A river flowing down a straight path will be moving the fastest in the middle of the river, just below the surface. But if that river approaches a bend, the speed changes.
SINCE FAST MOVING WATER DOES MORE EROSION, THE FAST OUTSIDE BEND IS WHERE EROSION OCCURS ON A RIVER
THE SLOWER INSIDE PART OF THE BEND IS WHERE DEPOSITION OCCURS ON A RIVER.
OUTSIDE BEND = FAST = EROSION
INSIDE BEND = SLOW = DEPOSITION