This spillway was designed following USBR guidelines (type II), where the engineers were interested in validating their designs without having to resort to physical lab models (expensive, and which also have their own sets of scaling problems).
The steps to analyze these types of problems in FLOW-3D are straightforward:
Post-processed with FlowSight, coming soon in FLOW-3D v11
Generation of a 3D CAD model based on the design blue prints (I happen to use Rhino3D, works pretty well for me)
Geometry import in FLOW-3D in the STL format
The usual FLOW-3D simulation steps:
set the boundary conditions
set the initial conditions
choose your physical models (in this case turbulence and air entrainment)
choose your outputs (hydraulic quantities, Froude #, etc.)
In the case of spillways, which have fairly large spatial scales compared to the water depth, it is EXTREMELY advantageous to use the code's domain removing capabilities. The best way to do this is to follow a 4 step approach:
Run the simulation with a coarse grid. This run will take 10 minutes at most, and even if this won't catch the full manifestation of the hydraulic jump, it will be enough to give you a good idea of where the fluid regions will be active.
Equipped with that information go back into your CAD package and create a domain removing solid which conforms reasonably well with the complement of your fluid form (my method is to super-impose a picture of the simulation result within my CAD model).
Add this new solid component to your simulation as a domain removing component.
You can now massively crank up the resolution of your simulation to fully capture the detail of the energy dissipation mechanism in good detail.