RESERVOIRS AND DAMS
A. Trevor Hodge
This history of dams goes back very far in history, one of the earliest being the Sadd-al-Kafara dam in Egypt, 30 km south of Cairo and dated to around 2650–2465 B.C.; it did not last long before failing. Two Minoan dams, of Cyclopaean masonry and intended for irrigation, have been found at Pseira, Crete, the largest being 3 m thick, 14 m long, and preserved to 3.5 m high. Among early dams serving aqueducts we may note the efforts of the Assyrian monarch Sennacherib, who in the period 703–690 B.C. constructed no less than four dams on rivers tributary to the Tigris, to supply Nineveh.1
Nevertheless, though today the large reservoir, artificially ponded behind a dam, is one of the commonest sources of city water, this was seldom done in Antiquity, leaving the spring as the preferred source. Yet classical reservoirs and dams did exist, though their study has been somewhat neglected. Most of them have been found in the arid regions on the edges of the Roman Empire, where the need to store and conserve water was greatest: essentially this means North Africa and the Middle East (including Asia Minor), where their relative remoteness accounts for the lesser attention paid to them.
Structurally, dams could be divided into three categories: gravity dams, arch dams, and arched dams. The vast majority of dams in the ancient world were gravity dams. Essentially, these were embankments, long, low, and usually straight. Structurally, they functioned by being so massive and heavy that the water pressure pushing on one side was unable to move it. Gravity dams can be subdivided into two sub-categories: earth and masonry. An earth dam, sometimes provided with a thin stone casing to retard erosion, will usually
1 For a general survey of dams and the principles of dam-building, see Smith
1971; this is the best survey at present in the field and much of this section is based
on it. See also, for the excellent illustrations, Garbrecht 1991. A condensed account
is Schnitter Reinhardt 1979, 20–5. Middle Eastern dams are described in Forbes
1955, 160–1. Sadd-al-Kafara: Smith 1971, 1–4; Pseira: Hope-Simpson and Betancourt
1990, 322; Sennacherib: Jacobsen and Lloyd 1935.