Using a Holistic Modeling Approach to Simulate Mud‐Induced Periodic Stratification in Hyper‐Turbid Estuaries.

This study focuses on a holistic modeling approach, in which water, fluid mud, and immobile mud are all calculated by only one set of equations. To integrate the immobile mud into this concept, a holistic transport equation including sediment transport and consolidation is developed. In some estuaries, extensive deepening and dredging resulted in tidal deformation and sediment import to such extent, that hyper‐turbid conditions developed. Recent measurements from the Ems estuary show that the locations of interfaces between water, fluid mud, and consolidated mud vary during a tidal cycle. Conditions are varying from fully mixed to stably stratified. As a suitable case study for the holistic model, a 1D vertical numerical simulation of the Ems has been set up, which is able to qualitatively reproduce the observed vertical velocity, concentration, and velocity shear profile. The simulation shows mud‐induced periodic stratification. Plain Language Summary: This study describes a 1D hydrodynamic‐numerical model, which is called holistic as water, fluid mud, and immobile bed are solved by only one set of equations. Many estuaries are deepened and straightened to enable passage for ever‐larger ships. In some estuaries, those artificial changes heavily influence the flow behavior and caused a shift to very high sediment concentrations resulting in thick layers of fluid mud. The presence of mud alters the flow‐ and turbulence behavior compared to pure water and subsequently must be included into the modeling equations. The model includes the immobile mud, where flow velocities and turbulence are zero. This is possible with a rearranged consolidation equation and the adaption of model parameters to be valid in cases of very high sediment concentration. Recent measurements from the Ems estuary show that the vertical concentration profile in the estuary strongly varies with time during one tidal cycle: There are phases of a stable fluid mud layer and phases of fully mixed conditions where no mud layer is present. As a possible application of the holistic model, a 1D vertical numerical simulation of the Ems estuary has been set up. The simulation results are in good agreement with field observations. Key Points: A holistic sediment transport equation including sediment transport and consolidation is developedThe rheological viscosity, the settling velocity, and a k‐ω turbulence model are adapted to be valid in the region of the immobile mudA 1D vertical simulation of the holistic model is set up to simulate the flow and sediment processes in hyper‐turbid estuaries [ABSTRACT FROM AUTHOR]