[phdoofus]

So, the deal is I've developed a shallow water solver to look at a problem in the emergence of complexity. It's a conservative finite volume code with cell centered variables (h, uh, vh) on an unstructured triangular mesh and uses MPI and OpenMP to scale. There is also variable bottom topography and bottom friction. This is basically looking at flow in a channel so the problem is cartesian. So far, I am not using any ghost cells at boundaries, though I do have halo cells for communications between MPI tasks. The code seems to work well and the side wall boundary conditions are working fine. I'm really looking at a problem where the flow is sub-critical. The one thing that I haven't been able to get right is the outflow boundary condition.
For one thing, there is no 'reference state' outside of the boundary. In fact, I start the problem with a completely dry state and , in general, at any time there may even be dry regions on the boundary (the Roe solver handles the dry regions just fine).
Can anyboy point me at a paper that describes how to implement something like this? Most of the time, I run into things that either aren't relevant to my problem or are vague enough to be confusing. I'm just not seeing how to relate this business about Riemann invariants to something I can set in my algorithm....
Ok, there. I've confessed my brain fart to the world. ;-)