Suspended Sediment Dynamics in the Macrotidal Seine Estuary (France): 2. Numerical Modeling of Sediment Fluxes and Budgets Under Typical Hydrological and Meteorological Conditions

Abstract

Understanding the sediment dynamics in an estuary is important for its morphodynamic and ecological assessment as well as, in case of an anthropogenically controlled system, for its maintenance. However, the quantification of sediment fluxes and budgets is extremely difficult from in‐situ data and requires thoroughly validated numerical models. In the study presented here, sediment fluxes and budgets in the lower Seine Estuary were quantified and investigated from seasonal to annual time scales with respect to realistic hydro‐ and meteorological conditions. A realistic three‐dimensional process‐based hydro‐ and sediment‐dynamic model was used to quantify mud and sand fluxes through characteristic estuarine cross‐sections. In addition to a reference experiment with typical forcing, three experiments were carried out and analyzed, each differing from the reference experiment in either river discharge or wind and waves so that the effects of these forcings could be separated. Hydro‐ and meteorological conditions affect the sediment fluxes and budgets in different ways and at different locations. Single storm events induce strong erosion in the lower estuary and can have a significant effect on the sediment fluxes offshore of the Seine Estuary mouth, with the flux direction depending on the wind direction. Spring tides cause significant up‐estuary fluxes at the mouth. A high river discharge drives barotropic down‐estuary fluxes at the upper cross‐sections, but baroclinic up‐estuary fluxes at the mouth and offshore so that the lower estuary gains sediment during wet years. This behavior is likely to be observed worldwide in estuaries affected by density gradients and turbidity maximum dynamics.

Suspended Sediment Dynamics in the Macrotidal Seine Estuary (France): 1. Numerical Modeling of Turbidity Maximum Dynamics

“…The Seine sediment supply is imposed at Poses at the same location as the river flow and is composed of the mud fraction. This mud flux, presented in Schulz et al (), varies with the Seine river flow following a relation based on Avoine et al () formula. Avoine et al () made a distinction between high river flow ( g/L) and low river flow ( g/L), based on a river flow threshold ( Q th ).…”

“…During a flood period (e.g., Q 5 1,500 m 3 /s), the river sediment supply cumulated over a semidiurnal tidal cycle ($12 h 25 min) reaches a maximum of 13 3 10 6 kg (cf. section 2.2.2 and Schulz et al, 2018), whereas the ETM mass can reach 250 3 10 6 kg. Consequently, the river sediment supply can contribute approximately 5% of the total ETM mass.…”

“…This study is associated with a companion paper Schulz et al (2018). While the present Part 1 focuses on the ETM dynamics from semidiurnal tidal cycle to hydrological time scales, Part 2 focuses on the quantification of sediment fluxes and budgets along the lower estuary, from wave events to annual time scales, for typical hydro-meteorological years (i.e., average, dry, wet, and stormy).…”

Modeling Mud and Sand Transfers Between a Macrotidal Estuary and the Continental Shelf: Influence of the Sediment Transport Parameterization

“…Due to the broad range of spatial and time scales involved, quantifying sediment fluxes between the estuary and the adjacent continental shelf is challenging, and only few studies have investigated their seasonal and annual variability (Dyer, 1989). Schulz et al (2018) summarized the various methods generally used to investigate such quantities. Approaches based on field data are challenging to implement due to the cost in time and money to collect sufficiently accurate measurements (Sommerfield & Wong, 2011).…”

“…Besides, it only provides information about the surface layer, which is not sufficient to quantify sediment fluxes accurately over the whole water column. Therefore, as proposed by Schulz et al (2018), one of the most appropriate ways to quantify suspended sediment fluxes is to use validated numerical models.…”