Old World Irrigation Technology in a New World Context: Qanats in Spanish Colonial Western Mexico
Beekman, Christopher S., Weigand, Phil C., Pint, John J., Antiquity
A qanat is a subterranean conduction device designed to tap the water table and bring the water to lower lands for irrigation, and is therefore a form of underground aqueduct. These features are an early example of technology transfer from the Old World to the New, and were already in use in various locations in Spanish Colonial America by the end of the 16th century. This paper documents a qanat system from Guadalajara, Jalisco, in western Mexico. We present a basic description of the qanat, an analysis of its hydraulic properties, and the evidence for its construction during the Colonial period (1521-1821) and continued maintenance in this century. The discovery of such an extensive, yet historically undocumented, irrigation system, in a region whose Colonial-period economy is still poorly understood, underlines the importance of investigating rural agrarian features as well as the urban communities that are the focus of so much of historic archaeology in Mexico. An appreciation of the importance of qanats and other Colonial irrigation features has been slow in coming, but recent works (e.g. CEHOPU 1993) indicate a growing interest.
Qanats in the Old and New Worlds
The term qanat literally means 'lance' or 'conduit' in the original Arabic (English 1968:170). A qanat hydraulic feature is defined as a horizontal channel dug into an alluvial fan until the water table is pierced or a spring is tapped. The ground water then flows downslope to emerge from the channel mouth as a stream. In addition, access shafts are dug at regular and frequent intervals, to facilitate the original construction of the conduit as well as to allow ventilation and entry for cleaning and maintenance (cf. English 1966; Forbes 1956; Drower 1954; Wulff 1967; 1968; Glick 1970). Qanat engineering is a major investment in agricultural intensification and is usually restricted to arid lands where water for irrigation is extremely scarce.
It has been postulated that they originate in Armenia, where tunnel digging employed in mining has a long history (Forbes 1956: 666; English 1968: 175). In the 1st millennium AD, qanats spread further throughout the Near East and the Mediterranean basin, and were brought to Spain after the Arab conquests of the 8th century (Gonzalez Tascon & Vazquez de la Cueva 1993). The Spanish brought qanat engineering overseas to the Canary Islands and, during the 16th century, to colonies in the New World. Qanats are found in various areas in Peru and Chile (Barnes & Fleming 1991), and in central and northern Mexico (Glick 1970: 352; Henao 1980; Kjell & Whiteford 1989; Wilken 1990), where they date from the 16th-20th centuries. The Persian examples are still the best studied, and some 37,500 qanat systems in the 1950s and 1960s irrigated approximately 15 million acres, which gives some indication of the qanat's modern contribution to agriculture.
Considerations of scale aside, the actual technology applied to qanat design and construction has changed little over the millennia or over space. Since there are no direct records concerning the qanat systems in western Mexico, a brief summary of qanat design and construction from other areas seems appropriate. While qanat construction is expensive (see the cost discussions in Wulff 1967; 1968), it is not as labour-intensive as one might imagine. Because of the physical constriction of the tunnel/well environment, construction teams seldom have more than 6-10 members, half of them on the surface and half underground. In the Persian case, the qanat excavators are a hereditary class of professionals, and highly respected (English 1966: 136-7).
The master digger decides where the mother well (a misnomer as this is not actually used as a well) should be dug. This vertical shaft is dug at or near the top of an alluvial fan, and is meant to determine the depth of a permanent and reliable deposit of ground water. Once this point is reached, a calculation can be made as to where the mouth of the channel should be located, and how much land can be irrigated from the projected qanat. …