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[1] Antidunes are bed forms characteristic of upper regime unidirectional flows. Contrary to bed forms developed in lower regime flows, antidunes not only can propagate in the downstream direction but can propagate upstream or remain stationary. In this work we analyze the stable hydraulic conditions that determine each of the three antidune movement possibilities, and a new theory is developed for distinguishing the occurrence of each of these conditions. The theory is developed from an energy balance over a symmetrical antidune; for this, the Bernoulli equation is applied between the antidune crest and antidune trough, and the pressure head is corrected to account for the centrifugal forces generated by curvilinear flow. Manipulation of the fundamental equations produces an antidune mobility dimensionless number (F a ), dependent on the Froude number, the mean water depth, and the antidune wavelength. The critical value of the antidune mobility number (F a = 1) corresponds to the stationary condition, while values higher and lower than the critical correspond to downstream and upstream propagation, respectively. Theory predicts that for a given Froude number, downstream-migrating antidunes are formed for higher water depth-wavelength ratios than for upstream-migrating antidunes. Likewise, by introducing a restriction for the maximum stationary wave height above antidunes, theory predicts that downstream-migrating antidunes could attain steeper height-wavelength ratios than upstream-migrating antidunes. Comparison with published experimental data in literature largely showed agreement between theory and experimental observations.

This is the accepted version of the following article: [Núñez-González, F., Martín-Vide, J. P., Kleinhans, M. G. (2016), Porosity and size gradation of saturated gravel with percolated fines. Sedimentology, 63: 1209–1232. doi: 10.1111/sed.12257], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/sed.12257/abstractFine particles may infiltrate through coarse alluvial beds and eventually saturate the subsurface pore space. It is essential to understand the conditions that lead to bed saturation, and to forecast the packing characteristics of saturated beds to assess the effect of excess fine sediment supply on a number of processes that occur in the stream-sediment boundary. To address this problem, in this study, a new method is introduced to predict the grain-size distribution for the saturated condition, and the resulting porosity decrease, given the characteristics of the bed and the supplied sediments. The new method consists of the numerical aggregation of infilling fines in a finite bed volume, during which the bed properties change to affect further infilling. An existing semi-empirical, particle packing model is implemented to identify these properties. It is shown that these types of models are adequate to describe regimes of natural sediment fabric quantitatively, and are thus useful tools in the analysis of sediment infiltration processes. Unlike previous developments to quantify saturated bed conditions, which assume that the supplied material is uniform and finer than the bed pore openings, the method developed herein considers poorly sorted fines, and can identify size fractions that are able to ingress into the bed due to being smaller than the particles that form the bed structure. Application of the new method to published experimental data showed that the final content of infiltrated fines is strongly sensitive to the initial bed packing density, highlighting the need to measure and understand open-work gravel deposits. In addition, the new method was shown to be suitable for assessing the degree of bed saturation, when it was applied to a published data set of field samples.Peer ReviewedPostprint (author's final draft

Natural levees can be observed worldwide in nearly all river systems characterized by frequent flooding in combination with the transport of suspended bed material. Several parameters and processes have been suggested to explain the formation and the highly variable geometry of natural levees. However, the effect of bedforms migrating in the main-channel has not been amongst the studied parameters and processes. To fill this gap, this study investigates the relationship between bedforms and natural levee formation by flume experiments. Experiments were conducted in a 2 m wide and 30 m long sediment recirculating flume, monitoring the bed level elevation in the main channel by ultrasonic sensors as well as recording the levee development on the floodplain by a camera. The effect of different bed configurations on the developed levees is compared, and discussed, showing that bedforms could enhance levee formation.

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