Coastal Erosion, Soil Mechanics, and Sediment Dynamics in the Bengal Delta: A Case Study from Kalapara, Bangladesh

Abstract

Shorelines in Bangladesh are among the most vulnerable regions to the compounded impacts of climate change, sea-level rise, and intensified natural hazards. Although sediment deposition in Bengal Delta’s promotes accretion in certain areas, many coastal zones are experiencing severe erosion, driving large scale population displacement and heightening socioeconomic vulnerability. This study examines shoreline change dynamics and geotechnical soil properties along the Kalapara coast in Patuakhali District over a 31-year period (1989–2020) through the integration of multi-temporal Landsat imagery and field-based geotechnical analysis. A total of 1,533 transects were evaluated using the Digital Shoreline Analysis System (DSAS), revealing that 77.9% of the shoreline experienced erosion, while only 22.1% showed accretion. Dhulasar union exhibited the most extreme rates of both erosion (33.57 m/yr) and accretion (22.88 m/yr), while Nilganj remained comparatively stable. Geotechnical testing of thirty shoreline soil samples from six unions indicated low specific gravity values (2.21–2.68), suggesting poor compaction and high susceptibility to erosion. The plasticity index ranged from -26.77 to 39.1, with Mohipur, Lalua, and Champapur dominated by non-plastic to low-plastic soils, and Dhulasar and Nilganj characterized by high plasticity and cohesive soils. Particle size analyses showed that most soils comprisedmedium to fine sand (up to 98.34%), with minimal silt and clay fractions; however, Nilganj, Latachapli, and Dhulasar contained higher proportions of silty-clayey material, contributing to enhanced slope stability and erosion resistance. These findings emphasize the critical role of soil mechanical properties in governing shoreline evolution and highlight the urgent need for integrated coastal zone management strategies that couple geotechnical stabilization with continuous remote sensing-based monitoring to protect vulnerable areas like Kuakata beach from irreversible coastal degradation.

Keywords

• Sediment Accretion
• Landsat Satellite Imagery
• Atterberg Limits
• Sieve Analysis
• Hydrometer Analysis

Supporting Institution

University of Barishal, Bangladesh

Ethical Statement

The authors declare no conflicts of interest.

Thanks

The corresponding author greatly thankful to Department of Geology and Mining, University of Barishal, USGS and Government of Bangladesh for technical support, availability of data through the entire study.

References

1. Rahman, S. A., Islam, Md. M., Salman, Md. A., & Rafiq, M. R. (2022). Evaluating bank erosion and identifying possible anthropogenic causative factors of Kirtankhola River in Barishal, Bangladesh: an integrated GIS and Remote Sensing approaches. International Journal of Engineering and Geosciences, 7(2), 179-190.
2. Nienhuis, J. H., Ashton, A. D., Roos, P. C., Hulscher, S. J. M. H., & Giosan, L. (2013). Wave reworking of abandoned deltas, Geophys. Res. Lett., 40, 5899–5903, doi:10.1002/2013GL058231.
3. Wright, L. D., & Coleman, J. M. (1973). Variations in morphology of major river deltas as functions on ocean wave and river discharge regimes, Am. Assoc. Pet. Geol. Bull., 57(2), 370–398.
4. Sifa, N. J., Jerin, T., Salman, M. A., Asaduzzaman, M., & Hossen, M. S. (2024). Assessment of Riverbank Erosion and its Societal Impacts Along the Payra River in Mirzaganj Upazila, Bangladesh. Journal CleanWas, 8(1): 38-44.
5. Rahim, M. A., Akter, N., Roy, D. K., Hasan, I., Salman, M. A., Goswami, S., Abir, T. M., Biswas, R. K., & Rakib, M. M. H. (2024). Assessment of Socio-Economic Impacts of River Bank Erosion: Enhancing Resilience in the Coastal Belt of Bangladesh. The Journal of Environment & Development, 33(4), 583612. https://doi.org/10.1177/10704965241246710.
6. Cooper, J. A. G., & Pilkey, O. H. (2004). Sea-level rise and shoreline retreat: time to abandon the Bruun Rule. Global and Planetary Change, 43(3–4), 157–171. https://doi.org/10.1016/j.gloplacha.2004.07.001.
7. Forbes, D. L., Parkes, G. S., Manson, G. K., & Ketch, L. A. (2004). Storms and shoreline retreat in the southern Gulf of St. Lawrence. Marine Geology, 210, 169–204. https://doi.org/10.1016/j.margeo.2004.05.009.
8. Orford, J. D., Forbes, D. L., & Jennings, S. C. (2002). Organisational controls, typologies and time scales of paraglacial gravel-dominated coastal systems. Geomorphology, 48(1–3), 51–85. https://doi.org/10.1016/S0169-555X(02)00175-7.

