Falling Streaks

Hello guys.
I am new here. I need extreme falling Streaks as you can see in the image. How should i do this? I want to put sand or snow on top of everything.
Thanks in advance

http://ali-rahimi.net/

Hi Ali, you might want to take a look at the erosion tool, and the various output maps (flow, deposition, wear), you can play with these and assign them highly contrasting colours. Also, play with the erosion settings to have these output maps produce more or less marked results.