The influence of periodic stratification on estuarine sand dunes

Estuarine sand dunes are large scale rhythmic bed patterns and can be seen as features that are in the transition zone between river dunes and marine sand waves. Here, we investigate the effect of time-varying stratification(referred to as Strain-Induced Periodic Stratification, SIPS) on the dynamics and dimensions of these bedforms. To this end, we present a process-based morphodynamic model which describes the motion of water and sediment; time-dependentstratification is implemented through the Munk-Anderson parameterizationfor turbulent eddy viscosity. A linear stability analysis shows that, also with SIPS, sand dunes emerge as free instabilities of the flat bed. Results show that SIPS leads to strain-induced circulation which affects the migration rate and migration direction of bedforms. Furthermore, the preferred bedform length reduces when maximum stratification is increased.