Benchmarking a new open-source 3D circulation model (ELCIRC)

Released recently as an open source code, ELCIRC (Eulerian-Lagrangian Circulation) solves the primitive shallow-water Navier-Stokes equations with turbulence closure submodels. Numerically it uses a semi-implicit finite-difference/volume method on unstructured horizontal grids and structured grids in the unstretched vertical direction. An Eulerian-Lagrangian method (ELM) is used to treat the advection, and wetting and drying is a natural part of the algorithm. The model has low-order accuracy, but is very flexible, computationally efficient, and robust. Overall, it has shown excellent ability to address complex river-to-ocean systems, and is currently used as the computational engine for our observation and forecasting system for the Columbia River estuary and plume. As a part of the development of ELCIRC, we carefully assessed its performance against a wide set of controlled benchmark problems: wave propagation on a slope, geostrophic flow in a straight channel, and adjustment under gravity, etc. In this paper we report on these benchmark studies, which provide very useful insights on the capabilities and limitations of the model. Using carefully defined error metrics, convergence studies are carried out. Compared against well-established higher-order models (in particular, ADCIRC and ROMS), ELCIRC has the capability of compensating for its low-order accuracy through inexpensive high resolution. Benchmarks will be made available electronically before the publication of the conference proceedings.