STUDI EKSPERIMENTAL PEMAMPATAN DAN KEKUA
International Conference on Environmental Technology and
Construction Engineering for Sustainable Development
ICETCESD-2011, March 10-12, 2011, SUST, Sylhet, Bangladesh
ENVIRONMENTAL IMPACTS OF USING SAND FILLED GEO-BAG
TECHNOLOGY UNDER WATER IN RIVER EROSION PROTECTION
OF MAJOR RIVERS IN BANGLADESH
MD. SARFARAZ WAHED, MD. SHIBLY SADIK* AND SYEDA MOHSINA MUHIT
Center for Environmental and Geographic Information Services, Bangladesh
SUMMARY:
Geotextile bag or geobag, a geosynthetic product made of polyester; polypropylene or
polyethylene has been used world wide for protecting riverbanks and hydraulic structures
from severe scouring and erosion. In Bangladesh, geobags have been used under water in
protective works since 1999 for its cost effectiveness and sustainability. The first large scale
adoption of Geobags was through the Jamuna Meghna River Erosion Mitigation Project
(JMREMP) of BWDB supported by the ADB. Since 2002, JMREMP has been using sand
filled Geobags under water with cement concrete (CC) blocks along the major rivers of the
country like Meghna and Jamuna. This study was conducted to assess the Ecological Impacts
of using Sand-filled Geo-Bags under water as a protective measure of river erosion. The
overall methodology of this study was a kind of systematic and sequential multidisciplinary
approach that included application of expert judgment, stakeholder consultation, local
people’s perception and simulation. The impact identification and evaluation was carried out
comparing the protective works using geobags with CC block and protective works without
geobags. Followed by the risk characterization and categorization, the risk assessment frame
work was formulated and employed to assess the overall risk of using geobag. Geobag
technology possesses minimal impacts on fish resources and facilitates fishing activities. The
protective works using geobag protects the terrestrial habitat while it shows some negative
impact on aquatic ecosystem by altering the habitat of the benthic community and local
shifting of the migratory routes of the dolphin. On the other hand it facilitates the algal
community to grow. Moreover, geobags is also friendly for the wildlife like jackal, fishing,
cat, amphibians for accessing river while assorted dumped CC blocks make barrier or
difficulties of accessing river for the wildlife.
Key Words: River bank erosion, protective measures, Sand filled Geobag, Ecosystem habitat,
Eco-friendly, Fisheries habitat and Ecological risk
1. INTRODUCTION
Protection of the river bank along the major rivers of Bangladesh has always been considered
as a challenging engineering task against the nature and Bangladesh Water Development
Board (BWDB) has been practicing different technology for controlling river bank erosion
with the purpose of protecting lives and livelihoods. Its impact on environment especially on
ecosystem is also a debating issue. In response to national concern on effective erosion
protection measure and its cost effectiveness, BWDB has adopted sand-filled geo-textile bags
(Geo bags) technology in many places for protective works at eroding riverbanks since 1999
while the technology has been being popular world widely due to its easier installation, cost
effectiveness and technical efficiency [1, 2 and 3]. It was first used in Bangladesh during
FAP-21 project to protect the riverbank erosion of the Jamuna River [2]. The JamunaMeghna River Erosion Mitigation Project (JMREMP), supported through ADB loan 1941
BAN (SF), is using geo-bags substantially from the year 2002 to protect the riverbank erosion
of Jamuna River [4]. The major vision and choice of the project are to develop innovative,
cost effective, environment friendly and sustainable riverbank protection solutions and it
suggests adopting the technology of using sand filled geobags under water in major rivers of
the country [2].
In response to concerns of different stakeholders, Bangladesh Water Development Board
(BWDB) felt that environmental impact assessment of the use of geobags placed under water
to protect eroding riverbanks might be carried out before envisaged nationwide extension of
using this technology. This paper has been prepared based on the EIA study carried out by
CEGIS as a technical adviser of BWDB [see 5] and only the ecological impacts including
fisheries are presented here.
2. COST EFFECTIVENESS OF GEOBAG
In compare to conventional erosion protection work using C.C. block, gravel, hard rock
etc, sand filled geobags technology involves less cost. World widely it has been seen that
erosion protection work using Geobags requires less installation and maintenance cost
[1], light weight equipment, less space for construction works, transportation cost, less
energy requirement [6]. A joint study of Bangladesh University of Engineering and
Technology (BUET), BWDB and Institute of Water Modeling (IWM) reveals that Geobag
used in different revetment work along the major rivers of Bangladesh (Jamuna and
Meghna) results 40% to 60% cost reduction [2]. The constructing materials (sand) of
geobag are locally available and cost-effective compared to importing boulders from
other countries. The manufacturing of geobags and quality control of the bags are easy
compared to the C.C. blocks and boulders.
3. TECHNICAL EFFICIENCY
Sand filled Geobags work as a substitute of C.C. blocks used as dumping material, even
though geo-bags are sometimes used as filter material below C.C. blocks [7]. A physical
modeling study under JMREMP [3] found that launching performance of sand filled
geobags is better than C.C. block but lower than rounded and angular rock. The joint
venture study of BWDB, BUET and IWM suggests [2] that the launching performance of
geobag could be found similar to hard materials if area coverage method is applied
instead of mass dumping method. The major advantages of Geobags are its availability
and easier implementation. Geobags are readily available and transportable (when empty)
and can be easily filled with local sand and formed with a range of sizes to fit specific
application. On the other hand, main demerit of geobag is its high sensitivity to UV
radiation and highly alkaline or acidic water [9 and 10]. Solar UV radiation stimulates its
polemeric ageing process. Depending on its constituent strains’ properties, its life
642
expectancy could be reduced 15% to 75% in one year exposure [9]. Ageing due to UV
radiation could be protected by using some stabilizers [11]. Geobags available in our
markets have resistance to 160 kilo Langley per year solar radiation [5] while Bangladesh
falls in the zone of 180 to 140 kilo Langley per year solar radiation [12]. Highly acidic
and alkaline water could also significantly reduce geobags’ property through chemical
degradation [10] and fortunately major rivers of Bangladesh show neutral pH (6 to 7) [2
and 5].
