In theory, FLO-2D does not impose a fixed upper limit on the number of grid elements in a model domain. In practice, the feasible grid size is governed by model complexity, numerical stability, and available computational resources. Most large-scale FLO-2D simulations are on the order of 1–2 million grid elements. Simpler applications, such as uniform overland flow models with minimal hydraulic structures, have been successfully run with grids approaching 6 million cells.
Grid cell size has a greater impact on model performance and stability than the absolute number of grid elements. Very small cells significantly increase computational cost and may lead to timestep restrictions or numerical instability. Guidance on selecting an appropriate grid cell size is discussed in the following question.