Back Ache and Bamboo:
An alternative approach to dyke construction
in flood prone communities in Nepal
Background Throughout Nepal the theory and practice of gabion box construction to protect river banks
and hill slopes is well known. In areas where rocks are abundant their construction represents a cost
effective and locally replicable way for communities to utilize relatively abundant natural resources for
local risk reduction and protection purposes1.
Practical Action has used this technique in
previous DRR2 projects, but during 2007/8, in
its DIPECHO3 supported Bardia and Banke
programme, it was faced with a number of
In Bardia in particular vulnerable riverside
communities are some distance from the hills
meaning that rivers do not have sufficient power
to carry large rocks to their locations, instead
depositing them in the foot hills and first few
kilometers of the plains. As such rocks are either
unavailable locally or only at a prohibitive cost.
This makes gabion spur and dyke construction
expensive and ultimately unsustainable, as
beyond the resources of communities to replicate
Additionally, due to the profusion of vertical river
banks in the area, the construction of traditional
gabion spurs and dykes is simply likely to protect
one area at the expense of another. The stone
structures simply deflecting the destructive
power of the river either down-stream or to the
opposing bank (in Practical Actions previous
DDR programme in Chitwan and Nawalaparasi
this was not a major consideration, as the far
bank consisted entirely of national park, where Cleaning bamboo before use. A practice which the
thick natural vegetation was largely impervious to community subsequently found unnecessary.
Under this scenario there has been a need for an alternative strategy if the project is to stop erosion and
provide a technology and approach communities can replicate long term.
Regular river bank erosion and collapse take place in the Terai4 primarily due to two factors;
1. The under cutting of vertical banks by flood waters (the water undermining the high bank,
leading to subsidence and collapse)
2. The creation of a rotational slippage plane, due to river bank soils becoming saturated by rain
fall and surface run-off, leading to sections of bank losing their integrity and shearing off.
To stop this occurring both factors had to be addressed within the project. As such an approach
incorporating a number of interlinked components was proposed.
An example of how typical river bank failure occurs, due to;
1. Under cutting of a vertical river bank by flood waters
2. The creation of a slippage plane, caused by inundation and soil saturation.
Bamboo protection has been used elsewhere in Nepal, as has the use of sloping banks and sand bag
protection. What was not clear to Practical Action was if all three had been used in combination before,
and as such the idea was floated with communities as a possible ‘pilot’.
Looking at Balapur, a village within Ward 6 of Gulariya, areas of the bank looked suitable to try this
combination, with a number of factors influencing the decision;
o Near vertical banks, of relatively weak clay/soil mix, experiencing annual under-cutting and
collapse, irrespective of the severity of the monsoon period flood/high water.
o The possible availability of land behind the bank for cutting back, to form a sloping bank, as not
intensely cultivated at present (instead being used mainly for rough grazing and pasture)
o The bank side being open to the full erosive power of the river, but not being at a structurally
weak point (such as the outside of a bend, where most cutting is likely to occur)
o High community mobilization and motivation to take action.
o The cost of stone gabion work being beyond the means of communities to support
Before the pilot could begin community members had to be convinced of the effectiveness of the
approach, particularly as it would involve a ‘voluntary’ loss of up to 8 metres (see below) of land before
the dyke could even be constructed. Given the extent of land loss experienced every year anyway,
community members eventually agreed, though there was skepticism from adjacent communities and the
residents of Balapur went as far as obtaining a written agreement from the landowner on whose land they
were testing the idea that he would not prosecute them if the project failed and even more land was lost !
“People were not
convinced. We had to make
a contract with land holders
mentioning they would not
claim against us if their
land was further lost !” -
Kali Parsad Tharu (PIC
President. Ward 6
River bank at Balapur before slope cutting by community volunteers.
To produce a stable slope in the sand/clay mix soil it was calculated a minimum angle of 35
degrees (from horizontal) was required, though obviously, as a general rule, the less the degree
from horizontal and the shallower the slope, the more stable it will be and the less likely to
“Previously people from
other places said that
we were mad, but now
they say they appreciate
what we have achieved
and they also want to
copy us” – Kali Prasad.
President Ward 6
The same piece of river bank during cutting of the sloping bank
As the vertical bank was about 6 metres high (at low water) this was eventually cut back by 8
metres, giving an angle in the low 30 degrees. This was achieved by first digging a channel at
30 degrees, as a guide and marker for the rest of the bank, which the rest of the slope copied.
The objective was to ultimately create not a barrier, to fight erosion (as in the case of a stone gabion
dyke), but a structure immune to erosion through its allowance of the water to non-destructively rise
up it (and later down it) without causing any obstruction likely to attract erosion by the river.
Once the slope had been created bamboo
poles when fixed both below and above the
water line. These were set up in several rows
parallel to the river bank. Strips of bamboo
were then woven between these poles to act as
Once this was completed old cement bags
were filled with sand from the river which also,
as a side effect, helped in part to lower the
river bed in the immediate area of the dyke.
