Flooding is a natural and inevitable process. Floods occur when a river's channel cannot hold all the water supplied to it by its watershed (the area the river drains).

When a river floods in the lower part of a watershed, the water overflows the channel out onto a floodplain. A floodplain is a flat area immediately adjacent to the river that has been built by river processes. Flat areas that stand above the floodplain are called terraces. These benchlike features are the remnants of older floodplain surfaces formed when the river stood at a higher level. Terraces often reflect some past climate conditions (such as the last ice age) when there may have been more precipitation and more sediment carried and then depositied by the river.