Effects of patchy distributed Artemisia capillaris on overland flow hydrodynamic characteristics

Laboratory-simulated rainfall experiments were conducted to quantify the effects of patchy distributed Artemisia capillaris on overland flow hydrodynamics. Rainfall intensities of 60, 90, 120, and 150 mm h–1 were applied on a bare plot (CK) and four different patched patterns: a checkerboard pattern (CP), a banded pattern perpendicular to slope direction (BP), a single long strip parallel to slope direction (LP), and a pattern with small patches distributed like the letter ‘X’ (XP). Each patterned plot underwent two sets of experiments, intact plant and root (the above-ground parts were removed), respectively. Results showed that flow velocity increased with rainfall intensity, and the lower slope velocity was higher than the upper slope. The removal of grass shoots significantly increased flow velocity. The contributions of grass shoots and roots to the reductions in flow velocity under different rainfall intensities were different. The shoots made greater contribution of 53–97% at 60 and 90 mm h–1, and the roots contributed more (51–81%) at 120 and 150 mm h–1. Mean flow depth increased with rainfall intensity and it declined after the aboveground parts were cleared. Reynold numbers (Re) in this study were 25–80, indicating a laminar flow in the study. Froude numbers (Fr) were ≥ 1 for CK and < 1 for patterned treatments. Fr of the lower slope was higher than the upper ones. Darcy-weisbach (f) and Manning (n) friction coefficient ranked in the order of CK<LP