Currently, the outflow BC in GeoClaw seems to just copy the flow states (water elevations & discharges) from boundary cells to ghost cells. While this may be good enough for open ocean cases, it seems to be improper for overland flows. The results of benchmark simulations show the fluid accumulates at the outflow boundaries.
The current solution in my mind is assuming the ghost cells have the same topographic slopes as the boundary cells do. Tests with the flow over a single slope plate show promising results with this idea.
However, it may not be necessary to implement this because it seems the computational domains of overland flows are typically larger than the actual wet regions. That's why this issue is deemed as a minor one.
Currently, the outflow BC in GeoClaw seems to just copy the flow states (water elevations & discharges) from boundary cells to ghost cells. While this may be good enough for open ocean cases, it seems to be improper for overland flows. The results of benchmark simulations show the fluid accumulates at the outflow boundaries.
The current solution in my mind is assuming the ghost cells have the same topographic slopes as the boundary cells do. Tests with the flow over a single slope plate show promising results with this idea.
However, it may not be necessary to implement this because it seems the computational domains of overland flows are typically larger than the actual wet regions. That's why this issue is deemed as a minor one.