I am trying to find some reference material regarding the sizing of riprap outfall basins for larger diameter outfall culverts. The only references I can find provide sizing tables for pipes with diameters up to 96". However, due to lack of significant head on the lake outfall structure, the outfall culvert has to be a box that has a greater outfall orifice area. The velocities coming out of the culvert are low enough to allow for a riprap outfall, but I just can't find any materials that would detail how to size the basin. Any suggestions are greatly appreciated.