Barbara Neumann, Athanasios T. Vafeidis, Juliane Zimmermann, Robert J. Nicholls
Coastal zones are exposed to a range of coastal hazards including sea-level rise with its related effects. At the same time, they are more densely populated than the hinterland and exhibit higher rates of population growth and urbanisation. As this trend is expected to continue into the future, we investigate how coastal populations will be affected by such impacts at global and regional scales by the years 2030 and 2060. Starting from baseline population estimates for the year 2000, we assess future population change in the low-elevation coastal zone and trends in exposure to 100-year coastal floods based on four different sea-level and socio-economic scenarios. Our method accounts for differential growth of coastal areas against the land-locked hinterland and for trends of urbanisation and expansive urban growth, as currently observed, but does not explicitly consider possible displacement or out-migration due to factors such as sea-level rise. We combine spatially explicit estimates of the baseline population with demographic data in order to derive scenario-driven projections of coastal population development. Our scenarios show that the number of people living in the low-elevation coastal zone, as well as the number of people exposed to flooding from 1-in-100 year storm surge events, is highest in Asia. China, India, Bangladesh, Indonesia and Viet Nam are estimated to have the highest total coastal population exposure in the baseline year and this ranking is expected to remain largely unchanged in the future. However, Africa is expected to experience the highest rates of population growth and urbanisation in the coastal zone, particularly in Egypt and sub-Saharan countries in Western and Eastern Africa. The results highlight countries and regions with a high degree of exposure to coastal flooding and help identifying regions where policies and adaptive planning for building resilient coastal communities are not only desirable but essential. Furthermore, we identify needs for further research and scope for improvement in this kind of scenario-based exposure analysis.
Eduardo Garzanti, Sergio Andò, Christian France‐Lanord, P. Censi et al.
Jim Best, Philip J. Ashworth, Charlie S. Bristow, Julie E. Roden
Abstract The three-dimensional subsurface alluvial architecture of a large (approximately 3 km long, 1 km wide, 12 m high), mid-channel sand braid bar in the Jamuna River, Bangladesh is described. Evolution of the bar and its depositional characteristics are assessed from a unique combination of ground-penetrating radar surveys, vibracoring, and trenching that are allied to a series of bathymetric surveys taken during growth of the bar over a 29-month period. This methodology permits identification of the formative processes of different packages of braid-bar sedimentation and provides a facies model for deposition within the entire bar. Mid-channel bar growth occurred in a region of flow expansion and was probably initiated by the stalling and amalgamation of large dunes. These dunes created a bar-core that grew by (i) propagation of a downstream-accreting slipface, (ii) vertical accretion through stacking of dunes on both bar stoss and top, and (iii) lateral accretion on the bar margins during recession of the flood hydrograph. Braid-bar sedimentation is dominated by four radar facies: (1) large-scale, predominantly planar, dipping reflections interpreted as cross-stratification, up to 8 m in height and greater than 100 m in width, that is produced by the cross-channel migration of bar margins, (2) medium-scale, trough-shaped and planar discontinuous reflections interpreted as cross-stratification up to 4 m in height and 300 m wide, that is deposited from large, sinuous-crested sand dunes, (3) discontinuous reflections, up to 2 m high and 30 m wide, interpreted as small-scale trough cross-stratification, that is the product of smaller sinuous-crested dunes, and (4) high-amplitude, undulating reflections interpreted as mud drapes, deposited in regions of slow flow, often in the bar-tail region at low stage. Dune size decreases vertically within the bar, in response to the progressively shallower flows on the emerging bar top. Later evolution of the bar, as one anabranch channel became dominant, created a 1.5 km extension to the bar tail with an 8 m high, angle-of-repose, bar-margin slipface, formed by flow transverse to the long axis of the bar. Seven styles of deposition can be defined that constitute the alluvial architecture: bar-margin slipface, vertical accretion in channel, bar-top vertical accretion, upstream accretion, lateral accretion, downstream accretion, and low-stage mud drapes. A model of braid-bar sedimentation is presented that shares many similarities with previous studies of smaller sand-bed braid bars with the dominance of dune-scale cross-stratification, the presence of large-scale, bar-margin cross-stratification, and the occurrence of lateral, vertical, upstream, and downstream accretion. However, the contribution of the bar-margin facies to the preserved stratigraphy highlighted herein may have been underestimated in previous models of braided rivers in which the braid bars were migrating slowly. This study suggests a scale invariance in several aspects of mid-channel bar sedimentation in sand-bed rivers and proposes a model of braid-bar sedimentation that may be applied widely within studies of braided alluvial architecture.
