With the procedural water, there is no way to do that. Maybe one of the old Cyberstorm animated rapids could do that for you. If you don't have them, they're on the DLS and are a TRS2004 era asset.
Yes, I have read that post and have the assets downloaded. They where great back in the day, but now the regular water has ripples which you can change fast, slow or really big but not direction of flow.
