Nha Trang Bay is an embayment at the mouth of the Cai River on the central coast of South Vietnam. The river is the principal source of sediment to the coastline, but intertidal reefs provide minor amounts of calcareous sand, and the continental shelf supplies some coarse quartz sand. The sediment supply to the coast and its distribution in Nha Trang Bay are closely related to the monsoon climate of the region. Northeast monsoons cause intense rainfall and runoff, combined with a unidirectional wind field causing strong southerly coastal currents. Most of the river sediment enters Nha Trang Bay during monsoons, and the sediment distribution reflects the monsoonal wave and current regime. Approximately one-fourth of the river-supplied sand enters the Nha Trang beach littor l cell, where it is transported south along the coast. Thus, the present configuration and orientation of Nha Trang beach are related also to monsoonal wave conditions. This pattern of sediment dispersion appears to have persisted during the Holocene still-stand of sea level, causing the accretion of an extensive beach-ridge coastal plain south of the river mouth. Similar orientation of the ancient beach ridges suggests that monsoonal waves have been the predominant factor in the development of the coastal plain.

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