Manoj Kumer Ghosh, Lalit Kumar, Chandan Roy
Maminul Haque Sarker, Iffat Huque, Mustafa Alam, Rob Koudstaal
Abstract Bangladesh consists mainly of riverine and deltaic deposits of three large and extremely dynamic rivers entering the country: the Brahmaputra, Ganges and Meghna rivers. The average flood discharges of these rivers (individually) are within the range of 14,000 to 100,000 m3/s. Islands and bars are very common features among them all. In Bangladesh, both islands and bars are known as chars, but in this article only the vegetated islands within the riverbanks are referred to as chars. They are difficult to access and form an extremely dynamic environment for around 600,000 people that try to make a living under extreme and hazardous conditions of frequent and intensive flooding and erosion. People displaced by char erosion have no other alternative than to settle on accreting char land elsewhere, creating a typical social and economic char environment. The economics of the char lands are largely based on agriculture, fishing and livestock‐rearing. Education, health and extension services and support to cope with the calamities of flood and erosion are minimal. This not only results in individual misery, but also in unrealized potential of resources on the chars. Satellite imagery, available from the ‘70s onward, have facilitated several comprehensive studies of the dynamics of the rivers and chars. They have, in combination with social surveys, provided a good understanding of the interaction between the physical environment and the livelihoods of the char dwellers. They have also enabled predictions, e.g. on the total area and mobility of chars in the next decade. This has improved understanding and predictive capability that could lead to a better utilization of the potential resources of the chars to improve the livelihoods of char dwellers.
Abhijit Mukherjee, Alan E. Fryar, William A. Thomas
Mead A. Allison
Detailed early chartmaking by the British East India Company and the Royal Navy in India and present-day Bangladesh provide one of the most accurate databases available to track the evolution of a major delta front over the last 200 years. Digital databases of shoreline position and shallow bathymetry of the Ganges-Brahmaputra delta front were constructed using geo-referenced and projection-corrected early and modern charts, and using LANDSAT imagery. In contrast with earlier published studies, these databases indicate the Ganges-Brahmaputra has an actively prograding subaerial delta: an average of approximately 7.0 km 2 / yr of new land have accreted in the river mouth region since 1792. Digitate shoals, forming in association with accretion of elongate islands in the river mouth region, are coalescing in 8-15 m water depth to form a relatively coarse-grained lobate feature that is prograding over the muddy, subaqueous delta on the inner shelf. The morphology of shoal growth suggests the Ganges-Brahmaputra mouth has evolved eastward over the late Holocene as a series of digitate shoal-channel complexes. West of the active river mouth in historical times, the delta front is sediment starved and is undergoing retreat at rates of about 1.9 km 2 / yr.
Ashraf Uddin, Neil Lundberg
Research Article| April 01, 1998 Cenozoic history of the Himalayan-Bengal system: Sand composition in the Bengal basin, Bangladesh Ashraf Uddin; Ashraf Uddin 1Department of Geology and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 Search for other works by this author on: GSW Google Scholar Neil Lundberg Neil Lundberg 2Department of Geology, Florida State University, Tallahassee, Florida 32306 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1998) 110 (4): 497–511. https://doi.org/10.1130/0016-7606(1998)110<0497:CHOTHB>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ashraf Uddin, Neil Lundberg; Cenozoic history of the Himalayan-Bengal system: Sand composition in the Bengal basin, Bangladesh. GSA Bulletin 1998;; 110 (4): 497–511. doi: https://doi.org/10.1130/0016-7606(1998)110<0497:CHOTHB>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Stratigraphic sequences preserved in the Bengal basin provide detrital information that documents a significantly older history of the eastern Himalaya than that available from Ocean Drilling Program and Deep Sea Drilling Project cores recovered from the Bengal fan. The Bengal basin, formed as a result of the Himalayan collision, is located at the juncture of the Indian craton to the west, the Shillong massif and the Himalayan belt to the north, and the Indo-Burman ranges to the east. Modal analyses of Eocene and Oligocene sandstones of the Cherra, Kopili, and Barail Formations document compositions that are dominated by subangular monocrystalline quartz grains with scarce to no feldspar grains, and few lithic fragments (Cherra and Kopili: Qt99F1L0; Barail: Qt90F3L7; Qt—total quartz, F—feldspar, L—lithic fragments). These compositions are similar to sands