Research Division

Perennial water-logging due to the excessive riverbed sedimentation has become the most menacing crisis to the people of South-West region of Bangladesh. Peripheral embankments, polders, made in 1960 have turned out to be curse while it had been built to save the area from natural disasters and to augment agricultural yield. Later on Bangladesh Water Development Board (BWDB) implemented Khulna-Jessore Drainage Rehabilitation Project (KJDRP) to solve this long-standing water-logging problem during 1994–2002. After that, a popular indigenous concept Tidal River Management (TRM) was adopted which allows the tidal flow during high tide where in low tide, clear water erodes the river bed and increases the depth of the river as well as deposits sediment on the low lying land. As the tidal flow is allowed to enter in low lying areas or natural depression (locally known as beel) the land remains drowned during the application of TRM for 5–6 year. So locals can do nothing with their land that they suffer and starve. Due to institutional limitations, mismanagement as well as long appliance period the process of TRM operation the area still needs further attention to solve institutional conflicts and disputes among farmers, fishermen and land owners because of shrimp firming and loss of indigenous varieties of fish and crop biodiversity. The study explains that TRM could be the best solution to menacing water-logging if it is made socially acceptable.

Bangladesh is a low lying riverine country formed by a deltaic plain at the confluence of the three mighty rivers Ganges, Brahmaputra, Meghna and their tributaries. Most of the flows of these major rivers are connected to the Bay of Bengal through Meghna Esuary. The Lower Meghna River with a very dynamic estuarine system conveys the maximum flow through the estuary to the Bay of Bengal during dry and wet season . The sediment load and flow volume in Lower Meghna is respectively the highest and the third highest (after Amazon and Congo) in the world (Ahmed S. 1998). Owing to this tremendous water volume and sediment load delivered by the rivers, the estuary is an area of an active land erosion-accretion and dynamic water circulation. The main physical processes in the estuary are mainly dependent on the estuarine morpho-dynamics that causes erosion and accretion in the scale of hundred sq. kilometers per year and cause several thousands of people to become landless and homeless every year (Biswajit et al., 2013) 2000-2013. Net accretion, net erosion and the erosion trend are derived from the image processed using ILWIS 3.7.2 and ArcMAP 10. It is obvious that the erosion rate was in decreasing order from the year 1973 to 1984, 3.4km2/yr to -8.4km2/yr. Analysis also showed that in the history of the last forty years erosion rate was higher from the year 2003 to 2005, -8.4km2/yr to 15.4km2/yr. Recent year analysis predicted that the deposition is higher than the erosion. However, further research should be focused on future channel shifting pattern, erosion rate and vulnerability of different locations as well as determining effective measures to decrease erosion severity and its consequences.

The Ganges-Brahmaputra-Meghna (GBM) Delta is the largest and one of the most significant tide dominated deltas of the world that provides rich and diverse ecosystem . The availability and diversity of the ecosystem resources depend on the spatial and temporal variations of the fluvio-tidal parameters, mainly caused by the presence of the fresh water flow and the tidal flow within the estuarine systems, of the estuaries of this delta. Recent data shows a declining trend of the fresh water flow in the major parts of these estuarine systems, which most likely affect the tidal flow and the saline intrusion into the delta, thus affecting the saline regime as well as the estuarine ecosystems that mainly depend on the availability of the fresh water flow in the upstream river system.