4. USE OF GEOBAG IN BANGLADESH
The sand filled geobags were firstly used in Bank Protection and River Training Pilot
Project, FAP 21/22 at limited extend. Later, in Pabna Irrigation and Rural Development
Project (PIRDP) and Meghna Dhonagoda Irrigation Project (MDIP), sand filled geobags
were used under the aegis of Jamuna Meghna River Erosion Mitigation Project
(JMREMP) during 2002. As on 2006-2007, sand filled geobags have been used under
water successfully in approximately 20 km of River bank protection work [2]. Recently,
this technology has been used for protecting river bank along the Major rivers of
Bangladesh i.e Jamuna, Ganges, Padma and Meghna.
5. METHODOLOGY
This study was carried out following the guideline for Environmental Assessment of
Water Management Projects [8] and the Environmental Assessment requirements of
Asian Development Bank (ADB). The environmental impact of sand filled geobags used
under water has been made comparing with protective works using only C.C. Block. The
environment intervened by protective works using only C.C. Block was considered as
control environment. Comparing with this control environment, the impacts of sand filled
geobags on Environment were identified.
5.1. Study area
The study was conducted by investigating two similar reaches (hydraulic, socio-economic
and environmental consideration): one is protection with geo-bags in addition to C.C.
blocks under water (study area) and other (control area) being protected by using C.C.
blocks only. In order to examine the effects of saline and non-saline water on geobags,
four major rivers (Ganges, Padma, Jamuna and lower Meghna) were selected covering
both saline and non-saline zone, which gave a comprehensive context of the whole
country. In total 6 control areas and 6 study areas were selected as summarized in the
Table 1.
643
Table 1: List of control and study area
Zone
River
Ganges
Non
Saline
Padma
Jamuna
Saline
Lower
Meghna
Location
Boiddnathpur, Chapai Nawabganj
Boiddnathpur, Chapai Nawabganj
Faridpur
PIRDP, Bera Pabna
Sirajganj Hardpoint
Sirajganj Hardpoint
Horar Hat, Bhola
Hakimuddin Bazar, Borhanuddin
Baliakandi, Tazumuddin
Ramprashad, Tazumuddin
Ramprashad, Tazumuddin
Control/study area
Study area
Control area
Study area
Control area
Study area
Control area
Control area
Study area
Study area
Study area
Control area
5.2. Materials and methods
The study was carried out through interdisciplinary approach while a multidisciplinary
team was involved. Local people participation was ensured through PRA and RRA
approach. World standard EIA process consisting with a composite set of adhoc, checklist
and matrix methods was employed in the EIA study where both secondary and primary
data were used. Local knowledge was incorporated in the study process through
Stakeholder Consultation, Key Informants Interview and Focus Group Discussion (FGD).
5.3. Impact evaluation and risk characterization
Considering all potential and observed impact, risk assessment was accomplished
eventually after characterizing and categorizing the risk of each potential and observed
impact of using geo-bags under water. For better understanding and screening, word
scenarios were developed for each categories of the risk. The basis of risk
characterization was likeliness and consequence of the impact. Followed by the risk
characterization and categorization, a risk assessment framework was developed that was
employed to assess the overall environmental risk of using geobag. An empirical scale
was developed to limit the subjective assessment of the risk. Table 2 shows the risk
assessment framework. The process of the risk assessment was carried out through
workshop where expertise of the EIA study team members as well as the experience of
BWDB Engineers were utilized to finalize the risk matrix.
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Table 2: Risk assessment framework
COMPONENT
CONSEQUENCE
No or insignificant
negative impact
Localized, short time
degradation of
sensitive ecological
habitat
Localized long term/ short
term, widespread,
degradation of ecological
habitat
Widespread, long term
degradation of ecological
habitat,
Permanent degradation of
ecological habitat
Fish Habitat,
production and
composition
No or insignificant
negative impact
Localized, short time
degradation of fish
habitat
Localized long term/ short
term, widespread,
degradation of habitat,
species proportional change
in fish composition
Widespread, long term
degradation of fish habitat,
and change fish
composition, effects on
sensitive habitat and species
Permanent degradation of
fish habitat, extinction of
any fish species
Ranking
Insignificant
Minor
Moderate
Significant
Catastrophic
Ecosystem
Terrestrial and
Aquatic
Ecosystem
Fisheries
Risk assessment framework
(Without application of mitigation and management measures)
IKELIHOOD OF OCCURANCE
Likelihood Descriptions
Ranking
Index
1
2
3
4
5
Consequence occurs immediate after the project
implementation
Frequent
5
5
10
15
20
25
Conditions may allow the consequence to occur during the
project lifetime
Likely
4
4
8
12
16
20
Exceptional consequences to occur within the project
lifetime
Occasional
3
3
6
9
12
15
Conditions do not seem to occur any consequence except
some extreme cases
Seldom
2
2
4
6
8
10
Reasonable to expect that the consequence will not occur
though it has rare possibility to occur
Rare
1
1
2
3
4
5
1- below 5: Low risk, mitigations may be
applied
5- below 10: Risk is Acceptable, mitigations
may be applied
10 – below 15: Medium risks, risk
reduction is required
645
15 – below 20: High risks, mitigations
must be applied
20 to – below 25: Extremely high,
mitigations must be applied
6. GENERAL DESCRIPTION OF THE PROTECTIVES WORKS IN THE STUDY
AREA
Though the design and specifications are different in different protective works, in general
protective works were found combined typed where C.C Block and sand filled geobags
were placed under water. The design includes, earth filled compaction, slope pitching works
over geotextile, assorted block placing and geobag placing on berm and geobag dumping.
