Camcorder vs. GoPro mounted on bike
The primal problem will be the stabilization. GoPro's Cameras offer a decent image-stabilization and are wide-angled. This allows shakes and bumps to have less of an impact. If you now go for a camcorder with, say, a lens of 50mm, you will experience an extreme increase in shakiness.

In other words: When you worry about your camera to break due to shakes and bumps, the footage will most likely not be great.

There are some options you have, which one to choose is on you.

First, you could try to buy a GoPro that can record in 4k (maybe you already own one). That way, you can hit two birds with one stone. On the one hand side, you will be able to zoom in digitally in post without losing any image quality, assuming you want to render in full HD (1920x1080). This fixes the issue of the wide-angle lens. On the other hand side, there will be plenty of material around the visible area, so a warp-stabilizer in After-Effects should easily help stabilize the footage, giving you a much more smooth result than opting to put a camcorder on your bike.

The other options would be to use a camcorder indeed, or even a tv-production or cinema-camera if you like, but staying off that bike. Either, you can rent or buy a Steady-Cam or Gimble (the ones from Ronin are very good) and run along. The Gimble or Steady-Cam will stabilize your Camera and will give you probably the best results (assuming you know how to properly use a Gimble / Steady-Cam).
This is also the priciest option though, I fear.

The other is to use the camcorder or higher-tier camera again, but stay still entirely. You can try to find a Spot on the path where the water flows around you a small bit, like in any curve of the river. Position yourself on the extended piece of land and just pan with the Subject, instead of moving at all. This would be the easiest and probably cheapest option, though it only really works well for short, preferably fast pace sequences, so you don't catch that the camera is stationary. Many people use this method to capture people running in forests: The actors simply run in a circle around the camera and the operator pans with them, which results in footage looking like they follow the subject horizontally.

I hope my answer was helpful, good luck with your project!