A floodplain(or floodplain) is a generally level area that land next to a river or stream. It stretches from the financial institutions of the flow to the external edges that the valley.

You are watching: Raised areas of earth designed to hold back the floodwaters

A floodplain is composed of 2 parts. The first is the key channel of the river itself, referred to as the floodway. Floodways deserve to sometimes be seasonal, an interpretation the channel is dry for part of the year. The floodway that the Todd flow in Australia’s northern Territory, for instance, is an ephemeral stream, an interpretation its channel can be dry because that months at a time.
Beyond the floodway is the overwhelming fringe. The overwhelming fringe extends indigenous the outer banks of the floodway come the bluff present of a river valley. Bluff lines, additionally called sink walls, mark the area wherein the valley floor starts to rise right into bluffs. The overwhelming fringe of the seasonal Todd flow extends the floodplain to 445 square kilometers (170 square miles).
Some floodplains are extraordinarily wide. The Barotse floodplain of the Zambezi River, for example, is a substantial wetland stretching thousands the kilometers through Angola, Zambia, and also Botswana. The Barotse floodplain has the sandy Kalahari basin, which is waterlogged during the merganser season and also an extension of the nearby Kalahari Desert during the dry season.
Some rivers have very narrow floodplains. In fact, some rivers, or parts of rivers, it seems to be ~ to have actually no floodplain at all. This rivers usually have actually a steep currently gradient—a an extremely deep, fast-moving channel. Ngonye Falls, Zambia, clues a remote stretch the the Zambezi River where the floodplain is extremely narrow. Together the Zambezi pipeline the broad floodplain of the sandy Kalahari, that enters a small basalt channel as fast-moving whitewater rapids.
There space two significant processes connected in the natural development of floodplains: erosion and also aggradation. The erosion that a floodplain explains the procedure in which planet is worn away by the activity of a floodway. Aggradation (or alluviation) the a floodplain explains the procedure in i m sorry earthen material rises as the floodway shop sediment.
A river erodes a floodplain as it meanders, or curve from side to side. The huge lowland floodplain of the Amazon River, because that instance, is sculpted with thousands of oxbow lakes that paper the meandering river and its tributaries end time. Oxbow lakes are developed when a meander, or bend, in the flow is reduced off from the river’s mainstem. Functions such as oxbow lakes and seasonal wetlands are frequently a component of floodplains developed through erosion and also deposition.
A meandering present can add to a floodplain’s aggradation, or buildup in soil elevation, and its erosion. A usual aggradation setting is a wide, shallow, braided river. Braided rivers often incorporate river deltas, whereby the key floodway is separated into discrete channels and also tiny islands. The process of subsidence, in which the key of a delta may sink because of sea level rise or human activity, frequently offsets aggradation in the floodplains in this areas. The huge aggradation the sediment around the Nile delta, for instance, is subsiding because of the rising level the the Mediterranean Sea.
The alluvium, or sediment, that a floodplain varies. That coarseness and also composition count on the neighboring landscape and the velocity the the currents that developed the floodplain. Part floodplains are mainly fine-grained silt, while others room sandy.
The deposit the alluvium developed as a flow or present breaks, or breaches, its financial institution is dubbed a crevasse splay. The formation of a crevasse splay is very comparable to the development of one alluvial fan. The thickest layer of sediment is nearest the breach, when the thinnest and youngest sediments are fanned out.
The layered sediments of countless floodplains can develop important aquifers. Clay, sand, and also gravel filter water as it look downward. Water purification systems often take advantage of this herbal phenomenon in a procedure called financial institution filtration. In bank filtration, water is intentionally filtered v the banks or floodplain the a river or lake. Adjacent wells then collection the filtered water, which is then prepared for more intense purification processes.
The sedimentary patterns of floodplains often provide scientists with evidence of previous geologic activity. Thick layers the sand may indicate flash flooding, for instance, if thin, evenly spaced class of silt might indicate an ext moderate and also predictable flood patterns.
One of the most essential geologic attributes of a floodplain is that fluvial terraces. Fluvial terraces room step-shaped areas of land that flank the financial institutions of a river or stream. Fluvial terraces note the older, higher-elevation routes of the stream, before erosion and also aggredation produced the present mainstem of the currently or river. Fluvial terraces can mark the bluff lines—outer edges—of a floodplain.
There space two major types of fluvial terraces: to fill terraces and cut terraces. To fill terraces are formed as a valley or alleyways is filled v alluvium. Alluvium can accumulation as a river meanders and overflows that banks, or it deserve to be deposited by a glacier.
While to fill terraces are associated with aggredation, reduced terraces are associated with erosion. Reduced terraces are often formed below fill terraces, as water erodes sediment.
Older floodplains and also river valleys have the right to have countless fluvial terraces. The Rhine sink of central Europe, for instance, has actually dozens of fluvial terraces created by the meandering Rhine as well as intense glaciation. Fluvial terraces in the Rhine permit geologists come examine much more than 100,000 years of Europe’s past.
floodplains have dazzling arrays of biodiversity. These seasonal riparian wetlands boast better biodiversity than the rivers themselves.
The floodplains that Congo river tributaries, because that instance, boast one of the many unusual fish ~ above the planet: the West african lungfish. The lungfish is adapted to the two seasons in the Congo floodplain. It uses its gills throughout the rainy season, and also its primitive lung during the dried season.
The Murray-Darling floodplain in south-east Australia has remained remarkably unchanged for hundreds of years. This floodplain is residence to endemic types such together the hairy-nosed wombat, the wedge-tailed eagle, and several species of orchid.
Tugay forests are unusual ecosystems the stretch follow me the floodplains of main Asia, including western China, the Stans, and Azerbaijan. Tugay woodlands are sometimes called riparian forests as result of their proximity to winding rivers. Tugay forests often serve as eco-friendly migration corridors through arid or semi-arid environments. Vegetation in tugay forests, such as willow, poplar, and tamarisk, is mainly dependent top top the water gave by the floodplain’s rivers and aquifers—not precipitation.
Floods are usually seasonal and can be predicted months ahead the time. This predictability can make floodplains ideal locations to construct urban areas. Rivers provide both a natural transportation network and resource of water for irrigation and also industry. The reasonably level land can be developed either as agricultural fields or sites because that habitation or business.
The 3 most old civilizations on earth all developed on productive floodplains. The floodplains between the Tigris and also Euphrates rivers, in what are today Syria and Iraq, are known as Mesopotamia, “the land in between the rivers.” old civilizations the Mesopotamia include Sumeria, Akkadia, Assyria, and Babylonia. The floodplains of the Indus River, in what is today Afghanistan, India, and Pakistan, offered rise to the Indus flow Civilization, also known together the Harappan civilization. Finally, old Egyptian society developed about the productive floodplains of the Nile.
floodplains are usually really fertile farming areas. Floods bring nutrient-rich silt and sediment, and distribute it throughout a broad area. Floodplains are flat and often have relatively couple of boulders or other large obstacles that may prevent farming.
The wealthy floodplains the the Pampas, for example, space nicknamed the “Breadbasket that Argentina.” these lowlands space susceptible come floods, yet are also home to few of South America’s most financially rewarding grain farms and also cattle ranches.
A floodplain’s flat terrain and also slow-flowing rivers can administer excellent transport corridors. Roads, bridges, railways, and even airports deserve to be constructed on the even surface. Ships and barges can often haul cargo much faster and an ext efficiently 보다 roadways.
The floodplains the the mighty Mississippi-Missouri river device in the central United States, for example, have served as an important transportation corridors because that centuries. Indigenous Americans deftly navigated the floodplains, make trade between the east Coast and also West coast of north America possible. During the 19th century, cities on Mississippi floodplains—St. Louis, Missouri; Memphis, Tennessee; brand-new Orleans, Louisiana—became an important centers of culture and commerce.
floodplains are organic flooding outlets for rivers. People, agriculture, and businesses top top floodplains are constantly at some risk.
The most terrible floods that the 20th century emerged on the floodplains that the Yellow river in China, because that example. The 1931 floods were several of the worst natural catastrophes ever recorded. The 1931 Yellow flow floods adhered to years the drought the left the topsoil ~ above floodplains brittle and also eroded. Hefty rains swelled the river and also forced the to rest its banks, drowning large swaths that land together the floodplain to be unable to effectively absorb the river’s overabundance water or dissipate that is energy.
Managing development of floodplains is a crucial responsibility for local and urban planners. The services of floodplains, including prime agricultural land and desirable housing locations, should be well balanced with the an individual and financial threats make by floods.
Many flood-plain settlements maintain flood meadows and water grasslands to minimize the affect of seasonal flooding. Overwhelming meadows are natural locations of meadow immediately adjacent to a floodway. Flood meadows are frequently used together pastures for livestock when they space not saturated with water.
Water grasslands are likewise grasslands surrounding to floodways. Unlike overwhelming meadows, water meadows space created and also maintained through people. Water grasslands are continuously irrigated through networks from the river. Water grasslands were usual features the the agricultural landscape in western Europe transparent the 19th century. The nutrient-rich, silty soils the water meadows supported rich pastures supplied for livestock, and growing hay and also other fodder.
Cities constructed on floodplains, such together St. Louis or brand-new Orleans, need to incorporate flood-control infrastructure into their organization and architecture. Evacuation procedures, emergency shelters, and also building codes need to be in place. Levees or other obstacles must be a part of the city design. Metropolitan planners try to keep locations near the floodway, dubbed a unique Flood peril Area, as totally free from advance as possible.
Sometimes, citizens on floodplains should relocate entirely. The tiny town the English, Indiana, for instance, was developed on the floodplain that the Blue River, a tributary the the Ohio. Damages caused by constant floods motivated the town’s residents and businesses to relocate the town center to elevated agricultural land several kilometers away. Around 75% that English to be torn down or relocated in 1990.
In many floodplains, a massive relocation is impossible for logistical and also economic reasons. In such cases, designers can divert the course the floodway—the river—itself. Artificial floodways are a type of man-made river channel.
The Red flow floodway, for example, can divert the path of the Red River around the city area the Winnipeg, Manitoba, Canada. During flooding episodes, the channel can draw away up to 4,000 cubic meter (140,000 cubic feet) of water per 2nd before the reaches the Winnipeg area. The floodway tote this outflow around the city before rejoining the mainstem that the Red river in a less-populated area of the floodplain. Because its building and construction in 1968, the Red flow floodway has actually saved Manitoba an ext than $32 exchange rate in overwhelming damage.
In various other places, conservationists and engineers have involved in floodplain restoration. Floodplain repair is the procedure of returning a floodplain come its condition before people amendment the see for advance or agriculture. Floodplain repair may incorporate removing dikes and levees, as well as flooding formerly drained marshes and swamps.
One the the most ambitious floodplain restoration projects is underway in the lower Danube floodplains that Bulgaria, Romania, Moldova, and Ukraine. The substantial projects target to mitigate flood damage by restoring overwhelming meadows, which will absorb overfill water. Floodplain restoration jobs will also carry out habitats for endangered varieties and reduce pollution in the Danube. (Flood meadows absorb chemicals from farming and industrial runoff.)
Houses and businesses that are developed on floodplains regularly require more insurance coverage than structures constructed on higher ground, because flood damage is much more likely come occur.
A certain is a flood insurance price map. FIRMs display Special overwhelming Hazard areas within a floodplain. A special Flood hazard Area is just an area that drops within border of a 100-year flood. That company are supplied to balance the risk of flood versus the price of insurance.
FIRMs are separated into various zones based upon the zone’s proximity to the floodway. Buildings in the A- or V-zones, for example, are near the financial institutions of the river. All structures in A zones are required to have actually flood insurance as result of their incredibly high threat of overwhelming damage. The floors and service facilities of A-zone structures (such together air-conditioning units and also plumbing) must accomplish a “base high overwhelming elevation.” basic high overwhelming elevations vary depending on the floodplain and also risk do by a 100-year flood. In the Charlotte, north Carolina, floodplain, because that example, the basic high flood elevation is one foot above the intended depth of floodwater in a 100-year flood.
There space strict rule for creating or remodeling buildings in the A-zone the a floodplain. Basements in A-zones need to not be provided as living spaces, because that example.
Urban planners commonly use firms to develop a city’s land-use policies and development zones. Industrial zones, i beg your pardon can include factories v toxic chemicals, might be located much from the floodway in order to prevent contamination of a community’s source of water. Residential zones, which room more complicated to evacuate than hotel-designated zones, may additionally be more limited along a floodway. Areas closest to the floodway, in contrast, are frequently designated as “green spaces” and parks.

