This may be later followed by a river flood as water moves away from the areal floodplain into local rivers and streams.

Various computational flood models have been developed in recent years ; either 1D models ( flood levels measured in the channel ) and 2D models ( variable flood depth measured across the extent of the floodplain ).

Other models such as TUFLOW combine 1D and 2D components to derive flood depth across the river channel and floodplain.

In other words, a floodplain is an area near a river or a stream which floods when the water level reaches flood stage.

Wetting of the floodplain soil releases an immediate surge of nutrients: those left over from the last flood, and those that result from the rapid decomposition of organic matter that has accumulated since then.

The extent of floodplain inundation depends in part on the flood magnitude, defined by the return period.

Where a detailed study of a waterway has been done, the 100-year floodplain will also include the floodway, the critical portion of the floodplain which includes the stream channel and any adjacent areas that must be kept free of encroachments that might block flood flows or restrict storage of flood waters.

When a floodway is shown on the Flood Insurance Rate Maps, the portion of the 100-year floodplain outside of the floodway is known as the flood fringe.

This floodplain map figures very importantly in building permits, environmental regulations, and flood insurance.

The Isle of Dogs is formed from the lock entrances to the former West India Docks and the largest current meander of the River Thames and the southern part of the borough forms a part of the historic flood plain of the River Thames ;< ref >< cite > BBC on Thames floodplain.

" Old Leavenworth " ( the original town, now practically abandoned ) was almost completely wiped out by the huge 1937 Ohio River flood, as it was built directly on the floodplain.

Following the great flood of 1785, the town moved from its initial location on the floodplain of the Mississippi River, to its present location two miles north and about a half mile inland.

This is partly because the Luapula drains out of the Bangweulu Swamps and floodplain which tend to regulate the water flow, absorbing the annual flood and releasing it slowly, and partly because Mweru's outlet, the Luvua, drops quickly and flows swiftly, without vegetation to block it.

Valley bottoms are smooth, and flood deposits created during and since the most recent Glacial period cause floodplain soils to be very productive.

Located around a hill in the southern part of the Vale of Clwyd-the older part of the town, the castle and Saint Peter's Square are located on top of the hill, while many newer parts of the town are on the floodplain of the River Clwyd ( which became apparent on several occasions in the late 1990s — new flood control works costing £ 3 million were inaugurated in autumn 2003 ).

Since 2000, the Lower Balonne floodplain in northwest New South Wales has not received enough water to flood the plains as it once did every two or three years.

The 3, 400 km < sup > 2 </ sup > floodplain of the lower reaches of the Diamantina has been identified as an Important Bird Area by BirdLife International because it has been estimated to support at least 450, 000 waterbirds when in flood, as well as globally significant numbers of the Nankeen Night-Heron, Royal Spoonbill, Little Curlew, Australian Bustard, Grey Grasswren, Inland Dotterel, Cinnamon Quail-thrush and Pied Honeyeater.

Between Retford and Bawtry, the floodplain is partly occupied by a number of sand and gravel pits, while beyond Bawtry, the river is constrained by high flood banks, to allow the low lying areas to be drained for agriculture.

It flows for 480km into the Bangweulu Swamps, which are part of Lake Bangweulu, and by the end of the rainy season in May, it delivers a flood which recharges the swamps and inundates a vast floodplain to the southeast, supporting the Bangweulu Wetlands ecosystem.

** Alluvial plain, formed over a long period of time by a river depositing sediment on its floodplain or bed which becomes alluvial soil.

The difference between a floodplain and an alluvial plain is that the floodplain represents the area experiencing flooding fairly regularly in the present or recently, whereas an alluvial plain includes areas where the floodplain is now and used to be, or areas which only experience flooding a few times a century.

Among the unique natural features that remain in the watershed are prairie fens, coastal plain marshes, bogs, floodplain forests, hardwood swamps, and moist hardwood forests.

A floodplain is part of the process, being the smaller area over which the rivers flood at a particular period of time, whereas the alluvial plain is the larger area representing the region over which the floodplains have shifted over geological time.

The Oder's floodplain was already saturated by the spring thaw, but German engineers also released water from a reservoir upstream, which turned the plain into a swamp.

When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain.

The glass pavilion is raised six feet above a floodplain next to the Fox River, surrounded by forest and rural prairies.

Irrigation is widely used, and marshlands in the Danube's floodplain have been diked and drained to provide additional tillable land.

It is usually earthen and often parallel to the course of a river in its floodplain or along low-lying coastlines.

The upper Nera cuts ravines in the mountains ; the lower in the Chiascio-Topino basin is in a fairly large floodplain.

Referring to the floodplain as a lake may be misleading, as less than half of Lake Chad is covered by water through an entire year.

Benalla is situated on a mostly flat floodplain of the Broken River catchment situated directly to the north and west of the Great Dividing Range.

Lewes Brooks, also of biological importance, is part of the floodplain of the River Ouse, providing a habitat for many invertebrates such as water beetles and snails.

Aggradational floodplain: This floodplain of a small meander ing stream in La Plata County, Colorado, is underlain by silt deposited above a dam formed by a terminal moraine left by the Wisconsin glaciation | Wisconsin Glacier.

The floodplain during its formation is marked by meandering or anastomotic streams, ox-bow lakes and bayous, marshes or stagnant pools, and is occasionally completely covered with water.

When the drainage system has ceased to act or is entirely diverted for any reason, the floodplain may become a level area of great fertility, similar in appearance to the floor of an old lake.

The floodplain differs, however, because it is not altogether flat.

The largest swamp in the world is the Amazon River floodplain, which is particularly significant for its large number of fish and tree species.

The Ochils meet the flat carse ( floodplain ) of the River Forth to the east of the distinctive geographical feature of Abbey Craig, a crag and tail hill upon which stands the 220 ft ( 67m ) high Wallace National Monument.

The western part of the county on the Mississippi River is part of the American Bottom floodplain, while the eastern portion of the county is relatively flat and was originally prairie.

Since it was a floodplain the area is relatively flat and the soil is mainly clay with layers of sand and gravel underneath.

However, the current downtown area – the original site of Manhattan – was built on a broad, flat floodplain at the junction of the Kansas and Big Blue rivers.

Genevieve grew slowly due to its location on a muddy, flat, floodplain, and in 1752, the town had only 23 full-time residents.

* Fluvial ( stream or river ) terrace, natural, flat surface or surfaces that border ( s ) and lies above the floodplain of a stream or river.

The little arable land that did exist was mostly within the river's floodplain, and in many places there was only a narrow strip of flat ground that would soon run against vertical cliffs or dense forests with rocky soil.

Below the horseshoe bend the Hoh River begins to meander widely through a broad and flat floodplain.

Unable to disgorge into the sea quickly enough, the river frequently overflows its banks and spreads across the flat land of its lower reaches, creating a huge floodplain.

In the early 19th century a straight road was built on the flat ground of the carse or floodplain to by-pass the old Hillfoots Road and improve the transport of goods to and from the Hillfoots villages.

The area of the municipality is flat and marshy as the entire southern section belongs to the floodplain of the Sava.

The northern of these two flat areas surrounded the floodplain of the Water of Leith, a small river that runs through Dunedin.

The whole region is flat and sandy, with the dry land generally no more than 50 m higher than the floodplain.

Their territory is divided up into West, East and Fly areas and the Gogodala occupy mostly the flat terrain and the floodplain areas.