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River bank erosion hmm

River bank erosion

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River bank erosion hmm

  1. 1. “River Bank Erosion in Bangladesh.” Composed by H.M.A. Mahzuz Assistant Professor (PhD Fellow), Department of Civil and Environmental Engineering, Shahjalal University of Science & Technology Sylhet, Bangladesh.
  2. 2. Riverbank erosion is one of the most unpredictable and critical type of disasters. It is vastly influenced by rainfall, soil structure, river morphology, topography of river and adjacent areas, and floods. Such calamity took less effect in lives but more in livelihood as agricultural land and homesteads along with other livelihood options that are evacuated.
  3. 3. Deltaic sediments of Quaternary formation characterize most of the lands of Bangladesh. The natural setting of Bangladesh is between the Himalayas and the Bay of Bengal together with the prevalence of tropical monsoon climate. The catchment area of the major rivers is about 1.65 million square km of which only 7.5 percent lies within the border of Bangladesh that generates 1200 km3 of run- off annually, only 10 percent of which is generated within Bangladesh. In addition to vast quantities of water, these rivers carry about 1.1 billion tons of sediment every year and are responsible for the prevalence of flooding and riverbank erosion in Bangladesh.
  4. 4. The combination of the large discharges and heavy sediment loads with high water content from the annual wet monsoon, a low degree of compaction and dredging, and a large amount of runoff materials result in highly variable and dynamic channel morphologies to adjust their bed configurations. The river channel may shift laterally by more than 300 meters in any season.
  5. 5. Study findings by Center for Environment and Geographic Information Services (CEGIS) based upon analysis of 30- year time series of satellite images reveals that the Jamuna and Padma rivers have widened more than three kilometres and destroyed about 1,30,000 ha of floodplain land. One of the most influential phenomenon is that climate change is expected to disturb the sediment balance. It is difficult to forecast whether there will be net accretion or erosion.
  6. 6. Riverbank erosion has important implications for channel adjustment and long-term channel change, meander development, catchment sediment dynamics, land loss and downstream sedimentation problems. Because of poor understanding of riverbank erosion processes, river dynamics and sediment transport models are weakly integrated into river management strategies. Furthermore, such knowledge gap complicated the relationship between flow energy and bank retreat rates erosion processes take place in bank erosion system and because of the duration of process and response along with the lack of information on erosion or accretion.
  7. 7. Despite decades of research, the erosion of cohesive riverbanks remains difficult to predict. Models of cohesive river bank erosion must include a wide variety of erosional processes including fluvial erosion induced by hydraulic forces and mass wasting processes related to soil strength and bank geometry. Bank erosion is strongly influenced by the pore water pressures and the moisture content within the bank, which are influenced by hydrologic processes and riparian vegetation.
  8. 8. Figure: A close look of the eroding Jamuna River
  9. 9.  River bank erosion:River bank erosion:  An endemic and recurrent natural hazard in BangladeshAn endemic and recurrent natural hazard in Bangladesh  When river enters the mature stage they become sluggishWhen river enters the mature stage they become sluggish and meander or braid, and continuous water oscillationsand meander or braid, and continuous water oscillations cause massivecause massive River bank erosionRiver bank erosion..  It is estimated that about 5% of total flood plain ofIt is estimated that about 5% of total flood plain of Bangladesh is directly affected and it is seen that bankBangladesh is directly affected and it is seen that bank erosion is taking place 94 out of 489 upazilla.erosion is taking place 94 out of 489 upazilla.
