The Physics of the Bend

Inside every river bend, a spiraling flow called helical flow operates. Water on the surface moves toward the outer bank (the cut bank), eroding it. Near the bottom, water moves toward the inner bank (the point bar), depositing sediment. This creates a corkscrew motion within the river channel.

The result is that the outer bank is steep and eroding while the inner bank is shallow and growing. Over time, meanders migrate laterally across the floodplain, sometimes moving several meters per year. The Mississippi River's meanders have shifted so dramatically that old state boundaries, once drawn down the middle of the channel, now leave bits of one state stranded on the far bank.