Quantification of the effects on the flow velocity caused by gramineous plants in the loess plateau in North-Western China

Abstract

Accurate prediction of the mean velocity of overland flow is the premise and foundation for establishing a soil erosion model, but it is difficult to accurately estimate the mean flow velocity with the presence of vegetation. To explore the variation law of the mean velocity of overland flow under the influence of gramineous plants typical in the Loess Plateau in North-Western China, indoor scouring tests with ten levels of vegetation coverage (9.42 %–94.25 %), seven unit discharges (0.278–1.667 L·m−1·s−1), and five slope gradients (4°–12°) were performed. The results showed that the mean flow velocity initially increased and then decreased with an increase in vegetation coverage, and the critical cover was affected by the unit discharge. For a slope of 4°, the mean flow velocity with a vegetation coverage of 94.25 % was only 21.6 %–32.0 % of that on a bare slope, indicating that vegetation can effectively reduce flow velocity. For each experiment conducted, with an increase in vegetation coverage, the overland flow gradually moved from laminar flow to transitional flow. Based on the principle of equivalent roughness and Manning's equation, a prediction model was also established in order to predict more accurately the mean velocity associated with overland flow, and it has been validated against the experimental results demonstrating a satisfactory agreement with the measured values (adj.R2 = 0.879, NSE = 0.867). These results provide further insights regarding the influence that the vegetation can have on the flow velocity and contribute to develop a better management of these environmental areas.