Preprints
https://doi.org/10.5194/esurf-2023-6
https://doi.org/10.5194/esurf-2023-6
23 Feb 2023
 | 23 Feb 2023
Status: this preprint is currently under review for the journal ESurf.

Confinement width controls the morphology and braiding intensity of submarine braided channels: Insights from physical experiments

Sam Y. J. Huang, Steven Y. J. Lai, Ajay B. Limaye, Brady Z. Foreman, and Chris Paola

Abstract. Submarine channels conveying sediment gravity flows are often topographically confined, but the effects of confinement width on channel morphodynamics is incompletely understood. We use physical experiments and a reduced-complexity model to investigate the effects of confinement width (B) and inflow-to-sediment discharge ratio (Qin/Qs) on the evolution of submarine braided channels. The results show that a larger confinement width results in increased active braiding intensity (BIA), and that BIA takes longer to stabilize (i.e., a longer critical time, tc). At a fixed confinement width, a higher Qin/Qs slightly decreases the BIA. Digital Elevation Models of Difference (DoD) of the experiments allow measurement of the morphological active width (Wa) of the submarine channels and the bulk morphological change (Vbulk) within an experiment, defined as the sum of total erosion and deposition. We find that Wa and Vbulk are proportional to B. We further confirm that BIA is proportional to both dimensionless sediment-stream power (ω**) and dimensionless stream power (ω*). These trends are consistent for submarine braided channels both with and without confinement width effects. Furthermore, we built a reduced-complexity model (RCM) that can simulate flow bifurcation and confluence of submarine braided channels. The simulated flow distribution provides reliable predictions of flow depth and sediment transport rate in the experiments. Using kernel density estimation (KDE) to forecast the probability and trends of cross-sectional flow distribution and corresponding BIA under extreme events, we find that skewness of the flow distribution decreases as discharge increases. The development of braided submarine channels, shown here to extend to conditions of topographic confinement, suggests that factors not modelled here (e.g., fine sediment) may be necessary to explain the abundance of single-thread submarine channels in nature.

Sam Y. J. Huang et al.

Status: open (until 19 Apr 2023)

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Sam Y. J. Huang et al.

Sam Y. J. Huang et al.

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Short summary
We use experiments and a model to study the effects of confinement width and inflow discharge ratio on the evolution of submarine braided channels. We find that confinement width controls most of the morphological changes. These trends are consistent for submarine braided channels both with and without confinement width effects, similarly to fluvial braided rivers. Furthermore, we built a model that can simulate flow bifurcation and confluence of submarine braided channels.