Dam

A dam is an engineering structure that completely blocks a watercourse, either permanently or temporarily, in order to raise its level and create a reservoir (Brunet et al. 1993: 61). A dam consists of two main elements: a retaining wall and facilities to discharge liquids and solids accumulated in its reservoir.

Only gravity dams are attested in ancient Arabia, i.e., the water body was held back by the weight of the retaining walls, whereas two main categories of dams are firmly attested between the first millennium BCE and the 7th century CE: storage dams and weirs (Charbonnier & Schiettecatte 2013: 77–80).

The former held back water in order to form a reservoir, where it could be stored for a long or short period of time. Water was drawn out of the reservoirs by several types of devices. Outlets controlled the flow of water toward a canal, which in turn fed an irrigation system (Fig. 1). Spillways, located in the upper part of the dam or set-up sideways, evacuated excess water during flood events and prevented collapse.

Unlike storage dams, weirs are designed to be overflowed. The purpose is to slow down and raise the level of a watercourse in order to divert part of the flow into a lateral water intake. Stepped courses downstream of some weirs are intended to reduce water velocity and avoid the development of whirlpools (Fig. 2).

Dams were only implemented in the western part of the Arabian Peninsula and the only well-dated dams from the pre-Islamic period are located in Southwest Arabia.

Storage dams are only located in the western mountains and are practically all dated between the 1st and the 4th centuries CE (i.e., the Ḥimyarite period) (Charbonnier & Schiettecatte 2013: 80–81; Robin & Dridi 2004).

The use of weirs is firmly attested since the early 1st millennium BCE in the lowlands of Southwest Arabia (Darles 2000: 93). The famous Maʾrib dam belonged to this category in the way it was operated (Fig. 3). Its 650-m-long and 16-m-high earthen levee harnessed the flood of Wādī Dhana and raised the water so that it could reach the level of monumental water intakes on both sides of the dam. Although the diversion of Wādī Dhana’s flood probably dates back to the Bronze Age, the visible remains of the dam can be dated from the mid-1st millennium CE (Darles et al. 2013: 13). At that time, it retained water in order to allow part of the flow to reach the level of the fields, which had been slowly raised due to the continuous accumulation of silts over the centuries (Brunner and Haefner 1986: 81). Several weirs are also attested in the western mountains during the Ḥimyarite period (Charbonnier & Schiettecatte 2013: 78–80).

The vast majority of documented storage dams and weirs were built in the mountains of Southwest Arabia during the Ḥimyarite period. They seem to have been built by local elites in order to enhance the value of the land by increasing its productivity and also to legitimise their power (Charbonnier & Schiettecatte 2013: 88–89).

See also Water Management

Julien Charbonnier

References and suggested readings

• Brunet R., R. Ferras & H. Thery 1993. Les mots de la géographie : dictionnaire critique. Montpellier, Paris: GIP Reclus, La Documentation Française.
• Brunner, U. & H. Haefner 1986. The Successful Floodwater Farming System of the Sabaeans, Yemen Arab Republic. Applied Geography 6: 77–86. DOI: 10.1016/0143-6228(86)90030-5.
• Charbonnier, J. & J. Schiettecatte. 2013. Les barrages de L’Arabie méridionale préislamique. Architecture, datation et rapport au pouvoir, in F. Baratte, C.J. Robin & E. Rocca (eds) Regards croisés d’Orient et d’Occident. Les barrages dans l’Antiquité tardive: 71–91. Paris: De Boccard.
• Darles, C. 2000. Les structures d’irrigation du Wādī Surbān au Yémen. PSAS 30: 87–97. https://www.jstor.org/stable/41223699
• Darles, C., C.J. Robin & J. Schiettecatte. 2013. Contribution à une meilleure compréhension de l’histoire de la digue de Maʾrib au Yémen, in F. Baratte, C. Robin & E. Rocca (eds) Regards croisés d’Orient et d’Occident : les barrages dans l’Antiquité tardive: 9–70. Paris: De Boccard.
• Robin, C.J. & H. Dridi. 2004. Deux barrages du Yémen antique. CRAI 148: 67–121. DOI: 10.3406/crai.2004.22690.

_{Alternate spellings: Retention wall, Barrage}