Hi Scott,
First, with the SSR, the flooded Stream hexes are impassable other than swimming, which makes you an unarmed counter, so in essence the level of the flooded hexes won't matter(who wants to be an unarmed counter?). Basically, the SSR makes the flooded hexes impassable.
But your questions are interesting from a logic perspective, but this is a design for effect thing and not a logical thing. Given the level of the flooded stream is impassable (in effect) it's level doesn't matter. The Deep Stream hexes I thing are designed to give the Brits a way to cross the stream other than the bridges.
By rule the Deep stream hexes will still allow crest status and crossing of the stream, and yes they are at a level lower (-1) than the flooded stream hexes.
So yes, if you wanted to you could try to pass a swimming TC to dive UP?!?

from 22W10 to 22V9. But you'd be an unarmed unit so why do it (unless it was on your ASL bucket list)
Basically the designers wanted to create an impassable barrier with a few choke points.
If you need a real life example to help envision a possible construct, think of hex O5 having an industrial sized sewer culvert that flow into the stream. The stream flows both ways under each bridge is a flood control gate or water fall that makes the stream deep from that point on...a stretch I know but a possible explanation.
Did that help?