20320130405015

International Journal of Civil Engineering OF CIVIL ENGINEERING AND
INTERNATIONAL JOURNAL and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 5, September – October (2013), © IAEME

TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 4, Issue 5, September – October, pp. 143-151
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2013): 5.3277 (Calculated by GISI)
www.jifactor.com

IJCIET
©IAEME

VETIVER AS A GREEN AND ECONOMICAL TECHNOLOGY TO
PROTECT RIVER BANK IN BANGLADESH
Arifuzzaman1, Md. Anisuzzaman2, Md. Mostafizur Rahman3 & Farhana Akhter4
1

2

Lecturer, Department of Civil Engineering, UITS, Dhaka, Bangladesh.
Graduate Student, Faculty of Geological Engineering, University of Padjadjaran, Indonesia.
3
4

ABSTRACT
River bank failures occur continuously throughout Bangladesh. From a strict economic
viewpoint, cost of ramification of these problems is high, and the national budget for such works is
never sufficient. It was found that the traditional practices for embankment protections are
expensive, not eco-friendly and sometimes not effective due to improper design and construction
fault for the designed life. On the other hand, protection of embankment slopes and river bank using
vetiver grass (Vetiveria zizanioides) is being used in many countries of the world. A device is
developed to determine the in-situ shear strength of the vetiver rooted block soil matrix and the bared
block soil. It is found that the cohesion and angle of internal friction of vetiver rooted soil matrix is
significantly higher than those of the bared soil. It is found that factor of safety of the embankment
protected by vetiver grass is 1.76 to 2.06 times higher than that of embankment without any
protection. The cost of slope protection by vetiver grass is significantly lower than the cost of other
available slope protection measures. Also, it generates zero carbon-di-oxide. Therefore, it can be said
that vetiver grass plantation might be an economical and sustainable green solution for the protection
of river banks against natural disasters in Bangladesh.
Key words: Bank Protection, Economical, Green, Natural Disaster, Vetiver Plantation.
1.

INTRODUCTION

Bangladesh is one of the most populated countries in the world having population density
more than 850 per square kilometer [1]. Bangladesh, with its repeated cycle of floods, cyclones, and
storm surges has proved to be one of the most disaster-prone areas of the world. During the years
from 1797 to 2007, Bangladesh has been hit by more than 60 severe cyclones. Bangladesh is a land
143

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
of rivers and has a largest sea beach in the world. River bank and embankment failure occurs each
and every year in our country. About 4000 km of coastal embankments and 4600 km of
embankments along the bank of big rivers have been constructed to safeguard against inundation,
intrusion of saline water and devastation [2].
According to the population census in 2001, some 35 million people live in the coastal region
which is 28% of the total population [1]. As the embankments and other hydraulic structures are the
first and immediate defense against the storm surge, they face the most severe damages. As for
example, cyclone SIDR destroyed fully 362 km and partially 1927 km of coastal embankment,
whose damage value is 32 million US$ [3].
But unfortunately, our State budget is never sufficient which confines rigid structural
protection measures to the most acute sections, never to the full length of the river bank or coastline
and embankment. This bandage approach compounds the problem. The traditional practice for
protection of such embankment slopes is to use cement concrete (CC) blocks, stone or wood
revetments, geotextile, geobags and improper plantation etc. These are expensive and in many cases
not effective to protect them during their designed lives. On the other hand, protection of slopes by
long rooted vegetation like vetiver grass (Vetiveria zizanioides) is being used in many other
countries efficiently. Many research have been conducted in abroad to know the performance of
vetiver grass against climatic change, slope protection, coastal embankment protection erosion
control and so on.
Hengchaovanich [4] analyzed slope stability based on vetiver root strength. Ke et al. [5]
tested vetiver as a bank protection measure on several test sites (in Australia, China, Philippines and
Vietnam). Their tests showed promising results for the use of vetiver grass as a bank protection
measure.
To evaluate the actual performance of vetiver grass for protection of river bank, it is
necessary to estimate the factor of safety against the natural forces. In-situ shear strength
determination of rooted soil matrix is essential to evaluate the performance of vegetative soil against
natural forces. However, no such research has been conducted to know the in-situ strength of vetiver
rooted soil matrix for proper understanding and analysis of slope stability. On this goal, the present
research investigates the usefulness of vetiver grass in protection of river bank against natural
hazards such as erosion, tidal surge and flood. The present study also compares the costs of different
slope or bank protection measures used in Bangladesh.
2.

