USE OF REMOTE SENSING AND GIS IN THE RECONSTRUCTION OF COASTAL PALEOGEOGRAPHY OF ALEXANDRIA, EGYPT

• A. Chalari, D. Christodoulou, G. Papatheodorou, M. Geraga, A. Stefatos, G. Ferentinos (Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 261 10 Rio-Patras, Greece)

The ancient city of Alexandria was one of the greatest ports of the Eastern Mediterranean, which now consists an area of great archaeological interest. The coastal zone of Alexandria hosts the ruins of one of the seven wonders of the ancient world, the famous Pharos, as well as many others ancient and historical monuments and shipwrecks.

In October of 1999 the Laboratory of Marine Geology and Physical Oceanography of the University of Patras carried out a marine geophysical survey in the coastal zone of Alexandria. Six scientific missions were carried out from that year until October 2002. The former three in partnership with the Greek Institute of Ancient and Medieval Alexandrian Studies from Cape Lochias to Stanley bay and the later three in partnership with the French Centre D'Etudes Alexandrines (CEA) under the directionship of Jean-Yves Empereur at the northern of the Qait Bay were the ancient Pharos used to stand.

High-resolution subbottom geophysical surveys were conducted utilizing a 3.5kHz sub-bottom profiling system and a side scan sonar surveillance utilized a dual-frequency EGandG 272 TD system. Survey navigation was provided by a single and differential global positioning system (DGPS), with an accuracy of ±15m and ±1m, respectively. An area of approximately 32.5km² was surveyed between Stanley Bay and Fort Qait Bay at the coastal zone of Alexandria.

The first goal of this survey was to reconstruct the coastal paleogeography of the Alexandria by examination of the geophysical data using GIS-ArcView. The second goal was the detection and recognition of ancient and historical shipwrecks and submerged man-made structures. A detailed sea-floor geomorphological map was constructed, showing that the seafloor is covered by rocks and loose sediments. The rocks cover about 65% of the surveyed area and locally form elongated ridges, which are running parallel to shoreline. The loose sediments consist of sand and sandy-mud. The sandy cover on the seafloor is well rippled by the waves. A GIS-ArcView system was used to incorporate both seafloor map and bathymetric data. This combined with the extend of paleoshorelines, which were detected by the subbotttom profiler, reveals a quite accurate reconstruction of the coastal paleogeography of ancient Alexandria.

A total of over 60 targets of potential archaeological interest were detected during the sonar survey. The 26 of those targets were visually inspected by the divers of the CEA and the results of the visual inspection has shown that the 62% of the targets were man-made objects with no archaeological interest, the 23% of the potential targets were natural features, the 3% need re-examination, the 12% were not found by the divers. However the visual inspection revealed that target number 23 is a shipwreck.