There are three different sizes of geobags that are used in protective works: Type A- 175 kg,
Type B- 150 kg, and Type C- 126 kg.
7. ECOLOGICAL IMPACTS OF USING SAND FILLED GEOBAG UNDER WATER
7.1 Impacts on ecosystem
7.1.1 Impact on water quality
Geobags used under water in protective works are chemically inert. Chemical analysis of
river water quality at study sites found within the standard of DoE. Water turbidity near
geobags using protective works is found very lower than that of C.C. block using protected
sites.
7.1.2 Impact on ecosystem habitat
The C.C. block using protective work requires huge site clearance activities including
removal of top soil, and vegetation. The construction works includes stone crashing, mixing,
block casting, construction materials transportation and storage, and vehicle movement may
source the fugitive particulate matter that might have impact on surrounding ecosystem
habitat especially on roadside vegetation, agricultural ecosystem and riverine ecosystem.
There will be potential of same impact during emergency dumping and rehabilitation if
further construction activities are required.
On the other hand, there is no such negative impact or condition that might allow having
potential negative impacts of using geobags on ecosystem habitat. The negative impacts
associated with site clearance and construction activities are minimal. During the dumping,
water turbidity increases that might affect habitat quality. Compare to protective works using
only C.C. blocks, geobags are more effective in arresting sediment [2] that improves the
water transparency, which is helpful for ecological productivity. However, these impacts are
localized, temporal and reversible.
During operational phase, the resultant negative impact of geobag use is also minimal. Some
small amount of land is required for stocking of sand and geobags for emergency dumping.
7.1.2 Impacts on terrestrial flora
C.C. Block using protection works involve huge site clearance and base stripping activities.
Moreover, the airborne particulate matters may be spreading over the surrounding
agricultural field, homestead, social and roadside vegetation that might reduce floral
productivity. In case of geobags using technology, base stripping and construction activities
are minimal and result less impact on terrestrial flora.
7.1.3 Impacts on terrestrial fauna
C.C. block used under water and on bank slope may make the accessibility to river difficult
for few terrestrial fauna like, Jackel, Bangel fox, fishing cat and amphibians. The assorted
blocks over the bank slope may restrict the river from easy access for drinking, bathing and
hunting purposes of mentioned wildlife and livestock. On the other hand, Geobag has no such
impacts on river access.
7.1.4 Impacts on aquatic flora
Like C.C. block using technology, during construction phase, geobag using technology has
some impacts on aquatic flora like floating and submergible plants due to covering the
limnetic zone. But the impacts are local and short term. Due to high siltation rate, the limnetic
zone will be resuscitated. However, geobags also provide grounds for some floating plants
and algal community. Algal communities are found more frequently and densely in geobag
dumping zone than that of C.C. block.
7.1.5 Impacts on aquatic mammals
Ganges, Padma, Jamuna and Meghna are the important migratory routes of Dolphin, the
sensitive aquatic mammals. Dolphins choose thalweg as their migratory route. The dumping
activities (in both case of C.C. block and sand filled Geobag) may cause the shifting of their
migratory route temporary. But the dumped sand filled geobags don’t block the free
movement of the mammals like hard edges of C.C. blocks.
7.1.6 Impact on benthic community
C.C. block doesn’t cover the complete benthic zone. In that case, benthos community can
easily grow in interlock and the gap between blocks. On the other hand, dumped Geobags
completely cover the benthic zone of the river bank slope that might impact on benthic
habitats. However, it has been come out from the field observation that the impacts on
benthic zone are local, short term, and reversible. The high siltation rate over the geobags
covers the dumped geobag within a year and restores the benthic habitat.
7.2. Impact on fisheries
7.2.1. Impact on fish habitat
During dumping, the fish habitat and assemblages near river bank might be disturbed and
some damage of benthonic and planktonic community might be resulted. In addition, the
covering of river bed with geobag in limnetic zone may have some effects on some fishes e.g
Ayre (Aorichthys aor), Rita (Rita rita), boal (Wallago attu), Pangas (Pangasius pangasius),
different types of baim, gutum (Lepidocephalus guntea), bala (Glossogobius giuris) and some
small fish species by limiting their feeding opportunity. The regeneration of algae and
benthos community over the dumped geobags were found during field visit that indicates the
restoration of food sources for fish. The local fishers also support the indication of restoration
of fish habitat.
7.2.2 Impact on fish migration
Fish uses the river channel as a migratory route for feeding and breeding purpose and shelter
for brood, post larvae and juvenile stages. Fish migration may be affected locally for short
term during dumping and it might happen in both cases of protective work. The prudent
impact is due to shifting of thalweg. Shifting of thalweg due to enhanced sedimentation rate
and control of bed scouring may results in local shifting of fish migratory routes. Geobag has
more functional effectiveness to control the bed scouring than that of CC block [2].
7.2.3 Impact on fish production
Sediment and dust material runoff from the construction activities during the construction
may cause increase in river turbidity that may reduce fish breeding and fertilization of fish
eggs. Hence the potential of generating dust and fugitive materials is higher in CC block
using protective works than that of goebag using protective works, the impact on fish
production during construction will be minor in case of geobag using technology of
protective works.
