A model comparison of flow and lateral sediment trapping in estuaries

Two different models for the distribution of flow and sediment over the cross-section of a tidally dominated channel are compared. The first is a state-of-the-art numerical model that solves the three-dimensional shallow water equations with prognostic density field. The second is an idealized model which includes residual and semi-diurnal tidalmotions and uses a diagnostic residual density gradient as baroclinic forcing. For bothmodels, an off-line sediment module is used to compute the lateral mean sediment distribution. For fairly high values of vertical diffusivity (~ 0.01 m2 s-1), a good qualitative agreement is found for residual flow patterns. The agreement of the amplitude of the semi-diurnal velocity components is satisfactory as well, although the phase distributions show deviations. The lateral mean sediment distributions are rather similar, and stem from a balance that is predominantly governed by mean concentration and residual currents. The flow patterns only differ qualitatively for either very low or very high tidal velocities. The sediment distributions only deviate for low tidal flow regimes

Effect of bottom stress formulation and tidal forcing on modeled flow and sediment trapping in cross-sections of tide-dominated estuaries

Field data collected in cross-sections of tide-dominated estuaries reveal that flow and suspended sedimentconcentration show pronounced spatial and temporal behavior, which depend on factors like tidal discharge,density gradients and the geometry of the cross-section. Models are capable of reproducing and explainingmany aspects of the observations, but also marked discrepancies occur between model results and data. Theobjective of the present study is to systematically investigate the sensitivity of model output to formulationsof physical processes. This is done by comparing two types of models. The first is a numerical model (NM)that solves the full shallow water equations with prognostic salt dynamics. The second is an IM that solves areduced set of equations for tidal water motion and uses a diagnostic salinity field. The IM can be used as atool to interpret the complex output of the NM. The NM, on the other hand, can be used to probe the limits ofapplicability of the IM and may give hints on further improvements of the IM