What are Flood Plains?

Characteristics

• A flood plain is the flat land that runs alongside a body of water, such as a stream or river, particularly around those that meander. In normal conditions, this land is dry. When water flows over the banks of a stream or river during times of flood, however, this land becomes flooded. An individual floodplain's size is influenced by the size of the river, the volume of water carried by the river during a specific amount of time and how often the river floods.

Formation

• When the volume of water in a stream or river rises, after a period of heavy rainfall, for example, water can rise above the level of the river's banks and flood the surrounding area. When this happens, the sediment that is carried along the course of a river from locations downstream and through erosion of its banks washes over the land on either side of it and is deposited there. The main components of this sediment are mud and sand. Flood plains form from the build-up of sediment that is deposited each time the river running through it floods. The geography of a floodplain can be subject to constant change, depending on the sediment deposited during a flood and also that which is deposited laterally, when a river deposits sediment to its sides, particularly at times of reduced speed in the flow of the river.

Importance

• Floodplains play an important role in times of flood. When a river floods, the surrounding flood plain reduces the velocity of the floodwater and acts like a sponge, absorbing a great deal of the excess water before it has a chance to cause damage further away. Flood plains and the plants that grow there also act like a filter for storm water, filtering out much of the pollution that it carries before it reaches the source of drinking water.

Wildlife

• Another important role of flood plains is the provision of a habitat for a variety of animals and plants. Many animals live alongside the river and the area surrounding it. The plants that grow in the floodplain can also limit the amount of sunlight that reaches the river which, in turn, limits algae growth. This means that there is more oxygen available in the water for aquatic plants and animals.

Urbanization

• The urbanization of flood plains causes a problem for humans and for the environment. The construction of roads and buildings alongside rivers increases the damage that is caused by floods as the flood plain cannot slow the flow of flooding waters or limit the distance that they reach through absorption. Urbanization also prevents pollution from being filtered out of storm water, increasing the impact that this pollution may have on humans and the environment.