Why floodplains flood

The relatively level land can be developed either as agricultural fields or sites for habitation or business. The three most ancient civilization s on Earth all developed on fertile floodplains. The floodplains of the Indus River, in what is today Afghanistan, India, and Pakistan, gave rise to the Indus River Civilization, also known as the Harappan civilization.

Finally, ancient Egyptian culture developed around the fertile floodplains of the Nile. Floods carry nutrient -rich silt and sediment, and distribute it across a wide area. Roads, bridges, railways, and even airports can be constructed on the even surface.

Ships and barges can often haul cargo faster and more efficient ly than roadways. The floodplains of the mighty Mississippi-Missouri river system in the central United States, for example, have served as vital transportation corridors for centuries.

During the 19th century, cities on Mississippi floodplains—St. People, agriculture , and businesses on floodplains are always at some risk. The most devastating floods of the 20th century occurred on the floodplains of the Yellow River in China, for example.

The floods were some of the worst natural disaster s ever recorded. The Yellow River floods followed years of drought that left the topsoil on floodplains brittle and eroded. Managing development of floodplains is a critical responsibility for regional and urban planner s. The benefits of floodplains, including prime agricultural land and desirable housing locations, must be balanced with the personal and economic threats posed by floods.

Many flood-plain settlements maintain flood meadows and water meadows to reduce the impact of seasonal flooding. Flood meadow s are natural areas of grassland immediately adjacent to a floodway. Flood meadows are often used as pasture s for livestock when they are not saturate d with water. Water meadow s are also grasslands adjacent to floodways. Unlike flood meadows, water meadows are created and maintained by people. Water meadows are continuously irrigated through channels from the river.

Water meadows were common features of the agricultural landscape in Western Europe throughout the 19th century. The nutrient-rich, silty soils of water meadows supported rich pastures used for livestock, as well as growing hay and other fodder. Cities built on floodplains, such as St. Louis or New Orleans, must incorporate flood-control infrastructure into their organization and architecture.

Evacuation procedures, emergency shelter s, and building codes must be in place. Levee s or other barriers must be a part of the city design. Urban planners try to keep areas near the floodway, called a Special Flood Hazard Area, as free from development as possible.

Sometimes, residents on floodplains must relocate entirely. The small town of English, Indiana, for instance, was established on the floodplain of the Blue River, a tributary of the Ohio. In many floodplains, a mass relocation is impossible for logistical and economic reasons. In such cases, engineer s can divert the path the floodway—the river—itself. Artificial floodways are a sort of man-made river channel. During flooding episodes, the channel can divert up to 4, cubic meters , cubic feet of water per second before it reaches the Winnipeg area.

The floodway carries this outflow around the city before rejoining the mainstem of the Red River in a less-populated area of the floodplain. In other places, conservationist s and engineers have engaged in floodplain restoration. One of the most ambitious floodplain restoration projects is underway in the Lower Danube floodplains of Bulgaria, Romania, Moldova, and Ukraine.

The extensive projects aim to reduce flood damage by restoring flood meadows, which will absorb excess water.

Flood meadows absorb chemicals from agricultural and industrial runoff. Houses and businesses that are built on floodplains often require more insurance coverage than buildings constructed on higher ground, because flood damage is more likely to occur.

A FIRM is a flood insurance rate map. A Special Flood Hazard Area is simply an area that falls within boundary of a year flood. FIRMs are used to balance the risk of flood against the rate of insurance. Buildings in the A- or V-zones, for example, are near the banks of the river. All buildings in A zones are required to have flood insurance due to their extremely high risk of flood damage.

In the Charlotte, North Carolina, floodplain, for example, the base high flood elevation is one foot above the expected depth of floodwater in a year flood. There are strict rules for constructing or remodeling buildings in the A-zone of a floodplain.

Basements in A-zones must not be used as living spaces, for example. Residential zones, which are more difficult to evacuate than hotel-designated zones, may also be more limited along a floodway. Floodplains usually only flood during the rainy season. Photograph by Chris Johns, National Geographic. Floodways are usually constructed on floodplains with low traffic and rare floods. Also called a riparian forest. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service. Interactives Any interactives on this page can only be played while you are visiting our website.

Related Resources. Rivers and Streams. View Collection. Environmental Hazards. However, many of these regions face flooding risks. Each year, millions of people are affected by floods that cause billions of dollars worth of damage.

The number of people living and working in floodplains is expected to increase, with a consequent increase in flood risk, as more urban and rural floodplains are targeted for development.

This means more and more people are at risk from flooding — a situation that is expected to worsen under climate change scenarios. Improving the resilience of floodplain communities can be achieved firstly through the quantification of the actual risk.

This must then be followed by mitigation of that risk through structural solutions such as levees and flood storages, or through non-structural solutions such as flood warning systems and regulatory measures like floodplain management planning.

At DHI, we have a long history working with governments and communities to assess, mitigate and manage flood risks.

Our flood forecasting technology has been integrated into local and national early warning systems. Areas of expertise Our areas of expertise Our expertise spans all water environments — from rivers and reservoirs, to oceans and coastlines, to cities and factories. Agriculture overview Integrated Solutions. Software Products. Aquaculture overview Integrated Solutions. Protection of life below water. Climate change. Climate change overview Solutions.

Health risks and safety planning Marine water and climate change Research and development Urban water and climate change Water resources management. Integrated Solutions. Coast and marine. Coast and marine overview Solutions. Coastal engineering Estuarine and sediment engineering Ports and terminals Survey and monitoring Vessel fuel consumption. The negative social and environmental consequences -- affecting everything from food security to the environment Infrastructure development along waterways and sea-level rise increase vulnerability for these communities.

But as coastal flooding increases And researchers Rarely do we consider what happens after we flush that toilet or turn off that tap. However, researchers Yet others live barely Their varied lifespans make rockfish a unique genus in which to pinpoint genes That's according to a study published in Nature, which helps answer a long standing question about what happens to tectonic