I glued the sand down with PVA, waited for it to dry. After a black primer I painted the sand with dark brown and followed with some drybrushing to a lighter brown. I then painted the stones in a dark grey and drybrushed it up to a lighter grey. I then covered with static grass, flock and various bushes.
I also made a few smaller pieces to go alongside the main piece, one example below.
Vitor