But to a greater or lesser extent, all watercourses present these turns, because the liquid does not flow at the same speed through each of its sections. This imbalance alters the forces it exerts on the walls of the channel through which it circulates, responsible for the erosion and sedimentation produced at the bottom and the banks.
The meanders arise mainly in alluvial plains where there is hardly any slope. What happens is that, in the section of the channel where the speed is greater, the erosion increases due to the centrifugal force, the water excavates the bank and creates a concave shape ; while on the other side, where the flow is slower, the sediment deposition increases and the wall becomes convex.
Although the process originates from a specific change in the current –the appearance of an obstacle–, once it has started, its effect increases progressively. After the formation of the first bend, the outer sheet of the stream goes faster and thus more liquid is propelled towards the opposite bank at an increasing angle and sufficient force to erode that side and create another turn. The process is different in each river, since it depends on the flow, speed and composition of the materials.
In river currents that flow rapidly down rocky terrain made of hard materials, erosion is slower and there are almost no bends. But in wide channels on soft soils, formed by clays from a sedimentary valley, wide meanders are created that accompany the river to the mouth.
