One of the guys reviewing the draft version of my book on DB Cooper had this to say about what would have happened if Cooper had belly-flopped into the Columbia (he works on a dive/recovery team on the Mississippi):
I have some points of fact that counter your statements regarding river survival, but maybe we can chat on an actual telephone about that some time.
The interwebs tells me the Columbia River was 50F/10C around November 24, maybe colder. That’s really the cut-off for bodies to not pop. Trust me.
And people don’t drift, he was not semi-buoyant. We do our usual search patterns basically as the radius of water depth. People pretty much drop like a rock.
Any additional weight would have stymied the bloating process. very likely, given the water temp, that Cooper popped in the Spring of 1972. If he went in the river. Not sure if any of your nerds on those forums are part of an actual recovery team, but just my two cents. Usual trend for bodies that go in, in that cold of weather, to not pop until the spring.
Also, research the barge activity on the Columbia. I know you researched dredging efforts. Which would indicate the river is heavily traffic. We’ve seen barges really alter the sub-surface landscape. Occasionally stir a body lose (happened this Spring, but luckily in another county)
So, if Cooper lands in the Columbia, his body stays on the bottom until the spring of 1972. The money on Tena bar would have to be deposited on Tena bar at this time, or it stayed on the bottom (detached from Cooper’s body) and was later dredged. This is still unlikely, since we’re pretty sure Cooper jumped before the airplane was over the Columbia, but it’s a possibility.