Hi kmar0099, The trough is lined with medium weight butyl pond liner that is carefully fitted to the trough and held in place with brushed aluminium edging.
The bottom of the trough over the liner has a 2" layer of gold gravel that not only adds texture to the rill but also helps to prevent the liner degrading by the sun.

Thanks, Frank. I'm looking to do a similar project and you've given me great inspiration!