The presence of aquatic vegetation in streams becomes an important factor when dealing with water quality assessment, river and wetland restoration, management of fisheries and recreational areas and other environment related issues, yet its effects on flow structure and mass transport are not fully understood. Aquatic vegetation plays an important role in several hydrodynamic processes, regulating the fate and transport of sediments and nutrients, and is a key factor for the foraging and mating habits of many living organisms in rivers, lakes and wetlands.

Several studies have been carried out on flows through aquatic vegetation, primarily focused on characterizing the velocity field and characteristic drag, as well as the transport and dispersion of passive scalars. Most of the previous laboratory studies use different approaches to mimic vegetation, from arrays of rigid cylinders to scaled plastic models of selected species. Such experiments provide a good understanding of the underlying physical processes within the plant canopy and have been a benchmark for numerical models.

To gain a better understanding of the processes involved, a series of experiments was conducted using live, highly flexible, emergent plants in a laboratory flume under low speed flow conditions, typical of lakes and quiescent rivers. Since plant morphology and vegetation density have proven to be determinant factors on flow structure, one of the most common aquatic invasive species in North America is chosen as the primary experimental species to simulate a relevant and common condition in nature. Morphology effects are included by means of an optically obtained detailed description of the frontal area (a [m^{-1}]) and volume fraction (\phi [ ]) as functions of flow depth.

Particle image velocimetry (PIV) was used to capture the detailed turbulent velocity field within a one-dimensional plant canopy, as well as just up- and downstream of the patch. This technique yields detailed insight into both the temporal and spatial variations over the areas studied.

The experimental results are discussed and comparisons made with predictions based on existing models. Based on those results, a simple model able to predict the velocity field within the plant canopy is developed, by making assumptions that are verified through the experimental data. Particular attention is paid to the near bottom boundary effects and Reynolds number (Re) dependence of the drag due to the vegetation, in an attempt to estimate the distinct vegetation density ranges where their contributions must be considered to increase the model's accuracy.