Toker Dam

Last updated October 04, 2019

Toker Dam is the fourth largest dam in Eritrea. Construction was begun in 1997 and completed in 2001, despite having to be halted for a few months in 1998 when Ethiopia and Eritrea were at war. Its primary designer was Natural Resources Consulting Engineers from Colorado, USA. Furthermore, NRCE Inc., was the primary consultant on the project. The construction contractor was Keagnam of South Korea.^[1]

Eritrea, officially the State of Eritrea, is a country in the Horn of Africa, with its capital at Asmara. It is bordered by Sudan in the west, Ethiopia in the south, and Djibouti in the southeast. The northeastern and eastern parts of Eritrea have an extensive coastline along the Red Sea. The nation has a total area of approximately 117,600 km² (45,406 sq mi), and includes the Dahlak Archipelago and several of the Hanish Islands. The name Eritrea is based on the Greek name for the Red Sea, which was first adopted for Italian Eritrea in 1890.

The project was designed to provide modern and effective service to the City of Asmara and neighboring villages. It further provides safe drinking water for the local population. The dam is a roller compacted concrete dam, and was one of the highest in sub-Saharan Africa at the time it was built.^[2]

Asmara or Asmera is the capital and most populous city of Eritrea, in the country's Central Region. It sits at an elevation of 2,325 metres (7,628 ft), making it the sixth highest capital in the world by altitude. The city is located at the tip of an escarpment that is both the northwestern edge of the Eritrean Highlands and the Great Rift Valley in neighbouring Ethiopia. In 2017, the city was declared as a UNESCO World Heritage Site for its well-preserved modernist architecture. Asmara was first settled in 800 BC with a population ranging from 100 to 1000. The city was then founded in the 12th century AD after four separate villages unified to live together peacefully after long periods of conflict.

The dam

The dam is 73 metres tall and is composed of 210,000 cubic metres (7,400,000 cu ft) of concrete. The upstream face is vertical and the downstream face is sloping, with a central spillway. The reservoir can hold 17,000,000 cubic metres (600,000,000 cu ft) of water; there is a pumping station at its toe, leading to a water filtration plant. This has a capacity of 20,000 cubic metres (710,000 cu ft) water per day which is delivered to the city of Asmara's distribution system.^[1]

During construction, the cofferdam was overtopped for about four days during a large flood, when the dam was about one third of its final height. The flood was in excess of the once in a hundred years flood expectation. The contractors had little warning but managed to get most of their equipment away from the critical area before the event struck. The conventional and roller-compacted concrete in the main dam were largely undamaged and construction work was resumed within a fortnight.^[3]

A cofferdam is an enclosure built within, or in pairs across, a body of water to allow the enclosed area to be pumped out. This pumping creates a dry work environment so that the work can be carried out safely. Enclosed coffers are commonly used for construction or repair of permanent dams, oil platforms, bridge piers, etc ., built within or over water.

Roller-compacted concrete (RCC) or rolled concrete (rollcrete) is a special blend of concrete that has essentially the same ingredients as conventional concrete but in different ratios, and increasingly with partial substitution of fly ash for Portland cement. The partial substitution of fly ash for Portland Cement is an important aspect of RCC dam construction because the heat generated by fly ash hydration is significantly less than the heat generated by Portland Cement hydration. This in turn reduces the thermal loads on the dam and reduces the potential for thermal cracking to occur. RCC is a mix of cement/fly ash, water, sand, aggregate and common additives, but contains much less water. The produced mix is drier and essentially has no slump. RCC is placed in a manner similar to paving; the material is delivered by dump trucks or conveyors, spread by small bulldozers or specially modified asphalt pavers, and then compacted by vibratory rollers.

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References

1 2 Luis Berga; J. M. Buil; C. Jofré; S. Chonggang (2003). Roller Compacted Concrete Dams: Proceedings of the IV International Symposium on Roller Compacted Concrete Dams, Madrid, Spain, 17-19 November 2003. CRC Press. pp. 283–288. ISBN 978-90-5809-564-0.
↑ "Adi Nefas Water Treatment Plant and Treated Water Pipeline, Eritrea". NRCE. Archived from the original on 24 November 2016. Retrieved 24 November 2016.
↑ "Dams and Extreme Events: Reducing Risk of Aging Infrastructure under Extreme Loading Conditions". 34th Annual USSD Conference San Francisco, California, April 7-11, 2014. USSD.Missing or empty |url= (help)

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[Berga-1] 1 2 Luis Berga; J. M. Buil; C. Jofré; S. Chonggang (2003). Roller Compacted Concrete Dams: Proceedings of the IV International Symposium on Roller Compacted Concrete Dams, Madrid, Spain, 17-19 November 2003. CRC Press. pp. 283–288. ISBN 978-90-5809-564-0.

[2] "Adi Nefas Water Treatment Plant and Treated Water Pipeline, Eritrea". NRCE. Archived from the original on 24 November 2016. Retrieved 24 November 2016.

[3] "Dams and Extreme Events: Reducing Risk of Aging Infrastructure under Extreme Loading Conditions". 34th Annual USSD Conference San Francisco, California, April 7-11, 2014. USSD.Missing or empty |url= (help)