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Quantifying the effects of grass distribution patterns on the relative hydrodynamic parameters of overland flow

Grass distribution pattern (GDP) plays a crucial role in soil erosion, which is driven by overland flow on hillslopes caused by rainfall. To quantify the effects of GDPs on the hydrodynamic characteristics of overland flow, indoor scouring experiments were conducted in a hydraulic flume across eight flow discharges (3–45 L min−1), six slope gradients (2–12°), and five GDPs—a vertical strip pattern parallel to the slope direction (VP), chequerboard pattern (CP), small patches distributed in an ‘X’‐shape (XP), a banded pattern perpendicular to slope direction (BP), and a random pattern (RP). The results showed that GDP had a significant effect on the hydrodynamic parameters of overland flow when compared with bare slope (BS). For the five GDPs, the relative water depth, relative flow velocity, relative Froude number, and relative resistance coefficient were positively affected by flow discharge (p < 0.001), and negatively affected by slope gradient (p < 0.001); whereas the effects on the relative Reynolds number were inverted. Compared with the other patterns, the effects of BP on retarding flow was the best, as it maintained particularly remarkable characteristics affecting all five relative hydrodynamic parameters. Through parameterising GDP as a calculation factor, the prediction models of relative flow velocity (adj.R2 = 0.788**, Nash–Sutcliffe efficiency [NSE] = 0.692), and relative Froude number (adj.R2 = 0.756*, NSE = 0.674) were established via nonlinear regression analysis. The effects of GDP on overland flow revealed here can help inform optimal GDP designs for water and soil conservation on sloped environments.