Flash bubble machine. Help

good day to you folks. I’m having trouble with my water game…mainly bubbles!

I have tried every thing possible to make bubbles start from a random section. move up a random amount of pixels. And then have it chose anywhere between 1 of these sections. And then move up a few more pixels and then be pushed by a current!

Heres an explanation picture…

(hopefully it shows up) if not here should be a correct link

http://www.imagehosting.com/show.php/812284_Diagram0001.jpg.html

(and if the links broken…I’m screwed)

I really don’t need you to code the part where it rises just parts of currents and random movement…