647
7.2.4 Impact on fish species composition
The overall fish composition of the river depends on habitat and availability of food. Surface
fishes may be affected during the dumping of geobags. Likewise the C.C. block use, the
surface fish species may also shift locally for short term in case of geobag using protective
work. The covering of the river bed of the limonitic zone by geobag may affect the bottom
fishes. After placing of geo-bags, the fishes those live in holes (e.g. ell and cat fish) may
migrate from protective areas. Field observation and fishers perceptions support that the
underwater environment is restored within one or two year that would favor the habitat for
ells and cat fishes again.
7.2.5 Impact on fishing effort
In C.C. block dumped area, fishers can’t use any gear for fishing. Irregular shape of the
blocks causes damage to their nets. The space between the blocks helps fishes to hide from
nets. On the other hand, no such impact has been noticed in the geo-bags dumped areas.
8. RISK ASSESSMENT
Each of the aforementioned potential and observed impact was evaluated through the risk
assessment framework (Table 2 in methodology) to characterize the risk that also depicts
priority what should be taken into consideration during formulating environmental
management plan. This additional assessment and evaluation of the risk of each impact will
direct the policy makers to decide whether the impact would be acceptable or not; whether
the impact would require the mitigation, enhancement contingency and monitoring measures.
The summery of the risk assessment is briefed in Table 3 where it is seen geobags use under
water possess low risk of affecting fisheries which might be acceptable and medium risk of
affecting ecosystem which requires adoption of mitigation measures.
Table 3: Risk characterization and assessment
Sl
no.
Key potential impact
Likeli
hood
Consequ
ence
Risk
Subjective
meaning of
Risk
Response/ Action
Risk on Ecosystem
3
Impact on terrestrial habitat:
minor impact during
construction by sourcing
fugitive particulate matter
3
2
6
4
Impact on Aquatic habitat:
Have local, short time and
reversible impacts on benthic
communities
Local shifting of migratory
route of dolphin due to
shifting of thalweg
4
3
12
4
3
12
4
2
8
Risk is
Acceptable,
mitigations
may be
applied
EMP with mitigation,
and monitoring is
required
4
2
1
Risk is
Acceptable,
Mitigation and
monitoring measures
5
Risk on Fisheries
6
Impact on Fish Habitat:
Condition may affect cat fish
and ell habitat locally and for
short time. Combined
method facilitate fish
assemblage
7
Impact on Fish production:
No significant change
648
Risk is
Acceptable,
mitigations
may be
applied
Medium
risks, risk
reduction is
required
Medium
risks, risk
reduction is
required
Mitigation measure may
required during
construction phase
EMP with mitigation and
monitoring measures for
pre, during and post
construction phase
EMP with mitigation and
monitoring measures for
pre, during and post
construction phase
Sl
no.
8
Key potential impact
Impact on Fish composition:
Local, short time and minor
reduction of cat fish and eel.
Likeli
hood
4
Consequ
ence
2
Risk
8
Subjective
meaning of
Risk
mitigations
may be
applied
Risk is
Acceptable,
mitigations
may be
applied
Response/ Action
may be adopt
Mitigation and
monitoring measures are
required
9. CONCLUDING REMARKS:
Use of sand filled geobags under water in erosion protection work is being popular due to
its cost effectiveness, availability and easier implementation. Some recent studies support
that its technical efficiency is similar or sometimes better than use of hard material.
Bangladesh Water Development Board has implemented numbers of river bank erosion
protection works using sand filled geobag under JMREMP and is going to adopt this
technology widely in erosion protection works of the country. Prior to nationwide
adoption of this technology, the interaction between goebag and environment has been
assessed through EIA and this paper presents only the ecological impacts of geobags use
under water.
Despite the cost effectiveness, there are potentiality of resulting some negative impacts
like short term shifting of some surface and bottom fishes, covering of river slope bed in
limnotic zone, temporal alteration of benthonic habitat and local shifting of Dolphin
migratory route due to induced sedimentation. However, these impacts are acceptable and
could be reduced by adopting mitigation measures. In compare to C.C. block use the
construction and post-construction impacts are very minimal as it involves less
construction activities, generating less construction waste and no chemical alteration to
water quality. At the end it can be concluded that, in compare to C.C. block use, the
geobag use is more ecosystem and fisheries friendly.
However for better environmental sustainability, an Environmental Management Plan
should be adopted with detail plan for mitigating negative impacts, enhancing expected
benefits and regular monitoring of EMP implementation and resulted impacts. Farther
research might be carried out in developing an appropriate Environmental Management
Plan that would be easier in following and implementing.
10. ACKNOWLEDGEMENT
Mr. Md. Abdul Quddus, Project Director, Jamuna Meghna River Erosion Mitigation
Project (JMREMP) is greatly acknowledged for his guidance and suggestion. Advice and
direction of Mr. Giasuddin Ahmed Choudhury, Executive Director, CEGIS are sincerely
acknowledged. Mr. Md. Waji Ullah, Team Leader EIA study and Mr. Mujibul Huq,
Environmental Advisor EIA study are also respectfully acknowledged for supervising and
continuous guidance in preparing this paper. Timely facilitation and support of Dr. Anil
Chandra Aich, Project Leader, EIA study is appreciated with gratitude.
649
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[2] BWDB [2008]. Technical report of Joint committee of BUET, IWM and BWDB on
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Protection Works (in Bangla). Bangladesh Water Development Board, Ministry of Water
Resources, The Government of People’s Republic of Bangladesh.
[3] NHC [2006]. Physical Model Study, Final report, Jamuna Meghna River Erosion
Mitigation Project (JMREMP), Northwest Hydraulic Consultant, Vancouver- Canada,
Bangladesh Water Development Board (BWDB), Ministry of Water Resources.
[4]
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[2009].
