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A specific energy diagram for antidunes
Published in Wim Uijttewaal, Mário J. Franca, Daniel Valero, Victor Chavarrias, Clàudia Ylla Arbós, Ralph Schielen, Alessandra Crosato, River Flow 2020, 2020
F. Núñez-González, J.P. Martín-Vide, N.R.B. Olsen
Among upper regime bedforms, antidunes are often cause of misinterpretation, confusion and an apparent lack of consensus among scientific disciplines. They are normally defined as symmetrical bedforms, that occur in supercritical flows, migrate upstream, and are characterized by a cyclic behaviour as they grow, destroy, give place to a plane bed and then reform again (e.g., DWA, 2015; Bridge & Demicco, 2008). Nevertheless, if the most widely accepted definition for antidunes is considered, none of these attributes is strictly required for classifying bedforms as antidunes. According to this definition, antidunes are sediment waves in-phase with the water surface, so that above the crest of an antidune there is a bump of the free surface, and above the trough of an antidune occurs a slump on the water surface.
Numerical modeling of antidune formation and propagation
Published in Silke Wieprecht, Stefan Haun, Karolin Weber, Markus Noack, Kristina Terheiden, River Sedimentation, 2016
The formation of antidunes is an interesting hydraulic phenomenon that has been studied for many years by engineers, geographers, geomporphologists and geologists. Antidunes are bed and water surface waves in rivers which are stationary or move slowly upstream or downstream. Contrary to ordinary dunes, the antidunes are charachterized with the surface and bed elevation profile being in-phase. Thi highest water levels are then located at the top of the antidunes, or the antidune crest. The lowest water level is located above the trough, where the bed level is lowest.
Hydraulic model of a braided channel to aid design of a grade-building structure
Published in Journal of Applied Water Engineering and Research, 2023
Robert Ettema, Christopher I. Thornton
The sub-channel dimensions of interest for model design were those characterizing the braided channel’s main sub-channels through the GBS site. But only a modicum of quantitative information existed regarding sub-channels’ dimensions. Therefore, a simplified set of characteristic dimensions for the main sub-channels in the network of sub-channels was established using two information sources: 2012 and 2013 Light Detection and Ranging (LiDAR) data, reported in CENWP (2013). LIDAR data indicated the reach to have a slope of about 0.003. The sub-channels were estimated to be about 22–61 m wide and about 1–1.3 m deep. Exact interpretation of the data was complicated because the cross-sections determined were not always orthogonal to the streamwise axis of sub-channels. Moreover, most sub-channels had bedforms (notably dunes and antidunes) and were non-uniformly wide and deep. CENWP (2013) also provided photographs showing conditions during a peak discharge of 170 m3/s; an estimate of flow depth an antidune height and wavelength indicated that flow depth, Y, was 0.6–0.8 m and flow velocity, U, was 2.4–2.8 m/s (ASCE 2008). The prototype flow rates of interest for modelling range from around 43 to 283 m3/s, with a focus being on the channel-forming flow of about 170 m3/s, about the 50% exceedance probability for flows at the project site. Accordingly, the model was used to determine a relationship between the water discharge of 170 m3/s and commensurate rate of bed-sediment transport. The presence of woody debris on exposed bars suggested that flow would have been 0.3–0.6 m deeper when the discharge peaked around 200 m3/s.