Vespasianus Titus Tunnel
Vespasianus Titus Tunnel built during the Roman period is located within the boundaries of the Ancient City of Seleuceia Pieria (Figure1). The antique city Seleuceia Pieria is situated near the actual village Cevlik, 35 km to the southwest of Antakya (the historical city Antioch on the Orontes), at the foot of Nur mountains in eastern Mediterranean coast in Turkey. Seleuceia Pieria was founded towards the end of the 4.century B.C. by Seleukos Nikator I, one of the generals of Alexander the Great. The city was reigned by the Ptolemeans during the second half of the 3.century B.C., and flourished later during the Roman period, beginning in the second half of the 1.century A.D., and became one of the most important ports of the Eastern Mediterranean Region. The upper city is separated from the lower one by steep rocky topography. The lower city, surrounded by fortification walls totaling 12 km, has been developed around the harbour of 16 hectares area.
Since the city was under the threat of the floods descended from the mountains and flowed through the city and the harbour was silted up and became inoperative, the Roman emperor, Vespasianus ordered to build a tunnel by digging the mountain in order to divert the floodwaters threatening the harbour. The diversion system was built with the principle of closing the front of the stream bed with a deflection cover and transferring stream waters to the sea through an artificial canal and tunnel.
The construction began in 1. century A.D. during the reign of the Roman emperor Vespasianus (69-79 A.D.), continued under his son Titus (79-81 A.D.) and his successors, completed in 2.century A.D. during the reign of another Roman emperor, Antonius Pius. A rock-carved inscription at the entrance of the first tunnel section bears the names Vespasianus and Titus, another inscription in the downstream channel that of Antonius.
The diversion system, displaying a broken alignment, consists of: a dam to divert the river flow; a short approach channel; the first tunnel section; a short intermediary channel; the second tunnel section; a long discharge channel.
The dam to divert the creek flowing into the harbour is a masonry structure of 16 m height, 5 m crest width and 49 m crest length; rising to elevation 44,30 m above sea level. The damming is completed by a shallow embankment of 126 m length towards the upstream direction.
The diversion begins with a 55 m long approach channel, converging to the entrance of the first tunnel section. This is a rectangular open channel, excavated in the karstified limestone formation.
First tunnel section
The first tunnel section, designated as tunnel I, has a simple horseshoe cross-section of 6.3 m width and 5.8 m height at the entrance (Figure.2), being 90 m long. The cross-section changes to an almost rectangular shape three meters after the entrance; and is 6.9 m wide and 6.5 m high at the outlet.
The width of the open channel between the first and second tunnel sections decreases to 5.5 m. The height of this 64 m long channel reaches up to 25-30 m and becomes narrower close to the surface, because of former karst solution channels encountered along its alignment.
Second Tunnel Section
The second tunnel section, designated as tunnel II, is 31 m long. Its entrance has a rectangular cross-section with 7.3 m width and 7.2 m height; the outlet is trapezoidal with 5.5 m base width and 7.0 m height (Figure.3). The total length of the two tunnel sections amounts to 121 m. There is a small rock-cut spring water conveyance channel of 0.4 m width and 0.3 m height on the left wall of the tunnels. Shortly after the outlet of the second tunnel section, there is an arch of a bridge, or rather an aqueduct, of 4.5 m height and 5.5 m span width, crossing the channel.
The open channel serving as the main discharge conduit, following the outlet of the second tunnel section, displays rectangular cross-sections excavated in karstified limestone formations. The widths vary from 3.8 to 7.2 m, the heights from 3.7 to 15 m. The discharge channel is 635 m long; so that the total length of the diversion system is around 875 m.
Hydraulic capacity of the system
The hydraulic capacity of the diversion system is computed as about 70 m3/s, based on determination of water surface levels through step-by-step integration. The hydraulic capacity of the tunnel sections is almost twice of the system, about 150 m3/s.