Strait of Euripus

The Euripus Strait (Greek: Εύριπος[ˈevripos]) is a narrow channel of water separating the Greek island of Euboea in the Aegean Sea from Boeotia in mainland Greece. The strait's principal port is Chalcis on Euboea, located at the strait's narrowest point.

The strait is subject to strong tidal currents which reverse direction approximately four times a day. Tidal flows are very weak in the Eastern Mediterranean, but the strait is a remarkable exception. Water flow peaks at about 12 km/hour, either northwards or southwards, and lesser vessels are often incapable of sailing against it. When nearing flow reversal, sailing is even more precarious because of vortex formation.

The Swiss scholar François-Alphonse Forel contributed to an understanding of the enigmatic phenomenon by his study of limnology and the discovery of seiche, where layers of water of differing temperature oscillate in thickness in a confined body of water. But the problem was solved completely only by D. Eginitis, director of the Athens Observatory, who published his conclusions in 1929.

There are two road bridges across the strait, both at Chalcis. One is the Euripus Bridge or Chalcis Bridge, a two-pylon, cable-suspended bridge built south of town in 1992, and commonly called the "New" or "High" bridge, with a span of about 215 m (705 ft). The strait is 160 m (525 ft) wide at this point. The bridge is accessible via a fork on the main road at Aulis.

The "Old" or "Low" or "Sliding" Bridge lies across midtown, and can slide away to allow shipping traffic. It is located at the narrowest point of the strait, where it is only 38 m (125 ft) wide. It accommodates two lanes of vehicular traffic. It was originally built as a retractable bridge in 1858, replaced by a rotating one in 1896. The existing, originally wooden bridge was built in 1962 and was extensively refurbished in 1998.

The current consensus is that the Euripus was closed by a dike of coarse sediment until about 6000 years ago. It was opened following an (unrecorded) earthquake and remained open (see Herodotus, e.a. VII.173 and VIII.66, on the sea-battle of Artemision) until 411 BC, when the Euboeans decided to renounce their status as an island subject to Athenian hegemony and make themselves part of Boeotia (Diodorus Siculus, Bibliotheca Historica, 13.47, sections 1-8). (There is no trace of this either in Thucydides or in Xenophon (in History of the Peloponnesian War and in Hellenica respectively.) Diodorus mentions specifically that gaps had to be left in the dike to allow the Euripus tides to flow through and that the current became much more intense owing to the narrowness of the passage and says that a single passage was left just wide enough for a single ship. Strabo (IX.2.2) wrote of some later time when there was a bridge two plethra long (approximately 50 m, which is probably an exaggeration). Some vestiges of the two ends of the dike of 411 probably remained, so that this later bridge was probably narrower than the channel that existed before 411 BC. We have no information about the depth, but even in the case of a channel about 50 m wide under Strabo’s bridge, the depth could have been scoured out to a level entirely sufficient for ancient shipping.

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