Overland Flow Resistance Law under Sparse Stem Vegetation Coverage

Abstract

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.

Near surface roughness estimation: A parameterization derived from artificial rainfall experiments and two-dimensional hydrodynamic modelling for multiple vegetation coverages

“…Vegetation coverage has the most significant effect on near surface runoff processes and surface resistance. Studies differentiate by vegetation type, flexibility, degree of submergence (Cantisani et al, 2014) or vegetation stem diameter (Zhang et al, 2021). A distinction is also often made between submerged and partially submerged vegetation (Kim et al, 2012;Wu et al, 1999).…”

Study on the resistance characteristics of layered vegetation to overland flow

“…The presence of vegetation interferes with the flow of overland flow and makes the flow pattern of overland flow extremely complex. According to the standard, overland flow can be divided into slow laminar flow, slow transitional flow, slow turbulent flow, fast laminar flow, fast transitional flow, and fast turbulent flow (Zhang et al, 2014). When the average water depth h and average velocity V are plotted in logarithmic coordinates, two parallel lines with Re and Fr as constants are obtained.…”

Influence of vegetation lodging on the flow regime and resistance characteristic of overland flow

“…By approximating $$$ \nu $$$ = 1 × 10 −6 m 2 /s and by plotting h and the average logarithmic V in logarithmic coordinates, we obtained two parallel lines with Re and Fr as constants. The values Re = 580, Re = 6500, and Fr = 1 were used as the boundaries, and the six‐zone flow regime was determined (Xu et al, 2017; Zhang et al, 2014).…”