At least, drainage ditch kayaking seems like a good idea.
I love the beginning of this clip, when the first guy is trying to convince his friend that this is going to be a good activity for the two of them. I mean, how did that conversation go?
"Hey, man, I think I've got this brilliant idea: we're going to launch ourselves into a deep ravine in a small plastic boat. Now, there isn't going to be any way for us to stop or really even slow down, until we get launched into the lake at the end. There are a bunch of large bridges that will act as obstacles. If we hit one at the speed I imagine we'll pick up, we will surely die. Also, the water is really shallow. And narrow! Most of the time, we won't really even be going down water - we'll just be cascading down leaves and rocks. So it's probably going to hurt at least a little bit. Like I said, there's no way for us to stop or slow down, so we're just about guaranteed to crash into one another once or twice. We're going to film it, and nothing bad ever happens on film. What do you think?"