Abstract
Riparian vegetation plays a vital role in inhibiting soil and water loss, but few studies have quantified the relationships between vegetation spatial pattern and the hydraulic characteristics of upslope runoff. This study investigated how hydraulic characteristics (e.g., runoff coefficient, flow regime, flow resistance, and flow shear stress of overland flow) responded to differences in vegetation cover (15% and 30%), slope gradient (5°, 10°, 15°, and 20°), and vegetation pattern in the riparian zone along the lower Yellow River, China, based on landscape pattern analysis and a runoff scouring experiment with flow rates of 9 and 15 L/min and an experimental plot size of 1 m × 3 m. We found that runoff generation on shallow slopes was moderated by increasing vegetation cover, but that this moderating effect decreased on steeper slopes. The regime of overland flow switched from laminar and subcritical on the 5° slope (Fr = 0.56–0.87) to laminar and critical on the 10°, 15°, and 20° slopes (Fr = 1.02–2.18). Flow resistance increased with vegetation cover and flow rate and decreased with slope gradients, and it was larger on shallow slopes with high vegetation cover. Flow shear stress had a range of 1.42–3.55 N m−2, and it increased with increasing slope gradient, vegetation cover, and flow rate. The hydraulic characteristics of upslope runoff, especially flow resistance, were significantly related to vegetation pattern at both the landscape and class levels. Flow resistance was negatively related to patch density, and positively related to perimeter–area fractal dimension and connectance index. The influencing mechanism of landscape patterns on soil erosion processes is dependent on the landscape scale, since the relationships between flow resistance and some landscape pattern indices (aggregation index, effective mesh size, and splitting index) were opposite at the landscape level compared to the class level. We conclude that fragmented vegetation distributions reduce flow resistance, and that riparian vegetation could be managed to inhibit slope erosion by increasing flow resistance.
Highlights
Soil erosion is a global environmental problem that can cause land degradation, decrease productivity, cause ecological deterioration, and may be a threat to the sustainable development of human society [1]
This result supports the viewpoint of Qin et al [35], who concluded that changes in the erosion dynamics of upslope runoff are determined by a combination of vegetation and topography and only by understanding the mechanism of their interacting effects on runoff and sediment characteristics can we provide theoretical support for high-efficiency soil and water conservation
We examined the relationship between riparian vegetation pattern and the hydraulic characteristics of upslope runoff in the riparian zone of the lower Yellow River, China
Summary
Soil erosion is a global environmental problem that can cause land degradation, decrease productivity, cause ecological deterioration, and may be a threat to the sustainable development of human society [1]. Research has developed from the study of how slope hydraulic parameters change with runoff volume and slope gradient, and the division and attribution of flow regime under variable slope gradients [4,7], to the critical hydraulic conditions of overland flow [7], and the hydraulic process of slope erosion [5,6], gradually changing from empirical analysis to the study of hydrodynamic mechanisms Most of these studies were simulation experiments with a bare slope of uniform soil texture and smooth surface [5,8,9], lacking any consideration of the complex underlying surface conditions that occurs in nature, especially the relationship between vegetation and hydraulic characteristics
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