Underground draining gallery

Underground draining galleries are structures designed to channel groundwater to the surface. In Arabia, the first evidence of this dates to the end of the second/beginning of the first mill. BCE. They were used continuously until today.

Underground draining galleries are structures intended to drain groundwater resources, in their upstream section, and channel the water to the surface by gravity, the gradient of the subterranean canal being lower than that of the natural terrain. They are generally ventilated by vertical shaft holes that are also used to remove the spoil when digging underground. These shafts usually form long, characteristic alignments in the landscape and are the best indicators of the presence of a draining gallery (Fig. 1). Different groundwater sources can be exploited by these structures, such as underflows, perched water tables or deep aquifers, depending on the context. The length (from tens of metres to several kilometres), depth (from a few metres to a few dozen metres), and the level of investment necessary to develop these structures are highly variable.

Nowadays, these structures are known by different names in different parts of Arabia: ʿayn in the north-western part of the peninsula, kharaz in central Arabia, ghayl in Yemen, and falaj in Oman and the United Arab Emirates. The same technology is also known under a variety of names in the Middle East and North Africa: qanāt in Iran, kārēz in eastern Iran or Afghanistan, fuqārah in Libya and Algeria and khattāra in Morocco (Boucharlat 2016: 281).

In the Arabian Peninsula, the earliest evidence for the exploitation of groundwater through this technology comes from Southeast Arabia, where absolute dating obtained from al-Madām and Salūt suggests that underground draining galleries were implemented throughout the Iron Age, from the late second-early first millennia BCE (Del Cerro & Córdoba, 2018: 96) to the mid first millennium BCE (Cremaschi et al. 2018: 138). However, the absolute dating of these structures is still rare. In the rest of Arabia, there is no clear evidence of underground draining galleries before the Islamic period.

The few excavated underground galleries in Southeast Arabia were merely dug into the ground, without any masonry reinforcements (Fig. 2). Downstream, the gallery could take the shape of a canal or a trench dug into the ground, sometimes covered with stone slabs (al-Tikriti 2002: 124), but not always, as the example of al-Madām (AM-2) shows (Del Cerro & Córdoba, 2018: 93).

The irrigation canals fed by these underground draining galleries could be lined with masonry sidewalls (Hīlī 15) or simply dug into the compact calcareous substratum (AM-2). There is some evidence for sluices regulating and orienting the flow of water on both sides, made of stone slabs or large potsherds (Del Cerro & Córdoba, 2018: 94).

The excavation of AM-2 has provided unprecedented and invaluable information regarding Iron Age field systems (Fig. 3). The irrigation system of al-Madām, entirely cut into the substratum, is estimated to extend over about 15 hectares (Del Cerro & Córdoba, 2018: 85).

While it was previously suggested that Iron Age underground draining galleries only exploited shallow water tables, detectable from the surface (Boucharlat 2016: 286-287), it is now suggested, based on evidence from AM-2, which was dug into the calcareous bedrock, that they could also tap deep aquifers (Benoist et al. 2021: 179).

See also Water Management

Julien Charbonnier

References and suggested reading

• al-Tikriti, W.Y. 2002. The south-east Arabian origin of the falaj system. PSAS 32: 117–138. www.jstor.org/stable/41223728
• Benoist, A., M. Degli Esposti, J. Charbonnier & T. Power 2021. Al-Madam and the Archaeology of the Falaj in South East Arabia, in A.J. Domínguez Monedero et al. (eds) Nomina in aqua scripta: Homenaje a Joaquín María Córdoba Zoilo: 165–182. Madrid: Universidad Autónoma de Madrid.
• Boucharlat, R. 2016. Qanāt and Falaj: Polycentric and Multi-Period Innovations. Iran and the United Arab Emirates as Case Studies, in A.N. Angelakis et al. (eds) Underground aqueducts handbook: 279–301. Boca Raton: CRC Press. DOI: 10.1201/9781315368566.
• Cremaschi, M., M. Degli Esposti, D. Fleitmann, A. Perego, E. Sibilia & A. Zerboni. 2018. Late Holocene onset of intensive cultivation and introduction of the falaj irrigation system in the Salut oasis (Sultanate of Oman). Quaternary Science Reviews 200: 123–140. DOI: 10.1016/j.quascirev.2018.09.029.
• Del Cerro, C. & J.M. Córdoba. 2018. Archaeology of a falaj in al Madam Plain (Sharjah, UAE); a study from the site. Water History 10: 85–98. DOI: 10.1007/s12685-018-0210-0.

_{Alternate spellings: Underground water channel, Qanat, Falaj, Kārīz, Kârîz, Qanât, Qanāt, Kariz, Karaz, Kharaz}