okay .. you take copy at first the skript from me... than you need some texture maybe like this:
gradient.bmp
sky1.tga
waterbump.bmp
and this put you in the where you have your gamedir... than you include the skript in the game/level and than you make two terrainmodel one with the street texture and one with what do you want or leave it black on this black model you do the skript.
The streetmodel you must prepare for overlay effekt you do a blackarea for all you want so see the env effekt...
finally you go in the WED and put the two terain models in it. the Streetmodel over the black terrain. than you activate overlay by the steet model and the action ffp_water2 by the black model ... than build the level an if you make it good this maybe look like my picture or better ^^.... I hope now you understand it..