Relict canals of the Tehuacan Valley, Mexico: A Middle- to Late-Holocene dryland socio-hydrological system

The travertine-lined irrigation canal networks of the Tehuacan Valley, Mexico allowed pre-Hispanic indigenous communities to overcome risks of crop failures in an arid setting. Segments of these systems are still in use today, therefore understanding when and how these irrigation networks functioned allows us to identify which attributes of a coupled socio-hydrological system are important for maintaining the long-term resilience of irrigation systems in drylands. This paper summarizes the results of an interdisciplinary study of this prehispanic irrigation network involving mapping, radiometric dating, and diatom analyses of materials extracted from the travertine lined canals. All of the canal networks were functioning by ca. 2000 BC, at the transition from the Late Archaic to the Formative period, which is before archeological evidence for widespread community-level aggregation. Provocatively, some canals are potentially as old as 6000-4000 BC, which would mean that hunter-gatherers initiated irrigation coevally with the introduction of semi-domesticated maize, a tropical species which would require supplemental water in this arid context. The canals both facilitated agricultural intensification and enhanced the distribution of aquatic ecosystems. The resilience of these systems to their unique spring dependent context demanded frequent maintenance and the integration of multiple canal networks to mitigate geohydrological vulnerabilities of reduced discharge. These conditions set up a long-term reciprocal dynamic between people and water in the Tehuacan Valley. The results demonstrate that rigidities inherent to tightly coupled socio-hydrological systems in dryland settings were overcome by institutional arrangements first developed by indigenous communities deep in prehistory.