Md. Munsur Rahman

Flow and erosion at a bend in the braided Jamuna River

Abstract The braided Jamuna River frequently changes its courses. Sometimes the secondary channel in a braided river acts as a single thread meandering channel. In the present study an attempt has been made to investigate the flow patterns and to estimate the rate of bank erosion in a bend along the Jamuna River. The three dimensional (3D) flow velocities were measured using Acoustic Doppler Current Profiler (ADCP). It is found that the near bank velocity is amplified by 1.1 to 1.3 times as compared with the section averaged velocity. A dominant secondary current is found in the upstream bend. The evolution as well as decay of the secondary current is not as clear as it is found in the laboratory experiments. It is revealed from the analysis of the flow process that the causes of higher rate of erosion at the study bend are the oblique flow near bankline, six times amplified shear velocity than critical shear velocity near bankline and the secondary current which acts as a sediment transporting agent from the outer bank towards the inner bank or the sand bar. Based on the flow processes, a simplified erosion prediction model is developed and applied to estimate the rate of erosion at a selected bend. Finally the predicted results have been compared with the observed data at the bend and all the available data at other bends along the Jamuna River.

Climate change adaptations of shrimp farmers: a case study from southwest coastal Bangladesh

Sustainability of brackishwater shrimp farming is of paramount importance for socio-economic development of southwest coastal Bangladesh. Here, shrimp farming is predominantly traditional, which is more vulnerable to climate change. Lack of understanding exists regarding the adaptation measures of local shrimp farmers in response to emerging impacts of changing climatic variables. This study provides the perceptions and adaptations of shrimp farmers in changing climatic context. A systematic random sampling method was employed to conduct a total of 240 questionnaire surveys and 60 key informant interviews from six sub-districts (Upazila) of southwest coastal Bangladesh to collect primary data. Changes in climate variables largely affect the shrimp yield by increasing frequency of shrimp disease, causing physical damage to farm structure and deteriorating quality of water. Shrimp farmers try to adapt to those changes in various ways, including increasing pond depth, exchanging tidal water, providing shade using aquatic plants, strengthening earthen dike and netting and fencing around the dike. Shrimp mixed cultivation is the most popular form of shrimp farming in the study area. More emphasis on implementing polyculture shrimp farming is necessary to improve climate change adaptation and to promote sustainability of this aquaculture practice in southwest coastal Bangladesh.

Integrative Analysis for the Ganges-Brahmaputra-Meghna Delta, Bangladesh

The Ganges-Brahmaputra-Meghna delta in Bangladesh is one of the world’s most dynamic deltas and supports high population densities based on large provisioning ecosystem services. Analysing the future of these ecosystem services and associated human livelihoods represents a complex multi-scale, multi-disciplinary problem. A conceptual framework aims to identify mechanisms that link physical processes (including climate change) with ecosystem services and social outcomes providing a shared basis for other analysis, including the design of an integrated model. This also allows the characteristics of co-production of ecosystem services at the landscape scale and significant trade-offs between types of ecosystem services to be incorporated. Adopting a systems-based approach of this scale is challenging but essential to support the effective management of coastal Bangladesh.

A Sustainable Future Supply of Fluvial Sediment for the Ganges-Brahmaputra Delta

Recent research highlights that delta submergence is an important issue for the Ganges-Brahmaputra-Meghna (GBM) delta. The only factor that could potentially offset losses in delta surface elevation is a sustainable supply of fluvial sediment. River sediments therefore have considerable economic and social value for ecosystem services and those they support. Analysis, using the HydroTrend model, indicates that an increase in the climate-driven supply of fluvial sediment to the GBM delta has the potential, through accelerated aggradation on the delta surface, to offset some of the adverse impacts of climate change due to rising sea levels in the Bay of Bengal. However, anthropogenic disconnections, such as dams, flood defences and polders disturbances, have the possibility to negatively affect this process.

Communicating Integrated Analysis Research Findings

Dissemination of research results and implications within Bangladesh is important to promote understanding both for the local population and those making decisions regarding ecosystem services. A variety of national to local dissemination tools are discussed with particular emphasis on indigenous cultural theatrical performances and workshops in local communities. A bespoke ‘Pot Song’ was developed which expresses the concept of ecosystem services, consequences of climate change and implications for local livelihoods. This achieved a high level of engagement with local communities, who appreciated the clarity of the information. The ‘Pot Song’ also provides a shared understanding as a basis for group discussions. This ensures a more productive use of limited time at workshops.

Ecosystem Services, Well-Being and Deltas: Current Knowledge and Understanding

Deltas are distinct in terms of the concentration of freshwater, nutrients and especially sediment inputs to a small concentrated area of the coastal zone, creating conditions ideal for fertile ecosystems, dense population and high economic activity. Ecosystem services within these areas can provide services significant in the maintenance of well-being for both rural and urban populations. There are significant feedbacks between environmental processes and social dynamics that drive the economic and well-being outcomes for current and future populations. This chapter reviews ecosystem services in deltas and summarises the state of knowledge in this field on how to manage delta ecosystems for the benefit of resident populations and wider society.

An Integrated Approach Providing Scientific and Policy-Relevant Insights for South-West Bangladesh

Bangladesh is identified as an impact hotspot for sea-level rise in multiple studies. However, a range of other factors must be considered including catchment management, socio-economic development and governance quality, as well as delta plain biophysical processes. Taking an integrated assessment approach highlights that to 2050 future changes are more sensitive to human choice/policy intervention than climate change, ecosystem services diminish as a proportion of the economy with time, continuing historic trends and significant poverty persists for some households. Hence under favourable policy decisions, development could transform Bangladesh by 2050 making it less vulnerable to longer-term climate change and subsidence. Beyond 2050, the threats of climate change are much larger, requiring strategic adaptation responses and policy changes that must be initiated now.