IRRIGATION SYSTEMS

We are concerned here with the engineering elements in the two related technologies of irrigation and water-supply. Indeed, so closely are they related that several of their constituents are identical. This applies to the main arteries bringing water to the distribution networks – canals and qanats – and to the methods of impounding and storing the water. As we shall see, the same arteries were sometimes used to serve both purposes. Irrigation and water-supply stimulated the development of other technologies, which are dealt with in other chapters of this book: water-raising machines in Chapter 6, dams in Chapter 8, and surveying in Chapter 10. Some aspects of these technologies will, however, be mentioned in this chapter.

A causal connection between government and large-scale hydraulic schemes was discussed and supported by F. Wittfogel (see Bibliography) in very profound and detailed studies. Wittfogel's findings have been challenged, but there seems little reason to doubt that his main thesis, that there is a correlation between large-scale public works on the one hand and strong, stable government on the other, has been established. In Chapters 6 to 11 of this book we are concerned with the history of Islamic engineering from a technical standpoint, without paying formal attention to the societal and political aspects of the subject. It is, however, impossible to avoid touching upon these aspects tangentially. The instances that we shall discuss of large-scale hydraulic works all support Wittfogel's correlation hypothesis. It seems to be the case, however, that it was the maintenance of existing systems, even more than the construction of new ones, that necessitated centralised irrigational bureaucracies.

Before examining the hydraulic systems of medieval Islam we need to identify the four different types of irrigation. Basin irrigation consists of levelling large plots of land adjacent to a river or canal, each plot being surrounded by dykes. When the river reaches a certain level the dykes are breached, allowing the water to inundate the plots.