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

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

3. Flow is divided in the riverbed
Three main command areas
Scan of Map
Flow is divided in the riverbed
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