College Objectives Explain how flooding benefits the surrounding land. Explain water diversion and tell the problems it causes. Flooding A flood is any high flow of surface waters that overtops normal confinements or covers land that is normally dry. Most streams are naturally bordered by flat, low lying areas known as floodplains . Floodplains have been carved into the landscape by stream erosion, and are covered in fine-grained sand, silt, and clay deposited by floodwaters.
Some streams have natural levees , mound-like deposits of sediment that border the stream channel.
Natural levees form as flood waters leave the channel and spread out onto the floodplain. As rushing water leaves the channel, its velocity drops, and coarser sediment is deposited adjacent to the stream. If the water in a stream is allowed to spread out over the natural floodplain, the impact of downstream flooding is lessened. Some municipalities vote to remove floodwalls because they are unsightly and spoil the view of the river. They are in trouble when it eventually floods.