Prediction of near-field shear dispersion in an emergent canopy with heterogeneous morphology

1 The evaluation of longitudinal dispersion in aquatic canopies is necessary to predict the behavior 2 of dissolved species and suspended particles in marsh and wetland systems. Here we consider the 3 influence of canopy morphology on longitudinal dispersion, focusing on transport before 4 constituents have mixed over depth. Velocity and longitudinal dispersion were measured in a 5 model canopy with vertically varying canopy density. The vertical variation in canopy 6 morphology generates vertical variation in the mean velocity profile, which in turn creates 7 mean-shear dispersion. We develop and verify a model that predicts the mean-shear dispersion in 8 the near field from morphological characteristics of the canopy, such as stem diameter and frontal 9 area. Close to the source, longitudinal dispersion is dominated by velocity heterogeneity at the 10 scale of individual stems. However, within a distance of approximately 1 m, the shear dispersion 11 associated with velocity heterogeneity over depth increases and eclipses this smaller-scale 12 process. 13 14