9. Salman, M. A., Rakib, M. H., Saha, S. C., Haque, M. E., & Hossen, M. S. (2025). Cyclone vulnerability assessment of the central coast of Bangladesh: A comprehensive study utilizing FAHP and geospatial techniques. PLoS One 20(7): e0326965. https://doi.org/10.1371/journal.pone.0326965.
10. Salman, A., Saha, A., Nomaan, S. S., Haque, E., & Asadi, T. (2024). Assessing Tropical Cyclone Destruction Using Landsat Satellite Imagery: A Case Study in Bangladesh. IDRiM Journal, 14(2), 54–68. https://doi.org/10.5595/001c.123359.
11. Addo, A., Larbi, K., Amisigo, L., & Ofori-Danson, P. K. (2011). Impacts of Coastal Inundation Due to Climate Change in a CLUSTER of Urban Coastal Communities in Ghana, West Africa. Remote Sensing, 3(9), 2029-2050. https://doi.org/10.3390/rs3092029.
12. Harley, M. D., Turner, I. L., Short, A. D., & Ranasinghe, R. (2011). A reevaluation of coastal embayment rotation: The dominance of cross-shore versus alongshore sediment transport processes, Collaroy-Narrabeen Beach, southeast Australia, J. Geophys. Res., 116, F04033, doi:10.1029/2011JF001989.
13. Ford, M. (2013). Shoreline changes interpreted from multi-temporal aerial photographs and high resolution satellite images: Wotje Atoll, Marshall Islands, Remote Sensing of Environment, Volume 135, Pages 130-140, ISSN 0034-4257, https://doi.org/10.1016/j.rse.2013.03.027.
14. Angnuureng, D. B., Almar, R., Addo, A., Castelle, B., Senechal, N., Laryea, S. W., & Wiafe, G. (2016). Video observation of waves and shoreline change on the microtidal James Town Beach in Ghana. Journal of Coastal Research, Special Issue No. 75, 1022–1026. https://doi.org/10.2112/SI75-205.1.
15. Kroon, A., Davidson, M. A., Huntley, D. A., Medina, R., Rawson, J., Van Koningsveld, M., & Aarninkhof, S. G. J. (2007). Application of remote sensing video systems to coastline management problems. Coastal Engineering, 54(6-7), 463-477. DOI:10.1016/j.coastaleng.2007.09.003.
16. Valentini, N., Saponieri, A., & Damiani, L. (2017). A new video monitoring system in support of Coastal Zone Management at Apulia Region, Italy, Ocean & Coastal Management, Volume 142, Pages 122-135, ISSN 0964-5691, https://doi.org/10.1016/j.ocecoaman.2017.03.032.
17. Alesheikh, A. A., Ghorbanali, A., & Nouri, N. (2007). Coastline change detection using remote sensing. International Journal of Environmental Science & Technology, 4, 61–66. https://doi.org/10.1007/BF03325962.
18. Fenster, M. S., Dolan, R., & Elder, J. F. (1993). A new method for predicting shoreline positions from historical data. Journal of Coastal Research, 9(1), 147–171.
19. Salman, M. A., Hasan, S. M. R., Ahmed, S., Tahsin, M., & Khan, N. (2018). Shoreline change rate along the southern coast of Bangladesh due to climate change using remote sensing & ArcGIS technology. International Journal of Emerging Technology and Advanced Engineering (IJETAE), Vol. 8 Issue 3 (Mar 2018), pp. 21–28.
20. Sarwar, M. G. M., & Woodroffe, C. D. (2013). Rates of shoreline change along the coast of Bangladesh. J Coast Conserv 17, 515–526. https://doi.org/10.1007/s11852-013-0251-6.
21. Mahamud, U., & Takewaka, S. (2018). Shoreline Change around a River Delta on the Cox’s Bazar Coast of Bangladesh. Journal of Marine Science and Engineering, 6(3), 80. https://doi.org/10.3390/jmse6030080.
22. Nmiss, M., Amyay, M., Atiki, N., & Ouammou, A. (2025). Shoreline Changes at the Souss and Massa rivers mouths, Morocco: A five decades analysis (1970-2024). International Journal of Engineering and Geosciences, 10(3), 456-476. https://doi.org/10.26833/ijeg.1646118.
23. Bowles, J. E. (2012). Physical and Geotechnical Properties of Soils (International Student Edition). McGraw-Hill.
24. Roy, S., & Dass, G. (2014). Statistical models for the prediction of shear strength parameters at Sirsa, India. International Journal of Civil and Structural Engineering, Vol. 4, No. 4. DOI 10.6088/ijcser.201404040002.
