Floodplain

Floodplain Development

Along the longitudinal river profile, tectonic interventions contribute to the formation of floodplains, creating different channel densities and patterns that influence hydraulic connections between lotic and lentic water bodies. Tectonic deformation of a river course leads to raised and subsided blocks displaying different hydrologic patterns (see A and B in Figure 2). Uplift blocks develop large and small lakes, whereas subsided blocks display complex anastomosing drainage patterns with a lot of irregular interconnected lakes.

Base level and climate changes to some extent influence floodplain development. The base level at the coast or valley mouth controls the upstream extent of horizontal and vertical channel migration, creating a landmass that can contain seasonal overbank flow and sediment deposition. Floodplain development is stabilized if there is a final standstill of the base level.

The scientists Wolman and Leopold proposed in 1957 a model of floodplain formation based [Page 1129][Page 1130]on geomorphologic reasoning and observation of streams. A floodplain is constructed entirely of horizontal layers of fine-grained sediments interrupted by coarse-grained channel deposit. It is dominated by braids and meanders migrating back and forth over the valley floor, leaving behind a sandy bar deposit.

The setting sun glints off the Amazon River and numerous lakes in its floodplain in this astronaut photograph from August 19, 2008.

Source: NASA.

Landsat 7 image showing floodplain of a section of the White Volta River in Ghana

Source: Author.

Figure 1 Floodplain and its related features

Source: Retrieved from http://www.geog.unt.edu/mcgregor/1710index.html. Redrawn by J. M. Insaidoo.

Satellite image showing land use in the floodplains of the Nile River (A) and the Mississippi River (B)

Source: Author.

According to Nevidimova, floodplains are formed due to the simultaneous horizontal and vertical displacement of the river channel. A displaced river in a horizontal plane leaves behind a low surface that gets inundated during high waters but changes with time.

Types of Floodplains

Geomorphologically, two types of floodplains can be distinguished, namely, hydrological flood-plains and topographic floodplains (Figure 3). A hydrological floodplain is the land adjacent to the base flow channel residing below the bankfull elevation, which is inundated once every year. Not every stream has such a floodplain. A topographic floodplain is the land adjacent to the [Page 1131][Page 1132]channel, including the hydrologic floodplain and other land up to an elevation base reached by a flood peak of a given frequency.

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