A calculation model of the mean flow velocity of overland flow considering a variety of grass covers and raindrop’s characteristics

The effect of vegetation distribution patterns, coverage, and raindrop impact on the overland flow velocity is highly intricate. To quantify these effects, a rigorous experimental campaign was conducted involving five rainfall intensities (ranging between 60 and 120 mm h−1), six vegetation patterns (diamond pattern - DP, random pattern - RP, checkerboard pattern - CP, vertical strip pattern aligned with the slope direction - VP, step strip pattern - SP, banded pattern perpendicular to the slope direction - BP), five vegetation coverage (ranging between 30% and 70%) and three slope gradients (ranging between 8.72% and 25.88%). The results obtained show that the BP configuration has the best flow velocity reduction effect, which can lessen the flow velocity by 58.68% - 69.27% compared with the bare slope, while the change for VP is only 4.80% - 6.30%. This indicates that BP yields significant soil and water conservation benefits. Furthermore, when the vegetation coverage is 30%, a concentrated flow formed between the vegetation patches under the RP and CP configurations, resulting in a higher overland flow velocity greater than the one recorded for the bare slope, which is unfavorable for soil and water conservation and should be avoided. Finally, a model was established to predict flow velocity and it was built by combining the equations of momentum and mechanical balance. After having calibrated the model and assessed its performance against research data available in literature, it was possible to confirm its reliability and consistency. These findings provide scientific guidance for assessing the soil and water conservation effectiveness of different vegetation patterns.