Numerical modeling of circulation in high-energy estuaries: A Columbia River estuary benchmark

Abstract

a b s t r a c tNumerical modeling of three-dimensional estuarine circulation is often challenging due to complex flow features and strong density gradients. In this paper the skill of a specific model is assessed against a highresolution data set, obtained in a river-dominated mesotidal estuary with autonomous underwater vehicles and a shipborne winched profiler. The measurements provide a detailed view of the salt wedge dynamics of the Columbia River estuary. Model skill is examined under contrasting forcing conditions, covering spring freshet and autumn low flow conditions, as well as spring and neap tides. The data set provides a rigorous benchmark for numerical circulation models. This benchmark is used herein to evaluate an unstructured grid circulation model, based on linear finite element and finite volume formulations. Advection of momentum is treated with an Eulerian-Lagrangian scheme. After the model's sensitivity to grid resolution and time step is examined, a detailed skill assessment is provided for the best model configuration. The simulations reproduce the timing and tidal asymmetry of salinity intrusion. Sharp density gradients, however, tend to be smoothed out affecting vertical mixing and gravitational circulation. We show that gravitational salt transport is underestimated in the model, but is partially compensated through tidal effects. The discrepancy becomes most pronounced when the stratification is strongest, i.e., under high river discharge and neap tide conditions.

Oblique Internal Hydraulic Jumps at a Stratified Estuary Mouth

“…Of these, sharp density and flow gradients are especially challenging to resolve, both numerically (e.g., Hofmeister et al 2010;Kärnä et al 2015) and observationally, yet they can be important when channel geometry does not vary smoothly. Klymak and Gregg (2001) found counterrotating eddies in the lee of a sill and narrows in Knight Inlet that caused significant biases in their along-channel estimates of volume flux.…”

Analytical and numerical study of the salinity intrusion in the Sebou river estuary (Morocco) – effect of the “Super Blood Moon” (total lunar eclipse) of 2015

“…Two kinds of models are typically used: numerical models and analytical models. Presently, numerical models are more popular especially two-dimensional (2-D) and 3-D models (Kärnä et al, 2015;Elias et al, 2012;Zhao et al, 2012;Li et al, 2012;Jeong et al, 2010;Wu and Zhu, 2010;Xue et al, 2009;An et al, 2009, etc. ) because they can provide more spatial and temporal detail.…”

Infrastructure for collaborative science and societal applications in the Columbia River estuary

“…AUV data have also contributed to a stringent benchmark for the CMOP modeling system, which has resulted in novel assessments (e.g., Fig. 8) and substantial improvements of modeling skill (Kärnä et al, 2015). In turn, AUV missions are planned and interpreted with the benefit of the CMOP numerical models, by exploring in silico (not shown) alternative paths of the AUVs through forecasted fields of water velocity, density, and turbidity.…”

“…The Virtual Columbia River is anchored on highresolution circulation simulations Burla et al, 2010a;Kärnä et al, 2015), upon which operational products are created and complementary (sediment dynamics and biogeochemical) models are built. The infrastructure for the circulation simulations integrates models, bathymetry, grids, forcing, and skill assessment strategies.…”

“…13) and multi-year simulation databases of circulation Burla et al, 2010a;Kärnä et al, 2015), the latter forming the basis for a Climatological Atlas for the estuary and plume (Fig. 14).…”