  10. 10.  Some Historical Changes of Physiography & RiverSome Historical Changes of Physiography & River Morphology in Bangladesh:Morphology in Bangladesh:  The changes of course of theThe changes of course of the TeestaTeesta from the Ganges to thefrom the Ganges to the BrahmaputraBrahmaputra during the flood of 1787.during the flood of 1787.  Recurring floods in Rangpur, Bogra & Pabna districts betweenRecurring floods in Rangpur, Bogra & Pabna districts between 1787 & 1830 accentuated the process of course changes of1787 & 1830 accentuated the process of course changes of thethe BrahmaputraBrahmaputra from the oldfrom the old BrahmaputraBrahmaputra, which flowed, which flowed passed Mymensingh town & joined thepassed Mymensingh town & joined the MeghnaMeghna at Bhairabat Bhairab bazaar, to the Jhenaidah, later developed in to thebazaar, to the Jhenaidah, later developed in to the JamunaJamuna ..  TheThe Ganges (Padma)Ganges (Padma) flowed separately to the Bay of Bengalflowed separately to the Bay of Bengal through Tetulia channel during (1764-1772). It has changed tothrough Tetulia channel during (1764-1772). It has changed to its present course by joining theits present course by joining the MeghnaMeghna near Chandpur.near Chandpur.  The 1762 earthquake uplifted the Madhupur tract creating theThe 1762 earthquake uplifted the Madhupur tract creating the Sylhet basin through subsidence compensatory to theSylhet basin through subsidence compensatory to the elevation of the Madhupur tract.elevation of the Madhupur tract.
  11. 11. CAUSE:CAUSE: -Bends -Meandering
  12. 12. Disaster ManagementDisaster Management Pre disaster During disater Post disaster Administrative -prediction -govt movement -awareness campaign - foreign aid and fund collection Technical: -Marginal embankment -guide banks - groynes or spurs -artificial cut off - pitching of banks - pitched island -miscellaneous methods Administrative: -local contribution -govt guidence -rehabilitation Technical: -temporary protection -foreign aid -rehabilitation -relief fund -damage assesment
  13. 13. Recent Exposure on the Buriganga: Fig: Bank erosion on the Buriganga
  14. 14. Recent Exposure on the Meghna: Fig: Bank Erosion On The Meghna
  15. 15. A Government Project to Protect River Bank Erosion: The Ministry of Planning & Planning Commission jointly took a project to protect different eroding places on the both banks of the Surma river flowing through Sylhet at a length of about 10km by river bank protection of 2352m(new) and repair of existing revetment works at length of 2395m erected earlier. The name of the project is Protection of Both the Banks of the River Surma in Sylhet Town. The project is under the plan of Fifth Five Year Plan. The project area is located under Sylhet Sadar upazilla in the district of Sylhet. Some gross information about the project: Investment cost & annual operating expenditure: EventEvent Total (in lakh Tk)Total (in lakh Tk) Investment cost of the project (including costInvestment cost of the project (including cost escalation)escalation) 1461.001461.00 Annual operating / recurring expenditure onAnnual operating / recurring expenditure on completion of the project at normal capacitycompletion of the project at normal capacity 34.3634.36
  16. 16. Estimated quantitative measurement of wealth protection by the project: Sl. no.Sl. no. Description of propertyDescription of property No./QuantityNo./Quantity Apporx. value(lakh Tk)Apporx. value(lakh Tk) 11 Mazar of Hazrat Borhanuddin(R:)Mazar of Hazrat Borhanuddin(R:) 11 100.00100.00 22 High School & Primary SchoolHigh School & Primary School 7 (3+4)7 (3+4) 800.00800.00 33 Large scale MadrasaLarge scale Madrasa 55 400.00400.00 44 Bridges on the Surma riverBridges on the Surma river 22 2000.002000.00 55 ShopsShops 780780 2000.002000.00 66 Paved roads on both banksPaved roads on both banks 23km23km 700.00700.00 77 Meghna petroleum depotMeghna petroleum depot 11 700.00700.00 88 Technical collegeTechnical college 11 300.00300.00 99 GraveyardGraveyard 22 200.00200.00 1010 Large rice millLarge rice mill 11 200.00200.00 1111 Police stationPolice station 11 200.00200.00 1212 Circuit houseCircuit house 11 200.00200.00 1313 Leprosy hospitalLeprosy hospital 11 200.00200.00 1414 Forest officeForest office 11 150.00150.00 1515 Water supply machine roomWater supply machine room 11 300.00300.00 1616 Ancient public libraryAncient public library 11 300.00300.00 1717 R&H officeR&H office 11 250.00250.00 1818 BuildingsBuildings 210210 450.00450.00 1919 MarketsMarkets 33 1000.001000.00 2020 Other private buildings & installationOther private buildings & installation L.S.L.S. 750.00750.00 TotalTotal 11200.0011200.00
