It's called, "Dam Tutorial". It shouldn't be to hard to find but to help you, press ctrl+F to open up a search window. In it, type, "dam" & that will take you right down to the link. After clicking on that link, click on, "Dam Tutorial (Part 1).wmv". You don't need to read the second part of that tutorial because that deals with the water rising behind the wave, which isn't possible multiplayer maps. It might work if you play the map only for skirmish play but it won't on multiplayer though. so keep the river in your map when the tutorial says to delete it, like what I did in my map above. Then just use a script to raise the water.
Me Myself And Pi wrote: