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
642 (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 Jamuna-Meghna 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
643
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
644
Table 1: List of control and study area
Zone River Location Control/study area
Non Saline
Ganges Boiddnathpur, Chapai Nawabganj Study area
Boiddnathpur, Chapai Nawabganj Control area
Padma Faridpur Study area
Jamuna PIRDP, Bera Pabna Control area
Sirajganj Hardpoint Study area
Sirajganj Hardpoint Control area
Saline Lower
Meghna
Horar Hat, Bhola Control area
Hakimuddin Bazar, Borhanuddin Study area
Baliakandi, Tazumuddin Study area
Ramprashad, Tazumuddin Study area
Ramprashad, Tazumuddin 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
645
Table 2: Risk assessment framework
Risk assessment framework
(Without application of mitigation and management measures)
COMPONENT CONSEQUENCE
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
15 – below 20: High risks, 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
647
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
648
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.
649
8 Impact on Fish composition: Local, short time and minor
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
650 REFERENCES
[1] Artieres, O, et al. Geosynthetics as Eco-friendly Defence against Erosion in Arctic Regions, 63rd Canadian Geotechnical Conference and the 6th Canadian Permafrost Conference, Calgary, Albarta, Canada, 2009.
[2] BWDB [2008]. Technical report of Joint committee of BUET, IWM and BWDB on Evaluating Effectiveness of Sand filled Geobags using Technology in Riverbank Erosion 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] CEGIS [2009]. Final Inception Report on Environmental Impact
Assessment (EIA) for use of Sand-filled Geo-Bags under Water. Submitted to Bangladesh Water Development Board. Center for Environmental and Geographic Information services (CEGIS).
[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
Speak in Favour of geosynthetic, available at
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 Engineers Journal of Hydraulic Engineering, Vol 133, No 4, pp. 431-439.
[8] WARPO [2005]. Guideline for Environmental Assessment for Water Management Projects, Water Resources Planning Organization (WARPO), Ministry of Water Resources, Bangladesh.
[9] Polisilk S.A. Resistance to Sun Light. Product manual of Polisilk S A. Barcelona. Accessed from http://www.polisilk.com/manu.html at 4/4/2010.
[10] Geofabrics [2009]. The Durability of Geotextile, Geofabrics limited, United Kingdom. [11] Reinert, G. and Fuso, F., 1997. Stabilisation of Textile Fibbers against Ageing, Rev. Prog. Coloration, vol 27, pp 332-41.
[12] Petanks, What is UV protection. Available in
