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Channels, terraces, pottery, and sediments – A comparison of past irrigation systems along a climatic transect in northern Jordan

Lucke, Bernhard, al-Karaimeh, Sufyan, Schörner, Günther
Journal of arid environments 2019 v.160 pp. 56-73
Mediterranean climate, cities, dry environmental conditions, hinterland, irrigation canals, land use, loess, nutrients, rainfed farming, rocks, runoff, runoff irrigation, soil, steppes, surveys, terraces, water resources, Jordan
This contribution compares the remains of irrigation systems along a climatic transect in northern Jordan: Gadara (today Umm Qeis) in the north-west, Abila (today Queilbeh) in the north, and Umm el-Jimal (ancient name unknown) in north-east Jordan. While Gadara and Abila were monumental ancient cities of the Decapolis city league, which are located in Mediterranean environments, Umm el-Jimal is a large urban site situated in the steppe. Rainfed agriculture is possible near Gadara/Umm Qeis and Abila/Queilbeh, but not at Umm el-Jimal. Our surveys of the hinterlands revealed evidence for runoff farming at Umm el-Jimal near some wadis, and at Abila/Queilbeh and Gadara/Umm Qeis near both springs and wadis. Contrary to our expectations, the extent of ancient irrigation near Umm el-Jimal appeared more limited and economically less important than at the two other sites. Although the steppe proved covered by an approximately 4 m deep loess cover, these fertile sediments were apparently utilized only to a limited degree for agriculture. This can be deduced from the petty amount of sediments that accumulated behind terrace walls, the small extent of the fields and from low concentrations of nutrients usually associated with manuring. The archaeological surface survey confirms this picture: in the steppe, widely spread pottery scatters were found only within the settlement and the necropolis. The sites to the west revealed larger and more sophisticated remains of irrigation systems, as well as higher concentrations of material culture scatters, which suggest far more intensive land use systems than in the east. The most extensive and sophisticated remains of irrigation canals were found on caliche crusts near Gadara/Umm Qeis. As these rocks are mostly bare of soil cover, they are well-suited to collect runoff and construct rock-cut canals to transport water. We conclude that the available water resources and the geology had the strongest influence on the construction of ancient irrigation systems in northern Jordan.