CAUSES OF EMBANKMENT OR RIVER BANK FAILURE AND PROTECTIVE
MEASURES

River Banks are dynamic interface zones involving the meeting of atmosphere, land and
river. From the field survey and past studies it was observed that, the most common causes of
embankments and river bank failure can be broadly classified into two major groups [6].
a)
Natural forces (such as; rainfall impact, wave action, wind action etc)
b)
Human interference (such as; travel paths for men and cattle, cattle grazing, unplanned
forestation of embankment slopes etc)
2.1 Natural forces
The natural forces which are responsible for embankment erosion or damage are discussed in
this section.
a)

Rainfall impact
Mean annual rainfall varies from 1500 mm in the northwest (Khulna district) to over 3750 mm
in the south (Cox’s Bazar) of Bangladesh. The heaviest rainfall occurs in July and ranges from 350
144

mm to over 875 mm accordingly. The slope erosion caused by rain runoff is enormous and its
speed/force grows exponentially towards the toe. Toe erosion is the combined effect of runoff and
wave action. Figure 1.a shows the impact of rainfall, surface runoff and high head of water on the
river side. From the Figure 1.a it is seen that due to heavy rainfall and surface runoff holes and
gullies are formed on the embankment surface and lead to initiate piping action.
b) Wave action
Tidal waves cause damage to the embankments located too near to the river. A severe hydraulic
load is steadily exerted on the toes and slopes and causes erosion. Cyclonic storms in the coastal
zone (occurring repeatedly) act upon the water surface, causing it to advance towards the shore with
enormous hydraulic loads. The waves thus formed eventually hit the embankment toe and slopes.
The high hydraulic loads exerted on the embankment cause erosion and if there is overtopping, the
physical structure of the embankment is destroyed.
Photograph of Figure 1.b shows the wave action on a river embankment. Figure 1.b shows
failure of an embankment slope due to wave and tidal action, where no protective measures and no
vegetation at the slope of embankment are used. From the Figure, it is seen that due to wave and tidal
action the slopes of the embankment change its original shape and becomes steeper. Therefore, the
factor of safety of embankment becomes lower and lower and the vulnerability of embankment
increases.
c)

Wind action
The slow and steady action of wind in the relatively sparse fields and river lines blows away the
topsoil of the embankments where it is sandy or a mixture of silt and sand. But wind with the high
velocity during cyclone may lead overturning or uprooting of trees on the embankment slope. This
may cause severe injury of the coastal embankment. Photograph of Figure 2 shows the failure of
embankment slope due to overturning or uprooting of trees during cyclone. It indicates that only
plantation can’t protect the embankment and also cause problem to transfer relief material and
communication during disaster. Therefore, it is essential to select long rooted trees with suitable
vegetation for environment friendly solution and the best performance of embankments.

2.2 Common practices for embankment protection
The traditional practice for protection of embankments/river banks in Bangladesh
Rainfall Impact

Initiate of hole

EGL

Piping

Runoff
EGL

Firm Base

(a)

(b)

Fig. 1: Reasons of embankment failure: (a) impact of rainfall, surface runoff and high head of water;
(b) slope of embankments are eroded or enhanced to fail due to wave action(JSCE Investigation
Report, 2008

145


Fig. 2: Photograph showing the failure of embankment due to overturning or uprooting of trees
during cyclone

(a)

(b)

