Saludos desde Puerto Rico!

I plan to make a 3 level, approximately 8"L x 24"W x 14"H wooden display, inspired by the sand-wood theme of mini zen gardens. The first level will be covered in sand and have an elevated space in the middle for an incense burner.

I want to do a two-tone sand design with divisions, but I want the divisions to be flexible and subtle. On the second or third level, I plan to make a curving, river-like feature. For that, I thought about using some kind of bendable aluminum/tin/etc strip, bending it to my liking and gluing it to the wood base before filling it with sand. However, I haven't found any such materials on ebay, michaels, etc.

Here are some examples:
https://www.pinterest.com/pin/112519690665105335/
I like the use of the circular division in the middle. For my purposes, the divider should be of a similar height and thickness, but also bendable.
http://www.mitokourakuen.com/zen-gar...en-gardens-32/
This design uses a rigid wooden division to separate the two sands.

Flexible wood or clay may also work.

I look forward to sharing ideas!