SILTATION BEHIND DAMS IN ANTIQUITY

Authors: Garbrecht, Jurgen; GARBRECHT, GUNTHER - N-A

Submitted to: American Society of Civil Engineers
Publication Type: Book / Chapter
Publication Acceptance Date: 4/12/2004
Publication Date: 6/27/2004
Citation: Garbrecht, J.D., Garbrecht, G.K. 2004. Siltation behind dams in antiquity. In: Rogers, J.R., Brown, G.O., Garbrecht, J.D., editors. Water Resources and Environmental History. Reston, VA: American Society Of Civil Engineers. p. 35-43.

Interpretive Summary: Building reservoirs and diversions on rivers has been a common practice since humans settled from nomadic life. While the impounded water served various beneficial purposes, the sediments that were carried along by the inflowing river gradually filled the reservoir storage space. Thus, reservoirs act virtual sand traps, and the lifetime of a reservoir is defined by the quantity of sediment entering the reservoir and the size of the available storage to hold the sediment. Sedimentation behind dams in antiquity and measures to extend the operational life of reservoirs were reviewed for the Marib and Kebar dams in Yemen and Iran, respectively. The Marib dam impounded floodwaters to enable irrigation of downstream oases. Over several centuries the sediments in the irrigation water raised the level of the irrigated area up to 15 m, and the dam was raised twice to compensate for the sedimentation effects. The Kebar dam was an arch dam for irrigation water withdrawals. Large openings on the upstream side of the dam were probably used during construction to pass the water of the river, but may also have served to periodically flush accumulated sediments. These examples illustrate that engineers of the time were keenly aware of reservoir sedimentation problems and were able to successfully extend the operational lifetime of the reservoirs by structural enhancements and possible reservoir sediment flushing.

Technical Abstract: The siltation behind dams in antiquity and measures to extend the operational life of reservoirs is illustrated for the Marib and Kebar dams in Yemen and Iran, respectively. For both dams siltation played a major role. The Marib dam impounded floodwaters to enable irrigation of downstream oases. Over several centuries, silts entrained in the irrigation water accumulated on the irrigated fields up to 15 m high, and the dam was raised to compensate for the loss of slope and conveyance due to the sedimentation. The Kebar dam was an arch dam designed as a small storage reservoir. In addition to small operational openings for irrigation water withdrawls, large openings on the upstream side of the dam were probably used during construction to pass the water of the river, but may also have been used for periodical flushing of accumulated sediments. Both examples show that the engineers of the time were keenly aware of reservoir siltation problems and were able to successfully extend the operational lifetime of the reservoirs by structural enhancements and probable sediment flushing.