Fig. 3: Poor performance of the revetment structure: (a) poor performance of sand bags against
cyclonic storm surge and (b) poor performance of CC blocks on a newly constructed embankment.
is to use cement concrete (CC) blocks, stone or wood revetments, geotextiles, geobags and plantation
etc. Usually, cement concrete (CC) blocks are used where storm surge is high. Sand bags and wood
revetments are used where flow of water is moderately high. Protection of embankment by plantation
is also another practice in our country. But unfortunately, it is also not effective during cyclone
because of overturning or uprooting of trees.
Photograph of Figures 3.a~3.b shows the poor performance of a revetment structure on a
newly constructed embankment. Figure 3.a shows that sand bags were washed away from some
portion of the embankment slope due to wave action. Thus it made the embankment slope
unprotected and vulnerable at this portion and this weak portion may lead the embankment failure.
Figure 3.b shows that protected embankment slopes by cement concrete (CC) blocks were failed.
The reasons of this failure may be the lack of proper compaction of embankment slope, existing soft
layer(s) below the embankment, lack of proper placement of CC blocks on the embankment slope or
high tidal surge make the embankment toe weak and wash away the soil particles below the CC
blocks, etc.

146

3.

EXPERIMENTAL PROGRAM

Field tests were conducted to determine the in-situ shear strength and failure strain of vetiver
rooted soil matrix and soil without root at Patuakhali region. Soil samples were also collected in
polythene bag during the field test for laboratory investigations.
3.1 In-situ shear strength of block samples
In-situ shear strength test was conducted in the field on twenty block samples. Tests were
conducted under different normal stresses at different depths. Normal stresses for the in-situ tests
were arbitrarily selected in the range between 10.96 kPa and 19.98 kPa.
3.1.1 Apparatus for in-situ shear strength test
A device was developed in this study to determine the in-situ shear strength of the vetiver
rooted soil and soil without root. The apparatus used for the in-situ shear strength tests were
hydraulic jack, pressure gauge, wooden plate, metal plate, metal box (approx. 29×15×19 cm3),
normal load and Linear Variable Displacement Transducer (LVDT). The capacity of the pressure
gauge used for this in-situ shear strength test was 800 psi and the capacity of LVDT was 50 mm.
Both the pressure gauge and LVTD were calibrated before using them in the test.
3.1.2 Preparation of block sample
Clump of vetiver grass was cut at the ground level with a sharp knife. Keeping the root
position undisturbed a trench of the size (1 m × 1m) was made up to the desired depth. Initially the
rooted area was greater than desired block sample size. After that the rooted area was made in
desired block sample shape by sharp knife. Photograph of Figures 4.a~4.b shows the preparation of
block soil sample for in-situ shear strength test.
3.1.3 Test set-up
Block samples (approx. 29×15×19 cm3) were tested at different depths (250 mm to 500 mm)
under different normal stresses at the field to know the in-situ strength of the rooted soil and soil
without root. After preparing the block sample in the desired shape the metal box (having bottom
face open) was smoothly pushed from the top of the block sample. Then normal load was placed on
the metal box. It was carefully ensured that, the bottom edge of the metal box could not touch the
ground level. Wooden plate was placed between the metal box and the hydraulic jack. The back sides
of the hydraulic jack was made hard and smooth enough by placing brick and wooden plate between
the jack and edge of the prepared hole.

(a)

(b)

Fig. 4: Photograph showing preparation of block sample: (a) trench surrounding the clump of vetiver
grass and (b) prepared block sample of desired shape

147


1
1) Hydraulic jack
2) Wooden plate
3) Metal box
(0.29 × 0.15× 0.19 m3)

