The role of near‐surface vegetation in modulating overland flow resistance in grasslands of the Chinese Loess Plateau

Vegetation restoration significantly increases overland flow resistance and decreases soil erosion. The cause of soil erosion is unknown, though grain resistance and form resistance are frequently confused with the overall overland flow resistance. The zonal specie of Bothriochloa ischcemum (Linn.). Keng (BI) and the dominant specie of Artemisia vestita Wall. ex Bess (AG) were selected to investigate the effect of vegetation near soil surface characteristics derived by vegetation restoration on overland flow resistance of grain resistance and form resistance. In total, 24 steel tanks were planted at six planting densities of 5, 10, 15, 20, 25, and 30 plants m −2 , and two tanks were used as bare soil controls. Their hydraulic characteristics were tested under a constant rainfall intensity (60 mm h −1 ) on a 26.2% slope. The results showed that the grain resistance ( f g ) and form resistance ( f f ) ranged from 0.06 to 0.35 and 18.01 to 95.77 under six planting densities. Vegetation increased overland flow resistance by more than 90%, which was mainly attributed to f f . Vegetation near soil surface factors of the aboveground part, biological soil crusts, and root collar increased f f by 18.71 to 82.13, 0.74 to 11.50, and 1.61 to 3.40, respectively. Compared with BI, the mean value of f g in AG was 48.87% lower, whereas the mean value of f f was 1.36 times greater. The f g decreased with soil organic matter as a power function. The f f decreased with the Reynolds number, Froude number, and flow velocity and increased with vegetation coverage, aboveground biomass, and root collar area as power functions. Soil properties explained the majority of the variation in f g , and near the vegetation soil surface factors explained the majority of the variation in f f . Finally, f f was simulated using the Reynolds number, vegetation coverage, and root collar area. In addition, a simulation equation for the total flow resistance was established by distinguishing the grain resistance and the form resistance, and the performance of the model developed in this study was satisfactory (NSE = 0.97).