The deposition of sediments through flooding rivers creates floodplains. These floodplains are quite natural, and are needed in nature. These floodplains often give water somewhere else to go before flooding a town or city. Water can sink through sediments, draining right into the land.
When the flooding is a little more intense, the floodplains can often provide more than just flood prevention for the towns and cities around the river. As water sinks into the ground through the sediment, the water is trapped. It can sink into water tables under the ground, and then can be used for drinking water. If there is standing water, the water can be used for irrigation. When floodplains are demolished for building, it can take away this natural barrier and help flooding get worse in the area.