A river has three sections, upper, middle and lower. Meander bends occur in the middle section when the river is not as high up and has a shallower slope (gradient) so it has more power to erode sideways. It also has a greater volume, as more tributaries have joined, so less water is touching the banks of the river thus there is less friction acting on it and it has more power. A meander starts at the deeper side of the river where it flows faster and has more power to erode sideways. i don't have time to finish this go to a siter for more information.