Many drowned river valley estuaries were formed between about 15,000 and 6000 years ago following the end of the Wisconsin (or 'Devensian') glaciation when a eustatic rise in sea level of 100 m to 130 m, flooded river valleys that were cut into the landscape when sea level was lower, creating the estuarine systems. Additionally, the general subsidence of coastal regions contributed to the development of drowned river valleys. Well developed drowned river valleys are generally found on coastlines with low, wide coastal plains. Their width-to-depth ratio is typically large, appearing wedge-shaped in the inner part and broadening and deepening seaward. Water depths rarely exceed 30 meters. Examples of this type of estuary include the Chesapeake Bay and Delaware Bay, along the U.S. mid-Atlantic coast, and along the U.S. Gulf coast, Galveston Bay and Tampa Bay[4].
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