A simple model for vertical profiles of velocity and suspended sediment concentration in straight and curved submarine channels

Abstract

We develop a simple model to describe vertical profiles of velocity and suspended sediment concentration in submarine channels. We consider a conservative turbidity current flowing in a confined channel under steady and uniform flow conditions. The turbulence closure for density stratification is adapted from the model of Mellor and Yamada (1982). Solutions are obtained for both straight and constant curvature channels. In the latter case, in order to evaluate the secondary flow induced by curvature, we take advantage of the fact that the ratio of flow depth to radius of curvature is typically small in the field, which leads to a solution of the governing equations through an appropriate asymptotic expansion.Comparison of results on longitudinal velocity profiles in straight channels with experimental and field observations shows an excellent agreement and allows for the prediction of concentration profiles and suspended sediment size from known bed slope, current thickness, and normalized velocity at the turbidity current-ambient water interface. The model is able to capture the presence of multiple circulation cells on the vertical and the sense of rotation of the near-bottom secondary flow that can be either reversed (directed outward) or normal oriented (directed inward) with respect to the classical fluvial orientation. The parameters controlling the orientation of secondary flow in submarine channels are identified, and the implications on the bed morphology are discussed. The potential use and future developments of the present approach are also discussed.

Turbulent diffusion modelling of sediment in turbidity currents: An experimental validation of the Rouse approach

“…See van Rijn (1993) and Garcia (2008) for reviews of suggested modifications that can increase the accuracy of the classic formulation of the Rouse equation. Moreover, Bolla Pittaluga and Imran (2014) found that modifications to the classic formulation did not significantly impact the results of predicted concentration profiles for turbidity currents. Moreover, Bolla Pittaluga and Imran (2014) found that modifications to the classic formulation did not significantly impact the results of predicted concentration profiles for turbidity currents.…”

Facies architecture of submarine channel deposits on the western Niger Delta slope: Implications for grain‐size and density stratification in turbidity currents

“…The strong relationships between grain size, bed thickness, and height above channel thalweg (HAT) observed in the Y channel (Figures and ) can be interpreted by considering velocity and suspended sediment concentration profiles in turbidity currents. We use an existing in‐channel sedimentation model developed by Bolla Pittaluga and Imran [] that is able to quantify the influence of flow properties on vertical and lateral changes in bed thickness and grain size in submarine channels. The model is a relatively simple formulation that is able to describe vertical profiles of turbidity currents flowing in a confined channel under steady and quasi‐uniform flow conditions.…”

“…Sample results of the numerical model developed by Bolla Pittaluga and Imran []. (a) Flow velocity and sediment concentration vary with increasing height above the thalweg.…”

“…In outcrop exposures, channel margin thin‐bedded facies are usually vertically offset from time‐equivalent thick‐bedded and coarser‐grained channel axis strata [e.g., Chapin and Keller , ; Kane and Hodgson , ; Khan and Arnott , ; Hubbard et al ., ]. This pronounced facies change is the product of the density stratification within the flow (i.e., the upward decrease in sediment concentration and grain size [ Straub and Mohrig , ; Bolla Pittaluga and Imran , ]). A number of studies interpret flow stratification from outcrop data [ Arnott , ; Dykstra and Kneller , ; Hubbard et al ., ; Hansen et al ., ].…”

A general model for the helical structure of geophysical flows in channel bends

“…However, the first physical experiments of helical circulation in turbidity currents showed an opposite direction of rotation -with the near-bed flow moving towards the outer bank (Corney et al, 2006;Keevil et al, 2006). To complicate matters further, both directions of helical circulation (river-like and river-reversed) have subsequently been observed in turbidity current experiments and models, depending on flow conditions and channel morphology (Imran et al, 2007;Islam and Imran, 2008;Cossu and Wells, 2010;Abad et al, 2011;Giorgio Serchi et al, 2011;Huang et al, 2012;Dorrell et al, 2013;Janocko et al, 2013;Bolla Pittaluga and Imran, 2014;Ezz and Imran, 2014).…”