You mean something like this? This was a bit of a challenge to figure out which is what I like. :) Create your beach terrain then use a cube and make it the same size as your terrain and apply the carribean resort water material. Now select the terrain and go to the editor/pictures and copy to get the G2H, will will use this for several things in the alpha channel. Exit terrain editor. Now select the cube and set the material as pictured above. Paste the g2h in the B channel of the material editor using picture (like you would if you were using a .jpg for a texture). Make sure you paste it in both the color and alpha sections (1st and 2nd boxes). Presto, now where it nears the beach it's clear and where it's deeper it's a darker blue. :)