Institute of Water and flood Management (IWFM), Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.
Institute of Water and flood Management (IWFM), Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.
Sci Total Environ. 2022 Jul 10;829:154547. doi: 10.1016/j.scitotenv.2022.154547. Epub 2022 Mar 15.
The Ganges-Brahmaputra-Meghna (GBM) delta is one of the world's largest deltas. It is currently experiencing high rates of relative sea-level rise of about 5 mm/year, reflecting anthropogenic climate change and land subsidence. This is expected to accelerate further through the 21st Century, so there are concerns that the GBM delta will be progressively submerged. In this context, a core question is: can sedimentation on the delta surface maintain its elevation relative to sea level? This research seeks to answer this question by applying a two-dimensional flow and morphological model which is capable of handling dynamic interactions between the river and floodplain systems and simulating floodplain sedimentation under different flow-sediment regimes and anthropogenic interventions. We find that across a range of flood frequencies and adaptation scenarios (including the natural polder-free state), the retained volume of sediment varies between 22% and 50% of the corresponding sediment input. This translates to average rates of sedimentation on the delta surface of 5.5 mm/yr to 7.5 mm/yr. Hence, under present conditions, sedimentation associated with quasi-natural conditions can exceed current rates of relative sea-level rise and potentially create new land mass. These findings highlight that encouraging quasi-natural conditions through the widespread application of active sediment management measures has the potential to promote more sustainable outcomes for the GBM delta. Practical measures to promote include tidal river management, and appropriate combinations of cross-dams, bandal-like structures, and dredging.
恒河-布拉马普特拉河-梅克纳（GBM）三角洲是世界上最大的三角洲之一。目前，该地区正经历着约 5 毫米/年的相对海平面快速上升，这反映了人为气候变化和土地沉降的影响。预计在 21 世纪，这一速度还将进一步加快，因此人们担心 GBM 三角洲将逐渐被淹没。在这种情况下，一个核心问题是：三角洲表面的沉积物堆积能否使其相对海平面保持在一定高度？为了回答这个问题，本研究应用了二维水流和形态模型，该模型能够处理河流和洪泛平原系统之间的动态相互作用，并模拟不同水流-沉积物条件和人为干预下的洪泛平原沉积物堆积。我们发现，在一系列洪水频率和适应情景（包括自然无圩区状态）下，保留的沉积物体积占相应沉积物输入量的 22%至 50%之间。这相当于三角洲表面每年的平均沉积速率为 5.5 毫米至 7.5 毫米。因此，在目前的条件下，与准自然条件相关的沉积物堆积可以超过当前的相对海平面上升速度，并有可能创造新的陆地。这些发现表明，通过广泛应用主动沉积物管理措施来鼓励准自然条件，有可能为 GBM 三角洲带来更可持续的结果。促进这一结果的实际措施包括潮汐河管理，以及合理组合横坝、带状结构和疏浚。