derived from the Indian craton, suggesting that they underwent intense chemical weathering, likely in a source with low relief and considerable transport. Himalayan tectonism during this time was probably significantly more distant from the Bengal basin than at present.Sandstones of the Miocene Surma Group (Bhuban and Boka Bil Formations) are rich in feldspar grains, argillite, and very low-grade metamorphic lithic fragments (Bhuban: Qt66F15L19; Boka Bil: Qt57F23L20) relative to older sandstones, suggesting onset of uplift and erosional unroofing in the eastern Himalaya, and initiation of stream systems supplying orogenic detritus to the Bengal basin. Sands of the upper Miocene to Pliocene Tipam Group and the Pliocene–Pleistocene Dupi Tila Sandstone contain abundant argillitic and low- to medium-grade metamorphic lithic fragments and feldspar grains (Tipam: Qt61F19L19; Dupi Tila: Qt70F13L17), suggesting continued orogenic unroofing. These younger sands are rich in potassium feldspar (P/F=0.30, 0.20) relative to plagioclase (P)-rich Bhuban and Boka Bil sandstones (P/F=0.66 and 0.48), suggesting a granitic source, probably the Miocene leucogranites of the High Himalayan Crystalline terrane.These results document for the first time contrasts in orogenic history recorded in the Bengal system vs. western Himalayan foreland basins. Sands deposited in the Bengal basin are generally more quartzose and less lithic than those from the western Himalayan foreland basins, and pre-Miocene strata in the Bengal system show little to no evidence of orogenic activity. In part, this probably reflects west to east progression of the Himalayan collision, but it probably also results from sedimentary systems propagating southward, ahead of the advancing mountain belt as it has been consuming the remnant ocean basin trapped between the Indian craton and the Burmese block. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Tharani Gopalakrishnan, Md Kamrul Hasan, A. T. M. Sanaul Haque, S. Jayasinghe et al.
Climatic and non-climatic stressors, such as temperature increases, rainfall fluctuations, population growth and migration, pollution, land-use changes and inadequate gender-specific strategies, are major challenges to coastal agricultural sustainability. In this paper, we discuss all pertinent issues related to the sustainability of coastal agriculture under climate change. It is evident that some climate-change-related impacts (e.g., temperature and rainfall) on agriculture are similarly applicable to both coastal and non-coastal settings, but there are other factors (e.g., inundation, seawater intrusion, soil salinity and tropical cyclones) that particularly impact coastal agricultural sustainability. Coastal agriculture is characterised by low-lying and saline-prone soils where spatial competition with urban growth is an ever-increasing problem. We highlight how coastal agricultural viability could be sustained through blending farmer perceptions, adaptation options, gender-specific participation and integrated coastal resource management into policy ratification. This paper provides important aspects of the coastal agricultural sustainability, and it can be an inspiration for further research and coastal agrarian planning.
Dilip Kumar Datta, V. Subramanian
Md. Mahmuduzzaman, Zahir Ahmed, A. K. M. Nuruzzaman, Fazle Rabbi Sadeque Ahmed
As Bangladesh belongs to one of the seaside countries, the adverse impact of saltwater intrusion is significant here. Salinity mainly affects land and water in the coastal areas. With the consequence of climate change, it gradually extends towards inland water and soil. This scenario of gradual salinity intrusion in the coastal area of Bangladesh is very threatening to the primary production system, coastal biodiversity and human health. The total amount of salinity affected land in Bangladesh was 83.3 million hectares in 1973, which had been increased up to 102 million hectares in 2000 and the amount has raised to 105.6 million hectares in 2009 and continuing to increase (Soil Resources Development Institute (SRDI), 2010) [1]. In the last 35 years, salinity had been increased around 26 percent in this country. Salinity intrusion is spreading into the non-coastal areas as well. Recently, International Rice Research Institute (IRRI)’s Seed Study, funded by USAID, has identified 12 districts of Bangladesh as salinity affected area through GIS mapping [2]. This paper analyzes the cause of salinity intrusion in the coastal belt of Bangladesh such as: critical geographical location of the country, low flow condition of the river by a barrage in the upstream neighboring country, faulty management of coastal polders, sea level rise, cyclone and storm surge, back water effect, precipitation and shrimp culture. This paper also helps the decision makers and planners in sustainable social, agricultural, environmental and other water resources management plan for the coastal region of Bangladesh.