25. Civelekler, E., & Pekkan, E. (2022). The application of GIS in visualization of geotechnical data (SPT-Soil Properties): a case study in Eskisehir-Tepebaşı, Turkey. International Journal of Engineering and Geosciences, 7(3), 302-313. https://doi.org/10.26833/ijeg.980611.
26. Civelekler, E. (2023). Using GIS for the allowable soil bearing capacity estimation according to the Terzaghi (1943) equation in Eskişehir city center, Türkiye. International Journal of Engineering and Geosciences, 8(3), 310-317. https://doi.org/10.26833/ijeg.1212584.
27. Nmiss, M., Amyay, M., Atiki, N., & Ouammou, A. (2025). Seasonal morphological changes and grain size distribution mapping on the Massa beaches using a tachometer and GIS. International Journal of Engineering and Geosciences, 10(2), 272-289. https://doi.org/10.26833/ijeg.1598677.
28. Prakash, S., & Jain, C. A. (2002). Soil Mechanics (and Foundation Engineering). McGraw-Hill.
29. Dafalla, M. A. (2013). Effects of clay and moisture content on direct shear tests for clay–sand mixtures. Advances in Materials Science and Engineering, 2013, Article ID 562726. https://doi.org/10.1155/2013/562726.
30. IPCC (2014). Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R. K. Pachauri & L. A. Meyer (Eds.)]. Geneva, Switzerland: IPCC.
31. IPCC (2018). Global Warming of 1.5 °C: An IPCC Special Report on the Impacts of Global Warming of 1.5 °C above Pre-Industrial Levels and Related Global Greenhouse Gas Emission Pathways. Geneva, Switzerland: IPCC.
32. Environmental Justice Foundation (2018). Our Impact 2018. London, UK: Environmental Justice Foundation.
33. Government of the People’s Republic of Bangladesh. “Kalapara Upazila – About Upazila.” Bangladesh National Portal, kalapara.patuakhali.gov.bd, 2020.
34. Himmelstoss, E. A. (2009). DSAS 4.0 Installation Instructions and User Guide. In A. H. Thieler, E. A. Himmelstoss, J. L. Zichichi, & A. Ergul (Eds.), Digital Shoreline Analysis System (DSAS) version 4.0—An ArcGIS extension for calculating shoreline change (U.S. Geological Survey Open-File Report 2008-1278). U.S. Geological Survey.
35. ASTM International (2023). ASTM D854-23: Standard test methods for specific gravity of soil solids by water pycnometer. ASTM International.
36. ASTM International (2022). ASTM D4318-22: Standard test methods for liquid limit, plastic limit, and plasticity index of soils. ASTM International.
37. Paul, B. K. (2009). Why relatively fewer people died? The case of Bangladesh’s Cyclone Sidr. Natural Hazards, 50, 289–304.
38. Mallick, B., & Vogt, J. (2012). Cyclone Aila and its aftermath: the resilience of the coastal people in Bangladesh. International Journal of Disaster Risk Reduction, 1, 62–72.
39. Dasgupta, S., Laplante, B., & Meisner, C. (2010). Climate change and storm surges in Bangladesh. Policy Research Working Paper 4901. World Bank.
40. BIWTA (Bangladesh Inland Water Transport Authority). (2020). Annual Tide Table Report.
41. Alam, M. S., & Uddin, M. S. (2013). Longshore sediment transport along the Kuakata coast, Bangladesh. Journal of Coastal Conservation, 17, 133–144.
42. Islam, M. R. (2011). Morphodynamic evolution of the Meghna Estuary. Estuarine, Coastal and Shelf Science, 93, 161–169.
43. Stephens, S., & Hossain, M. S. (2006). Wave climate and coastal processes along the Bangladesh coast. Ocean Engineering, 33, 1373–1390.
44. Rahman, M. M., & Kamal, A. H. (2019). Bank erosion in tidal channels of the Meghna Estuary. Geomorphology, 329, 128–140.
45. Islam, M. N., & Khan, M. H. (2018). Hydro-morphological drivers of riverbank erosion in coastal Bangladesh. Water, 10(10), 1407.
46. Gain, A. K., & Schwab, M. (2012). River embankment and land-use change impacts on erosion. Environmental Management, 50, 478–493.
47. Hasan, M. R., & Akter, S. (2020). Tourism pressure and dune degradation at Kuakata beach. Journal of Coastal Research, 36(5), 901–912.
48. Das, S. K., & Haque, M. E. (2019). Influence of soil cohesion and grain size on coastal erosion. Engineering Geology, 257, 103–119.