  17. 17. Fig: Photograph of bank erosion on the Surma
  18. 18. Fig: Photograph of bank erosion on the Surma
  19. 19. Fig: Photograph of bank protection on the Surma
  20. 20. Fig: Photograph of bank protection on the Surma
  21. 21. Case Study (Effects of Riverbank Erosion on Livelihood , January 2012 A.F.M Azim Uddin and Jayanta Kumar Basak, Unnayan Onneshan - The Innovators, 16/2, Indira Road, Farmgate, Dhaka-1215, Bangladesh ): Two case studies are presented those were conducted in the most vulnerable regions of Bangladesh 1) Kapasia Union of Gaibandha District, and 2) Kazipur and Khasrajbari Union of Sirajganj District)
  22. 22. 1) The study findings revealed that on an average, 256.1 ha and 622.2 ha of total land area of Gaibandha and Sirajganj respectively were eroded per year during the period of 1973-2009. 2) During this period, the study areas i.e., Kapasia, Kazipur and Khasrajbari observed 5.82 ha, 6.89 ha and 9.36 ha erosion per year respectively. In 2011, the erosion was found 60.8 ha, 178.76 ha and 203.36 ha of land respectively that is an indication of increased erosion rate. The main reason of such variation is because of climate change induced intensifying rainfall pattern and unplanned interverntions. 3) From the study, it has been observed that the total economic loss arising from such erosion were 44,48,736 and 4,19,39,962 BDT in Gaibandha and Sirajganj respectively.
  23. 23. 4) A vast majority of the effected people (45.3 and 40.8 percent in Gaibandha and Sirajganj respectively) are in the income group of 3001- 4000 BDT (i.e. poor income level ). 5) Empirical data showed that bank erosion displaced a total number of 486 and 4028 inhabitants in Gaibandha and Sirajganj respectively during the study period. Table: Eroded area due to bank erosion during 1973-2009 District
  24. 24. Figure: Causes of Riverbank Erosion
  25. 25. Figure: Comparison of Erosion by Year
  26. 26. Figure: Way to Cope Up with Household Loss
  27. 27. Table: Migration Pattern observed in Gaibandha Table: Migration Pattern observed in Sirajganj
  28. 28. GOVERNMENT STRATEGIES TO LESSEN THE IMPACT Government response to this problem at local, regional and national levels has been limited to structural measures i.e., embankments, barrages, etc., and very little attention has been paid in developing non-structural and self- help strategies. Most often, measures are taken immediately after the disasters and interventions are taken in the form of relief provisioning.
  29. 29. CONCLUSION: The marginalized and poor people not only lose property but also experiences socioeconomic deprivation through displacement. Because of the dynamic character of the rivers and the failure of structural measures, the sufferings of the people are assumed to continue. Long-term policies and strategies should be taken to cope up with the bank erosion taking into account the social and institutional adjustment measures. Land relocation assurance is one of the appropriate strategies to cope up with such disaster. In addition, a floodplain zoning is essential to lessen the vulnerability of riverbank erosion.
  30. 30. Furthermore, measures should be taken in different level to minimize the loss: a) Sustainable embankment construction and its maintenance b) Training on disaster preparedness involving local institution/ local government c) Massive afforestation with the experience of local knowledge and its maintenance d) Action against deforestation e) Form an alliance among SAARC countries in order to ensure water distribution within the subcontinent.