A strand plain is a broad, shore‑parallel sand belt directly attached to the mainland whose surface is dominated by well‑defined, parallel or semi‑parallel sand ridges separated by shallow swales. This ridge‑and‑swale morphology is characteristic of shoreface accretionary systems and records repeated episodes of lateral accretion, migration and episodic reworking by storms and normal wave climates.
Morphologically and hydrologically a strand plain differs from a barrier island system because it lacks the intermediary water bodies and tidal networks (lagoons, tidal marshes) and the tidal inlets that isolate barrier islands from the mainland. As a consequence, the sand body of a strand plain remains contiguous with the adjacent shoreline rather than forming a detached chain of islands.
Strand plains principally form through coastal reworking processes: waves and longshore currents redistribute coarse sediment delivered to the coast, commonly concentrating and sorting sand on either side of river mouths. For this reason strand plains are interpreted as part of the continuum of wave‑dominated deltas. Their sedimentary composition is typically coarse sand mobilized by alongshore drift and wave action; the stacked ridge units are a stratigraphic record of successive accretionary pulses and lateral migration.
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Strand plains can persist over long intervals under appropriate coastal conditions. Historical evidence, for example, indicates a strand‑plain configuration in the Western Netherlands by about 100 AD, demonstrating their development during Holocene–late Holocene transgressive and progradational phases.
Strand plains occur worldwide on wave‑dominated, high‑energy shorelines often adjacent to river mouths. Representative mapped examples include the Caravelas strandplain (Bahia, Brazil), Western Louisiana and Eastern Texas (USA), the west coast of Namibia, southeast and southwest Australia and the Gulf of Carpentaria (Australia), Letea and Caraorman in the Danube Delta (Romania), Kustvlakte (Suriname), and Cayo Costa (Florida, USA).