantified the influences of canopy, biocrusts, and roots on 30° deposit slopes planted with Melinis minutifora and Chrysopogon zizanioides via rainfall simulation experiments. Intact M. minutifora and C. zizanioides effectively decreased flow velocities (v) by 35.3% and 29.5%, and increased Darcy–Weisbach friction coefficients (f) by 239.6% and 130.8% compared to that of the control treatments, respectively. The roots of M. minutifora contributed most to the decrease of v and the increase of f, while roots and canopy of C. zizanioides decreased v and increased f to the greatest extents, respectively. Biocrusts increased f and decreased v for all rain intensities when they were combined with roots. However, when they grew on bare slopes, these positive effects were only observed in response to 60 mm h−1 rain events, but were reversed for 120, and 180 mm h−1 rain events. Canopy decreased flow shear stress (τ) and stream power (ω), while roots showed a contrasting result, and the effects of biocrusts varied on different slopes. The influences of plants and components also varied with rain intensities. Sediment yield rates showed significant relationships with v, Re, τ, and ω and could be predicted using linear regression of τ or ω. This study highlights the effects of canopies, roots of different vegetation types, and biocrusts on the hydraulic process on steep colluvial deposit. The presented results aid the decision-making and management of vegetation restoration of collapsing gullies.