Andrew D. Miall, Brian G. Jones
Abstract The Hawkesbury Sandstone has long been assumed to represent the deposits of a large braided river system, comparable in style and magnitude with the modern Brahmaputra River of Bangladesh. Such an interpretation is based mainly on the common occurrence of very large-scale crossbedding, but no architectural studies of the unit have hitherto been carried out. This paper represents a first attempt to estimate the magnitude of Hawkesbury channels and bars on the basis of the preserved architectural evidence. Photomosaics were constructed of two cliff sections south of Sydney, one 5.6 km in length. On the basis of these profiles we estimate that characteristic channel-scale architectural elements are at least 2.7 km wide, and individual macroforms are 5-10 m high, indicating the constructional depth of typical channels. Hollow elements (scoop-shaped units interpreted to have formed at channel confluences) are up to 20 m deep. These magnitudes are large, but measurably smaller that those of channels and bars in the modern Brahmaputra River of Bangladesh.
Md. Reaz Akter Mullick, Ahad Hasan Tanim, S M Samiul Islam
Bangladesh coast is recognized as one of the hotspots of several coastal hazards like coastal flood, sea level rise, increased tropical cyclone occurrence etc. To understand the problem followed by necessary coastal management recommendation, an integrated coastal vulnerability index i.e., Composite Vulnerability Index (CVI) was developed for the coastal region applying geospatial technique. Three sub-indices, namely, Coastal Characteristics Vulnerability sub-index (CCVI), Coastal Forcing Vulnerability Sub-index (CFVI) and Socio-economic vulnerability sub-index (SEVI) were separately estimated and combined to determine the CVI. Since, the classical set theory of traditional vulnerability classification is inadequate to express the natural variability of vulnerability at continuous scale, this study offered a framework of vulnerability representation using fuzzy set theory. The approach was effective to handle the uncertainty of large scale vulnerability analysis with the normalization of featured factors applying three fuzzy membership functions i.e., Fuzzy-Large, Fuzzy-Small and Fuzzy-Linear in geospatial analysis. The analysis was carried out at 10 m cell level and classified with five vulnerability classes i.e., very high, high, moderate, low and very low. The analyses show that the Chittagong coast and Feni district are very highly vulnerable. High tide amplitude (>4 m), cyclone track density and mild coastal slope are responsible for the high vulnerability of the Chittagong coast. On the other hand, Feni district shows the highest SEVI which is resulted from high population density and socio-economic conditions. Presence of mangrove forest results a reduced CFVI which significantly decrease the vulnerability of Pirojpur, Satkhira, Khulna and Bagerhat district. Based on the responsible vulnerability index, necessary coastal protection measures are recommended for the coast. It is expected that the comprehensive vulnerability map with CVI can be a key element for coastal management of Bangladesh. Furthermore, the classification of vulnerability under different class will help to develop necessary coastal protection measures according to the resiliency of the coastal community.
Amelie Paszkowski, S. L. Goodbred, Edoardo Borgomeo, M. Shah Alam Khan et al.
Munsur Rahman, Maruf Dustegir, Rezaul Karim, Anisul Haque et al.
The physical sustainability of deltaic environments is very much dependent on the volume of water and sediment coming from upstream and the way these fluxes recirculate within the delta system. Based on several past studies, the combined mean annual sediment load of the Ganges-Brahmaputra-Meghna (GBM) systems has previously been estimated to vary from 1.0 to 2.4 BT/year which can be separated into components flowing from the Ganges (260 to 680 MT/year) and Brahmaputra (390 to 1160 MT/year). Due to very limited data and small contribution of the Meghna system (6-12 MT/year) to the total sediment flux of the GBM system, the data of the Meghna is not considered in the analysis assuming the sediment flux from GB system as the sediment flux of GBM. However, in this paper our analysis of sediment concentration data (1960-2008) collected by Bangladesh Water Development Board shows that the sediment flux is much lower: 150 to 590 MT/year for the Ganges versus 135 to 615 MT/year for the Brahmaputra, with an average total flux around 500 MT/year. Moreover, the new analysis provides a clear indication that the combined sediment flux delivered through these two major river systems is following a declining trend. In most of the planning documents in Bangladesh, the total sediment flux is assumed as a constant value of around 1 billion tons, while the present study indicates that the true value may be around 50% lower than this (with an average decreasing trend of around 10 MT/year).
