Geoarchaeological evidence for the construction, irrigation, cultivation and resilience of the 15th-18th-century AD terraced landscape at Engaruka, Tanzania.

Agricultural landscapes are necessarily human manipulated landscapes, most obviously in areas modified by terracing, irrigation, or both. Examples exist in temperate, arid and desert environments worldwide, and have attracted the attention of many disciplines, from archaeologists, palaeoecologists and geomorphologists interested in landscape histories, to modern economists, agronomists, ecologists and development planners studying sustainable resource management. This paper combines these interdisciplinary interests by exploring the role archaeology can play in assessing landscape sustainability; focussing on Engaruka, Tanzania. Archaeologically famous as the largest abandoned irrigated and terraced landscape in east Africa, the site has been seen as an example of economic and/or ecological collapse, and has long been assumed to have been irrigated out of necessity; the assumption being that agriculture would be near impossible without irrigation in what is now a semi-arid environment. Geoarchaeological research refutes this assumption, demonstrating that the site flooded with sufficient regularity to allow the construction of over 1000ha of alluvial sediment traps, in places over 2m deep. Soil micromorphology and geochemistry also record changes in irrigation, with some fields inundated to creating paddy-like soils. These techniques can be applied to both extant and abandoned systems, thereby contributing to an understanding of their history, function and sustainability.