The tide dominated Meghna estuary is characterized by a sequence of distributary channels and islands/chars. While there are a few studies on morphological processes of the Meghna estuary in general, studies on the physical processes of the islands/chars in the estuary are sparse. Close to two million people live on some of these fragile islands and chars. Given the lack of scientific literature on the formation and dynamic processes of the islands/chars, the chapter analyzes time-series historical maps and satellite images in an attempt to fill the knowledge gap. The study reconstructed the history of the Meghna estuary and islands and chars using maps and satellite images, recorded various noticeable events in the estuary and islands, and identified related drivers. Thereafter, the processes of formation of islands/chars and the time required for this in different physical environments were verified. The dynamics of the islands/char formation include the processes of erosion/accretion, increase/decrease in size, changes in shape, and migration of islands/chars.@en

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.@en

Every river is unique. Therefore, effective erosion management in rivers should be based on their morphological processes. The Arial Khan, a major and very dynamic river in Bangladesh, creates huge bank erosion which is one of the main sources of the sufferings of the local people. This article proposes a cost effective and efficient method of erosion management based on the morphological process of the Arial Khan River. Satellite images, old maps and hydro-morphological data have been used to understand the morphology and planform of the river. Erosion in this river does not continue at a particular location or for more than 5 years. A quicker and cheaper option for bank protection would be suited for local scale erosion management. On the other hand, planform analysis of the Arial Khan River shows that the meandering length and amplitude are four and one kilometers respectively. In addition, as the river in an active delta, it should also be allowed the flexibility for land formation and development. For long term erosion management, fixing the nodal sections might be more efficient and cost-effective as well as environmental friendly than a rigid and costly solution. @en

While most of the large deltas in the world are suffering from sediment starvation, the Bengal delta is prograding at a substantially high rate. The progradation expedites the shifting process of delta building estuaries as well as their associated distributaries, which play an important role in the eco-system of the delta by influencing the salinity, sediment and also the flooding pattern. A future projection of the delta shifting is essential for long-term development planning of the delta. This article reports the findings of a preliminary investigation using available data. Historical maps, time-series satellite images, digital elevation maps based on topographic surveys of the 1950s and 1990s, as well as water level and hydrographic surveys have been used for the investigation. During the last two hundred and forty years, the main delta building estuary has changed its location as well as the associated distributaries. It has been observed that huge sediment generated from the 1950 Assam earthquake expedited the shifting processes. However, due to lack of time-series and reliable data, quantification of the shifting process is not possible. It also makes future projection more uncertain. Nevertheless, it can be assertained that delta shifting processes, especially shifting of the distributaries towards the southwest direction will continue in the coming decades, which is very much relevant for long-term planning of the delta.@en

Due to flat terrain and dense population, the Bengal Delta is highly vulnerable to sea level rise. At present the delta building process is active in the Meghna Estuary. Information on sediment dispersal processes in the estuary and their response to different exogenic and anthropogenic forces is an important requirement for managing the sediment and developing adaptive measures to counter the potential impact of climate change. Historical maps, satellite images and tidal water level data were analysed and the response of the Meghna Estuary to extreme events, e.g. the 1950 Assam earthquake, as well as anthropogenic interventions, was assessed. The issue of sediment management was addressed, based on an understanding of the response of the estuary to the extreme natural event and anthropogenic interventions, along with an assessment of the response of the estuary to sea level rise. Among other interventions, emphasis has been directed to promoting vertical accretion by injecting sediment into polders.@en

Bangladesh is dominated by three great rivers – the Jamuna–Brahmaputra, Ganga, and Meghna – that combine to feed sediment into one of the World's largest deltas in the Bay of Bengal. The Jamuna River has developed in a region of significant tectonic activity associated with Himalayan uplift and development of the Bengal foredeep. The bedload, although only ~10% of the total sediment load, is critical in generating a wide array of bedforms of different scale that drive channel change and migration. Within the Jamuna River, the ubiquitous occurrence of bifurcations and confluences is a key aspect of the river channel pattern and dynamics, and these features form important nodes in the braidbelt. The nature of floodplain sedimentation and inundation is vital in planning annual crop growth and may adopt great significance in the ongoing debate on the sources, causes, and accumulation of arsenic in the groundwaters of Bangladesh.@en

