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Case - ‘River Engineering Approach’ Wadi Labka – Gabion/ Soil Diversion Spurs

6.8. Case - ‘River Engineering Approach’ Wadi Labka – Gabion/ Soil Diversion Spurs. Wadi Labka (En-River), Eritrea. Wadi Labka Gorge. Three main command areas. Flow is divided in the riverbed. Scan of Map. Riverbed downstream of gorge. Flow. Traditional method of diversion.

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Case - ‘River Engineering Approach’ Wadi Labka – Gabion/ Soil Diversion Spurs

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  1. 6.8 Case - ‘River Engineering Approach’Wadi Labka – Gabion/ Soil Diversion Spurs

  2. Wadi Labka (En-River), Eritrea Wadi Labka Gorge

  3. Three main command areas Flow is divided in the riverbed • Scan of Map Riverbed downstream of gorge Flow

  4. Traditional method of diversion Combination of earthen bunds protected with acacia brushwood and natural vegetative bunds (tamarisk)

  5. Vegetative bunds not always protected

  6. Increasingly difficult to find acacia shrubs for the traditional bunds Haulage may take more than three days

  7. Construction of agims with bulldozer and gabions • Replacement of upper section of the traditional agims with soil bunds and gabions • Gabions at section where flood channel hits the diversion bund • Flood protection on left bank to prevent further movement of Wadi Labka to the left

  8. Construction of agims with bulldozer and gabions

  9. Labor for gabion filling provided by farmers without charge

  10. Wall of gabion baskets with earthen protection Another layer of gabions will be added and the earth bund will be increased Use of geotextile will reduce wash out of fine material at the bottom and prevent collapse

  11. Scope of work • 1200 meter gabion works • 120 days of bulldozer use • Total costs USD 430,000 • Total cost/ ha USD 110 This may be compared with the cost of civil engineering headworks (incl. breaching bund, link canal and culvert, estimated at USD 7,000,000 (or USD 1800/ha) for the same system

  12. River engineering versus civil engineering • This ‘river engineering’ approach taken is low cost • It is also more appropriate than the civil engineering: • It follows the traditional system of diverting flood flows, based on splitting the flow in smaller proportions to make its management easier • It follows the existing wate rights and does not interfere with it • Very large floods will wash out part of the structures but will also ensure that the floods remains in the river bed and does not enter the command area, causing erosion

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