Constructing brick or wood raised water feature + bed

[NullCipher]

I'm playing around with some ideas on how to solve a messy area in our garden. So far I've added a brick mow strip around the edges of the garden (concreted in)

I've now got the final stretch to do, but the section has always given me a headache due to the Silver Birch growing in an awkward place and it's roots that are close to the surface. The stump nearest the decking has now gone:

As I can't brick past the tree, I was thinking about creating a raised planter around the silver birch, and then infilling the gap between this and the deck with a raised water feature. These would either be done using timber or brick + render. Quick sketch up render:

I'm struggling on what to do to be honest as both options seem to have their own problems.

Timber:
If I go for the timber option, then I can most likely drive some stakes into the ground and concrete them in place where there are no roots. Stakes can be driven in-between the roots, but they won't be concreted in.
This should be OK for around the tree, but then the water feature presents a bit of a tricker problem. I can probably get a more solid base around here, but then theres the issue of the timber warping under the pressure of the water, as well as any expansion in the frost..

Brick:
If I go for the brick option, then I'm going to struggle to get a solid 2 course foundation in some areas. My main concern would be around the front of the tree and water feature, as well as the middle part.

Both ideas also suffer from the problem that if the roots grow upwards then they may push the work i've done around.

Any suggestions on what to do here?

 

[endecotp]

There's also a limit to how much you can increase the ground level before the tree gets unhappy.
I'd probably try to keep it simple, maybe extend the border into the current lawn in a semicircle from the tree and have either no or shallow edging.

 

[NullCipher]

Aware of that one. Couldn't be bothered to put it in the render but the trunk will be left exposed

 

[endecotp]

I think it's more the roots being buried that you need to worry about.
May be OK if most of them are beyond the extent of the box.
Fill it with something air-permeable e.g. big pebbles, not solid topsoil.

 

[NullCipher]

Thanks.

Any suggestions on how to take either the brick or timber walls?