ABSTRACT
Dalrymple et al. (1992) define an estuary as ‘… the seaward portion of a drowned valley system which receives sediment from both fluvial and marine sources and which contains facies influenced by tide, wave and fluvial processes.’ Modern estuaries first developed when coastal river valleys were flooded at the end of the last postglacial marine transgression. Sea level stabilized around 6,000 years before present, and since that time estuaries have been infilling. Estuaries that received a large sediment influx relative to their accommodation space during the Holocene have completely infilled and are now prograding as coastal deltas (Chapter 6). Estuaries that received a more modest sediment supply still have accommodation space and are continuing to infill. Sediment enters an estuary from both the land (river) and the sea (waves and tides). The fundamental difference between deltas and estuaries is that, averaged over many years, the net sediment transport in deltas is seaward whereas in estuaries it is landward. Deltas are progradational systems that are presently extending the coastline, whereas estuaries occupy coastal embayments that are presently infilling.
