You know, that's one thing that I've been wondering...
Water parks built in the '70s and '80s had lot of rides built from concrete and foam (e.g. Surf Hill/Congo River Rapids). What I was wondering is if these rides are no longer built because of legal/code reasons or if it's just more economical to build the rides you see today with steel towers and fiberglass slides.
What was so nice about Wild Rivers is that most of the major rides were built on a single hill. Walking up concrete paths, with some stairs, and being surrounded by vegetation really gave the park a natural feel. It was nice to be out in the sun, just walking around and hop from ride to ride.
The water parks I see built today are usually on flat land with a bunch of steel towers. So much of your time is spent winding up stairs, surrounded by steel, in the shade, sometimes cold ... just very disconnected from everything else around you.
I, too, love the concrete/foam built into hills waterslides of yesteryear. Where I grew up, there was a place in Vacaville, California called Blue Lagoon that had 4-5 slides built into a hill and then Manteca Waterslides had a ton. They always seemed so long and lush.
Are there any waterparks left that still have these type of slides? I'd love to go to some this summer if anybody can name a few for me.