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

Fluvial, tidal, and combined hydro-morphodynamics interaction in a complex, seasonal, sediment transport regime has been the subject of extensive research. It becomes particularly challenging when there is limited data. The Ganges-Brahmaputra-Meghna (GBM) Delta is one example of a huge system lacking data. Bathymetric data simultaneously covering the rivers and estuaries is hardly present, let alone sequences of bathymetries or a system-wide sediment budget. Hence it is difficult to understand and predict future developments. This research aims to make a sediment budget for the GBM delta with a process-based model. It is a first-ever sediment budget simulation for the GBM system. A process-based morphological model, Delft3D, has been used to reproduce the bathymetric evolution over time and the associated sediment budget. This chapter demonstrates the possibilities for the application of a robust modeling system to assess the morphodynamic evolution and sediment budget and pathways. The Ganges and Jamuna rivers carry sediment load in the ranges of 216–1038 million tonnes/yr and 80–228 million tonnes/yr respectively. The total accumulation in the estuary system is 1150 million tonnes/yr, out of which more than eighty percent of sediment is in suspension. The model results show that about 22% of the total sediment coming into the system is deposited in the floodplains and tidal plains and causes river morphology changes. The rest of the sediment is lost to the pro-delta, to the deep ocean bed, or leaves the domain. The results also indicate that Padma, Gorai, Pussur-Sibsa, Bishkhali, Shahbajpur channel, Lower Meghna, Tentulia Channel, and Arial Khan rivers are mainly in the aggrading phase, whereas, the Ganges, Jamuna, and Baleshwar are in the degrading phase. This particular delta model offers many opportunities to compare with sediment data, where it deals with a poorly surveyed area.@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

The Ganges-Brahmaputra-Meghna (GBM) Delta is a good example of a large estuarine system with sparse data. This study describes the development and validation of a morphodynamic process-based model (Delft3D) as a tool to predict the dynamic system as a response to climate change, sea-level rise, subsidence and other influences. The modelled sediment transport of the Ganges and Jamuna systems is between 200 and 1100 million ton/year, which is in line with observations. On annual basis sand accounts for less than 20% of the sediment load in the system with the remaining sediment being much finer. Analysis of modelled bed level changes over time reveals that only a few river systems are in an aggrading phase. The 2D model exhibits that about 22% of the supplied sediment deposits in the delta system on floodplains and tidal plains, whereas the remaining 78% of the sediment causes subaquatic delta progradation or is lost in the deep ocean bed. Although the model does not reproduce all-natural phenomena at all spatial scales, it will be a valuable tool to describe and explore the morphodynamic development of the GBM Delta over decadal to centennial timescales for macro-scale understanding, planning, and management.@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