• Adrian J. Boas

On Moving Rivers

Diversion Tunnel in the Kidron Valley [Photograph courtesy of Jon Seligman and The Israel Antiquities Authority]

Returning home from six years of war service in the Australian Infantry, my father, an engineer by trade, found work on the Tarrago River Scheme in west Gippsland, Victoria. He designed a means of diverting the flow of the small perennial river by the construction of a concrete tunnel, a siphon and an open concrete channel. It was one of several projects carried out with the aim of preventing flooding by directing the flow of the river through a series of urban concrete culverts before it emptied into Western Port Bay east of Melbourne. Prior to these changes the flooding of the Tarrago River had caused the formation of the extensive swampland north of the bay that prevented the use of what was particularly fertile farmland. The drainage projects enabled the successful development of the region.

The Frankish settlers in the Latin East carried out numerous urban and rural projects similarly aimed at improving natural conditions and enabling development. These involved the construction of channels for sewage disposal, river diversions, dams, artificial lakes, pools and aqueducts. In Acre the Hospitallers constructed a sophisticated subterranean sewage system, and outside the city major earthworks were carried out to divert the natural outlet of the Belus River and redirect it via an artificial channel into the eastern moat of the city. Elsewhere streams were dammed in order to divert water. Below Montfort Castle a dam was constructed across the Keziv stream. It created a large artificial lake and water from the lake was carried via an aqueduct to the adjacent mill where it powered two mill wheels. A dam was constructed in the Hinnom Valley outside the western wall of Jerusalem to create a reservoir known as Germain's Pool. Aqueducts were built in many places in order to carry water from streams or springs to cisterns and open pools in castles and settlements. These were intended to provide drinking water or water for agricultural or industrial purposes. Aqueducts such as the large one to the south of the city of Tyre provided water for irrigating the sugarcane fields. Reservoirs were constructed in villages such as Magna Mahumeria (al-Bira) north of Jerusalem or Khirbat Lowza or the road west of the city.

Perhaps the most interesting water diversion scheme was carried out in Jerusalem itself, or, to be more precise, just outside the city walls to the east in the Kidron Valley. In 1998 archaeologists discovered and exposed the well-built barrel-vaulted structure, 32.9 metres long and 5.9 metres wide, running east-west across the valley. Twenty shafts were constructed on the northern side of the vault to collect water from the stream known in the Middle Ages as the Torrens Cedron and to channel it into the vault through which it was diverted to a position further to the west where it was released. This was important because the stream's natural flow led directly to one of the holiest churches of the city, the Church of the Tomb of the Virgin which stood at the very base of the valley, and to its focal point, the underground tomb monument of the Virgin Mary. The church was a major pilgrim site, visited by virtually everyone who arrived in Jerusalem. It was also the location of the tomb of Queen Melisende and it served the adjacent community of Benedictine monks. Without this diversion it would be exposed to frequent and devastating flooding, as indeed was the case both before it was built and after it had fallen into disrepair in the thirteenth century. Indeed, a more recent attempt to alleviate the problem of flooding to the church was what led to the discovery of this remarkable medieval structure.