During the 19th century, remains of an ancient harbour were found underwater at a depth of 5 to 6 metres in the eastern port of Alexandria, northern Egypt. A research programme was undertaken to determine when the harbour of Alexandria was submerged underwater.
In the study, which was recently published in the International Journal for Egyptian Archaeology and Related Disciplines, data was collected through underwater surveys by scuba diving and by coring campaigns on land.
In order to understand changes in relative sea levels during the last six millennia, the research team of French and Egyptian researchers had correlated sea level geomorphological indicators such as notches and pebble beaches, archaeological indicators such as harbour structures, and biological indicators such as marine macrofauna, bioconstructions, and bio depositions.
Findings of the study indicate that the rate of the relative sea level rise is about 80 mm per century between the middle of the sixth millennium and the 5th‒6th c. AD. An abrupt relative sea level rise (3.5m + 1.5 m) occurred during the mid 8th c. to the end of 9th c. AD. In the 8th c. AD, a similar phenomenon was observed for Heracleion (25 km east of Alexandria).
Thus, a wide movement of sinking affected in a synchronous manner the western coastal margin of the Nile Delta. Since this 8th- 9th c. AD event, the subsidence has increased around 2m. The role of abrupt sinking events and subsidence remain determining in the deltaic context to anticipate future coastal adaptations and the risk of submersion.
First author of the study Jean-Philippe Goiran told Daily News Egypt that the result of the paper “is important for two main reasons: First, it is answering a very old question. Indeed, during the 19th century, remains of the ancient harbour structures of Alexandria were found underwater at a depth of 5 to 6 metres in the eastern port of Alexandria.”
In regard to the question of when did this ancient harbour structure collapse occur? Goiran said that in the 8th c. AD, a similar phenomenon was observed for Heracleion (25 km east of Alexandria). Thus, a wide movement of sinking affected in a synchronous manner the western coastal margin of the Nile Delta.