As a result I get this:

Wave systems

Actually I didn't know what it is gong to be when I have started it bit know I see a river here.

I want to use Filters> Distort>Twirl.

Wave systems

Result:

Wave systems
 


I suggest you to paint a little. To make the illustration more real, create a new layer on the top and begin to paint.

First I want to fix Sand color.

Wave systems



Wave systems



Wave systems