No river flows straight for very long. And whether you’re paddling in a creek a few boat lengths wide or a monstrous beast wider than a football pitch, navigating a river’s corners is something you’re going to be doing a lot of. As such, it is important to become proficient at it.
Water has mass, and under the laws of physics (can you tell this was written by an ex-physics teacher yet?), any mass will move in a straight line unless acted on by an outside force. In a river, this means that (in general), water flows straight until it hits the bank of a river which then forces it to change direction. What this means to the paddler is that most of the water will flow to the outside of a corner.
In any turn on a river, the water on the outside will be flowing faster and there will be more of it. Channels on the outside of a bend will be deeper and often have steeper banks. Hydraulics will be more forceful and rocks and hazards will generally be more dangerous and/or create more powerful waves.
The speed and turbulence at the outside of a corner can often make it a fun and exciting place to be for an experienced paddler. It is where the main current goes and so provides a fast-track down the river for someone with the right skills and when there is a clear and open channel absent of hazards.
Conversely, the inside of corners will typically have slower moving, shallower water, and less steep banks. As such inside corners often offer great line choices for less experience paddlers, safer and slower lines around bends, and provide easier exits for the scouting of and/or portage opportunities around rapids. Using an inside corner can sometimes also allow the paddler to slow down and ‘sneak up’ on a corner that they can’t see around and maintain the option of egress while getting a better look at what’s around the bend.
Although hazards such as rocks, strainers, and other obstacles can be present on the inside of corners, they are usually more easily negotiated because the water moves slower. Additionally in bigger and flood prone rivers it is usually the outside of corners that become catches for debris and trees, and it is often the outside banks that suffer more erosion that can topple trees directly into the river forming sweepers and strainers. This is another good reason to favor inside corners on new rivers.
For a new paddler, or even an experienced on on an unknown river, it is therefore a general rule of thumb to err towards the inside line if there is any doubt as to one’s ability to safely run the outside line.