Dear EFDC Team and users:What factors determine the speed of model calculation?

Instead, perhaps think about it in terms of what limits the size of the timestep in the model. A model that can utilize larger timesteps will always run faster.One big factor will be the resolution and complexity of your model grid. A complex grid with small cell sizes will require more computational effort to run.If your boundary conditions vary rapidly, that will also impact the maximum size of the timestep. For example if you have a discharge series which varies rapidly from 100 cms to 0 cms, then that could result in instability near that boundary. Likewise, if you use an open boundary that varies rapidly that will definitely produce instabilities and slow down your model.It also depends on what kinds of prognostic variables you are simulating in your model. For example, a simulation with just hydrodynamics will always be more efficient than one with temperature or sediment transport, as an example.One thing you may look at is the limiting cell analysis feature that was introduced in EFDC_Explorer 8.4. You can find that feature in the Model Analysis Tab under Miscellaneous. That feature identify which cells had the minimum timestep at each iteration and compile them into a frequency histogram. You can use this information to examine cells which may be slowing your model down, and try adjusting the properties of that cell or the surrounding cells to address the problem.

Thank you very much.