Experimental river delta size set by multiple floods and backwater hydrodynamics

Area of Science:

• Geomorphology
• Sedimentology
• Fluid Dynamics

Background:

• River deltas globally are threatened by sea-level rise, subsidence, and storms, necessitating quantification of their growth.
• Delta formation involves sediment lobe construction, with theories linking lobe size to backwater hydrodynamics, though testing is difficult on slow-evolving natural deltas.

Purpose of the Study:

• To investigate the physical mechanisms controlling delta lobe size through laboratory experiments.
• To test the hypothesis that delta lobe size is determined by hydrodynamic processes within the river system.

Main Methods:

• Constructed the first laboratory delta with successive, constant-sized sediment lobe deposition.
• Analyzed flow dynamics, including flood events and Froude number, to identify factors influencing deposition patterns.
• Monitored the location and stability of river avulsion nodes relative to the shoreline.

Main Results:

• Demonstrated that characteristic delta lobe sizes emerge due to a spatially fixed avulsion node.
• Identified multiple river floods and Froude-subcritical flows as key drivers of persistent nonuniform flow and deposition peaks in the backwater zone.
• Contrasted this with experiments lacking multiple floods, which produced uniform flows and delta lobes of variable size.

Conclusions:

• The spatial stability of the avulsion node, driven by specific flood dynamics, dictates delta lobe size.
• Findings offer insights for sustainable delta management and interpreting deltaic deposits on Earth and Mars.