creating a floating (streaming) water layer on a stationary layers of water

kelps are efficient for reusable energy & bone meal production &
max height of a kelp can be 26 blocks.

So my design aim:

• have 26 (height) layers of stationary water for kelps to grow.
• make the 2nd layer from bottom slabbed to be able to break all kelps
  from their 2nd breakpoint whenever you wish.
• let the design makes broken kelps reach to the surface eventually by
  buoyancy of water
• 27th layer must be a floating, streaming water layer (width of 8) to
  transport the kelps to the edge in the flowing direction.

please see the sketch attached (sorry it’s layout is improper 🙁

L : layer

• width : I said 8 since 1 layer of water can transport items upto 8
  blocks. Your solution proposal of course may change this.
• height: I said 27 since max height of a kelp can be 26 blocks + 1
  layer of floating water become 27 layers. Your solution proposal of
  course may change this. (if >1 layers needed after 26th layer)
• len(gth): I said 5 since one may break farest kelp if slabbed layer is
  only at 1 side. If slabbed layers are at both sides then length can
  be 2 * 5 = 10.

I tried:

• filled 25 layers with stationary water
• filled 26th layer with a solid block
• made a flowing (streaming) water on 27th layer
• broke the solid blocks on 26th layer
• dived into water and tried to fill 26th layer with water again

I encountered several issues at my different trials:

• kelps did not go up (buoyancy of water failed)
• kelps stucked at edge (hoppers couldn’t pull them or they didn’t
  fall)

may you please help me?

1. is this achieveable?
2. how to achieve this design idea?

thanks, regards