The decibel readings on and around the FlowRider will differ depending on where you are standing of course, but the range is from 65-87dBs.
A sound is considered to be “noisy” when two people standing three feet apart are forced to raise their voice in order to overcome an ambient sound. That decibel rating is 80 dB’s. 60 Decibels is described as a normal conversation whereas 80-90 decibels is similar to the level of noise you would experience in a noisy restaurant.
A couple things to remember with the noise emitted from a FlowRider though are that A) it’s definitely going to be louder when you are actually ON the attraction vs. when you are spectating and B) it is an ambient sound, so there is no disruptive rise and fall of noise level.
For an outdoor development it is typically not necessary to incorporate noise mitigating devices however it certainly doesn’t hurt. On the other hand it would be worthwhile to consult with a specialist while designing an indoor venue. Things like hard square concrete walls behind the Attraction are not recommended. It is better to incorporate objects and shapes that cause the soundwaves to bounce around and not travel in a straight line.
There are companies out there that specialize in the supply of noise mitigating devices. One such group is www.soundproofcow.com . They can provide water resistant sound mitigating panels that can be applied to walls and ceilings. It may also make sense to install hanging baffles if the space warrants it.
It should also be noted that the bulk of the noise is the sound of rushing water in a way similar to a waterfall.