Final
Inception
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[5] CEGIS [2009]. Draft Final Report on Environmental Impact Assessment (EIA of using
Sand Filled Geo-bags under Water. Submitted to Bangladesh Water Development Board
(BWDB), Center for Environmental and Geographic Information Services (CEGS).
[6] Kent von Maubeuge, Naue Fasertechnik GmbH & Co. KG. Both Economy and Ecology
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http://geosynthetica.net/tech_docs/NaueEconomyEcology.pdf, accessed on 15 January 2011.
[7] Korkut, R., Martinez, E. J., Morales, R., Ettema, R., and Barkdoll, B., 2007, Geobag
Performance as Scour Countermeasure for Bridge Abutments, American Society of Civil
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Bangladesh.
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650
Construction Engineering for Sustainable Development
ICETCESD-2011, March 10-12, 2011, SUST, Sylhet, Bangladesh
ENVIRONMENTAL IMPACTS OF USING SAND FILLED GEO-BAG
TECHNOLOGY UNDER WATER IN RIVER EROSION PROTECTION
OF MAJOR RIVERS IN BANGLADESH
MD. SARFARAZ WAHED, MD. SHIBLY SADIK* AND SYEDA MOHSINA MUHIT
Center for Environmental and Geographic Information Services, Bangladesh
SUMMARY:
Geotextile bag or geobag, a geosynthetic product made of polyester; polypropylene or
polyethylene has been used world wide for protecting riverbanks and hydraulic structures
from severe scouring and erosion. In Bangladesh, geobags have been used under water in
protective works since 1999 for its cost effectiveness and sustainability. The first large scale
adoption of Geobags was through the Jamuna Meghna River Erosion Mitigation Project
(JMREMP) of BWDB supported by the ADB. Since 2002, JMREMP has been using sand
filled Geobags under water with cement concrete (CC) blocks along the major rivers of the
country like Meghna and Jamuna. This study was conducted to assess the Ecological Impacts
of using Sand-filled Geo-Bags under water as a protective measure of river erosion. The
overall methodology of this study was a kind of systematic and sequential multidisciplinary
approach that included application of expert judgment, stakeholder consultation, local
people’s perception and simulation. The impact identification and evaluation was carried out
comparing the protective works using geobags with CC block and protective works without
geobags. Followed by the risk characterization and categorization, the risk assessment frame
work was formulated and employed to assess the overall risk of using geobag. Geobag
technology possesses minimal impacts on fish resources and facilitates fishing activities. The
protective works using geobag protects the terrestrial habitat while it shows some negative
impact on aquatic ecosystem by altering the habitat of the benthic community and local
shifting of the migratory routes of the dolphin. On the other hand it facilitates the algal
community to grow. Moreover, geobags is also friendly for the wildlife like jackal, fishing,
cat, amphibians for accessing river while assorted dumped CC blocks make barrier or
difficulties of accessing river for the wildlife.
Key Words: River bank erosion, protective measures, Sand filled Geobag, Ecosystem habitat,
Eco-friendly, Fisheries habitat and Ecological risk
1. INTRODUCTION
Protection of the river bank along the major rivers of Bangladesh has always been considered
as a challenging engineering task against the nature and Bangladesh Water Development
Board (BWDB) has been practicing different technology for controlling river bank erosion
with the purpose of protecting lives and livelihoods. Its impact on environment especially on
ecosystem is also a debating issue. In response to national concern on effective erosion
protection measure and its cost effectiveness, BWDB has adopted sand-filled geo-textile bags
(Geo bags) technology in many places for protective works at eroding riverbanks since 1999
while the technology has been being popular world widely due to its easier installation, cost
effectiveness and technical efficiency [1, 2 and 3]. It was first used in Bangladesh during
FAP-21 project to protect the riverbank erosion of the Jamuna River [2]. The JamunaMeghna River Erosion Mitigation Project (JMREMP), supported through ADB loan 1941
BAN (SF), is using geo-bags substantially from the year 2002 to protect the riverbank erosion
of Jamuna River [4]. The major vision and choice of the project are to develop innovative,
cost effective, environment friendly and sustainable riverbank protection solutions and it
suggests adopting the technology of using sand filled geobags under water in major rivers of
the country [2].
In response to concerns of different stakeholders, Bangladesh Water Development Board
(BWDB) felt that environmental impact assessment of the use of geobags placed under water
to protect eroding riverbanks might be carried out before envisaged nationwide extension of
using this technology. This paper has been prepared based on the EIA study carried out by
CEGIS as a technical adviser of BWDB [see 5] and only the ecological impacts including
fisheries are presented here.
2. COST EFFECTIVENESS OF GEOBAG
In compare to conventional erosion protection work using C.C. block, gravel, hard rock
etc, sand filled geobags technology involves less cost. World widely it has been seen that
erosion protection work using Geobags requires less installation and maintenance cost
[1], light weight equipment, less space for construction works, transportation cost, less
energy requirement [6]. A joint study of Bangladesh University of Engineering and
Technology (BUET), BWDB and Institute of Water Modeling (IWM) reveals that Geobag
used in different revetment work along the major rivers of Bangladesh (Jamuna and
Meghna) results 40% to 60% cost reduction [2]. The constructing materials (sand) of
geobag are locally available and cost-effective compared to importing boulders from
other countries. The manufacturing of geobags and quality control of the bags are easy
compared to the C.C. blocks and boulders.
