Construction, maintenance and abandonment of hydraulic systems: hydroclimatic or social constraints? A case study of prehistoric Hohokam irrigation systems (Phoenix, Arizona, USA)

Abstract

On the North American continent, irrigated agriculture principally occurred in the semi-arid American Southwest. The Hohokam built major irrigation systems along the plains of the Salt River in the Phoenix Basin (Arizona) between the seventh and the fifteenth century A.D. Their occupation in the basin is structured around three major phases: the Pioneer Period: 600–750 A.D., the PreClassic Period: 750–1150 A.D. and the Classic Period: 1150–1450 A.D., during which they constantly coped with a constraining environment and mainly a rare resource, water. In order to understand long-term socio-environmental dynamics, hydraulic structures are ideal objects of study as they can be studied from a chronological and geoarchaeological perspective. The analysis of 60 dates (radiocarbon, OSL, archaeomagnetic and ceramic) obtained from 47 irrigation canals used from the Pioneer to the Classic Period allowed us to discuss the temporalities of irrigation networks (construction/abandonment). Characterizing and classifying the depositional environment where the dates were obtained was key to identify phases of low flow, periodic sedimentation or uncontrolled flooding. Results were correlated with regional geomorphic changes, climatic evolutions, as well as demographic data in order to discuss the relative impact of environmental shifts, settlement pattern and population pressure on water management. This approach also offers an illustration of the vulnerability and adaptation of agrarian communities to socio-environmental constraints in semi-arid environments.