When you have a tidal or sluggish river at a tsunami impact point, the wave can often run for miles up the reversed stream. Looking back over time, I didn't see any tidal reversals in that stream -- but neither did I see any rapids indicating any significant gradient.
And, that river is clearly "at the neck of the funnel"...
It's not often that you see bridge trusses mangled like that.
TXnMA