3. TECHNICAL EFFICIENCY
Sand filled Geobags work as a substitute of C.C. blocks used as dumping material, even
though geo-bags are sometimes used as filter material below C.C. blocks [7]. A physical
modeling study under JMREMP [3] found that launching performance of sand filled
geobags is better than C.C. block but lower than rounded and angular rock. The joint
venture study of BWDB, BUET and IWM suggests [2] that the launching performance of
geobag could be found similar to hard materials if area coverage method is applied
instead of mass dumping method. The major advantages of Geobags are its availability
and easier implementation. Geobags are readily available and transportable (when empty)
and can be easily filled with local sand and formed with a range of sizes to fit specific
application. On the other hand, main demerit of geobag is its high sensitivity to UV
radiation and highly alkaline or acidic water [9 and 10]. Solar UV radiation stimulates its
polemeric ageing process. Depending on its constituent strains’ properties, its life
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expectancy could be reduced 15% to 75% in one year exposure [9]. Ageing due to UV
radiation could be protected by using some stabilizers [11]. Geobags available in our
markets have resistance to 160 kilo Langley per year solar radiation [5] while Bangladesh
falls in the zone of 180 to 140 kilo Langley per year solar radiation [12]. Highly acidic
and alkaline water could also significantly reduce geobags’ property through chemical
degradation [10] and fortunately major rivers of Bangladesh show neutral pH (6 to 7) [2
and 5].
4. USE OF GEOBAG IN BANGLADESH
The sand filled geobags were firstly used in Bank Protection and River Training Pilot
Project, FAP 21/22 at limited extend. Later, in Pabna Irrigation and Rural Development
Project (PIRDP) and Meghna Dhonagoda Irrigation Project (MDIP), sand filled geobags
were used under the aegis of Jamuna Meghna River Erosion Mitigation Project
(JMREMP) during 2002. As on 2006-2007, sand filled geobags have been used under
water successfully in approximately 20 km of River bank protection work [2]. Recently,
this technology has been used for protecting river bank along the Major rivers of
Bangladesh i.e Jamuna, Ganges, Padma and Meghna.
5. METHODOLOGY
This study was carried out following the guideline for Environmental Assessment of
Water Management Projects [8] and the Environmental Assessment requirements of
Asian Development Bank (ADB). The environmental impact of sand filled geobags used
under water has been made comparing with protective works using only C.C. Block. The
environment intervened by protective works using only C.C. Block was considered as
control environment. Comparing with this control environment, the impacts of sand filled
geobags on Environment were identified.
5.1. Study area
The study was conducted by investigating two similar reaches (hydraulic, socio-economic
and environmental consideration): one is protection with geo-bags in addition to C.C.
blocks under water (study area) and other (control area) being protected by using C.C.
blocks only. In order to examine the effects of saline and non-saline water on geobags,
four major rivers (Ganges, Padma, Jamuna and lower Meghna) were selected covering
both saline and non-saline zone, which gave a comprehensive context of the whole
country. In total 6 control areas and 6 study areas were selected as summarized in the
Table 1.
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Table 1: List of control and study area
Zone
River
Ganges
Non
Saline
Padma
Jamuna
Saline
Lower
Meghna
Location
Boiddnathpur, Chapai Nawabganj
Boiddnathpur, Chapai Nawabganj
Faridpur
PIRDP, Bera Pabna
Sirajganj Hardpoint
Sirajganj Hardpoint
Horar Hat, Bhola
Hakimuddin Bazar, Borhanuddin
Baliakandi, Tazumuddin
Ramprashad, Tazumuddin
Ramprashad, Tazumuddin
Control/study area
Study area
Control area
Study area
Control area
Study area
Control area
Control area
Study area
Study area
Study area
Control area
5.2. Materials and methods
The study was carried out through interdisciplinary approach while a multidisciplinary
team was involved. Local people participation was ensured through PRA and RRA
approach. World standard EIA process consisting with a composite set of adhoc, checklist
and matrix methods was employed in the EIA study where both secondary and primary
data were used. Local knowledge was incorporated in the study process through
Stakeholder Consultation, Key Informants Interview and Focus Group Discussion (FGD).
5.3. Impact evaluation and risk characterization
Considering all potential and observed impact, risk assessment was accomplished
eventually after characterizing and categorizing the risk of each potential and observed
impact of using geo-bags under water. For better understanding and screening, word
scenarios were developed for each categories of the risk. The basis of risk
characterization was likeliness and consequence of the impact. Followed by the risk
characterization and categorization, a risk assessment framework was developed that was
employed to assess the overall environmental risk of using geobag. An empirical scale
was developed to limit the subjective assessment of the risk. Table 2 shows the risk
assessment framework. The process of the risk assessment was carried out through
workshop where expertise of the EIA study team members as well as the experience of
BWDB Engineers were utilized to finalize the risk matrix.
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Table 2: Risk assessment framework
COMPONENT
CONSEQUENCE
No or insignificant
negative impact
Localized, short time
degradation of
sensitive ecological
habitat
Localized long term/ short
term, widespread,
degradation of ecological
habitat
Widespread, long term
degradation of ecological
habitat,
Permanent degradation of
ecological habitat
Fish Habitat,
production and
composition
No or insignificant
negative impact
Localized, short time
degradation of fish
habitat
Localized long term/ short
term, widespread,
degradation of habitat,
species proportional change
in fish composition
Widespread, long term
degradation of fish habitat,
and change fish
composition, effects on
sensitive habitat and species
Permanent degradation of
fish habitat, extinction of
any fish species
Ranking
Insignificant
Minor
Moderate
Significant
Catastrophic
Ecosystem
Terrestrial and
Aquatic
Ecosystem
Fisheries
Risk assessment framework
(Without application of mitigation and management measures)
IKELIHOOD OF OCCURANCE
Likelihood Descriptions
Ranking
Index
1
2
3
4
5
Consequence occurs immediate after the project
implementation
Frequent
5
5
10
15
20
25
Conditions may allow the consequence to occur during the
project lifetime
Likely
4
4
8
12
16
20
Exceptional consequences to occur within the project
lifetime
Occasional
3
3
6
9
12
15
Conditions do not seem to occur any consequence except
some extreme cases
Seldom
2
2
4
6
8
10
Reasonable to expect that the consequence will not occur
though it has rare possibility to occur
Rare
1
1
2
3
4
5
1- below 5: Low risk, mitigations may be
applied
5- below 10: Risk is Acceptable, mitigations
may be applied
10 – below 15: Medium risks, risk
reduction is required
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15 – below 20: High risks, mitigations
must be applied
20 to – below 25: Extremely high,
mitigations must be applied
6. GENERAL DESCRIPTION OF THE PROTECTIVES WORKS IN THE STUDY
AREA
Though the design and specifications are different in different protective works, in general
protective works were found combined typed where C.C Block and sand filled geobags
were placed under water. The design includes, earth filled compaction, slope pitching works
over geotextile, assorted block placing and geobag placing on berm and geobag dumping.
