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Sediment Re-circulation in the Ganges-Brahmaputra-Meghna Delta and its implications for Ecosystem Services Munsur Rahman1, Anisul Haque1, Mashfiqus Salehin1 , Stephen Darby2 , Robert J. Nicholls3,Judith Wolf4 MunirAhmed5, Mostafa Ali Reza Hossain6, MaminulHaque Sarker7, Shampa1, Mansur Ali Jisan1,Hafez Ahmed1, Md. Nurul Kadir1, Ali Mohammad Rezaie1,Sumaiya1, Shah Alam1, Ishtiaq Ahmed1 and Orchi Rubaiya1 ABSTRACT The Ganges-Brahmaputra-Meghna (GBM) delta is home to about 100 million people who depend on the ecosystem services supported by this rich deltaic environment. The deltaic environment is largely influenced by the amount of sediment coming into the system and the way these sediments are distributed within the estuarine systems of the GBM delta. In this paper, we compute the incoming volume of suspended sediments to the GBM delta and the way these sediments are re-distributed among the estuaries using the Delft 3D and HEC RAS unsteady flow models. The implications of flow/ sediment parameters on the ecosystem services(for example: fisheries) along each of the estuaries is also established. The available estimates(FAP1993)indicate that the annual total sediment volume (including sand and silt/clay) reaching the GBM system is ~960 million tonnes, of which around 60% are comprised of silt/clay and 40% are sand. The sand fraction is important for delta building processes, whereas the silt fraction contributes to reshaping the estuarine system and supporting ecosystem services through re-circulation processes. Using the measured suspended sediment concentration data and simulated water discharge (from the 1D HEC RAS model)in the major rivers, the yearly average suspended sediment transport has been estimated. It is found that the annual volume of suspended sediment reaching the GBM system is around 580 million tonnes, which is very similar to the estimated values in FAP studies during 1990's, lending a degree of confidence to our model simulations. The model resultsof water and sediment flow within the GBM estuarine system show that the clockwise recirculation processthrough which the incoming fluvial sediments (suspended)in the Meghna estuary (eastern most) are being redistributed into each of the estuarine systems (through clockwise recirculation)are the primary source of nutrients that underpin key ecosystem services. It is found that a deep estuary with a high flow velocity and low sediment concentrationattracts bigger fish species with less species diversity. On the other hand, a shallow estuary with low velocity but higher sediment concentrationattracts smaller fish species with high species diversity. Any change of this hydromorphological regime due to either climatic or human activities will have significant impacts on fishery resources and species diversity. Topic: Coastal systems and wetlands Presentation preference: oral presentation Previous Submissions: parts of the material are in process of writing for an online journal Has the submitted material been presented or submitted to another event? NO Email of Contact Author: [email protected] 1 Institute of Water and Flood Management (IWFM), BUET, Dhaka, Bangladesh. 2 Geography and Environment, University of Southampton, UK. 3 Department of Coastal Engineering, University of Southampton, UK. 4 National Oceanographic Center, Liverpool, UK. 5 6 Technological Advancement for Rural Development Bangladesh Agricultural University, Bangladesh
