Angereb Reservoir
| Angereb Reservoir | |||||||||
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| Coordinates | 12 ° 36 '57 " N , 37 ° 29' 12" E | ||||||||
| Data on the structure | |||||||||
| Lock type: | Earthfill dam | ||||||||
| Construction time: | 1986 | ||||||||
| Height above the river bed : | 30 m | ||||||||
| Crown length: | 400 m | ||||||||
| Data on the reservoir | |||||||||
| Reservoir length | 750 m | ||||||||
| Reservoir width | 650 m | ||||||||
| Storage space | formerly 5 million m³ | ||||||||
| Particularities: |
Water supply for Gondar |
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The Angereb Reservoir is located east of the city of Gonder in the Amhara region in Ethiopia at an altitude of 2123 m above sea level. d. M. It was created in 1986 to improve the water supply for the rapidly growing population of Gondar, which was estimated at 250,000 in 2014. However , the reservoir may soon lose its function due to sedimentation .
The reservoir
The Angereb Reservoir is filled by the Little Angereb , which rises in the approximately 2,700 m high mountains north of Gonder and flows as Magech into Lake Tana after the reservoir south of Gonder .
The earthfill dam, which is around 30 m high and 400 m long at the crown, forms a reservoir with a storage volume of originally around 5 million m³. The water is pumped from a removal shaft to a water treatment plant and on to the location a few meters higher. The dam has a drain and an open overflow channel on the side slope as flood relief.
The catchment area
The catchment area consists of barely (still) forested mountainous land, which is cultivated by the increasing population up to ever greater heights for their own use, mostly on less than half a hectare per family. The wood from the rare trees is used as firewood for cooking and for sale to third parties. Agriculture and livestock farming lead to increasing erosion . In addition to the alternation of rainy and dry seasons, droughts and extreme rainfall have intensified erosion. Rivers therefore carry large amounts of soil material with them, which give them an ocher yellow color and which are deposited as sediment in reservoirs and lakes.
sedimentation
When planning the dam, it was envisaged that the dam's bottom outlet would be opened regularly during the peak of the rainy season in order to flush out the sediments. This did not happen, so that the bottom outlet could soon no longer be fully opened. In order to avoid the sediment deposits, the water extraction, which was supposed to be 5 m below the surface, was raised several times so that in 2007 it was only 0.5 m below the water level.
The Angereb Reservoir is now viewed as a reservoir with no bottom outlet. It is estimated that its volume has already been reduced by 15%. The long-term average is likely to have flowed 76,800 tons of sediments into the lake per year.
Countermeasures
The Corvallis Sister Cities Association from Corvallis , Oregon , USA , a twin town of Gonder, is working together with the Oregon State University there to reduce sediment input. For this purpose, the catchment area immediately above the reservoir is being reforested in cooperation with the Gonder sites and in coordination with the local population. The need for firewood is also to be reduced by encouraging women to replace their open, three-stone hearths with easy-to-make, enclosed hearths made of clay that use half as much wood. In several planting seasons since 2008, initially the areas immediately above the reservoir and in the following years various areas higher up were planted with seedlings .
Individual evidence
- ↑ a b c d Angereb Watershed Restoration ( memento of October 20, 2014 in the Internet Archive ) on the website of the Corvallis Sister Cities Association
- ^ Tana & Beles Integrated Water Resources Development Project, World Bank Project Appraisal Document No: 43400-ET, p. 1
- ↑ Ahmed Saleh (Coordinator): Assessment of the current state of the Nile Basin Reservoir Sedimentation Scheme. ( Memento of the original from October 9, 2010 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Nile Basin Capacity Building Network 'NBCBN', 2005, p. 17
- ↑ Nancy Raskazier: Searching for solutions Article of November 30, 2010 in the Corvallis Gazette-Times