There are three different sizes of geobags that are used in protective works: Type A- 175 kg,
Type B- 150 kg, and Type C- 126 kg.
7. ECOLOGICAL IMPACTS OF USING SAND FILLED GEOBAG UNDER WATER
7.1 Impacts on ecosystem
7.1.1 Impact on water quality
Geobags used under water in protective works are chemically inert. Chemical analysis of
river water quality at study sites found within the standard of DoE. Water turbidity near
geobags using protective works is found very lower than that of C.C. block using protected
sites.
7.1.2 Impact on ecosystem habitat
The C.C. block using protective work requires huge site clearance activities including
removal of top soil, and vegetation. The construction works includes stone crashing, mixing,
block casting, construction materials transportation and storage, and vehicle movement may
source the fugitive particulate matter that might have impact on surrounding ecosystem
habitat especially on roadside vegetation, agricultural ecosystem and riverine ecosystem.
There will be potential of same impact during emergency dumping and rehabilitation if
further construction activities are required.
On the other hand, there is no such negative impact or condition that might allow having
potential negative impacts of using geobags on ecosystem habitat. The negative impacts
associated with site clearance and construction activities are minimal. During the dumping,
water turbidity increases that might affect habitat quality. Compare to protective works using
only C.C. blocks, geobags are more effective in arresting sediment [2] that improves the
water transparency, which is helpful for ecological productivity. However, these impacts are
localized, temporal and reversible.
During operational phase, the resultant negative impact of geobag use is also minimal. Some
small amount of land is required for stocking of sand and geobags for emergency dumping.
7.1.2 Impacts on terrestrial flora
C.C. Block using protection works involve huge site clearance and base stripping activities.
Moreover, the airborne particulate matters may be spreading over the surrounding
agricultural field, homestead, social and roadside vegetation that might reduce floral
productivity. In case of geobags using technology, base stripping and construction activities
are minimal and result less impact on terrestrial flora.
7.1.3 Impacts on terrestrial fauna
C.C. block used under water and on bank slope may make the accessibility to river difficult
for few terrestrial fauna like, Jackel, Bangel fox, fishing cat and amphibians. The assorted
blocks over the bank slope may restrict the river from easy access for drinking, bathing and
hunting purposes of mentioned wildlife and livestock. On the other hand, Geobag has no such
impacts on river access.
7.1.4 Impacts on aquatic flora
Like C.C. block using technology, during construction phase, geobag using technology has
some impacts on aquatic flora like floating and submergible plants due to covering the
limnetic zone. But the impacts are local and short term. Due to high siltation rate, the limnetic
zone will be resuscitated. However, geobags also provide grounds for some floating plants
and algal community. Algal communities are found more frequently and densely in geobag
dumping zone than that of C.C. block.
7.1.5 Impacts on aquatic mammals
Ganges, Padma, Jamuna and Meghna are the important migratory routes of Dolphin, the
sensitive aquatic mammals. Dolphins choose thalweg as their migratory route. The dumping
activities (in both case of C.C. block and sand filled Geobag) may cause the shifting of their
migratory route temporary. But the dumped sand filled geobags don’t block the free
movement of the mammals like hard edges of C.C. blocks.
7.1.6 Impact on benthic community
C.C. block doesn’t cover the complete benthic zone. In that case, benthos community can
easily grow in interlock and the gap between blocks. On the other hand, dumped Geobags
completely cover the benthic zone of the river bank slope that might impact on benthic
habitats. However, it has been come out from the field observation that the impacts on
benthic zone are local, short term, and reversible. The high siltation rate over the geobags
covers the dumped geobag within a year and restores the benthic habitat.
7.2. Impact on fisheries
7.2.1. Impact on fish habitat
During dumping, the fish habitat and assemblages near river bank might be disturbed and
some damage of benthonic and planktonic community might be resulted. In addition, the
covering of river bed with geobag in limnetic zone may have some effects on some fishes e.g
Ayre (Aorichthys aor), Rita (Rita rita), boal (Wallago attu), Pangas (Pangasius pangasius),
different types of baim, gutum (Lepidocephalus guntea), bala (Glossogobius giuris) and some
small fish species by limiting their feeding opportunity. The regeneration of algae and
benthos community over the dumped geobags were found during field visit that indicates the
restoration of food sources for fish. The local fishers also support the indication of restoration
of fish habitat.
7.2.2 Impact on fish migration
Fish uses the river channel as a migratory route for feeding and breeding purpose and shelter
for brood, post larvae and juvenile stages. Fish migration may be affected locally for short
term during dumping and it might happen in both cases of protective work. The prudent
impact is due to shifting of thalweg. Shifting of thalweg due to enhanced sedimentation rate
and control of bed scouring may results in local shifting of fish migratory routes. Geobag has
more functional effectiveness to control the bed scouring than that of CC block [2].
