Download `River Engineering Approach` Wadi Labka – Gabion

6.11
Case: Wadi Labka –
What to Do When Traditional System
Becomes Unsustainable
Wadi Labka (En-River), Eritrea
Wadi Labka Gorge
Three main command areas
 Scan of Map
Flow is divided in the
riverbed
Riverbed downstream of gorge
Flow
Traditional method of diversion
Combination of earthen bunds protected with
acacia brushwood and natural vegetative bunds
(tamarisk)
Vegetative bunds not always
protected
Increasingly difficult to find acacia
shrubs for the traditional bunds
Haulage may take
more than three
days
What to do in this area?
 The traditional system is becoming gradually
non-sustainable.....
 There is a gorge yet the river widens out
considerably
 There are command areas on either bank of
the river
Discussion
in groups...
In the end..
 An ‘improved traditional system approach’
was followed - in this case focussing on river
engineering rather than the development of a
headworks>>>>>>
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
Agim = Traditional diversion bund
Construction of agims with
bulldozer and gabions
Labor for gabion filling provided by
farmers without charge
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
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 a civil
engineering approach that was
considered earlier
•Headworks (incl.
breaching bund)
•Single off-take
•Link canal and culvert,
estimated at USD
7,000,000 (or USD
1800/ha) for the same
system
River engineering
versus headworks approach
This ‘river engineering’ approach taken is lower cost. The
headworks option in fact was dropped earlier as being too
costly
 In this case the river engineering approach was also more
appropriate than the headworks approach:


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 water 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