To explore the characteristics of overland flow resistance under the condition of sparse vegetative stem coverage and improve the basic theoretical research of overland flow, the resistance characteristics of overland flow were systematically investigated under four slope gradients (S), seven flow discharges (Q), and six degrees of vegetation coverage (Cr). The results show that the Manning roughness coefficient (n) changes with the ratio of water depth to vegetation height (h/hv) while the Reynolds number (Re), Froude number (Fr), and slope (S) are closely related to vegetation coverage. Meanwhile, h/hv, Re, and Cr have strong positive correlations with n, while Fr and S have strong negative correlations with n. Through data regression analysis, a power function relationship between n and hydraulic parameters was observed and sensitivity analysis was performed. It was concluded that the relationship between n and h/hv, Re, Cr, Q, and S shows the same law; in particular, for sparse stem vegetation coverage, Cr is the dominant factor affecting overland flow resistance under zero slope condition, while Cr is no longer the first dominant factor affecting overland flow resistance under non-zero slope condition. In the relationship between n and Fr, Cr has the least effect on overland flow resistance. This indicates that when Manning roughness coefficient is correlated with different hydraulic parameters, the same vegetation coverage has different effects on overland flow resistance. Therefore, it is necessary to study overland flow resistance under the condition of sparse stalk vegetation coverage.

The commercial CFD package Fluent and the Reynolds stress model were used to simulate the hydraulic characteristics with three types of vegetation distribution: longitudinal, interlaced and patch. Each type was aggregated to the middle line l of the water flow in an equal proportion of 0.5, resulting in a total of nine landscape vegetation arrangements. The numerical model was verified and showed a high level of consistency with the experimental comparison; the results indicate the following: (1) As the distribution of landscape vegetation on both sides becomes increasingly concentrated from a loose state to the middle line l of the flow, the flow velocity declines and the maximum Reynolds stress rises, and the greater the Reynolds stress, the more powerful the shear layer, contributing to turbulence, generating mass and momentum exchange and enhancing the vertical transport of momentum. (2) Compared with the gap area, the flow velocity in the vegetation area is smaller, the turbulent kinetic energy is larger and the maximum Reynolds stress of the bottom flow is larger; the larger sediment particles tend to deposit in the gap area, while smaller sediments tend to deposit in the vegetation area. At the same time, the vegetation area is more prone to deposits than the gap area. (3) Under the same vegetation density, whether in the test area or the wake area, the water blocking capacity and the deposition capacity are in the following order: patch distribution pattern > interlaced distribution pattern > longitudinal distribution pattern.