4

6

3
2

Sample is inside
the box

5

4) Normal load
5) Metal plate
6) LVDT

Failure line

Figure 5: Schematic diagram of the Experimental set-up
Then horizontal force was applied to the box from one side by hydraulic jack. Calibrated
pressure gauge was used to measure the horizontal force. The block sample was failed at the bottom
and the deflection of sample was measured by Linear Variable Displacement Transducer (LVDT)
which was fixed to the ground surface by metal plate. For this purpose, Linear Variable
Displacement Transducer (LVDT) having capacity of 50 mm was used to determine the horizontal
deformation. LVDT was placed on a metal box and fixed it with the metal plate by magnetic stand.
The metal plate is placed on the ground and the metal was fixed with the ground by metal clamp.
Figure 5 shows the schematic diagram of the test set-up for the in-situ test.
3.2 Laboratory tests
A detailed laboratory test was carried out on samples collected from Patuakhaali region. Tests
were conducted according to ASTM standards [7].
4.

RESULTS AND DISCUSSIONS

4.1 In-situ shear strength of block samples
Figure 6a shows the peak shear stress versus normal stress graph of bared and vetiver rooted
soil matrix at Patuakhali region. It is seen that the peak shear stress of vetiver rooted soil matrix is
always higher than that of bared soil for a particular normal stress. Strength of vetiver rooted soil is
about 1.90 times higher than that of the bared soil. Figures 6b show the increment of peak shear
stress versus normal stress of vetiver rooted soil matrix. It is seen from the Figure 6b that the
enhanced effective soil cohesion due to vetiver root matrix is 10.4 kPa and the enhanced effective
angle of internal friction is 21o, respectively. It means that Vetiver grass root might be able to protect
the river bank and embankment slopes from natural forces.
4.2 Stability of slopes
Stability of slopes for different heights and different slope angles are estimated by using mass
procedure of slope stability analysis. For this analysis it is considered that the density of sol is 18
kN/m3. The cohesion and angle of internal friction of vetiver rooted soil and bared soil is considered
15 kPa and 9 kPa and 35˚ and 18˚, respectively. Stability of slopes for different heights and different
slope angles are presented in the Table 1. It is found From the Table 1 that for a particular soil the
factor of safety of vetiver rooted soil slope is 1.8 to 2.1 times higher than that of the slope without
root.

148


15

(kPa)

40

(kPa)

τ

max

30

Increment of τ

max

Peak shear stress, τ

Depth from EGL = 300 mm

Depth from EGL = 300 mm

20

10

Veriver rooted soil matrix
Bared soil
15

20

= 0.38 σ + 10.4
n

10
Enhanced cohesion, c' = 10.4 kPa
o

Enhanced angle of friction,φ ' = 21
Vetiver rooted soil matrix

0
10

max

5
10

25

Normal stress, σ (kPa)

15
20
Normal stress, σ (kPa)

25

n

n

(a)

(b)

Figure 6: (a) Peak shear stress versus normal and (b) Increment of peak shear stress of vetiver rooted
soil matrix versus normal stress

Table 1: Comparison of factor of safety of embankment slope (by Mass Procedure)
Height of
embankment,
H (m)

Side
slope

Factor of safety of
embankment slopes
without protection,
Fsb

Factor of safety of
embankment slopes
with vetiver grass
protection, Fsv

Ratio
F
= sv
Fsb

(h : v)

2

2:1

2.7

5.4

2.00

3

2:1

2.4

4.3

1.79

3

1:1

1.6

3.0

1.88

4

2:1

1.8

3.8

2.11

4.3 Cost of different slope protection measures
According to the rate schedule of Local Government Engineering Department, LGED (July,
2009), the cost of vetiver application per square meter is 22 taka including labour and placement
cost. Again, according to the work schedules of Water Development Board of Bangladesh, WDB
(Dhaka Division Rate Schedule, 2009-2010) the cost of geotextiles and cement concrete blocks
including labour and placement cost per square meter are 151 taka and 5843 taka, respectively.
According to the rate schedule, the cost of one kilometer embankment section is estimated. Table 2
shows the cost estimation of the different slope protective measures. From the Table 2, it is seen that
the cost of slope protection for one kilometer of embankment by vetiver grass is 2109 US $, by
geotextiles is14475 US $ and by CC blocks is 560093 US $. Therefore, it is seen that the cost of
slope protection by vetiver grass is significantly lower than the other methods of slope protective
measures.

