Vegetation behavior in riparian environment represent an important research topic in hydraulics and
ecohydraulics. Therefore, one of the most important research challenge is to deepen interactions between
flow and vegetation, in order to better understand its effects on flow resistance and turbulent characteristics of
the flow. In vegetated flow models, the flow regime is often separated in two layers: vegetated layer and
surface layer. Flow resistance models, based on two-layer approach, are often tested with experimental data
relative to vegetation density and submergence ratio ((i.e., the ratio between h=flow depth and hv=vegetation
height, h/hv) varying in wide ranges. The aim of the paper is to deepen how variability of submergence ratio
and the non-dimensional vegetation density can affect the reliability of the flow resistance models. In
particular, in this paper, the results of the statistical test applied to the most cited and used literature models
for evaluating the flow resistance of rigid vegetation, are shown. The test have been carried out with
experimental data from literature, by the mean of different statistical parameters, considering the different
ranges of vegetation density and submergence ratio. The results shows that vegetation density and
submergence ratio can affect the reliability of the model
