Numerical Modelling of Bed A5 flow, Agadir basin, Offshore Morocco, NW Africa.

Lucky Imagbe, David Waltham

Research output: Contribution to journalArticle


Sediment grains entrainment and suspension in low-concentration flows is generally assumed to be controlled by the magnitude of the basal shear stress and the resulting flow velocity fluctuations. However, recently published work from the Agadir Basin, offshore Morocco, demonstrates that sand-sized sediment grains of ca 300 m were transported across hundreds of kilometres by a flow that is less than 10 m thick leading to the deposition of Bed A5. This led to the suggestion that turbulence may not solely account for supressing the grains early settling in the flow’s long run-out.
This paper applies a widely-used, simple, numerical turbulence model to investigate if sediment grains of this size can plausibly be suspended in Bed A5 flow of this thickness by turbulence alone.
Analytical results, however show that the reported field observations and inferences of this long run-out thin Bed A5 flow transporting sand-sized sediments into the Agadir basin could not be replicated by a numerical flow model that is based solely on the turbulence-suspension theory. Instead, the flow model demonstrated that relatively thicker mud-rich turbidity current flows can achieve long distance transport of sand in Agadir basin.
Therefore, it is suggested that turbulence and other sediment grain support mechanisms such as hindered settling and grain-grain collisions not incorporated in the flow model may have significantly contributed to the long-distance transport of sand grains by the thin turbidity current flows across the Agadir basin.
Finally, the paper demonstrates that the applied turbulence-suspension model is consistent with the observed grain-size variations across the Agadir basin. Hence, the assumption that grains in a low concentration turbidity current are suspended purely by turbulence, does not require modification at present.
Original languageEnglish
Pages (from-to)1-21
Number of pages21
JournalJournal of African Earth Sciences
Publication statusIn preparation - 12 Aug 2018

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