1.6
Experience and challenges of
spate irrigation projects in
Tigray
(By Demisew Abate)
Part I : Introduction
What is spate irrigation?
o Spate irrigation is a flood harvesting and
management system, involving the diversion of
flowing flood using some deflecting technologies
(using simple deflectors of bunds constructed from
earth, sand, stones, brushwood and recently
gabions, masonry or concrete structures) on the
beds of normally dry creeks or river channels in to a
farmland.
 Spate irrigation is a type of river basin water
management that is unique to the semi arid
environment. Here water is harvested from river
basins or large parts thereof by diverting water from
ephemeral rivers/streams.
Introduction cont’d
 Flood flows usually flowing for only a few hours with
appreciable discharges, and with recession flows
lasting for one to a few days, are channeled through
short steep canals to bunded basins, which are
flooded to depths of 0.5 m or more
 Subsistence crops, often sorghum, are planted only
after irrigation has occurred
 Crops are grown from one or more irrigation using
residual moisture stored in the deep alluvial soils
formed from sediments deposited from previous
irrigations
Limitations
Some basic features of spate irrigation
 It requires high level of cooperation between
farmers to divert and manage the distribution of
flood flows.
 It requires very high labor input to maintain intakes,
canals and field systems
 It is a subsistence activity with low returns,
generating highly variable incomes between good
and bad years
Limitations…

It is uncertain due to



the unpredictable timing, frequency, duration and volume
of floods
the occasional very large floods that wash out diversion
structures and frequent change to the stream channels at
the diversion site
At present little guidance concerning the improvement or
development of spate systems is available, which makes
the implementation of improved systems to be liable to
some risks
Part II. Spate irrigation experiences
in Tigray
2.1 Traditional spate irrigation
 Traditional spate irrigation has been
experienced in the southern zone of
Tigray (Raya Azebo and Alamata
weredas) since long time ago.
 They construct simple deflector bunds
out of sand, stones, earth,
brushwood/tree branches, and other
locally available materials to divert
floods from different reaches of the
ephemeral stream beds, convey it
through earthen canals and spread
over their fields.
Traditional Spate…
Advantages of traditional schemes
•
Flexible and adjustable to changes in river bed
topography & flow alignment
• Ease of operation and maintenance
• Equitable water use/water rights
• Appropriate & low cost
• Relatively efficient
• Limit diversion of high flows & high sediment loads
Traditional Spate…
Wash out of traditional bunds and
spurs after a flood (Raya area)
Limitations
•
Frequent Wash out by
floods - high labor input
• Time consuming
• Diversion of flood not
sustainable
• Erosion of canal intakes
• It encourage
deforestation
2.2 Modern Spate irrigation
 The regional government has been made efforts to
improve or modernize the traditional spate irrigation
systems in the Raya Valley area since the last
decade.
 As a result, TWRME has implemented more than13
modern spate irrigation schemes so far ; among
them
S.
No
Scheme
Woreda
Command
Remarks
1
Hara
Alamata
400
*
2
Tirki
-do-
380
*
3
Fokisa
-do-
250
constructed
4
Ula-ula
-do-
250
-do-
5
Tengago
-do-
250
-do-
6
Dayu
-do-
200
-do-
7
Burka
R/ Azebo
280
-do-
8
Beyru
-do-
500
-do-
9
Haya
-do-
250
-do-
10
Buffe
-do-
200
-do-
Modern Spate irrigation…
o Modern spate irrigation schemes have been
implemented since 1995 E.C in Alamata and Raya
Azebo woredas
o In the 1998 E.C rainy season, an evaluation of the
performance of the schemes has been carried out
o The evaluation study shows that some schemes are
performing well and others have major physical and
social problems that resulted in low performances
Modern Spate irrigation…
Limitations
•
Failure of diversion head works to divert the required
volume of flow due to:
• blockage of under sluices/off-takes by
boulders, sediments and trash
• Erosion of downstream protection works
• mal-functioning of under sluice gates by high
floods and sediment/boulder abrasion
Modern Spate irrigation…
Limitations…
•
Sedimentation and/or erosion of conveyance
canals & farm lands
• Failure to divert the required volume of flood (low
diversion efficiency)
• O & M complexities or poor O&M practices of
farmers
• Social impacts , inequity of flood distribution
between u/s and d/s users, not satisfying farmers
preferences
Modern Spate irrigation…
Advantages of Modern Spate Irrigations
 The replacement of numbers of existing
traditional diversion structures by a single
permanent modernized diversion structure
eliminates the need of farmers to rebuild
diversions after floods
 It discourages deforestation as compared to the
traditional once
 Effective and durable
Example of a site with observed problems
Scheme name : Tirke spate irrigation
Main problems:






Erosion of d/s scour protection works
(insufficient scour depth provided)
Mechanical damage of Under sluice pillars by
the impact of big boulders
Silting up and/or blockage of closed pipe inlets
High sediment accumulation in canal head
reaches
Lacks proper O&M by farmers
Under sizing of canal inlets
Wide & angular under sluice piers, that catch
trash & boulders during floods
 All these problems lead to low diversion
efficiency and mal-functioning of the
scheme during the time of evaluation
Tirke spate irrigation…
o Farmers were consulted to express their
ideas & they indicated that they would
prefer the improved spate to have:
• An off-take or canal inlet with a
deflection angle of less than 60
degrees for smooth diversion of flood
• A wide off-take (more than the
existing 2.0 m) so as to divert more
flood flow
• Open and un-gated inlets instead of
the existing gated and closed pipe
inlets for ease of silt removal
• No under sluices so as to avoid any
loss of water downstream through
leakage
Factors that contributed to the problems at
Tirke scheme
 Problems related to design- no standard guidelines
available so far
 Implementation approach with no active
participation of farmers
 Poor construction quality
 No or poor operation & maintenance by farmers
 Absence of strong farmers organizations
Example of a spate irrigation with good
performance
Name of scheme: Fokissa spate irrigation
o Efforts were made to incorporate some
improvements following the experiences gained
during the operation of previously implemented
schemes and consultation of the farmers from same
schemes
Fokissa spate irrigation
The improvements include:
o A relatively wider offtake (3.0 m by 1.0 m size)
• Off-take aligned at an
angle of 60 degrees
• Un-gated, open offtake structure
• Good management by
farmers, especially in
regard to water
distribution (equity of
water rights)
Fokissa
spate cont…
Fokissa
spate irrigation

As a result this scheme has
been operating in a good
condition although the
following limitations were
observed:
 Frequent sediment
deposition of up to a depth
of 70 cm in the upper
reaches of the canal due to
lack of proper operation of
the de-silting basins at the
canal head reaches & mild
canal bed slopes
Fokisa spate Main canal
Fokisa spate irrigation area
3.0 Main lessens learned
 The planning & design of the rehabilitation and
improvement works have been carried out with out
effective participation of the farmers
 Farmers valuable knowledge regarding their
preferences on the scope & type of works, changes
in layout, location of diversion structure, type,
alignment & size of off-takes, etc were not
considered
 The investment costs have been very high and it is
doubtful if they can be justified in purely economic
terms
Main lessens…
 The O&M of the larger schemes is difficult &
expensive

•

In particular sedimentation at intakes and in canals is
often not properly controlled in modernized spate systems
New structures have promoted larger inequity in the
distribution of irrigation water due to the collapse of
traditional water rights
Modernized diversion structures give much larger control
over spate flows to favoured groups of upstream farmers
Main lessens…
 Smaller farmer managed schemes, where small
improvements have been introduced to improve
the reliability of existing traditional intakes, or
improvements to intakes constructed using
masonry or gabions, have been generally far
more successful and cost effective
Main lessens…
 As much of the available surface water is already
effectively used, the major benefits from any
investment must derive from increased
productivity of water use
 Therefore, the emphasis in the development of
spate irrigations should be focused first on the:

Improvement of the reliability of existing systems of water
diversion, allocation, distribution, water management &
conserving soil moisture, within the framework of existing
water rights and O&M practices
4.0 Recommended principles
o The success of any intervention will largely depend
on incorporating the following principles in the
development approach
•
•
In all but the largest and more technically complex
schemes, farmers should drive the planning, design &
execution of the rehabilitation and/or improvement works,
as well as any amendment to existing water rights
Engineers need to provide a range of technically &
economically viable options, and then assist farmers in
selecting the most appropriate improvements for their
particular scheme
Recommended principles
 In most cases, low-cost, simple and maintenance-
friendly technology should be used
 The replacement of numbers of existing traditional
diversion structures by a single permanent
modernized diversion structure eliminates the need
of farmers to rebuild diversions after floods
 However there is a strong probability that
concentrating diversion at one location will result in
conflict between u/s & d/s farmers due to
inequitable distribution of available spate water
Recommended principles..
 It is suggested that this approach should only be
adopted when:
•
Downstream water users are not disadvantaged
• The sedimentation problems can be managed
• Appropriate & sustainable maintenance can be assured
5.0 Challenges (problem faced)
 It was believed that the rehabilitation of the
traditional spate irrigation system by
designing a proper diversion and conveyance
structures would thereby increase the
efficiency of traditional spate irrigation
system. However it was found that designing,
constructing and managing these projects
was not an easy task.
Challenges …
 Hence, This presentation will be winding up
on the issues most challenging with design of
spate irrigation and expect from the training a
better approach and solutions by addressing
and appreciating the most serious problems
under listed
Challenges …
The amount of runoff that has to be diverted
(flood diversion ratio.doc)
2) Siltation problems ( off takes, canals and
piped structures) -Estimating sedimentation
1)
rates on spate irrigated fields
3) Availability of Standard guidelines (at
present little guidance concerning the
improvement or development of spate
systems is available, which makes the
implementation of improved systems to be
liable to some risks)