These were used to ‘face’ the slope, making it
even more impervious to the destructive
powers of the river.
To stabalise and create long term strength to
the bank live bamboo and lemon grass
seedlings were also planted along the bank,
between the sand bags, to ultimately
‘naturalise’ the bank. Finally, to stop soil saturation and possible slippage due to water seeping
in to the slope from the landward side, a lateral catchment drain was dug at the top of the bank.
This was dug so that water emanating from the landward side of the slope could be drained to
either end of the dyke, preventing it from percolating down and into the substance of the slope,
so weakening it from within.
1. Bank before the intervention
2. Calculation for cutting back of bank to create optimum slope
3. Positioning of bamboo poles, bamboo matting fences and sand bags
4. Completion of dyke with construction of lateral drainage channel
In original calculations it was estimated that Gabion work necessary to protect this 150 meter
length of bank would cost 1,700,000Nrs (approx £13,600/€19,000/$27,200)5. This was
beyond the budget of the project, but more importantly beyond the resources of the community
to replicate themselves, un-aided, long-term.
Sand bag filling and fence weaving during low water at Balapur during June 2008
In constructing the sloping protection work using local materials only 92,866 Nrs was spent in
total (£750/€1050/$1500). 56,000Nrs was spent on bags, while bamboo was purchased at a
subsidised price (of about 50% of market rate) from the communities own collectively owned
resources at 28,185Nrs. The remainder of the cost was made up of the cost of string, to tie
bags, and a small amount for transportation.
On top of this labour equivalent to 160 people working for 16 days (= 2,560 person days) was
contributed by the community. At a low daily wage rate of 125 Nrs per day this equates to
320,000 Nrs. However, as the community members contributed this free of charge, it was not
factored into the ‘costs’ by the community themselves.
Who contributed ?
Interestingly nearly all families contributed some labour, with families and individuals with no
real likelihood of benefiting from the dyke (living far from the river bank) also taking part. The
only minor incentive was 700Kgs of rice contributed by a local NGO, BASE, from supplies
provided by the WFP.
This equated to a one off distribution of 4.5 kg per person. At a per kg price of 35Nrs this
equated to just 158Nrs per person, or a total of 24,500Nrs for all labour volunteered.
Within the community they developed a programme where everyone contributed to all activities,
rather than individuals just working on one aspect of the programme. As such everyone
contributed some time to shelter construction, setting up early warning systems and dyke
construction, so collective ownership, as well as skills development and understanding were
The experience of the 2008 monsoon
During both early and late August 2008 water levels of 4.5 metres, as measured on recently
installed flood gauges were recorded. This is about 3.5 metres from the top of the bank (so 8
meters on the locally installed gauges is the critical level for local flood, as this is the point at
which river water would over flow the banks).
Following the floods the following issues and impacts were observed;
1. Some ripping and deterioration of sand bags was observed, but oddly this was at the higher
levels of the bank, rather than the lower where the bags were almost totally submerged.
After discussion it was decided this was
most likely the result of the fabric of the
bags breaking down under extreme sun light
(whereas they were protected under water).
The bags used were old cement bags, so in
future Practical Action will advise on the use
of new, rice-type bags, as these are thought
to be of better quality and more durable.
Additionally the possibility of using bags
made of natural fibers may be explored. All
damage to the bags caused by the floods of
July/August 2008 has already been repaired
by the community, at very little cost.
Damaged bags on the upper level of the dyke.
2. At the extreme down
stream end of the dyke the
lateral drain at the top was
not fully completed before
the on-set of the monsoon.
As such water percolating
through the dyke caused
the leading edge of the
dyke to collapse and a
section of bags to slip
about a meter (though they
were not washed away).
This has proved the value
and effectiveness of the
drain and as such this has
now been extended to
ensure protection of the
Slippage caused by saturation of the dyke from the landward side
3. Bamboo matting woven between the posts has almost totally been washed away, as have
some posts. This was foreseen and is acknowledged by the community as a component which
will have to be replaced annually. However the posts have also caught a lot of floating debris
which community members are convinced has added to the strength and resilience of the dyke.
The posts and matting have also encouraged the deposition of sand and silt (due to flood waters
being forced to slow down), which have also added strength to the dyke.
“We missed the fact that
we should use the bamboo
immediately after cutting,
as live it can create a living
performed very well this
year because the dyke
sieves and catches mud
and other materials”
– Kali Prasad. President
Ward 6 project
Bamboo shoots beginning to
spontaneously sprout from posts on
the Balapur dyke. August 2008
5. As the communities were not totally convinced of the effectiveness of the approach stone
spurs were build both upstream and down stream of the sloping bank. Interestingly the gabion
spur down stream in particular was badly distorted by this years flood (indicating the floods
power and ferocity) and is unlikely to last many years before being completely destroyed.
