Density stratification controls the bedform phase diagram of saline‐gravity currents versus open‐channel flows

Abstract

ABSTRACTSedimentary bedforms such as ripples and dunes are generated both by river flows and sediment‐laden gravity currents. Gravity current deposits are usually parameterized using existing bedform phase diagrams which are based on data from laboratory experiments and field observations of open‐channel flows. Yet, it is not evident that open‐channel flow bedform phase diagrams are applicable to gravity current deposits. Gravity current hydrodynamics are dependent on vertical density variation, that is density stratification, and therefore are fundamentally different from open‐channel flows. New experiments to produce gravity current deposits are conducted and compared to existing open‐channel flow data. It is shown that a parameter phase‐space based on the lower layer of stratified gravity currents (i.e. that part below the velocity maximum) significantly improves the prediction of bedform type compared to bedform phase diagrams derived from layer‐averaged parameters. These results confirm that bedforms produced by gravity currents can only be predicted accurately using the characteristics of the lower layer of stratified flow.