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This is the peer reviewed version of the following article: [Hassan, M. A., Chartrand, S. M., Radić, V., Ferrer-Boix, C., Buckrell, E., & McDowell, C. (2022). Experiments on the sediment transport along pool-riffle unit. Water Resources Research, 58, e2022WR032796. https://doi.org/10.1029/2022WR032796], which has been published in final form at https://doi.org/10.1029/2022WR032796. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. This study examines channel dynamics and mixed-load bed load transport through a riffle and pool sequence forced by downstream channel width variations within an experimental flume. The experiment consisted of four runs across which we compare and contrast local and spatially-averaged bed surface texture and topography, sediment transport rates and sediment mobility at five locations across a pool-riffle pair. Sediment transport was measured using mini Helley-Smith (HS) samplers and particle tracers seeded in the monitored riffle and pool. In this study, “local” sediment transport rates were highly variable across the five monitoring locations. The lowest sediment transport rate was recorded at the riffle tail whereas the highest rates were measured at the riffle head and the pool centre. The texture of the bed surface and transported load do not explain measured bedload transport trends and depending on how the measurements are aggregated differing interpretations are supported. In general, the bed texture in the pool was finer than the texture in the riffle, however specific grain-size percentile classes derived from pooled population analysis suggests little to no difference between pool and riffle texture. The combined results highlight the importance of acknowledging and applying analysis techniques to better understand the inherent variability of bedload transport within channel reaches where morphology differs, such as pools and riffles.

Dam removal is commonly used for river restoration. However, there are still some uncertainties associated with dam removal, mainly related to the sediment transport rates released downstream from the deposit that had previously filled the impoundment. This research studies the physical response to dam removal in the antecedent deposit by answering the following questions: (a) how does an initial channel excavated into the deposit evolve, and (b) what is the time distribution of the material released during the early stages of the process. These goals are achieved by an experimental campaign using a poorly sorted mixture of sediment in the antecedent deposit. The research shows that for the given conditions of our experiments, the rate at which the sediment is released depends on the height of the removed dam, the water discharge and the maximum potential volume of sediment to be eroded. This investigation provides new insights of the width evolution when the sediment is composed of a poorly sorted mixture. This evolution is linked to the bed degradation rates: channel narrows during a rapid incisional phase, and subsequently widens when bed degradation rates decrease. Channel width changes propagate upstream as a convection-like perturbation associated with a kinematic wave starting at the location of the antecedent dam. These features are modeled through a new numerical model accounting for mixtures. More specifically, a set of equations has been derived for the variation of bed elevation, channel bottom width, and bed grain-size distribution, which when solved numerically, describe the observed channel processes.