Beyond this the existing
‘natural’ vertical bank has
again been cut back, by
between 1.5 and 2 meters,
with this likely to continue
year on year. In reality
however this level of erosion
is very small, as only a small
distance further down stream
bank up to a depth of 20
meters has been lost, which
is more ‘normal’.
Badly damage stone spur
immediately below the sand bagged
Community members are convinced the relatively small amount of land lost in the area
immediately down stream of the dyke is the result of the main channel of the river being
redirected across towards the far bank, where it was some years previously.
While it is not possible to claim this is solely the result of the dyke, the fact that the sloping
bank allows water to rise unrestricted up it, where previously the vertical bank gave only the
opportunity to undermine it, does seem to have effected the rivers morphology and made it more
likely to deposit materials than remove them.
“We never expected the result we have achieved…. now we have seen the reality and
seen the real effects, this is why this work is so wonderful and exciting for us” -
Sobendra Chaudhary – PIC secretary
The community of Balapur are now keen to extend the sloping bank work both up and down
stream of the existing pilot plot and have already approached local NGOs and the municipality
for support. Similarly communities from further down stream, from Ward 10, are also interested
in using the approach, while staff from the DWIDP (Department for Water induced Disaster
Preparedness) among others have also visited, to assess the approach and gather information, as
this is not an approach currently practiced by themselves.
Practical Action itself intends to further explore technical aspects of the approach, such as
alternative materials and the influence of different soil types, while it’s also committed to using
the expertise which now exists within the community in Balapur to further disseminate the
approach both in terms of the technology used and the approach to community mobilisation.
Learning and future developments
o Using this approach dykes can be added to, improved, or repaired incrementally as time and
resources permit. In the case of gabion work this type of construction will always require a
major financial outlay.
o Unless banks are cut back to a sufficiently low angle undermining may still occur. The angle
is likely to be less critical in structurally less critical locations, such as the inside of bends,
but far more so in highly vulnerable areas such as the outsides of bends, where maximum
Balapur dyke mid-monsoon. Post-monsoon the stone gabion work was badly damaged
while the sloping bank remained almost totally intact.
o The creation of upslope drainage seems critical to bank stability. To stint on this aspect is
likely to be counter productive and could result in total slope failure.
o In the case of Balapur the line of sandbags currently ends about 2 metres below the top/line
of the lateral drain. Community members now realise this gives further opportunity for
surface run-off and rain water ingress into the dyke and as such will soon extend this line of
bags to the very top.
o Making the slope of the bank inconsistent could offer the potential for flood water to exploit
an area of weakness. As such the community in Balapur have decided to take greater care in
maintaining a completely uniform slope angle in future dyke work.
o The use of non light-degradable bags seems fairly critical. In future experimentation with
other technologies might also be worth exploring, such as the covering of slopes with matting
or netting and the use of natural rather than man-made fibers.
o Originally it was planned that bags would only be 2/3 filled, with the unfilled section
underlying the next bag above. In the event, due to bags being smaller than ideal, all bags
were fully filled. While these have served satisfactorily in future the original plan is likely to
be reverted to, as overlaying can only add strength.
o It is too early to assess the success of planting bamboo within the fabric of the slope. Long
term however it will be worth experimenting with other plant varieties as well as looking at
creating ‘live’ barriers by artificially encouraging barrier plants to inter-grow and combine
with structural measures such as the vertical bamboo poles already used. In the construction
of the bamboo components of the dyke bamboo which had been cut 15-20 days previously,
and allowed to dry, was mainly used. However 6 or 7 ‘fresh’ poles were used which have
subsequently sprouted and are setting down roots. In the past it was the practice to cut off
all the “eyes” or “knots” on the bamboo but now the community believe they should use
unprocessed, freshly cut bamboo, so it can grow.
Keeping community participation records.
“We will extend this work on the other bank also, by which we will save our village. To
achieve this we will collect local materials such as bamboo, sticks and other raw
materials” – Kali Prasad. President Ward 6 project implementation committee.
“Yesterday (27th August) we visited the site along with other PIC members, villagers
and people who use the place as a ferry crossing. The river level was 3.4 metres so
we went to observe the level and to see the work was still intact. It was” – Sobendra
Chaudhary – PIC secretary.
See the Practical Action “Technical Brief” on Gabion box construction in Practical Actions previous DIPECHO
project in Chitwan and Nawalaparsi at http://practicalaction.org/practicalanswers/index.php?cPath=57
Disaster Risk Reduction
DIPECHO is the disaster preparedness component/funding line within the European Commissions broader
Humanitarian Aid department (ECHO)
The Terai is a flat flood plain extending the entire length of Nepal, along its boarder with India.
All prices and exchange rates used are as of 1st September 2008.