Floodplains usually only flood throughout the rainy season.

Photograph by chris Johns, nationwide Geographic

Exner Equation A math calculation known as the Exner equation help geologists and also hydrologists determine the level of a floodplain. The Exner equation describes the relationship in between the sediment that is transported through a river and also the sediment the is deposited by a river. The equation is conquered by the density and distribution the sediment in a river. is the change in bed elevation.

is time. is grain pack density.
is sediment flux.

The ax “floodway” is periodically used because that a road constructed at soil level top top a overwhelming plain. Floodways are usually constructed on floodplains with low traffic and also rare floods.

the art and science of cultivating land for growing plants (farming) or elevating livestock (ranching).

process in i m sorry water is intentionally filtered with the banks or flood level of a river or lake.

deposit that creates when a stream breaks its natural or fabricated levees and also deposits sediment top top a flood plain.

type that fluvial (river-formed) earthen terrace in i m sorry the flow stream erodes the material aggraded on its banks.

place where victims of natural disasters, refugees, and other civilization relocated native their houses can continue to be for brief periods of time.

person who plans the building of things, together as frameworks (construction engineer) or building materials (chemical engineer).

type that fluvial (river-formed) earthen terrace formed by the buildup of sediment on a river\"s banks.

to remove particles native a substance by pass the substance with a display or other material that catches larger particles and also lets the rest of the substance happen through.

area connecting wildlife habitats disturbed and interrupted by human activity. Likewise called a green corridor.

an event emerging naturally that has actually large-scale results on the environment and also people, such as a volcano, earthquake, or hurricane.

increase in the median reach of the ocean. The present sea level rise is 1.8 millimeters (.07 inch) per year.

person who works to produce or boost the natural, built, economic, and social atmospheres of city areas.

See more: What Are The Characteristics Of A Young River, What Are Three Characteristics Of A Young River

area that grassland alongside a river or stream, purposely flooded to keep fertility and also dissipate floodwaters.


sign up with our ar of educators and receive the latest information on national Geographic\"s resources for you and also your students.

Educational resources in your Inbox

join our community of educators and receive the latest information on national Geographic\"s resources for you and your students.