Misconceptions for Risks of Coastal Flooding Following the Excavation Of
Total Page:16
File Type:pdf, Size:1020Kb
N° 108 - 2007 37 Misconceptions for risks of coastal flooding following the excavation of the Suez and the Corinth canals in antiquity Méconnaissance des risques de submersion littorale et creusement des canaux de Suez et de Corinthe dans l’Antiquité Stathis C. STIROS Department of Civil Engineering Patras University Patras 26500, Greece e-mail: [email protected] Abstract - During antiquity, numerous attempts were made to excavate Résumé - Durant l’Antiquité, de nombreuses tentatives ont été effectuées canals through the Suez (Egypt) and the Corinth (Greece) isthmuses, but these afin de percer les canaux de Suez (Egypte) et de Corinthe (Grèce). Elles se sont projects were never completed. The main explanation provided by historical toutes soldées par des échecs. La principale raison retenue par les sources sources is the risk of flooding of coastal areas by water flowing through these historiques est la question des différences de niveau marin de part et d’autre canals, since an up to 10 m difference was assumed to exist at their inlets. des isthmes qui furent évaluées jusqu’à 10 m. Par conséquent, les Anciens Obviously, such considerable elevation offsets which would also render the craignirent d’établir des canaux non praticables du fait de l’importance des canals non-navigable due to a continuous flow of water, reported to derive courants et d’inonder les zones basses adjacentes. Il semblerait que tous from leveling measurements. Examination of the evidence reveals that such ces risques ont été volontairement exagérés par les détracteurs des canaux. large errors in ancient geodetic surveys are unlikely, but there exist important Certains notables ont vraisemblablement profité de l’abandon des différents differences in the tidal ranges and the coastal environments on either side of projets. Les deux canaux ne seront finalement percés qu’au XIXe siècle. the two isthmuses. It appears therefore that the impacts of minor water flow Depuis leur ouverture, les canaux fonctionnent normalement et témoignent from one side of the canal to the other, observed in the modern canals, were de l’absence notable de différence de niveau de la mer de part et d’autre de exaggerated during antiquity by detractors (especially the risk of flooding), leurs embouchures who eventually succeeded in getting the projects abandoned. 1 - Introduction suggest that the plans for such impressive works were mostly abandoned because geodetic studies revealed a 10 m difference in sea-level elevation at their inlets. In light of this, it was hypothesized that excavation of both canals would lead to flooding of the low-lying coasts, while the expected continuous flow of water from one inlet to the other would hinder ship navigation. This postponed the construction of the canals until the nineteenth century; since this time the canals operate without locks, confirming the absence of significant sea-level differences (LEWIS, 2001). Such gross errors in leveling appear surprising, given that engineers in ancient Greece and Egypt were notorious for their mastery of surveying techniques. These skills are for instance epitomized first by the ~1000 m long tunnel of Eupalinus (Samos Island, Aegean Sea), successfully excavated in ~540 BC (KIENAST, 1995), and second, by qanats. The latter, widespread in the Middle East and not uncommon in the Mediterranean, Fig. 1 - Location map. are underground sub-horizontal water channels up to tens of Fig. 1 - Carte de localisation. kilometers long, excavated at the bottom of deep wells (ENGLISH, 1998; STIROS, 2006). STIROS (2006) has shown that ancient During antiquity, a number of major engineering works, surveyors were able to obtain high accuracies in leveling. requiring high technical and geodetic s����������������������kills, was undertaken. This makes geodetic errors unlikely for the Suez and Corinth These included projects to build the Suez canal in Egypt and canals. In light of this, we re-evaluate the available information the Corinth canal in Greece (Fig. 1), both eventually completed concerning the early history of these two canals, and try to during the nineteenth century. The reasons for the failure of shed some light on the real causes of their abandonment in the projects were not a lack of funding, changes in the political antiquity, as well as on the misconceptions for the threat of situation, or unresolved technical problems. Historical sources coastal flooding following their excavation 38 2 - The suez canal up to foreign invasion. Pliny also noted that some feared contamination of freshwater reserves by saline Red Sea water (Pliny, Natural History VI 33). For these reasons only the part of the canal from the Nile to the Bitter Lakes, 34 miles long, was completed (Fig. 2). Inscriptions on �������������������a number of granite stelae state that “I ordered the canal to be dug up from the River called Pirava (the Nile), which