149

Table 2: Comparison between costs of different slope protective measures
Slope Protective
Measures

Cost Per Sq.
Meter

Height

Length

Width

Area

Cost

(m)

(m)

(m)

(m2)

(USD)

(USD)
Vetiver Grass

3.0

1000

6.71

6710

2109

Geotextiles

2.157

3.0

1000

6.71

6710

14475

CC block

5.

0.314

83.471

3.0

1000

6.71

6710

560093

CONCLUSIONS

River bank and embankment failures happen continuously throughout Bangladesh. It is found
that the general reasons of embankment failures are erosion due to rain splash, wave action and
overtopping of storm surge. Poor maintenance practice, overturning or uprooting of trees also
enhance embankment failure. The traditional practice for embankment protection is to use cement
concrete blocks, stone or wood revetments, geotextile and plantation etc. These are expensive and
not so effective to protect the embankments for the designed life. Protection of embankments by
bioengineering process (e.g., using vetiver grass) is being used in many countries efficiently. The
special attributes of vetiver grass is its longer life, strong and long finely structured root system and
high tolerance of extreme climatic change. It is seen that the enhanced effective soil cohesion due to
vetiver root matrix is 10.4 kPa and the enhanced effective angle of internal friction is 21o,
respectively. Again vetiver plantation can enhance the factor of safety for a particular soil is 1.8 to
2.1 times higher than that of the slope with bared soil.
The cost of slope protection by vetiver grass is significantly lower than the cost of other
available slope protection measures. Also, vetiver plantation generates zero carbon-di-oxide.
Therefore, it can be said that vetiver grass plantation might be an economical and sustainable green
solution for the protection of river banks against natural disasters in Bangladesh.
6.

REFERENCES
[1] BBS (2007). “Bangladesh Bureau of Statistics”, Statistical Year Book of Bangladesh, 26th
Edition, Ministry of Planning, Government of the People’s Republic of Bangladesh.
[2] Bangladesh Water Development Board, BWDB (2000). “The Dampara Water Management
Project.” A Joint Project by Bangladesh Water Development Board and Canadian
International Agency.
[3] DMB (2008). “Disaster Management Bureau”, Cyclone Sidr in Bangladesh: damage, loss,
and needs assessment for disaster recovery and reconstruction, a report prepared by the
Government of Bangladesh assisted by the International Development Community with
Financial Support from the European Commission.
[4] Hengchaovanich, D. (1998). “Vetiver grass for slope stabilization and erosion control.” Tech.
Bull. No. 1998/2, PRVN/ORDPB, Bangkok, Thailand.
[5] Ke, C.C., Feng, Z.Y., Wu, X.J., and Tu, F.G. (2003). “Design principles and engineering
samples of applying vetiver eco-engineering technology for landslide control and slope
stabilization of riverbank.” Proc. of the 3rd International Conference on Vetiver, Guangzhou,
China.
150

[6] Islam, M.S., and Arifuzzaman. (2010). “Performance of vetiver grass in protecting
embankments in Bangladesh coast against cyclonic tidal surge.” Proc. of the 5th National
Conference and Expo on Coastal and Estuarine Habitat Restoration, Texas, USA.
(http://www.estuaries.org/pdf/2010).
[7] ASTM (1989). Annual Book of ASTM Standards, Vol. 04.08, Soil and Rock; Building
stones; Geotextiles.
[8] Ishwar Chand Sharma and Prof.Naresh Chandra Saxena, “Environmental Hazard and
Disaster in Disposing Marble Slurry”, International Journal of Civil Engineering &
Technology (IJCIET), Volume 3, Issue 1, 2012, pp. 62 - 66, ISSN Print: 0976 – 6308,
ISSN Online: 0976 – 6316.

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