How tough are water rides at Hurricane Harbor on your back?

People who don't suffer back pain won't even understand this question, so just skip it.

I have a bad back. No matter what I do, it will always be like this. I can't go on roller coasters because of the incredible stress they put on the spinal disks. But next year I'm thinking about trying the water rides at Hurricane Harbor. How much of a jolt do they deliver to your back? For example, if I am in a car, and the driver slams on the brakes, that kills my back. The same forces apply on these rides. When the ride hits the bottom and slows down, it could be quite jarring.

I also wanted to try Dive Devil at Magic Mountain. Since you're supported in a harness, it appears that your back is not stressed.