follows in Egypt to the sea that comes out of Persia (The Red Sea)” and suggest that the canal to the Red Sea was completed by Darius. In reality, it appears that the connection between Bitter Lakes and the Red Sea was made over land, using camels and horses. This interpretation is supported by the fact that a canal was excavated in the area �����������������������������������������during the Ptolemaic (Hellenistic) period ~270 BC, with the construction of a lock to counteract the expected flow of water. The town of Arsinoe was founded at the canal’s inlet, near present-day Suez���������� (��������Fig. 2). The ancient canal was repaired by the Roman emperor Trajan ~100 AD, and was extended to meet the main branch of the Nile Fig. 2 - Location map of the Suez canal area. Names in italics denote ancient near Cairo (Fig. 2). It remained navigable until the 3rd century sites. Dashed lines with numbers in circles indicate partially excavated AD, while repairs were made to the southern branch between sections of the ancient canal during 1: Pharaonic and Persian times (up to 500 BC); 2: Hellenistic times (~270 BC); 3: Roman times (~100 AD). the Bitter Lakes and Suez. The exit of this canal was not at Fig. 2 - Carte de localisation de la région du canal de Suez. Les noms en Arsinoe, but a few kilometres to the west. The Roman canal italique correspondent aux sites antiques. Les pointillés avec des cercles soon silted up, but was again re-opened in the seventh century localisent les secteurs creusés durant : 1. Périodes pharaonique et perse (jusque vers 500 avant J.-C.) ; 2. Période hellénistique (vers 270 avant J.-C.) ; AD by Amr ibn al-Aas, the Arab conqueror of Egypt, and 3. Période romaine (vers 100 après J.-C.). came to be known as the “Canal of the Commander of the Believers to the God.” Amr ibn al-Aas planned its extension The present-day Suez canal, completed in 1869, represents a to the Mediterranean, but his project was dropped on military system of artificial water channels and lakes along the isthmus grounds (the fear that it would facilitate invasions), and for connecting Asia and Africa, and separating the Red Sea from these reasons the canal was closed in 776 AD. the Mediterranean. The isthmus is about 160 km long, of low Shortly after the opening of marine routes around Africa in elevation and flat-topped (Fig. 1a) and has been formed by Late the fifteenth century, the Venetians drafted the first modern Quaternary tectonic uplift (cf. JACKSON et al., 1988; GVIRTZMAN, plans for a Suez canal to shorten the distance to India; work 1994). was resumed by Napoleon around 1800. Yet again, however, his engineers estimated a 10 m elevation difference between 1.1 - Historical and archaeological background the Red Sea and the Mediterranean. The result was debated by The construction history of the Suez canal is unclear, but Fourier and Laplace, famous mathematicians and physicians has been summarized by various authors (e.g. MARLOWE, 1964; of the period, but nonetheless served as a catalyst to the LEWIS, 2001). Plans for a navigable channel in this region are abandonment of Napoleon’s project. Interestingly, parts of the very old, with ancient reports and archaeological remains ancient canal were used as an aqueduct bringing fresh water for indicating that an early canal had been excavated in the isthmus the workers and the engineering works during the construction 2-3,000 years ago. of the modern canal (MARLOWE, 1964; LEWIS, 2001). The first historical report is that of Aristotle Meteorologika( 353b), the famous fourth century BC philosopher, who 1.2 - Reconstructing the history of the ancient reported that Pharaoh Seti (or Sesostris, around 1300 BC) canal and the Persian king Darius, who occupied Egypt in circa The available historical, archaeological and geomorphological 500 B C, tried to excavate a canal similar to the present-day data allow us to suggest that the geomorphology (a low-altitude, one. Their projects were, however, abandoned due to fears over flat area) and the geology (soft Quaternary and Holocene freshwater contamination by saline water caused by flow of sediments) of the Suez isthmus facilitated early plans for an saline water due to altitudinal differences between the Red Sea irrigation channel between the eastern (Pelusiac) branch of the and the Mediterranean. Interestingly, a channel mentioned in Nile near the town of Bubastris, to the swampy area of Lake an inscription at Karnak, dating from Pharaoh Seti’s reign, is Timsah and the Great Bitter Lake (Fig. 2). This was a sizeable usually taken as evidence of an early Suez canal. task for, as can be seen in the satellite photo (Fig. 3), the Around 100 AD, the Greek historians Diodorus Siculus channel was to be excavated along stable, low-elevation ground (Historical Library 1, 33.9-10), Strabo (Geography XVII 1.25) following an E-W trending abandoned branch of the Nile River and the Roman historian Pliny (Natural History VI 33), probably (Wadi Tumilat) flowing into the Red Sea.