Sorting in grain flows at the lee side of dunes

Abstract

Sediment sorting at the lee side of ripples, dunes and bars has already been recognized long ago. A predictive model of the sorting is necessary but unavailable for implementation in sediment transport models for sediment mixtures. Relevant processes in sedimentological and physical literature are reviewed and compared to the sparse data of sediment sorting. A synthesis is given of the most important variables governing the sorting processes for the benefit of future experimentation and modelling. These variables are the sorting (standard deviation, skewness and bimodality) of the sediment mixture delivered to the brink point, the height of the dune or bar relative to the average grain size of the mixture, the velocity of the flow above the brink point relative to the settling velocity for all grain size fractions, and the frequency of the grain flows. In addition, the initiation mechanism and frequency of the grain flows affect the pattern and effectiveness of sorting. D

River bedform inception by flow unsteadiness: A modal and nonmodal analysis

“…Research interest about these morphologies derives from their relevance in hydraulic engineering and environmental applications. River bedforms not only interfere with river navigation [1,2] and human infrastructure [3,4], they also induce differential pressure gradients that modify the flow field and consequently the overall hydraulic resistance, induce hyporheic fluxes [5,6], and affect underground flows through preferential patterns within ancient sedimentary deposits [7,8]. The present work focuses on dunes and antidunes (see Fig.…”

Autogenic cyclicity of foreset sorting in experimental Gilbert-type deltas

“…During the grain flow, kinematic sorting takes place which moves the large grains to the top of the grain flow. Meanwhile, the large grains easily move over the small grains and deposit downslope, whereas the small grains are deposited further up the slope (Kleinhans, 2004(Kleinhans, , 2005; and references therein).…”

米粒子を用いた実験マイクロデルタ堆積物中にみられる堆積過程を反映した二種類の3次元粒子配列

“…The term grain flow refers to discontinuous mass flow (avalanche) of grains on the lee slope, and it has been the focus of a number of studies (e.g., Allen, 1970;Hunter, 1985;Dingler and Anima, 1989;Ikehara, 1990). As the amount of suspended load increases, the volume of sediments that settles on the entire surface of the lee slope increases; hence, the grain-fall deposits are more likely to be preserved, rather than being relocated by subsequent grainflow events (Jopling, 1965;Hunter, 1985;Kleinhans, 2004). Some experiments have been conducted to study the relationship between the ratio of grain fall to grain flow and either the shape of laminae (Jopling, 1965) or vertical grain-size sorting (e.g., Kleinhans, 2004Kleinhans, , 2005a.…”

“…As the amount of suspended load increases, the volume of sediments that settles on the entire surface of the lee slope increases; hence, the grain-fall deposits are more likely to be preserved, rather than being relocated by subsequent grainflow events (Jopling, 1965;Hunter, 1985;Kleinhans, 2004). Some experiments have been conducted to study the relationship between the ratio of grain fall to grain flow and either the shape of laminae (Jopling, 1965) or vertical grain-size sorting (e.g., Kleinhans, 2004Kleinhans, , 2005a. To facilitate the interpretation of ancient depositional processes and environments from sedimentary records, further information on the abovementioned relationships is required, and analysis of three-dimensional grain fabrics may be useful.…”