Emergent vegetation covering floodplains and wetlands has an important role in fluvial ecosystems. Since natural systems are not homogeneous, the flow within the stem array is influenced by several space scales, determined by the number-density of stems and its spatial modulation. The aim of this study is to characterize experimentally the spatial variation of the flow at the smallest spatial scales over a wavelength of the largest scale. To meet the proposed objectives, an experimental test was carried out where two stem’s densities were alternated with a fixed period, allowing the interaction of three different wavelengths: two different inter-stem spaces and the characteristic length between the two densities. The measurements of velocity fields were made using Particle Image Velocimetry (PIV). The data treatment was done with the Double Averaged methodology (DAM) to account for the great spatial variability of the flow.