7.2.3 Impact on fish production
Sediment and dust material runoff from the construction activities during the construction
may cause increase in river turbidity that may reduce fish breeding and fertilization of fish
eggs. Hence the potential of generating dust and fugitive materials is higher in CC block
using protective works than that of goebag using protective works, the impact on fish
production during construction will be minor in case of geobag using technology of
protective works.
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7.2.4 Impact on fish species composition
The overall fish composition of the river depends on habitat and availability of food. Surface
fishes may be affected during the dumping of geobags. Likewise the C.C. block use, the
surface fish species may also shift locally for short term in case of geobag using protective
work. The covering of the river bed of the limonitic zone by geobag may affect the bottom
fishes. After placing of geo-bags, the fishes those live in holes (e.g. ell and cat fish) may
migrate from protective areas. Field observation and fishers perceptions support that the
underwater environment is restored within one or two year that would favor the habitat for
ells and cat fishes again.
7.2.5 Impact on fishing effort
In C.C. block dumped area, fishers can’t use any gear for fishing. Irregular shape of the
blocks causes damage to their nets. The space between the blocks helps fishes to hide from
nets. On the other hand, no such impact has been noticed in the geo-bags dumped areas.
8. RISK ASSESSMENT
Each of the aforementioned potential and observed impact was evaluated through the risk
assessment framework (Table 2 in methodology) to characterize the risk that also depicts
priority what should be taken into consideration during formulating environmental
management plan. This additional assessment and evaluation of the risk of each impact will
direct the policy makers to decide whether the impact would be acceptable or not; whether
the impact would require the mitigation, enhancement contingency and monitoring measures.
The summery of the risk assessment is briefed in Table 3 where it is seen geobags use under
water possess low risk of affecting fisheries which might be acceptable and medium risk of
affecting ecosystem which requires adoption of mitigation measures.
Table 3: Risk characterization and assessment
Sl
no.
Key potential impact
Likeli
hood
Consequ
ence
Risk
Subjective
meaning of
Risk
Response/ Action
Risk on Ecosystem
3
Impact on terrestrial habitat:
minor impact during
construction by sourcing
fugitive particulate matter
3
2
6
4
Impact on Aquatic habitat:
Have local, short time and
reversible impacts on benthic
communities
Local shifting of migratory
route of dolphin due to
shifting of thalweg
4
3
12
4
3
12
4
2
8
Risk is
Acceptable,
mitigations
may be
applied
EMP with mitigation,
and monitoring is
required
4
2
1
Risk is
Acceptable,
Mitigation and
monitoring measures
5
Risk on Fisheries
6
Impact on Fish Habitat:
Condition may affect cat fish
and ell habitat locally and for
short time. Combined
method facilitate fish
assemblage
7
Impact on Fish production:
No significant change
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Risk is
Acceptable,
mitigations
may be
applied
Medium
risks, risk
reduction is
required
Medium
risks, risk
reduction is
required
Mitigation measure may
required during
construction phase
EMP with mitigation and
monitoring measures for
pre, during and post
construction phase
EMP with mitigation and
monitoring measures for
pre, during and post
construction phase
Sl
no.
8
Key potential impact
Impact on Fish composition:
Local, short time and minor
reduction of cat fish and eel.
Likeli
hood
4
Consequ
ence
2
Risk
8
Subjective
meaning of
Risk
mitigations
may be
applied
Risk is
Acceptable,
mitigations
may be
applied
Response/ Action
may be adopt
Mitigation and
monitoring measures are
required
9. CONCLUDING REMARKS:
Use of sand filled geobags under water in erosion protection work is being popular due to
its cost effectiveness, availability and easier implementation. Some recent studies support
that its technical efficiency is similar or sometimes better than use of hard material.
Bangladesh Water Development Board has implemented numbers of river bank erosion
protection works using sand filled geobag under JMREMP and is going to adopt this
technology widely in erosion protection works of the country. Prior to nationwide
adoption of this technology, the interaction between goebag and environment has been
assessed through EIA and this paper presents only the ecological impacts of geobags use
under water.
Despite the cost effectiveness, there are potentiality of resulting some negative impacts
like short term shifting of some surface and bottom fishes, covering of river slope bed in
limnotic zone, temporal alteration of benthonic habitat and local shifting of Dolphin
migratory route due to induced sedimentation. However, these impacts are acceptable and
could be reduced by adopting mitigation measures. In compare to C.C. block use the
construction and post-construction impacts are very minimal as it involves less
construction activities, generating less construction waste and no chemical alteration to
water quality. At the end it can be concluded that, in compare to C.C. block use, the
geobag use is more ecosystem and fisheries friendly.
However for better environmental sustainability, an Environmental Management Plan
should be adopted with detail plan for mitigating negative impacts, enhancing expected
benefits and regular monitoring of EMP implementation and resulted impacts. Farther
research might be carried out in developing an appropriate Environmental Management
Plan that would be easier in following and implementing.
10. ACKNOWLEDGEMENT
Mr. Md. Abdul Quddus, Project Director, Jamuna Meghna River Erosion Mitigation
Project (JMREMP) is greatly acknowledged for his guidance and suggestion. Advice and
direction of Mr. Giasuddin Ahmed Choudhury, Executive Director, CEGIS are sincerely
acknowledged. Mr. Md. Waji Ullah, Team Leader EIA study and Mr. Mujibul Huq,
Environmental Advisor EIA study are also respectfully acknowledged for supervising and
continuous guidance in preparing this paper. Timely facilitation and support of Dr. Anil
Chandra Aich, Project Leader, EIA study is appreciated with gratitude.
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