Timestep formula (Water Overlay)

An adaptive timestep is implemented according to Kurganov and Petrova (2007)^[1]. At every timestep, the courant-number is kept smaller than 0.25 for every active computation cell.

Especially at low depths, choosing the appropriate timestep is critical to avoid numerical instability. Therefore the following principles are used to determine the right time step:

the timestep is chosen so that all computation cells follow one of the following criteria..
if a cell's water depth is below the flooding threshold of 5 × 10^-3 m, no flow is assumed between that cell and its neighboring cells.
If the cell's water depth is above the flooding threshold, the maximum timestep is assumed to be 100 × the water depth at that cell.
if the waterdepth increases, the timestep is assumed to be not larger than the formula above.

If the numerical flux decreases, larger timesteps are allowed than set by Kurganov and Petrova^[1], depending on the configured calculation.

References

↑ ^1.0 ^1.1 A Second-Order Well-Balanced Positivity Preserving Central-Upwind Scheme for the Saint-Venant System ∙ Kurganov A, Petrova G (2007) ∙ Page(s): 15 ∙ Found at: https://people.tamu.edu/~gpetrova//KPSV.pdf ∙ (last visited: 2016-02-25)