Why Do Rivers Bend?
By Sam Nunes, Environmental Educator
Have you ever noticed the difference between a natural flowing river and a man-made canal? Canals move straight to their destination while rivers wind back and forth along the landscape as the water journeys towards the ocean. Humans make canals to travel the shortest amount of distance between two locations, such as between the Caribbean and the Pacific Ocean at the Panama Canal. If efficiency is so vital in ecosystems, why would nature increase the distance water has to travel to get to the ocean?
One’s first thought might be of course water must wind and bend around obstacles such as mountains, but rivers that flow through flat grasslands and fields show the same behavior. It’s actually small disturbances in topography that set off chain reactions that alter the path of a river.
Any kind of weakening of the sediment on one side of a river due to animal activity, soil erosion, or human activity can draw the motion of the water towards that side. When the water flows more strongly to the weak side of the river, it carves out the land on that side of the river through erosion. Meanwhile, the water on the other side begins to deposit more sediment along its banks. This back and forth motion continues all the way down the river as long as there are no obstacles blocking the process. Interestingly enough, the length of the S curve in the river caused by the bends tends to be about 5-6 times the width of the river.
Keep your eye out for each bend in the river. Over time the layout of these streams changes and sometimes disappears. We can even see evidence of this type of stream behavior on Mars in the remnants of stream erosion on the rocks and landscape. This behavior is literally out of this world!