Landscape patches influencing hillslope erosion processes and flow hydrodynamics

Abstract

Exploring overland flow resistance and sediment delivery capacity under different landscape vegetation conditions is critical for better understanding hydrodynamic mechanisms of soil erosion processes and hydrological connectivity on hillslopes. To evaluate flow resistance relations and sediment transport for landscape vegetation coverage and combinate effect of vegetation patches, field simulated rainfall experiments were conducted using a series of overland runoff and sediment transport rates in 3 m (L) × 2 m (W) experimental plots with coverages of 0%, 20%, 40%, 60% and 90% in a uniformly distributed condition and composited flow paths of different patches (horizonal path, vertical path, random patches and S-shaped path) in the same coverage (40% and 60%). The runoff rates for the grassland with coverages of 20–90% were decreased by 19.3–61.4% (P < 0.05), and the sediment concentrations were reduced by 81.7–97.8% (P < 0.05) compared to the bare land. The Darcy-Weisbach resistance coefficient doubled and the stream power declined by 60.0% when grassland coverage increases to 90%. The runoff rates varied little among the conditions of horizontal, vertical, random and S-shaped flow paths at the coverage of 60%, while the rate apparently reduced by 34.1% (P < 0.05) when the vertical flow path became horizontal under the same coverage of 40%. The sediments for poorly connected flow paths could reduce sediment >90% either on high-coverage or low-coverage grassland. Our field experiments confirmed that the increase of vegetation coverage and the combination of landscape patches could significantly reduce runoff rates, sediment yields and flow velocities, increase surface roughness, promote flow resistance and diminish hydraulic shear stress and the stream power. The poorly-connected paths (horizontal and random) exhibited a stronger flow resistance and weaker sediment transport capacity than the well-connected paths (vertical and S-shaped).