Definition

A delta plain is a low-elevation floodplain formed at the mouth of a river.

Characteristics

A delta plain is one type of low-lying coastal plain, formed where a river empties into the sea (or, rarely, into a freshwater body, as in the case of the Selenga Delta, Figure 1a). Large deltas can generally be subdivided into an upper deltaic plain influenced primarily by fluvial processes and a lower deltaic plain, dominated by wave and tidal processes (Figure 1b). The river flows through the “active” section, but there is commonly an abandoned section containing paleochannels marking former river courses (Wright et al., 1974).

Delta Plain, Figure 1
figure 41figure 41

(a) The Selenga River, draining into Lake Baikal, has bifurcated into numerous distributaries that dissect delta plain wetlands (Source Google Earth, © DigitalGlobe); (b) the principal components of a large delta plain, for example, (c) the Red River Delta plain (After Woodroffe and Saito, 2011); (d) the extensive plains flanking the Tuross River, as it drains into a barrier estuary in southeastern Australia, are much better developed than those where a smaller creek empties into Coila Lake, a coastal lagoon (Image: © Commonwealth of Australia, ACRES, Geoscience Australia).

Full size image

The Red River Delta in northern Vietnam (Figure 1c) can be differentiated into a river-dominated upper delta plain where channels are flanked by levées and meander scroll bars marking former river courses, a southern wave-dominated section with sequences of shore-parallel beach ridges, and an eastern tide-dominated section with numerous tapering tidal creeks (Mathers and Zalasiewicz, 1999).

Similar near-horizontal alluvial plains can form along estuaries, sometimes called deltaic-estuarine plains. For example, coastal lagoons (e.g., Coila Lake, Figure 1d) and barrier estuaries (e.g., Tuross Lake) become gradually infilled as fluvial sediment builds a bayhead delta into the estuarine basin.

Extensive, perennially or seasonally flooded, wetlands may characterize delta plains in their natural state (Figure 1a). Megadeltas in southeastern Asia are often the location for intensive rice cultivation, but also support megacities (e.g., Hanoi, Figure 1c), many of which require augmentation of levées for flood mitigation. The ease with which land can be cleared and the fertility of soils has encouraged their agricultural use (e.g., Figure 1d).

Cross-references