Storm surge and sea level rise (SLR) are affecting coastal communities, properties, and ecosystems. While coastal ecosystems, such as wetlands and marshes, have the capacity to reduce the impacts of storm surge and coastal flooding, the increasing rate of SLR can induce the transformation and migration of these natural habitats. In this study, we combined coastal storm surge modeling and economic analysis to evaluate the role of natural habitats in coastal flood protection. We focused on a selected cross-section of three coastal counties in New Jersey adjacent to the Jacques Cousteau National Estuarine Research Reserve (JCNERR) that is protected by wetlands and marshes. The coupled coastal hydro-dynamic and wave models, ADCIRC+SWAN, were applied to simulate flooding from historical and synthetic storms in the Mid-Atlantic US for current and future SLR scenarios. The Sea Level Affecting Marshes Model (SLAMM) was used to project the potential migration and habitat transformation in coastal marshes due to SLR in the year 2050. Furthermore, a counterfactual land cover approach, in which marshes are converted to open water in the model, was implemented for each storm scenario in the present and the future to estimate the amount of flooding that is avoided due to the presence of natural habitats and the subsequent reduction in residential property damage. The results indicate that this salt marshes can reduce up to 14% of both the flood depth and property damage during relatively low intensity storm events, demonstrating the efficacy of natural flood protection for recurrent storm events. Monetarily, this translates to the avoidance of up to $13.1 and $32.1 million in residential property damage in the selected coastal counties during the '50-year storm' simulation and hurricane Sandy under current sea level conditions, and in the year '2050 SLR scenario', respectively. This research suggests that protecting and preserving natural habitats can contribute to enhance coastal resilience.

The recurrent flood risks on coastal areas in the United States due to storm surge are likely to increase with warmer climate, frequent storms, and increasing coastal population. In addition, the increasing rate of sea level rise (SLR) is expected to cause submergence of wetlands and marshes across the coastal landscape. Before decision makers can develop effective floodplain management and climate adaptation plans, they need reliable scientific information about the extent of flooding and estimate of future damage due to storm surge, sea level rise and marsh migration. In this study, coastal flood vulnerability in the Chesapeake Bay regions is investigated by using a coupled storm surge and waves model (ADCIRC+SWAN) for low and high intensity historical storms. Regional rate of SLR are combined with respective marsh migration projections in the modeling approach to estimate the future change in flooding, in addition to the existing inundation. To estimate flood damage, modeling res...

The project team is acknowledged for its contributions and thoughtful input throughout the project, and in particular, during the development of this report. We kindly acknowledge the contributions of Eric Messick, Lisa Auermuller, Mike De Luca, and Celso Ferreira. Each of you made this project possible through analytic efforts, expert review, local knowledge, guidance, and meeting space. We would like to thank the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing high performance computing resources that have contributed to the research results reported within this paper. We would like to give special thanks to our reviewers: Pete Wiley, Rick Lathrop, and Ty Wamsley. Finally, we thank all of our colleagues working throughout the Jacques Cousteau NERR for the benefit of coastal communities and habitats.

Bangladesh's vulnerability to storm surge and success in reducing their impacts on the coastal communities are well-known. However, global warming is expected to increase both the frequency and the intensity of tropical cyclones. Also, the country still lacks in good quality data and information that can offer enhanced services to effectively design coastal defense systems and adapt to climate changes. This study developed a storm surge inundation model and database using the available tropical cyclones' database and simulated inundation for the past 31 cyclones in the Bay of Bengal, near the coastal regions of Bangladesh. The model uses a suite of Delft3D hydrodynamic and Delft Dashboard cyclone models. The model was calibrated and validated for two major cyclones, namely Sidr and Aila, using the available data for different bed roughness, track sources, and wind drag coefficient conditions. The results suggested that spatially varying bed roughness and wind varying drag conditions provide a more reliable prediction of inundation over the coast. The results also show that historical track data from Indian Meteorological Department optimize the model performances. The inundation database indicates that depending on the intensity and location, tropical cyclones can cause the maximum inundation of 1-5 m in the coastal lands of Bangladesh. More than 70% of the storms lead to the maximum inundation of more than 2 m, and about 25 and 7% of the storms can cause the maximum inundation of more than 3 and 4 m, respectively. The study also discusses the potential applications and shares insights on the implications of the inundation database that can offer improved information for enhanced climate services in Bangladesh. The database can be advanced with information about sectoral loss and damage as well as citizen science that will not only provide necessary information to design coastal protection structures and emergency measurements but also contribute to build long-term climate adaptation plans in the data-scarce region.