Sediment eddy diffusivity in meandering turbulent jets: Implications for levee formation at river mouths

Abstract

[1] Depositional patterns characteristic of river mouths are controlled by the sediment-laden turbulent jet exiting from rivers. Here we show that jet instability, developing at river mouths with small width-to-depth ratio, can affect these patterns. Numerical simulations indicate that sediment eddy diffusivity, which is a measure of the spreading of sediments out of the jet core, depends on the interplay between sediment settling and large coherent flow structures, which are associated with unstable jets. Our results suggest that optimal conditions for eddy diffusivity are met when the time scale of sediment settling is equal to the characteristic eddy time scale. In this condition, sediments are deposited at the farthest distance from the jet centerline, thus promoting the formation of lateral deposits. Settling time scales much greater or much smaller than the eddy time scale is associated with low eddy diffusivity, which promotes the formation of a central deposit. Such eddy-mediated sediment transport is more evident in the Zone Of Established Flow than in the Zone Of Flow Establishment, since the former is characterized by fully developed vortices. A simplified model is proposed to estimate the settling and eddy time scales and to predict the optimal condition for levee formation.

A reduced-complexity model for river delta formation – Part 2: Assessment of the flow routing scheme

“…Interestingly, this process not only produces bifurcations, but also trifurcations. Accordingly, DeltaRCM suggests that distributary channel networks are not necessarily solely built by mouth-bar-induced flow bifurcation (Edmonds and Slingerland, 2007;Mariotti et al, 2013).…”

Sediment transport and topographic evolution of a coupled river and river plume system: An experimental and numerical study

“…River plumes interact with evolving bed topography, which in cases can lead to the formation of levees and mouth bars [e.g., Edmonds and Slingerland , ; Rowland et al ., ; Edmonds et al ., ; Edmonds and Slingerland , ; Rowland et al ., ; Mariotti et al ., ; Canestrelli et al ., ; Falcini et al ., ], yet the process of plume self‐channelization is not well understood. Most previous experimental work on sediment‐laden plumes and deltas has emphasized the role of aggradational levees in confining river plumes.…”

Three-dimensional numerical modelling of flow field in shallow reservoirs

“…Similar results were obtained by Adamson et al (2003) and Stovin and Saul (1996) regarding storage chambers and storage tank sedimentation, respectively. Kolyshkin and Ghidaoui (2003) came to a similar conclusion about the development of an asymmetric flow pattern in the wake flows, and Mariotti et al (2013) also presented the analysis of flow instabilities in the river mouth zone with a small width-to-depth ratio. Recently, Peltier et al (2014a) presented a review of the experiments regarding shallow reservoirs, and suggested the domains for existence of varying flow patterns, including meandering flows, in shallow reservoirs (Peltier et al, 2014b).…”