Vekseid is correct - the water returned to the sea some time after the tsunami as the city was some 5 meters above sea level. Compared to ancient times, the sea retreated at about kilometer from the original shore due to the sediments brought by the Delta of the River Nile.
Believe it or not, I have been to Leukaspis some 5 years ago - by the pictures, it does not seem that they digged a lot since then. Even so, I have to say that the pics do not show the real treasure of the city: there are some fine mosaics there, which somehow incorporate Egyptian motifs. For those interested, I think it is worth travelling from Alexandria to El Alamein.