Shallow delta hydrodynamics - the subgrid topography model
Using the Fine Resolution Environmental Hydrodynamic Model (Frehd), the surface elevation and salinity transport in the Nueces Delta (TX, USA) was modeled and validated with field data. The simulation results highlighted the necessity of preserving high-resolution surface connectivity at practical coarse-grid scale.
We developed a porosity-type subgrid model to simulate effects of subgrid-scale topographical features on coarse-grid models. The main purpose of developing subgrid model is to allow fast simulation of hydrodynamics and scalar transport over large domains (e.g. large coastal wetlands, floodplains, etc.). Compare to existing subgrid models, the proposed model automatically preserves high-resolution surface connectivity during grid-coarsening, which makes it well-adapted for general topography with complex river networks or topographical features of various scales.
The figure below shows modeled salinity in the Nueces Delta (TX). The left/right columns are simulations without/with the subgrid model. It can be seen that without the proposed subgrid model, simulation result deteriorates when grid resolution increases from 5m to 30m (fig c).
The video below shows a sample simulation of salinity transport at the Nueces Delta.
For more info:
Li, Z. and Hodges, B.R., 2019, On modeling subgrid-scale macro-structures in narrow twisted channels, Advances in Water Resources, https://doi.org/10.1016/j.advwatres.2019.103465
Li, Z. and Hodges, B.R., 2019, Modeling subgrid-scale topographic effects on shallow marsh hydrodynamics and salinity transport, Advances in Water Resources, (129) 1-15 , https://doi.org/10.1016/j.advwatres.2019.05.004
Li, Z. and Hodges, B.R., 2018, Model instability and channel connectivity for 2D coastal marsh simulations,Environ Fluid Mech, https://doi.org/10.1007/s10652-018-9623-7