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Characterizing the advection and dispersion of gravel bedload particles in response to fluid flow is a longstanding problem in river hydraulics. At the smallest or "local" scale, bed sediment movement is characterized by a series of individual hops and rests referred to as the transport step length and waiting time (Hassan & Bradley, 2017;Nikora et al., 2002). At a larger or "global" scale, the cumulative motion over floods, seasons, or years can be measured to obtain an overall "travel distance" ( 𝐴𝐴 𝐴𝐴 ; Hassan & Bradley, 2017;Nikora et al., 2002). Advances in bedload tracers have allowed us perhaps the best opportunity to observe the kinematics and untangle the controls of gravel transport (Hassan & Roy, 2016). Active tracers have internal batteries used to power accelerometers, recorders, or transmitters, that can be used to characterize motion on the local scale (Cassel

The distribution of aquatic vegetation within conveyance channels plays a key role in the determination of their hydraulic characteristics, especially where the vegetation is patchy, as is commonly found in nature. This paper reports the results of a laboratory flume study on flow and turbulence conditions caused by patches of the emergent rush Lepironia articulata. Acoustic Doppler velocimeter measurements were taken within and downstream of singleand multiple-patch configurations of this plant, and the effects of varying incident flow rate (0 . 16-0 . 32 m/s) and stem-scale porosity (12-4% solid volume fraction) were investigated. The results showed that flow encountering a single patch formed a turbulent wake downstream of the vegetation. Within this wake, the Reynolds stress increased downstream initially, and then decayed. When a second patch was positioned within the region of maximum Reynolds stress, the Reynolds stress decreased by between 25 and 50%. The amount of this reduction was dependent on the porosity of the vegetation and the flow rate, and was greater at lower flow rates and porosities. These changes in turbulent flow fields around patches of emergent vegetation are likely to be important in determining sediment budgets in their vicinity.

Vegetation porosity in a vegetated channel has been identified as the main parameter that contributes to the flow behaviour and resistance in the channel. Estimation of vegetation porosity is quite a challenging task due to the diverse characteristics of vegetation. In this study, several porosity measurement methods based on vegetation frontal area and vegetation volume were used to estimate the porosity of vegetation (Lepironia articulata) in a laboratory flume for various flow and vegetation characteristics. Digital image analysis was one of the methods used to estimate porosity. The study also involved measurements of velocity using a three-dimensional acoustic Doppler velocimeter and flow depths at different spatial locations along the flume. The volumetric method for porosity measurement, which considers the fraction of the actual volume of the vegetation to the volume of water, is considered more practical and accurate than the other methods that were studied. The results of this study indicate that, by assuming vegetation to be cylindrical in shape and considering only the frontal area of the most upstream vegetation, porosity could be underestimated by 14%. Digital image analysis gave a difference of only 5%. From the laboratory data, correlations between the mean velocity, water depth and vegetation porosity were established. It was observed that by reducing the vegetation porosity by 8%, the velocity could reduce by between 35-60% depending on flow rate.