The main rivers of Bangladesh are boon and bane for the country. They supply water and fertile sediments allowing multiple crops per year, hundreds of waterways for navigation, rich fish stock and habitat diversity. But especially the dynamic, unpredictable Brahmaputra influenced rivers erode fertile floodplain land with long established settlements, flood embankments, roads, and all other communal infrastructure. The high sediment load and resulting continuous shifting of river courses impedes navigation and the inflows into the important distributary offtakes. Stabilization of these largest and most unpredictable rivers on the planet presents a huge challenge. Bangladesh has systematically developed the technology and experience to stabilize longer reaches of riverbanks and has commenced towards a holistic approach to stabilizing the Brahmaputra System from the Assam border to the Bay of Bengal. Current developments are concentrated in the Flood and Riverbank Erosion Risk Management Investment Program, from which we present three recent key developments. First, we demonstrate phased gradual stabilization of the 60 km reach just upstream of the confluence with the Ganges following an adaptive approach, responding to massive riverbank erosion but also seizing the opportunities offered by the rivers during particular years towards systematic stabilization and land reclamation. Second, we show how an array of morphological prediction methods and mathematical models, developed over the past 25 years, is used for the planning and the design of interventions for stabilization. Third, we demonstrate our experiences with an innovative construction method for long guiding revetments, consisting of sand-filled geo-textile bags under water. Additionally, we discuss the feasibility, costs, benefits, environmental impacts and social impacts of river stabilization also with special attention to the pivoting role of stable distributary offtakes in the context of a wider river management plan.@en

The main rivers of Bangladesh are boon and bane for the country. They supply water and fertile sediments allowing multiple crops per year, hundreds of waterways for navigation, rich fish stock and habitat diversity. But especially the dynamic, unpredictable Brahmaputra influenced rivers erode fertile floodplain land with long established settlements, flood embankments, roads, and all other communal infrastructure. The high sediment load and resulting continuous shifting of river courses impedes navigation and the inflows into the important distributary offtakes. Stabilization of these largest and most unpredictable rivers on the planet presents a huge challenge. Bangladesh has systematically developed the technology and experience to stabilize longer reaches of riverbanks and has commenced towards a holistic approach to stabilizing the Brahmaputra System from the Assam border to the Bay of Bengal. Current developments are concentrated in the Flood and Riverbank Erosion Risk Management Investment Program, from which we present three recent key developments. First, we demonstrate phased gradual stabilization of the 60 km reach just upstream of the confluence with the Ganges following an adaptive approach, responding to massive riverbank erosion but also seizing the opportunities offered by the rivers during particular years towards systematic stabilization and land reclamation. Second, we show how an array of morphological prediction methods and mathematical models, developed over the past 25 years, is used for the planning and the design of interventions for stabilization. Third, we demonstrate our experiences with an innovative construction method for long guiding revetments, consisting of sand-filled geo-textile bags under water. Additionally, we discuss the feasibility, costs, benefits, environmental impacts and social impacts of river stabilization also with special attention to the pivoting role of stable distributary offtakes in the context of a wider river management plan.@en

Human interventions in the river basin upstream as well as within the river itself have caused sediment shortage in the delta system and hence the majority of the deltas are in eroding phase. The sediment dispersal process; which is governed by geometry and topography, coastline, and tidal dynamics; is an important issue for destining the delta formation. Coarse sediment in rivers results in a change in river morphology; whereas fine sediment consists primarily of silt and clay transported in suspension by a river from its catchment and floodplain plays an essential role in estuary morphology. As a result of this research, it will be possible to determine how sediment disperses in the Meghna estuary, and how sediment texture affects erosion and accretion. A hypothesis was formulated if the sediment texture determines the pattern of sediment accumulation, considering other factors are remaining the same. A set of data were collected in the Meghna Estuary area considering an analysis based on old maps and satellite images archived in CEGIS. We have found that when sediment is deposited by fluvial processes, the coarser content is higher. As a result of this research, it will be possible to determine how sediment disperses in the Meghna estuary, and how sediment texture affects erosion and accretion.@en