Submarine braided channels in response to channel confinement shapes and inflow-to-sediment discharge ratios: Insights from physical experiments

Submarine braided channels, driven by turbidity currents, have been revealed on several deep-sea fans, displaying similar morphological features to fluvial braided rivers. Past experimental studies on submarine braided channels have shown that active braiding intensity (BI_A) is proportional to fixed confinement width, dimensionless stream power (ω^*) and dimensionless sediment-stream power (ω^**). However, the field-scale submarine braided channels may not restrict to a fixed confinement width (B); instead, the confinement shape often exhibits gradual widening or narrowing. In this study, we use physical experiments to investigate the influence of confinement shapes and inflow-to-sediment discharge ratios (Q_in/Q_s) on the evolution of submarine braided channels. In the experiments, three confinement shapes were simulated: diamond, hourglass, and reversed trapezoid. The experimental results show that the BI_A is strongly proportional to the varying confinement width, i.e., increasing confinement width facilitates the degree of braiding; decreasing confinement width suppresses the degree of braiding. The measured BI_A is proportional to both the ω^* and ω^**. Additionally, increasing Q_in/Q_s causes a slightly decrease of BI_A. The measured active width (W_a) is proportional to the bulk change (V_bulk). These relations all agree with the published trends of both fluvial and submarine braided channels. For the geometric properties of sandbars, the measured sandbar aspect ratio and sandbar compactness ratio remain constant regardless the change of confinement shape or Q_in/Q_s. Finally, the experimental results may aid our understanding to the morphological evolution of submarine braided channels and provide insights to the stacking patterns of hydrocarbon reservoirs.

 

Keywords: submarine braided channels, turbidity current, physical experiment, confinement shape, active braiding intensity