Mead A. Allison, E. Kepple
Muhammad Al-Amin Hoque, Naser Ahmed, Biswajeet Pradhan, Sanjoy Roy
The eastern coastal region of Bangladesh, which has a 377 km-long coastline, is highly vulnerable to multi-hazardous events, such as tropical cyclones, coastal floods, coastal erosion and salinity intrusion. The vulnerability of this coastal region is likely to increase under the future climate change context. This research aims to develop a coastal vulnerability index (CVI) of multi-hazardous events for the eastern coastal region of Bangladesh. Eight parameters, mostly focused on physical vulnerability, were considered in this study. Various thematic layers were prepared for each parameter using spatial techniques, and all parameters were assigned a vulnerability ranking. Finally, a CVI was developed and the related values were categorised into five distinct classes (i.e., very high, high, moderate, low, and very low). Results indicate that approximately 121 km (32%) of the coastline of the study area is in high-to very high-vulnerability zones. Low elevations, gentle slopes, high storm surge impacts, sandy coastlines, high shoreline erosion rates and high sea-level changes are the most important factors of high to very-high vulnerability zones. The moderately vulnerable area covers approximately 119 km (32%) of the coastline. Meanwhile, 78 (21%) and 59 (16%) km of the coastlines are in low-to very low-vulnerability zones, respectively. These coastlines are characterised by steep slopes with high elevations, low tide range and storm surge heights as well as less erosion. The CVI results were validated by qualitative observations acquired from the field. The findings of this study can be applied by policymakers and administrators to develop effective mitigation plans and minimise the likely impacts of coastal multi-hazards.
Jakia Akter, Maminul Haque Sarker, Ioana Popescu, Dano Roelvink
Akter, J.; Sarker, M.H.; Popescu, I., and Roelvink, D., 2016. Evolution of the Bengal Delta and its prevailing processes.Bangladesh, occupying low-lying floodplains and tidal plains, has one of the largest and the most disaster-prone populous deltas in the world. The Bengal Delta is a tide-dominated delta, where tides play the key role in the sediment dispersal process and in shaping the delta. There are many studies and reports on river-dominated deltas, but research is sparse on tide-dominated deltas. The Ganges and Brahmaputra Rivers, which combined form one of the three largest riverine sources of water and sediment for the world's oceans, have developed the Bengal Delta to its present form with an aerial extent of 104 km2. About 1012 m3 of water with 109 tonnes of sediment per year make this system morphologically active. In the last five decades, the Bengal Delta has prograded at a rate of 17 km2/y, whereas most large deltas elsewhere in the world suffered from sediment starvation. Delta progradation always makes the river system unstable, and rapid changes cause the delta to become dynamic. Sea level rise induced by unequivocal climate change and subsidence would make the delta more vulnerable in the coming decades. Although some literature is available on the millennium-scale development process of the Bengal Delta, sound knowledge on the decade- to century-scale processes of the delta development for facing the threats of climate change and deltaic subsidence is limited. In addition, there are significant differences in opinions and widely varying findings in the literature to the response of the delta to different natural and human interventions. Against this backdrop, relevant available literature on Bengal Delta and deltas elsewhere in the world, is reviewed and evaluated to provide direction for future research that would help to form a way out of the present situation and a way into sustainable planning for this delta.
Ashraf Uddin, Neil Lundberg
Charlie S. Bristow
Abstract The Brahmaputra River is one of the world’s largest sand-bed braided rivers with a channel belt up to 15 km wide, a mean channel depth of 5 m and maximum scour depths of up to 40 m. The recorded discharge varies by around 60 000 cumecs every year following the annual monsoon, producing dramatic stage fluctuations with the water level falling between 7 and 8 m from bankfull to low flow stage. In the dry season large areas of bar top and channel bed are exposed and low flow channels cut natural sections through bar tops exposing the internal stratification. Elements of upstream, downstream and lateral accretion are identified, although the high width/depth ratio of channels (up to 500:1) results in extremely low depositional dips on bed bounding surfaces. Within the accretionary elements vertical and lateral changes in sedimentary structures are ubiquitous and varied but some patterns can be discerned. Channel deposits are dominated by sinuous-crested dunes and trough cross-stratification. Upper stage plane bed lamination, often with a very low angle depositional dip, has been observed in beds up to 4 m thick and is generally found at the base of the exposed bar top sections. Trough cross-stratification in bar tops occurs in sets from 0.1 m to 3 m thick with rapid vertical and lateral changes in set thickness. Very large sets of trough cross-stratification, >3 m thick, do not occur in the bar top sections. Current ripple lamination is most abundant on the tops of bars with very high rates of climb associated with high rates of sediment deposition. From these observations a generalised vertical sequence of bar top origin might include trough cross-stratification overlain by upper stage plane bed lamination, isolated sets of trough cross-stratification truncated and capped by current ripple lamination. This sequence, which is considered to represent the deposits of a single flood, may occur within the upstream, downstream or lateral accretion elements. However, it should be noted that vertical and lateral changes in facies are extremely abundant with many changes in sedimentary structures and reactivation surfaces within each depositional episode.